(E1) Linear Tomography

what is tomography

radiogrpahic technique that employs motion to show anatomical structures lying in a plane of tissue while blurring detail in images of structures above and below the plane of interest

• allows visualization of structure that may otherwise be superimposed over other anatomy

most tomography has been taken over by

MRI and CT

tomo- means

cut, section or layer

-graphy means

the process of recording

when was tomography developed

1921

who developed tomography

• andre edmund bocage- french dermatologist

• jean keiffer- american radiographer

what are the older terms for tomography

• planigraphy

• stratigraphy

• laminography

• section radiography

what are the advantages of tomography

• demonstration of anatomical structure in coronal while blurring out surrounding structures

• valuable with routine kidney imaging with radiography

• useful when computerized modalitites are too expensive or unavailable

disadvantages of tomography

• more exposures to radioation (within safe levels)

• equipment more expensive due to complexity of equipment

tomography basic principles

• x-ray tube travels in an arc

• based on movements of 2 or 3 parts of the system

  • tube, object, IR

• usually the tube and IR move in opposite directions during an exposure

the anatomy of interest is placed in a focus point called a____

fulcrum

tomography imaging is accomplished by setting th fulcrum to a number that would correspond how far the _____ is from the ____

anatomy of interest, table top

during a tomography exposure the anatomy ____ and ____ the fulcrum will be blurred out by the movement of the tube and IR

above and below

image creation basic

• center over anatomy of interest (AOI)

• tube and IR rotate corresponding to AOI

• angulation shoots anatomy in both directions caused a blurred appearance

• the AOI will be projected in the same location on the IR while other anatomy is projected in varying locations

the more blurring that occurs around the anatomy of interest the ____ the area of interest will be

sharper

what is tomogrpahic amplitude

• arc or angle that the tube travels

• exposure may or may not be on during entirety

tomogrpahic amplitude is _____ greater than or equal to the exposure

always

tomorgraphic amplituve and section thickness are ____ related

inversely

tomographic amplitude: larger angle=

thinner section

tomographic amplitude: smaller angle=

thicker section

what is the exposure amplitude

• arc or angle that the tube travels while the exposure is being taken

• the exposure is active during the entire exposure amplitude

exposure amplitude is always ___ or ____ than the tomographic amplitude

equal to or less than

what is blur

streaking/smearing that occures outside the area of interest (focal plane) which results in a loss of all recorded detail

the relationship between the blurring and the IR exposure of objects is _____ related

inversely

increased blurring causes ____ density

decreased

• object is more transparent

blur is affected by (more info on slide 14 of PP)

• tomogrpahic amplitude

• distance from fulcrum

• distance of object from IR

• orientation of tube motion

when anatomy is more perpendicular to the movement of the tube it is more ____

blurred

what are phantoms

also called blurred edges or blurred margins

• created by geometrical relationship between the tube movement and the anatomical structures in the patient

• dangerous to diagnostic process

• most common type is streaking

what can phantoms also be caused by

blur or overlap and displacement of blur margins dur to tomogrpahic motion at smaller angles

• increased exposure amplitude + reduced section thickness will decrease phantom images

what is the fulcrum

• the pivot point that the tube and IR rotate aorund

• where anatomy of interest should be

• can be set and moved up or down to obtain proper focus

what is the focal plane

section of anatomy to be imaged

• section level, layer hieght, object plane or depth of focus

• allows for acceptable recorded detail

what is the focal plane controlled by

the fulcrum

what is section thickness

width of the focal plane and controlled by tomogrpahic amplitude (angle)

what is sectional interval

the distance between fulcrum levels

what are the two types of motion

• simple motions

• complex motions

what are the two types of simple motions

• linear

• curvilinear

what is linear simple motion

tube and IR movement along a striaght line

• advantage: inexpensive

• disadvantage: increase SID and OID at both ends of the motion

what is curvilinear simple motion

maintains SID and OID at the ends of the motion

what is complex motions

• more advanced motions require specialized equipment

• requires 3-6 second exposure times

• as complexity increases- thinner sections are possible and more phantoms eliminated

examples of tomogrpahy exams

• IVU/IVP

• TMJ

• Hips

• Shoulders

• Spines

what is digital tomosynthesis

term used for digital radiographic tomogrpahy

• in one exposure, multiple images are created

• reprocessing can be done and manipulated to recreate various planes without re-exposing patient

what is breast tomosynthesis

3 dimensional mammography

• tube moves aross the breast tissue in an arc

• captures multiple images at different angles

• reconstructed to 3D

what is the most important tomographic exposure factor

time

time must be set properly in order to allow the full ____

exposure amplitude

too short of a time=

less blur and random phantoms

too long of a time=

decrease the density at each end of the exposure= increase detail= less blur outside of the focal plane

mA and tomography

with more complicated motion, low mA stations are necessary to compensate for longer times

kVp and tomography

• modifications in kVp utilized in making changes with image exposure

• decrease scatter- contrast may be a problem

what is narrow angle tomography (Zonography)

• utilizes less than a 10 degree angle

• procudes thick sections with good contrast, poor detail

• usefl for identificaiton of structures in which location is unkown

what is wide angle tomography

• produces thinner slices

• used for good recorded detail but poor contrast'

• useful for small bone structures (inner ear)

what is panoramic tomography

• slit scan images of curved surfaces

• useful with the face, head, and mandible