Quantitative graphical analysis of simultaneous dynamic PET/MRI for assessment of prostate cancer

Purpose: Dynamic FDG imaging for prostate cancer characterization is limited by generally small size and low uptake in prostate tumors. Our aim in this pilot study was to explore feasibility of simultaneous PET/MRI to guide localization of prostate lesions for dynamic FDG analysis using a graphical approach. Methods: Three patients with biopsy-proven prostate cancer underwent simultaneous FDG PET/MRI, incorporating dynamic prostate imaging. Histology and multiparametric MRI findingswere used to localize tumors, which in turn guided identification of tumors on FDG images. Regions of interest were manually placed on tumor and benign prostate tissue. Blood activity was extracted from a region of interest placed on the femoral artery on PET images. FDG data were analyzed by graphical analysis using the influx constant K_i (Patlak analysis)when FDG binding seemed irreversible and distribution volume V_T (reversible graphical analysis) when FDG binding seemed reversible given the presence of washout. Results: Given inherent coregistration, simultaneous acquisition facilitated use of MRI data to localize small lesions on PET and subsequent graphical analysis in all cases. In 2 cases with irreversible binding, tumor had higher K_i than benign using Patlak analysis (0.023 vs 0.006 and 0.019 vs 0.008 mL/cm³ per minute). In 1 case appearing reversible, tumor had higher V_T than benign using reversible graphical analysis (0.68 vs 0.52 mL/cm³). Conclusions: Simultaneous PET/MRI allows localization of small prostate tumors for dynamic PET analysis. By taking advantage of inclusion of the femoral arteries in the FOV, we applied advanced PET data analysis methods beyond conventional static measures and without blood sampling.