Patient Exposure and Protection Flashcards
Beam limitation
Protects the patient by limiting the area of the body and the volume of tissue being irradiated; removes long wavelength rays
Collimator
Contains two sets of lead shutters; variable aperture device
Higher set of lead shutters on collimator
Placed near the tube window to absorb off-steam (off-focus radiation)
Lower set of lead shutters on collimator
Placed near the bottom of the collimator box to restrict the beam further as it exits
Positive beam limitation (PBL)
Automatic collimation - does not allow you to widen the lightfield
Three types of beam limitations
Collimator, Cylinder cones, and Aperture diaphragm (flat piece of lead with a circle or square opening in the middle)
Two types of filtration
inherent & added
Total filtration must equal ___ mm of aluminum for x-ray tubes operating at greater than 70 kvp
2.5 mm of Aluminum
Example of inherent filtration
Oil around tube & the glass envelope of the x-ray tube
Example of added filtration
aluminum sheets placed in the path of the beam neat the x-ray window, mirror placed in the collimator head
Exposure techniques should use an _____ kVp for the part being imaged and the ____ mAs to reduce the amount of radiation striking the patient.
Exposure techniques should use an OPTIMAL kVp for the part being imaged and the LOWEST mAs to reduce the amount of radiation striking the patient.
Purpose of Grid
To remove scatter radiation from the exit beam
Problem with using a grid?
Higher dose to patient due to the increase of mAs needed
Minimum SID for a portable
12 inches
Minimal SID for fluoroscopy
15 inches
