Effects of count rate performance on image quality in an LAFOV PET/CT system

The development of Long Axial Field-of-View (LAFOV) positron emission tomography (PET) combined with computed tomography (CT) warrants reconsideration of the administered activity required for clinical imaging. This study investigated the relationship between body size, administered activity (18F), and image quality using two patient-like phantoms representing normal (78.5 kg) and obese (194.3 kg) body profiles. The phantoms were scanned in selected five-minute periods within a total duration of 27 and 21 hours, respectively, following the decay of the activity. Analysis of the trues, scatter, and randoms demonstrated a close to linear propagation of the trues with activity up to a point where saturation was reached. The normal body profile phantom achieved higher signal-to-noise ratios (SNRs), reaching system saturation at a lower activity (680 MBq) than the large phantom, representing the obese body profile (970 MBq). The SNR2 showed a nonlinear correlation with the noise equivalent count rate (NECR), whereas SNR2 had a linear correlation with the trues. The study demonstrated the count rate capabilities up to and beyond the saturation limit. Furthermore, we illustrated the possibilities of scanning patients with ultralow dose administration in the range of 0.03-0.07 MBq/kg body weight. However, achieving robust clinical diagnostic quality - particularly for low-contrast lesions - at these activity levels requires further clinical investigation. Utilizing these ultralow activity concentrations requires extending the scan duration to compensate for image quality, especially when examining obese patients.