Attenuation Applications

Question 1

Is compton scatter more likely to be created at higher or lower kVp?

Answer 1

Lower kVp is higher probability of creating compton scatter

Question 2

Is Photoelectric absorption more likely to be created at higher or lower kVp?

Answer 2

More probability at lower kVp

Question 3

What occurs more at lower energy, photoelectric effect or compton scatter?

Answer 3

Photoelectric effect

Question 4

When does compton scatter and PE decrease?

Answer 4

As kVp increase

Question 4

What occurs more at higher kVp’s, compton scatter or PE?

Answer 4

Compton scatter

Question 4

Once a photon reaches 20 kEV, what is likely to happen to the photon

Answer 4

More likely to be absorbed than scatter

Question 5

At what kVp is a photon more likely to scatter in the bone?

Answer 5

40

Question 5

At what kVp can you see differences in the image due to differential absorption?

Answer 5

80kVp

Question 6

What is most likely to happen to the photons once they get above 80 kVp?

Why?

Answer 6

You see differencds in images due to scatter. Decrease in subject contrast because it only shows differencesin density, not atomic number

Question 7

How do you find the differences in atomic number and density?

What do you need to remeber when figuring out the math equation?

Answer 7

Divide the smaller number by the larger number and REMEBER THE PROPORTION EQUATION

Question 7

Will you see more or less subject contrast with low energy and the PE?

Answer 7

More subject contrast

Question 8

Will you see more or less subject contrast with high energy and compton scatter?

Answer 8

Less subject contrast

Question 8

At low energy, are you more likely to see PE or CS? What about high energy:?

Answer 8

Image formation at low energy: PE
Image formation at high energy: CS

Question 9

What tissues are present in chest imaging?

Answer 9

Air, soft tissue, bone

Question 10

What tissues are present in mammography?

Answer 10

1. Soft tissue
2. Fat
3. Glands
4. Tumours

Very similar to soft tissue and close in density

Question 11

What has higher subject contrast naturally, chest imaging, or mammography? What about lower subject contrast?

Answer 11

Chest imaging: Higher natural subject contrast
Mammography: Lower subject contrast

Question 12

When imaging the chest, what are we trying to achieve with subject contrast?

How and why?

Answer 12

-Trying to reduce subject contrast with high energy to decrease subject since it naturally has high subject contrast

Question 13

When preforming a mammogram, what are we trying to achieve with subject contrast?

How and why?

Answer 13

Trying to increase subject contrast with low energy too see more absorption and to highlight the differences in atomic number while still seeeing differences in density.

Question 14

What is the range of kVps (average) that shows the a chest image?

Answer 14

110-130 kVp for more SC

Question 15

What is the kVp that allows us to see the breasts? Why?

Answer 15

30 kVp for more PE and more charectoristic photons

Question 16

Does K-edge absorption happen in humans?

Answer 16

No, only happens with materals of high atomic number

Question 17

What is k-edge absorption

Answer 17

A sharp decrease in absorption once you reach the k-edge (the k-shells binding energy in a material)

Question 18

When is L-shell absorption most likely to happen?

Answer 18

-Greatest probability with very low E photons (12 kEV)

Question 19

What are the two types of k-edge absorption?

Answer 19

L shell
K shell

Question 20

When is absorption most likely to take place with k and L shell when refereing to the k-edge? When does probability drop off?

Answer 20

-Greatest probability of absorption happening if the energy is just above the binding energy of tungsten -Zero probability if the enrgy is less than the binding energy of tungsten

Question 21

What things in x ray display k-edge absorption?

Answer 21

1. Heavy element filters 2. Contrast studies 3. Image receptors 4. Lead sheilding

Question 22

What do k-edge filters in the tube do?

Answer 22

They are made of a high atomic number, and only let through a narrow range of photons in the beam

Question 23

What will heavy element filters absorb?

Answer 23

Will absorb low E photons-any E just above the k-edge (the binding E of te k shell)

Question 24

What type of photons will heavy element filters allow through?

Answer 24

-Lets through photons below BE of the material of the filter -Will let through photons way above BE -charecterisitc radiation that is made from itself since the target is also made of the same material

Question 25

What is the purpose of contrast studies? How does it work?

Answer 25

To better visualize anatomy-show structures and function by absorbing radiation with thier high atomic #

Question 26

What are two examples of things you can see with contrast studies?

Answer 26

-Vessels -GI tract

Question 27

What are two types of contrast? What is thier binding E?

Answer 27

1. Iodine: BE=33kEV 2. Barium: BE=37 kEV

Question 28

What are some examples of what IR could be made of?

Answer 28

1. Gadolinium oxysulfate 2. Cescium iodide 3. Selenium

Question 29

What are the benefits of having a faster IR? ## Footnote Generally, what is the k-edge

Answer 29

-Need less mAs -All have a k-edge of what is closer to our energy in our beam, so more absorption takes place and a decrease in dose occurs

Question 30

What type of IRs do we use now days and what is their K-edge?

Answer 30

Use rare earth detectors-k-edge is around 30

Question 31

Why does lead provide scatter protection?

Answer 31

-Has a high atomic number and a k-edge that matches our beam, so theres more absorption

Question 32

What are some examples of scatter protection?

Answer 32

1. Lead sheilding 2. Lead walls/glass 3. Grids