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