MR Elastography of Dynamic Postprandial Hepatic Stiffness Augmentation in Chronic Liver Disease

Introduction: Mesenteric blood flow increases markedly in response to the presence of food in the gut, with portal blood flow increasing up to 100% or more postprandially, compared with the fasting state (1). If the impedance to portal outflow remained constant, the increased flow would result in an increase in portal venous pressure. Yet, in normal humans, the portal venous pressure remains stable after eating, due to a reflex decrease in hepatic sinusoidal resistance (1). In contrast, patients with cirrhosis typically experience a 30-40% increase in hepatic venous pressure gradient (HVPG) after eating (2-3). It is thought that mechanical distortion of the intrahepatic vasculature caused by fibrosis impairs the autoregulatory mechanism (4). The repeated episodes of transient portal hypertension after eating are thought to accelerate the development of portal-systemic varices (3). Increased portal pressure may cause stretching of hepatic parenchyma and there is now evidence that stretching of hepatic stellate cells is instrumental in the progression of hepatic fibrosis (5). MR Elastography (MRE) is an MRI-based technique for quantitatively assessing the mechanical properties of soft tissues by visualization propagating shear waves (6). Multiple studies have shown that MRE can demonstrate increased liver tissue stiffness in patients with hepatic fibrosis and that the stiffness increases systematically with the stage of fibrosis (7-8). The goal of this research was to measure hepatic stiffness in volunteers and in patients with hepatic fibrosis before and after a test meal which is known to increase mesenteric blood flow. We hypothesized that hepatic stiffness would increase postprandially in patients with hepatic fibrosis, presumably due transiently increased portal pressure, whereas this response would not be observed in normal volunteers. If the hypothesis is confirmed, it would provide preliminary evidence that hepatic stiffness reflects portal venous pressure in addition to the presence of fibrosis and the comparison of preand postprandial liver stiffness would provide a new potentially useful parameter for characterizing hepatic fibrosis. Fig.1 Methods: All experiments were implemented on a 1.5 T whole-body GE imager (Signa, GE Healthcare, Milwaukee, WI, USA). We have previously compiled pre and postprandial hepatic stiffness measurements in 3 normal subjects. At the time that this abstract was written, 3 additional normal volunteers and 7 patients with biopsyproven hepatic fibrosis were evaluated with MRE (further accrual is ongoing). An initial MRE examination was performed during standardized conditions in the morning after overnight fasting. The imaging procedure lasted 10~15 minutes. Immediately thereafter the subject consumed 470 ml liquid test meal (Ensure plus, 1.5 kcal/ml, Ross products division, Abbott laboratories, Columbus, Ohio) that consists of protein, carbohydrates, fat, vitamins and minerals, with an energy content of 700 kcal. Thirty minutes after finishing this meal, a second identical examination was performed. The imaging protocol included wave image acquisition with a gradient echo based MRE sequence with gradient moment nulling in two selected axial planes with identical imaging parameters as shown in reference (8). Total imaging time for the MRE acquisitions was 64 seconds. Identical parameters, positioning, analysis ROI’s were used for both the preand postprandial acquisitions.