Electronic Readout for Next-Generation Ultra-Fast Time-of-Flight Positron Emission Tomography Systems

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 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 associated costs. This level of timing performance can be achieved with state-
of-the-art (SoA) electronic readout for silicon photomultiplier (SiPM)-based scintillation detectors in single pixel,
bench top coincidence measurements. Readout capable of demonstrating experimental limits in achievable CTR
leverage low noise, high frequency signal processing to facilitate a single photon time response that is near the
limit of the SiPMs architecture. This readout strategy can optimally exploit fast luminescence and prompt optical
photon populations, and promising measurements show detector concepts employing this readout can greatly
advance TOF-PET detector CTR, relative to SoA in clinical systems. However, the technique employs power
hungry components which make the electronics chain impractical for channel-dense TOF-PET detectors and
systems. If compact, tractable readout topologies that achieve this performance can be created, they offer a
platform for the development and translation of novel detector concepts to push system CTR ≤100 ps. We
propose to design and experimentally evaluate an analog, multichannel application specific integrated circuit
(ASIC) that implements SoA front end signal processing and time pickoff methods into a compact form factor,
capable of bringing SoA CTR demonstrated for new PET detector concepts into systems. Thus, when coupled
with existing high resolution, multichannel time-to-digital converters (TDCs), this new development thereby offers
a direct pathway to realize greatly advanced CTR in large scale, clinical PET imagers.

Grant Number: 5R21EB034885-02
NIH Institute/Center: NIH
Principal Investigator: Joshua Cates