Computed Tomography

panoramic CT (2D)

image made following line drawn by computer that follows mandible path so image looks like pantomograph

5th generation scanners (3c)

spiral/helical -has lsip ring so can do single motion all around patient

orthoradial CT (2D)

take image slices at 90 degrees along the computer drawn line above to get images so can decide where to put implants, etc.

pitch (P)

= table travel per rotation ____________________________ collimation of single slice (aka slice thickness)

measurements on CT

-1:1 ratio -not subject to projection geometry

axial CT

-first type ever done -takes image slices top to bottom -uses bone windows (bone uses high number =4,000, while soft tissue uses low number = 300)

multiplanar reconstruction (MPR)

-how you look at all images together -all 3 dimensions

sagittal CT

-image taken from one side to other

CDCT machine

-patient seated -machine rotates around head

how are they made?

-source of radiation and film rotate around patient on table -computer gets info back and interprets patient as a grid from imaging in several directions -can distinguish between entities by differences in attenuation

coronal CT

-takes pic front to back -used a lot to visualize sinuses -use bone windows -restorations in teeth interfere with image= beam hardening

3D reformatted CT

-use data to piece together so looks like skull -shows where fractures are -can rotate around any axis -surface rendering: selected when want to ignore things on inside -volume rendering: when want to see inside

HU of different substances

bone = 1000 water= 0 fat= -80 --> -100 air= -1000

4th generation scanners (3b)

rotate---fixed

3rd generation scanners

rotate---rotate

isodense measurements (2D)

select portion of image with certain radiopacity and ask computer to find all areas with similar radiopacity

1st and 2nd generation scanners

translate---rotate