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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.