Zheng_2024_Eur.Radiol_34_4550

OBJECTIVES: To investigate the earliest optimal timing for positron emission tomography (PET) scans after (68)Ga-fibroblast activation protein inhibitor-04 ([(68)Ga]Ga-FAPI-04) injection. METHODS: This prospective study enrolled patients who underwent 60-min dynamic (68)Ga-FAPI-04 total-body PET/CT scans; the images were reconstructed at 10-min intervals (G0-10, G10-20, G20-30, G30-40, G40-50, and G50-60), and the [(68)Ga]Ga-FAPI-04 uptake patterns were evaluated. The standardised uptake value (SUV), liver signal-to-noise ratio (SNR), and lesion-to-background ratios (LBRs) for different time windows were calculated to evaluate image quality and lesion detectability. The period from 30 to 40 min was then split into overlapping 5-min intervals starting 1 min apart for further evaluation. G50-60 was considered the reference. RESULTS: A total of 30 patients with suspected malignant tumours were analysed. In the images reconstructed over 10-min intervals, longer acquisition times were associated with lower background uptake and better image quality. Some lesions could not be detected until G30-40. The lesion detection rate, uptake, and LBRs did not differ significantly among G30-40, G40-50, and G50-60 (all p > 0.05). The SUVmean and LBRs of primary tumours in the reconstructed images did not differ significantly among the 5-min intervals between 30 and 40 min; for metastatic and benign lesions, G34-39 and G35-40 showed significantly better SUVmean and LBR values than the other images. The G34-39 and G50-60 scans showed no significant differences in uptake, LBRs, or detection rates (all p > 0.05). CONCLUSION: The earliest optimal time to start acquisition was 34 min after injection of half-dose [(68)Ga]Ga-FAPI-04. CLINICAL RELEVANCE STATEMENT: This study evaluated (68)Ga-fibroblast activation protein inhibitor-04 ([(68)Ga]Ga-FAPI-04) uptake patterns by comparing the image quality and lesion detection rate with 60-min dynamic [(68)Ga]Ga-FAPI-04 total-body PET/CT scans and identified the earliest optimal scan time after [(68)Ga]Ga-FAPI-04 injection. KEY POINTS: A prospective single-centre study showed that the earliest optimal time point to start acquisition was 34 min after injection of half-dose [(68)Ga-fibroblast activation protein inhibitor-04 ((68)Ga]Ga-FAPI-04). There were statistically significant differences in standardised uptake value, lesion-to-background ratios, and lesion detectability between scans before and after 34 min from the injection of [(68)Ga]Ga-FAPI-04, but these values did not change further from 34 to 60 min after injection. With a reasonable acquisition time, the image quality could still meet diagnostic requirements.