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The Applications of PhotodetectorsThe Applications of Photodetectorsin (Bio)Medical Imagingin (Bio)Medical Imaging
Roger Lecomte, Ph.D.Roger Lecomte, Ph.D.
Centre Centre dd’’ImagerieImagerieMMéétaboliquetabolique & & FonctionnelleFonctionnelle
4th International Conference onNew Developments in Photodetection
Palais des Congrès - Beaune, France June 19-24, 2005
4th International Conference onNew Developments in Photodetection
Palais des Congrès - Beaune, France June 19-24, 2005
OUTLINEOUTLINE•• Historical overview & applicationsHistorical overview & applications
•• γγ--camera & SPECT / camera & SPECT / µµSPECTSPECT•• PET / PET / µµPETPET
•• Small animal PETSmall animal PET•• Very high resolutionVery high resolution•• DepthDepth--ofof--interaction (DOI)interaction (DOI)
•• MultiMulti--modality imagingmodality imaging
Historical OverviewHistorical Overview
~1950: (Cassen et al.)
Rectilinear scannerLarge PMT + NaI(Tl) + Collimator
1953: (Brownell & Sweet, Nucleonics 11:40-45, 1953)
First clinical positron imaging deviceTwo coincident NaI(Tl)-PMT detectors2-D scanning motion
http://http://www.mit.edu/~glb/alb.htmlwww.mit.edu/~glb/alb.htmlR. Nutt, Mol. R. Nutt, Mol. ImagImag. Biol. 4:11. Biol. 4:11--26, 200226, 2002
ORGAN WITH ORGAN WITH RADIOACTIVITYRADIOACTIVITY
COLLIMATORCOLLIMATOR
Late 1950’s:Anger camera or γ-cameraPMT array (19) + single large NaI (Tl)Position decoding by light sharingSpatial resolution:
Intrinsic: ~10 → 3-4 mm FWHMSystem: 10-15 mm FWHM
Summing Matrix Circuits (SMC) combine signals from PMTs such that:
Amplitude ∝ Distance from center
X = k(X+ - X-)/ZX = k(X+ - X-)/ZZ = total light signal = X+ + X- + Y+ + Y-
γγ--CameraCamera
γγ--CameraCamera TodayToday
Workhorse of nuclear medicine
http://www.is2research.com/
Improvements:Large imaging area (up to 91 PMTs)Square & rectangular imaging FOVVariety of configurations for specific needsDigital signal processing → improved ∆E & ∆xMultiple heads Rotating gantry for tomography (SPECT)
99mTc Sestamibi64 × 64 matrix 48 45-sec steps Gated 8 frames/R-R HRGP Collimator (250 cpm/µCi)
512 x 512HRLE Collimator (190 cpm/µCi)
Bone scan Cardiac SPECT imaging
Facultéde génie
( ) 22
⎟⎠⎞
⎜⎝⎛+⎟
⎠
⎞⎜⎝
⎛ +≅
abR
ad ba
R ie
Pinhole SPECT
a : pinhole – detector distanceb : pinhole – object distancede : effective pinhole diameterRi : intrinsic detector resolutionM : magnification = b/a
DetectorDetectorareaarea
PinholePinhole
bbaa
RotatedRotatedobjectobject
Magnification improves resolutionNo physical limit of resolution !!Sensitivity drops as resolution improvesLong measuring timeLimited FOVDistorted image, prone to artifacts
Spatial resolution in pinhole SPECT
Biological imaging with γ-camera:Fixed γ-camera, rotating subjectSystem spatial resolution: 1-1.5 mm FWHM Low sensitivity: << 0.1%Long measuring time: >> 30 min
Habraken et al, J Nucl Med 42:1863–9, 2001
Pinhole SPECT with Standard Pinhole SPECT with Standard γγ--CameraCamera
75 gold micro-pinhole, 0.6 mm diamFixed γ-camera & subject, rotating pinholeSystem spatial resolution: 0.5 mm FWHM
0.1 µlIncreased effective FOVImproved sensitivity: 0.22%Reduced measuring time: ~ 30 min
Beekman et al, 2004 IEEE NSS/MIC, Rome, October 2004
Cylinder containing 75 gold pinhole apertures focused on the center of the cylinder.
U-SPECT-I based on a triple detector SPECT system
Cardiac perfusion study in a mouse, showing the right and left myocardium along the three main axes (6 mCi 99mTc-tetrofosmin, acquired in 30 min at 30 min post injection).(SNM Animal co-Image of the Year 2004)
Papillary muscle
MultiMulti--Pinhole SPECTPinhole SPECT
Single Crystal Single Crystal vsvs PixelsPixelsSingle Crystal DetectorSingle Crystal Detector
120 mm diam × 6 mm thick NaI(Tl) plate5” PS-PMTSignificant “barrel” distortion & non-linearityGood uniformityEdges difficult to recoverFair spatial resolution ~ 4 mm
PixelatedPixelated DetectorDetector2 × 2 × 3 mm3 CsI(Tl) array, 120 mm diam5” PS-PMTReduced distortionBetter linearityPoor uniformityArtefacts due to readoutBetter spatial resolution ~ 3.5 mm
⇒⇒ Most imperfections can be removed by Most imperfections can be removed by signal/image correction algorithmssignal/image correction algorithms
Jeong et al, NSS/MIC 2003, M6-59
Pharmaceutical: [99mTc]-MDPDose: ~1 mCiPinhole: 1 mm pinholeImaging distance (pinhole-center): 3.5 cmViews/Rotation: 128/360 degreesAcquisition time: 30 seconds/view or ~1 hour
PS-PMT + Array of 2×2×6 mm3 NaI(Tl) 125×125 mm2 imaging FOVSquare 1 to 3 mm pinholeSystem spatial resolution: 1-2 mm FWHM
1-8 µlSensitivity: 0.001-0.01%
McElroy et al, IEEE Trans Nucl Sci 49:2139–47, 2002http://www.gammamedica.com/products/a_spect/spect.html
Dedicated Pinhole Dedicated Pinhole µµSPECTSPECT
Thin, light detection headDiscrete CsI(Tl)-SiPD detectorsIndividual readout with lowlow-noise electronicsSpatial resolution:
Intrinsic: 3.1 mm (~crystal size)Photodiodes
(4,096)
Array of Array of CsI(TlCsI(Tl) + ) + SiSi pp--ii--nn PDPD
System response comparison:System response comparison:Point Spread FunctionPoint Spread Function
http://www.digirad.com
Solid State Solid State γγ--CameraCamera
1973-74: PETT II hexagonal array, 24 NaI(Tl) detectors,Ter-Pogossian et al., Washington University, St.Louis.
Positron Imaging DevicesPositron Imaging Devices
1973: First circular ring PET scanner, 32 NaI(Tl) detectors. Built at BNL, transferred to Montreal Neurological Institute in the mid 70's.
1977-78: Positome IIFirst BGO PET scanner 64 BGO detectorsC.J. Thompson,MontrealNeurological Institute.
1978: PETT III / Ortec ECAT II, first commercial PET scanner96 NaI(Tl) detectors → 9.5 mm FWHM
1977-81: LBL Donner 280 crystal PET scanner8 mm NaI(Tl) / 9.5 mm BGO → ~8 mm FWHM
1986: LBL Donner 600 crystal brain PET scanner, 3 mm BGO → 2.6 mm FWHM
3 mm
10 mm
Limits of PMT Individual CouplingLimits of PMT Individual Coupling
• Single ring
• Non-symmetric crystals → non-isotropic resolution
• Poor light collection due to sub-optimal coupling
• Large nb of electronic channels
14 mmØPMT
Derenzo et al, IEEE Trans Nucl Sci 34:321-5, 1987
AngerAnger CameraCamera
☺ Inexpensive☺ Isotropic spatial resolution
→ ~5 mm FWHM
☺ High energy resolution→ Efficient scatter rejection
Poor stopping powerLimited count rate / high dead time
⇒ Excellent spatial resolution possible by reducing crystal thickness at the expense of sensitivity (Green et al)
⇒ Count rate performance can be improved by: − Local triggering− Slotted surface / Detector granularity− Faster scintillator
Large continuous NaI(Tl) barsC-PET Module
Adam et al, J Nucl Med 42:1821-30, 2001
Anger Camera with Discrete DetectorsAnger Camera with Discrete Detectors
• Discrete GSO 4 × (4-6) × 10 mm3
- same efficiency as 19 mm NaI- photofraction ~2 × NaI
→ 4 times faster, but 1/5 light output of NaI
• 5 mm slots in light-guide- limit light dispersion- improve positioning - reduce pile-up at high rate
• Local triggering on 7 PMTs
• Resolution 3-3.5 mm FWHM- ~ linear positioning / distortions
First proposed by Burnham et al, IEEE TNS 35:675-9, 1988 Surti & Karp, J Nucl Med 45: 1040-9, 2004
Allegro
Light Sharing: Block DetectorLight Sharing: Block Detector
• Array of (semi)discrete detectors measured by 4 square PMTs
• Event positioning from light distribution probability map
• Crystal identification by look-up table
• Resolution loss due to: - photon statistics- non-linear positioning & distortion- pile-up at high rate
EXACT HR Block
Casey & Nutt, IEEE TNS 33:460-3, 1986 HR+
• Block measured by 4 std round PMTs→ reduced cost
• Thin reflector paint interface→ better packing fraction→ more uniform signal (better ∆E)
• One half PMT lost on edges • Adopted by CTI for HRRT (high
resolution brain scanner)
Quadrant Quadrant SharingSharing Wong et al, IEEE TNS40:962-6, 1993
Light Sharing: Block Detector ConceptLight Sharing: Block Detector Concept
Clinical PET ImagingClinical PET Imaging
Courtesy University of Ottawa Heart Institute
18FDG
82Rb
~ 70 kg human ~ 70 kg human →→ ~ 6~ 6--10 mm 10 mm ~ 1 cc~ 1 cc
Extent of breast cancer with multiples metastases(Whole-body FDG-PET scan,
CTI/Siemens EXACT HR+)
F. Bénard, UdeS
~ 300 g rat~ 300 g rat →→ ~ ~ 2 mm ( 2 mm ( ×× 5 )5 )~10 ~10 µµl ( l ( ×× 100 )100 )
Individual Coupling & Independent Processing Lecomte et al, IEEE TNS 43:1952-7, 1996Sherbrooke APD PET scanner
APD Detector Module
BGOScintillator
3×5×20 mm3
AvalanchePhotodiode
Resolution 1.75 mm (intrinsic)2.1 × 2.1 × 3.1 mm3 or 14 µl
Efficiency 200 cps/µCi ( 0.51% )Sensitivity 2 kcps/µCi/ml/cmPeak NEC 61 kcps (11 cm∅)
Individual Readout & Charge SharingLSO / MC-PMT
UCLA microPET Cherry et al, IEEE TNS 44:1161-6, 1997
LSO2×2×10 mm3
8×8 array
MC-PMT24 mmlong F.O.
Positioning histogram
Resolution 1.85 mm (intrinsic)1.9 × 1.9 × 1.9 mm3 or 6.6 µl
Efficiency 208 cps/µCi ( 0.54% )Sensitivity 2 kcps/µCi/ml/cmPeak NEC 18 kcps
• Individual optical coupling• Electronic position decoding from
charge distribution on PMT anode • Light loss in F.O. → ∆E~25%• Loss of intrinsic spatial resolution
due to charge sharing
Normal
Infarct
1 cm
É. Croteau, UdeS
Rat PET ImagingRat PET Imaging
Whole-body PET Scan 18F- + 18FDG, 250 g rat (Sherbrooke APD PET Scanner)
J. Cadorette, UdeS
~ 300 g rat~ 300 g rat →→ ~ ~ 2 mm ( 2 mm ( ×× 5 )5 )~10 ~10 µµl ( l ( ×× 100 )100 )
~ 30 g mouse~ 30 g mouse →→ ~ ~ 1 mm ( 1 mm ( ×× 2 2 !! ))~ 1 ~ 1 µµl ( l ( ×× 10 10 !! ))
??
Spatial Resolution in PET*
≈0.7 mm
Geometric Coding
Intrinsic
Non-colinearity
Positronrange
( ) ( ) 0022.0 2 2222 rDbdaFWHM +++=
Physical limit
TomographicReconstruction
1.2<a<1.3
* Derenzo & Moses, “Critical instrumentation issues for resolution <2mm, high sensitivity brain PET”, in Quantification of Brain Function, Tracer Kinetics & Image Analysis in Brain PET, ed. Uemura et al, Elsevier, 1993, pp. 25-40.
For 1 mmFor 1 mm :
b ~ 0d ~ 1.2 mm
b ≠ 0d < 1.2 mm
D=15 cm~0.4 mm
18F~0.6 mm
≈0.7 mm
0
1
2
3
0 1 2 3 4 5Crystal Size (mm)
FWH
M R
esol
utio
n (m
m)
Light Sharing (b~2.1 mm)Electronic Coding (b~1.1 mm)
Individual Coupling (b~0 mm)
Crystal Resolution (d/2)
A-PET (Philips)
APD-BGO(Sherbrooke)
Tomitani
Donner 600(Berkeley)
SHR-2000 (Hamamatsu)
Exact HR(CTI)
Hammersmith RatPET(UCLA)
MADPET(Munich)
HIDAC
BaF2/TMAE(VUB)
microPET II
Ge eXplore (Suinsa)
SHR-7700 (Hamamatsu)
HRRT(CTI)
TierPET (Julich)
microPET (UCLA)YAPPET (Ferrara)
ATLAS (NIH)
LabPETFocus
ClearPET
IntrinsicIntrinsic Spatial Resolution of PET ScannersSpatial Resolution of PET Scanners
Light Channeling & Charge SharingLight Channeling & Charge SharingClearPETClearPET
2 2 ×× 22 ×× 8 mm8 mm3 3 LuAPLuAP/LYSO/LYSO Crystals Crystals 8 8 ×× 8 array on R76008 array on R7600--M64 8 M64 8 ×× 8 MC8 MC--PMTPMTLight channeling with maskLight channeling with mask
FWHM = 1.60 mm FWHM = 1.60 mm →→ Intrinsic FWHM ~ 1.5 mm Intrinsic FWHM ~ 1.5 mm ((b ~ 0.8 mm)
Mosset et al, IEEE NSS/MIC 2004
b ~ 0.8 mm)
1.56 1.56 mmmm
MCMC--PMTPMT Light maskLight mask Crystal array in Crystal array in TyvekTyvek matrixmatrix
PhoswichPhoswich crystal crystal assembly for Depth assembly for Depth Of Interaction (DOI) Of Interaction (DOI) measurementmeasurement
Coarse Light SharingCoarse Light Sharing
APDAPD--LSO Block LSO Block DetectorDetector Casey, Lecomte et al, IEEE MIC 1998
0
2000
4000
6000
0 100 200
•• MonolithicMonolithic 2 2 ×× 2 APD 2 APD arrayarray ofof 4.5 4.5 ×× 4.5 mm4.5 mm22
pixels (pixels (PerkinElmerPerkinElmer))
•• 4 4 ×× 4 LSO 4 LSO arrayarray (8.5 (8.5 ××8.5 8.5 ×× 10 mm10 mm33 block)block)
•• 1.91.9 ×× 1.91.9 ×× 1010 mmmm33 LSO LSO elementselements
•• 0.3 mm slots 0.3 mm slots packedpackedwithwith TeflonTeflon powderpowder
•• CodingCoding resolutionresolution of of 4% or 4% or b ~ 0.3 mmb ~ 0.3 mm
→→ IntrinsicIntrinsic FWHM ~ 1.2 mmFWHM ~ 1.2 mm
~4%~4%
Coarse Light SharingCoarse Light Sharing
•• 2 2 ×× 2 APD array of 5 2 APD array of 5 ×× 5 mm5 mm22 pixels pixels (S8664(S8664--55, 55, HamamatsuHamamatsu))
•• 9 9 ×× 9 LSO array on 2 9 LSO array on 2 ×× 2 APD array2 APD array
•• 22 ×× 22 ×× 2020 mmmm33 LSO elementsLSO elements
•• Crystals wrapped in proprietary Crystals wrapped in proprietary reflectorreflector
•• No spatial resolution data, but all No spatial resolution data, but all crystals resolved in positioning crystals resolved in positioning histogramhistogram
•• ~21% average energy resolution~21% average energy resolution
•• 2.47 ns average coincidence timing 2.47 ns average coincidence timing resolutionresolution
APDAPD--LSO Block LSO Block DetectorDetector Grazioso et al, IEEE MIC 2004
Positioning histogramPositioning histogram
Light Sharing with Dual ReadoutLight Sharing with Dual ReadoutPSPS--APD ModuleAPD Module
1.65 1.65 ×× 1.651.65 ×× 22 mm22 mm3 3 MLSMLS crystals crystals 8 8 ×× 8 array on dual 14 8 array on dual 14 ×× 1414 mmmm22 PSPS--APDsAPDsNo data on resolution but clear identification of each crystal No data on resolution but clear identification of each crystal Significant Significant ““pincushionpincushion”” distortion
Burr et al, IEEE NSS/MIC 2003
distortion
Significant Significant ““pincushionpincushion”” distortiondistortion
Coded Light SharingCoded Light Sharing
Miyaoka et al, IEEE MIC 2000MiCEMiCE Detectors (Detectors (Micro Crystal ElementMicro Crystal Element))
0.80.8 ×× 0.80.8 ×× 6 mm6 mm3 3 MLSMLS Crystals Crystals 5 5 ×× 5 array on 4 channels of 645 array on 4 channels of 64--channel MCchannel MC--PMTPMTb ~ 0.4 mm b ~ 0.4 mm →→ Intrinsic FWHM ~ 0.7 mm !Intrinsic FWHM ~ 0.7 mm !
~0.4 mm
Positioning histogramPositioning histogram
Light Piping & Charge SharingLight Piping & Charge Sharing
microPETmicroPET IIII0.975 0.975 ×× 0.9750.975 ×× 12.5 mm12.5 mm3 3 LSOLSO Crystals Crystals 14 14 ×× 14 array on H7546 6414 array on H7546 64--channel MCchannel MC--PMT with F.O. bundlesPMT with F.O. bundlesFWHM = 1.21 mm FWHM = 1.21 mm →→ Intrinsic FWHM ~1.0 mm Intrinsic FWHM ~1.0 mm ((b ~ 0.8 mm)b ~ 0.8 mm)
Tai et al, Phys Med Biol 48:1519-37, 2003
31 g mouse injected with37 MBq (1 mCi) of 18F-
Light Piping & Charge SharingLight Piping & Charge Sharing
microPET II Detector Studies
~0.4~0.4mmmm
LSOLSO Crystals Crystals 1.01.0 ×× 1.01.0 ×× 10 mm10 mm33
12 12 ×× 12 array directly coupled by individual F.O to 6412 array directly coupled by individual F.O to 64--channel PMTchannel PMT
Chatziioannou et al, Phys Med Biol 46 (2001) 2899
b ~ 0.4 mm b ~ 0.4 mm →→ Intrinsic FWHM ~ 1.0 mmIntrinsic FWHM ~ 1.0 mm
√√ Good packing Good packing fractionfraction
•• Poor light Poor light collectioncollection
Individual Coupling & Independent ProcessingIndividual Coupling & Independent Processing
Munich APD PET (MADPET II) Munich APD PET (MADPET II)
PTFE
LSO
APD array
3M foil
4 4 ×× 8 APD 8 APD ArrayArray (Hamamatsu (Hamamatsu PhotonicsPhotonics))22 ×× 22 ×× 6 mm6 mm33 LSO LSO individuallyindividually coupledcoupledb ~ 0 mm b ~ 0 mm →→ IntrinsicIntrinsic FWHM ~ 1.2 mmFWHM ~ 1.2 mm
Pichler et al, IEEE MIC 2000
Individual Coupling & Independent ProcessingIndividual Coupling & Independent Processing
Sherbrooke APD LabPETSherbrooke APD LabPET™™ ScannerScanner88--pixel, pixel, quadquad--APDAPD detectordetector module (module (PerkinElmerPerkinElmer))22 ×× 22 ×× ~10 mm~10 mm33 crystalscrystalsb ~ 0 mm b ~ 0 mm →→ IntrinsicIntrinsic FWHM ~ 1.2 mmFWHM ~ 1.2 mm
Good light collection (Direct APD Good light collection (Direct APD coupling to scintillator)coupling to scintillator)Potential use as CT detectorPotential use as CT detectorSealed module for reliabilitySealed module for reliabilityParallel digital signal processingParallel digital signal processing
Depth of Interaction (“DOI”)
x
d
x
L1
d
L2
x
L
d
Correction for DOI
• Use FOV << Size of scanner ⇒ Cost
• Geometric Correction: redefine effective ring diameter ⇒ Inaccurate
• Measure DOI:
- Pulse Height Discrimination (PHD) (Rogers, IEEE TMI 14 (1995) 146-150)⇒ Sensitive to scatter (object & detector)
- Light coding (Thompson et al, IEEE TNS 42 (1995) 1012-1017)⇒ Light loss causes degradation of resolution
- Pulse Shape Discrimination (PSD) (Lecomte, US Patent 1988)⇒ Insensitive to scatter, one readout channel per detector⇒ Requires scintillators with different decay times
- Signal Ratio (Huber et al, IEEE TNS 44 (1997) 1197-1201)⇒ Continuous measurement of DOI, not sensitive to scatter⇒ Requires 2 readout channels per detector (expensive)
• Bismuth Germanate (BGO)
• 36 mm × 36 mm × 20 mm
• 2 mm × 2 mm elements
• Crystal element centres are 1.4 mm apart on the diagonal
• Light from distal elementreaches PS-PMT throughfour elements below
The ANIPET Detector Block
1.4 mm
Proximal element
6.5 mm
11.5 mm
PS - PMT
1.85 mm
20.0 mm
Distal element
12 mm deep
The Triple Phoswich Module Imaging PhysicsLaboratory 1998
9x9 Array, 2.2 mm pitch 19.6 mm
19.6
mm
18F Field Flood ImageEach crystal is 2 mm x 2mm x 4mm deep.
LSOLSOGSOGSOBGOBGO
PSPMT R5900-C8
X1 X2 X3 X4Y1
Y2Y3
Y4
Crystals are glued together and doubly Teflon-wrapped. Entrance surface is roughened and covered with Teflon.
Seidel et al, IEEETNS 46 (1998) 485Dyn A Dyn B
Phoswich Diagrams Imaging PhysicsLaboratory 1998
Entire Detector Single Phoswich Elements
Full Charge LSO
BGO
GSO#52
#9
Delayed Charge
Parameters: delay = 130 ns, width = 600 ns
Detector Module DesignDetector Module Design
LSO Array
64 Element
PD Array
1” Square PMT1" Square Photomultiplier Tube
30 mm
Array of 64 Photodiodes
64 Scintillator Crystals
3 mm square
1"
1"
• Photomultiplier tube (PMT) provides timing pulse• Custom 64 element PD array identifies hit crystal• PD/(PD+PMT) ratio measures depth of interaction
Dual APD ReadoutDual APD Readout
PSPS--APD ModuleAPD Module Burr et al, IEEE NSS/MIC 2003
1.65 1.65 ×× 1.651.65 ×× 22 mm22 mm3 3 MLSMLS crystals crystals 8 8 ×× 8 array on dual 14 8 array on dual 14 ×× 1414 mmmm22 PSPS--APDsAPDs~ 3 mm FWHM DOI resolution~ 3 mm FWHM DOI resolution
OUTLINEOUTLINE•• Historical overview & applicationsHistorical overview & applications
•• γγ--camera & SPECT / camera & SPECT / µµSPECTSPECT•• PET / PET / µµPETPET
•• Small animal PETSmall animal PET•• Very high resolutionVery high resolution•• DepthDepth--ofof--interaction (DOI)interaction (DOI)
•• MultiMulti--modality imagingmodality imaging
PET/CT Dual Modality Imaging
DualDual--ModalityModality PET/CT PET/CT ImagingImaging
FDG-PET X-Ray CT PET/CT
Transaxial slices through the mid-section of the thorax. The increased FDG uptake in the PET image suggestive of abnormal glucose metabolism correlates well
with the large lung mass seen on the central CT slice. (Courtesy Dave Townsend, U. Pittsburgh)
Abdominal image for intestinal cancer search
Anatomic Localization in Small Animals?Anatomic Localization in Small Animals?
Balb/c Mouse, 18F-FES
A. Aliaga & F. BénardUdeS
CoCo--linear PET/SPECT/CT Systemlinear PET/SPECT/CT System
Gamma Medica Flex™Pre-Clinical Platform Flexible combination of coFlexible combination of co--linear linear
•• Pinhole Pinhole µµSPECT (0.6SPECT (0.6--2.5 mm)2.5 mm)•• XX--Ray Ray µµCT (43 CT (43 µµm)m)•• µµPET (~2 mm, 7.5%)
www.gammamedica.com
PET (~2 mm, 7.5%)
Solid BGO Ring Solid BGO Ring Quadrant Sharing Quadrant Sharing ArchitectureArchitecture
microCT/PET prototypeGoertzen, Meadors, Silverman, Cherry, Phys Med Biol 47; 4315-4328, 2002.
DEPARTMENT OF BIOMEDICAL ENGINEERING
Lead Shielding(1.5 mm)
Simultaneous microPET/CT ImagingGoertzen, Meadors, Silverman, Cherry, Phys Med Biol 47; 4315-4328, 2002.
18F-FDG scan of mouse. 230 µCi injected, 50 minute uptake period.CT parameters of 40 kVp, 0.6 mA.
Data collected over 200 views in a time of 18 minutes.
DEPARTMENT OF BIOMEDICAL ENGINEERING
CT PET Fused CT-PET
Simultaneous microPET/CT ImagingGoertzen, Meadors, Silverman, Cherry, Phys Med Biol 47; 4315-4328, 2002.
18F– scan of mouse. 700 µCi injectedCT parameters: 40 kVp, 0.6 mA.
Data collected over 400 views in a time of 40 minutes.
DEPARTMENT OF BIOMEDICAL ENGINEERING
Dual Modality Scanner: PET/SPECTDual Modality Scanner: PET/SPECTDahlbom et al, IEEE TNS 44:1114-9, 1997
Combined PET/CTCombined PET/CTBérard et al, IEEE TNS 52, 2005
•• PET detectors and electronics used for PET & CT image acquisitioPET detectors and electronics used for PET & CT image acquisitionn•• CT image acquired in CT image acquired in photon countingphoton counting modemode•• Concurrent (simultaneous?) PET and CT image acquisitionConcurrent (simultaneous?) PET and CT image acquisition
µµfocus Xfocus X--ray ray source source
PET detector ringPET detector ring
Scanner design:1.2 × 1.2 mm2 pixels
448 pixels/ring
20.5 cm diameter ring
M ~ 2.5 – 3.8 for rats~ 2.5 – 5.5 for mice
Low power X-ray source µfocus rod anode (<50 µm)
Diagnostic CT image quality (∆µ/µ ~1%) achieved in ~60 s per rotation @ 1 Mcps
CT counting imageCT counting image1.1 mm FWHM1.1 mm FWHM
88 88 µµGyGy1 to 7 mm rods1 to 7 mm rods
Air(~Lung)
Teflon(~Bone)
Plexiglas(~Fat)
Simultaneous PET/MRISimultaneous PET/MRI
SplitSplit--coil MR magnetcoil MR magnet1T 15 cm FOV1T 15 cm FOV
~1 m F.O. light~1 m F.O. light--guidesguides
http://www.pet-mr.com/
100 Gauss
5 Gauss
1212××12 12 LSO LSO crystal arraycrystal array
PSPS--PMTsPMTs600 Gauss600 Gauss(unshielded)(unshielded)
Positioning Positioning histogram for histogram for
readout at 1 m readout at 1 m (no field)(no field)
Combined Optical/PETCombined Optical/PETProut et al, IEEE TNS 51:752-6, 2004
⇒⇒
Open end crystals Open end crystals in contact with in contact with surface of animalsurface of animal
Images of two red Images of two red LEDsLEDsSingle Photon Spectrum of red light
511 keVspectrum
(22Na)Xenogen CCD IVIS system OPET detector
(direct contact)
Portable SystemsPortable Systems
Portable PET Probeswith “Tracking”
Miniature PET Scanner forunanesthetised rat
Readout chip
APD
LSO
SocketVaska et al, IEEE MIC
2001, 2003, 2004 Weinberg et al, IEEE MIC 2001
ConclusionConclusion
•• PhotodetectionPhotodetection with scintillators remains the with scintillators remains the leading technology for most applications in leading technology for most applications in medical and biomedical imaging medical and biomedical imaging
•• Further developments of ultraFurther developments of ultra--high resolution high resolution imaging devices are more and more challenging imaging devices are more and more challenging as physical limits are being reachedas physical limits are being reached
•• Implementation of new multiImplementation of new multi--modality imaging modality imaging scanners raises new problems, but also offers scanners raises new problems, but also offers new opportunities for unanticipated new opportunities for unanticipated developmentsdevelopments
PartagePartage de chargede charge
Chambres multi-fils (HIDAC, Oxford)“HIgh Density Avalanching Cathode” detector
Jeavons et al, IEEE TNS46 (1999) 468-473
Interaction dans parois de PbPhotoélectron éjecté dans trousCharge amplifiée et extraiteMesure de position par calcul du centre de gravité de la charge surfils anodesTrou 0.5 mm → ~0.95 mm FWHMInconvénients:− Faible efficacité− Taux de comptage limité− Résolution temporelle limitée− Pas de résolution en énergie
• GE Advance:Discrete BGO with interfaces:
polished + reflector ground + airground + optical coupling
• CTI Exact HR:Pseudo-discrete crystals cut to different depthSlits filled with diffuse reflectorLight-guide profile selected to maximize crystal separation
Modulated light channellingModulated light channelling
Light Sharing: Block Detector ConceptsLight Sharing: Block Detector Concepts
PhoswichPhoswich Detector (PSD)Detector (PSD)
APD
PhoswichDetector
Start
Stop
SCA
Preamp
Timing FilterAmplifier( / )τ τ
i d
200/200 ns
0.25 sµ
20/20 ns or
20/50 ns
CFD
CFD
8 ns
200 ns
Pulser
1
2
3
4
PSD CircuitShaping Amplifier
Gate
Gate
ADC
SCA Energy
Time
5
0
10000
20000
30000
40000
50000
-20 0 20 40 60 80 100 120 140 160 180 200PSD Time (ns)
Cou
nts
×10
CsI(Tl)
BGOGSO
LSO 511 keV (68Ge)
Ref
APDGSO
LSO
BGOCsI(Tl)
0
3000
6000
9000
0 50 100 150 200Channel Number
Cou
nts
CsI(Tl)
BGO
LSO
GSO
Total
511 keV (68Ge)
APDGSO
LSO
BGOCsI(Tl)
Saoudi et al, IEEE TNS 46 (1999) 462-467
• Up to 4 scintillators can be identified• Also possible by delayed integration (Green et al)
or advanced digital processing
QuadQuad--APDAPD QuadQuad--ScintillatorScintillator DetectorDetector ModuleModule
YSOCsI(Tl)LSOBGO
Optical Septa
OpticalCoupling
0
1000
2000
3000
4000
0 50 100 150 200Channel
Cou
nts
YSO
LSOCsI
BGO
Total BGO/LSO/YSO/CsIAir Interface511 keV
0
5000
10000
15000
20000
-20 0 20 40 60 80 100 120 140 160 180 200Zero Cross Time
Cou
nts
CsI(Tl)BGO
511keVAir Interface
LSO
Ref
. Pul
se
YSO
QuadAPD array
Lecomte et al, IEEE MIC 1998
• Four scintillators having different decay times
• 2x2 APD array • Crystal Identification by pulse
shape discrimination (PSD)