We investigated whether the time between synthesis and injection and the resulting decrease in specific activity affects the normal organ and tumor uptake of the PSMA ligand, 18 F-rhPSMA-7.3, in patients with prostate cancer. Methods: The biodistribution of 18 F-rhPSMA-7.3 on PET/CT scans performed with a high specific activity (median=178.9MBq/µg, n=42) and a low specific activity (median=19.3MBq/µg, n=42) were compared. Results: Tracer uptake by the parotid gland, submandibular gland and spleen was moderately, but significantly lower in the "low specific activity" group than in the "high specific activity" group (median SUV mean 16.7 vs. 19.2; 18.1 vs. 22.3, and 7.8 vs. 9.6, respectively). No other statistically significant differences were found for normal organs or tumor lesions. Conclusion: A 10-fold decrease in specific activity has only minor effects on the biodistribution of 18 F-rhPSMA-7.3. These findings suggest that 18 F-labeled PSMA ligands can be centrally produced and shipped to PET clinics in a similar way to 18 Ffluorodeoxyglucose.

We present a 78-year-old man with suspicion of prostate cancer due to a PSA of 200 ng/mL, who underwent 18F-PSMA-1007 (prostate specific membrane antigen) PET/CT for primary staging. Besides heterogeneous uptake to the prostate, an increased PSMA uptake in the cecum was observed, located in the thickened cecal wall with suspicion of a secondary malignancy. Colonoscopic biopsy followed by hemicolectomy confirmed the diagnosis of colon adenocarcinoma. This case demonstrates the importance of bioptic workup of suspicious findings on PSMA PET/CT, which are unlikely to be related to prostate cancer as PSMA ligand uptake is not exclusively prostate cancer specific.

Although 99mTc red blood cell (RBC) scintigraphy is a very specific method to differentiate a hemangioma from other hepatic masses, several cases of false-positive 99mTc RBC scintigraphy have been previously reported throughout the literature. We report an additional case that presented in a 15-month-old boy with hepatoblastoma showing increased labeled RBC activity mimicking hemangioma.