JNMT: Retrograde filling of urinary bladder improves quality of FDG PET/CT

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Retrograde filling reduces urinary FDG activity and improves the quality of FDG PET/CT images for pelvic tumor interpretation and is recommended to assess bladder wall lesions and malignancies in other pelvic locations, according to a study published this month in the Journal of Nuclear Medicine Technology.

High FDG activity in the urinary bladder makes interpretation difficult and, in many cases, obscures or obliterates pelvic lesions. Eliminating high FDG activity in the urinary tract is important in the diagnosis of pelvic tumors using PET.

The feasibility of selective pelvic PET/CT with retrograde bladder irrigation in evaluating pelvic pathologies was assessed by Ana Maria Garcia Vicente, MD, and colleagues from General University Hospital, Ciudad Real, Spain in the study.

The study included 38 patients (22 women) with PET/CT, with a mean age of 61 years and a neoplastic background (most of them of pelvic pathology). The most prevalent findings were 14 urothelial, 12 gynecologic, and seven rectal cancers. All but three patients had undergone previous surgical procedures or radio or chemotherapy and 22 patients had suspected pelvic pathology on a previous diagnostic CT scan.

All patients underwent a standard PET/CT protocol (from head to upper thighs) 60 minutes after the intravenous injection of 370 MBq of FDG. Additional delayed pelvic PET/CT images were acquired by Vincente and colleagues with a filled-bladder technique, within two hours of the standard acquisition.

A lesion was classified as malignant if it showed a standardized uptake value greater than 2.5 or, in the case of subcentimetric lesions, any uptake greater than background activity that persisted or increased on delayed pelvic imaging, according to Vincente and colleagues. All lesions were evaluated histologically or by clinical follow-up.

The sensitivity, specificity, positive predictive value, negative predictive value and accuracy of PET/CT in the pelvic assessment were 100 percent, 83 percent, 74 percent, 100 percent and 76 percent, respectively, according to Vincente and colleagues.

The retrograde filling reduced the interference with physiologic urinary accumulation of FDG in patients with possible pelvic lesions; no false-negative results were documented. “In 18F-FDG PET studies, retrograde filling of the urinary bladder is recommended to assess bladder wall lesions and malignancies in other pelvic locations,” concluded Vincente and colleagues.