Microscopic Diffusion Anisotropy in Formalin Fixed Prostate Tissue

Diffusion tensor microimaging at 16.4 T with 40µm isotropic voxels was to investigate anisotropic water diffusion in prostate tissue at spatial resolution approaching the cellular scale. Nine normal tissue and two cancer samples were collected from the peripheral zone of six formalin fixed radical prostatectomy specimens. Fibromuscular stromal tissue exhibited microscopic diffusion anisotropy (mean fractional anisotropy range 0.47-0.66) significantly higher (P < 0.01, Student t-test) than in epithelium-containing voxels (mean fractional anisotropy range 0.31-0.54) in six of the seven normal tissue samples in which both compartments could be measured. Fiber tracking in both normal and cancer tissue samples demonstrated heterogeneity of principle stromal fiber directions which would be expected to give rise to low ensemble anisotropy at the scale of imaging voxels in vivo. It is concluded that measures of ensemble fractional anisotropy at the scale of imaging voxels in vivo are unlikely to provide clinically useful discrimination between cancer and normal tissue.