Background and objective 18F-fluorodeoxyglucose (FDG) is physiologically excreted into urine, which can obscure intravesical lesions and complicate the detection of bladder cancer on FDG positron emission tomography-computed tomography (PET/CT). This study aimed to evaluate the standardized uptake values (SUVs) of bladder cancer on FDG PET/CT and to assess the effects of reader experience and PET threshold modification on tumor detectability. Methods We retrospectively identified 15 patients with histologically confirmed bladder cancer who underwent MRI and PET/CT before surgery between April 2003 and December 2020. A nuclear medicine physician performed quantitative analyses using PET, CT, and PET/CT fusion images, as well as pelvic MRI, to measure the maximum standardized uptake value (SUVmax) of tumors and intravesical urine. Four radiologists independently reviewed axial PET, CT, and PET/CT fusion images. In the first session, readers were blinded to clinical information and used a fixed display threshold. In the second session, readers were informed of the presence of bladder cancer and permitted to adjust PET display thresholds. Results Among the 15 patients (median age: 75 years; 12 men), the median tumor size was 35 mm (range: 7-105 mm). Median SUVmax was 19.9 for tumors and 11.5 for urine. In blinded readings, less-experienced readers detected tumors in 60% of cases, whereas experienced readers detected 66.6%. After adjusting the threshold with increased cancer awareness, detection rates improved to 100% and 93.3%, respectively. Conclusions Bladder cancers demonstrated relatively high FDG uptake on PET/CT; however, lesion conspicuity varied depending on urinary FDG excretion. Quantitative assessment of tumor-to-urine metabolic contrast using the contrast rate (CR) and adjustment of PET display thresholds improved lesion detection in this cohort. These findings suggest that optimization of image interpretation strategies may enhance the diagnostic utility of PET/CT for intravesical tumor evaluation, although further studies with larger patient populations are required to validate these findings.
Yoshida et al. (Wed,) studied this question.