Comparison of Image Quality and Radiation Dose Between Fixed Tube Current and Combined Automatic Tube Current Modulation in Craniocervical CT Angiography

8/7/2019 Comparison of Image Quality and Radiation Dose Between Fixed Tube Current and Combined Automatic Tube Current Modulation in Craniocervical CT Angiography

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Scientific Principles of MedicalDevices- Computerised

Tomography (CT) Imaging

RAD 5313

Terence Cesare


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Comparison of Image Quality and

Radiation Dose between Fixed TubeCurrent and Combined Automatic Tube

Current Modulation in Craniocervical CT

Angiography

Lee,E.J., Lee, S.K., Agid,R.,Howard,P., Bae, J.M., terBrugge, K.,

Oct 2009,

AJNR30, 1754-1759


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Objectives


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Original research

To prove that the combined Automatic TubeCurrent Modulation (ATCM) technique in

Craniocervical CT angiography (CCTA)

performed on a 64-slice Multidetector rowComputed Tomography (MDCT) system

substantially reduces radiation exposure,whilst maintaining diagnostic image quality.


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Background


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Problem Statement

Optimisation of dose to:

Maintain diagnostic image quality

At lowest possible radiation dose

Which is the best tube current technique touse in CCTA when using a 64-slice

MDCT?


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Relevance CT has increased greatly its clinical

applications.

CT increased concern on:

Radiation dose Optimisation of techniques (ALARA principle)

In CCTA, little is known on the optimal

imaging parameters for MDCT (Lee et al,2009).


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Limitations Different Patients were assessed

The ability of showing depictions ofvascular structures was only evaluated.

Effective dose Body mass index


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Literature Review


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Automatic Tube Current Modulation

(ATCM) Same as the automatic exposure control

(Rizzo et al, 2006.) ATCM is based on the principle that X-ray

attenuation and quantum image noise are

determined by the size of the object andits tissue density Kalra et al, 2004.

Kalra also states that ATCM maintainsconstant image quality and increasesradiation dose efficiency.


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Angular or xy-axes modulation techniques

The z-axis modulation techniques

Combined (xyz-axes) ATCM techniques,merge the complementary techniques of

angular and z-axis modulation. Fixed Tube Current (FTC) gives constant

current throughout whole exposure in all

directions (x/y/z)


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CT manufactures differ in their approach

to ATCM: Philips: DoseRight

Siemens: CARE Dose 4D

GE: AutomA (z-axis) / SmartmA (x/y-axis)

Toshiba: SureExposure3D


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Craniocervical CT AngiographyCCTA vs. MRA vs. DSA

Ionising vs. Non-ionising Invasive vs. Non-invasive

Length of procedure & Availability

Procedure expenses Contrast

Bone Repeats

Diagnostic vs. Therapeutic


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CT radiation dose Radiation dose and mAs.

CTDIvol (CT dose index)(mGy)

Represents the average dose delivered to thescan volume in a specific examination.

DLP (dose-length product)(mGy-cm)

Represents the integrated dose across the

scan length.


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Methodology


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Toshiba Aquilion 64 50 consecutive adult patients

25 scanned using FTC (300mA)

25 scanned using ATCM (101-300mA) The other parameters were held constant:

Scan length (from the aortic arch to the vertex)

Voltage of 120kV Matrix size of 512*512

FOV of 2832cm

Slice thickness of 0.5mm

Pitch of 1.0 Isotropic voxel size of 0.5mm

I.V. contrast administration

Acquisition time of 1116s


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Image processing:

Axial Coronal

Sagittal multiplanar volume-reformatted

maximum intensity projections (MIP)

3D volume-rendered (VR) reconstructions


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Ethical Considerations The institutional review board approved the study.


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Data

Statistical Analysis

Image Analysis

Radiation Dose


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Statistical Analysis The Mann-Whitney U test is a non-

parametric test Commonly used to compare between two

populations that are related.

Data is usually ordinal

5-point scale


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Image Analysis Comparison between patients:

Age

Length of scan

Max. transverse neck diameter (level of hyoid)

Image quality was based on objective

evaluation of image noise. The latter was

measured at 2 levels (lowest and highestcurrent site).


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Image Analysis (cont.) Image scoring was performed independently by 2

experienced neuroradiologists Blinded

Axial, Coronal, MIP and 3D VR were evaluated by

the latter. 5-point scale was used to evaluate: Vascular delineation

Visibility of small arterial detail

Subjective image noise

Certainty of diagnosis N.B. A score of 3 or more was considered as an acceptable level


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Radiation Dose The DLP was recorded for both

techniques Also CTDIvol was calculated using the

formula:

DLP = CTDIvol scan length (cm).


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Resultsand

Conclusions


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Conclusion Lee et al concluded that Combined ATCM

technique for CCTA provided similarlyacceptable levels of depiction of the

craniocervical vessels and diagnostic

acceptability, as well as a reduction inradiation dose (18%), compared with the FTC

technique.


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Critique SURE Exposure 3D controls and modulates

the current in the x, y, and z directions toachieve and maintain a uniform userselected noise level in the images (Lee et

al, 2009). Operator-selected image quality settings

play a key role in the dose efficiency of

ATCM (Schindera et al, 2008).

What was the user selected noise level?


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Future Research The tube current isnt the only parameter

that affects radiation dose. Other scanning parameters include:

Pitch,

Slice thickness,

Scanning volume,

Voltage.

ASIR (Adaptive Statistical Iterative Reconstruction)

MBIR (Model - Based Iterative Reconstruction)


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References Kalra, K., Maher, M.,Toth, Kamath, R., Halpern, E., Saini,S. (2004). Comparison of Z-

Axis Automatic Tube Current Modulation Technique with Fixed Tube Current CTScanning of Abdomen and Pelvis. Radiology, 232, 347353. doi:

10.1148/radiol.2322031304. Kalra, K., Maher, M.,Toth, M.,Schmidt, B.,Westerman, B., Morgan, H., et al (2004)

Techniques and Applications of Automatic Tube Current Modulation for CT.Radiology, 233, 649657. doi:10.1148/radiol.2333031150.

Lee,E.J., Lee, S.K., Agid,R., Howard,P., Bae, J.M., terBrugge, K., (2009) Comparison

of Image Quality and Radiation Dose between Fixed Tube Current and CombinedAutomatic Tube Current Modulation in Craniocervical CT Angiography. AJNR, 30,1754-1759. doi:10.3174/ajnr.A1675.

Rizzo, S., Kalra, M., Schmidt, B., Dalal, T.,Suess, C.,Flohr, T., et al. (2006.)Comparison of Angular and Combined Automatic Tube Current ModulationTechniques with Constant Tube Current CT of the Abdomen and Pelvis. AJR, 186,673679. doi:10.2214/AJR.04.1513.

Su, J.,Jaw, T., Chen C., Kuo, Y., Hsieh, T., Lee, S., et al. (2010) Automatic TubeCurrent Modulation versus Fixed Tube Current in Multi-detector Row ComputedTomography of Liver: Comparison of Image Quality and Radiation Dose. Chin JRadiol, 35, 131-142.


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Comparison of Image Quality and Radiation Dose Between Fixed Tube Current and Combined Automatic Tube Current Modulation in Craniocervical CT Angiography