Collimators Flashcards
(88 cards)
FOV
total area accepting gamma from area
umbra
area of FOV which the entire crystal has an unobstructed view
penumbra
area of FOV which is visible to only part of the crystal
radius of resolution
radius between the penumbral limits
FOV = ____ + _____
FOV = umbra + penumbra
single aperture collimator
collimator with one hole
typical range for the number of holes a collimator has
4,000 to 46,000
(L)
length of collimator/lead hole
(r)
radius of the hole at the crystal surface
N
number of holes in the collimator
transmission/sensitivity
- area of the crystal not obstructed by lead septa of collimator
- fraction of incident radioactivity transmitted through the collimator
septum
thickness of lead between the hole
angle of acceptance
even wider than penumbral limits due to septal penetration
what affects resolution and sensitivity?
radius and number of of the holes, length of holes
septal thickness, and distance between source and collimator
what improves resolution?
- increasing length of the hole
- decreasing the radius or width of hole (which in turn increases number of holes)
- decreasing distance between source and collimator
hole length for a high resolution collimator
increased hole length
hole length for LEGP or LEAP collimator
medium length hole
hole length for high sensitivity collimator
decreased hole length
what photon energy is used for a high energy collimator?
300 keV
as energy increases, the ____ decreases because _____ increases.
number of holes decrease due to the fact that septum needs to increase
where is spatial resolution best?
at the surface of the collimator
(resolution/sensitivity) is independent of the distance in multi-hole parallel hole collimators.
sensitivity
explain image size in terms of distance.
image size is independent of distance
but scatter makes it appear slightly larger
slant hole collimators
parallel, cylindrical holes at a 15-30 degree slant