Demetrios J. Halazonetis Cone-beam Computed Tomography in Orthodontics: Limitations and future directions.

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Presentation transcript:

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

reconstruction

Voxels (Volume elements)

≈ 100 million voxels (200 Mb) 400 slices 512 x density:

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

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

5.resolution artifacts: what lies between voxels?

voxel ≈ 0.5 mm interpolation what lies between voxels?

interpolation

6.partial averaging effect what lies within voxels? patience, I am almost done!

partial averaging effect

partial averaging effect

partial averaging effect

partial averaging effect

creating 3D pictures

screen ray casting

transparency threshold

thresholding, iso-surface

transfer function: combination of color & transparency for 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

overlapping voxel density distributions

NewTom

i-CAT

medical CT

medical CT 120 kV, 100 mAsCBCT 110 kV, 10 mAs grey color (voxel value) = tissue density + artifacts

Acknowledgements Dr. Katsaros and Dr. Stratoudakis (for providing CT data). All CT data rendered by the Viewbox software ( 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.