Purpose-To determine the relationship between parameters measured from luminal water imaging (LWI), a new MRI T 2 mapping technique, and the corresponding tissue composition in prostate.Material and Methods-17 patients with prostate cancer were examined with a 3D multi-echo spin echo sequence at 3T prior to undergoing radical prostatectomy. Maps of seven MR parameters, called N, T 2-short , T 2-long , A short , A long , geometric mean T 2 time (gmT 2 ), and luminal water fraction (LWF), were generated using non-negative least squares (NNLS) analysis of the T 2 decay curves. MR parametric maps were correlated to digitized whole-mount histology sections. Percentage area of tissue components, including luminal space, nuclei, and cytoplasm plus stroma, was measured on the histology sections by using color-based image segmentation. Spearman's rank correlation test was used to evaluate the correlation between MR parameters and the corresponding tissue components, with particular attention paid to the correlation between LWF and percentage area of luminal space.Results-N, T 2-short , A long , gmT 2 , and LWF showed significant correlation (P<0.05) with percentage area of luminal space and stroma plus cytoplasm. T 2-short , and gmT 2 also showed significant correlation (P<0.05) with percentage area of nuclei. Overall, the strongest correlation was observed between LWF and luminal space (Spearman's coefficient of rank correlation=0.75, p < 0.001).