RADI 108 - Conventional Tomography

"a radiographic technique that is designed to bring into focus only that anatomy lying in a plane of interest while blurring structures on either side of the plane"

tomography

tomography is also known as ...

planigraphy, stratigraphy, larninography, body-section radiography - because all of these terms are confusing, the international commission selected tomography as the appropriate terminology

the x-ray tube and IR move in opposite directions around a stationary ___ during the exposure

fulcrum (pivot point)

the ___ the distance from the fulcrum, the ___ the blurring

greater

what is the tomographic amplitude (or arc or angle)

the total distance the tube travels (always = to or greater than the EA)

what is the exposure amplitude (or arc or angle)

the distance the tube travels during the exposure

what is the fulcrum?

the pivot point around which the tube and IR move

what is the focal plane (or object plane)

the area within the image that is in focus and shows satisfactory detail

what is the grossman principle (fixed fulcrum)

the fulcrum is fixed and the pt (table height) is moved up and down to change the focal (section) level

what is the planigraphic principle?

the fulcrum is adjustable while the pt remains stationary, most common, AKA adjustable or variable fulcrum

TRUE or FALSE: the exposure angle is inversely proportional to the section thickness

TRUE

no exp angle =

no slice

section thickness

the section (slice) thickness is the depth of the focal plane (area within focus) - controlled by exp angle

section interval

the distance between the fulcrum levels of successive slices, should never exceed the section thickness - could cause gaps

Tomographic tube movement is either ____ or ____

linear or complex (pluridirectional)

- linear: simplest, common for IVUs

complex tube movements

curvlinear - maintains SID & OID, circular, elliptical, figure 8, trispiral, hypocycliodal

- often require 3-6 sec exposures, long exp time means small mA

___ and ___ movements give the max tomographic amplitude and the thinnest cut - used on small complex anatomy like carpal bones and auditory ossicles

trispiral, hypocycliodal

zonogrraphy

amplitude of less than 10 degrees, usually 1-5 degree angles are used, large slice thickness, used to locate lesions when the exact location is unknown (ex. lung lesion)

panoramic tomography

slit scan radiography of the curved surfaces, used for mandible, teeth, facial bones, etc, IOML parallel to the floor