Lesson 3 - Qualities of the Radiographic Image

Question 1

Define Sharpness (Film Screen)

Answer 1

Photographic Sharpness - divergence of light within the phosphor layer of the intensifying screens
- one x-ray photon creates multiple light photons. They diverge, give us many areas of unsharpness.

Question 2

Define Geometrical Unsharpness

What affects geometrical unsharpness

Answer 2

Attributed to the geometrical aspects of the x-ray tube and positioning.
SID, OID and focal spot size affect geometrical unsharpness

Question 3

Focal Spot size:
Decrease fss ________ sharpness
Increase fss _________ sharpness

Answer 3

Decrease fss INCREASE sharpness. Two points are closer together - sharper image
Increase fss DECREASE sharpness - more divergence as not a single point source, more focal spot blur/unsharpness

Question 4

S number

What is acceptable range?

Answer 4

an indication of the amount of exposure that the IR received
200-400 acceptable.
If below 200 it is OVERexposed - IR saw too much radiation (too dark, too dense)
If above 400 it is UNDERexposed - IR did not see enough radiation.

Question 5

kVP and S number

mAs?

Answer 5

If need a higher S# (need less radiation to IR) can increase kVP - but only on the condition that the penetrating ability is not affected.
**Lower mAs to increase S# - this is the better way to adjust.

Question 6

It’s possible to take 2 different exposures of the same thing, using same technique and get 2 different S numbers. What would be the reason?

Answer 6

Scatter

Question 7

Film screen useful density range

Answer 7

0.25-2.0 above base + fog. If more than range it is overexposed, less it’s underexposed. Direct relationship

Question 8

Higher the kVp, the ______ scatter

Answer 8

higher the kVp the MORE scatter - potentially degrade the image

Question 9

define pneumbra

Answer 9

shadow around image

Question 10

Role of kVp in influencing the contrast scales in film-screen radiography

Answer 10

Increase kVp - longer scale of contrast, more shades of gray. Able to penetrate more x-ray photons which provide detail in image. Penetrating more tissue types. Increase kVp - decreases differential absorption

Question 11

Effect of scatter on radiographic and subject contrast

Answer 11

Scatter radiation results in reduced image contrast - both subject and radiographic.