Is Water Diffusion Isotropic in the Cirrhotic Liver? A Study with Diffusion-weighted Imaging at 3.0 Tesla

Rationale and Objectives: Water molecule motion has been shown to be isotropic in healthy liver as assessed by diffusion-weighted imaging (DWI). The purpose of this study was to investigate whether this assumption is still valid in the cirrhotic liver. Materials and Methods: Twelve cirrhotic patients and 12 controls underwent DWI on a 3.0T-system. We used an echo-planar sequence independently applying unidirectional motion-probing gradients along read-(x), phase-(y), and slice-(z) directions, respectively. Liver apparent diffusion coefficient (ADC) and perfusion fraction (f) were calculated along each gradient direction, based on two b-values sets (0-400 and 0-800 seconds/mm ²). Measurement was repeated at two different axial slices of the liver. Results: No significant difference among x, y, and z- ADC (and f) of the liver was found within controls and cirrhotic patients (P > .01), regardless of the set of b-values or the slice of measurement. ADC was lower in cirrhotic patients than in controls (difference of 0.24-0.39 × 10 ^-3 mm ²/seconds at b = 800 seconds/mm ²; P = .000-0139). Perfusion fraction f was lower in cirrhotics than in controls, irrespective of the b-values set or the slice of measurement (difference of 0.05-0.15; P < .0001-0885). Conclusion: The liver shows isotropic water diffusion in cirrhotics, despite fibrotic distortion leading to decreased ADC as compared to controls. Our results emphasize that the correlation between parenchymal changes in liver fibrosis and the ADC estimate remains an elusive goal based on the state-of-the-art DWI technique.