Performance comparison of two commercial small animal PET scanners: ClearPETT and rPET-1T

It is usually difficult to compare different designs of Positron Emission Tomography (PET) small-animal scanners because of the disparity of measurements protocols. In this work we compare two commercial PET scanners installed at CIEMAT (Madrid, Spain): the ClearPET and the rPET-1, using an assessment procedure that fulfilled the recommendations of the new NEMA NU 4-2008 standard to evaluate small animal PET systems, including spatial resolution, sensitivity, scatter fraction and count losses studies. The scanners evaluated have significant geometrical differences, like the axial field of view (110 mm on ClearPET versus 45.6 mm on rPET-1), the configuration of the detectors (one pair of planar blocks on rPET-1, versus whole ring detectors on ClearPET) and the use of an axial shift between ClearPET module detectors. Our experiments showed a FWHM (FOV center, averaged over the three axes) of 1.98 mm for the rPET-1 and 2.15 mm for the ClearPET, with a small variation across the transverse axis on both scanners (≪1 mm). The absolute sensitivity was 1.0% per detector pair for rPET-1 and 4.7% for ClearPET. Regarding count losses studies, the obtained peak NEC rate is 73.4 kcps at 0.51 MBq/ml for the ClearPET and 29.2 kcps at 1.35 MBq/ml for the rPET-1, considering a NEMA mouse-like phantom.