NEMA NU-04-based performance characteristics of the LabPET-8™ small animal PET scanner

Abstract

The objective of this study is to characterize the performance of the preclinical avalanche photodiode (APD)-based LabPET-8™ subsystem of the fully integrated trimodality PET/SPECT/CT Triumph™ scanner using the NEMA NU 04 - 2008 protocol. The characterized performance parameters include the spatial resolution, sensitivity, scatter fraction, counts rate performance, and image quality characteristics. The PET system is fully digital using APD-based detector modules with highly integrated electronics. The detector assembly consists of phoswich pairs of LYSO and LGSO crystals with dimensions of 2×2×14 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> having 7.5 cm axial and 10 cm transverse field-of-view (FOV). The spatial resolution and sensitivity were measured using a small <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">22</sup> Na point source at different positions in the scanner's FOV. The scatter fraction and count rate characteristics were measured using a mouse- and rat-sized phantoms fitted with <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">18</sup> F line source. The overall imaging capabilities of the scanner were assessed using the NEMA image quality phantom and laboratory animal studies. The NEMA-based radial and tangential spatial resolution ranged from 1.7 mm at the center of the FOV to 2.59 mm at a radial offset of 2.5 cm and from 1.85 mm at the center of the FOV to 1.76 mm at a radial offset of 2.5 cm, respectively. Iterative reconstruction improved the spatial resolution to 0.84 mm at the center of the FOV. The total absolute system sensitivity is 12.74% for an energy window of 250-650 keV. For the mouse-sized phantom, the peak noise equivalent count rate (NECR) is 183 kcps at 2.07 MBq/cc whereas the peak true count rate is 320 kcps at 2.5 MBq/cc with a scatter fraction of 19%. The rat-sized phantom had a scatter fraction of 31%, with a peak NECR of 67 kcps at 0.23 MBq/cc and a peak true count rate of 186 kcps at 0.27 MBq/cc. The average activity concentration and percentage standard deviation (%STD) are 126.97 kBq/ml and 7%, respectively. The performance of the LabPET-8™ scanner was characterized based on the NEMA NU 04 - 2008 standards. The all in all performance demonstrates that the LabPET-8™ system is able to produce high quality and highly contrasted images in a reasonable time, and as such it is well suited for preclinical molecular imaging-based research.