Characterizing the Diffusion Properties of Prostate Tissue Using Paired MR Microscopy and Multidimensional Diffusion MRI

ABSTRACT Purpose To characterize the diffusion properties of prostate epithelium and stroma in benign tissue and cancer. Methods Paired MR microscopy (20 μm) and multidimensional diffusion MRI (dMRI) (160 μm, b = 1000–2000 s/mm 2 , ∆ = 15–120 ms) were performed at 16.4 T on 17 fixed prostate tissue samples (14× benign, 2× Gleason 3 + 3, 1× Gleason 4 + 4). MR microscopy images were used to segment epithelial, stromal, and luminal components in each sample. For each dMRI sequence, aggregate epithelial and stromal signal contributions in benign tissue were estimated using a linear epithelium‐stroma‐lumen signal model. Four diffusion signal models were fit to these aggregate signals. Quality‐of‐fit was assessed using the small‐sample corrected Akaike Information Criterion (AICc). Voxel‐wise model fitting was also performed to compare parameter estimates in benign tissue and cancer. Results Aggregate dMRI signal estimates for both epithelium and stroma were best described by the Ball + Sphere model (lowest AICc). A higher sphere fraction (0.278 vs. 0.175) and lower ball‐compartment diffusivity (0.611 vs. 0.943 μm 2 /ms) were estimated for epithelium compared to stroma. The ADC model provided the worst fit in both cases (highest AICc). For Gleason 3 + 3 cancer, ADC and Ball + Sphere parameter estimates were consistent with the values found for benign epithelium and stroma; however, raised sphere fraction estimates were seen in Gleason 4 + 4 cancer. Conclusion Direction‐averaged diffusion in fixed prostate epithelium and stroma is well described by the Ball + Sphere model. The diffusion properties of epithelium in Gleason 3 + 3 cancer and benign tissue appear to be similar; however, a marked increase to the volume fraction of restricted water was found for Gleason 4 + 4 epithelium.