Transcript of Demetrios J. Halazonetis Cone-beam Computed Tomography in Orthodontics: Limitations and future...
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Demetrios J. Halazonetis Cone-beam Computed Tomography in
Orthodontics: Limitations and future directions.
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how CT works major artifacts 3D pictures
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how CT works Godfrey Hounsfield Nobel prize in Medicine, 1979
Allan Cormack
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x-ray source detectors
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acquisition
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reconstruction
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Voxels (Volume elements)
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100 million voxels (200 Mb) 400 slices 512 x density: 0 -
4095
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cone-beam CT (CBCT)
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NewTom 9000 / NewTom 3G i-CAT
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medical CT CBCT grey color (voxel value) = tissue density
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medical CT CBCT grey color (voxel value) = tissue density +
artifacts
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1.ringing
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2.beam hardening high energy
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(cupping) 2.beam hardening
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3.noise (cupping) 2.beam hardening
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2.beam hardening (streaking)
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4.partial object effect
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5.resolution artifacts: what lies between voxels?
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voxel 0.5 mm interpolation what lies between voxels?
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interpolation
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6.partial averaging effect what lies within voxels? patience, I
am almost done!
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partial averaging effect
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100 0 2000 0 partial averaging effect
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100 0 2000 0 150 100 50 partial averaging effect
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100 0 2000 0 150 100 50 partial averaging effect
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creating 3D pictures
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screen ray casting
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transparency threshold
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thresholding, iso-surface
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transfer function: combination of color & transparency for
range of voxels
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transfer function:
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simple thresholding: single iso-surface transfer function:
volumetric object 3D rendering
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voxel density distributions voxel density bonesoft tissue
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voxel density voxel density distributions bonesoft tissue
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overlapping voxel density distributions
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NewTom
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i-CAT
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medical CT
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medical CT 120 kV, 100 mAsCBCT 110 kV, 10 mAs grey color (voxel
value) = tissue density + artifacts
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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.