Sensitivity of multifrequency magnetic resonance elastography and diffusion-weighted imaging to cellular and stromal integrity of liver tissue.

Microscopic structural alterations of liver tissue induced by freeze-thaw cycles give rise to palpable property changes. However, the underlying damage to tissue architecture is difficult to quantify histologically, and published data on macroscopic changes in biophysical properties are sparse. To better understand the influence of hepatic cells and stroma on global biophysical parameters, we studied rat liver specimens freshly taken (within 30min after death) and treated by freeze-thaw cycles overnight at either -20 degrees C or -80 degrees C using diffusion-weighted imaging (DWI) and multifrequency magnetic resonance elastography (MRE) performed at 0.5T in a tabletop MRE scanner. Tissue structure was analyzed histologically and rheologic data were analyzed using fractional order derivatives conceptualized by a called spring-pot component that interpolates between pure elastic and viscous responses. Overnight freezing and thawing induced membrane disruptions and cell detachment in the space of Disse, resulting in a markedly lower shear modulus mu and apparent diffusion coefficient (ADC) (mu[-20 degrees C]=1.23+/-0.73kPa, mu[-80 degrees C]=0.66+/-0.75kPa; ADC[-20 degrees C]=0.649+/-0.028mum(2)/s, ADC[-80 degrees C]=0.626+/-0.025mum(2)/s) compared to normal tissue (mu=9.92+/-3.30kPa, ADC=0.770+/-0.023mum(2)/s, all p<0.001). Furthermore, we analyzed the springpot-powerlaw coefficient and observed a reduction in -20 degrees C specimens (0.22+/-0.14) compared to native tissue (0.40+/-0.10, p=0.033) and -80 degrees C specimens (0.54+/-0.22, p=0.002), that correlated with histological observations of sinusoidal dilation and collagen distortion within the space of Disse. Overall, the results suggest that shear modulus and water diffusion in liver tissue markedly decrease due to cell membrane degradation and cell detachment while viscosity-related properties appear to be more sensitive to distorted stromal and microvascular architecture.