chapter 11 EXAM 5 Flashcards by Payton Gould

safety requirements are required for:

tube housing 
xray control panel 
radiographic exam table
source to image distance indicator 
other devices and accessories

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xray tube housing requirements

lead lined metal tube housing to protect patient and tech from leakage, scatter and off focus radiation

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leakage radiation

radiation that does not exit form the collimator opening but penetrates the protective tube housing and the sides of the collimator

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primary beam (direct radiation, useful beam)

radiation that emerges directly from the xray tube and moves without deflection toward a wall, door, etc

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the tube housing is constructed so that leakage radiation measured at a distance of what from the xray source does not exceed what when the tube is at it’s highest mAs/Kv

1m from the xray source does not exceed 1 mGya/hr

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the tube housing also does what

it confines high voltage to prevent electric shock

makes cooling of xray tube possible

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control panel/console requirements

must indicate the conditions of exposure and indicate when xray tube is energized
usually satisfied with use of kVp and mAs

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radiographic exam table requirements

must be strong and support the pt.

thickness must be uniform and radiolucent to absorb only a minimal amount of radiation

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what is the xray table typically made of

carbon fiber material

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source to image receptor distance indicator requirements

can be a tape measure or a laser

distance and centering indicators

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distance and centering indicators must be accurate to within what of the SID

within 2% and 1% of the SID

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t or f

under no circumstances should the xray beam exceed the size of the image receptor

true

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collimation is accomplished primarily through the use of

a light localized, variable aperture collimator

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other types of collimators include

aperture diaphragms

cones and cylinders

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all collimation devices reduce what and improve what

scattered radiation and improves image quality

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light localizing variable aperture rectangular collimators have 2 sets of adjustable lead shutters they do what

reduces the amount of off focus radiaiton

2. consists of 2 pairs that can be adjusted independently

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light localizing variable aperture rectangular collimators have

a light source and a mirror

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skin sparing :
to minimize skin exposure to electrons produced by photon interaction with the collimator, the patient’s skin surface should be at least

15 cm below the collimator

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space bars

some collimators contain space bars to prevent collimators from being closer than 15 cm to the pt.

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what is luminance

the brightness and quantifies the intensity of a light source

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brightness is measured in

nit or candela per square meter

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a reading of 15 foot candles corresponds to a collimator light source with a lumincance of about

161 nit or 161 candela per square meter

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the xray beam and the light beam must coincide to within what of the SID

within 2% of the SID

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Positive Beam Limitation PBL

ensures that the radiographic beam is no larger than the IR

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PBL was required on all xray systems in the US between the years of

1974 and 1994 | not required anymore

state regulartoy standards require accuracy of

2% of the SID with PBL | some state may require only 3%

aperture diaphragm

simplest of all beam limiting devices | rectangular shape is most common and can be used in many systems

cones and cylinders

modifications of the aperture diaphragm restricts the useful beam to the required size reduce scatter and improve contrast resolution

t or f | sharper size restriction is achieved when the cone or cylinder is longer

true

filtration (also called hardening of the xray beam)

reduces exposure to patient's skin and superfical tissue by absorbing most of the lower energy photons increases the quality of the beam

2 types of filtration

1. inherent filtration | 2. added filtration

examples of inherent filtration

glass envelope insulating oil glass window

the inherent filtration material amounts to about what aluminum equivalent

0.5mm aluminum equivalent

the collimator provides an additional inherent filtration of what aluminum equivalent

0.1mm aluminum equivalent

added filtration

sheets of aluminum or the equivalent that are added to the tube

the inherent filtration and added filtration combine to equal

the required amount necessary to filter the useful beam

does the kVp of an xray unit determine the amount of filtration required?

yes

the regulatory standard for total filtration of 2.5 mm Aluminum equivalent is required for fixed xray unit operating above

70 kVp

because each xray tube and collimator has a total inherent filtration of 1.5mm aluminum equivalent, the manufacturer place and additional

1mm Al Eq filter between the tube housing and collimator to meet the minimum regulatory requirement

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

1.5 mm Al Eq

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

0.5mm Al Eq

mobile diagnostic units and fluoroscopic equipment requre a minimum filtration of

2.5 mm Al Eq

what are commonly used as filters in mammography

molybdenum and rhodium filters

when the xray target is made of molybdenum each of the following filters may be used

a 0.3mm molybdenum filter | a 0.025 mm rhodium filter

when the xray target is made of rhodium what filter can be used

a 0.025 mm rhodium filter

as filtration is increased, so is what | but what is decreased

the beam quality increases but quantity is decreased

Half value layer HVL

the thickness of a designated absorber necessary to reduce an xray beam to half of its original intensity

for diagnostic beams the HVL is expressed in

millimeters of aluminum

HVL is the best method for

specifying xray quality or effective energy of the xray beam

compensating filters

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

2 kinds of compensating filters

1. wedge | 2. trough

exposure reproducibility

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

sequential radiation exposures should be reproducible within

+ or - 5%

exposure linearity

the ability of a radiographic unit to produce a constant radiation output for various combos of mA and time

exposure linearity must be within what for adjacent mA stations

10%

intensifying screens are made up of

predominantly rare earth screens

intensifying screens

convert xray energy into visible light to produce radiographic density on the film significantly reduces exposure time enhances film exposure process

effect of faster screen film systems on patient dose: | when the speed of screen film systems doubles the radiation exposure is reduced by

50%

as kV increases, effective screen speed

increases | increased kv with less mAs

rare earth intensifying screens absorb about how much more energy than their predecessors

radiographic grids

remove scattered radiation before reaching the IR and improves contrast and visibility of detail

when are grids used

when the pt. body part exceeds 10cm

grids always increase what but improve what

increase patient dose | improves quality of recorded image

an increase in what exposure factor is required with the use of a grid

increased mAs

as grid ratio increases, patient dose

increases

grid ratio

the ratio of the height of the lead strips in the grid to the distance between them

t or f high ratio grids reduce scatter more effectively than low ratio grids, however, high ratio grids require more radiation exposure increasing patient dose

true

a source to skin distance of at least what must be used in mobile radiography for patient safety

30cm

when the source to skin distance is short, the patient's entrance exposure is

significantly greater than the exit exposure

decrease in SID increases the

source to skin dose

the sensitivity of the phosphor used in CR is about equal to a what speed screen film combination

200 speed screen film combination

kv controls

radiographic contrast

what are the advantages that DR systems have over both CR and conventional screen film systems

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

what is a disadvantage to DR systems

they don't allow the user to change the grid or have a preinstalled grid that is not easily accessible to the user

fluoroscopic systems inculde

xray tube image intensifier c arm

what are the 3 advantages of image intensification

1. increased image brightness 2. saving of time for the radiologist 3. patient dose reduction

image intensification requires less milliamperage than old fashioned fluoro. how much mA with image intensification is used

1.5-2 mA is used in image intensification | 3-5 mA was used before

in fluoro the increase in magnification results in a decrease in

image clarity and the resulting image is dimmer

intermittent of pulsed fluoro significantly decreases

patient dose, especially in long procedures

integral dose

product of dose and volume of tissue irradiated

the source to skin distance for stationary fluoro must not be less than and for mobile fluoroscopes

``` 38 cm 30 cm (mobile) ```

fluoroscopic technical factors for children need a decrease in kVp by as much as

25%

a minimum of how much filtration must be permanently installed in the path of the useful beam of the fluoroscopic unit

2.5 mm Al Eq

with image intensification a total of how much filtration should be used

a total of 3 mm Al Eq or greater is preferred

patient dose decreases by how much during fluoro procedures when aluminum filtration increase from 1 to 3 mm of Al

dose decreases by 1/4th

when kVp ranges from 80-100 in standard image intensification fluoroscopy, an xray beam HVL of how much is considered acceptable

3-4.5

cumulative timing device

a resettable device that times the dray beam on time that will sound an audible alarm or temporarily interrupt the exposure after it has been activated for 5 mins

current federal standards limit entrance exposure rates of general purpose intensified fluoroscopic units to a max of

100 mGya per minute

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

200 mGya per minute

high level fluoro is used in what procedures

interventional procedures

a primary protective barrier of how much is required for a fluoroscopic unit

a primary protective barrier of 2mm lead equivalent

t or f the exposure control switch/foot pedal on fluoro units must be the dead-man type AKA only continuous pressure applied by the operator will keep it activated

true

t or f | image intensifier distance should be as short as possible to reduce patient entrance dose

true

t or f | cine procedures can result in the highest patient dose of all diagnostic procedures

true

in cine procedures, when film rates are high so is

patient dose

when a smaller viewing mode or a lower speed cine film is used, patient exposure

increases

pulse progressive systems

xray beam is turned off while image is being scanned, decreasing dose and pulsed back on for the next image.

High level control fluoro HLCF

an operating mode in which exposure rates are substantially higher than those normally allowed in routine procedures

the higher exposure rate of the HLCF allows

visualization of smaller and lower contrast objects that don't usually appear during routine fluoro

in 1994 the FDA limited tabletop exposure rate of fluoroscopic equipment to what? unless HLC mode was present in which case routine fluoro was limited to what when the system was not in HLC mode and what when it was in HLC mode

100 mGya/min 50 mGya/min unlimited

FDA has recommended a notation be placed in the patient's record if a skin dose in the range of what is received the location of the area of the pts. skin should also be recorded

a dose of 1-2 Gyt

since 2000, alarmed state regulatory agencies have imposed a restricition on high level radiation exposure rates with the image intensifier at a distance of 30 cm above the tabletop, the max continous fluoro entrance exposure rate for HLCF is

200 mGya / min