MR elastography of prostate cancer: quantitative comparison with histopathology and repeatability of methods.

The purpose of this work was to assess trans-perineal prostate magnetic resonance elastography (MRE) for (1) repeatability in phantoms/volunteers and (2) diagnostic power as correlated with histopathology in prostate cancer patients. The three-dimensional (3D) displacement field was obtained using a fractionally encoded gradient echo sequence using a custom-made transducer. The repeatability of the method was assessed based on three repeat studies and by changing the driving frequency by 3% in studies on a phantom and six healthy volunteers. Subsequently, 11 patients were examined with MRE prior to radical prostatectomy. The areas under the receiver operating characteristic curves were calculated using a windowed voxel-to-voxel approach by comparing the 2D registered slides, masked with the Gleason score. For the repeatability study, the average intraclass correlation coefficient for elasticity images was 99% for repeat phantom studies, 98% for 6Hz phantom studies, 95% for volunteer repeat studies with 2min acquisition time, 82% for +/- 2Hz volunteer studies with 2min acquisition time and 73% for repeat volunteer studies with 8min acquisition time. For the patient study, the average elasticity was 8.2 +/- 1.7kPa in the prostate capsule, 7.5 +/- 1.9kPa in the peripheral zone (PZ), 9.7 +/- 3.0kPa in the central gland (CG) and 9.0 +/- 3.4kPa in the transition zone. In the patient study, cancerous tissue with Gleason score at least 3+3 was significantly (p<0.05) different from normal tissue in 10 out of 11 cases with tumors in the PZ, and 6 out of 9 cases with tumors in the CG. However, the overall case-averaged area under the curve was 0.72 in the PZ and 0.67 in the CG. Cancerous tissue was not always stiffer than normal tissue. The inversion algorithm was sensitive to (i) vibration amplitude and displacement nodes and (ii) misalignment of the 3D wave field due to subject movement. Copyright (c) 2014 John Wiley & Sons, Ltd.