Promising Detector Concepts to Advance Coincidence Time Resolution for Time-of-Flight Positron Emission Tomography

In this paper, we describe design considerations and promising detector technologies for time-of-flight positron emission tomography (TOF-PET). During a positron emission tomography scan, TOF-PET enables positron annihilation events to be positioned closer to their true origin along system response lines, thus facilitating improved reconstructed image signal-to-noise ratio, which has benefits such as better disease visualization and quantification, lower injected dose, and/or lower study duration. The degree of this image signal-to-noise ratio boost is determined by the annihilation photon pair coincidence time resolution of the detector system. Thus, there has been much research and development to advance detector coincidence time resolution, which is the foundation for future TOF-PET system designs. But when considering novel TOF-PET detector designs, it is important to select approaches that enhance coincidence time resolution without a tradeoff of decreasing detection efficiency (e.g., employing thin or low-density detector materials or low intra- or inter-module packing fraction, etc.). One might even argue that high coincidence detection efficiency (a.k.a. sensitivity) is the primary goal of any new positron emission tomography system design. In this paper, we will briefly discuss fundamental limitations on positron emission tomography coincidence time resolution using scintillation detectors and describe new detector configurations and electronic readout designs that attempt to address those constraints and achieve as low as 100 ps coincidence time resolution without compromising overall detection efficiency. We also concisely describe an innovative, non-scintillation-based, fast detection concept, which borrows ideas from the field of optics and could, in theory, achieve similar to 1 ps coincidence time resolution. If successful, these technologies will lead to next-generation systems that enhance TOF-PET's ability to visualize and quantify disease.