Radiation Protection CHapter 11 Flashcards

1
Q

Box shaped and contains the radiographic beam defining system. this system consist of 2 sets of adjustable lead shutters mounted within the device at different levels, a light source to illuminate the x-ray field, and permit it to be centered over the area of clinical interest and a mirror to deflect the light beam toward the patient to be radiographed

A

light-localizing variable aperture rectangular collimator

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2
Q

Upper shutters–mounted as close as possible to the tube window to reduce the amount of off-focus radiation (x-rays emitted from parts of the tube other than the focal spot) coming from the primary beam and exiting at various angles from the x-ray tube window

A

first set shutters

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3
Q

Lower Shutters– mounted below the level of the light source and mirror and function to confine further the radiographic beam to the area of clinical interest

A

second set shutters

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4
Q

What does the second set of shutters consist of?

A

two pairs of lead plates oriented at right angles to each other

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5
Q

Refers to the brightness of a surface– specifically it quantifies the intensity of a light source-must be adequate to permit the localizing light beam to outline the margins of the radiographic beam adequately on the patients anatomy

A

luminance

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6
Q

consist of electronic sensors in a cassette holder that sends signals to the collimator housing

A

positive beam limitation (PBL)

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7
Q

simplest of all limitation devices- consist of a flat piece of lead with a hold of designated size and shape cut in the center (can be rectangular, square, or round)

A

aperture diaphragm

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8
Q

To reduce exposure to the patients skin and superficial tissue by absorbing most of the lower energy photons

A

filtration

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9
Q

Includes the glass envelope encasing the x-ray tube, the insulating oil surrounding the tube, and the glass window in the tube housing

A

inherent filtration

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10
Q

What is the aluminum equivalent for inherent filtration?

A

0.5 mm

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11
Q

Consists of sheets of aluminum (or equivalent) of appropriate thickness

A

added filtration

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12
Q

where is added filtration located?

A

outside the glass window of the tube housing above the collimator shutters

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13
Q

the combination of inherent and added filtration (these combine to equal required amount necessary to filter useful beam adequately)

A

total filtration

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14
Q

Total Filtration regulatory standards

A

2.5 mm aluminum equivalent for fixed x-ray units operating above 70 kVp

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15
Q

when the thickness of a designated absorber (such as aluminum) is required to decrease the intensity of the primary beam by 50% of its initial value (laws regulate that so much of the low energy rays must be removed)

A

half-value layer

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16
Q

due to the fact that computerized images can be manipulated after exposure and repeat images are rare, patients receive higher radiation doses than necessary to produce the initial images

A

dose-creep

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17
Q

process that allows the fluoroscopist to see the most recent image without exposing the patient to another pulse of radiation

A

last-image hold

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18
Q

resettable device that times the x-ray beams “on time” and sounds an audible alarm or temporarily interrupts the exposure after the fluoroscope has been activated for 5 minutes

A

cumulative timer

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19
Q

The x-ray tube housing that encloses the x-ray tube must be constructed so that leakage radiation does not reach the patient. At what distance is this measured from the x-ray source and at what dose?

A

1m (3.3 ft) does not exceed 100 mR/hr when the tube is operated at its highest voltage at the highest current that allows continuous radiation

20
Q

why the x-ray tabletop must be as radiolucent as possible?

A

so that it will absorb only minimal amounts of radiation, thereby reducing the patients radiation dose (because of lower techniques)

21
Q

know the material that the radiographic table is commonly made of

A

a carbon fiber material

22
Q

what is the most common x-ray beam limitation device

A

light-localizing variable aperture rectangular collimator

23
Q

know the types of x-ray beam limitation devices

A

light localizing variable aperture rectangular collimator, aperture diaphragm, cones, cylinders

24
Q

know what these devices join to do

A

confine the useful, or primary beam. before it enters the area of clinical interest, thereby limiting the quantity of body tissue radiated

25
Q

why does the luminance of the collimator light have to be adequate?

A

to permit the localizing light beam to outline the margins of the radiographic beam adequately on the patients anatomy

26
Q

know what happens to the collimator when PBL is activated?

A

the collimators are automatically adjusted so that the radiation field matches the size of the IR

27
Q

know how the radiographer ensures that the collimation is adequate

A

by collimating the radiographic beam so that it is no larger than the IR

28
Q

what dimensions of the hole in the aperture diaphragm determine

A

the size and shape of the radiographic beam

29
Q

know some examples of radiographic exams that would use cones

A

head projections, sella turcica, paranasal sinuses, vertebral column, and chest

30
Q

know how filtration decreases the overall intensity of radiation

A

effectively removes low-energy (soft) x-rays from a polyenergetic x-ray beam without severely decreasing the xray beam intensity

31
Q

how much filtration the light localizing variable aperture rectangular collimator adds

A

1.5 mm aluminum equivalent

32
Q

what is the most commonly used metal for filters in diagnostic radiology

A

aluminum (z-13)

33
Q

why is this metal used

A

(light weight, sturdy, relatively in expensive, and is readily available)

34
Q

what is the source skin distance in general radiology

A

12”

35
Q

what does DR mostly eliminate the need for

A

repeats due to improper technique

36
Q

even with digital radiography, what is still your responsibility as a radiographer

A

to determine and use technical factors the first time you expose

37
Q

know the 3 benefits of image intensification fluoroscopy

A
  1. increased image brightness
  2. saving the radiologist time
  3. patient dose reduction
38
Q

what is the significant impact that pulsed or intermittent fluoroscopy has made

A

significantly decreases patient dose, especially in long procedures and helps extend the life of the tube

39
Q

what is the required and preferred SSD for fluoroscopy

A
required= minimum 12"
preferred= 15"
40
Q

know the function of a filter in fluoroscopy

A

reduce patient dose

41
Q

in fluoroscopy what is the total aluminum equivalent filtration that must be permanently installed?

A

2.5 mm

42
Q

what are the maximum current federal standards that limit entrance skin exposure rates of general purpose intensified fluoroscopic units

A

10 roentgens/per minute

43
Q

what is the primary protective layer required for an image intensifier

A

2mm lead equivalent

44
Q

know how to reduce patient entrance dose for c-arm procedures

A

the patient to image intensifier distance should be as short as possible

45
Q

know whos responsibility it is to monitor and document fluoroscopic procedure times

A

radiographer