Prostate probe with SPECT technique
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Prostate probe with SPECT techniqueNSS – MIC 2010 - November 5 - Knoxville F. Garibaldi- INFN – Roma1 – gr. Coll. ISS
the medical problem
the proposal Layout Multimodality SiPM/electronics
summary and outlook
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Radionuclides imaging techniques
Patient injected with radioactive drug. Drug localizes according to its metabolic properties.Gamma rays, emitted by radioactive decay, that exit the patient are imaged.
1.CollimatorOnly gammas that are perpendicular to imaging plane reach the detector
2.ScintillatorConverts gammas to visible light3.Photodetector
Convert light to electrical signal
4.Readout ElectronicsAmplify electrical signal and interface to computer5.Computer decoding procedureElaborate signal and gives image output
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PETCompton Cameramechanical collimation
Multi pinhole
Source
Image Plane
1st Detector
2nd DetectorScattered - Rays
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Single photon techniques
- simple(r)
- cheape(r)
- extending the radiotracers available
- dual tracer looking at two different biological processes
pros
cons- efficiency- spatial resolution
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Compton Prostate Imaging Probe
Internal Compton Probe External Compton Probe
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Predicted Internal Probe Performance
4mm Point-to-Point, 1cm from probe (Monte Carlo simulation + ML reconstruction)
141keV 171keV 245keV 364keV 511keV
Imaging Distance 10 cm
Compton ProbeHigh-Sensitivity CollimatorHigh-Resolution Collimator
Efficiency Resolution 1.8e-3 2.47mm 1.11e-4 15.9mm 4.00e-5 10.5mm
Comparison with SPECT for In-111
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Relative Uptake of In-111 Prostascint
Organ Relative Uptakes
Prostate 1.0
Liver 2.0
Blood 1.5
Bone 0.7
Kidney 1.0
Spleen 1.0
Bladder 0.6
Rectum 0.4
Testes 0.6
Averaged from three In-111 Prostascint SPECT scans
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Conventional SPECT Reconstructions
5:1 10:1 15:1 20:1
w / tumor
bkgd
171 and 245 keV, 8.8M events / 40 slices
Spatial resolution ~15mm FWHM
Prostate
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Compton Prostate Probe Reconstructions
5:1 10:1 15:1 20:1
w / tumor
bkgd
245 keV only, 1.2 million events, 8mm lesion
Prostate
Spatial resolution ~2mm FWHM
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Internal Detector Details
10–12 layers of 1mm thick Si detectors + position and orientation sensor
Exploded View
Assembled Unit
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Compton Probe Promising but Challenging
• First detector– Energy resolution – largely addressed– Timing resolution – still an issue– Packaging – solvable
• Second detector– Countrate capability – solvable – Cost – always an issue
• System– Image reconstruction – solvable
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Detector Packaging
Unfolded energy spectrum
“Raw” energy spectrum
Use Tape Automated Bonding (TAB)
(Very thin kapton tape with aluminum traces)
Kapton microcables
Detector
VATA ASIC
Kapton “hybrid” board
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Timing
0 50 100 150 200 250 3000
0.5
1
1.5
2
2.5
x 10-9
Time (ns)
Sig
na;
200 V = Vdep
Threshold
0 50 100 150 200 250 3000
0.5
1
1.5
2
2.5
x 10-9
Threshold
500V = Vdep + 300V
Time (ns)
Sig
nal
• Desired time resolution <10ns FWHM
• Poor timing from Si is evident
• Slower signal generation from events near backplane
• Large range of pulse-height coupled with leading-edge trigger is a big issue time-walk
• Signal generation depends on 3D interaction position and recoil electron direction time-jitter
Signal generation at two biases for three depths
BGO-Silicon timing spectrum for 511 keV source
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How Challenges Affect Performance• Consider anticipated countrate with In-111 Prostascint (from Monte
Carlo simulations):– ~4 Mcps on second detector– ~40 kcps on scattering detector– 50 ns time window for present Si detectors (may need to be even
larger)• Crandom= 2 x 4x106 x 4x104 x 50x10-9 = 16,000 cps !
• Ctrue was only ~10 kcps (or less)
• Performance dominated by randoms!
• Energy sum window can be used to reject randoms but only if the second detector also has good energy resolution
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Source
Image Plane
1st Detector
2nd DetectorScattered - Rays
Single photon Compton camera ( N. Clinthorne. Michigan )
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External Multipinhole Alternative
External probes will have small FOV and limited-angle tomography but…
• SPECT/CT can identify prostate region
• Probe can be computer-steered to image desired FOV
• Conventional SPECT can be used to “complete” probe data
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Endorectal Multipinhole?
Pinhole aperture array -- side view
Pinhole aperture array -- bottom view
Detector
Probe Shell
Pinhole Collimation (multiplexed or not)
30mm
~15mm
• Some tomographic capability
• Requires high detector resolution (0.5–1 mm + depth-of-interaction)
• High enough efficiency and resolution?
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W. Moses – Rome workshop 2005
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111In-ProstaScint is not a good radiotracer but a new one proposed by M. Pomper looks promising.
Radionuclides Single photon
The single photon endorectal probe provides 2D imaging. We have to try to have 3 D images
( using multipinhole collimation and/or adding
up a SPECT tomograph (spatial resolution would
be dominated by the small probe (see later, the PET
case))
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our proposal-insert scintillator pixels into square holes of the collimator
better performances (spatial resolution (?) and sensitivity (thicker scintillator))
-using diverging collimator better performances (reducing scan time)
-using multipinhole collimation better performances (increasing sensitivity, tomographic
recinstruction)
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New radiotracers coming soon (M. Pomper , Johns Hopkins)Radiotracers available for SPECT and PET
(from “New agents and Techniques for Imaging prostate cancer” A. Zahreer, S. Y. Cho, M. Pomper”, to be published on JNM)SPECT: Prostascint, Bombesyn, 99mTechnetium nanocolloid (limphonodes), other coming soon…PET C—11 Choline, F-18-Choline, Ga-68 Dotabomb (Hofmann (Rome workshop)) many others coming… (collaboration with Johns Hopkins for testing in ISS (mice models for prostate available) and/or at JHU)
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