Maximum range for a positron emitted from F-18
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2.2 mm
spect data collection modes
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step-and-shoot -- detectors stop rotating during image acquisition
Continuous -- detectors move continuously
diverging collimator
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many holes aimed at a focal point behind the scintillation camera; amount
of minification increases as object moved away from camera; lung study
spect contrast agents
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Ga-67 -- emits photons, attached to ligands to bind with tissues
Tc-99m -- most common
Tl-201
Image subtraction
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, each pixel count in one image subtracted from corresponding pixel count
in the other
negative numbers set to 0
resultant = change in activity occurring in pt during time interval between
acquisitions of two images
scatter coincidence
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when one or both photons from single annihilation are scattered but both
detected
can be true coincidence because both interactions result from single
positron annihilation, but misplaced
source of noise reducing image contrast
alignment of projection images to axis of rotation spect
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radioactive line source placed on AOR, each projection image depicts
vertical straight line near center of image
misalignment = point source is doughnut artifact, loss of spatial resolution
rate of random coincidences between any pair of detectors
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Rrandom = 2tS1*S2
t = coincidence time window
S1 and S2 = actual count rates of detectors (singles rates)
spect technique
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inject a photon emitting radioisotope into the bloodstream; most effective
= radioisotope that has chemical properties that allows the isotope to
concentrate in areas of interest
Goal of multimodality imaging
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improve target delineation and allow functional definition of tumors
How final image is weighed in patient based on depth in PET
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if torso has diameter D, split into two portions a and b, probability of
detection (both photons escaping patient) is PD = e^(-ua)*e^(-ub) = e^-
u(a+b) = e^-uD
Give this one a try later!
2.2 mm
spect data collection modes
,Give this one a try later!
step-and-shoot -- detectors stop rotating during image acquisition
Continuous -- detectors move continuously
diverging collimator
Give this one a try later!
many holes aimed at a focal point behind the scintillation camera; amount
of minification increases as object moved away from camera; lung study
spect contrast agents
Give this one a try later!
Ga-67 -- emits photons, attached to ligands to bind with tissues
Tc-99m -- most common
Tl-201
Image subtraction
Give this one a try later!
, each pixel count in one image subtracted from corresponding pixel count
in the other
negative numbers set to 0
resultant = change in activity occurring in pt during time interval between
acquisitions of two images
scatter coincidence
Give this one a try later!
when one or both photons from single annihilation are scattered but both
detected
can be true coincidence because both interactions result from single
positron annihilation, but misplaced
source of noise reducing image contrast
alignment of projection images to axis of rotation spect
Give this one a try later!
radioactive line source placed on AOR, each projection image depicts
vertical straight line near center of image
misalignment = point source is doughnut artifact, loss of spatial resolution
rate of random coincidences between any pair of detectors
, Give this one a try later!
Rrandom = 2tS1*S2
t = coincidence time window
S1 and S2 = actual count rates of detectors (singles rates)
spect technique
Give this one a try later!
inject a photon emitting radioisotope into the bloodstream; most effective
= radioisotope that has chemical properties that allows the isotope to
concentrate in areas of interest
Goal of multimodality imaging
Give this one a try later!
improve target delineation and allow functional definition of tumors
How final image is weighed in patient based on depth in PET
Give this one a try later!
if torso has diameter D, split into two portions a and b, probability of
detection (both photons escaping patient) is PD = e^(-ua)*e^(-ub) = e^-
u(a+b) = e^-uD
