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Medical Radiation Sciences 2 > Practice questions > Flashcards

Practice questions Flashcards

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USMLE® Step 1 flashcards
1
Q

Where is all radiation incident?

A

Incident on ALL transducers

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2
Q

List 2 basic methods/processes of operation in radiation dectors?

A
  1. Ionize it by interacting with atoms
  2. Excitation
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3
Q

List 3 basic modes of operation of radiation detectors:

A
  1. Pulse
  2. Rate
  3. Intograte
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4
Q

What modes of radiation detector operation allows for the detection of raidation?

A
  1. Pulse
  2. Rate
  3. Intograte
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5
Q

Which of the modes of operation provides the most accurate count of raidation incident on a transducer? Why?

A

Integrate mode; because it counts the total amount of radiation even if the radiation if fluxuating

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6
Q

Why is it important to know the rate even though its not completely accurate?

A

Because it allows for detection of the amount of radiation to notify you on general intensity

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7
Q

True or false?

Integrate mode detectors require low resolving times.

A

True

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8
Q

List 2 factors that can improve the sensitivity of a radiation detector:

A
  1. Increase the size of the ion chamber/DELs
  2. Amplify the signal (it can also lower the dose to the patient)
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9
Q

List 3 ways in which accuracy of radiataion detectors can be improved:

A
  1. Increase sensitivity
  2. Low resolving time
  3. Range that it will be able to detect
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10
Q

What is meant by the term “intrinsic efficiency” of a transducer?

A

Inherent to the material itself, not other enviormental factors, it is how well the radiation is detected/the stopping power

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11
Q

What can affect the intrinsic efficancy of a transducer?

A

a. Atomic number of transducer elements
b. Mass density of transducer elements
c. Physical state of transducer material

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12
Q

What 2 properties of a transducer effect it’s absolute efficiancy?

A

1.Intrinic efficiency
2.Geometric efficiancy

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13
Q

What operates on the basis of saturation of a detection chamber?

A

Gieger muller tubes

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14
Q

Which is not found in a PMT and why?
a. Anode
b. Dynode
c. Photocathode
d. Air

A

D; we dont want air interacting with the tube photons

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15
Q

What is the element used in thermoulminescent phosphor TLDs?

A

Lithium floride

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16
Q

What is th primary reason LiFl is the phosphor of choice in TLDs?

A

It is simular in Z# and denisty to human tissue

17
Q

What is the source of energy applied to LiFL to cause its luminescence?

A

Heat by annealing

18
Q

What term is used to describe any residual latent image on the CR following processing?

A

Ghosting

19
Q

How is ghosting resolved in CR plates?

A

Flooded with a very intense whhite light to give e- energy to escape the F traps

20
Q

Explain the term fading with respect to CR cassettes:

A

The natural dropping of e- from F centers over time from not processing the latent image

21
Q

List the ways in which the emmission efficancy in conventional PSP CR plates has been improved:

A
  1. Needle shaped phosphor
  2. Reflective layer
  3. Barium floride dopped with eroupium
22
Q

In floro with variable mA and fixed kV, the kV setting is determined by what?

A
  1. Manually choosing KV
  2. Choosing the body part
23
Q

In terms of conventional floro, what should the mA be?

A

Less than 5 mA

24
Q

In the input phosphor, what gets converted into what?

A

X-rays, light

25
Q

What is the purpose of the aluminum substrate coated on the external surface of the input phosphor?

A

To take any photons travelling backwards and reflect it forward to the photocathode

26
Q

What is the input phosphor made of?

A

Cesium iodide

27
Q

Why does an increase in thickness in the input phosphor layer result in reduced SR?

A

More diverging photons

28
Q

T/F?

An increase in phosphor thickness can result in relatively reduced dose;

A

True, better at absorption so you can use decrease in dose

29
Q

What feature ensures that all photoelectrons travel the same distance to the focal point within the II?

A

The curve of the IP

30
Q

The pupose of the OP is what?

A

To turn electrons into light

31
Q

The acceleration of e to a higher KE within the II contributes to what?

A

Fulx and brightness gain

32
Q

T/F

When using mobile floro with fixed SID, geometric mag can be achieved by increasing OID.

A

True

33
Q

With a brightness gain of 8000 in a 25 cm input phosphor, what is the flux gain if the output phospor size is 2.5 cm?

A

FG=80

34
Q

What does magnification in floro result in?

A

Increase in SR

35
Q

What is S distoriton due to?

A

External magnetic feild

36
Q

What is veiling glare a result of?

A

Scatter

37
Q

What is the conversion factor?
17 cm II tube
Flux gain=120
Output phosphor=2.5cm

A

55.5

Medical Radiation Sciences 2 (13 decks)

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