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1. Medical Radiation Sciences > Attenuation Applications > Flashcards

Attenuation Applications Flashcards

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USMLE® Step 1 flashcards
1
Q

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

A

Lower kVp is higher probability of creating compton scatter

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2
Q

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

A

More probability at lower kVp

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3
Q

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

A

Photoelectric effect

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4
Q

When does compton scatter and PE decrease?

A

As kVp increase

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4
Q

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

A

Compton scatter

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4
Q

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

A

More likely to be absorbed than scatter

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5
Q

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

A

40

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5
Q

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

A

80kVp

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6
Q

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

Why?

A

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

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7
Q

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

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

A

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

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7
Q

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

A

More subject contrast

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8
Q

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

A

Less subject contrast

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8
Q

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

A

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

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9
Q

What tissues are present in chest imaging?

A

Air, soft tissue, bone

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10
Q

What tissues are present in mammography?

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

Very similar to soft tissue and close in density

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11
Q

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

A

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

12
Q

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

How and why?

A

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

13
Q

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

How and why?

A

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.

14
Q

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

A

110-130 kVp for more SC

15
Q

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

A

30 kVp for more PE and more charectoristic photons

16
Q

Does K-edge absorption happen in humans?

A

No, only happens with materals of high atomic number

17
Q

What is k-edge absorption

A

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

18
Q

When is L-shell absorption most likely to happen?

A

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

19
Q

What are the two types of k-edge absorption?

A

L shell
K shell

20
Q

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

A

-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

21
Q

What things in x ray display k-edge absorption?

A
  1. Heavy element filters
  2. Contrast studies
  3. Image receptors
  4. Lead sheilding
22
Q

What do k-edge filters in the tube do?

A

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

23
Q

What will heavy element filters absorb?

A

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

24
Q

What type of photons will heavy element filters allow through?

A

-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

25
Q

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

A

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

26
Q

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

A

-Vessels

-GI tract

27
Q

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

A
  1. Iodine: BE=33kEV
  2. Barium: BE=37 kEV
28
Q

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

A
  1. Gadolinium oxysulfate
  2. Cescium iodide
  3. Selenium
29
Q

What are the benefits of having a faster IR?

Generally, what is the k-edge

A

-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

30
Q

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

A

Use rare earth detectors-k-edge is around 30

31
Q

Why does lead provide scatter protection?

A

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

32
Q

What are some examples of scatter protection?

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

1. Medical Radiation Sciences (18 decks)

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