GATE simulations to study extended axial FOVs for the PennPET Explorer scanner

Clinically, PET/CT is widely used in oncology and cardiology. In the realm of research, dynamic PET imaging provides valuable information about ongoing biologic processes in the body. Currently, all commercial PET scanners have an axial field of view (AFOV) less than 25 cm, and whole-body scans are taken in multiple static, step-and-shoot bed positions. We are currently building a scanner with a larger AFOV, called the PennPET Explorer. The increased sensitivity from extending the AFOV beyond 25 cm will allow for lower dose imaging, improved count statistics, and simultaneous whole-body static and dynamic imaging. To quantify the effect of extending the AFOV of a PET scanner, we have created GATE simulations of the 16.4-cm AFOV Philips Vereos PET/CT scanner, and extended this to 23cm (E23) and 70-cm (E70) AFOV PET scanners. The simulation model is based on the 1:1 coupled digital detectors used in the Vereos scanner that has a timing resolution of 320 ps. NEMA NU2-2012 sensitivity, spatial resolution, count rate, and image quality standards were run on each of the three simulated scanners and corroborated with measured data from the Vereos. Additionally, low-dose studies were emulated using the image quality simulations from the E23 and E70 scanners. While there was little variation in contrast recovery coefficient (CRC) values across the three geometries, there were notable differences in sensitivity, spatial resolution, and count rate performance. Sensitivity increased from 5.5 kcps/MBq on the Vereos to 10.8 kcps/MBq on the E23 and 90.5 kcps/MBq on the E70. Transaxial spatial resolution at the scanner center (FWHM: 4.0 mm) did not degrade with increased AFOV, while the axial resolution at the center degraded slightly from 3.8 mm (Vereos) to 4.5 mm (E70) due to increased axial parallax errors. At 55 kBq/cc - the activity concentration at peak noise equivalent count rate (NECR) (155 kcps) measured on the Vereos scanner - the NECR were 550 kcps and 4440 kcps for the E23 and E70 scanners, respectively. Lowdose studies showed equivalent CRC measurement precision between the full dose E23 scanner and ${\textstyle \frac {1}{2}}- {\textstyle \frac {1}{4}}$ dose on the E70 scanner. Moving forward, these simulated scanners, along with scanners with even longer AFOVs, will assist in planning both static and dynamic patient studies on the PennPET Explorer when operational.