RAD 120 - Ch 29 Distortion - Review Questions

What is distortion?

a misrepresentation of the size and shape of the structures being examined

What is the difference between size and shape distortion?

Size Distortion is the misrepresentation of the size of an object and can only be magnification in conventional radiography. Shape Distortion is the misrepresentation of the actual shape of the structure being examined by unequal magnification.

How do the SID and the OID affect size distortion?

The greater the SID and the smaller the OID, the less the size distortion.

What is the magnification factor formula?

The magnification Factor (M) is the degree of magnification and is calculated by:

M = SID/SOD

What is the difference between elongation and foreshortening?

Elongation projects the object so it appears to be longer than it really is, whereas foreshortening projects it shorter.

How does the alignment of the anatomical part affect shape distortion?

The long axis of the anatomical part, or object, is intended to be positioned perpendicular to the central ray and parallel to the image receptor. When this does not occur, distortion may occur.

How do the direction and degree of angulation affect shape distortion?

Angulation refers to the direction and degree the tube is moved from its normal position perpendicular to the image receptor. The angulation of the tube is designed to cause a controlled or expected amount of shape distortion to avoid superimposition. As long as the specified angulation is applied, the image is comparable to norms and is of diagnostic quality.

How can shape distortion be used to advantage?

Shape distortion is used primarily to avoid superimposition of anatomical structures.