Week 4 - Image Quality

Question 1

things that affect Technical - Sharpness of image

Answer 1

• geometric - magnification and distortion
• motion unsharpness (blurring)

Question 2

Geometric factors: magnification

Answer 2

• all radiographs display images which are larger than the structures they represent
• as close to 1:1

Question 3

to reduce magnification

Answer 3

• increase distance (height) of receptor to x-ray tube
• decrease the object image distance

Question 4

magnification is undesirable in most cases:

Answer 4

• inaccurate measurement of anatomy especially if for pre surgical planning
• causes unsharpness due to penumbra (penumbra - causes the magnificaiton)
• causes ‘distortion’ due to anatomy being variable distances from the tube

Question 5

Distortion will occur if:

Answer 5

• all elements of an object do not lie at the same distance from the source of x-ray
• the subject plane is not parallel to the image plane
• these conditions commonly occur

Question 6

Distortion is:

Answer 6

anatomy is not represented in its correct proportions due to unequal magnification of different areas of the same object

Question 7

Motion unsharpness

Answer 7

any relevent movement between the patient - film - tube will cause blurring
- patient movement = biggest factor
- undesirable

Question 8

Patient movement reduced by:

Answer 8

good communication
short exposure time
restraining devices
foam pad and sand bag (radioopaque)

Question 9

subject factors influencing image quality

Answer 9

Some are out of our control:
- body habitus
- age
- injury
- communication problems
- cognitive state
- equipment

May prevent the correct imaging projections being obtained