James Corbeil

Measurements and Ray-Tracing Simulations of Light Spread in LSO Crystals

We report on measurements of the absolute light output from LSO crystals for irradiation with 511 keV gamma rays as a function of interaction position, reflector arrangement, detector coupling geometry and optical coupling to an adjacent crystal. The light output for this series of geometrical configurations is simulated with the ZEMAX ray-tracing software. By fine-tuning the optical parameters of the bulk and at the interfaces of the crystal, a model is obtained which yields good agreement with experimental data for all configurations. The resulting parameter set is applied to calculate the light distribution in a 12 times 12 crystal block detector. A comparison of measured and calculated block position profiles shows good agreement, demonstrating the potential of the simulation model to predict block detector performance data and provide guidelines for future array designs.

Quarter-Trio Mapping Electronics Readout Scheme for APD Block Detector in PET

Quarter-trio mapping (QTM) is a new detector readout scheme for avalanche-photodiode (APD) block detectors in positron emission tomography (PET). This design simplifies the detector readout electronics, and more efficiently utilizes APDs in detector blocks hence reducing cost. With the QTM design, eight APDs are positioned in each detector block. The APDs are positioned in such a way that 12 times 12 crystal elements each of 2.5 mm times 2.5 mm times 20 mm can be identified. Moreover, we developed an efficient electronics readout QTM scheme in which only four output channels instead of eight are sent to main electronics to readout eight APD signals. Compared with nine APDs in a 3 times 3 array setup, initial results from eight APDs in QTM readout shows that the 12 times 12 crystal block can be well identified. The timing resolution (crystal block of 12 times 12 elements vs. single plastic scintillator) is about 2.95 ns vs. 2.84 ns from a 3 times 3 crystal array. More experiments are on going to further improve the energy and timing performance.

MR-Compatible blood sampler for PET

An MR-compatible automatic blood sampler prototype for quantifying radioactivity in blood has been built and tested. The determination of the so-called input function is necessary to investigate the kinetics of the administered radiotracer in PET studies. The counting detector consists of 2 coincident LSO blocks (50times40times 30 mm3) coupled each to a single APD (10 times 10 mm2 active area). Preliminary experimental and numerical results indicate that a specific sensitivity of about 1 cps / (nCi / ml) can be achieved. Tests during bimodal simultaneous MR/PET scans will be carried out in the future with a Siemens 3 T-Trio MR scanner and a brain PET insert.