Post on 19-Jan-2016
description
Demetrios J. Halazonetis
Cone-beam Computed Tomography in Orthodontics:Limitations and future directions.
• how CT works• major artifacts• 3D pictures
how CT works…
Godfrey Hounsfield
Nobel prize in Medicine, 1979
Allan Cormack
x-ray source
detectors
acquisition
acquisition
acquisition
reconstruction
reconstruction
Voxels (Volume elements)
Voxels (Volume elements)
≈ 100 million voxels (200 Mb)400
slices512 x 512 x
density:0 - 4095
cone-beam CT(CBCT)
cone-beam CT(CBCT)
cone-beam CT(CBCT)
cone-beam CT(CBCT)
NewTom 9000 / NewTom 3G
i-CAT
medical CT CBCT
grey color (voxel value) = tissue density
medical CT CBCT
grey color (voxel value) = tissue density+ artifacts+ artifacts
1. ringing
1. ringing
2.beam hardening
high energy
(cupping)
2.beam hardening
3. noise
(cupping)
2.beam hardening
2.beam hardening(streaking)
4. partial object effect
4. partial object effect
4. partial object effect
4. partial object effect
5. resolution artifacts:
what lies between voxels?
what lies between voxels?
voxel ≈ 0.5 mm
interpolation
what lies between voxels?
what lies between voxels?
interpolation
6. partial averaging effect
what lies within voxels?
patience, I am almost done!
partialaveragingeffect
partialaveragingeffect
100
100
100
0
200 0
0
partialaveragingeffect
100
100
100
0
200 0
0
150
150
100
100
100
50
partialaveragingeffect
100
100
100
0
200 0
0
150
150
100
100
100
50
partialaveragingeffect
partialaveragingeffect
creating 3D pictures
screen
ray casting
transparency threshold
thresholding, iso-surface
transfer function:
combination ofcolor & transparencyfor range of voxels
combination ofcolor & transparencyfor range of voxels
transfer function:
simple thresholding:single iso-surface
transfer function:volumetric object
3D rendering
voxel density distributions
voxel density
bonesoft tissue
voxel density
voxel density distributions
bonesoft tissue
overlappingvoxel densitydistributions
NewTom
i-CAT
medical CT
medical CT 120 kV, 100 mAs CBCT 110 kV, 10 mAs
grey color (voxel value) = tissue density+ artifacts+ artifacts
Acknowledgements
• Dr. Katsaros and Dr. Stratoudakis (for providing CT data).
All CT data rendered by the Viewbox software (www.dhal.com).
Note: Software and hardware improve at a fast rate and lead to better image quality. The images that were shown may not be representative of the state of the art today.