September 2017

Dr. Goldan is awarded his first NIH-R21 grant for the feasibility study of picosecond avalanche selenium detectors for time-of-flight (TOF) PET.

The latest integration of PET with MR has greatly advanced the clinical capability in cancer detection, staging, and monitoring of treatment. A time-of-flight (TOF) PET system uses timing information to determine if two registered photons are in “time coincidence” (in which case they belong to the same positron annihilation event), and uses the arrival time difference to localize each annihilation event. The use of TOF information in PET enables (1) simultaneous PET/MR imaging with enhanced resolution (especially for obese patients), (2) improved lesion detectability, and (3) shorter examination time with coregistration. Furthermore, TOF-PET has already shown to substantially reduce artifacts that are induced by MR imaging-based attenuation correction. Thus, TOF-PET/MR has immense potential to become a “one-stop shop” imaging technology that provides simultaneous functional, molecular and morphologic assessments of neurologic, cardiovascular, onco- logic, and musculoskeletal diseases. However, existing state-of-the-art TOF-PET/MR systems (such as the recently introduced SIGNA TOF PET/MR system developed by GE) all utilize a detector ring based on silicon photomultipliers (SiPMs) which still require further improvement to enhance cells’ photon detection e ciency (PDE), reduce optical crosstalk, and increase uniformity and yield. These problems cause the TOF imaging system to have suboptimal clinical effectiveness. In addition, the relatively high cost and small area of SiPMs prohibits large axial field-of-view to maximize geometric detection e ciency and approach the fundamental sensitivity limits of PET. Our hypothesis is that a novel low-cost amorphous selenium (a-Se) detector structure with avalanche multiplication gain and unipolar time differential (UTD) charge sensing can have optimal coincidence timing resolution (CTR) for TOF-PET. The objective of this exploratory R21 proposal is to demonstrate the feasibility of a-Se for TOF-PET by building single pixels on a glass substrate and measuring their CTR.