Whole-body single-bed time-of-flight RPC-PET: Simulation of axial and planar sensitivities with NEMA and anthropomorphic phantoms

A single-bed, whole-body positron emission tomograph based on resistive plate chamber detectors has been proposed (RPC-PET). RPC-PET with an axial field-of-view (AFOV) of 2.4 m is feasible and yields an absolute NEMA NU 2-1994 sensitivity enhancement of 20 (4.5) in respect to 16-cm AFOV PET systems with (without) time-of-flight (TOF). These results, however, do not correlate directly with lesion detectability. It is the planar (slice) sensitivity that dictates the exposure time necessary to obtain enough statistics to detect a lesion. This planar sensitivity is currently obtained with a NEMA NU 2-2001 line-source phantom. After validating our simulations with measurements published for existing scanners (GE Advance, Siemens TruePoint and TrueV), we study here by simulation the axial sensitivity profiles of state-of-the-art BGO- and LSO-based PET scanners, and compare the results with RPC-PET. Planar sensitivity results indicate that RPC-PET is expected to outperform 16-cm AFOV scanners by a factor 6 for a 70-cm long scan. If the axial extent is elongated to 1.5 m (approximately head to mid-legs), the sensitivity gain increases to 12. Yet, PET systems with larger AFOV do provide a larger solid angle coverage, at the expense of larger attenuation in the object. In order to quantitate these competing effects, we have studied both point- and line-sources immersed in a water cylinder. For 1.5-m-long scans, the planar sensitivity drops over one order of magnitude in all scanners simulated. In this scenario, RPC-PET outperforms 16-cm AFOV scanners by a factor of 55 (9) with (without) considering the TOF benefit. Regarding the TOF benefit, RPC-PET has a sensitivity gain of 18 when compared to modern, 16-cm AFOV scanners with 600 ps FWHM TOF resolution. We finally show that object scatter in an anthropomorphic phantom is similar for a whole-body, single-bed RPC-PET in respect to a modern, scintillator-based scanner.