title: Optimization of a LSO-Based Detector Module for Time-of-Flight PET.
abstract: We have explored methods for optimizing the timing resolution of an LSO-based detector module for a single-ring, "demonstration" time-of-flight PET camera. By maximizing the area that couples the scintillator to the PMT and minimizing the average path length that the scintillation photons travel, a single detector timing resolution of 218 ps fwhm is measured, which is considerably better than the ~385 ps fwhm obtained by commercial LSO or LYSO TOF detector modules. We explored different surface treatments (saw-cut, mechanically polished, and chemically etched) and reflector materials (Teflon tape, ESR, Lumirror, Melinex, white epoxy, and white paint), and found that for our geometry, a chemically etched surface had 5% better timing resolution than the saw-cut or mechanically polished surfaces, and while there was little dependence on the timing resolution between the various reflectors, white paint and white epoxy were a few percent better. Adding co-dopants to LSO shortened the decay time from 40 ns to ~30 ns but maintained the same or higher total light output. This increased the initial photoelectron rate and so improved the timing resolution by 15%. Using photomultiplier tubes with higher quantum efficiency (blue sensitivity index of 13.5 rather than 12) improved the timing resolution by an additional 5%. By choosing the optimum surface treatment (chemically etched), reflector (white paint), LSO composition (co-doped), and PMT (13.5 blue sensitivity index), the coincidence timing resolution of our detector module was reduced from 309 ps to 220 ps fwhm.
authors: Lawrence Berkeley National Laboratory, Berkeley, CA 94720 USA (telephone: ++1-510-486-4432,  wwmoses@lbl.gov ).
authors: W W
authors: WW
authors: Moses
authors: M
authors: M
authors: Janecek
authors: M A
authors: MA
authors: Spurrier
authors: P
authors: P
authors: Szupryczynski
authors: W-S
authors: WS
authors: Choong
authors: C L
authors: CL
authors: Melcher
authors: M
authors: M
authors: Andreaco