Performance evaluation of the whole-body PET scanner ECAT EXACT HR + following the IEC standard

The performance parameters of the whole-body PET scanner ECAT EXACT HR⁺ (CTI/Siemens, Knoxville, TN) were determined following the standard proposed by the International Electrotechnical Commission (IEC). The tests were expanded by some measurements concerning the accuracy of the correction algorithms and the geometric fidelity of the reconstructed images. The scanner consists of 32 rings, each with 576 BGO detectors (4.05×4.39×30 mm³), covering an axial field-of-view of 15.5 cm and a patient port of 56.2 cm. The transaxial FWHM determined by a Gaussian fit in the 2D (3D) mode is 4.5 (4.3) mm at the center. It increases to 8.9 (8.3) mm radially and to 5.8 (5.2) mm tangentially at a radial distance of r=20 cm. The average axial resolution varies between 4.9 (4.1) mm FWHM at the center and 8.8 (8.1) mm at r=20 cm. The system sensitivity for unscattered true events is 5.85 (26.4) cps/Bq/ml (measured with a 20 cm cylinder). The 50% dead-time losses were reached for a true event count rate (including scatter) of 286 (500) kcps at an activity concentration of 74 (25) kBq/ml. The system scatter fraction is 0.24 (0.35). With the exception of the 3D attenuation correction algorithm, all correction algorithms work reliably. The results reveal that the ECAT EXACT HR⁺ has a good and nearly isotropic spatial resolution. Due to the small detector elements, however, it has a low slice sensitivity which is a limiting factor for image quality