Imaging performance of the LabPET™ APD-based digital PET scanner

The LabPET™ is an APD-based digital PET scanner with quasi-individual crystal readout and highly parallel digital architecture for high-performance in vivo molecular imaging of small animals. The scanner is built from LGSO and LYSO crystals (2×2×10/12 mm³) assembled side-by-side in a phoswich fashion and read out by an APD. The LabPET™ exists in two versions: LabPET4 (3.75 cm axial length) and LabPET8 (7.5 cm axial length). This paper focuses on advanced scanner characteristics such as count rate and imaging performance. After a global timing alignment and further optimization of APD operating bias, an overall timing resolution of 6.6 ns for LYSO-LYSO, 10.3 ns for LGSO-LGSO and 8.6 ns for mixed coincidences was measured. Using an energy window of 250–650 keV, scatter fraction is estimated to 18% and 28% for the NEMA mouse and rat phantoms, respectively. The peak NEC count rate with the same energy window is respectively 142/252 kcps at 207/131 MBq for the mouse phantom and 37/121 kcps at 245/168 MBq for the rat phantom with the LabPET4/LabPET8 scanners. When imaging an Ultra Micro Hot Spot Phantom for 1 hour with 33 MBq of ¹⁸F, 1 mm hot spots can be clearly distinguished in the MLEM reconstructed image. Recovery coefficients for 1.35 mm hot spots converge to 0.65 and to unity for 2 mm hot spots. The LabPET™ offers excellent capabilities and performance for molecular imaging of small animals.