Abstract
574
Introduction: Fully-digital PET cameras have been introduced with a new technology involving SiPM solid state detectors, instead of photomultiplier tubes, and providing marked enhancements in timing resolution. This technology has the potential to enhance most parameters of image quality but direct comparisons with last-generation analogic PET cameras are lacking. The aim of this study was to compare the performances of the Vereos digital PET camera (Philips®), determined according to NEMA NU-2 2012 standards, with those provided by a last-generation analogic PET, the Ingenuity TF (Philips®).
Methods: Spatial resolution, count rate performances, scatter fraction, sensitivity and image contrast parameters were determined on both cameras by using the dedicated phantoms and the recording and reconstruction PET parameters involved in the NEMA NU 2-2012 standards. Timing resolution was additionally evaluated with a Noise-Equivalent-Count-Rate (NECR) measurement.
Results: Mean spatial resolution values were 4.00, 4.44 and 5.13 mm at respectively, 1, 10 and 20 cm from the center of the field of view for Vereos, whereas the corresponding values were 4.75 mm, 4.93 mm and 5.49 mm for Ingenuity. Count rate performance, scatter fraction, sensitivity and image contrast parameters were also significantly enhanced for Vereos, as compared with Ingenuity (see Table), with the contrast recovery coefficient being dramatically higher with Vereos, especially for the hot spheres of the smallest 10-mm diameter (in % of the real contrast: 62.8 vs. 38.1). Effective sensitivity, which combines absolute sensitivity and signal to noise ratio gain from time of flight information: was 1) equivalent between Vereos and Ingenuity for the recording of low-activity concentrations (≍ 7 MBq/mL) (22.1 vs. 18.3 kcps/kBq for an object with a diameter of 20 cm) and 2) exhibited a marked deterioration for higher activities with Ingenuity but not with Vereos.
Conclusions: All parameters of image quality, determined with the NEMA standards, are significantly enhanced with the Vereos digital PET, when compared with a last-generation analogic PET. This enhancement is particularly remarkable: 1) for the contrast of the smallest hot foci and thus for their expected detectability in vivo and 2) for the stability in the effective count sensitivity over a wide range of recorded activities, a property that is required for dynamic kinetics PET analyses.