Conventional Tomography

What is 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

What is the tomographic principal?

The x-ray tube and image receptor move in opposite directions around a stationary fulcrum (pivot point) during the exposure

An object placed in the fulcrum will appear ______, while objects outside the focal plane will appear ________

Sharp, blurred

The greater the distance from the fulcrum, the _____ the blurring

Greater

What is blur?

Loss of nearly all recorded detail of objects outside the focal plane

The tomographic amplitude (TA) is the ___________ the tube travels (always equal to or greater than the exposure amplitude)

Total distance

The exposure amplitude (EA) is the distance the tube travels during?

The exposure

Fulcrum

Pivot point around which the tube and IR move

Focal plane (or object plane)

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

What is the Grossman Principal?

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

What is this image demonstrating?

Grossman principal

What is the Planigraphic principal?

The fulcrum is adjustable while the patient remains stationary (most common)

What is this image demonstrating?

Section (slice) thickness

• depth of the focal plane (area within focus)

• controlled by the exposure angle/amplitude

The exposure angle is ______ proportional to the section thickness

Inversely

The ______ the angle (the more the tube in moving), the thinner the slice

Greater

What is the exposure angle for regular x-ray?

0

Section interval

• the distance between the fulcrum levels of successive slices

• should not exceed the section thickness

What is the tomographic tube movement usually?

Linear or complex (pluri-directional)

Linear tube movement

• the simplest motion

• tube travels in a straight line

• the SID and OID change during tube travel

• used for and IVU

The tube motion should be _________ to the long axis of the object

Perpendicular

The total tomographic arc is limited to ____ degrees

48

What are the complex tube movements?

• curvilinear (maintains SID and OID)

• circular

• elliptical

• figure eight

• trispiral

• hypocycloidal

What tube movement is this?

Hypocycloidal

Tri-spiral and hypocycloidal movements give the ________ tomographic amplitudes and the ________ cut

Maximum, thinnest

What are try-spiral and hypocycloidal movements used for?

Carpal bones and the auditory ossicles

Complex motions often require ____ to _____ second exposures

3-6

What does a long exposure time mean for your mA?

Small mA

Zonography

• specialized tomographic procedure

• usually 1-5 degree angles are used

• large slice thickness

• used to located a lesion when the exact location is unknown (ex: lung lesion)

Panoramic tomography

• slit scan radiography of the curved surfaces

• used for the mandible, teeth, facial bones, etc

• both the tube and the film rotate past the slit during the exposure

What line has to be parallel to the floor for panoramic tomography

IOML

Where does the fulcrum go for panoramic tomography?

Middle of head