Ch. 29 Carlton

What is Assessing Distortion?

Geometric property of image quality.
Always exists and can only be minimized.

What is two types of Distortion?

Size & Shape

What is the fcatorss affecting Size Distortion?

SID & OID

What are the factors affecting Shape Distortion?

Alignment & Angulation

What controls the factors affecting Size Distortion?

SID and OID

What is the effect of factors affecting Size Distortion?

Magnification only.

Digital systems can resize images

by post-processing.

What is SID?

Major factor for magnification.

How does SID affect magnification?

Longer SID yields less magnification.

What is a result of using a longer SID?

Decreased Entrance Skin Exposure (ESE).

What is OID?

Critical distance for magnification and spatial resolution.

What should you do with OID to get better images?

Minimize OID whenever possible.

What is the formula for Magnification Factor?

M = \frac{SID}{SOD}

What is the formula for Magnification Factor?

M = \frac{Image \space size}{Object \space size}

How do you calculate Object Size?

O = I/M where I = image size.

How does image size compare to object size in medical radiography?

Image size is always larger than object size in medical radiography.

What is Shape Distortion?

Misrepresentation by unequal magnification.

What is one type of Shape Distortion?

Foreshortening & Elongation

What is part of Alignment that affects Shape Distortion?

Central Ray, Anatomical Part & Image Receptor

What affects Angulation?

Degree & Direction

What is an issue with Central Ray Alignment?

Off-centering of tube.

What is an issue with Central Ray Alignment?

Incorrect positioning of part.

What is another issue with Central Ray Alignment?

Off-centering of image receptor.

How do you calculate Shape Distortion?

Effect cannot be calculated; subjective evaluation.

What knowledge is required to evaluate shape distortion?

normal anatomy and projections.