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Limited Field-of-View Cone Beam CT Imaging
of the Temporomandibular Joints:
Comparative Dosimetry and Diagnostic Efficacy
by
Tricia Dawn Lukat
A thesis submitted in conformity with the requirements
for the degree of Master of Science in Oral and Maxillofacial Radiology
Discipline of Oral and Maxillofacial Radiology, Faculty of Dentistry
University of Toronto
© Copyright by Tricia Dawn Lukat 2013
ii
Limited Field-of-View Cone Beam CT Imaging of the Temporomandibular Joints:
Comparative Dosimetry and Diagnostic Efficacy
Tricia Dawn Lukat
Master of Science in Oral and Maxillofacial Radiology
Discipline of Oral and Maxillofacial Radiology, Faculty of Dentistry University of Toronto
2013
Abstract
Imaging of the osseous structures of the temporomandibular joint is best accomplished
using computed tomography (CT). Cone beam CT offers a reduced radiation dose and
improved spatial resolution compared to multislice helical CT. This study evaluates
comparative dosimetry for temporomandibular joint imaging using two different cone
beam CT systems, the Hitachi CB MercuRay and Kodak 9000 3D. These systems
demonstrate differing properties with respect to field-of-view sizes, operational technique
factors, and spatial resolution. The Kodak 9000 3D unit offers an effective radiation
dose reduction of greater than ten-fold compared with the Hitachi CB MercuRay,
depending on kVp and mA. A subsequent clinical study evaluating the effect of spatial
resolution on the ability to detect osseous changes related to temporomandibular joint
degenerative disease found no significant difference in diagnostic efficacy between high
and low spatial resolution images, however, observers consistently associated high
spatial resolution with superior image quality.
iii
Acknowledgements
Thank you to my supervisor, Dr. Ernest Lam, for inspiring my interest in Oral and
Maxillofacial Radiology. Your support throughout these last three years has been
unending and deeply appreciated, and you motivate me to strive for excellence in
everything that I do.
Dr. Michael Pharoah, you have taught me to respect both the science and the art of this
specialty, and I will be forever honored to be one of your students.
Special thanks to Drs. Susanne Perschbacher, Milan Madhavji, and Ernest Lam, for the
countless hours spent reviewing images of temporomandibular joints.
To Drs. Michael Pharoah, Marie Dagenais, David Mock, Robert Wood, and Howard
Tenenbaum, for your time, support, and guidance as members of my thesis committee.
Jason (“Bongo”) Wong, my Summer 2012 Sidekick, your meticulous work on the
comparative dosimetry project will never be forgotten.
Thank you to my co-residents for assisting me with patient recruitment for the clinical
component of this study.
And finally, to my husband and best friend Dean, whose selflessness, understanding, and
encouragement made this entire experience possible.
iv
Table of Contents
Abstract............................................................................................................................... ii
Acknowledgements ........................................................................................................... iii
Table of Contents............................................................................................................... iv
List of Tables ................................................................................................................... viii
List of Figures.................................................................................................................... ix
List of Appendices.............................................................................................................. x
Chapter 1: Introduction....................................................................................................... 1
1.1 Evolution of temporomandibular joint imaging .................................................. 1
1.1.1 Hard tissue imaging ........................................................................... 1
1.1.2 Soft tissue imaging ............................................................................ 3
1.2 Ionizing radiation and patient radiation dose....................................................... 4
1.2.1 Biological effects of ionizing radiation ............................................. 4
1.2.2 Principles of radiation protection for diagnostic imaging ................. 4
1.2.3 Comparative dosimetry...................................................................... 5
1.3 Image quality ....................................................................................................... 6
1.3.1 Contrast resolution............................................................................. 6
1.3.2 Spatial resolution ............................................................................... 7
1.3.2.1 CT image geometry ............................................................ 7
1.3.2.2 Nyquist limitation and sampling frequency........................ 8
1.3.2.3 Detector element size.......................................................... 8
1.3.2.4 Image reconstruction filter.................................................. 9
1.3.3 Prior research on spatial resolution and diagnostic efficacy ............. 9
v
1.4 Diagnostic imaging of the temporomandibular joints ....................................... 10
1.4.1 Patient selection criteria................................................................... 10
1.4.2 Goals ................................................................................................ 10
1.4.3 Choice of imaging modality ............................................................ 11
1.5 Degenerative joint disease ................................................................................. 12
1.5.1 Pathophysiology .............................................................................. 12
1.5.2 Structural changes............................................................................ 12
1.5.3 Diagnostic imaging.......................................................................... 13
1.6 Statement of the problem ................................................................................... 14
1.6.1 Comparative dosimetry.................................................................... 14
1.6.2 Image quality ................................................................................... 15
1.7 Aim .................................................................................................................... 16
1.8 Objectives .......................................................................................................... 17
1.9 Hypotheses ......................................................................................................... 18
1.9.1 Primary hypotheses.......................................................................... 18
1.9.2 Null hypotheses ............................................................................... 18
Chapter 2: Materials and Methods.................................................................................... 19
2.1 Part A: Comparative dosimetry ......................................................................... 19
2.1.1 Overview ......................................................................................... 19
2.1.2 Materials for dosimetric measurements........................................... 20
2.1.3 Imaging techniques.......................................................................... 20
2.1.4 Dosimetry calculations .................................................................... 22
2.1.5 Statistical analysis............................................................................ 23
2.2 Part B: Voxel size and diagnostic efficacy ........................................................ 28
2.2.1 Overview ......................................................................................... 28
2.2.2 Ethics approval ................................................................................ 28
vi
2.2.3 Equipment modifications required for clinical use.......................... 28
2.2.3.1 Modified chin support ...................................................... 29
2.2.3.2 Estimation of subject intercondylar distance.................... 29
2.2.4 Study design .................................................................................... 30
2.2.4.1 Inclusion criteria ............................................................... 30
2.2.4.2 Exclusion criteria .............................................................. 30
2.2.4 Image processing and downsampling.............................................. 31
2.2.5 Image analysis ................................................................................. 31
2.2.6 Statistical analyses ........................................................................... 32
Chapter 3: Results............................................................................................................. 39
3.1 Part A: Comparative dosimetry ......................................................................... 39
3.2 Part B: Voxel size and diagnostic efficacy ........................................................ 41
Chapter 4: Discussion ....................................................................................................... 47
4.1 Part A: Comparative dosimetry ......................................................................... 47
4.1.1 Hitachi CB MercuRay versus Kodak 9000 3D dosimetry .............. 47
4.1.2 Translating exposure to risk ............................................................ 51
4.1.3 Kodak 9000 3D technique factor modulation.................................. 52
4.1.4 Future directions in comparative dosimetry research...................... 54
4.2 Part B: Voxel size and diagnostic efficacy ........................................................ 55
4.2.1 Effect of voxel size on detection of osseous changes...................... 55
4.2.2 Effect of voxel size on perceived image quality.............................. 57
4.2.3 Study limitations.............................................................................. 57
4.2.4 Drawbacks of limited field-of-view imaging .................................. 60
4.2.5 Practical considerations ................................................................... 60
vii
Chapter 5: Conclusions..................................................................................................... 62
References ........................................................................................................................ 63
Appendices ....................................................................................................................... 71
viii
List of Tables
Table 1. Anatomical correlates of optically stimulated luminescence (OSL) dosimeters in
RANDO® man anthropomorphic phantom...................................................................... 26
Table 2. Effective tissue dose calculation factors............................................................. 27
Table 3. Mean effective tissue doses and total effective doses with respective standard
deviation values for each of the temporomandibular joint imaging modalities and
technique settings ............................................................................................................. 40
Table 4. Fleiss’ kappa for interobserver reliability........................................................... 42
Table 5. Cohen’s kappa for intraobserver reliability ........................................................ 43
Table 6. Radiographic feature identification results based on the McNemar !2 test for
paired groups .................................................................................................................... 44
Table 7. Effect of voxel size on visual analog scale (VAS) responses by observers based
on a paired samples t-test.................................................................................................. 45
ix
List of Figures
Figure 1. Left lateral view of the anthropomorphic RANDO® man phantom ................ 24
Figure 2. Sample optically stimulated luminescence (OSL) dosimeter placement at level
4 of the anthropomorphic RANDO® man phantom to measure absorbed dose for the lens
and orbit of the right and left eye ..................................................................................... 25
Figure 3. Modified chin support used during patient positioning for Kodak 9000 3D
temporomandibular joint imaging .................................................................................... 34
Figure 4. Caliper tool used for estimation of subject intercondylar distance ................... 35
Figure 5. Kodak acquisition modular software medio-lateral crosshair positioning guide
based on estimated subject intercondylar distance ........................................................... 36
Figure 6. Correct subject positioning within the Kodak 9000 3D cone beam CT unit for
temporomandibular joint imaging .................................................................................... 37
Figure 7. Downsampling technique applied to a temporomandibular joint image volume
acquired using the Kodak 9000 3D cone beam CT system.............................................. 38
Figure 8. Visual analog scale (VAS) ratings of image quality for the overall average from
all observers, as well as from each observer independently, for the 76µm and 300µm
voxel sizes......................................................................................................................... 46
Figure 9. Native Hitachi CB MercuRay cone beam CT temporomandibular joint images
(panoramic mode, 0.290mm) compared to Kodak 9000 3D images downsampled to
300µm using the anthropomorphic RANDO® man phantom.......................................... 59
x
List of Appendices
Appendix 1. Landauer specification sheet for InLight® nanoDot™ dosimeters ............. 71
Appendix 2. Health Sciences Research Ethics Board approval letter .............................. 73
Appendix 3. Patient information and consent forms ........................................................ 74
Appendix 4. Observer calibration PowerPoint exercise ................................................... 82
Appendix 5. Sample observer score sheet for identification of radiographic features and
visual analog scale ............................................................................................................ 86
Appendix 6. Translating exposure to risk: calculations.................................................... 87
!
1
Chapter 1
1 Introduction
1.1 Evolution of Temporomandibular Joint Imaging
Diagnostic imaging of the temporomandibular joint has evolved significantly since its
inception. Advances in imaging technology have allowed for progressive improvements
in visualization of both osseous and soft tissue components of this joint.
1.1.1 Hard Tissue Imaging
The fundamental osseous structures of interest in temporomandibular joint imaging
consist of the mandibular condyle, glenoid fossa, and articular eminence. Two-
dimensional planar views were the initial modalities used to radiographically evaluate
hard tissue structures of the temporomandibular joint, and multiple orthogonal views
were acquired to emphasize different aspects of the complex joint anatomy. Transcranial
and transpharyngeal views provide lateral profile views of the temporomandibular joint,
and preferentially depict the lateral and medial aspects of the condyle, respectively. To
avoid excessive superimposition of the joint anatomy with the adjacent skull base,
transcranial and transpharyngeal views both required a degree of obliquity and thus did
not provide an accurate representation of the condylar-fossa relationship. The open
mouth transorbital view provides a frontal view of the condyle, free from
superimposition by the articular eminence, and the open Townes view portrays a similar
depiction of the condylar neck region. Despite the compilation of information from
multiple radiographic views, superimposition of overlying anatomical structures hindered
detection of subtle osseous changes within the temporal and condylar joint components,
thereby rendering significant diagnostic limitations (1).
Panoramic radiography is a specialized application of tomography, in which objects lying
within a horseshoe-shaped focal trough are clearly portrayed while objects outside this
2
region appear blurred and are not well imaged. The temporomandibular joints are
located within this focal trough, and panoramic imaging is often used as a preliminary
tool to assess patients presenting with joint related complaints. However, this technique
has several shortcomings, including inaccuracies in representation of joint position,
anatomical superimpositions, poor spatial resolution, image distortion, and views limited
to the lateral and central regions of the condyle. Although modern panoramic units offer
specialized protocols for temporomandibular joint imaging, there is no evidence that this
confers a diagnostic advantage for detection of osseous abnormalities (2). Only gross
pathological changes are readily and reliably demonstrated by panoramic imaging
techniques.
The advent of conventional tomography enabled a solution to the issue of overlapping
anatomical structures associated with the use of traditional planar and panoramic views.
Conventional tomography uses the technique of motion blurring to render objects located
outside of the focal plane relatively “invisible” compared to the object of interest, which
is centrally positioned within the focal plane. The generation of thin orthogonal cross-
sectional slices permits visualization of all aspects of the joint structures, with negligible
effects of superimposed anatomy. Studies have demonstrated that use of sagittal and
coronal tomographic views render superior diagnostic accuracy compared to panoramic
radiography in the detection of osseous temporomandibular joint changes (3,4).
Computed tomography (CT) applies mathematical algorithms to digitally acquired
projection data to completely remove overlying structures, as opposed to simply blurring
them out as with conventional tomography. The first documented use of CT imaging to
evaluate the temporomandibular joint was in 1978 by Wegener et al. (5), and this
technique is now accepted as the imaging modality of choice to visualize osseous
structures of the temporomandibular joint (6,7). More recently, the introduction of cone
beam CT has provided an alternative imaging modality to assess hard tissue structures of
the joint, with a purported reduction in radiation dose to the patient and superior image
quality compared to multislice helical CT (8,9). Prior research also suggests that the
diagnostic accuracy of cone beam CT is significantly greater than that of panoramic
3
imaging and conventional linear tomography for detection of cortical erosions involving
the temporomandibular joints (2).
1.1.2 Soft Tissue Imaging
While the aforementioned imaging modalities provide information about the osseous
structures of the temporomandibular joint, no details are provided regarding the articular
disc or its associated attachments. Although CT images with soft tissue algorithms were
investigated as a potential tool to evaluate the disc, the specificity is poor and this
approach is no longer endorsed (10). Arthrography was the first technique utilized to
provide indirect visualization of the disc through coupling of radiography, fluoroscopy,
or tomography with the injection of iodinated contrast media into the superior and/or
inferior joint spaces. Due to the invasive nature of the procedure and accompanying
discomfort for the patient, this imaging approach has been largely replaced by the use of
magnetic resonance (MR) imaging. Unlike the previously mentioned imaging
modalities, MR does not involve the use of ionizing radiation, but rather utilizes a strong
magnetic field and radiofrequency energy to generate images. MR imaging provides
superior soft tissue contrast to all other imaging modalities, and can directly demonstrate
the articular disc. Acquisition of both closed and open mouth views gives information
about the position, shape, and integrity of the articular disc, and allows for assessment of
internal derangements. While MR imaging provides some information about the osseous
structures of the joint, autopsy studies demonstrate that the sensitivity and specificity of
detecting osseous changes by MR imaging is inferior to that provided by CT imaging
(0.50 and 0.71 for MR versus 0.75 and 1.00 for CT) (10). It is generally accepted that
both the sensitivity and specificity parameters should exceed a value of 0.70 for a
temporomandibular joint imaging examination to be considered clinically useful (11).
Consequently, CT and MR are typically regarded as complementary imaging modalities.
4
1.2 Ionizing Radiation and Patient Radiation Dose
1.2.1 Biological Effects of Ionizing Radiation Planar imaging, panoramic radiography, conventional tomography, and CT (both
multislice helical and cone beam) all utilize ionizing radiation to produce diagnostic
images. Through primarily free radical-mediated interactions with biological
macromolecules, ionizing radiation is capable of causing cellular damage. Most of the
deleterious effects of ionizing radiation arise due to DNA damage, which may result in
lethal, cell-killing effects or sublethal genetic changes. At radiation doses used in
diagnostic imaging, sublethal effects are the primary concern. Sublethal DNA damage
may be resolved by intrinsic repair mechanisms, or may persist and potentially result in
carcinogenesis depending on the particular gene or genes involved. Carcinogenesis is
classified as a stochastic effect of radiation, in which the event probability increases
proportional to dose, but the severity is unaffected. There is no “threshold dose” for
stochastic effects of radiation; technically, a single x ray photon is capable of causing
DNA damage and evoking the subsequent chain of events (12). Because of the known
risk associated with the use of ionizing radiation, strict radiation protection practices
must be applied to diagnostic imaging procedures. While these conservative concepts
are refuted by some critics due to potential inaccuracies when the effects of high dose
radiation exposure are extrapolated to the much lower doses used during diagnostic
imaging, the burden of proof ultimately requires adherence to the most cautious radiation
protection protocols.
1.2.2 Principles of Radiation Protection for Diagnostic Imaging
While no maximum dose limits are established for diagnostic exposure of patients, the
principles of justification and optimization endorsed by both the National Council on
Radiation Protection (NCRP) and the International Commission on Radiological
Protection (ICRP) are recognized aspects of responsible radiology practice. The
principle of justification states that the health benefit to the patient outweighs any
potential risk conferred by radiation exposure, thereby acknowledging that the risks of
5
diagnostic imaging are low but not zero, as per the linear no-threshold dose-response
model. All radiographic examinations are considered prescriptions, and should be
ordered following a thorough history and clinical examination. The concept of
optimization is predicated on the ALARA (“as low as reasonably achievable”) principle,
with economic and social factors taken into account. While initially developed for
occupational radiation protection, this doctrine can and should be applied to patient
imaging so that exposure techniques are optimized to minimize patient dose while
maintaining diagnostic image quality. Modification of technique factors, the application
of appropriate views and imaging volumes, and use of protective barriers such as leaded
aprons and thyroid collars whenever possible are all imperative and modifiable measures
that reduce patient radiation dose (12,13).
1.2.3 Comparative Dosimetry
Numerous studies have evaluated the relative dose burden imparted upon patients by
various diagnostic imaging procedures involving the craniofacial region. Particular
attention has focused around comparative dosimetry of multislice helical CT versus cone
beam CT (8,14,15,16,17,18). The average effective dose for an adult head CT
examination is approximately 2000 microsieverts (µSv) (19). Adapting a specific
temporomandibular joint protocol to multislice helical CT through field-of-view
limitation, the effective dose is reduced to about 600µSv (20). Although it is generally
accepted that cone beam CT examinations render a lower radiation dose to patients, there
is immense variability in dose depending on the particular cone beam CT system being
used. Reported effective doses from various cone beam CT units range from 5.3µSv for
a limited field-of-view examination of the anterior maxilla using a Kodak 9000 3D unit
(21) to 1073µSv for a 12-inch field-of-view acquisition of the craniofacial complex,
using a Hitachi CB MercuRay unit operating at 120kVp and 15mA (8). The field-of-
view size, operating technical factors such as voltage (kVp), current (mA), and exposure
time, as well as use of a continuous or pulsed x ray beam all contribute to radiation dose
variability of different cone beam CT units (1,8). A study by Palomo et al. (22)
demonstrated an overall dose reduction of approximately 0.62 times (38%) when
6
reducing the operating voltage of the Hitachi CB MercuRay cone beam CT system from
120kVp to 100kVp, with all other technique factors held constant. It was also
demonstrated that reducing the field-of-view from 12-inches to 6-inches results in a
decrease in absorbed dose to tissues remaining within the primary x ray beam by about
5% to 10%, which is likely the result of diminished scatter radiation produced by field-
of-view restriction. Tissues and organs outside of the primary beam field experience a
significant reduction in absorbed dose values (up to 95%). While the use of cone beam
CT clearly offers an inarguable dose profile advantage over multislice helical CT, there is
significant latitude for optimization of patient dose by modification of imaging
parameters within specific cone beam CT systems.
Although the vast majority of comparative dosimetry studies involving cone beam CT
imaging are published in the oral and maxillofacial literature, the medical community is
also beginning to consider lower dose options to the traditional CT systems. Ruivo et al.
(23) describe the use of an i-CAT cone beam CT unit for in vivo postoperative imaging
of cochlear implants. Comparative dosimetry assessment revealed an effective dose of
80µSv for the i-CAT technique, compared to 3600µSv for a 16-slice CT and 4800µSv
for a 4-slice CT unit. In addition to a significant radiation dose reduction, the cone beam
CT images also demonstrated less metallic artifacts from the cochlear implant electrodes
and an overall improvement in perceived image quality.
1.3 Image Quality
While dose is an important factor to consider when exposing a patient to ionizing
radiation, other parameters such as image quality and subsequent diagnostic efficacy
must also be implicitly considered. Contrast resolution and spatial resolution are the two
fundamental determinants of image quality (19).
1.3.1 Contrast Resolution
Contrast resolution is defined as the ability to detect subtle changes in grayscale and
distinguish this from background noise in the image (19). Noise is determined by the
7
number of x ray photons reaching the detector; the more photon interactions per detector
element, the better the signal-to-noise ratio of the resulting image. Technique factors are
key determinants of contrast resolution, and include voltage (kVp), current (mA), and
exposure time for both multislice helical and cone beam CT. Increasing any of these
factors results in improved contrast resolution through an increased number of photon-
detector interactions and a greater signal-to-noise ratio, but this occurs at the expense of
increased patient dose. In multislice helical CT, a pitch value of less than one (defined as
the ratio of gantry movement distance to nominal slice thickness) improves contrast
resolution by decreasing image noise, but again at the cost of increasing dose. Greater
slice thickness in multislice helical CT improves contrast resolution by increasing the
number of detected photons per detector element and in turn reduces image noise. The
reconstruction filter applied to multislice helical CT also impacts contrast resolution;
application of a ramp filter with roll-off at high spatial frequencies reduces image noise,
thereby improving contrast resolution while at the same time reducing spatial resolution.
Lastly, iterative reconstruction techniques result in multislice helical CT images with
higher contrast resolution compared to the use of filtered back projection reconstruction
methods (19). Relative to multislice helical CT, cone beam CT images demonstrate poor
contrast resolution due to a high amount of scatter radiation and subsequent image noise
associated with cone beam geometry, as well as due to inherent flat panel deficiencies
that result in a non-linear response to incoming x ray photons (1).
1.3.2 Spatial Resolution
Spatial resolution is defined as the ability of an imaging system to record separate
structures that are positioned closely together; that is, it reflects the level of detail seen on
an image (19). Several factors influence spatial resolution in both multislice helical and
cone beam CT.
1.3.2.1 CT Image Geometry
CT techniques require a long object-to-detector distance, which results in significant
magnification of the object being imaged. This geometrical principle, in combination
8
with focal spot blooming associated with the use of high current techniques and x ray
beam divergence, all contribute to a reduction in CT spatial resolution by ultimately
increasing the focal spot size.
1.3.2.2 Nyquist Limitation and Sampling Frequency
Digital imaging techniques, including helical multislice and cone beam CT, define object
size in terms of spatial frequency, expressed graphically as a sine wave. Smaller objects
correspond to a higher spatial frequency. The Nyquist frequency, or limitation, refers to
the spatial frequency of a particular object. For a small, high frequency object to be
accurately imaged, the sampling frequency (i.e., the rate of data “measurement”) must be
at least twice that of the object’s Nyquist limit. This sampling frequency is a determinant
of the limiting spatial resolution of a given imaging system, which defines the smallest
object that is reliably depicted on the final image.
1.3.2.3 Detector Element Size
A smaller detector volume element (“voxel”) size results in increased spatial resolution
as a result of reduced partial volume averaging effects. This applies to both multislice
helical and cone beam CT. While voxel length and width (x- and y-dimensions) in
multislice helical CT are equivalent and determined by the picture element (“pixel”) size
of the detector, the voxel height is generally greater and determined by the acquired slice
thickness in the axial (z) dimension. Typical multislice helical CT pixel sizes are 0.5 mm
for a 25 cm diameter field-of-view, and the acquired slice thickness ranges from
approximately 0.5mm up to 5mm (24). Cone beam CT utilizes a flat panel detector to
acquire circumferential two-dimensional planar images around the area of interest. There
is no inherent acquired “slice thickness” of cone beam CT; rather, cross sectional images
are reconstructed from the two-dimensional projection data, and the displayed voxel size
is a direct product of the native pixel dimensions. This technique results in isotropic
voxels (i.e., equal dimension in x-, y-, and z-planes), and permits multiplanar
reconstruction of the images without loss of spatial resolution. Voxel sizes in cone beam
9
CT imaging range from 0.076mm to 0.4mm, depending on the particular unit and
protocol being used.
1.3.2.4 Image Reconstruction Filter
A reconstruction filter applied to the CT images is used to balance image noise (i.e.,
contrast resolution) and spatial resolution, depending on the imaging task at hand.
Sharpening or edge enhancement filters increase spatial resolution at the expense of
increased image noise, which is a useful application for visualization of hard tissue
structures. Smoothing filters conversely reduce image noise while reducing spatial
resolution, and are applied when soft tissue structures are of interest. While multislice
helical CT images offer both bone and soft tissue algorithms by utilization of these
differing reconstruction filters, only bone algorithms are useful and applicable to cone
beam CT images (19).
1.3.3 Prior Research on Spatial Resolution and Diagnostic Efficacy
Voxel size is a known determinant of image spatial resolution. The ability to detect
subtle hard tissue findings on CT imaging requires use of a sufficiently small voxel size
such that partial volume effects do not obscure the findings of interest. Librizzi et al.
(25) evaluated the effect of voxel size on the ability to detect cortical erosions of the
temporomandibular joints using dry human skulls. Their protocol used the Hitachi CB
MercuRay cone beam unit operating at 120kVp and 15mA. Modulation of voxel size
with this system requires a companion change in the field-of-view; the
0.2mm/0.3mm/0.4mm voxel sizes correspond to the 6-inch/9-inch/12-inch field-of-view
settings, respectively. A clear advantage of using dry human skulls is the ability to elicit
information regarding the sensitivity, specificity, and receiver operator characteristic
(ROC) curve. The data from this study demonstrated that images acquired using the 6-
inch field-of-view with 0.2mm voxel size provided a significant diagnostic advantage
compared to those attained using the 12-inch field-of-view and 0.4mm voxel size. It is
important to note that the change in field-of-view produces a concurrent change in the
10
amount of scatter radiation, which affects image signal-to-noise ratio and contrast
resolution, and therefore overall image quality.
Other dental disciplines such as endodontics have evaluated the influence of voxel size
on the diagnostic ability of cone beam CT. Liedke et al. (26) assessed the effect of voxel
size on evaluation of simulated external root resorption, using an i-CAT cone beam CT
unit. The field-of-view was held constant at 8cm, and the voxel sizes evaluated were
0.2mm, 0.3mm, and 0.4mm. No significant differences in sensitivity, specificity,
positive predictive value, or negative predictive value were demonstrated between the
three different voxel sizes. However, the likelihood ratios indicated that the 0.2mm and
0.3mm voxel sizes permitted an easier diagnosis of external root resorption compared to
the 0.4mm voxel size.
1.4 Diagnostic Imaging of the Temporomandibular Joint
1.4.1 Patient Selection Criteria
A position paper by the American Academy of Oral and Maxillofacial Radiology
(AAOMR) recommends the use of selection criteria to establish the need for
temporomandibular joint imaging (27). Acquisition of a thorough patient history and
clinical examination is required to determine if the use of imaging tools will impact the
patient’s diagnosis and/or treatment and that the benefit of radiation exposure outweighs
the potential risks. When considering the dose imparted upon a patient by diagnostic
imaging procedures utilized in Oral and Maxillofacial Radiology, the stochastic risk of
carcinogenesis is of primary concern. The most conservative, linear no-threshold model
implies that while the risk of stochastic events is low, it is not zero, thus prudent selection
criteria must be exercised to avoid unnecessary radiation exposure.
1.4.2 Goals
The goals of temporomandibular joint imaging are defined by the AAOMR as follows: 1)
to evaluate the integrity of the structures when disease is suspected, 2) to confirm the
11
extent of known disease, 3) to stage the progression of known disease, or 4) to evaluate
the effects of treatment. The AAOMR also states, “If there is a choice between imaging
modalities that are expected to equally influence the management of the patient, the least
expensive, in terms of cost and radiation dose, should be selected.” (27) This statement
is congruent with the radiation protection principle of optimization, which indicates that
the total exposure remains as low as reasonably achievable (“ALARA”), with economic
and social factors taken into account (13). Selection of appropriate views with
collimation to the area of interest, optimized technique factors (including voltage,
current, and exposure time), and use of leaded aprons and thyroid collars, all act as
effective dose reduction protocols that minimize patient exposure.
1.4.3 Choice of Imaging Modality
The choice of imaging tool for assessment of the temporomandibular joint is dependent
on the diagnostic question. Direct visual examination is considered the gold standard for
assessment (11), however this poses obvious impracticality in living subjects. Computed
tomography (CT) or cone beam CT are considered first line imaging modalities for
visualization of the hard tissue structures of the joint, thus are well suited for diagnosis of
osseous abnormalities including arthridities, neoplasia, and trauma (28,29,30,31). The
use of magnetic resonance (MR) imaging provides excellent depiction of the soft tissue
joint components, and is considered the diagnostic tool of choice for assessment of
abnormalities of articular disc position, disc perforation, and joint effusion. While MR
imaging does allow evaluation of the osseous structures, hard tissue image quality is
inferior to that of CT (10). Additional factors such as cost of the procedure,
invasiveness, radiation dose, potential side effects, and impact of information gained
from imaging the patient must also be considered.
12
1.5 Degenerative Joint Disease
1.5.1 Pathophysiology
One of the most common pathological conditions involving the hard tissue structures of
the temporomandibular joints is degenerative joint disease, also referred to as
osteoarthritis. Degenerative joint disease is characterized as a non-inflammatory
arthritis, in which mechanical intra-articular stresses overwhelm intrinsic joint repair and
remodeling mechanisms. This ultimately results in a loss of equipoise between the
formation and degradation of the articular cartilage and underlying subchondral bone,
which leads to aberrations in normal joint anatomy (1,32,33). While the pathophysiology
of degenerative joint disease is complex, it is generally accepted that the primary insult is
mechanical in nature, followed by a subsequent release of inflammatory mediators and
free radicals that propagate the disease process (34,35).
1.5.2 Structural Changes
The manifestations of osteoarthritis are usually observed as a combination of
degenerative and proliferative components. The articular fibrocartilage of the
temporomandibular joint undergoes softening, fibrillation, ulceration, and loss, with
subsequent exposure of the underlying cortical bone (36). This process is followed by
the appearance of cortical erosions along the articulating surfaces. Formation of
subchondral bone cysts (Ely cysts) may also occur. Proliferative effects are a
compensatory effort by the joint components to meet increased functional demands, and
include structural changes such as subchondral sclerosis and osteophyte formation (32).
Though the presence of articular surface flattening is often denoted as a feature of
degenerative joint disease, this may simply represent adaptive joint remodeling that
serves to increase the articulating surface area over which forces are distributed (1).
13
1.5.3 Diagnostic Imaging
Based on an underlying pathophysiology that involves the hard tissues of the joint, the
structural changes of degenerative joint disease are best visualized using a technique that
optimally depicts the osseous joint components. The Research Diagnostic Criteria for
Temporomandibular Disorders (RDC/TMD) Validation Project concluded that multislice
helical computed tomography (CT) is a superior modality to either panoramic
radiography or magnetic resonance (MR) imaging for assessment of temporomandibular
joint osteoarthritis (7). Prior studies have shown that the use of cone beam CT
demonstrates no significant difference in detection of osseous abnormalities within the
temporomandibular joint compared to multislice helical CT (9,37). Cone beam CT
affords the advantage of a reduced radiation dose burden, and therefore should be
considered the modality of choice for assessing hard tissue structures of the
temporomandibular joints for changes related to degenerative joint disease (8).
Information acquired from these diagnostic imaging procedures may help assist and
direct patient management. Patient education, lifestyle modifications, limitation of
parafunctional habits, and pharmacotherapy may all potentially play a role in limiting the
progression and burden of degenerative joint disease. Furthermore, imaging allows the
clinician to rule out other more ominous disease processes that may mimic
temporomandibular joint dysfunction.
14
1.6 Statement of the Problem
1.6.1 Comparative Dosimetry
As radiologists, we have a responsibility to follow the principle of ALARA (“as low as
reasonably achievable”) when exposing patients to ionizing radiation. Although
effective radiation doses involved in diagnostic radiography are exceedingly low
compared to those used to develop dose-response curves related to observable biological
effects, ALARA requires the acceptance of the most conservative, linear no-threshold
model. This implies that no dose is deemed entirely safe, and thus it is prudent to ensure
patient exposure is minimized while still providing diagnostic quality images. While
cone beam CT offers a reduced radiation dose compared to multislice helical CT, there is
a wide range of effective doses rendered by commercially available cone beam CT
systems. Though the standard protocol for temporomandibular joint imaging at the
author’s institution offers simultaneous bilateral scanning of the right and left joints, the
resulting field-of-view encompasses a far greater volume than the desired area of interest.
Honda et al. (38) published a paper outlining the use of “ortho cubic super-high
resolution computed tomography” for temporomandibular joint imaging by an adapted
Scanora cone beam CT unit. This technique provided a field-of-view restricted to the
circumferential volume surrounding the temporomandibular joint, measuring 38mm in
diameter by 32mm in height, with a voxel size of 0.136mm. However, no effective
radiation dose values were provided by this study to permit comparison to larger field
techniques.
Previous dosimetry studies measuring effective radiation dose for various cone beam CT
systems during maxillofacial imaging procedures indicate a significantly greater dose for
the large field-of-view Hitachi CB MercuRay compared to the limited field-of-view
Kodak 9000 3D unit (8,21). However, no study has directly assessed the effective
radiation dose imparted when the field-of-view is centered about the temporomandibular
joints. Depending on which anatomical structures lie within the irradiated tissue volume,
effective radiation dose will change accordingly. The comparative dosimetry for
15
standard large field-of-view cone beam CT temporomandibular joint imaging compared
to a limited field-of-view technique has not been previously explored.
1.6.2 Image Quality
Not only does the Kodak 9000 3D cone beam CT unit offer the potential for a reduction
in radiation dose to the patient, it also features a smaller voxel size (0.076mm versus
0.20/0.29/0.40mm) and thus improved spatial resolution compared to the Hitachi CB
MercuRay. Spatial resolution has a significant impact on the amount of image detail
appreciated by an observer, and in turn is a critical component of diagnostic efficacy. To
date, studies investigating comparative image quality of various computed tomographic
techniques have largely revolved around multislice helical CT versus cone beam CT.
Only one published study by Librizzi et al. (25) compared the effect of field-of-view and
voxel size on diagnostic efficacy and effective dose when using cone beam CT to detect
erosions of the temporomandibular joint. However, this in vitro study was done using
artificially created erosions in dry human skulls, and compared voxel sizes ranging from
0.2mm to 0.4mm with concurrently varying field-of-view from 6-inches to 12-inches.
Increasing the field-of-view results in increased scatter radiation and decreased image
contrast resolution, thereby creating a confounding factor when evaluating diagnostic
efficacy of the varying image voxel size. No study to date has evaluated the use of
isolated voxel size variation on the ability to detect in vivo osseous changes within the
temporomandibular joints.
16
1.7 Aim
The first aim of this research was to establish comparative dosimetry values for the
effective radiation dose from various cone beam CT examinations of the
temporomandibular joints. In addition to the traditional technique of utilizing a single
large field-of-view acquisition to simultaneously image the right and left joints, an
alternative limited field-of-view technique was also explored to determine the effect of
reducing both the irradiated field size and operating technique factors on the effective
radiation dose values.
The clinical component of this study was designed to assess the effect of cone beam CT
voxel size on the ability to detect osseous changes associated with degenerative joint
disease of the temporomandibular joint. Software manipulation permitted synthetic
transformation of acquired native image data into a larger voxel size, thereby creating a
forum for comparison of the effect of spatial resolution on diagnostic efficacy. Cone
beam CT examinations at two different voxel sizes were also evaluated to determine if
modifying spatial resolution is related to a difference in perceived image quality by
observers.
17
1.8 Objectives
1. To calculate and compare the effective radiation dose values for
temporomandibular joint imaging procedures using two different cone beam CT
systems, each operating under differing technique factors and field-of-view parameters.
2. To determine the effect of modulating cone beam CT technique factors on
effective radiation dose.
3. To evaluate the effect of voxel size on diagnostic efficacy in detecting osseous
changes in the temporomandibular joint associated with degenerative joint disease.
4. To determine the effect of voxel size on perceived cone beam CT image quality.
18
1.9 Hypotheses
1.9.1 Primary hypotheses
1. The cone beam CT unit used during temporomandibular joint imaging has an
effect on the calculated effective radiation dose. Increased exposure and field-of-view
parameters will increase the effective dose.
2. Both voltage (kVp) and current (mA) are directly related to the effective radiation
dose (i.e., increasing one or both of these technique factors will result in an increase in
calculated effective radiation dose).
3. Cone beam CT image voxel size is inversely related to the ability to detect
osseous changes observed in degenerative joint disease of the temporomandibular joint
(i.e., smaller voxel size improves diagnostic efficacy of osseous changes).
4. Images with smaller voxel size (higher spatial resolution) will be designated as
higher image quality compared to those images with larger voxel size (lower spatial
resolution).
1.9.2 Null hypotheses
1. The cone beam CT unit used for temporomandibular joint imaging has no effect
on effective radiation dose, regardless of exposure and field-of-view parameters.
2. Modulating cone beam CT technique factors of voltage (kVp) and current (mA)
has no effect on calculated effective radiation dose.
3. Alteration of voxel size of acquired cone beam CT images has no effect on the
ability to detect osseous changes in the temporomandibular joint.
4. Image voxel size has no effect on perceived image quality by observers.
19
Chapter 2
2 Materials and Methods
2.1 Part A: Comparative Dosimetry
2.1.1 Overview
At the author’s institution, the standard protocol for imaging of the osseous structures of
the temporomandibular joint is the use of a Hitachi CB MercuRay cone beam CT unit
(Hitachi Medical Systems, Tokyo, Japan), using a spherical 9-inch (22.9cm) field-of-
view, and operating at 100 kilovoltage potential (kVp), 10 milliamperes (mA), and 9.6
seconds (s) of total exposure time. This technique permits simultaneous, bilateral
imaging of both temporomandibular joints within a single cone beam CT volume.
This study evaluates the use of a limited field-of-view cone beam CT imaging technique
to perform separate acquisitions of the right and left temporomandibular joints. The
Kodak 9000 3D cone beam CT system (Carestream Dental, Rochester, NY, USA) offers
a limited field-of-view cylindrical imaging volume, measuring 5cm in diameter and
3.7cm in height. Standard adult technique factors operate at 70kVp and 10mA, with a
total exposure time of 10.8s.
Although previous data suggest that effective radiation doses imparted by the Kodak
9000 3D cone beam CT unit (5.3µSv to 38.3µSv) (21) are significantly lower than those
of the Hitachi CB MercuRay (407µSv to 1073µSv) (8), these measurements were not
performed with the field-of-view centered about the temporomandibular joints. Thus,
this comparative dosimetry study evaluates the effective radiation dose rendered during
temporomandibular joint imaging using the a single, 9-inch field-of-view Hitachi CB
MercuRay acquisition versus successive right and left joint scans using the Kodak 9000
3D unit.
A supplementary comparative dosimetry study was designed to evaluate the effect of
varying technique factors using the Kodak 9000 3D cone beam CT unit for
20
temporomandibular joint imaging. In addition to the standard adult setting of 70kVp and
10mA used in the initial part of this study, the unit offers three additional preset kVp/mA
combinations optimized for variable patient sizes: child 68kVp/6.3mA, youth/small adult
70kVp/8mA, and large adult 74kVp/10mA. These exposure settings were applied to the
same protocol for bilateral limited field-of-view temporomandibular joint imaging as
described in the following sections.
2.1.2 Materials for Dosimetric Measurements
An anthropomorphic RANDO® man phantom (Alderson Research Laboratories,
Stanford, CT, USA) comprised of a human skeleton embedded in isocyanate rubber
provided an experimental model to acquire dosimetric measurements. The isocyanate
rubber is equivalent to human soft tissues in both density and atomic number, and thus
provides a comparable radiation attenuation profile (39). The phantom is sectioned into
2.5cm thick axial slices; the first ten were used in this study, extending from the vertex of
the head to the level of the clavicles (Figure 1). Twenty-five optically stimulated
luminescence (OSL) dosimeters (InLight® nanoDot™, Landauer, IL, USA) placed in
various locations throughout the head and neck region of the anthropomorphic phantom
(Table 1) were used to measure absorbed radiation doses for both cone beam CT units
(Figure 2). Dosimeter sites of placement were selected to represent radiosensitive organs
and regions relevant to dental imaging, following the methods described by Ludlow et al.
(40). The OSL dosimeters are comprised of aluminum oxide scintillator crystals, which
produce and trap light when exposed to ionizing radiation. The standard unscreened
nanoDot™ used in this study has a reported lower limit of detection of 10µSv and
accuracy of ±5% (Appendix 1). To calibrate for background radiation exposure,
unexposed control dosimeters were submitted along with the experimental dosimeters for
analysis by Landauer.
2.1.3 Imaging Techniques
The RANDO® man phantom was positioned in the Hitachi CB MercuRay unit with the
occlusal plane parallel to the floor, the mid-sagittal plane centered medio-laterally in the
21
imaging field, and the condylar head level centered supero-inferiorly within the volume.
A single cone beam CT acquisition was performed using the panoramic mode (“P-
mode”, 9-inch field-of-view) setting, with technique factors of 100kVp, 10mA, and 9.6s.
Measurements were performed in triplicate for this protocol.
Positioning of the RANDO® man phantom in the Kodak 9000 3D cone beam CT unit
required greater exactness to ensure that both the temporal and condylar components of
the temporomandibular joint were completely imaged and centered within the volume.
Bilateral indicator guides affixed to the surface of the anthropomorphic phantom were
aligned with the temporal supports to maintain consistency in vertical and horizontal
positioning between successive acquisitions. The image sensor was first oriented parallel
to the anatomical mid-sagittal plane to align the rotational center of the cone beam unit
with the temporomandibular joint region of interest. Antero-posterior localization was
determined by positioning the laser indicator light approximately 1cm anterior to the
external auditory meatus landmark. The supero-inferior position was defined by
centering the midpoint of the 3.7cm vertical field-of-view light over a point
corresponding to the level of the condylar head in the closed mouth position. Finally, the
medio-lateral position was set using the Kodak 9000 3D Module software, placing the
crosshair immediately medial to the condylar head of interest (right or left). These
alignment parameters produced a dataset with the RANDO® man condylar head
omnidirectionally centered within the imaging volume. The Kodak 9000 3D acquisitions
were attained using technique factors of 70kVp, 10mA, and a 10.8s scan time, and both
unilateral and bilateral measurements were acquired. Three successive scans were
performed on each set of OSL dosimeters to ensure absorbed dose quantities exceeded
the lower limit of detection, and each series was performed at minimum in triplicate.
The evaluation of varying technique factors was performed using an identical protocol to
that described above for the Kodak 9000 3D unit, but with appropriate exposure setting
modifications for the three different patient sizes. Technique factors were manually
modified rather than selecting the preset patient size hotkeys to retain patient positioning
parameters as described above. Only bilateral temporomandibular joint measurements
were acquired during this component of the study.
22
2.1.4 Dosimetry Calculations
Single scan measured absorbed doses (AD, provided in millirads, mrad) for each
dosimeter were first converted into SI units (microgray, µGy) by the following formula:
AD (µGy) = AD (mrad) * (10µGy/1mrad)
The converted absorbed dose data (µGy) were then transformed into equivalent doses
(EQD, microsieverts, µSv) using the following equation:
EQD (µSv) = AD (µGy) * wR
where wR is the radiation weighting factor for the particular type and energy of radiation
involved (for diagnostic x rays, wR = 1).
The following formula was applied to determine effective doses for each tissue type, T
(EFDT, µSv):
EFDT (µSv) = !(EQDn / n * wT * fT)
where wT is the tissue weighting factor for tissue type T, and fT is the fraction of tissue
type T irradiated within the field-of-view. Tissue weighting factors were based on the
2007 International Commission on Radiological Protection (ICRP) recommendations
(41). Values applied for the fraction of tissue irradiated followed those suggested by
Ludlow et al. (40), which were originally estimated for full field-of-view craniofacial
imaging. Table 2 outlines details of parameters used for calculation of the effective
tissue doses, including the 2007 ICRP tissue weighting factors (wT), estimated fraction of
tissue irradiated (fT), and OSL dosimeter identification numbers corresponding to the
particular tissue types.
Finally, all weighted effective tissue doses were summated to provide a total effective
dose (EFDtotal, µSv) for each imaging modality using the following equation:
EFDtotal (µSv) = !(EFDT1 + EFDT2 + … + EFDTn)
23
2.1.5 Statistical Analyses
Mean total effective doses for each of the imaging techniques were established based on
the triplicate scan data, and are expressed as mean effective dose (µSv) ± standard
deviation (µSv). The difference in effective dose between groups was determined by
one-way analysis of variance (ANOVA) and Tukey post-hoc statistical tests. All
statistical analyses were performed using SPSS version 17.0 software (SPSS Inc,
Chicago, IL, USA). Data were deemed statistically significantly different when p<0.05. !
24
Figure 1. Left lateral view of the anthropomorphic RANDO® man phantom.
25
Figure 2. Sample OSL dosimeter placement at level 4 of the anthropomorphic
RANDO® man phantom to measure absorbed dose for the lens and orbit of the right and
left eye.
26
Table 1. Anatomical correlates of OSL dosimeters in RANDO® man anthropomorphic
phantom, as described by Ludlow et al. (40).
Phantom
Level Anatomical Location OSL ID number
Anterior calvarium 1 Midbrain 2 Posterior calvarium 3
2
Left calvarium 4 3 Pituitary fossa 5
Right lens 6 Right orbit 7 Left lens 8
4
Left orbit 9 5 Right cheek 10
Right parotid gland 11 Right ramus 12 Left parotid gland 13 Left ramus 14
6
Cervical spine 15 Right mandibular body 16 Right submandibular gland 17 Right sublingual gland 18 Left sublingual gland 19 Left mandibular body 20 Left submandibular gland 21
7
Left back of neck 22 Right thyroid surface 23 Thyroid midline 24 9 Pharynx 25
!!!!!!!
27
Table 2. Effective tissue dose calculation factors.
Tissue/Organ Tissue weighting factor, wT
a
Estimated fraction
irradiated, fTb
OSL ID number(s)
Bone marrow 16.5% Mandible 1.3% 12, 14, 16, 20 Calvarium 11.8% 1, 3, 4 Cervical spine
0.12
3.4% 15 Thyroid 0.04 100% 23, 24 Esophagus 0.04 10% 25 Skin 0.01 5% 6, 8, 10, 22 Bone surface 16.5%
Mandible 1.3% 12, 14, 16, 20 Calvarium 11.8% 1, 3, 4 Cervical spine
0.01
3.4% 15 Salivary glands 100%
Parotid 100% 11, 13 Submandibular 100% 17, 21 Sublingual
0.01
100% 18, 19 Remainder
Lymphatic nodes 5% 11-21, 24, 25 Muscle 5% 11-21, 24, 25 Extrathoracic airway 100% 7, 9, 11-21, 24, 25 Oral mucosa
0.009 eachc
100% 11-14, 16-21 a Based on 2007 International Commission on Radiological Protection (ICRP) recommendations (41). b Based on recommended values by Ludlow et al. (40). c Remainder tissue/organs tissue weighting factor 0.12 total, divided by 13 possible tissues/organs.
!!!!!!
28
2.2 Part B: Voxel Size and Diagnostic Efficacy
2.2.1 Overview
The Hitachi CB MercuRay 9-inch field-of-view temporomandibular joint imaging
protocol provides reconstructed images with a 0.29mm isotropic voxel size, whereas the
voxel size of reconstructed images acquired by the Kodak 9000 3D unit is 0.076mm
(76µm). A known inverse relationship between voxel size and spatial resolution
indicates that the Kodak 9000 3D images are of higher spatial resolution compared to
those rendered by the Hitachi CB MercuRay.
Since the ability to visualize small changes within the osseous structures is dependent on
the amount of image detail and sharpness, it is reasonable to theorize that images with
higher spatial resolution may provide a diagnostic advantage.
The clinical component of this study was designed to determine the effect of voxel size
on diagnostic efficacy of osseous changes within the temporomandibular joints related to
degenerative joint disease. By utilizing a software-mediated downsampling technique,
the voxel size of Kodak 9000 3D images can be altered, thereby permitting the
comparison of differing spatial resolutions applied to a single cone beam CT acquisition.
2.2.2 Ethics Approval
The Health Sciences Research Ethics Board of the University of Toronto granted ethics
approval for the clinical component of this study, following the completion of
comparative dosimetry analysis (Appendix 2). Patient identifiers were kept confidential
and were removed from the data and thesis.
2.2.3 Equipment Modifications Required for Clinical Use
To translate the technique previously described for imaging the temporomandibular
joints using the Kodak 9000 3D cone beam CT unit from an inanimate anthropomorphic
phantom to living human subjects, two modifications were required.
29
2.2.3.1 Modified Chin Support
A plastic molded chin rest provided by Kodak was used to aid patient positioning and
stabilization during cone beam CT acquisition. Though this chin support adequately
maintained vertical patient positioning, it did not provide a means to adjust the antero-
posterior parameter. To overcome this obstacle, a Hoffman open jaw compressor clamp
(Avogadro’s Lab Supply Inc., Miller Place, NY, USA) was used to provide an anterior
stop for the chin rest position (Figure 3). This clamp could be easily adjusted to meet the
unique antero-posterior positioning requirements for each individual patient.
2.2.3.2 Estimation of Subject Intercondylar Distance
Antero-posterior and supero-inferior positioning using the indicator light was equally
effective and predictable for either the anthropomorphic phantom or a living subject.
However, the medio-lateral positioning is determined strictly by the Kodak software
module crosshairs rather than by a physical landmark projected on the particular subject
being imaged. Determination of the idealized position of the Kodak software module
crosshairs for RANDO® man was found to be located just medial to the medial pole of
the condylar head of interest. A caliper was created to estimate the intercondylar
distance for RANDO® man based on the measured distance between the right and left
preauricular areas (Figure 4). This was found to be approximately 13cm.
To determine the optimized crosshair position for various estimated intercondylar
distances, the facial midline was marked and the anthropomorphic phantom was
manipulated through a series of controlled and measured lateral shifts. For example, by
shifting the midline mark by 1cm to the right and imaging only the right
temporomandibular joint, this simulated an intercondylar distance of 15cm, while
shifting the midline mark by 1cm to the left and imaging the right temporomandibular
joint represented an intercondylar distance of 11cm. This provided a means to better
predict medio-lateral crosshair positioning requirements for living human subjects, in
which a range of intercondylar distances naturally exists (Figure 5).
30
2.2.4 Study Design
A prospective crossover design was used for the clinical component of this study.
Twenty-two subjects with suspected degenerative joint disease presenting to the Oral and
Maxillofacial Radiology clinic at the University of Toronto, Faculty of Dentistry for
temporomandibular joint imaging were recruited for this study. Patient information and
consent forms are provided in Appendix 3. Intercondylar distance was estimated using
the caliper tool, which assisted medio-lateral positioning of the software module
crosshairs. All subjects were imaged with the Kodak 9000 3D cone beam CT unit, using
the bilateral temporomandibular joint acquisition technique with the modifications
previously described, resulting in a total of 44 joints imaged. Operating technique
factors were 70kVp, 10mA, and 10.8s, and all images were acquired at the native voxel
size of 76µm. Figure 6 illustrates correct subject positioning within the Kodak 9000 3D
cone beam CT unit for temporomandibular joint imaging.
2.2.4.1 Inclusion Criteria
Informed consent-capable patients presenting with signs and/or symptoms of
degenerative joint disease of the temporomandibular joints were included in the study.
These clinical features include the following: 1) crepitus on opening/closing; 2) pain on
mandibular movement; 3) limited mandibular opening (may be associated with joint
pain); 4) lateral palpation of the condyle causing increased patient pain and/or
discomfort; and 5) loading of the joint causing increased patient pain and/or discomfort.
2.2.4.2 Exclusion Criteria
Exclusion criteria were applied to those subjects presenting with signs and/or symptoms
of isolated soft tissue abnormalities of the temporomandibular joints (i.e., disc
displacement without clinical evidence of associated degenerative joint disease), cases of
acute trauma to the craniofacial structures, and pregnant female subjects.
31
2.2.5 Image Processing and Downsampling
Acquired images were saved in two formats using the CS 3D Dental Imaging software
(Carestream Dental, Rochester, NY, USA): 1) at a default 76µm (0.076 mm) voxel size
(high resolution), and 2) at a downsampled 300µm (0.300 mm) voxel size (low
resolution). This provided a total of 88 temporomandibular joint cone beam CT volumes
for review.
Downsampling merges the data from several adjacent voxels into a single larger voxel.
This results in a reduction of spatial resolution due to increasing the voxel size, but also
reduces image noise thereby improving contrast resolution. The CS 3D Dental Imaging
software provides downsampling options of 100µm, 200µm, 300µm, 400µm, 500µm, and
1mm. The choice to use 300µm downsampled images provided a theoretical simulation
of the spatial resolution of the Hitachi CB MercuRay system conventionally used at our
institution for temporomandibular joint imaging, which has a native voxel size of
0.29mm. The downsampling procedure provided a realistic and practical comparison
between high and low spatial resolution cone beam CT images, and precluded the need
for duplicate scanning of each subject. Figure 7 provides an illustration of the effect of
the downsampling technique on a representative temporomandibular joint Kodak 9000
3D cone beam CT volume.
2.2.6 Image Analysis
Each image volume was anonymized, blindly coded, and randomized by an individual
not acting as an observer in the study. Three observers (all nationally certified Oral and
Maxillofacial Radiologists) independently reviewed the images of the
temporomandibular joints using the CS 3D Dental Imaging software. Prior to review of
the study sample cases, the three observers underwent a calibration exercise to improve
interobserver reliability (Appendix 4). After a washout period of two weeks, one of the
observers reviewed a subset of the series (22 volumes, 25% of the total study sample) a
second time to determine intraobserver reliability. Observers were free to manipulate the
data in any plane of view, to modulate image brightness and contrast, and to use the
32
zoom function as desired. To facilitate and expedite case analyses, observers were
permitted to utilize a computer and monitor of their choice, and no restrictions regarding
ambient viewing conditions were imposed. No time limit was imparted upon the
observers to reach an interpretation for each case. Agreement on the presence or absence
of a feature between two of the three examiners was interpreted as truth. There was no
attempt made to resolve disagreement between observers.
The following features of degenerative joint disease involving the condylar or temporal
component of the joint were noted for each case as a dichotomous variable (yes if the
feature is present, no if the feature is absent): 1) cortical erosion; 2) subchondral
sclerosis; 3) flattening; 4) osteophyte or joint mouse/mice; and 5) Ely (subchondral) cyst.
In addition to evaluation for the presence of specific radiographic features, a visual
analog scale was provided for each volume. Observers were asked to place a single hash
mark along a 10cm line that represented their perceived image quality, ranging from low
image quality on the left to high image quality on the right.
A sample score sheet for identification of radiographic features and the visual analog
scale is depicted in Appendix 5.
2.2.7 Statistical Analyses
Interobserver reliability was evaluated using Fleiss’ kappa using an Excel-based program
designed for multirater data, as the SPSS software does not provide an algorithm for
comparing more than two observers (42,43). All remaining data analysis was carried out
using SPSS version 17.0 software (SPSS Inc, Chicago, IL, USA). Cohen’s kappa was
used to determine intraobserver reliability. Kappa values of agreeability were defined
according to the criteria defined by Landis and Koch (44). The McNemar’s chi-squared
test for paired groups evaluated the effect of voxel size on detection of osseous changes
related to degenerative joint disease for each of the aforementioned categories of
radiographic findings. All cases demonstrated a small number of discordant pairs (<25),
thus the SPSS software automatically used the binomial distribution to provide a two-
sided significance value, rather than using the conventional chi-squared distribution.
33
Finally, the paired samples t-test was used to measure the effect of changing voxel size
on visual analog scale ratings by the observers. Data were considered significant when
p<0.05.
34
Figure 3. Modified chin support with the Hoffman open jaw compressor clamp attached
to modulate subject antero-posterior positioning in the Kodak 9000 3D cone beam CT
unit during a temporomandibular joint imaging procedure.
35
Figure 4. Caliper tool for estimation of intercondylar distance.
!
36
Figure 5. Kodak acquisition module software medio-lateral crosshair positioning guide
based on estimated intercondylar distance.
37
Figure 6. Correct subject positioning within the Kodak 9000 3D cone beam CT unit for
temporomandibular joint imaging.
38
Figure 7. Downsampling technique applied to a temporomandibular joint image volume
acquired using the Kodak 9000 3D cone beam CT system. (A) and (B) represent
corrected coronal and sagittal images, respectively, at the native 76µm voxel size.
Images (C) and (D) represent corrected coronal and sagittal images, respectively, at a
downsampled 300µm voxel size.
A B
C D
39
Chapter 3
3 Results
3.1 Part A: Comparative Dosimetry
Table 3 outlines the mean effective tissue doses and the summated total mean effective
doses for the various cone beam CT imaging modalities and technique factors
investigated during the comparative dosimetry study. The mean effective radiation dose
for the Hitachi CB MercuRay technique was 223.6±1.1µSv, compared to 9.7±0.1µSv and
20.5±1.3µSv for the unilateral and bilateral Kodak 9000 3D acquisitions, respectively,
when operating at the standard adult (70kVp, 10mA) setting. Modifying the Kodak
technique factors resulted in mean effective doses of 9.7±0.1µSv (68kVp, 6.3mA),
13.5±0.5µSv (70kVp, 8mA), and 19.7±0.6µSv (74kVp, 10mA) for the child, youth, and
large adult settings, respectively.
The difference in mean effective dose between groups was significant at p<0.0001,
determined by one-way ANOVA. Tukey post-hoc analysis showed that all bilateral
acquisition groups significantly differed from one another (p<0.05), with the exception of
the Kodak standard adult and large adult settings (p=0.652).
40
Table 3. Mean effective tissue doses and total effective doses with respective standard
deviation values for each of the temporomandibular joint imaging modalities and
technique settings.
Mean Effective Tissue Dose (µSv)
Imaging Modality/Technique Setting
Bilateral Kodak
Hitachi
Unilateral Kodak Child Youth Standard
Adult Large Adult
Tissue/Organ
100kVp 10mA
70kVp 10mA
68kVp 6.3mA
70kVp 8mA
70kVp 10mA
74kVp 10mA
Bone marrow 58.23 1.72 1.54 2.17 3.28 3.21
Thyroid 18.90 0.94 0.51 0.93 1.87 1.51
Esophagus 1.99 0.11 0.06 0.12 0.22 0.14
Skin 2.25 0.36 0.40 0.49 0.49 0.61
Bone surface 4.87 0.14 0.13 0.18 0.27 0.27
Salivary glands 36.73 1.85 1.67 2.31 3.84 3.32
Brain 30.32 0.86 1.58 2.18 2.42 3.13
Lymphatic nodes 1.51 0.08 0.07 0.10 0.16 0.14
Muscle 1.51 0.08 0.07 0.10 0.16 0.14
Extrathoracic airway 32.00 1.71 2.06 2.75 4.09 4.08
Rem
aind
er
Oral mucosa 35.29 1.88 1.60 2.22 3.72 3.18
Mean effective dose (µSv) 223.6 9.7 9.7 13.5 20.5 19.7
Standard deviation (µSv) 1.1 0.1 0.1 0.5 1.3 0.6
41
3.2 Part B: Voxel Size and Diagnostic Efficacy
Tables 4 and 5 depict interobserver and intraobserver reliability data, respectively, for
detection of osseous changes related to degenerative joint disease. Interobserver
reliability for all radiographic features combined yielded kappa coefficients of 0.31 and
0.30 for the 76µm and 300µm voxel sizes, respectively. This denotes “fair” strength of
interobserver agreement overall, according to the Landis and Koch criteria.
Intraobserver reliability kappa coefficient for all radiographic features combined was
0.69, which indicates “substantial” strength of agreement.
Table 6 outlines the effect of voxel size on detection of osseous changes related to
degenerative joint disease as determined by the McNemar "2 test for paired groups.
Based on majority data (considered to be when at least two of the three observers agree
on the presence or absence of an osseous finding), there was no significant difference in
feature detection when comparing the 76µm and 300µm voxel sizes. Even when each
observer’s responses were considered individually, only a single observer found condylar
flattening to differ significantly (p<0.05) between the two different voxel sizes.
The mean visual analog scale (VAS) response by observers for the 76µm images was 7.4,
compared to 7.1 for the 300µm voxel size. This difference was statistically significant
(p=0.020) as determined by the paired samples t-test (Table 7). All observers tended to
rate the 76µm images with slightly higher perceived image quality (Figure 8).
42
Table 4. Fleiss’ kappa for interobserver reliability.
VOXEL SIZE
76µm 300µm RADIOGRAPHIC FEATURE Number (n) of
positive agreementsa kappa Number (n) of
positive agreementsa kappa
Cortical erosion 10 0.21 15 0.14
Subchondral sclerosis 18 0.11 18 0.19
Flattening 19 0.26 17 0.03
Osteophyte/joint mouse 9 0.56 6 0.19 CO
ND
YL
AR
C
OM
PON
EN
T
Subchondral (Ely) cyst 5 0.55 6 0.68
Cortical erosion 7 -0.07 5 0.03
Subchondral sclerosis 13 0.22 6 0.16
Flattening 9 0.20 11 0.32
Osteophyte/joint mouse 1 0.40 3 0.33 TE
MPO
RA
L
CO
MPO
NE
NT
Subchondral (Ely) cyst 0 -0.01 0 -0.01
All radiographic features combined 91/440 (20.7%) 0.31 87/440 (19.8%) 0.30
a Number (n) of positive agreements (i.e., at least two out of three observers denoted the feature as “present”) out of a possible of 44 for each radiographic feature category. For all radiographic features combined, the number of positive agreements represents a summation of the column total.
43
Table 5. Cohen’s kappa for intraobserver reliability.
Number (n) of positive findingsa RADIOGRAPHIC FEATURE
First Observation Second Observation
kappa
Cortical erosion 6 7 0.46
Subchondral sclerosis 13 14 0.52
Flattening 18 18 0.70
Osteophyte/joint mouse 6 7 0.46 CO
ND
YL
AR
C
OM
PON
EN
T
Subchondral (Ely) cyst 3 5 0.70
Cortical erosion 0 1 n/ab
Subchondral sclerosis 4 6 0.49
Flattening 9 9 0.62
Osteophyte/joint mouse 0 0 n/ab TE
MPO
RA
L
CO
MPO
NE
NT
Subchondral (Ely) cyst 0 0 n/ab
All radiographic features combined 59/220 (26.8%) 67/220 (30.5%) 0.69
a Number (n) of positive findings out of a possible of 22 for each radiographic feature category. For all radiographic features combined, the number of positive findings represents a summation of the column total. b No kappa coefficient can be calculated if the first and/or second categorical observations demonstrated no significant findings (all responses = 0).
44
Table 6. Radiographic feature identification results based on the McNemar "2 test for
paired groups.
Two-sided p-value (exact significance)a RADIOGRAPHIC FEATURE
Majority Observer 1 Observer 2 Observer 3
Cortical erosion 0.180 1.000 1.000 0.344
Subchondral sclerosis 1.000 1.000 0.065 0.774
Flattening 0.727 1.000 0.375 0.021
Osteophyte/joint mouse 0.250 0.500 0.500 0.289 CO
ND
YL
AR
C
OM
PON
EN
T
Subchondral (Ely) cyst 1.000 1.000 0.500 1.000
Cortical erosion 0.687 1.000 0.210 0.625
Subchondral sclerosis 0.092 0.687 0.581 0.581
Flattening 0.687 1.000 1.000 0.508
Osteophyte/joint mouse 0.500 0.500 1.000 n/ab TE
MPO
RA
L
CO
MPO
NE
NT
Subchondral (Ely) cyst n/ab n/ab 1.000 n/ab
a All cases demonstrated a small number of discordant pairs (<25), thus the binomial distribution was used to provide a two-sided significance value, rather than using the conventional chi-squared distribution. b No p-value can be calculated if the first and/or second categorical observations (76µm or 300µm) demonstrated no significant findings (all responses = 0).
45
Table 7. Effect of voxel size on visual analog scale (VAS) responses by observers based
on a paired samples t-test.
Voxel Size Mean VAS Rating
n (number of paired observations) t-statistic dfa Significance (two-
sided p-value)
76µm 7.4 132
300µm 7.1 132 2.351 131 0.020
a Degrees of freedom, which is determined by the number of paired observations minus 1 (df = n – 1).
46
Figure 8. Visual analog scale ratings of image quality for the overall average from all
observers, as well as from each observer independently, for the 76µm and 300µm voxel
sizes.
47
Chapter 4
4 Discussion
4.1 Part A: Comparative Dosimetry
4.1.1 Hitachi CB MercuRay Versus Kodak 9000 3D
The dosimetry data demonstrate that utilization of separate right and left
temporomandibular joint limited field-of-view cone beam CT acquisitions provides more
than a ten-fold reduction in effective radiation dose compared to the larger single field
acquisition for a standard adult patient (223.6µSv for the Hitachi CB MercuRay 9-inch
field-of-view acquisition versus 20.5µSv for two limited field-of-view Kodak 9000 3D
acquisitions). Because the estimated fractions of tissues irradiated were based on 12-inch
field-of-view cone beam CT estimates, which includes the active bone marrow of the
entire cranium, mandible, and most of the cervical vertebrae, the thyroid gland, and all
major salivary glands, our results for the Kodak 9000 3D acquisition may be an
overestimation of the percentage of tissue irradiated within the limited field-of-view
temporomandibular joint imaging volume. Therefore, the dose reduction provided by the
Kodak 9000 3D might be, in reality. even greater than indicated by our calculations. The
effective radiation dose of the bilateral Kodak 9000 3D acquisitions is comparable to that
imparted by most digital panoramic radiographic systems, which has been reported to
range between 14.7µSv to 24.5µSv (45). In addition to generating high quality three-
dimensional images of the temporomandibular joints, the limited field-of-view imaging
protocol may offer dental practitioners equipped with only a limited field-of-view cone
beam CT unit an opportunity to provide temporomandibular joint imaging for their
patients at a radiation dose comparable to a typical panoramic radiograph.
Previous dosimetry data indicate a significant difference in effective radiation dose
between the Hitachi CB MercuRay and Kodak 9000 3D cone beam CT systems, but did
not specifically measure radiation dose when the field-of-view is centered about the
temporomandibular joints. Ludlow and Ivanovic investigated comparative dosimetry of
48
64-slice medical CT and eight different cone beam CT units, including the Hitachi CB
MercuRay, using a similar technique to our study protocol (8). Cone beam CT devices
were compared using varying field-of-view sizes, and International Commission on
Radiological Protection (ICRP) tissue weighting factors were based on the 2007
guidelines. The 6-inch, 9-inch, and 12-inch field-of-view effective doses for the Hitachi
CB MercuRay operating at “maximum quality” settings of 120kVp and 15mA were
407µSv, 560µSv, and 1073µSv, respectively. The Hitachi CB MercuRay produced the
highest effective dose of all the cone beam units when considering the 9-inch field-of-
view; only the 64-slice Somaton multidetector medical CT dose was greater (860µSv).
The 12-inch field-of-view effective dose for the Hitachi CB MercuRay was also
evaluated using “standard quality” settings of 100kVp and 10mA, and this rendered an
effective radiation dose of 569µSv, which represents about a 47% reduction in dose
compared to when the “maximum quality” technique factors were used. If the effective
dose for a 9-inch field-of-view acquisition of 560µSv while operating at 120kVp and
15mA from the Ludlow and Ivanovic study is scaled by the same 47% reduction in dose
when using 100kVp and 10mA settings, this would theoretically yield an effective dose
of approximately 297µSv. The present study demonstrated an effective dose of
223.6µSv for a 9-inch field-of-view Hitachi CB MercuRay temporomandibular joint
study, which is in reasonable agreement with this hypothetical value based on the
aforementioned study.
Jadu et al. evaluated effective radiation doses for cone beam CT sialography, centering
either the parotid or submandibular gland within the image field (46). The study
compared effective doses for the 6-inch, 9-inch, and 12-inch field-of-view options for the
Hitachi CB MercuRay, operating at variety of kVp and mA settings. When the parotid
gland was centered within the image field, the respective effective doses for the 6-inch,
9-inch, and 12-inch fields-of-view were 97µSv, 275µSv, and 466µSv with 100kVp and
10mA exposure settings. Centering the submandibular gland generated effective doses
of 261µSv, 275µSv, and 466µSv, respectively. The increased effective dose during
submandibular gland imaging using a 6-inch field-of-view was explained by increased
exposure of the radiosensitive thyroid gland. These data also demonstrate good
agreement with the present study; as expected, centering the temporomandibular joints
49
within the field-of-view imparts less radiation dose upon radiosensitive structures such as
the thyroid, submandibular, and sublingual glands, which explains why the measured
effective radiation dose in this study is less than that found by Jadu et al.
In comparison to the large field-of-view cone beam CT imaging modalities, little work
has been published on the effective dose from limited field systems. Ludlow compared
effective radiation doses for the anterior and posterior regions of the maxilla and
mandible using the Kodak 9000 3D unit, operating at 70kVp and 10mA (21). Effective
doses ranged from 5.3µSv for the anterior maxilla to 38.3µSv for the posterior mandible.
Conceivably, the posterior maxilla would most closely represent the temporomandibular
joint region of interest in the present study. The effective radiation dose for this area was
found by Ludlow to be 9.8µSv, which is in good agreement with our 9.7µSv result for a
unilateral temporomandibular joint Kodak 9000 3D acquisition.
Based on earlier dosimetry studies, it is clear that there is large variation in the effective
radiation dose imparted by various cone beam CT systems. The comparative dosimetry
study by Ludlow and Ivanovic (8) demonstrated a range in effective dose from 69µSv
rendered by the Classic i-CAT standard scan compared to 560µSv for the Hitachi CB
MercuRay operating in the panoramic mode (9-inch field-of-view), with both machines
utilizing an equivalent field-of-view technique. Technical factors used in the study for
the two devices vary considerably; the Hitachi CB MercuRay utilizes a scan time of 10s,
operating at 120kVp and 15mA, whereas the Classic i-CAT standard settings operate at
120kVp and 5mA over a 20s acquisition time. Clearly, when using the Kodak 9000 3D
for bilateral temporomandibular joint acquisitions, the dose reduction is more significant
when comparing the values to the Hitachi unit versus the i-CAT system. However, this
Kodak temporomandibular joint imaging technique does still provide approximately a
three- to four-fold dose reduction compared to that from the relatively low dose classic i-
CAT standard scan.
It should be noted that this study used optically stimulated luminescence (OSL)
dosimeters, whereas the aforementioned studies utilized thermoluminescent dosimeters.
The decision to use OSL dosimeters was predicated on their enhanced sensitivity to low
50
dose radiation compared to the thermoluminescent dosimeters, with a purported lower
limit of detection of 10µGy (Appendix 1). While dose readouts for thermoluminescent
dosimeters require heating and result in destruction of the dosimeter, OSL dosimeter
readout is achieved by use of stimulation with 540nm light photons and can be repeated
if required (47). An ideal dosimeter is equally sensitive to radiation exposure in all
directions, such that orientation of the dosimeter has no bearing on the amount of
radiation absorbed. In this study, the orientation of the OSL dosimeters was consistent
between scan repetitions, with the flat 1x1cm surface of the dosimeters oriented parallel
to the incoming x ray beam. Reproducibility in dosimeter orientation is necessary to
ensure that absorbed dose data are fairly compared and contrasted between different
acquisitions. Variability in dosimeter orientation between studies creates a potential
confounding factor for data comparison. A study comparing measured radiation doses
by thermoluminescent and OSL dosimeters found a strong correlation between the two
systems (r2=0.99), which suggests that comparison between data produced by the two
dosimeters is feasible (48). This experiment also demonstrated significant angular
dependence of both the thermoluminescent and OSL dosimeters, but no significant
difference in the magnitude of angular dependence between the two systems was
observed. This finding implies that consistency in dosimeter orientation is indeed of
paramount importance to validate comparisons between absorbed dose data within an
investigation, but also creates uncertainty in the ability to reliably evaluate data between
different studies.
Another potential limitation in interpretation of the existing comparative dosimetry
research involves reported variability in dosimeter-derived measurements based on the
number of dosimeters used to obtain absorbed dose values. For example, the studies by
Ludlow (21) and Pauwels et al. (49) both evaluated dosimetry for the Kodak 9000 3D
cone beam CT unit in the anterior maxilla using the 2007 International Commission on
Radiological Protection (ICRP) tissue weighting factors, with reported effective doses of
5.3µSv and 19µSv, respectively. Whereas Ludlow placed thermoluminescent dosimeters
at 24 sites throughout an adult skull phantom, Pauwels et al. used approximately 150
dosimeters. The use of a greater number of thermoluminescent dosimeters is believed to
increase measurement accuracy since the absorbed dose for a particular organ is
51
calculated as a mean of all absorbed doses measured by the dosimeters placed within that
specific area of interest. More dosimeters reduce the variability in measured dose
resulting from a slight change in position of the primary beam, and also improve
reproducibility of dosimetric data. Because optically stimulated luminescence (OSL)
dosimeters are significantly larger than thermoluminescent dosimeters (3mm x 3mm x
1mm), there are obvious limitations to the number of dosimeters that could be placed
without structural compromise and an alteration in the attenuation profile characteristics
of the anthropomorphic phantom.
4.1.2 Translating Exposure to Risk
Dosimetry studies often provide an annual background radiation effective dose
equivalency to the measured radiation dose imparted by a particular radiographic
examination (8,45). Based on the most recent data published for the United States
population, the annual background radiation dose is approximately 3.1mSv (3100µSv)
per person (50), which equates to about 8.5µSv each day. While there is a tendency to
directly compare the dose burden rendered by a diagnostic imaging procedure to
“equivalent days of background radiation”, caution must be exercised in interpreting
these data in this way. Background radiation delivers a chronic, whole body exposure,
and often involves high-energy gamma rays or particulate radiation, whereas diagnostic
imaging results in an acute exposure applied to a limited anatomical region and generally
utilizes lower energy x ray photons. Taking these disclaimers into account, the
background equivalency for a temporomandibular joint examination by the Hitachi CB
MercuRay is approximately 26.3 days, compared to about 2.4 days for the bilateral
standard adult Kodak 9000 3D technique (Appendix 6). This comparison is likely most
useful as an aid to provide inquisitive patients with a concept of the relative amounts of
radiation they are exposed to during an imaging procedure.
A further extrapolation of comparative dosimetry research is to estimate excess
population risk, which again makes several important assumptions including a normal
population distribution regarding both age and gender. A risk coefficient of 0.055 events
per sievert (41,45) is the commonly accepted value for carcinogenesis risk determination.
52
In our study, the Hitachi CB MercuRay temporomandibular joint examination would thus
result in a probability of 12 cases of fatal cancer per one million exposures, versus 1.1
cases in one million bilateral standard adult Kodak 9000 3D exposures (Appendix 6).
Similar to comparing effective radiation dose to background radiation, this provides a
tool for explaining the risk of a procedure to a patient in the simple and easily
understandable terms of “x in a million”.
4.1.3 Kodak 9000 3D Technique Factor Modulation
Modulation of the voltage and current exposure factors on the Kodak 9000 3D results in
a significant reduction in effective radiation dose when the child (9.7µSv) and
youth/small adult (13.5µSv) settings were used compared to the standard adult settings
(20.5µSv). Radiosensitivity is inversely related to age; young patients are approximately
ten times more sensitive to the deleterious effects of ionizing radiation compared to
adults (12). This observation is consistent with the Law of Bergonie and Tribondeau
(51), which states that radiosensitivity is greatest for cells with a high mitotic rate, with
many potential future divisions, and that are undifferentiated. While these
generalizations were initially applied to the cellular level, extrapolation of this data to a
young individual undergoing active growth and development is only logical. As a result,
the use of prudent selection criteria and dose reduction techniques is imperative in
younger patient populations. This becomes particularly important in cases where
multiple radiographic examinations are required to monitor disease progression. Juvenile
idiopathic arthritis involves the temporomandibular joints in approximately 40% of cases
(1), and the potentially progressive nature of the disease often necessitates serial imaging
studies. The use of a bilateral limited field-of-view cone beam CT temporomandibular
joint examination for these patients using the youth/small adult technique factor settings
yields a 34% lower dose than the standard adult protocol, and provides superior images
of the osseous joint structures compared to magnetic resonance (MR) imaging.
It is important to note that while minimizing radiation dose is important, this cannot be
done at the expense of diagnostic image quality. X ray beam current (mA) is
proportional to the signal-to-noise ratio of an image. Increasing the mA setting by a
53
factor of two concurrently increases the signal-to-noise ratio by a factor of !2, or 1.41
(19). This implies that the use of the child (6.3mA) and youth (8mA) exposure settings
would result in a signal-to-noise ratio of 0.79 and 0.89 that of the standard adult
technique, respectively. If this results in image quality that is no longer diagnostic, the
advantage of a reduction in effective radiation dose is nullified. The inclusion of the
high-density temporal bone in the imaging volume also must be considered, as extensive
beam attenuation in this region may further contribute to deteriorated image quality
under low current conditions. Analysis of image quality using these varying technique
factors in child- and youth-sized anthropomorphic phantom should be performed before
routine implementation of such dose reduction protocols can be recommended.
No significant difference was noted between the standard adult and large adult
techniques (20.5µSv versus 19.6µSv, p=0.652). These two techniques varied only in
voltage setting (70kVp for standard adult versus 74kVp for large adult), with the current
held constant at 10mA. An increase in potential kilovoltage results in a more energetic x
ray beam and a greater number of x ray photons; that is, it increases both beam quality
and quantity. Higher energy photons have a reduced chance of being absorbed and
contributing to dose (19). Thus, while the net number of x ray photons is increased by
increasing the kVp setting, the actual number of photons absorbed is also decreased,
which may provide an explanation why the standard adult and large adult effective
radiation dose values did not demonstrate a significant difference.
A potential limitation of this study component arises from the use of a single
anthropomorphic phantom intended to simulate an average sized adult male subject. The
author’s institution did not have access to a child, youth/small adult, or large adult
phantom, thus all of the experiments involving modulation of technique factors were
performed using the standard adult male equivalency. As a phantom increases in size,
there is a greater volume of tissue between the surface and center of the phantom, and the
absorbed radiation dose at the center is roughly half that measured at the surface (52).
Conversely, a smaller phantom resembling a pediatric subject would demonstrate more
uniform surface and central doses due to less peripheral attenuation of the x ray beam.
This equates to a higher absorbed dose in a smaller subject, and ultimately a higher
54
calculated effective dose (53). However, head diameter varies relatively little between
pediatric and adult subjects, relative to other anatomical sites such as the abdomen (54).
When comparing a standard and large sized adult, the difference in head diameter is
likely to be of even less clinical significance. Thus, the use of a 16cm phantom for head
CT scans is generally considered acceptable for the purpose of calculating comparative
dosimetry values in all age groups (55). While our effective radiation dose data for the
child and youth technique factor settings would likely be marginally increased if the
respective sized phantoms were utilized, our current protocol is still deemed acceptable
and valid within the present dosimetry research and body of knowledge.
4.1.4 Future Directions in Comparative Dosimetry Research
Though most dental comparative dosimetry studies to date utilize dosimeters placed
within an anthropomorphic phantom, issues such as variability in dosimeter positioning
relative to the incoming x ray beam and the use of a limited number of dosimeters to
estimate total doses to organs or tissues result in methodological weakness. A recent
publication outlined the use of an alternative technique known as the Monte Carlo dose
computation to measure dosimetry for the next generation i-CAT cone beam CT unit
(56). Monte Carlo analyses use computer-based simulations to estimate both primary
and scattered photon interactions within a standardized International Commission on
Radiological Protection (ICRP) computational phantom (57), and purportedly mitigates
many of the shortcomings of dosimeter-based techniques (19,56). Using the 16cm
diameter by 13cm height field-of-view for dentoalveolar imaging, the Monte Carlo
effective dose was calculated at 66µSv (56), compared to a value of 83µSv published by
Pauwels et al. (49) using approximately 150 thermoluminescent dosimeters for the same
cone beam CT acquisition. As more researchers adopt the Monte Carlo technique for
comparative dosimetry analyses, there will likely be some modest revisions to the
presently accepted effective radiation dose values for various oral and maxillofacial cone
beam CT imaging protocols.
55
4.2 Part B: Voxel Size and Diagnostic Efficacy
4.2.1 Effect of Voxel Size on Detection of Osseous Changes
The clinical component of this study evaluated the effect of Kodak 9000 3D cone beam
CT image voxel size on the ability to detect osseous changes related to degenerative joint
disease, in which each case acted as its own control. While it was hypothesized that
osseous changes would be better appreciated when viewing images with a smaller voxel
size (i.e., higher spatial resolution), this was not in fact found to be the case. No
significant difference between the native 76µm voxel size and the downsampled 300µm
voxel size was detected for any of the degenerative joint disease related changes when
observer data were compiled. Even when each observer was considered on an individual
basis, only one individual rated a difference in visualization of condylar component
flattening between the two different voxel sizes. One would expect that subtle changes
such as small cortical erosions would be more readily observed at a higher spatial
resolution, whereas detection of more grossly evident changes such as flattening and
subchondral sclerosis would be less dependent on voxel size. Unfortunately, because
observers were not required to quantify the size of cortical erosions, statistical analyses
of these data are not possible. It is important to note that while no significant difference
was noted between the two groups, this finding can only be applied to Oral and
Maxillofacial Radiologists and cannot be reliably extrapolated to other dental
practitioners. Further analysis is required to determine if differences in training and
experience play a role in the detection of osseous changes under varying spatial
resolution parameters.
Interobserver agreement for both the 76µm and 300µm voxel sizes was found to be only
“fair”, with respective kappa coefficients of 0.31 and 0.30. The low frequency of some
of the radiographic features may have contributed to these relatively low interobserver
agreement values (Table 5), and ultimately this may have weakened the statistical
analysis when evaluating the effect of voxel size on detection of osseous changes. A
possible improvement in the study design would include attempted resolution of observer
disagreement to reach a true consensus on radiographic feature identification, rather than
56
the majority approach utilized in the current analysis. Furthermore, observers were given
a forced decision matrix model when evaluating the temporomandibular joints for
osseous changes related to degenerative joint disease. There was no opportunity for
observers to indicate a level of confidence in their designation of the presence or absence
of a particular radiographic feature. While obvious osseous changes would be
considered by most as an objective finding and show little interobserver variability, more
subtle changes likely demonstrate greater subjectivity and depend on each observer’s
unique threshold for diagnosis. The inclusion of a visual analog scale for observers to
rank their confidence level would provide an additional dimension for data analysis.
Additionally, increasing the number of cases evaluated would increase study power and
reduce the likelihood of a type II statistical error, in which a false null hypothesis is not
rejected.
The finding that voxel size does not impact the ability to detect osseous changes cannot
be extrapolated beyond the Kodak 9000 3D to other cone beam CT imaging systems,
including the Hitachi CB MercuRay. While downsampling Kodak 9000 3D data to
300µm theoretically provides a spatial resolution similar to the native Hitachi CB
MercuRay panoramic mode 0.29mm voxel size, the resulting images differ
conspicuously (Figure 9). Diversity in the type of sensor and field-of-view both
contribute to variability in image quality, which is primarily determined by the
parameters of spatial resolution and contrast resolution. The Hitachi CB MercuRay uses
an image intensifier sensor united with a charge coupled device (CCD) camera, while the
Kodak 9000 3D uses a complementary metal oxide sensor (CMOS). Factors such as
thickness and atomic number of the detector material and the speed of the sensor all
contribute to the final spatial resolution and contrast resolution of an imaging system.
The next contributory factor to image quality difference between the two cone beam CT
systems involves the field-of-view, which is much larger for the Hitachi CB MercuRay
compared to the Kodak 9000 3D (9-inch/22.9cm sphere versus 5cm diameter by 3.7cm
high, respectively). By increasing the field-of-view, there is a concordant increase in the
amount of scatter radiation. This results in more image noise (i.e., a decreased signal-to-
noise ratio) and ultimately reduces image contrast resolution. Field-of-view modulation
has no impact on spatial resolution. One advantage of this study design is the ability to
57
isolate the test variable, voxel size, while maintaining consistency in all other variables
through the manipulation of a single cone beam CT acquisition into two different
viewing parameters. This eliminated potential confounding factors from the data
analysis, thereby permitting stronger and more focused study conclusions.
4.2.2 Effect of Voxel Size on Perceived Image Quality
While images with a smaller voxel size conferred no diagnostic advantage, observers
denoted the higher spatial resolution cone beam CT datasets to be of superior image
quality. Downsampling the data from 76µm to 300µm reduced the spatial resolution, but
increased the contrast resolution through improvement of the signal-to-noise ratio. This
suggests that Oral and Maxillofacial Radiologists find spatial resolution a more important
parameter than contrast resolution when evaluating image quality. An objective
evaluation of the effect of downsampling on contrast resolution through calculation of
the signal-to-noise and contrast-to-noise ratios is a potential area of further research.
4.2.3 Study Limitations
While this is the first clinical study to describe the use of the Kodak 9000 3D cone beam
CT system for temporomandibular joint imaging and to compare the effect of spatial
resolution on diagnostic efficacy of osseous changes within the temporomandibular
joints, the use of living patients as subjects renders specific limitations. While it would
have been more realistic to directly compare the ability to detect osseous changes when
using the conventional Hitachi CB MercuRay unit versus the alternative Kodak 900 3D
cone beam CT system, this is not consistent with ethical radiology practice or the
principles of radiation protection. The downsampling technique thus provided an
alternative means to simulate cone beam CT data at two different voxel sizes without the
need to perform multiple acquisitions. The use of living human subjects also precluded
comparison of imaging findings with the gold standard for detection of osseous changes
related to degenerative joint disease, which is direct visualization performed through
autopsy studies or the use of dry skull specimens. As a result, it was not possible to
evaluate the number of true and false radiographic findings, both positive and negative,
58
reported by observers in this study. This limits the calculation of sensitivity, specificity,
accuracy, and receiver operating characteristic (ROC) curve data.
59
Figure 9. Native Hitachi CB MercuRay panoramic mode 0.290mm temporomandibular
joint images compared to 300µm downsampled Kodak 9000 3D images using the
anthropomorphic phantom. (A) and (B) represent corrected coronal and sagittal images,
respectively, for the Hitachi CB MercuRay. Images (C) and (D) represent corrected
coronal and sagittal images, respectively, for the Kodak 9000 3D at a downsampled
300µm voxel size.
B
A
C
D
60
4.2.4 Drawbacks of Limited Field-of-View Imaging
The Kodak 9000 3D cone beam CT system offers an excellent alternative to conventional
large field-of-view temporomandibular joint imaging. However, the clinical component
of this study highlighted a few specific challenges associated with this novel protocol.
Centering the joint within the image volume is technique sensitive and requires a
significant time investment compared to positioning a patient for a large field-of-view
study. Medio-lateral positioning was by far the most unpredictable parameter, even with
use of the caliper and indicator guide. Variability in subject soft tissue profiles likely
explains this issue. Problems with supero-inferior positioning were most often noted
when the condylar head was difficult to palpate upon mandibular opening, thus
complicating the supero-inferior landmarking step. Such errors were generally confined
to incomplete imaging of the temporal component of the joint, specifically cropping off
the roof of the glenoid fossa. Antero-posterior localization was the most predictable
parameter, probably because an easily identifiable anatomical landmark (1cm anterior to
the external auditory meatus) was used as a reference.
Although there were a small number of re-acquisitions required because of these
positioning difficulties, modifying the inaccurate parameter provided resolution in the
follow-up scan with a high degree of certainty. Even with an additional acquisition using
the Kodak 9000 3D unit, the total effective radiation dose is still vastly less than what
would be rendered by the Hitachi CB MercuRay system.
4.2.5 Practical Considerations
Based on the aforementioned voxel size data, one may initially conclude that it is still
desirable to use the higher spatial resolution images since the perceived image quality is
greater, despite conferring no diagnostic advantage. However, the storage footprint and
portability of cone beam CT data should also be taken into account. A typical bilateral
Kodak 9000 3D temporomandibular joint study acquired at a 76µm voxel size requires
about 404 megabytes (MB) of computer data storage. Downsampling the same study to
100µm or 200µm reduces this requirement to 186MB (54% reduction) or 26MB (94%
61
reduction), respectively. When the data are downsampled to the 300µm voxel size used
in this study, which demonstrated no difference in diagnostic efficacy compared to the
native 76µm voxel size, the storage requirement is reduced to 8MB, a 98% reduction.
Not only does this produce a significant reduction in the storage footprint, but it also
allows for enhanced file transferability via e-mail communication. While one of the
advantages of digital imaging is greater portability of information between practitioners,
this becomes limiting when large file sizes must be transferred. The downsampling
module creates a quick and simple solution to this problem.
The practical economic implications of this study must also be addressed. Limited field-
of-view cone beam CT units are significantly less expensive than the larger field-of-view
systems. Many clinicians are averse to the limited field scanners based on the notion that
imaging is confined to the dentoalveolar regions. This research outlines a
straightforward technique to expand the conventional capabilities of a limited field-of-
view cone beam CT system, providing high quality images the temporomandibular
joints. Furthermore, the restricted irradiated volume of tissue results in a significantly
reduced radiation dose, which must always be an implicit part of the decision making
process when prescribing a radiographic examination.
62
Chapter 5
5 Conclusions
This is the first study to evaluate comparative dosimetry specific to temporomandibular
joint cone beam CT imaging. The use of bilateral limited field-of-view Kodak 9000 3D
cone beam CT acquisitions of the temporomandibular joints provides more than a ten-
fold reduction in the effective radiation dose compared to the Hitachi CB MercuRay
technique traditionally used at our institution. Modulation of the Kodak 9000 3D cone
beam CT system exposure factors provides a further opportunity to reduce radiation
dose, particularly to younger, more radiosensitive patients.
While the Kodak 9000 3D cone beam system offers the smallest voxel size of any
commercially available cone beam CT unit at 76µm, there was no significant difference
in the detection of osseous changes related to degenerative joint disease by Oral and
Maxillofacial Radiologists when comparing the native high spatial resolution images to
those with a downsampled voxel size of 300µm. Despite no effect on diagnostic
efficacy, perceived image quality was consistently higher for images with greater spatial
resolution.
The use of a limited field-of-view cone beam CT temporomandibular joint imaging
protocol offers a viable alternative to conventional larger field-of-view techniques, and
should be considered a first line tool for imaging the osseous component of the
temporomandibular joint.
63
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Appendix 1 Landauer Specification Sheet for
72
73
Appendix 2
Health Sciences Research Ethics Board Approval Letter
74
Appendix 3
Patient Information and Consent Forms Title of Research Project Development of a limited field-of-view cone beam CT imaging technique for evaluation of the temporomandibular joints (TMJs) Investigator(s)
1. Principal Investigator Dr. Trish Lukat DDS
M.Sc. candidate Division of Oral and Maxillofacial Radiology Faculty of Dentistry, University of Toronto 124 Edward Street, Division of Oral and Maxillofacial Radiology Toronto, ON M5G 1G6 647-985-8165
2. Faculty Supervisor Dr. Ernest Lam DMD, PhD, FRCD(C)
Associate Professor Division of Oral and Maxillofacial Radiology Faculty of Dentistry, University of Toronto 124 Edward Street, Division of Oral and Maxillofacial Radiology Toronto, ON M5G 1G6 416-979-4932 x4385
Purpose of the Research
The purpose of this study is to evaluate the diagnostic performance of a high-resolution limited field-of-view cone beam CT scan of the temporomandibular joints (TMJs) with respect to detection of bony changes related to degenerative joint disease (also kn
75
Description of the Research Subject population
Adult patients referred to the Special Procedures Clinic in the Discipline of Oral and Maxillofacial Radiology at the Faculty of Dentistry, University of Toronto for evaluation of the osseous structures (bones) of the temporomandibular joint(s). Inclusion criteria
Informed consent-capable individuals with a suspected degenerative joint disease condition associated with one or both of the temporomandibular joint(s) as determined by clinical examination of the patient. See Appendix A for details. Exclusion criteria
Individuals excluded from this study include: subjects with clinical signs and symptoms of isolated soft tissue abnormalities of the temporomandibular joint (e.g. disk displacement without clinical evidence of associated degenerative joint disease); cases of acute trauma to the craniofacial structures, in which comprehensive rather than localized imaging is indicated; and pregnant subjects. Background information
The current protocol for temporomandibular joint cbCT imaging at our institution utilizes a Hitachi CB MercuRay unit, with a 9-inch field-of-view and 100kVp and 10mA exposure settings. This technique permits simultaneous bilateral scanning of the right and left temporomandibular joints, generates images with a voxel size of 0.290mm, and exposes the patient to an effective radiation dose of 223.6 1.1 Sv.
The present study utilizes an alternative high-resolution/reduced radiation dose temporomandibular joint imaging technique using a Kodak 9000 3D unit to perform separate limited field-of-view cbCT scans of the right and left TMJs. This modality has a field-of-view of 5.0cm diameter by 3.75cm in height and uses 70kVp and 10mA exposure settings. The patient will be scanned twice, one scan for each joint; this exposes the patient to a total effective radiation dose of 20.5 1.3 Sv, which offers more than a 10-fold reduction in dose compared to using the present standard of care protocol described above. Due to a smaller voxel size within the Kodak sensor (0.076mm), the resultant images are also of comparatively higher spatial resolution compared to those generated using the Hitachi CB MercuRay. Temporomandibular joint cone beam CT procedure
A thorough explanation of the cone beam CT procedure will be given to each patient prior to consenting to the examination. Upon approval, a Resident in Oral and Maxillofacial Radiology at the Faculty of Dentistry, University of Toronto, will perform the cone beam CT procedure. The Principal Investigator or a faculty member will closely supervise the Resident. Temporomandibular joint cone beam CT imaging procedures are routinely performed in the Special
76
Procedure clinic, and the supervising faculty members are experienced in the performance of this procedure. As part of the comprehensive radiographic assessment, a panoramic radiograph will be taken prior to cone beam CT imaging to assess for abnormalities or pathology located outside the joints.
Positioning of the patient within the Kodak 9000 3D unit requires precision to ensure that both the condylar and temporal components are completely imaged. A chin rest and temporal supports are used to stabilize the patient in the appropriate position, and this permits imaging of the temporomandibular joints in the closed mouth position. With the occlusal plane parallel to the floor and the patient in maximum intercuspation, the antero-posterior position is first determined by positioning the indicator light approximately 1cm anterior to the external auditory meatus landmark. The supero-inferior position is then determined by centering the midpoint of the 3.75cm vertical field-of-view light over a point corresponding to the level of the condylar head in the closed mouth position. Finally, the medio-lateral position is set using the Kodak 9000 3D Module software, based on patient intercondylar distance estimated by caliper measurement. The procedure will be repeated for the contralateral joint; the patient position will not require modification, only the crosshairs will be adjusted within the software prior to imaging the second joint.
The results of the temporomandibular joint examination will be reported to the patient at the completion of the examination. As well, a digital copy of the radiographic images that were obtained for the patient will be couriered to the referring dentist or physician accompanied by a radiographic report stating the findings of the examination.
Image analysis
The cbCT images for each joint of each patient will be anonymized and reviewed using (1) the default, high-resolution 0.076mm voxel size, and (2) a voxel downsampling technique where the resultant voxel size will be rendered at 0.300mm. The downsampling technique will be performed using the Carestream CS 3D Dental Imaging Software, and will provide images of reduced spatial resolution. This will permit a comparison of images viewed under two differing conditions (high versus low spatial resolution), while sparing the patient from being exposed to two different imaging modalities. Three observers, all nationally certified Oral and Maxillofacial Radiologists, will review the cbCT images for each patient independently. As the images are digitally acquired, they will be reviewed at computer workstations where the observers will have the advantage of enhancing the images by manipulating brightness and contrast. The reviewing radiologists will be blinded to the clinical data and will be required to fill out a form similar to that displayed in Appendix B for each image series. The presence or absence of a particular radiographic feature will be based on agreement of at least two of the three observers, and there will be no attempt to reconcile disagreements. As well, one of the observers will review a portion of the series twice so that intraobserver reliability may be determined.
77
Potential Harm, Injuries, Discomforts or Inconvenience Cone beam CT imaging of the temporomandibular joint is non-invasive,
and carries negligible risk. A strict aseptic technique is always followed during the procedure as a standard of practice. Possible drawbacks of the alternative Kodak imaging protocol compared to the standard Hitachi protocol include longer scan times to acquire images of each joint individually and a greater precision requirement with respect to patient positioning due to a smaller field-of-view. However, the trade off of a lower radiation dose to the patient deems this a viable alternative, despite the potential disadvantages.
With respect to radiation doses, we have recently completed a dosimetric study comparing the effective radiation doses using the Hitachi CB MercuRay and the Kodak 9000 3D to image the temporomandibular joints. An anthropomorphic phantom with optically stimulated luminescence (OSL) dosimeters placed in 25 locations throughout the head and neck region of the phantom was subjected to the two imaging modalities. The Hitachi CB MercuRay was operated using a 9-inch field-of-view, 100kVp, and 10mA; the Kodak 9000 3D technique was performed individually for each joint using the default 5cm diameter by 3.75cm height field-of-view, and operating at 70kVp and 10mA. The results were presented at the 2011 meeting of the American Academy of Oral and Maxillofacial Radiology in Chicago, IL. Our results found that the effective doses for the Hitachi CB Mercuray temporomandibular joint acquisition were 223.6 1.1 Sv, compared to 20.5 1.3 Sv for the bilateral Kodak 9000 3D modality. Effective radiation dose for a unilateral joint acquisition using the Kodak 9000 3D is 9.7 0.1 Sv. Potential Benefits
By agreeing to participate in this study, patients undergoing cbCT imaging of the temporomandibular joint will benefit from this dose-reduction technique to acquire three-dimensional images of their joints. We hypothesize that the superior spatial resolution of the Kodak 9000 3D unit will provide more detailed diagnostic information than the current technique using the lower-resolution Hitachi CB MercuRay unit. We believe that the additional information obtained by this technique will allow for more accurate quantification of osseous changes within the temporomandibular joint related to degenerative joint disease, thereby aiding the treating physician or dentist in choosing the most appropriate management option for the patient and improve the quality of patient care. Alternatives
If you elect at any time not to participate in this study, the current temporomandibular joint imaging protocol using the Hitachi CB MercuRay unit will be offered. Confidentiality
Confidentiality will be respected and no information that discloses the identity of the subject will be released or published without consent unless
78
required by law. Patient data will be anonymized with the identities of the patients known only to the Principal Investigator.
Participation Participation in research is voluntary. If you choose to participate in this
study you can withdraw at any time. Should you choose to withdraw, your data will be removed from the database. There will be no consequences with respect to your future care in the Faculty. Contact If you have any questions about this study, please contact:
Dr. Trish Lukat DDS
M.Sc. candidate Division of Oral and Maxillofacial Radiology Faculty of Dentistry, University of Toronto 124 Edward Street, Division of Oral and Maxillofacial Radiology Toronto, ON M5G 1G6 647-985-8165 [email protected]
If you have any complaints or concerns about how you have been treated as a research participant, please contact:
Zaid Gabriel Research Ethics Officer, Health Sciences [email protected] or 416-946-5806
79
Appendix A. Clinical examination criteria for signs/symptoms of degenerative joint disease associated with the temporomandibular joint(s). History Patient describes unilateral or bilateral joint pain that is aggravated by mandibular movement. Pain is usually constant; may worsen in the late afternoon or evening. Patient may describe parafunctional habits.
Clinical Characteristics Limited mandibular opening may be noted as a result of joint pain. Crepitus on opening/closing. Pain on mandibular movement. Lateral palpation of the condyle may increase patient pain/discomfort. Loading of the joint may increase patient pain/discomfort.
80
Appendix B. Sample score sheet for observers to record presence of radiographic features of degenerative joint disease. If the feature noted in the column is present, place a check mark ( ) in the respective box. CONDYLAR COMPONENT TEMPORAL COMPONENT
CASE ID
corti
cal e
rosi
ons
subc
hond
ral
scle
rosi
s
flatte
ning
oste
ophy
te o
r jo
int m
ouse
/mic
e
Ely
(sub
chon
dral
) cy
st
corti
cal e
rosi
ons
subc
hond
ral
scle
rosi
s
flatte
ning
oste
ophy
te o
r jo
int m
ouse
/mic
e
Ely
(sub
chon
dral
) cy
st
1
2
3
100
81
CONSENT FORM By signing this form, I agree that: Yes No The study has been explained to me. All of my questions were answered. Possible harm and discomforts and possible benefits (if any) of this study have been explained to me.
I understand that I have the right not to participate and the right to stop at any time.
I understand that I may refuse to participate without consequence to continuing care at the Faculty.
I have a choice of not answering any specific questions. I am free now, and in the future, to ask any questions about the study. I have been told that my personal information will be kept confidential. I understand that no information that would identify me, will be released or printed without asking me first.
I understand that I will receive a signed copy of this consent form. I hereby consent to participate. ______________________________ ________________ Signature Date Name of Participant and Age: ____________________________________ Telephone #: ____________________________________ Name of person who obtained consent: ___________________________ ____________________________ __________________ Signature Date
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Appendix 4
Observer Calibration PowerPoint Exercise
83
84
85
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Appendix 5
Sample Observer Score Sheet for Identification of Radiographic
Features and Visual Analog Scale
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87
Appendix 6
Translating Exposure to Risk: Calculations
A. Background radiation equivalency for temporomandibular joint cone beam CT
imaging techniques
Annual background effective radiation dose: 3.1mSv (3100 Sv)
Daily background effective radiation dose: 3100 Sv / 365 = 8.5 Sv
Hitachi CB MercuRay effective radiation dose (100kVp/10mA): 223.6 Sv
223.6 Sv / 8.5 Sv background dose/day = 26.3 days
Bilateral Kodak 9000 3D effective radiation dose using standard adult acquisition
parameters (70kVp/10mA): 20.5 Sv
20.5 Sv / 8.5 Sv background dose/day = 2.4 days
B. Estimated population risk of carcinogenesis per one million exposures
associated with temporomandibular joint cone beam CT imaging techniques
Risk coefficient for radiation-induced carcinogenesis: 0.055 events/Sv, where one
of fatal cancer
Hitachi CB MercuRay effective radiation dose: 223.6 Sv (2.236E-4Sv)
0.055 events/Sv * 2.236E-4Sv * 1,000,000 exposures 12 cases of fatal cancer per one
million exposures
Bilateral Kodak 9000 3D effective radiation dose using standard adult acquisition
parameters: 20.5 Sv (2.05E-5Sv)
0.055 events/Sv * 2.05E-5Sv * 1,000,000 exposures 1.1 cases of fatal cancer per one
million exposures