Scatter

Question 1

What is scatter?

Answer 1

Is a form of image noise that causes distortion/fog on an image

Question 2

What impact does scatter have on grayscale and contrast?

Answer 2

It reduces both significantly in an image causing the quality to go down

Question 3

Where is scattered ratiation produced?

Answer 3

Inside the patient as a result of compton interactions

Question 4

What percentage of scatter is produced by compton interactions?

Answer 4

0.97

Question 5

What 3 factors increase the amount of scatter radiation produced?

Answer 5

High levels of kVP, large field size and large body thickness

Question 6

What part of the beam is scattered radiation a part of?

Answer 6

The remnant beam

Question 7

What is the amount of scatter in the remnant beam a direct function of?

Answer 7

The amount of tissue exposed

Question 8

What plays a key role in the reduction of scatter?

Answer 8

Collimation

Question 9

What direction does scatter radiation flow in upon interaction?

Answer 9

It occurs in all directions

Question 10

What type of scatter flows directly back at the tube 180 degrees?

Answer 10

Backscatter

Question 11

What angle does forward scatter move in?

Answer 11

Small angle close to the direction of the incident beam

Question 12

What angle does side scatter move in?

Answer 12

At a 90 degree angle to the incident beam

Question 13

Why is scatter of concern to technologists?

Answer 13

Depending on the angle of the scatter it can bounce in the direction of the tech and cause exposure

Question 14

How does kVp affect scatter?

Answer 14

Scatter increases as a result of high kVp, because as kVp increases so does the probability of compton interactions, but the increase is nominal

Question 15

Why is reducing kVp not an effective method in reducing scatter?

Answer 15

Because kVp is necessary for penetration and its benefits far outweigh its downside

Question 16

How does large field size affect scatter?

Answer 16

With more tissue exposed, there is a higher chance of scatter events within the tissue

Question 17

What other interactions come into play with larger field sizes?

Answer 17

Interactions with the tabletop and other objects, which can both produce scatter

Question 18

What is the primary mechanism for reducing field size and scatter?

Answer 18

Collimation since it directly reduces the field size

Question 19

How does large soft tissue part thickness affect scatter?

Answer 19

Larger parts increase the percentage of scatter interactions

Question 20

What can be used to reduce part thickness/scatter?

Answer 20

Compression paddles, which only sligtly decrease scatter

Question 21

What large body part is the exception to increased scatter?

Answer 21

The chest, since the tissue density is low despite its size, so it will not produce scatter

Question 22

What tool is added to machines to reduce scatter?

Answer 22

Grid

Question 23

How does scatter affect contrast?

Answer 23

They indirectly proportional, so as scatter increases contrast decreases and vise versa

Question 24

Why is scatter bad for images?

Answer 24

It distributes a blanket of exposure over the image

Question 25

What does scatter provide in a diagnostic image?

Answer 25

Radiographic Fog and unwanted information that can degrade the overall image

Question 26

What is the angle of scatter based on?

Answer 26

The original energy of the incoming photon

Question 27

What direction do scattered xrays that retain most of their energy move in?

Answer 27

Move in a forward direction close to that of the original

Question 28

What direction do scattered xrays that retain 84% of their energy move in?

Answer 28

Move at a right angle

Question 29

What direction do scattered xrays that retain 68% of their energy move in?

Answer 29

Move in a backwards direction (back scatter)

Question 30

What direction do more xrays scatter in and why?

Answer 30

Back scatter because most scattered photons have low energy

Question 31

Who/what is scatter bad for?

Answer 31

The image because it creates noise, the patient because it causes ionization, and anyone in the room bc it leaves the patient