Radiation Protection CHapter 11 Flashcards
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
luminance
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
filtration
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
dose-creep
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
12”
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
- increased image brightness
- saving the radiologist time
- 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
radiographer
