Question
click below
click below
Question
Normal Size Small Size show me how
Carlton Adler Ch 41
Question | Answer |
---|---|
what is a tomogram? | the actual image? |
what is a tomograph? | the piece of equipment used |
what is tomography? | the modality/ exam |
principle of tomography | synchonized movement of two elements, objects in plane of fulcrum sharp, objects farther away blurred |
pivot point around the movement occurs, object being examined is placed at this point | fulcrum |
where is object being imaged placed? | fulcrum |
method to overcome superimposition | tomography |
three elements of tomography | tube, object, IR |
terms used to describe section of interested in tomography | slice or cuts |
what is the result of a tomographic image? | area of fulcrum is sharp because it has not moved in relationship to tube & IR during position |
arc or angle the tube travels. Total distance traveled by the tube | tomographic amplitude |
arc or angle the tube travels during the exposure | exposure amplitude |
what kind of slices do we take in tomography | only coronal slices |
blurring of anatomic structures lying outside to focal plane | motion blur |
what is properly imaged in tomography | only the object lying in the focal plane |
how is blur demonstrated on the tomogram? | objects lying outside focal plane demonstrate increasing blur the further away from the object plane |
how does blur effect density? | increased blurring causes decreased density. Objects are more transparent, permits objects with the focal plane to be seen through the blurring |
how is tomographic amplitude (arc) related to blur | direct relationship. Increase in arc, increase in blur |
how is distance from fulcrum related to blur? | directly. Increase in distance of an object from fulcrum, increase in blur |
how is distance from IR related to blur? | directly, increase in object from IR, increase in blur |
as the tube approaches perpendicularity, what happens to blur? | blur increases |
blurred edges or margins | phantoms |
when are phantoms produced? | during complex tomographic motion |
occurs when tube motion is parallel to long axis of object | phantoms |
The tomographic arc is greater or less than the exposure arc? | greater than or equal to |
the exposure arc is greater or less than the tomographic arc? | less than or equal to |
what decreases phantom images | reduced section thickness and increased exposure amplitude |
pivot point | fulcrum |
how do you adjust fulcrum? | move table up or down OR move fulcrum up or down, patient remains stationary. |
region within the image exhibits satisfactory recorded detail and is controlled by the fulcrum | focal plane |
controlled by the exposure angle (amplitude) | width of the focal plane |
what is the relationship between thickness and exposure angle? | inverse relationship- as angle increases, section thickness decreases. |
what determines section thickness? | tomography angle |
controlled at the table, increments of 1/2 cm or 1 cm. | section interval |
cannot exceed the section thickness | section interval |
most common and most widely used type of motion | linear |
variety of motions | pluridirectional |
types of pluridirectional movements | curvilinear, circular, elliptical, figure eight, trispiral, hypocycloidal |
slice thickness relationship to movements | more complex motion uses thinner slices |
must match length of time required for x-ray tube to complete the tomo amplitude | exposure time |
what kind of mA used for tomogram? | low mA, 100 mA |
narrow angle, small exposure amplitude, 10º arc- produce thick sections, application in chest and renal studies | Zonography |
when lesion has been localized and fine detail is needed - produces thinner sections | wide angle tomography |
curved, used mostly for head, mandible. Tube & IR collimated to a slit and travel in opposite directions | panoramic tomography |
technique used to produce rad image with depth perception, making it 3D | stereoradiography |
common uses for stereoradiography | chest, skull, shoulder, sinus, FB |