(Tuesday, 7/31/2018) 11:00 AM - 12:15 PM
Room: Room 202
Purpose: To determine the feasibility of using a solid-state photomultiplier based on amorphous Selenium (a-Se) in avalanche mode with unipolar time differential (UTD) charge sensing to achieve time resolution sufficient for time-of-flight (TOF) PET imaging in simultaneous PET/MRI.
Methods: A multi-well Se-SSPM, which we named the Nano-Electrode multi-Well High-gain Avalanche Rushing Photoconductor (NEW-HARP), was constructed using lithography to achieve UTD charge sensing and avalanche multiplication gain. Fabrication quality was checked using electron microscopy. Using Monte Carlo techniques, we simulated the timing jitter/spread of our NEW-HARP detector and compared it to that of a conventional planar a-Se detector to determine and compare the single-photon timing resolution (SPTR) of each. To experimentally test the SPTR, we repeatedly exposed our NEW-HARP detector to picosecond laser pulses and determined the FWHM of the output signal’s timing jitter. We tested the SPTR at different high voltage (HV) bias potentials to determine optimal performance.
Results: Simulations revealed our NEW-HARP detector could achieve an SPTR=50ps, which is 2 orders of magnitude better than that of a conventional planar a-Se detector (SPTR=5ns). Experimental tests showed we were able to achieve SPTR=85ps at HV=2000V, SPTR=61ps at HV=2200V, and SPTR=52ps at HV=2400V, making HV=2400V the optimal bias potential for NEW-HARP. Based on Cramer-Rao lower bound calculations on coincidence time resolution (CTR), this value of SPTR corresponds to a theoretical CTR of 70ps with an optimal photon detection efficiency (PDE) of 75% at blue wavelengths.
Conclusion: We demonstrate the potential of our proposed NEW-HARP detector for TOF PET imaging. Currently, TOF PET systems only achieve a CTR of ~200ps due to poor system-level PDE (SiPM PDE<20%), whereas the CTR required to reduce patient scan time is <100ps. Our next step is to fabricate and test a full ring of PET detectors using NEW-HARP as the photomultiplier coupled to LYSO scintillators.
Keywords
PET, Photon Detectors, Amorphous Selenium
Taxonomy
IM- PET : Development (new technology and techniques)
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