A group from Chicago, Argonne and Fermilab are interested in the development of large-area systems to measure the time-of-arrival of relativistic particles with (ultimately) 1 pico-second resolution, and for signals typical of Positron-Emission Tomography (PET), a resolution of 30 pico-seconds (sigma on one channel). These are respectively a factor of 100 and 20 better than the present state-of-the-art. This would involve development in a number of intellectually challenging areas: three-dimensional modeling of photo-optical devices, the design and construction of ultra-fast (200 GHz) electronics, the `end-to-end' (i.e. complete) simulation of large systems, real-time image processing and reconstruction, and the optimization of large detector and analysis systems for medical imaging. In each of these areas there is immense room for creative and innovative thinking, as the underlying technologies have moved faster than the applications. We collectively are an interdisciplinary (High Energy Physics, Radiology, and Electrical Engineering) group working on these problems, and it's interesting and rewarding to cross the knowledge bases of different intellectual disciplines. The picosecond club

- 2”x2” Burle/Photonis anodes 10-micron pore tubes (skew timing over a 2”x2” tube ~100 ps) - Hamamatsu PLP-10 picosec laser

TESTING A SILICON PHOTOMULTIPLIER TIME-OF FLIGHT (TOF) SYSTEM IN FERMILAB’S TEST BEAM FACILITY Anatoly Ronzhin, Mike Albrow, Erik Ramberg – Fermilab, Jerry Vavra – SLAC, Henry Frisch, Tyler Natoli, Camden Eartly, Heejong Kim, Andrew Kobach, Fukun Tang, Scott Wilbur, Jean-Francois Genat – University of Chicago, Ed May, Karen Byrum, John Anderson, Gary Drake – Argonne National Laboratory 12 September, 2008

Optimization of LSO for Time-of-Flight PET W. W. Moses 1, M. Janecek 1, M. A. Spurrier 2, P. Szupryczynski 2,3, W.-S. Choong 1, C. L. Melcher 2, and M. Andreaco 3 1 Lawrence Berkeley National Laboratory 2 University of Tennessee, Knoxville 3 Siemens Medical Solutions October 21, 2008 Motivation Reflector Optimization LSO Optimization PMT Optimization Outline: This work was supported by the NIH (NIBIB grant No. R01-EB006085).

Time-of-Flight in PET Can localize source along line of flight. Time of flight information reduces noise in images. Variance reduction given by 2D/c  t. 500 ps timing resolution  5x reduction in variance! c = 30 cm/ns 500 ps timing resolution  7.5 cm localization Time of Flight Provides a Huge Performance Increase! Largest Improvement in Large Patients Time of Flight Provides a Huge Performance Increase! Largest Improvement in Large Patients D

Commercial TOF PET w/ LSO ~550 ps Coincidence Timing Achieved

Our Goal: “Demonstration” TOF PET Camera Achieve the Best Timing Possible w/ LSO With better timing resolution (  t), huge gains predicted (23x variance reduction for 100 ps timing) Measure image improvement vs. timing resolution Use LSO scintillator –Don’t change other factors that influence SNR (efficiency, scatter fraction, etc.)

What Limits Timing Resolution? Crystal Geometry 326 ps PMT 422 ps Light Sharing 454 ps PMT Array 274 ps Baseline 160 ps Non-TOF Block Detector Module Many Factors “Optical Geometry” Particularly Important Many Factors “Optical Geometry” Particularly Important

Proposed Side-Coupled Design Proposed Geometry (Side-Coupled Crystal) Scintillator Crystal PMT Shorter Optical Path Length & Fewer Reflections Conventional Geometry (End-Coupled Crystal) 384 ps (543 ps coinc.) 218 ps

Detector Module Design PMT (Hamamatsu R-9800) Two LSO Crystals (each 6.15 x 6.15 x 25 mm 3 ) Reflector (on all five faces of each crystal, including the face between the two crystals) Optical Glue (between lower crystal faces and PMT) Hole in Reflector On Top Face of Crystals Two Side-Coupled Scintillator Crystals per PMT

Detector Ring Geometry Crystals Decoded by Opposing PMT Exploded View Top face of each crystal (with hole in reflector) is coupled via a small (<1 mm) air gap to the edge of one opposing PMT. Light seen by the opposing PMT is used to decode the crystal of interaction. Crystal of Interaction

Camera Geometry Section of Detector Ring Detector ring is 825 mm diameter, 6.15 mm axial 192 detector modules, 384 LSO scintillator crystals Adjustable gap (6 – 150 mm) between lead shields allows “scatter-free” and “3-D” shielding geometries Lead Shielding Modules “Real” Single-Ring PET Camera for Humans & Phantoms

Surface & Reflector Optimization Method Measure Percentage Change in Timing Measure Timing of “Raw” Crystal (saw cut finish, Teflon tape reflector) Apply Surface Treatment Apply Reflector Re-Measure Timing Compute Percent Change Repeat for 5 Crystals & Average Results Do for All Surface / Reflector Combinations (>100 crystals, each measured twice) R x 6.15 x 25 mm 3 Reflector on 5 Sides Optical Grease No Hole on Top Same PMT for all measurements

Surface & Reflector Results ReflectorSaw CutChemicallyMechanically EtchedPolished Air Gap Teflon1.00 ± ± ± 0.09 ESR1.01 ± ± ± 0.08 Lumirror1.03 ± ± ± 0.12 Glued ESR0.99 ± ± ± 0.18 Lumirror1.04 ± ± ± 0.22 Melinex1.01 ± ± ± 0.20 Epoxy1.00 ± ± ± 0.15 Paint0.96 ± 0.03 Average Average

Optimization: LSO Composition Predicted Timing Resolution  1/sqrt(I 0 ) Want High Total Light Output & Short Decay Time Possible By Co-Doping LSO With Calcium Predicted Timing Resolution  1/sqrt(I 0 ) Want High Total Light Output & Short Decay Time Possible By Co-Doping LSO With Calcium Both Scintillators Have Same Light Output (photons/MeV) Red Decay Time is 2x Longer Than Blue Decay Time I(t) = I 0 exp(-t/  ) Light Output = I 0  I0I0

Optimization: LSO Composition Ca-Doping Gives High Light Output & Short  Normal LSOHigh Light Out Short  The Good Stuff! = Ca-doped 0.1% 0.2%0.4% 0.3%

Ca-Doping Gives Good Timing Resolution ~15% Improvement Over Normal LSO Ca-Doping Gives Good Timing Resolution ~15% Improvement Over Normal LSO Normal LSO Scaled by 1/sqrt(I 0 ) Measured Results: LSO Composition = Ca-doped 0.1% 0.2% 0.4% 0.3%

Optimization: Photomultiplier Tube Predicted Timing Resolution  1/sqrt(QE) Want High Quantum Efficiency Version of PMT Predicted Timing Resolution  1/sqrt(QE) Want High Quantum Efficiency Version of PMT Peak QE Blue Sensitivity Index

Increased QE Improves Timing Resolution by 7% Expect 10% Improvement with 35% SBA PMT Increased QE Improves Timing Resolution by 7% Expect 10% Improvement with 35% SBA PMT Normal (“28% QE”) PMTs Measured Results: High QE PMTs Scaled by 1/sqrt(Blue Index) = “32% QE” PMTs

Summary TOF PET with Significantly Better Timing is Possible To Achieve, We Must “Think Outside the Block Detector” TOF PET with Significantly Better Timing is Possible To Achieve, We Must “Think Outside the Block Detector” Hardware SingleCoinc.TOF (ps fwhm)(ps fwhm) Gain End-Coupled Crystal Side-Coupled Crystal Etched, Reflector Paint Ca-Doped LSO % QE PMT % QE “SBA” PMT

Depth of Interaction & 150 ps Timing Resolution 11x Reduction in Variance in Practical Geometry Depth of Interaction & 150 ps Timing Resolution 11x Reduction in Variance in Practical Geometry Scintillator Array Thinned SiPM Array Future TOF-PET? (one layer for SPECT)