Ch.9 Scatter control

Question 1

Coherent, Compton, Photoelectric Effect

Answer 1

3 types of radiation interactions with matter

Question 2

occurs at low energy levels
- known as “Thompson scatter”

Answer 2

Coherent Scatter

Question 3

occurs at kVp levels of 40-125
- incoming photon interacts with an OUTER orbital electron, removing it from the atom (ionization) and processed in a different direction
-** as kVp is increased the interactions are also increased

Answer 3

Compton Effect

Question 4

incoming photon collides with an INNER orbital electron that is absorbed in the processes creating absorbed dose in the patient
-Known as “Secondary Radiation” or “True Absorption”
-** as kVp is increased, the effect is Decreased

Answer 4

Photoelectric Effect

Question 5

Volume of tissue
Kilovoltage
Field Size
Density of matter
- the pt is the principle source of scatter since the body is mostly made of water

Answer 5

Factors Affecting Quantity of Scatter

Question 6

What is the Grid Ratio of the following:
Grid cassettes & Mobile radiography
General purpose
General purpose, Chest
High-kilovoltage radiography

Answer 6

5:1 & 6:1
8:1
12:1
16:1

Question 7

a device placed between the patient and the IR made of thin lead strips
-they absorb scatter while permitting remnant radiation to pass through

Answer 7

Grids

Question 8

the relationship between the height of the lead strips & the width of the interspacing material (higher the ratios= more precise alignment)
-determines how much variation in the direction of the incoming photon is allowed without the photon being absorbed by the grid

Answer 8

Grid Ratio

Question 9

number of lead strips per inch (range from 60-196 lines/inch)

Answer 9

Grid Frequency

Question 10

lead strips are aligned with the xray beam at a specific SID
(general purpose grids)

Answer 10

Focused Grids

Question 11

the lead strips of a focused grid are precisely aligned with the xray beam at a specific SID

Answer 11

Grid Radius

Question 12

a range of distances within the grid that will not absorb an under amount of useful radiation

Answer 12

Focal Range

Question 13

“Grid Striping”
the image includes an image of the grid itself
-objectionable & can reduce detail

Answer 13

Grid Lines

Question 14

Excessive absorption of useful radiation
-appears as decreased radiographic density on the side of the image
-** Prevented by ensuring the beam is always properly aligned with the center of the grid at the appropriate distance

Answer 14

Grid-cutoff

Question 15

use grid device
use an air gap
minimize field size
decrease kVp

Answer 15

methods of scatter control

Question 16

decreasing ____ improves contrast even when a grid is used because it decreases the _____ of scatter that penetrates the grid

Answer 16

Collimation; quantity

Question 17

should be considered when other methods fail to provide sufficient contrast
-decreasing increases contrast in 2 ways:
- narrows the scale of contrast
- lower levels decrease the energy
*** by decreasing ___ you MUST increase mAs to compensate

Answer 17

Decreasing kVp