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

The development of Long Axial Field-of-View positron emission tomography combined with computed tomography warrants reconsideration of the administered activity required for clinical imaging. This study investigated the relationship between body size, administered activity (¹⁸F), and image quality (IQ) 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 h, 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 SNR²showed a nonlinear correlation with the noise equivalent count rate, whereas SNR²had 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^-1body weight. However, achieving robust clinical diagnostic quality-particularly for low-contrast lesions-at these activity levels requires further clinical investigation. Utilising these ultralow activity concentrations requires extending the scan duration to compensate for IQ, especially when examining obese patients.