Design of a time-of-flight PET imaging probe

There have recently been a number of research groups investigating the use of high resolution detector inserts within the imaging field of view to provide improved spatial resolution for a limited imaging volume within the system's field of view. We investigate the design of such a detector with both very high spatial resolution (e.g., <;1mm FWHM intrinsic) and temporal resolution (e.g., <;150psec FWHM intrinsic) to support time-of-flight (TOF) PET. On application for such a device would be for high resolution, endorectal PET prostate imaging. For this application the imaging probe could be in coincidence with a full PET detector ring or a detector panel situated over the prostate. The aim of this work is to explore the intrinsic spatial resolution and timing resolution capabilities of an imaging detector composed of a monolithic LYSO crystal readout on multiple sides using two-dimensional arrays of MPPC devices. The different probe designs were investigated: 25.6 by 25.6 by 25.6 mm^3 detector readout on six sides by 8×8 arrays of MPPC devices; 25.6 by 25.6 by 12.8 mm^3 detector readout on six sides by MPPC devices; and 25.6 by 25.6 by 12.8 mm^3 detector readout on two sides by MPPC devices. In addition, the optic ray tracing program SCOUT (Scintillation Camera OUTput) was used to study the characteristics of the light photon arrival times for the different detector geometries. Simulation results indicate that a three dimensional intrinsic spatial resolution of <;0.6 mm can be achieved for a 25.6 by 25.6 by 25.6 mm^3 detector readout on six sides by 8×8 arrays of MPPC devices. Further, placing sensors on all sides of the monolithic crystal detector should lead to optimum timing capabilities for a given crystal geometry since the design minimizes the path length each optical photon travels before it is detected.