Design study of a lower-cost ultrahigh-resolution high-sensitivity PET for neuroimaging

Abstract

Current clinical PET with 4-6 mm intrinsic resolution (6-9 mm practical) limits many important brain studies. The objective of this study is to use our existing technology for realizing an ultrahigh resolution high-sensitivity PET with a lower cost for neuroimaging. This proposed neuro-PET has a 54-cm detector ring diameter, a large 21-cm axial field of view (AFOV) for capturing the whole brain and carotid arteries for acquiring arterial input function for quantitating imaging. The system has 131,856 lutetium yttrium orthosilicate (LYSO) small detectors (1.4 × 1.4 mm2) coupled to 924 photomultiplier tubes (19-mm) with PMT-quadrant-sharing (PQS) design. We propose to use 11-mm shallow detectors to reduce the depth-of-interaction (DOI) image blurring and to reduce the costly LYSO material by half, and use the effective sensitivity gained by the time-of-flight (TOF) to compensate for the sensitivity loss by the shallow detectors. Despite the tiny 1.4 × 1.4 mm2 detector cross-section restricting light output, our preliminary study shows that a 550-ps (FWHM) TOF time resolution was achieved (enabled by the excellent timing characteristic of our PQS detectors). Hence, there would a gain of 2x effective sensitivity for the 18-cm brain. Monte Carlo simulations show transaxial image resolutions of 1.58 and 2.06 mm at 1, and 9 cm respectively, without resolution-recovery algorithm, demonstrating slow DOI degradation. The large AFOV and small detector ring diameter give this system another 2x higher sensitivity than the typical clinical PET. This camera will use our existing detector technology, transformable gantry, and production-engineering tooling developed in the last few years. The production cost of this ultrahigh resolution neuro-PET would be less than $400K. This ultrahigh-resolution PET with resolution approaching MRI and CT, also allows more meaningful image correlation, and provides ultrahigh resolution functional imaging for small brain nuclei structures, which would open new doors for functional neuroimaging and neuroscience. The lower cost, larger AFOV and higher sensitivity would facilitate the use of this dedicated brain PET.