Prostate diffusion imaging with distortion correction

Purpose: Diffusion imaging in the prostate is susceptible to distortion from B0 inhomogeneity. Distortion correction in prostate imaging is not routinely performed, resulting in diffusion images without accurate localization of tumors. We performed and evaluated distortion correction for diffusion imaging in the prostate. Materials and methods: 28 patients underwent pre-operative MRI (T2, Gadolinium perfusion, diffusion at b=800s/mm2). The restriction spectrum protocol parameters included b-values of 0, 800, 1500, and 4000s/mm2 in 30 directions for each nonzero b-value. To correct for distortion, forward and reverse trajectories were collected at b=0s/mm2. Distortion maps were generated to reflect the offset of the collected data versus the corrected data. Whole-mount histology was available for correlation. Results: Across the 27 patients evaluated (excluding one patient due to data collection error), the average root mean square distortion distance of the prostate was 3.1. mm (standard deviation, 2.2. mm; and maximum distortion, 12. mm). Conclusion: Improved localization of prostate cancer by MRI will allow better surgical planning, targeted biopsies and image-guided treatment therapies. Distortion distances of up to 12. mm due to standard diffusion imaging may grossly misdirect treatment decisions. Distortion correction for diffusion imaging in the prostate improves tumor localization.