In Vivo Quantification of Water Diffusion, Stiffness, and Tissue Fluidity in Benign Prostatic Hyperplasia and Prostate Cancer

Abstract

OBJECTIVES: Water diffusion, tissue stiffness, and viscosity characterize the biophysical behavior of tumors. However, little is known about how these parameters correlate in prostate cancer (PCa). Therefore, we paired tomoelastography of the prostate with diffusion-sensitive magnetic resonance imaging for the quantitative mapping of biophysical parameters in benign prostatic hyperplasia (BPH) and PCa. MATERIALS AND METHODS: Multifrequency magnetic resonance imaging elastography with tomoelastography processing was performed at 60, 70, and 80 Hz using externally placed compressed-air drivers. Shear-wave speed (SWS) and loss angle (φ) were analyzed as surrogate markers of stiffness and viscosity-related fluidity in the normal peripheral zone (PZ), hyperplastic transition zone (TZ), which is consistent with BPH, and PCa lesions. The SWS and φ were correlated with the normalized apparent diffusion coefficient (nADC). RESULTS: Thirty-nine men (median age/range, 67/49-88 years), 25 with BPH and 14 with biopsy-proven PCa, were prospectively enrolled in this institutional review board-approved study. The SWS in PCa (3.1 ± 0.6 m/s) was higher than in TZ (2.8 ± 0.3 m/s, P = 0.004) or tended to be higher than in PZ (2.8 ± 0.4 m/s, P = 0.025). Similarly, φ in PCa (1.1 ± 0.1 rad) was higher than in TZ (0.9 ± 0.2 m/s, P < 0.001) and PZ (0.9 ± 0.1 rad, P < 0.001), whereas nADC in PCa (1.3 ± 0.3) was lower than in TZ (2.2 ± 0.4, P < 0.001) and PZ (3.1 ± 0.7, P < 0.001). Pooled nADC was inversely correlated with φ (R = -0.6, P < 0.001) but not with SWS. TZ and PZ only differed in nADC (P < 0.001) but not in viscoelastic properties. Diagnostic differentiation of PCa from normal prostate tissues, as assessed by area under the curve greater than 0.9, was feasible using nADC and φ but not SWS. CONCLUSIONS: Tomoelastography provides quantitative maps of tissue mechanical parameters of the prostate. Prostate cancer is characterized by stiff tissue properties and reduced water diffusion, whereas, at the same time, tissue fluidity is increased, suggesting greater mechanical friction inside the lesion. This biophysical signature correlates with known histopathological features including increased cell density and fibrous protein accumulation.

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