Ch 11 Beam Restricting Devices Flashcards Preview

Slockett's Rad Exposures > Ch 11 Beam Restricting Devices > Flashcards

Flashcards in Ch 11 Beam Restricting Devices Deck (29):
1

Why do we need to employ beam restricting devices?

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

2

What are the two principle factors that the scatter produces?

1. Patient size
2. Field size (we have control over)

3

As field size increases, so does ______ radiation.

Scatter

4

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

Reduces

5

What do beam restrictors do?

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

6

The bigger the field size, the _____ scatter radiation.

More

7

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

Increase it

8

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

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

9

Scatter radiation _____ image contrast.

Reduces

10

What are aperture diaphragm beam restrictors?

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

11

What does the aperture diaphragm beam restrictor do?

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

12

What are cones and cylinders?

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

13

Do cones reduce SID?

No

14

Cones and cylinders ____ image contrast.

Improve

15

What is a variable aperture collimator?

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

16

What is the most common beam restricting device?

Variable aperture collimator

17

When was PBL mandated, then removed?

1974 removed in 1994

18

What is PBL?

Positive beam limitation

19

What is penumbra?

Fuzzy border outside the image

20

How can penumbra be minimized?

By using the correct SID

21

What is off focus radiation?

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

22

Off focus radiation _____ image blur.

Increases

23

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

3mm

24

What does the bottom shutters do?

Reduce penumbra

25

What does the upper shutters do?

Reduce off focus radiation

26

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

40-45

27

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

Equidistant

28

What are lead blockers?

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

29

What are lead masks?

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