Instrumentation; newer info

alkathryn's version from 2016-04-11 23:03


Question Answer
Matrix: More pixels, better ___Resolution and images, more definition
Larger matrix size,Smaller pixels
Larger the matrix,More counts
Large matrixbetter resolution
Short image timesmaller matrix
More photons you have to make up an image,better it will look
Dynamic key points:less counts, less time, smaller matrix, FLOW
Larger matrix key points:more pixels, better resolution, takes longer, more counts
SPECT imaging proceduresCardiac, bone, brain, octreoscan, abdominal
SPECT done with Parallell collimators and LEGP
SPECT movesAround the patient
Dual head camera cuts imaging timeIn Half
SPECT creates a ____ image3 dimensional
128x128 makes _____ stops.128
Longer you image, more chance...Patient will move
SPECT opposite ofPlanar
PlanarImage in one plane, 2D image of a 3D object
Most NM images arePlanar
All cameras capable ofplanar imaging.
SPECT slicesTransaxial, Coronal, Sagittal
Flood performedDaily
Bars performedAt least once per week
BARS assessesResolution (Spatial) and Linearity (image without distortion)
Jaszczak SPECT Phantom assessesResolution and Uniformity
Flood performed on days whenused on patient
Per NRC, BARS is doneat least once per week.
BARS assesseslinearity & resolution
All cameras aredigital
Cobalt source new5-25 mCi
Cobalt source cost$2-4,000
How long does cobalt source last2-3 years
Cobalt source goes on collimator fortotal system (extrinsic) uniformity
Cobalt source also calledcookie tray
How many counts does cobalt source count2000-5000 K counts
Finer matrix needsmore counts
IntrinsicNO collimator; see in
Technetium source iswater filled
Downfalls of tech sourcemore exposure, heavy, less convenient
Benefits of tech sourcecheaper, more accurate
Ways to crack the crystalmechanical shock during collimator change & thermal shock - crystal temp changes more than 10*/hour
Non-uniformity Artifact from Collimator damageCrushed lead septa & lead foil separation
Non-uniformity artifact from cracked/broken crystalmechanical or thermal shock
Non-uniformity from PMT drift
PMT voltage drift causespeak shift and differences in sensitivity and non-uniformity of blotchy nature showing a pmt pattern
Uniformity is best for ____ isotopes, such assingle energy. tech, cobalt, iodines
Intrinsic usesa point source
Point course is0.5 mCi of Tech-99m
Intrinsic is notconvenient- take collimator off, possibly damage crystal--is cheaper
BARS usesCo with collimator, Tc without collimator
Intrinsic done at a distance>5 useful FOV - size of crystal in greatest dimension
BARS identifiessmallest visible bar pattern
Lower gamma ray energy has lessspatial resolution
Detaildistinguishing objects by their size, spatial resolution
Detailspatial resolution
Contrastdistinguishing objects by their differences in count density
Contrastseeing objects over one another
Air gap10 cm
Uniformity practiceflood images of 5-15 million counts each day of use, before imaging begins
Spatial Resolution practicefour-quadarnt bar phantom images 5-10 million counts once per week
Linearity practicesame as spatial resolution
Uniformity extrinsic floodwith installed collimator
Uniformity intrinsic floodtest isotopes of Tc & others, collimator off
Spatial resolution extrinsicwith collimator
Spatial resolution intrinsicto test isotopes of Tc & others, collimator off
COR done only onSPECT system
COR confirmsthat camera goes around the circle (verifies circular orbit)
COR variesby camera
COR uses apoint source
COR performedweekly, typically--determined by manufacturer
If bullseyes/ring artifactuniformity calibration needs to be redone
Energy peakingdaily
Uniformity donedaily
Resolution doneweekly
Linearity doneweekly
SPECT phantom donequarterly by technologist
COR validation doneweekly by technologist
COR calibrationas needed by physicist
Gamma camera QC done bytechnologist
Uniformity correction matrix bytech/physicist
GM meter is not ___ but is very ____efficient, sensitive
Ionization chambers are not very ___ finding small amounts of radiationsensitive
Ionization chamber measuresdirect energy from ionizations
GM region photons maypass through without ionizing/being detected
GM Region Vlots of ion pairs, allows detection of very small amounts of radiation, due to gas amplification
Cardiac SPECT systems cut scan down to3 minutes
2D PETcollimator, more precise
3D PETno septa (lots more counts)
FOV term in PETBed position
PET is very ___sensitive
What makes PET more sensitiveNo Collimator and many crystals
Sinogram displayof the lines of response
Sinogram israw data from which we make our pictures
Sinogram used tocreate the image for daily QC
Why NaI isn't efficient for PETlow density, not efficient for 511 keV photons
Types of PET crystalsLutetium Oxyorthosilicate (LSO), Gadolinium (GSO), Bismuth Germanate (BGO)
PET crystals have betterstopping power, energy resolution
PET is ____ more sensitive than gamma camera>50 times
PET detectors are more acceptable to loss of events becausethey rely on 2 events
Lose 1 photon, loseboth. event
PET collimation occurs byAnnihilation reaction, coincidence timing window, tungsten or lead septa (2D)
PET tungsten limitsthe planes on which photons can strike the crystal
TruesGOOD counts
Trues are180 degrees, within timing window, from same annihilation
Typically _____ trues in a whole body image40-60 million
Randoms2 photons within the timing window not from same annihilation event
How to reduce randomscoincidence timing window is adjusted
Adjust coincidence timing windowreduce randoms
Narrow timing windowreduces randoms
Scatterfrom same annihilation event, strike within coincidence timing window, not at 180 degrees
Scatter due totissue attenuation
Scatterdegrades image quality
To reduce scattertungsten or lead septa, NARROW photopeak
Narrow photopeak reducesscatter
Small window reducesscatter
PET QCenergy and linearity, normalization, blank scan, singles, coincidence timing, dose calibrator
PET normalization performedquarterly
Blank scan AKAair scan
Blank scan donedaily
Blank scan used forattenuation correction
Blank scan similar todaily uniformity floods
Singles donedaily or weekly
Singles togain adjustment. compare adjacent detector
Singles ensureuniform sensitivity response from individual detector
Coincidence timing window (randoms)adjust timing delays so events from all detector blocks are timed equivalently
Coincidence timing window typically6-12 nanoseconds
Dose calibrator AKAAbsolute Activity Calibration
Absolute activity calibration done usinga calibration phantom
Absolute activity Recalibration recommendedat least quarterly
Absolute activity calibration allowsROI info to be converted from counts/voxel into absolute activity--required for SUV conversion
SUV requires accuratepatient weight, injected activity and decay correction w/n 5 minutes, calibration of PET scanner
SUV ____ over timeincreases
FDG patients must be scanned with+/- 10 minutes time window
SUV is underestimated in small lesions smaller thandiameter < 3 * 6mm
Benefits of updated QCartifact free images, improved interpretation, impact on reconstruction, improved uptime

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