X-ray beam restrictors

3 factors that determine the quantity of scattered radiation produced within the patient
kilovoltage (kVp_

part thikness

x-ray field size
how to decrease scattered radiation production within the patient
lower kVp

decrease part thickness

decrease x-ray field size
lower kVp
patient radiation dose increases exponentially as lower kVp techniques are substituted
decrease part thickness
not easily done

recumbent radiography

compression bands
recumbent radiography
less crays get through better
decrease x-ray field size
most effective at small x-ray field sizes

could hide necessary diagnostic information
x-ray beam restrictor
device attached to the opening of the x-ray tube housing to regulate the size and shape of the x-ray beam
types of beam restricting devices
aperture diaphragms

cones & cylinders

light beam collimator
why beam restriction decreases scattered radiation to the film
decrease x-ray field size which increases the angle of escape for scattered radiation
as angle of escape increases the angle of capture (to hit the film)
gets smaller and scattered photon is less likely to strike the smaller image
average scatter photon deflects about

only few x-ray photons are able to strike/fog the image
which type of x-ray beam restricting devices are in common usage today
light beam collimators (majority)

extension cylinders (for spot views)
an x-ray system not equipped with a collimator is
difficult to use and should be avoided
why does x-ray beam restriction reduce the amount of scattered radiation on film
increases the angle of escape for scatterred radiation
advantages of a light beam collimator
infinite variety of x-ray field sizes

light beam to accurately position the central ray (CR)

back-up calibrated knobs to use when the collimator light bulb burns out
when film is loaded into Bucky tray (positive beam limiting devices)
sensors in the tray detect the size and position of the film then signal motors in the collimator to position the shutters accordingly
positive beam limiting devices (PBL) must be accurate to within
2% of the FFD being used
positive beam limiting devices (PBL) properly exposed film shows
evidence of collimation on three sides
effectively reduces scatter fog only with (collimator special considerations)
small x-ray fields

to see significant improvement in film quality, x-ray field sizes must be restricted as much as diagnostically possible
beam restriction decreases (collimator special considerations)
film density
decrease film density
small x-ray fields produces less scatter fog causing less optical density (OD) or underexposed film
to maintain constant film density (collimator special considerations)
an increase in mAs is necesssary
increase collimation causes
decrease scatter fog which decreases OD requiring more mAs
when shooting a tightly-collimated spot film, you need to increase the
mAs 50 to 100% or it will be underexposed
backscatter is produced when
x-ray beam penetrates the patient, bucky & strikes the metal cassette tray & tray cabinet
backscatter scatters
backwards towards patient to fog film
what helps to control backscatter and primary beam leak
extrafocal radiation test checks for
presence of excessive extrafocal radiation
entrance shutters at the top of good collimators remove up to (extrafocal radiation)
90% of the extrafocal radiation in the x-ray beam

noticeably improving image sharpness and resolution
x-ray/light beam alignment test
how well the collimator light beam lines up with the x-ray beam

should be performed annually
2 reasons for restricting (collimating) beam size
decreased scattered radiation results in increased image resolution (quality)

decreased ionizing radiation dose to the patient
early radiographers restricted the x-ray beam to
improve image quality
what are the reasons to collimate your films properly
increase image quality and decrease radiation dose