Ch 11 Beam Restricting Devices

Question 1

Why do we need to employ beam restricting devices?

Answer 1

1. To reduce patient dose
2. Reduce Scatter
3. Achieve optimal radiographs within technique range

Question 2

What are the two principle factors that the scatter produces?

Answer 2

1. Patient size

2. Field size (we have control over)

Question 3

As field size increases, so does ______ radiation.

Answer 3

Scatter

Question 4

Reducing the beam, ______ scatter which also results in lower OD

Answer 4

Reduces

Question 5

What do beam restrictors do?

Answer 5

Limit the size of the x-ray field to only the anatomic structure of interest

Question 6

The bigger the field size, the _____ scatter radiation.

Answer 6

More

Question 7

When you collimate, what do you have to do to your technique?

Answer 7

Increase it

Question 8

What are the (3) types of beam restricting devices?

Answer 8

1. Variable aperture diaphragm
2. Aperture Collimator
3. Cones & cylinders

Question 9

Scatter radiation _____ image contrast.

Answer 9

Reduces

Question 10

What are aperture diaphragm beam restrictors?

Answer 10

Lead lined metal diaphragm attached to the x-ray tube head

Question 11

What does the aperture diaphragm beam restrictor do?

Answer 11

Projects the image 1cm smaller on all sides, leaving a border around the edges.

Question 12

What are cones and cylinders?

Answer 12

Extended metal structures that restricts the beam to the required field size

Question 13

Do cones reduce SID?

Answer 13

No

Question 14

Cones and cylinders ____ image contrast.

Answer 14

Improve

Question 15

What is a variable aperture collimator?

Answer 15

• Restricts pt dose by restricting the volume of tissue irradiated
• Decreases scatter radiation

Question 16

What is the most common beam restricting device?

Answer 16

Variable aperture collimator

Question 17

When was PBL mandated, then removed?

Answer 17

1974 removed in 1994

Question 18

What is PBL?

Answer 18

Positive beam limitation

Question 19

What is penumbra?

Answer 19

Fuzzy border outside the image

Question 20

How can penumbra be minimized?

Answer 20

By using the correct SID

Question 21

What is off focus radiation?

Answer 21

X-rays that are produced when the projectile electrons stray and interact at positions on the anode other than the focal spot

Question 22

Off focus radiation _____ image blur.

Answer 22

Increases

Question 23

Off focus radiation is absorbed by the collimator shutters made of ___ lead.

Answer 23

3mm

Question 24

What does the bottom shutters do?

Answer 24

Reduce penumbra

Question 25

What does the upper shutters do?

Answer 25

Reduce off focus radiation

Question 26

The light field you see is projected off a mirror on the path of the x-ray beam at a _____ degree angle .

Answer 26

40-45

Question 27

The light source and the x-ray source should be _______ from each other to ensure their light fields are the same size.

Answer 27

Equidistant

Question 28

What are lead blockers?

Answer 28

Anything that is impregnated with lead (ex: Lead aprons and lead strips)

Question 29

What are lead masks?

Answer 29

Lead that is cut to a particular size or shape for a specific patient and exam