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Prostate probe with SPECT technique

Prostate probe with SPECT technique NSS – MIC 2010 - November 5 - Knoxville F. Garibaldi- INFN – Roma1 – gr. Coll. ISS . the medical problem the proposal Layout Multimodality SiPM/electronics summary and outlook. Patient injected with radioactive drug.

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Prostate probe with SPECT technique

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  1. Prostate probe with SPECT technique NSS – MIC 2010 - November 5 - Knoxville F. Garibaldi- INFN – Roma1 – gr. Coll. ISS • the medical problem • the proposal • Layout • Multimodality • SiPM/electronics • summary and outlook

  2. Patient injected with radioactive drug. Drug localizes according to its metabolic properties. Gamma rays, emitted by radioactive decay, that exit the patient are imaged. Radionuclides imaging techniques • Collimator • Only gammas that are perpendicular to imaging plane reach the detector • Readout Electronics • Amplify electrical signal and interface to computer • Scintillator • Converts gammas to visible light • Computer decoding procedure • Elaborate signal and gives image output • Photodetector • Convert light to electrical signal

  3. Compton Camera mechanical collimation PET Multi pinhole

  4. Single photon techniques pros • simple(r) • cheape(r) • extending the radiotracers available • dual tracer  looking at two different biological processes cons • - efficiency • spatial resolution

  5. Compton Prostate Imaging Probe Internal Compton Probe External Compton Probe

  6. Predicted Internal Probe Performance 141keV 511keV 171keV 245keV 364keV 4mm Point-to-Point, 1cm from probe (Monte Carlo simulation + ML reconstruction) Comparison with SPECT for In-111

  7. 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 Relative Uptake of In-111 Prostascint Averaged from three In-111 Prostascint SPECT scans

  8. Conventional SPECT Reconstructions 5:1 10:1 15:1 20:1 w / tumor Prostate bkgd 171 and 245 keV, 8.8M events / 40 slices Spatial resolution ~15mm FWHM

  9. Compton Prostate Probe Reconstructions 245 keV only, 1.2 million events, 8mm lesion Prostate 5:1 10:1 15:1 20:1 w / tumor bkgd Spatial resolution ~2mm FWHM

  10. Internal Detector Details 10–12 layers of 1mm thick Si detectors + position and orientation sensor Exploded View Assembled Unit

  11. 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

  12. Detector Packaging Use Tape Automated Bonding (TAB) (Very thin kapton tape with aluminum traces) Kapton microcables “Raw” energy spectrum Detector VATA ASIC Unfolded energy spectrum Kapton “hybrid” board

  13. Timing • 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 BGO-Silicon timing spectrum for 511 keV source Signal generation at two biases for three depths

  14. 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

  15. Single photon Compton camera (N. Clinthorne. Michigan )

  16. 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

  17. Endorectal Multipinhole? 30mm ~15mm • Some tomographic capability • Requires high detector resolution (0.5–1 mm + depth-of-interaction) • High enough efficiency and resolution?

  18. W. Moses – Rome workshop 2005

  19. Radionuclides Single photon • 111In-ProstaScint is not a good radiotracer but a new one proposed by M. Pomper looks promising. 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))

  20. 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)

  21. 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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