beam restrictors

2 reasons beam restrictors are used

limit patient dose and improve contrast

list 2 factors that contribute to the production of scatter

increased field size and increased kVp

list 2 things a technologist can do to limit/reduce patient dose

collimate, use a higher kVp so the mAs is lowered

list 2 types of beam restrictors that are not commonly used today

aperture diaphragm and cones/cylinders

what is the primary purpose of a beam limiting device

to reduce patient dose

a material made of a high atomic number will absorb _____ scatter than a material with a low atomic number

some

how should technical factors be adjusted when cones or cylinders are used?

increase mAs by 25-50%

scatter with never create ____

diagnostic information

field size should never exceed what

size of the IR

equipment that automatically collimates to the size of the IR is called

automatic collimator

if the collimator mirror is 5’ from the focal spot, how far must it be from the light source to create an accurate field of view?

5”

list a drawback to using an aperture diaphragm close to the tube source

increased penumbra

the collimator mirror must be placed at a _____ angle to produce an accurate field light

45 degree

what device, other than collimators can be used with a large body part to improve image contrast?

lead blocker

blurring at the edge of an image caused by diverging beam striking the edge of the beam restrictor is called

penumbra

define off focus radiation

radiation created within tube, but not at the actual focal spot

what artifact does off-focus radiation produce

ghosting

what components of the collimator helps prevent off-focus radiation from reaching the image receptor

1st and 2nd shutters

explain the impact of coning down on image quality

reduce patient dose/increase contrast

is it ever appropriate for the FOV to be larger than the image receptor

no

define positive beam limiting device

most common, useful beam restrictor, most effective @ producing sharp image edges

under what circumstance is it appropriate to “override” the PBLD

making the FOV smaller than IR

penumbra can be reduced by placing a beam limiting device

farther from the x-ray source

what is the danger in over-collimation

double patient exposurre

central ray alignment must be within ____ of SID

1%

light field congruence must be within _____ of SID

2%

collimator mirror filtration = _____ aluminum

1 mm

a filter that improves image quality by reducing scatter, but does not reduce patient dose:

lead blocker

which beam restrictor is the most efficient

collimator