Quantitative Graphical Analysis of Simultaneous Dynamic PET/MRI For Assessment of Prostate Cancer

Abstract

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 is 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 multi-parametric MRI findings were used to localize tumors, which in turn guided identification of tumors on FDG images. Regions-of-interest (ROIs) were manually placed on tumor and benign prostate tissue. Blood activity was extracted from an ROI placed on the femoral artery on PET images. FDG data was analyzed by graphical analysis using the influx constant Ki (Patlak analysis) when FDG binding appeared irreversible, and distribution volume VT [(reversible graphical analysis (RGA)] when FDG binding appeared reversible given 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 two cases with irreversible binding, tumor had higher Ki than benign using Patlak analysis (0.023 vs. 0.006 and 0.019 vs. 0.008 mL/cm3/min). In one case appearing reversible, tumor had higher VT than benign using RGA (0.68 vs. 0.52 mL/cm3). Conclusion Simultaneous PET/MRI allows localization of small prostate tumors for dynamic PET analysis. By taking of advantage of inclusion of the femoral arteries in the field-of-view, we applied advanced PET data analysis methods beyond conventional static measures and without blood sampling.

18F-fluoro-2-deoxy-d-glucose (FDG) uptake. What are we looking at?

“…Nevertheless, Sokoloff et al observed a measurable 2DG washout from rat brain, whose radioactivity content decreased with a half-life of 7.7 ± 1.6 and 9.7 ± 2.6 h in gray and white matter, respectively [2]. Similarly, a slow, yet measurable, tracer release has been subsequently confirmed from several cancers, suggesting the possible presence of a G6Pase function in tissues of different origin [28,29]. This slow washout has been largely disregarded according to the consideration of its negligible interference on imaging performed within 1 h after tracer injection.…”

Slice profile effects on quantitative analysis of hyperpolarized pyruvate

“…Vascular extravasation (k ve ) was assumed to occur at a rate of 0.0066 s −1 , volume fractions of the vascular (1 − v e ) and extravascular space (v e ) were assumed to be 0.0372 and 0.9628, respectively. These perfusion values represent the average prostate cancer values reported in literature [32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] and simulations were also performed at the higher and lower ends of these ranges (k ve [0.0045 − 0.0219] and v e [0.9015 − 0.9915]), which only had minor impacts on the measured k pl errors (data not shown). The AIF was modeled as a gamma variate 49 following:…”

Comparison of time curves from dynamic 18F-fluciclovine positron emission tomography and dynamic contrast-enhanced magnetic resonance imaging for primary prostate carcinomas

“…In the initial perfusion phase contrast agents and radioactive labelled tracers act as blood-pool agents, whereas tissue distribution and uptake depend on the chemical and biological properties of these agents. A prostate cancer study with dynamic 18 F-fluorodeoxyglucose (FDG) PET/MR revealed a possible additional value of dynamic PET [12] . There are some studies with dynamic FACBC PET/CT [13] , [14] , [15] , [16] , [17] , [18] , but only two have explored the early dynamic phase [16] , [17] .…”