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)