3. kVp-Differencial absorption and contrast

Question 1

Define the two types of contrast:

Answer 1

1. Subject Contrast-A measurement of intensity of the remnant beam caused by Diff absorption. How much diff absorb. is occurring between two areas-cannot see or change
2. Image contrast: Differences within the image caused by the patient’s anatomy-the degree of difference between adjacent brightness values

Question 2

What happens to absorption when we increase KVP

Answer 2

It lowers absorption

Question 3

What is the peak measuring in KV?

Answer 3

The maximum V difference between cath. and anode since not all e will travel at the same V

Question 4

What characteristics do low energy photons produce?

Answer 4

-Easily absorbed
-differential absorption increases
-Higher subject contrast

Question 5

What are some characteristics of high energy photons?

Answer 5

-More penetration
-Differential absorption decreases
-Lower subject contrast

Question 6

What is the 15% rule of thumb?

Answer 6

-If you want to keep IR intensity the same and decreases patient dose, increase KVP by 15% and decrease your mAs by half

Question 7

What are 4 ways to control scatter?

Answer 7

1. Use of grids
2. Thickness-less matter less scatter
3. Collimation
4. Proper kVp selection

Question 8

When should you use a grid?

Answer 8

If the thickness of the patient’s anatomy is at least 10 cm

Question 9

If there is more matter will there be more or less scatter?

Answer 9

More scatter

Question 10

If you increase kVp., will there be more or less scatter overall?

Answer 10

Less scatter overall, but more scatter will reach the IR since scattered photons gain more energy

Question 11

Why is kVp more important to change?

Answer 11

Because it determines the penetration and contrast. Also, as the kVp increases, so does beam quality.