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Nuclear Medicine: Planar Imaging and the Gamma Camera. Katrina Cockburn Nuclear Medicine Physicist. Methods of Analysis. Once tracer has traced – need some method of analysing distribution. Imaging Gamma Camera, PET Camera. Compartmental Analysis Sample Counter. Radiation Detectors. - PowerPoint PPT Presentation
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Nuclear Medicine: Nuclear Medicine: Planar Imaging and the Planar Imaging and the
Gamma CameraGamma CameraKatrina CockburnKatrina Cockburn
Nuclear Medicine PhysicistNuclear Medicine Physicist
Methods of AnalysisMethods of Analysis
Once tracer has traced – need some Once tracer has traced – need some method of analysing distributionmethod of analysing distribution
Imaging Imaging Gamma Camera, Gamma Camera,
PET CameraPET Camera
Compartmental Compartmental AnalysisAnalysis
Sample CounterSample Counter
Radiation DetectorsRadiation Detectors
Converts incident photon into electronic Converts incident photon into electronic signalsignal
Most commonly used detectors are Most commonly used detectors are scintillationscintillation Photon interacts with crystal to convert Photon interacts with crystal to convert
incident photon into light photonsincident photon into light photons PMT changes light into electrical signalPMT changes light into electrical signal Electrical signal recorded and analysedElectrical signal recorded and analysed
Imaging Equipment Imaging Equipment
The Gamma CameraThe Gamma Camera Basic principle hasn’t Basic principle hasn’t
changed since 1956!changed since 1956!
Scintillation ImagingScintillation Imaging
Administration of IsotopeAdministration of Isotope
Scintillation ImagingScintillation Imaging
Localisation and UptakeLocalisation and Uptake
Scintillation ImagingScintillation Imaging
Localisation and UptakeLocalisation and Uptake
Scintillation ImagingScintillation Imaging
Localisation and UptakeLocalisation and Uptake
Scintillation ImagingScintillation Imaging
Localisation and UptakeLocalisation and Uptake
Scintillation ImagingScintillation Imaging
Localisation and UptakeLocalisation and Uptake
Scintillation ImagingScintillation Imaging
Localisation and UptakeLocalisation and Uptake
Scintillation ImagingScintillation Imaging
Localisation and UptakeLocalisation and Uptake
Enhanced contrast Enhanced contrast between Organ of between Organ of Interest and rest of Interest and rest of bodybody
Scintillation ImagingScintillation Imaging
Imaging distributionImaging distributionGamma-rays emitted by Gamma-rays emitted by radiopharmaceuticalradiopharmaceutical
Collimator ‘selects’ only Collimator ‘selects’ only those rays travelling at those rays travelling at right angles to face of right angles to face of cameracamera
Scintillation events in Scintillation events in crystal recorded crystal recorded
Early Scintillation StudyEarly Scintillation Study
Components of a Modern Gamma Components of a Modern Gamma CameraCamera
The components of a modern gamma The components of a modern gamma cameracamera Lead ShieldLead Shield
CollimatorCollimator
LightguideLightguide
PMTsPMTs
ElectronicsElectronics
CrystalCrystal
The CollimatorThe Collimator The collimator consists of:The collimator consists of:
a lead platea lead plate array of holesarray of holes
It selects the direction of It selects the direction of the photons incident on the photons incident on the crystalthe crystal
It defines the geometrical field of view of the It defines the geometrical field of view of the cameracamera
The CollimatorThe Collimator
In the In the absenceabsence of collimation: of collimation: no positional relationship between source – destination no positional relationship between source – destination
In the In the presencepresence of collimation: of collimation: all all γ-γ-rays are excluded except for those travelling rays are excluded except for those travelling
parallel to the holes axis – true image formationparallel to the holes axis – true image formation
Patient Patient
Detector Detector
Types of CollimatorsTypes of Collimators
Several types Several types of collimator:of collimator: Parallel-Hole Parallel-Hole Converging Converging DivergingDiverging Pin-HolePin-Hole
Energy Ranges of CollimatorsEnergy Ranges of Collimators
Type of Type of CollimatorCollimator
Energy Energy RangeRange
Typical Typical NuclideNuclide
Low Energy Low Energy (LE)(LE)
0 - 200 keV0 - 200 keV Tc-99mTc-99mTl-201Tl-201
Medium Medium Energy (ME)Energy (ME)
200 - 300 keV200 - 300 keV In-111In-111
High Energy High Energy (HE)(HE)
300 – 400 keV300 – 400 keV I-131I-131
The Scintillation CrystalThe Scintillation Crystal
First step of image First step of image formationformation
Photon Photon detected by its detected by its interaction in the interaction in the crystalcrystal
γ-γ-rays converted into rays converted into scintillationsscintillations
ScintillationScintillation Can be thought of as Can be thought of as
“partial ionisation”“partial ionisation” Electrons excited and Electrons excited and
gain energygain energy As electrons fall As electrons fall
back to ground back to ground state, photons state, photons emittedemitted
Use of doping (eg Use of doping (eg NaI:Tl) creates NaI:Tl) creates smaller gapssmaller gaps
Scintillation Crystal PropertiesScintillation Crystal Properties
High stopping efficiency Stopping should be without scatter High conversion of γ-ray energy into visible light Wavelength of light should match response of
PMTs Crystal should be transparent to emitted light Crystal should be mechanically robust Thickness of scintillator should be short
Properties of NaI(Tl) ScintillatorProperties of NaI(Tl) Scintillator The crystal – NaI(Tl)
emits light at 415 nm high attenuation
coefficient intrinsic efficiency:
90% at 140 keV conversion efficiency:
10-15% energy resolution:
15-20 keV at 150 keV
Disadvantages of NaI(Tl) crystalDisadvantages of NaI(Tl) crystal
NaI(Tl) crystal suffers from the NaI(Tl) crystal suffers from the following drawbacksfollowing drawbacks:: Expensive (~£50,000 +)Expensive (~£50,000 +) FragileFragile
sensitive against mechanical stresses sensitive against mechanical stresses sensitive against temperature changessensitive against temperature changes
Hygroscopic Hygroscopic encapsulated in aluminium caseencapsulated in aluminium case
Lightguide and Optical CouplingLightguide and Optical Coupling Lightguide acts as optical coupler Lightguide acts as optical coupler Quartz doped plexiglass (transparent Quartz doped plexiglass (transparent
plastic)plastic) The lightguide should:The lightguide should:
be as thin as possiblebe as thin as possible match the refractive index of the scintillation crystalmatch the refractive index of the scintillation crystal
Silicone grease to couple lightguide, crystal Silicone grease to couple lightguide, crystal and PMTand PMT
No air bubbles trapped in the greaseNo air bubbles trapped in the grease
The Photomultiplier TubeThe Photomultiplier Tube
A PMT is an evacuated A PMT is an evacuated glass envelopeglass envelope
It consists of:It consists of: a photocathodea photocathode an anodean anode ~ 10 dynodes~ 10 dynodes
The Photomultiplier TubeThe Photomultiplier Tube Photocathode of PMT emits 1 Photocathode of PMT emits 1
photoelectron per ~ 5 – 10 photonsphotoelectron per ~ 5 – 10 photons PhotoelectronPhotoelectron accelerated towards first accelerated towards first
dynodedynode Dynode emits 3 – 4 secondary eDynode emits 3 – 4 secondary e-- per per
photoelectronphotoelectron Secondary eSecondary e-- accelerated towards next accelerated towards next
dynodedynode Multiplication factor ~ 10Multiplication factor ~ 1066
Output of each PMT proportional to the Output of each PMT proportional to the number of light photonsnumber of light photons
PMT PropertiesPMT Properties The photocathode The photocathode
shouldshould be matched to blue lightbe matched to blue light have high quantum have high quantum
efficiencyefficiency High stability voltage High stability voltage
supply: ~1kVsupply: ~1kV
Positional and Energy Co-ordinatesPositional and Energy Co-ordinates PMT signals processedPMT signals processed
spatial spatial informationinformation – – X and Y signalsX and Y signals energy information – Z signalenergy information – Z signal
Z signal – the sum of the outputs of all PMTsZ signal – the sum of the outputs of all PMTs proportional to the total light output of the crystalproportional to the total light output of the crystal Light output proportional to the energy of incident gamma Light output proportional to the energy of incident gamma
Pulse height analyser accepts or rejects the pulsePulse height analyser accepts or rejects the pulse
Pulse Height AnalysisPulse Height Analysis Z-signal goes to PHAZ-signal goes to PHA PHA checks the energy of the PHA checks the energy of the γγ-ray-ray If Z-signal acceptableIf Z-signal acceptable
γ-γ-ray is detectedray is detected position position
determined by determined by X and Y signalsX and Y signals
20% window still20% window stillincludes 30% ofincludes 30% ofscattered photonsscattered photons
Determining the Position of EventsDetermining the Position of Events
Image Acquisition TechniquesImage Acquisition Techniques
StaticStatic -- (Bones, Lungs)(Bones, Lungs) DynamicDynamic -- (Renography)(Renography) GatedGated -- (Cardiac)(Cardiac) TomographyTomography
SPECTSPECT PETPET
List ModeList Mode -- (Cardiac)(Cardiac)
Static ImagingStatic Imaging
Camera FOV divided into regular matrix of pixelsCamera FOV divided into regular matrix of pixels Each pixel stores number of gamma rays Each pixel stores number of gamma rays
detected at corresponding location on detectordetected at corresponding location on detector Typical Matrix Sizes: 256Typical Matrix Sizes: 25622, 128, 12822, 64, 6422
Camera Computer Memory
Image Display
1
Static ImagingStatic Imaging
Camera FOV divided into regular matrix of pixelsCamera FOV divided into regular matrix of pixels Each pixel stores number of gamma rays Each pixel stores number of gamma rays
detected at corresponding location on detectordetected at corresponding location on detector Typical Matrix Sizes: 256Typical Matrix Sizes: 25622, 128, 12822, 64, 6422
Camera Computer Memory
Image Display
1
1
Static ImagingStatic Imaging
Camera FOV divided into regular matrix of pixelsCamera FOV divided into regular matrix of pixels Each pixel stores number of gamma rays Each pixel stores number of gamma rays
detected at corresponding location on detectordetected at corresponding location on detector Typical Matrix Sizes: 256Typical Matrix Sizes: 25622, 128, 12822, 64, 6422
Camera Computer Memory
Image Display
1
1
1
Static ImagingStatic Imaging
Camera FOV divided into regular matrix of pixelsCamera FOV divided into regular matrix of pixels Each pixel stores number of gamma rays Each pixel stores number of gamma rays
detected at corresponding location on detectordetected at corresponding location on detector Typical Matrix Sizes: 256Typical Matrix Sizes: 25622, 128, 12822, 64, 6422
Camera Computer Memory
Image Display
1
1
1
1
Static ImagingStatic Imaging
Camera FOV divided into regular matrix of pixelsCamera FOV divided into regular matrix of pixels Each pixel stores number of gamma rays Each pixel stores number of gamma rays
detected at corresponding location on detectordetected at corresponding location on detector Typical Matrix Sizes: 256Typical Matrix Sizes: 25622, 128, 12822, 64, 6422
Camera Computer Memory
Image Display
2
1
1
1
Static ImagingStatic Imaging
Camera FOV divided into regular matrix of pixelsCamera FOV divided into regular matrix of pixels Each pixel stores number of gamma rays Each pixel stores number of gamma rays
detected at corresponding location on detectordetected at corresponding location on detector Typical Matrix Sizes: 256Typical Matrix Sizes: 25622, 128, 12822, 64, 6422
Camera Computer Memory
Image Display
2
1
1
11
Static ImagingStatic Imaging
Camera FOV divided into regular matrix of pixelsCamera FOV divided into regular matrix of pixels Each pixel stores number of gamma rays Each pixel stores number of gamma rays
detected at corresponding location on detectordetected at corresponding location on detector Typical Matrix Sizes: 256Typical Matrix Sizes: 25622, 128, 12822, 64, 6422
Camera Computer Memory
Image Display
3
1
1
11
Static ImagingStatic Imaging
Camera FOV divided into regular matrix of pixelsCamera FOV divided into regular matrix of pixels Each pixel stores number of gamma rays Each pixel stores number of gamma rays
detected at corresponding location on detectordetected at corresponding location on detector Typical Matrix Sizes: 256Typical Matrix Sizes: 25622, 128, 12822, 64, 6422
Camera Computer Memory
Image Display
3
1
1
11
Dynamic ImagingDynamic Imaging
Series of sequential Series of sequential static framesstatic frames E.g. 90 frames each E.g. 90 frames each
of 20s durationof 20s duration Image rapidly Image rapidly
changing distribution changing distribution of activity within the of activity within the patientpatient
Used in RenographyUsed in Renography
Dynamic Imaging AnalysisDynamic Imaging Analysis
ROIsCurves showing changing renal activity over time
Split Renal Function
Gated ImagingGated Imaging
Several frames Several frames acquired covering the acquired covering the cardiac cyclecardiac cycle
Acquired over many Acquired over many cyclescycles