Tomography

Question 1

What is the principle of Tomography?

Answer 1

Tomography is a radiographic technique that employs motion to show anatomical structures lying in a plane of tissue while blurring or eliminating the detail in images of structures above and below the plane of interest.

Question 2

What is focal plane?

Answer 2

It refers to an individual tomographic image / slice that shows tissues within that section sharply defined and in focus.

Question 3

What is another term for focal plane?

Answer 3

Focal Trough

Question 4

Why is tissues and structures outside the tomographic section not visible?

Answer 4

They are blurred and out of focus.

Question 5

What are the blurring principles?

Answer 5

Structure in focal plane maintain same position on file resulting in a sharp image.

Structures above and below the focal plane will move from one end of the film to the other, resulting in a blurred image.

Question 6

Where should the pivot point be positioned?

Answer 6

At the mid-level of the anatomy of interest. E.g. if the kidney is located 8cm above the image receptor, that will be our pivot point.

Question 7

The amount of blurring depends on which factors?

Answer 7

Amplitude of tube travel (more blur with wide-angle motion)
Distance from focal plane (more blur at long object - focal plane distances)
Distance from film (more blur at long object film distances)
Orientation at tube travel (object needs to be orientated perpendicular to motion)

Question 8

The wider the angle, the _____ the section.

Answer 8

Thinner

Question 9

The narrower the angle, the _____ the section.

Answer 9

Thicker

Question 10

What tomographic angle is that of conventional projection radiography?

Answer 10

0 degrees - everything is in focus!

Question 11

What are the disadvantages of linear Tomography?

Answer 11

High patient dose with multiple cuts
High cost
Long exposure times
Motion artifacts with long exposure times are more common

Question 12

What is an clinical application of conventional tomography?

Answer 12

Dentistry. Orthopantogram (OPG)

Question 13

Define focal trough.

Answer 13

Focal trough is a three dimensional curved zone, or image layer (always fixed). A narrow zone of focus. Only images within are in focus. Images are most clear (sharpest resolution) in the middle and become less clear further from central line.