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Fluoro Cram > Part 1: Factors impacting pt dose > Flashcards

Part 1: Factors impacting pt dose Flashcards

1
Q

To reduce pt exposure, you want to use ___ kVp and ___ mA

A

HIGH kVp

LOW mA

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2
Q

To reduce pt exposure you want to use ____ image intensifier mode with strict ____

A

Largest

Collocation

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3
Q

To reduce exposure you want to keep the patient to detector distance or patient to image intensifier distance as (long/short) as possible

A

Short

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4
Q

In fluoroscopy, the x ray output/pt radiation dose is (directly/indirectly) proportional to the mA used

A

Directly

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5
Q

X-ray tube voltage is what unit?

A

kVp

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6
Q

What is kVp used to determine?

A

The maximum photon energy in keV of the X-ray beam produced

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7
Q

Most important step to take to avoid unnecessary pt radiation exposure

A

Collimation!

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8
Q

Good collomation means the X-ray beam is (increased/reduced)

A

Reduced

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9
Q

More colliamtion = lower size of X-ray beam = ?image quality?

A

Improved

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10
Q

Because X-ray tubes in fluoroscopy operate at 125-150 kVp, filtration must be at least how much?

A

3mm aluminum equivalent

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11
Q

___ inch target to panel distance is optimal for fluoroscopy.

___ inch is the minimum

A

18” (fixed unit, ideal amount)

12” minimum (mobile unit)

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12
Q

On fluoroscopy system equipped with ABC where X-ray tube is fixed to table below, moving the image intensifier AWAY from the pt (increases/lowers) pt radiation dose

A

Increases

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13
Q

The image intensifier serves as primary protective barrier and must be at least ___ of lead equivalent for equipment operating about 125 kVp

A

2mm

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14
Q

Bucky slot cover

A

Caused when Bucky tray is moved to the end of the table and leaves a 2” wide opening at operator’s gonad level

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15
Q

Bucky slot cover must be at least ___ lead equivalent

A

0.25mm

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16
Q

Protective curtain drapes of at least ___ lead equivalent must be positioned between fluoroscopist and patient

A

0.25mm

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17
Q

Doubling the exposure time does what to pt radiation dose?

A

Doubles it

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18
Q

The input phosphor absorbs ___ and converts their energy into ___

A

X-rays -> light photons

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19
Q

In an image intensifier, after X-rays are converted to light photons, the light photons are immediately absorbed by the ___ which causes ___ to be given off in direct proportion to the intensity of the fluorescent light.

A

Photocathode

Electrons

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20
Q

In an image intensifier, after the electrons are given off, they are sped up by the ___ and focused with little distortion by ___ onto the ___.

A

Accelerating anode

Electrostatic lenses

Output phosphor

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21
Q

In an image intensifier, the output phosphor (screen) absorbs electrons and emits ___ which are then available for processing by the video system.

A

Light photons

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22
Q

How is brightness gain in the image intensifier achieved?

A

By acceleration of the electrons and minification of the output image

Aka electronic gain and minification gain

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23
Q

What is quantum mottle?

A

A grainy or blotchy appearance to the image which is due to a low number of absorbed photons

24
Q

The mottle level can be adjusted by changing what?

A

Exposure factors (kVp and mA)

25
Q

How do you increase the number of available X-ray photons?

A

Increase exposure

26
Q

Most fluoroscopists use ___mA in manual mode for adult fluoroscopy to marinating adequate X-ray photon stability?

A

2 to 5

27
Q

How is subject contrast reduced in general?

A

With high kVp

28
Q

Subject contrast is chiefly determined by what?

A

The kVp

29
Q

Detector contrast is determined by what?

A

Image intensifier
Type of tv camera target
Amplitude of brightness/signal
Brightness/contrast settings on monitor

30
Q

What units are used to measure resolution?

A

Line pairs per millimeter (lp/mm)

31
Q

Overall resolution of an image is expressed in what terms?

A

Modulation transfer function (MTF)

32
Q

Size distortion is caused by what?

Shape distorts caused by what?

A

Size: object to image distance

Shape: geometric problems in shape of intensification tube

33
Q

What is the cause of vignetting?

A

The peripheral image is displayed over a larger area of the output screen causing brightness loss at the periphery

34
Q

What part of the image intensifier changes the field of view from standard to magnification mode?

A

Electrostatic lens

35
Q

Fluoroscopy TV systems are ___ systems

A

Closed circuit

36
Q

___ is the operation of camera shutters at the same frequency as X-ray pulses.

A

Synchronization

37
Q

Framing frequency in cinefluorography is usually a division of ___

A

60

(E.g. 7.5, 15, 30, 60, 90, 120)

38
Q

A higher lens f-number means what?

A

Less light is available to form the image on the cine film

39
Q

There is an up to 95% dose reduction when utilizing ___ during fluoroscopy.

A

Video disk recording

40
Q

What two advantages to video tape recording have over cinefluorography?

A
  1. Instant replay of the image
  2. Pt radiation exposure is not increased
41
Q

Does video tape or cinefluorography have a fixed frame rate of about 30/sec?

A

Video tape

42
Q

When spot filing, you place the cassette between ___ and ___.

A

The patient

The image intensifier

43
Q

What makes spot film cassettes have the best resolution?

A

They’re made using higher mA (100+) with short exposure time (less motion)

They’re acquired with very high resolution cassette detectors

44
Q

Contrast media is chosen based on what two qualities?

A

Low toxicity

High atomic number

45
Q

What is the function of a radiographic grid?

A

To reduce scatter radiation produced in the pt before it reaches the image intensifier or X-ray film

46
Q

What is a cassette front made out of?

A

Low atomic number material (carbon fiber, aluminum, cardboard)

47
Q

Pro and con of 35mm cine film vs. 16 mm

A

35mm: more pt exposure, higher image quality

48
Q

Cinefluorography is almost entirely utilized on which organ?

A

Heart

49
Q

Cinefluorography delivers about how much more radiation dose than fluoroscopy for the same kVp?

A

10 times

50
Q

What are the most important factors in attenuation and absorption?

A

Tissue density

Elemental composition

51
Q

What is remnant radiation?

A

The primary radiation that exits the human body

52
Q

Minimum source to skin distance for mobile fluoroscopy units.

Minimum source to skin distance for stationary fluoroscopy units.

With some circumstances, absolute minimum?

A

Mobile: 30 cm or 12”

Fixed: 38 cm or 15”

Absolute: 10 cm or 8”

53
Q

Scatter radiation is mainly produced by ___

A

Compton interactions

54
Q

What 3 factors affect an increase in scattered radiation?

A
  1. High kVp
  2. Large field exposed (area exposed)
  3. Thick body part (volume exposed)
55
Q

Minimum source-to-tabletop distance?

A

Should be <38 cm or 15”

Absolutely not <30 cm or 12”

Fluoro Cram (8 decks)

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