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Special Applications for Scintillating Crystals in Medical Imaging

Explore the use of scintillating crystals in medical imaging for studying diseases related to the dopamine neurotransmitter system in the brain and developing new imaging detectors. Learn about RatCAP, a tomograph for imaging awake rats, wrist detectors for non-invasive measurements, and simultaneous PET and MRI imaging. Discover how PET can be used to study neurophysiological activity and behavior in animals and the advancements in crystal arrays and readout electronics.

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Special Applications for Scintillating Crystals in Medical Imaging

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  1. Special Applications for Scintillating Crystals in Medical Imaging Craig Woody Brookhaven National Lab SCINT 2007 Wake Forest University June 7, 2007

  2. Using Nuclear Medicine to Help Solve Problems in Today’s Society Drug Addiction Nicotine Addiction Alcoholism Attention Deficit Disorders Obesity These diseases are all related to the dopamine neurotransmitter system in the brain and can be studied using Positron Emission Tomography C.Woody, SCINT 07, 6/7/07 2

  3. MAO A DA DA DA 11C-Cocaine DA DA DA DA DA DA DA DA DA DA DA DA DA DA DA DA DA signal The Dopamine System in the Brain Striata All drugs which are abused by humans increase the dopamine levels in the brain C.Woody, SCINT 07, 6/7/07

  4. New Medical Imaging Detectors Being Developed at BNL • RatCAP • new tomograph for brain imaging of unanaesthetized rats using PET • Wrist Detector • non-invasive measurement of blood input function for human PET studies • Simultaneous PET and MRI • small animal or breast imager based on a non-magnetic version of the RatCAP • Beta Microprobe • Anger PET Camera C.Woody, SCINT 07, 6/7/07

  5. Imaging Awake Animals One often wants to use PET to study neurophysiological activity and behavior in laboratory animals in order to better understand these effects in humans. • Animals need to be anesthetized during PET imaging due to their inability to lie motionless in the scanner • Anesthesia can greatly depress brain functions and affect the neurochemistry that one is trying to study • Cannot study animal behavior while under anesthesia C.Woody, SCINT 07, 6/7/07

  6. RatCAP: RatConscious Animal PET A miniature, complete full-ring tomograph mounted to the head of an awake rat. • Compact, light weight (< 200 g), low power detector • Small field of view (38 mm dia. x 18 mm axial) • Attached to the head of the rat and supported by a tether which allows reasonable freedom of movement for the animal C.Woody, SCINT 07, 6/7/07

  7. Tomograph Ring Ring containing 12 block detectors of 2x2 mm2 x 5 mm deep LSO crystals with APDs and integrated readout electronics APD (Hamamastu S8550) 4x8 array of LSO crystals (2x2x5 mm3) Actual RatCAP Ring LSO Socket Readout chip APD C.Woody, SCINT 07, 6/7/07

  8. Crystal Arrays LSO • Minimize size and weight • High stopping power • Fast timing for coincidence measurements Chose 2.2 x 2.2 x 5 mm3 crystals to match to Hamamatsu S8550 APDs Gamma ray efficiency @ 511 keV ~ 41% Overall sensitivity of the RatCAP ~0.5% (comparable to other small animal PET scanners) Background from 176Lu decay gives ~ 2600 dps for whole system (true coincidence rate ~ 80 cps) C.Woody, SCINT 07, 6/7/07

  9. Ray Tracing Optimization of Light Collection • Best light yield was found to be with no optical coupling between crystals and reflectors and silicon cookie between crystals and APD • Maximize photoelectron yield • LSO  25,000 g/MeV • light collection ~ 0.6 • area matching to APD = 0.53 • APD QE ~ 70% Average p.e. yield ~ 5400 p.e./MeV s ~ 15% (2.7 max/min) over 384 pixels  s ~ 8.5% (2.0 max/min) with gain matching of APDs C.Woody, SCINT 07, 6/7/07

  10. Production of Crystal Arrays Cutting, polishing and assembly process • Slabs cut and stacked with reflector between layers without glue (no optical coupling on sides) • Layers are cut and stacked to form pixel arrays • Glued to a reflector on a thin glass plate on one end (opposite readout) Produced by Proteus/Agile Engineering C.Woody, SCINT 07, 6/7/07

  11. Readout Electronics Custom ASIC (0.18 mm CMOS) 32 ch. preamp, shaper, disc. ~ 1W total power 4.5 x 3.3 mm ZCD Bare chip (1st prototype) New chip • VGA • Improved timing • Energy window • LVDS interface Totally Digital Output 5 bit address Leading edge gives timing No ADC’s Minimizes cabling Packaged chip C.Woody, SCINT 07, 6/7/07

  12. Threshold scan Threshold (mV) Differential pulse height spectrum 2t ~28 ns FWHM ~ 23% Thresh Threshold (mV) Energy and Time Resolution Results with version 1 of the chip New chip gives 18.7% energy resolution and 6.6 ns timing resolution, and has variable gain for each channel for better energy matching Average threshold ~ 146 keV C.Woody, SCINT 07, 6/7/07

  13. RatCAP Support System Weight is completely counterbalanced (animal feels only inertia) Inner ring attaches to head which mounts to tomograph Gimbal ring allows head movement C.Woody, SCINT 07, 6/7/07

  14. Animal Training C.Woody, SCINT 07, 6/7/07

  15. Mounting the RatCAP to the Head C.Woody, SCINT 07, 6/7/07

  16. Wearing the RatCAP Rat during awake image acquisition C.Woody, SCINT 07, 6/7/07

  17. RatCAP Version 2 New design features • Redesigned ASIC, flex circuit, TSPM and DAQ • Larger aperture (40 mm) • Accommodates larger crystals (5  7 mm) for improved sensitivity ( ~ x2) • Integrated cooling • Non-magnetic • Improved mounting system to rat’s head RatCAP II C.Woody, SCINT 07, 6/7/07

  18. FDG Awake Saggital Transverse Coronal Images with RatCAP II 11C-Raclopride (ex vivo) Transverse Coronal Saggital C.Woody, SCINT 07, 6/7/07

  19. Wrist Scanner for Measuring Radioactivity in the Blood Studies of dynamical processes with PET requires measuring the tracer concentration in the blood as a function of time. RatCAP modules C.Woody, SCINT 07, 6/7/07

  20. Imaging the Wrist Artery Artery Vein Human Wrist 1 cm MicroPET R4 Wrist Scanner C.Woody, SCINT 07, 6/7/07

  21. PET image MRI Image Simultaneous PET/MRI Simultaneous PET/MRI imaging provides high resolution anatomical data from MRI along with functional information from PET Compared with PET/CT • Images are perfectly co-registered • Less radiation dose (~ ½ of PET/CT) • MRI provides better soft tissue contrast C.Woody, SCINT 07, 6/7/07

  22. RatCAP detectors and electronics PET/MRI Based on the RatCAP Design A non-magnetic version of the RatCAP detector is inserted into an existing MRI scanner and PET and MRI images are obtained simultaneously Used with anesthetized rats C.Woody, SCINT 07, 6/7/07

  23. Simultaneous PET-MRI Rat Brain Images MRI PET Overlay RatCAP I C.Woody, SCINT 07, 6/7/07

  24. Simultaneous PET-MRI Images with RatCAP II MRI Striatum phantom PET Overlay C.Woody, SCINT 07, 6/7/07

  25. Beta Microprobe LSO crystal attached to an optical fiber and read out with a PMT Positrons in PET have energies of a few hundred keV ( range ~ several mm in blood or tissue ) Can be detected directly using plastic or crystal scintillators C.Woody, SCINT 07, 6/7/07

  26. Comparison of LSO vs Plastic Scintillator Range and energy loss of positrons in LSO and plastic scintillator Response of LSO and plastic scintillation probes to betas (32P) and gamma rays (137Cs). C.Woody, SCINT 07, 6/7/07

  27. b+ Input Function Measured with Microprobe Input function measured in the tail vein of a rat LSO microprobe (0.3 mm dia. x 0.5 mm) inserted inside an 18 gauge syringe needle Region of sensitivity around the probe can be selected by adjusting the readout threshold to improve spatial resolution C.Woody, SCINT 07, 6/7/07

  28. Rat Brain Studies with Microprobe Uptake of 11C-methylphenidate in the nucleus accumbens region of a rat brain with an LSO probe nucleus accumbens ~ 2 mm C.Woody, SCINT 07, 6/7/07

  29. LSO slab APD   Anger PET Camera Goal: ~1 mm FWHM spatial resolution Concept: • Use Anger camera technique • LSO and APDs • Photosensor on both sides for DOI (no lightguide necessary) Advantages over current small-crystal designs • Higher sensitivity - no gaps • Scalable to higher resolution - thickness determines resolution • Stackable to increase sensitivity • Lower cost vs. P.Vaska BNL Medical Dept. C.Woody, SCINT 07, 6/7/07

  30. Possible Application to Small Animal Imaging LSO 1 mm spatial resolution would be very advantageous in imaging mice 6 cm dia boules of LSO  Annulus detector with no edge effects Depth of interaction from two layer readout Whole body mouse scanner C.Woody, SCINT 07, 6/7/07

  31. Summary • New scintillating crystals such as LSO have opened up many new and exciting possibilities for medical imaging • Applications of PET to both human and animal studies has greatly improved our ability to diagnose and treat many types of diseases • The prospect for new even brighter and faster scintillators holds great promise for making further advances in nuclear medicine and improved health care C.Woody, SCINT 07, 6/7/07

  32. The Team BNL MRI Group RatCAP Group P. Vaska, D.Schlyer, C. Woody, J.-F. Pratte, S. Junnarkar, J.Fried, P. O’Connor, V. Radeka, S. Stoll, M. Purschke, W.Lenz, S.-J. Park, S. Southekal, A. Kriplani, S. Krishnamoorthy, S. Maramraju, D.Tomasi, S.Solis-Najera, S.D.Smith, W.Rooney, D.Schulz, D.Lee, W. Schiffer, V.Patel, S.Dewey, F.Henn, J.Neill, D.Kaluhiokalani, R.Lecomte, R.Fontaine C.Woody, SCINT 07, 6/7/07

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