Simulation of ultra-low dose 68Ga-FAPI total-body PET/CT imaging

1155 Objectives: To explore the feasibility of ultra-low-dose imaging for oncological patients by exploiting the high detection sensitivity of the state-of-the-art PET/CT scanner with 194-cm-long axial field-of-view (uEXPLORER, United Imaging Healthcare). Methods: This study enrolled a total of 25 oncological patients (age 54.88±13.82 years, weight 58.21±9.02 kg) who underwent 10-min total-body 68Ga-FAPI PET/CT examinations with an administered dose of 1.85 MBq/kg. By truncating the list-mode PET data (600 s, 300 s, 180 s, 60 s, 40 s, and 20 s) to decreasing statistic count density, we simulated 10-min 68Ga-FAPI PET imaging with a various dose of 1.85 MBq/kg, 0.93 MBq/kg, 0.56 MBq/kg, 0.19 MBq/kg, 0.12 MBq/kg, and 0.06 MBq/kg, respectively. In this study, the reconstruction method was clinically widespread time-of-flight ordered-subsets expectation maximization with point-spread function (OSEM-TOF-PSF). To evaluate image quality, we systematically analyzed objective and subjective results. For objective studies, the metrics, for instance, the SUVmax at lesions, the SUVmean and SD at muscle, and the lesion-to-background ratio (LBR), have been documented and compared between the PET images with the different low dose subsets. For subjective studies, two radiologists applied Likert 5-point scales method to assess the low-dose PET images from the aspects of the overall image quality, the lesions conspicuity, and the image noise. Besides, the lesion detectability has been tested by comparison the total number of suspected lesions, where the full-dose PET image served as a reference for localizing the suspected lesions. Results: The SUVmax and SD at muscle increase gradually as the dose reduces (Figure 1). There are significant differences between the different low-dose subsets (p < 0.05). Nevertheless, the SUVmean at muscle is relatively stable. For the SUVmax at lesions, there is no significant difference between different low-dose subsets, revealing a stable LBR. In the case of 1/30-standard dose, the subjective evaluation indicated that the lesion conspicuity has an arguable diagnostic level. Surprisingly, a total of 208 lesions have been completely reidentified in such ultra-low dose. Conclusions: The feasibility of ultra-low-dose total-body 68Ga-FAPI PET/CT imaging has been proved in oncological patients by utilizing uEXPLORER. With taking into account of lesion detectability and image quality, we suggest that the clinical total-body 68Ga-FAPI PET/CT examinations could be performed with 1/10 of the standard administered dose (0.19 MBq/kg) and acquisition time of 10 min or other equivalent conditions with a time-activity product of 1.9 MBq/kg∙min/bed.