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
