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

5. how CT works major artifacts 3D pictures

6. how CT works… Godfrey Hounsfield Nobel prize in Medicine, 1979 Allan Cormack

7. x-ray source detectors

39. acquisition

42. reconstruction

47. Voxels (Volume elements)

48. ≈ 100 million voxels (200 Mb) 400 slices 512 x density: 0 - 4095

49. cone-beam CT (CBCT)

53. NewTom 9000 / NewTom 3G i-CAT

55. medical CT CBCT grey color (voxel value) = tissue density

56. medical CT CBCT grey color (voxel value) = tissue density + artifacts

57. 1.ringing

59. 2.beam hardening high energy

60. (cupping) 2.beam hardening

61. 3.noise (cupping) 2.beam hardening

62. 2.beam hardening (streaking)

64. 4.partial object effect

68. 5.resolution artifacts: what lies between voxels?

70. voxel ≈ 0.5 mm interpolation what lies between voxels?

72. interpolation

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

74. partial averaging effect

76. 100 0 2000 0 partial averaging effect

77. 100 0 2000 0 150 100 50 partial averaging effect

78. 100 0 2000 0 150 100 50 partial averaging effect

82. creating 3D pictures

83. screen ray casting

87. transparency threshold

92. thresholding, iso-surface

93. transfer function: combination of color & transparency for range of voxels

94. transfer function:

101. simple thresholding: single iso-surface transfer function: volumetric object 3D rendering

103. voxel density distributions voxel density bonesoft tissue

104. voxel density voxel density distributions bonesoft tissue

105. overlapping voxel density distributions

106. NewTom

107. i-CAT

108. medical CT

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

110. 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.