Sensitivity and Count Rate Performance Studies of the BrainPET-7T Insert With 18 F, 124 I, and 22 Na

The BrainPET-7T insert is designed for simultaneous human-brain PET imaging with ultra-high-field MRI. It offers a high sensitivity and signal-to-noise ratio by detector blocks of pixelated LSO scintillators with a height of 2.4cm, digital silicon photomultiplier readout, and enhanced data processing methods. This makes it particulary interesting for +--emitter applications, such as dual-isotope imaging, which rely on the detection of triple coincidences. We investigated the scanner sensitivity using the isotopes 124I and 22Na, in comparison to 18F. Count rate performance was assessed using 124I and 18F for different energy window settings with an analysis following the NEMA NU 2-2018 protocol. For the count rate determination, an adapted strategy for estimating the scatter fraction for +--emitters was applied. The peak double coincidence sensitivity for 18F measured at the center and off-center was between 10.16(8)% and 12.37(10)% for energy windows of 440 to 594keV and 420 to 650keV. The true triple sensitivities obtained at the isocenter were 3.13(9)% and 4.88(12)% for 124I and between 0.8662(23)% and 3.112(5)% for 22Na depending on the selected energy window and rejection rule. The maximum RNEC of the 18F-measurement was 276kcps at 16.3kBqmL-1, while the maximum Rtrue was 780kcps at 22.7kBqmL-1 for an energy window of 440 to 594keV. The scatter fraction ranged from 28% to 33% and the random fraction from 3% to 40%. In the case of 124I, the ratio of estimated true triples to doubles was ≈6%, with a higher random fraction of 27% for triples compared to 2.8% for doubles. These results demonstrate the potential feasibility of employing the BrainPET-7T insert for +--emitter applications.