Study of the correlation of IVIM parameter maps with FDG PET

Abstract

Intravoxel incoherent motion (IVIM) is a magnetic resonance technique to quantify the influence of microscopic perfusion-related motion and differentiate it from pure molecular diffusion. IVIM has the potential to provide valuable clinical information about microcirculation in the capillary network of healthy tissues as well as malignant tumors. Our goal was to study the correlation of IVIM parameter maps with concurrent FDG-PET data, in view of their potential use in clinical PET/MR protocols. MethodsData were acquired from ten oncology patients using a tri-modality setup and fitted with a bi-exponential model. The fitting was first solved in the least squares sense and then again using iteratively reweighted least squares. The resulting parameter maps were compared with PET FDG data by an experienced radiologist. ResultsAmong the pathologies encountered in our patient population were lesions of the liver, spleen, kidney, abdominal wall, prostate and cervix. The qualitative comparison with PET confirmed that IVIM maps provide complementary information about functional inhomogeneity within the tumor. Visual inspection by experienced radiologists showed improved reading of tumor heterogeneity in six of our ten patients when considering FDG uptake together with perfusion fraction maps. The use of a large set of b values was instrumental for data validation and outlier rejection. Robust fitting was shown to increase the accuracy of the fit in 70% of the voxels, leading to average changes of IVIM parametric maps: perfusion fraction f∈[3.9×10–3, 4.7×10−2], diffusion coefficient D ∈[−1.2×10−4, −3.0×10−6] and pseudo-diffusion coefficient D*∈[−1.6×10−1, −9.2×10−3]. ConclusionsThe results suggest that IVIM imaging could be successfully integrated in clinical PET/MR protocols. Clinical validation shows the complementarity of obtained parameter maps with concurrent FDG PET data. Ongoing work is aimed at determining the optimal acquisition protocol depending on the motion properties of the target area.