MR elastography to measure the effects of cancer and pathology fixation on prostate biomechanics, and comparison with T1, T2 and ADC

MRI is under evaluation for image-guided intervention for prostate cancer. The sensitivity and specificity of MRI parameters is determined via correlation with the gold-standard of histopathology. Whole-mount histopathology of prostatectomy specimens can be digitally registered to in vivo imaging for correlation. When biomechanical-based deformable registration is employed to account for deformation during histopathology processing, the ex vivo biomechanical properties are required. However, these properties are altered by pathology fixation, and vary with disease. Hence, this study employs magnetic resonance elastography (MRE) to measure ex vivo prostate biomechanical properties before and after fixation. A quasi-static MRE method was employed to measure high resolution maps of Young's modulus (E) before and after fixation of canine prostate and prostatectomy specimens (n = 4) from prostate cancer patients who had previously received radiation therapy. For comparison, T-1, T-2 and apparent diffusion coefficient (ADC) were measured in parallel. E (kPa) varied across clinical anatomy and for histopathology-identified tumor: peripheral zone: 99(+/-22), central gland: 48(+/-37), tumor: 85(+/-53), and increased consistently with fixation (factor of 11 +/- 5; p < 0.02). T-2 decreased consistently with fixation, while changes in T-1 and ADC were more complex and inconsistent. The biomechanics of the clinical prostate specimens varied greatly with fixation, and to a lesser extent with disease and anatomy. The data obtained will improve the precision of prostate pathology correlation, leading to more accurate disease detection and targeting.