beam restriction Flashcards
what is the purpose of beam restriction
patient safety (smaller field size irradiates less, tfr lower dose)
how does beam restriction help image quality
less tissue means less scatter
higher subject contrast
higher image quality
who is Dr William rollins
the father of radiation protection
when was the aperture diaphragm first used
around 1899
what came after the diaphragm
cones and cylinders
how did cones and cylinders help
further reduced the beam from being longer
what was a drawback of using cones and cylinders
made circular x-rays only on a rectangular plate
how does the variable aperture collimator we use today restrict the beam
2-3 sets of lead shutters
what does the first shutter set do
reduces off-focus radiation
what does the second shutter set do
allow field size/shape collimation
at what angle is the mirror
45
what distance does the bulb have to be from the mirror
the same distance as the focal spot is from the mirror
what happens when the build is too close to the mirror
light beam > x-ray beam
what happens when the bulb is too far from the mirror
light beam < x-ray beam
how do you check the accuracy
with a 9 penny test
