Performance investigation of a time-of-flight PET/CT scanner

The physical PET performance of the first prototype of the recently introduced Biograph mCT TOF PET/CT scanner (Siemens Molecular Imaging) has been evaluated. The PET component incorporates 192 detector blocks, 5.4 cm x 5.4 cm in cross-section; each block comprises a 13 x 13 matrix of 4 x 4 x 20 mm³ crystal elements. The four detector block rings cover a 21.8 cm axial field-of-view with a 78 cm diameter patient port. Data are acquired within a 4.1 ns coincidence time window and with an energy threshold of 435–650 keV. The recent NEMA NU 2-2007 standard [1] was utilized to evaluate the preliminary physical performance of the scanner with additional measurements that specifically addressed the TOF capability. An average spatial resolution of 4.4 mm (FWHM) and 5.2 mm (FWHM) were measured at 1 cm and 10 cm from the center of the transverse field-of-view. The system sensitivity for a line source was 0.96 % and 0.94 % respectively at 0 cm and 10 cm from the center of the transverse FOV. We report a scatter fraction of 32% and a noise equivalent count (NEC) rate peaking at more than 180 kcps. The energy and timing resolution were measured with a ¹⁸F line source resulting in 11.7% (FWHM) and less than 550 ps (FWHM) respectively. We observed no significant variation in time, energy and spatial resolution for a singles count rate of more than 45 Mcps.