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Principles of Cone Beam Volumetric Tomography
Planmeca ProMax 3D Models
Planmeca ProMax 3D family offers a solution for the most demanding imaging needs, producing various imaging sizes with one concept – an ideal imaging size for different maxillofacial applications.
Extended applicationsUnique new imaging capabilities for: •Implant planning•Oral surgery•Impacted teeth•3rd molar extractions•Occlusion analysis•TMJ analysis•Periodontics•Airway studies
Emerging new diagnostic applications
3D technology•CBCT - Cone Beam Computed Tomography
•CBVT - Cone Beam Volumetric Tomography
•DVT – Digital Volume Tomography
•A technological advance from traditional ‘CAT Scan’, ‘medical CT’ or ‘fan beam CT’
Medical CT
Medical CT vs CBVT
X-ray source
object
Line detector
Movement of translation and axis of rotation
X-ray source
object
axis of rotation
Flat panel detector
CBCT volume capture
CBCT volume capture
Z
Y
X
Medical CT vs. CBVTMedical CT:
Slices are acquired then reconstructed to create the volume
Medical CT vs. CBVTCBCT:
The volume is acquired then slices are reconstructed from the volume
ProMax 3D technology•Stroboscopic effect, images
taken using short X-ray pulses during the scan
•300/450 images taken during the scan
•Cumulative exposure time 2.8 -12 sec for 18 sec scan
•Enhanced clarity of the images
•Reduced radiation dose
ProMax 3D Max & Mid Scanning
• Symmetric scanning• C-arm rotates• Magnification 1.8x• Scan angle 200 deg• 300 frames• Max. volume Ø100 x 130
mm
• Asymmetric off-set scanning
• Elbow arm rotates• Magnification 1.44x• Scan angle 360 deg• 450 frames• Max. volume Ø230 x 160
mm
Asymmetric off-set scanning
Sensor shift changes the acquisition geometry and reduces the final image quality
The shift of whole c-arm remains the acquisition geometry constant and produces better final image
Back projection – basic images
Back projection
ProMax 3D Technology 3D image volume is a cylinder
Cylinder consists of more than 120 million voxels
Voxel size 0.1 x 0.1 x 0.1 mm,0.2 x 0.2 x 0.2 mm,0.4 x 0.4 x 0.4 mm or 0.6 x 0.6 x 0.6 mm
Isotropic voxel• CBVT has always an isotropic voxel• The reconstruction can produce any
size of voxel• The voxel is always perfect cube• The measurements are exact• Voxel size is typically 0.1 – 0.5 mm
• CT has an anisotropic voxel• The voxel is always a “brick”• The pitch (= distance between spiral
rounds = layer thickness) varies and causes distortion in the 3D measurements.
• The layer thickness is typically 0.5 – 0.8 mm
Pulsed X-ray
Pulsed X-ray produces sharp images with less dose.
X-ray Tube – Patient – Image Intensifier – TV Camera – Digital Image
X-ray Tube – Patient – Flat Panel- Digital Image
Modern Flat Panel Technology for maximum performance
3D Technology –Flat PanelPlanmeca ProMax 3D flat panel imaging chain
Conventional imaging chain with Image Intensifier
Image intensifier
3D Technology – Flat Panel• Image intensifier has both
distortion and brightness non-uniformity which is absent from the flat panel detector
• Image intensifier needs periodical maintenance. It has limited life span 3-6 years.
• It is sensitive to magnetic or electrical fields.
• It is over 60 years old technology.
3D technology – Tube Current Modulation• Different attenuation
properties across and along the patient's head
• Tube current (mAs) can be dynamically adjusted
• Reduces patient dose and improves image quality
more
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ComparisonPlanmecaProMax 3D s
Planmeca ProMax 3D
Planmeca ProMax 3D Mid
Planmeca ProMax 3D Max
Voxel size 100 / 200 µm * 100 / 200 / 400 µm
100 / 200 / 400 / 600 µm
100 / 200 / 400 / 600 µm
Max. 3D volume (diam. x height )
Ø50 x 80 mm Ø80 x 80 mm Ø160 x 90 mm Ø230 x 160 mm
Max. 3D volume withstitching, (diam. x height)
Ø90 x 130 mm Ø150 x 130 mm Ø160 x 160 mm Ø230 x 260 mm
Stitching, vertical Yes Yes Yes Yes
Stitching, horizontal Yes Yes No No
SmartPan imaging Yes Yes Yes No
Dimax Panoramic imaging
Optional Optional Optional No
Dimax Cephalostat Optional Optional Optional No
Motorised patient supportfor vertical movement
No No Yes Yes
CBCT vs. Medical CT
Cone Beam Imaging is:• Faster• Smaller• Safer (lower dose)• Less expensive• More convenient• Dentally specific• Higher resolution• Better image quality
WHAT ARE THE DOSES?
Radiation dose
International Commision on Radiological Protection, Standards for absorbed dose from 1990 and 2007
Radiation dose
Medical CT 1200-3300 µSvDr Stuart White, UCLA
Dig. Pan ca 7 µSvFMS 90 uSvDr Sharon Brooks, O of Michigan, ICRP 1990
Dig. Pan 6,7 µSvFMS 84 uSvDr Stuart White 1992, ICRP 1990
Typical panoramic dose 24.5 µSvDr Ludlow, ICRP 2007
Radiation doseThe estimated effective patient dose, Planmeca ProMax 3D software version 1.21.4, Dr. Mika Kortesniemi:
IMAGING PROTOCOL High and Normal Resolution modes
Low Dose mode
IMAGING OBJECT Left 3rd molar Left 3
rd molar
FOV [d cm x h cm] 8 x 8 8 x 8
TUBE VOLTAGE [kV] 84 84
TUBE CURRENT [mA] 12 8
EXPOSURETIME [s] 12 2.8
CURRENT TIME PRODUCT[mAs]
144 22.4
CURRENT TIME PROFILE[MIN(mAs) / MAX(mAs)]
1.0 0.3
Effective dose [mSv] (ICRP 1990)
0.122 0.021
Effective dose [mSv]
(ICRP 2007)
0.252 0.045• Radiation dose of CBCT 20-
250 µSv• Same level as 2-10 panoramic
images• Same level as full mouth series
with film • Essentially lower than medical
CT
Dose – Radon, background, smoking
US Study: • Average yearly dose of 2070 µSv from
radon• Average yearly dose of 320 µSv from
smoking• Average yearly dose of 4000 µSv from
background radiation in Denmark
Dose – Flight
www.gsf.de/epcard
Dose – Risks
ec.europa.eu/energy/nuclear/
radioprotection/publication/doc/136_en.pdf
Age:<10 *310-20 *220-30 *1,530-50 *0,550-80 *0,380+ negligible
Modality: Risk of fatal cancer (per million):Intraoral 0,02 – 0,6Occlusal 0,4Panoramic 0,21 – 1,9Ceph 0,34CT mandible 18,2 – 88CT maxilla 8 – 242
The EndMore information:Erkki HiltunenProduct Manager, X-raystel: +358 20 7795 456 [email protected]
Mark NiemiProduct Manager, X-raystel: +358 20 7795 743 [email protected]
More information:Osku SundqvistProduct Manager, Softwaretel: +358 20 7795 [email protected]
4/2011
