Scintillation Photon Counting Detectors for 100 ps Time-of-Flight PET Imaging

Project Summary
Clinical time-of-flight positron emission tomography (TOF-PET) systems capable of excellent coincidence time
resolution (CTR) promise to drastically enhance effective 511 keV photon sensitivity. The ability to more precisely
localize annihilation origins along system response lines constrains event data, providing improved signal-to-
noise ratio (SNR) and reconstructed image quality by associating 511 keV photons more closely to their true
origin. This SNR enhancement increases as CTR is improved, and a major goal of ongoing PET instrumentation
research and development is to push system CTR ≤100 ps full-width-at-half-maximum (FWHM). At this level of
performance, events are constrained ≤1.5 cm, providing more than a five-fold increase in SNR relative to a
system with no TOF capability. Advanced systems capable of ≤100 ps FWHM CTR would effectively more than
double or quadruple the effective 511 keV system sensitivity, in comparison to state-of-the-art, clinical TOF-PET
systems (250-400 ps FWHM CTR). Thus, advancing CTR is also a pathway for greatly improved system
sensitivity without increasing detection volume and system cost. Standard PET detectors comprising segmented
arrays of high-aspect-ratio scintillation crystal elements cannot achieve this level of performance and are
ultimately limited by poor light collection efficiency and depth-dependent scintillation photon transit time jitter
seen by the photodetector. To address this, we propose to develop a new detector readout concept which allows
scintillation photons to be counted and a unique timestamp to be assigned for the first arriving photon at each
photosensor pixel. We will leverage this new advancement in scalable PET detector readout and produce PET
detector modules capable of high resolution, three-dimensional positioning capabilities and 100 ps FWHM CTR
in a design that also makes no sacrifices on 511 keV photon detection efficiency. The new detector design will
be integrated into large area detector modules that span the full axial extent (>20 cm) of a clinical PET system,
including front-end signal and back-end data processing. We will construct a prototype tomographic imaging
setup and quantify relevant system performance metrics and the imaging performance of future clinical systems
made from this new detector. The proposed PET detector technologies can have a significant impact on
quantitative PET imaging. The image SNR enabled by the significant boost in effective sensitivity can be
employed to substantially reduce tracer dose and shorten scan time/increase patient throughput, or to better
visualize and quantify smaller lesions/features in the presence of significant background, which are important
features that can make PET more practical and accurate, as well as help to expand its roles in patient
management.

Grant Number: 5R01EB033402-04
NIH Institute/Center: NIH
Principal Investigator: Joshua Cates