Purpose Compare the value of imaging using positron 18 F-labeled fibroblast activation protein inhibitor-42 ( 18 F-FAPI-42) and 18 F-labeled deoxyglucose ( 18 F-FDG) for assessment of AKI. Procedures This study analyzed cancer patients who received 18 F-FAPI-42 and 18 F-FDG PET/CT imaging. Eight patients had AKI with bilateral ureteral obstruction (BUO), eight had BUO (CKD1–2) with no acute kidney disease (AKD), and eight had no ureteral obstruction (UO) with normal renal function. The average standardized uptake value (SUV ave ) of the renal parenchyma (RP-SUV ave ), the blood pool SUV ave (B- SUV ave ), SUV ave in the highest region of the renal collective system (RCS-SUV ave ), and the highest serum creatinine level (top SCr) were recorded. Results The 18 F-FAPI-42 and 18 F-FDG results showed that radiotracer of renal parenchyma was more concentrated in the AKI group than in the other two groups, whereas the RP-SUV ave from 18 F-FAPI-42 was higher than that from 18 F-FDG in the AKI group (all P  < 0.05). 18 F-FAPI-42 imaging in the AKI group showed uptake by the renal parenchyma with a diffuse increase, but very little radiotracer in the renal collecting system, similar to a “super kidney scan.” The renal parenchyma also had an increase of SUV ave , with accumulation of radiotracer in the renal collecting system. AKI was more severe when a patient had a “super kidney scan” in both kidneys ( P  < 0.05). The B-SUV ave level was higher in the AKI group than in the other two groups in 18 F-FAPI-42 (both P  < 0.05). Conclusions 18 F-FAPI-42 imaging had higher RP-SUV ave than 18 F-FDG imaging in cancer patients who had BUO with AKI. An increased renal parenchyma uptake in both kidneys and low radiotracer distribution in the collecting system suggest more severe AKI.