Radiation Protection CHapter 11 Flashcards Preview

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Flashcards in Radiation Protection CHapter 11 Deck (45):

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

light-localizing variable aperture rectangular collimator


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

first set shutters


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

second set shutters


What does the second set of shutters consist of?

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


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



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

positive beam limitation (PBL)


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)

aperture diaphragm


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



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

inherent filtration


What is the aluminum equivalent for inherent filtration?

0.5 mm


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

added filtration


where is added filtration located?

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


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

total filtration


Total Filtration regulatory standards

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


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)

half-value layer


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



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

last-image hold


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

cumulative timer


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?

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


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

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


know the material that the radiographic table is commonly made of

a carbon fiber material


what is the most common x-ray beam limitation device

light-localizing variable aperture rectangular collimator


know the types of x-ray beam limitation devices

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


know what these devices join to do

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


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

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


know what happens to the collimator when PBL is activated?

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


know how the radiographer ensures that the collimation is adequate

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


what dimensions of the hole in the aperture diaphragm determine

the size and shape of the radiographic beam


know some examples of radiographic exams that would use cones

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


know how filtration decreases the overall intensity of radiation

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


how much filtration the light localizing variable aperture rectangular collimator adds

1.5 mm aluminum equivalent


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

aluminum (z-13)


why is this metal used

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


what is the source skin distance in general radiology



what does DR mostly eliminate the need for

repeats due to improper technique


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

to determine and use technical factors the first time you expose


know the 3 benefits of image intensification fluoroscopy

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


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

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


what is the required and preferred SSD for fluoroscopy

required= minimum 12"
preferred= 15"


know the function of a filter in fluoroscopy

reduce patient dose


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

2.5 mm


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

10 roentgens/per minute


what is the primary protective layer required for an image intensifier

2mm lead equivalent


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

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


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