PERFORMANCE EVALUATION OF A WHOLE-BODY PET SCANNER USING THE NEMA PROTOCOL

This study evaluates the performance of the newly developed high-resol ution whole-body PET scanner ECAT EXACT HR+. Methods: The scanner cons ists of four rings of 72 bismuth germanate block detectors each, cover ing an axial field of view of 15.5 cm with a patient port of 56.2 cm. A single block detector is divided into an 8 x 8 matrix, giving a tota l of 32 rings with 576 detectors each, The dimensions of a single dete ctor element are 4.39 x 4.05 x 30 mm(3). The scanner is equipped with extendable tungsten septa for two-dimensional two-dimensional measurem ents, as well as with three Ge-68 line sources for transmission scans and daily quality control, The spatial resolution, scatter fraction, c ount rate, sensitivity, uniformity and accuracy of the implemented cor rection algorithms were evaluated after the National Electrical Manufa cturers Association protocol using the standard acquisition parameters , Results: The transaxial resolution in the two-dimensional mode is 4. 3 mm (4.4 mm) in the center and increases to 4.7 mm (4.8 mm) tangentia l and to 8.3 mm (8.0 mm) radial at a distance of r = 20 cm from the ce nter, The axial slice width measured in the two-dimensional mode varie s between 4.2 and 6.6 mm FWHM over the transaxial field of view, In th e three-dimensional mode the average axial resolution varies between 4 .1 mm FWHM in the center and 7.8 mm at r = 20 cm. The scatter fraction is 17.1% (32.5%) for a lower energy discriminator level of 350 keV. T he maximum true event count rate of 263 (345) kcps was measured at an activity concentration of 142 (26.9) kBq/ml. The total system sensitiv ity for true events is 5.7 (27.7) cps/Bq/ml. From the uniformity measu rements, we obtained a volume variance of 3.9% (5.0%) and a system var iance of 1.6% (1.7%). The implemented three-dimensional scatter correc tion algorithm reveals very favorable properties, whereas the three-di mensional attenuation correction yields slightly inaccurate results in low- and high-density regions. Conclusion: The ECAT EXACT HR+ has an excellent, nearly isotropic spatial resolution, which is advantageous for brain and small animal studies, While the relatively low slice sen sitivity may hamper the capability for performing fast dynamic two-dim ensional studies, the scanner offers a sufficient sensitivity and coun t rate capacity for fully three-dimensional whole-body imaging.