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Radiation Protection > chapter 11 > Flashcards

chapter 11 Flashcards

1
Q

radiation generated in the x-ray tube that does not exit form the collimator opening but rather penetrates the protective tube house and to some degree the sides of the collimator

A

leakage radiation

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2
Q

radiation that emerges directly from the x-ray tube collimator and moves without deflection toward a wall, door, viewing window and so on. also called direct radiation or useful beam

A

primary beam

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3
Q

Tube housing is constructed so that leakage radiation measured at a distance of 1m from the x-ray source does no exceed _____ when the tube is operated at its highest voltage at the highest current that allows continuous

A

1mGya/hr (100mR/hr)

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4
Q

2 other functions of the tube housing

A
  1. confines the high voltage entering the tube to prevent electric shock
  2. makes cooling of the x-ray tube possible
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5
Q

what is the radiographic table made of

A

carbon fiber material

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6
Q

For the SID the distance and centering indicators must be accurate within what percent of the SID respectively

A

2% and 1%

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7
Q

collimation is accomplishes primarily through the use of what?

A

light localized, variable aperture collimator

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8
Q

what are other types of collimators

A

aperature diaphragms and cones and cylinders

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9
Q

what does the 2 sets of collimators do?

A

1st set- reduces the amount of off focus radiation

2nd set- consists of 2 pairs that can be adjusted independently

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10
Q

to minimize skin exposure to electrons produced by photon interaction with the collimator, the patients skin surface should be how far below the collimator

A

15cm

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11
Q

what do some collimators have to prevent collimators from being closer than 15 cm to the patient

A

spacer bars

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12
Q

what is luminance

A

refers to the brightness and quantifies the intensity of the light source

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13
Q

what is luminance measured in

A

nit or candela per square meter

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14
Q

the x-ray beam and the light beam must coincide within ___% of the SID

A

2%

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15
Q

consists of electronic sensors that sends signals to collimator housing. when activated collimators are automatically adjusted to radiation field matches the size of the IR

A

Positive beam limitation (PBL)

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16
Q

State regulatory standards require accuracy of __% of the SID with PBL.

A

2%, some states may require an accuracy of only 35

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17
Q

simplest of all beam limits devices, consists of a flat piece of lead with a hole of designated size and shape that is attached to the x-ray tube head

A

aperture diaphragm

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18
Q

what is the purpose of filtration

A

reduces exposure to patients skin and superficial tissue by absorbing most of the lower energy photons (long wave) from the heterogeneous beam, it increases the mean energy, or quality of the x-ray beam, hardening of the beam

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19
Q

the absorbed dose of the patient ____ when the correct amount of types of filtration are placed in the path of the radiographic beam

A

decrease, it absorbs some of the photons and decreased the quantity of incident radiation. the remaining photons in the beam as a whole, are more likely to be absorbed in body tissue

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20
Q

Two types of filtration

A

inherent filtration and added filtration

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21
Q

what are the parts of the inherent filtration

A

glass envelope, insulating oil, and glass window

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22
Q

what glass window inherent material amounts to ___ of aluminum equivalent

A

0.5mm Al

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23
Q

What can they use to added filtration

A

sheets of aluminum (or equivalent) of appropriate thickness.

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24
Q

the regulatory standard for total filtration of ____ is required for fixed units operating above 70kVp

A

2.5mm Al Eq

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25
Q

what determines the amount of filtration required

A

kVp

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26
Q

stationary fixed radiographic equipment operating at 50-70kVp require a total filtration of?

A

1.5mm Al Eq

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27
Q

stationary fixed radiographic equipment operating below 50 kVp requires a total filtration of?

A

0.5mm Al Eq

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28
Q

mobile diagnostic units and fluoro equipment require a minimum of?

A

2.5mm Al Eq

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29
Q

what are the commonly used filters in mammo

A

molybdenum and rhodium

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30
Q

when the x-ray target is made of molybdenum each following filters may be used?

A

0.3 mm molybdenum filter and 0.025mm rhodium filter

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31
Q

when the x-ray target is made of rhodium what filter may be used

A

0.025mm rhodium filter

32
Q

what is the most widely selected material as a filter

A

Aluminum (Z=13)

33
Q

what is efficient in removing low energy x-ray through the photoelectric effect, it is readily available, inexpensive and easily shaped

A

aluminum

34
Q

As filtration is increased so is beam quality and quantity is ___

A

decreased

35
Q

what must be measured to verify adequate filtration

A

half value layer (HVL)

36
Q

the thickness of a designated absorbed necessary to reduce an x-ray beam to half its original value

A

half value layer

37
Q

when and who checks the HVL

A

physicist at least once and year or when x-ray tube has been replaces or repairs have been made on housing collimating system

38
Q

what is the best method for specifying x-ray quality or effective energy of the x-ray beam

A

half value layer

39
Q

HVL is measure in what

A

mm of aluminum

40
Q

devices that partially attenuate x-rays directed toward a thinner or less dense, area while permitting more x-rays to strike the thicker, or denser area

A

compensating filters

41
Q

compensating filter are made out of

A

aluminum, lead acrylic or other suitable materials

42
Q

do compensating filters increase or decrease dose?

A

decrease by reducing repeat exposure

43
Q

as consistency in output radiation intensity for identical generator settings from one individual exposure to subsequent exposures

A

reproducibility

44
Q

sequential radiation exposures should be within ___%?

A

+/- 5 %

45
Q

included in the code of diagnostic x-ray equipment, it is the ability of radiographic unit to produce a constant radiation output for various combinations of mA and exposure time

A

exposure linearity

46
Q

exposure linearity must be within ___% for adjacent mA

A

10%

47
Q

what do intensifying screens do

A

convert x-ray energy into visible light to produce radiographic density on the film

48
Q

what film speed are standard for general radiography

A

400 speed systems

49
Q

film screen combinations range from

A

200-1200

50
Q

as kV increased, effective screen speed____.

A

increases

51
Q

why do they use carbon fiber as a material for front of cassette

A

less dose, carbon fiber absorbs about half as much radiation as previously used cassette materials

52
Q

as grid ratio increased, patient dose___

A

increases

53
Q

the ratio of the height of lead strips in the grid to the distance between them. High ratio grids reduce scatter more effectively than do low ratio grids. however, high ratio grids require more radiation exposure

A

grid ratio

54
Q

A source skin distance (SSD) of at least ___ must be used in mobile radiography for patient safety

A

30cm (12 inches)

55
Q

for CR And DR it is still customary to used a grid for anatomy measuring over___ for techniques that exceed 70 kVp

A

10 cm

56
Q

Dr systems have the following advantages over both CR and conventional SFS..

A

lower dose
ease of use
immediate imaging results
manipulation of the image

57
Q

benefits of image intensification fluoro include

A
  1. increased image brightness
  2. saving of time of the radiologist
  3. patient dose reduction
58
Q

product of dose and volume of tissue irradiated

A

integral dose

59
Q

the source to skin distance must not be less than ___ for stationary fixes fluoroscopes

A

38cm (15 in)

60
Q

SSD for mobile fluoroscopes?

A

12 inches

61
Q

fluoroscopic technical factors for children necessitate a decrease in kVp by as much as __%

A

25%

62
Q

patient dose decreases by how much during fluoro procedures when aluminum filtration increased from 1-3mm of aluminum

A

one fourth

63
Q

in standard image intensification fluoroscopy, an x-ray beam HVL of what is considered acceptable when kVp ranges from 80-100

A

3-4.5mm aluminum

64
Q

current federal standards limit entrance exposure rates of general purpose intensified fluoroscopic units to a maximum ___ mGya per min

A

100mGy or 10R/min

65
Q

entrance exposure rates for fluoroscopy equipment equipped with high level control may produce a skin entrance exposure rates as high as ____ per minute

A

200 mGya per min (20R/min)

66
Q

a primary protective barrier of __mm of lead equivalent is required for fluoroscopic units

A

2mm

67
Q

a spacer or collimator is usually installed to prevent any part of the patient from coming closer than __ to the tube target

A

30cm

68
Q

Cine or movie camera uses how big of film to recoded the image from the output phosphor

A

16-35mm

69
Q

what is the most common cine size used and why

A

35mm and because image quality is better

70
Q

which procedure can have that highest patient dose ?

A

cine procedures

71
Q

what are the cine cameras have film frame rates.

A

7.5, 15, 30, 60

72
Q

switching from 23cm to a 15cm FOV and 30-60 frames per second can do what to the tabletop exposure rate

A

approx. doubles the tabletop exposure rate, if both are doubles the exposure rate goes up by factor of 4

73
Q

Factors that play a role in determining dose levels

A
  • image intensification input phosphor exposure level set by vendor
  • grid factor
  • SSD
74
Q

Collimating (increases or decreases) the integral dose while (increases or decreases) image quality

A

decreases, increases

75
Q

In 1994, the FDA limited the tabletop exposure rate of fluoroscopic equipment to ___ mGy/min unless HLC mode was present, in which case routine fluoro was limited to ___ mGy.min when the system was not in HLC mode and unlimited when it was in HLC mode

A

100mGy

50mGy

76
Q

FDA has recommended a notation be placed in patients record if a skin dose of ___Gy is received

A

1-2 Gy

Radiation Protection (1 decks)

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