Introduction to Positron Emission Tomography - Waisman ...

Introduction toPositron Emission Tomographywith your host, Terry OakesPositronAnnihilationγ #1 γ #2180 o

Positron AnnihilationpositronemittingatomneighboringatomPositron range:1-10 mmγ #1 γ #2positronannihilationGamma-Ray range:10 mm -8180 o

Positron Emission Tomographydetectorringdetector #2γ #2detector #1γ #1

Positron Emission Tomographydetector #2γ #2detector #1γ #1

Positron Emission Tomography

Positron Emission Tomography

Positron Emission Tomography

P.E.T. measures Concentration of Radioactivity1) Gamma-rays escape from body:External detection possible.2) Two gamma rays emittedoat 180 when a positronannihilates:The annihilation occuredsomewhere betweenthe two detectors.3) Regions with greaterradioactivity levelsproduce more LORs:Concentration of radioactivitycan be measured and quantified.

P.E.T. yields Quantitative results.( µCi/cc tissue )Corrections must be applied to raw data:1) Dead-time, Random events2) Calibration3) Normalization4) Scatter-correction5) Attenuation correction6) Reconstruction

Corrections to Sinogramscolor scaleraw sinogram(20 cm cylinder)trim(remove edges)Scatter-CorrectNormalized,without Scatter-CorrectionNormalizemash(combine angular views)

Effect of Corrections on ImagesScattercorrectedNormalizedXXXXXXAttenuationcorrectedXXXUniform20 cm cylindercolor scale

CalibrationConverting“counts/pixel”to“microCi / cc tissue”detectorringMeasure response ofthe PET scanner to aknown concentrationof radioactivity.knownradioactivityconcentrationObtainCalibration Factorapplicable for all scans.( CF ~ (µCi/cc)/counts )

Normalizationdetectorring

NormalizationIndividual detectors responddifferently to the same levelof radioactivity.Normalization produces auniform response to thesame level of radioactivity.

Gamma-ray attenuation proportional to:1) density of object2) pathlength through objectAttenuation CorrectionAttenuation can be corrected with adensity-weighted map of the object.gamma-rayattenuatedrotatingradioactiveline-sourceAttenuation causes a non-uniform loss of events;more gamma rays passing through the middle of the object are lost.

Scatter CorrectionScattered gamma rays causerecorded events to be mispositioned.Scatter tends to increase the concentrationmeasured toward the center of the object.gamma-rayscatterednumber of eventsscatteredeventsunscattered(true) eventsradial bin

PET Data Acquistionraw sinogramRadioactive sourcein PET scanner

P.E.T. data are acquired as discrete Lines of Response (LORs)radial binsradial binsradial binsAngular View #1(theta = 0)Angular View #2(theta = 45)Angular View #3(theta = 90)

Three Angular ViewsAngular View #1(theta = 0)Angular View #2(theta = 45)Angular View #3(theta = 90)

Sinogram#1Angular View #1(theta = 0)#2angular views#3Angular View #2(theta = 45)radial binsAngular View #3(theta = 90)

Image Reconstructionit’s magic!raw sinogramReconstructed Image