Objective:

To determine the optimal scanning time point for

68

Ga-fibroblast activation protein inhibitor (FAPI)-04 positron emission tomography (PET)/computed tomography (CT) imaging and to evaluate the differences in the pharmacokinetics of

68

Ga-FAPI-04 between tumors and obstructive inflammation.

Methods:

A retrospective analysis of clinical data from patients who underwent

68

Ga-FAPI-04 PET/CT imaging due to abdominal tumors in The First Affiliated Hospital of Naval Medical University between January and November 2021 was conducted. The maximum standard uptake value (SUV

max

)

tumor-to-background ratio (TBR)

and signal-to-noise ratio (SNR) were compared across different time points using the Kruskal-Wallis H test

while the retention index (RI) for tumors and obstructive inflammation was analyzed using the Mann-Whitney

U

test.

Results:

A total of 31 patients were included in this study. The SUV max values for tumor lesions at 15 min

1 h

and 2 h were 8.52 (4.18–18.4)

8.59 (4.69–13.8)

and 7.64 (3.22–21.0)

respectively

with corresponding TBR values of 4.22 (1.87–17.76)

4.67 (2.20–29.05)

and 4.30 (2.48–35.20). Although the SUV

max

and TBR at 1 h were higher than those at other time points

the differences were not statistically significant (

P

＞0.05). The SNR values at 15 min

1 h

and 2 h were 6.41 (2.45–8.24)

5.0 (1.68–5.57)

and 3.02 (1.39–6.97)

showing significant differences (H value: 51.691

P

＜0.001)

with the highest SNR observed at 15 min. Furthermore

the RI for tumors at 15 min and 1 h was significantly higher than that for obstructive inflammation (-0.195–0.415

vs

-0.422–0.115)

with a statistically significant difference (

P

=0.018).

Conclusion:

The image SNR is highest at 15 min after the inj

ection of

68

Ga-FAP1-04

making it a suitable time point for routine clinical scanning. Additionally

the RI at 15 min and 1 h is beneficial for distinguishing between tumors and obstructive inflammation.