Scatter Radiation

Question 1

Factors that influence scatter

Answer 1

kVp, patient size, field size

Question 2

Source of occupational exposure

Answer 2

Compton scatter

Question 3

As ___ increases, Compton interactions also increase

Answer 3

kVp (energy)

Question 4

T/F: Modern digital filming is more sensitive to scatter than older filming modalities

Answer 4

True

Question 5

T/F: Field size and collimation are inversely related

Answer 5

True

Question 6

Automatic collimators use ____ to match the light field with the cassette size

Answer 6

Positive beam limiting (PBL)

Question 7

Go on the tube head/window to limit the beam coming out

Answer 7

Aperture diaphragm

Question 8

“Cleans up” scatter radiation using lead strips that absorb scattered x-rays

Answer 8

Grids

Question 9

Use of a grid requires more ___

Answer 9

mAs

Question 10

Increase in patient size [increases/decreases] amount of scatter

Answer 10

increases

Question 11

Grid Ratio =

Answer 11

h/D
(h= height of lead strips)
(d= distance between them)

Question 12

Use of a grid is recommended for anatomy greater than:

Answer 12

4 inches (10 cm) thickness

Question 13

Number of lead lines per unit length

Answer 13

Grid frequency

Question 14

T/F: The higher grid frequency, the more distinct grid lines on x-ray image

Answer 14

False

Question 15

Two types of grid patterns:

Answer 15

Cross-hatched and linear

Question 16

An aperture diaphragm that has an extended flange attached to it

Answer 16

Cone/cylinder

Question 17

The orientation of the lead lines relative to one another

Answer 17

Grid focus

Question 18

Grid conversion factor =

Answer 18

mAs with grid / mAs without grid

Question 19

A decrease in the number of transmitted photons that reach the IR because of some misalignment of the grid

Answer 19

Grid cutoff

Question 20

Occurs when using an SID outside the recommended focal range

Answer 20

Off-focus grid cutoff

Question 21

Concept that much of the scatter will miss the IR if there is an increased distance between the patient and the IR

Answer 21

Air gap technique

Question 22

mAs should be increased __% for every centimeter of air gap

Answer 22

10

Question 23

A beam-restricting device that has two or three sets of lead shutters is a(n):

Answer 23

Collimator

Question 24

A device consisting of very thin lead strips with radiolucent interspaces intended to absorb scatter radiation emitted from the patient is a:

Answer 24

Grid

Question 25

A larger the x-ray beam field size results in:

Answer 25

increase in scatter produced and increase in fog

Question 26

T/F: As collimation decreases, exposure to the IR increases.

Answer 26

True

Question 27

Changing from an 8:1 grid to a 12:1 grid, along with making the appropriate adjustments, will result in: A: an image with increased contrast B: using more mAs C: Increased patient dose

Answer 27

A, B, and C

Question 28

T/F: Digital IRs are not sensitive to scatter radiation

Answer 28

False

Question 29

Grids that move during the exposure:

Answer 29

are reciprocating grids and are part of the Potter-Bucky diaphragm

Question 30

If an excellent knee radiograph is produced using 10 mAs and an 8:1 ratio grid, how much mAs will be needed if no grid is available?

Answer 30

2.5 mAs

Question 31

T/F: Placing a lead shield behind the patient’s lower back during lumbar spine imaging absorbs the scatter and reduces the amount striking the IR.

Answer 31

True

Question 32

Significant collimation requires an increase of _____________ of the mAs.

Answer 32

30 - 50%

Question 33

The most common cause of grid cutoff is due to:

Answer 33

off-level misalignment.

Question 34

The unrestricted primary beam produces a(n) _________ area of exposure.

Answer 34

round

Question 35

What is the grid conversion factor for a 12:1 ratio grid?

Answer 35

5 x

Question 36

Why does the air-gap technique work?

Answer 36

The scatter photons are more likely to miss the image receptor.

Question 37

T/F: A good alternative to collimation is electronic masking.

Answer 37

False

Question 38

A larger field size will result in ___ scatter production

Answer 38

Increased

Question 39

An increase in collimation results in a [increase/decrease] in radiographic contrast

Answer 39

Increase

Question 40

When making a significant increase in collimation, _____ should be increased

Answer 40

mAs

Question 41

The purpose of a grid in radiography is to:

Answer 41

Increase image contrast

Question 42

With which one of the following grids would a convergent line be formed if imaginary lines from its grid lines were drawn in space above it?

Answer 42

Linear focused

Question 43

With exposure technique compensation, which of the following would result in the greatest radiation exposure to the patient?

Answer 43

a 12:1 grid ratio

Question 44

Off-focus grid cutoff occurs by using an SID that is not:

Answer 44

within the focal range of the grid

Question 45

Which of the following are tools that the radiographer can use to limit scatter radiation?

Answer 45

beam-restricting devices and radiographic grids

Question 46

What purpose does positive beam limitation serve?

Answer 46

To reduce patient exposure by limiting the exposure field to the same size as the image receptor in the Bucky tray

Question 47

As beam restriction increases: a. less volume of tissue is irradiated and higher image contrast b. less scatter is produced and higher image contrast c. less scatter is produced and less volume of tissue is irradiated d. all options are correct

Answer 47

D

Question 48

Which of the following is not a way to reduce the production of scatter radiation? a. Reduce the tissue thickness. b. Reduce the exposure field size. c. Increase collimation. d. Increase the grid ratio.

Answer 48

D

Question 49

What is the result of imaging a thicker part or patient?

Answer 49

More Compton interactions