Laurence Annet

Purpose: To assess whether hepatic fibrosis is associated with a restriction in the diffusion of water that can be analyzed with diffusion‐weighted MR imaging (DWI) of the liver.Materials and Methods: DWI was performed in 10 normal rats and 15 rats with liver fibrosis. Echo‐planar DWI was performed in the living rats at 1.5 T and repeated immediately after the animals were killed. Afterwards the livers were explanted, fixed in Bouin solution, and imaged with a DW spin‐echo sequence at 4.7 T. Fibrosis was quantified by densitometry on Sirius red‐stained histological sections.Results: In living rats the apparent diffusion coefficient (ADC) decreased with the severity of liver fibrosis (controls: 1535 ± 294 mm²/second; CCl₄ (5 weeks) 1129 ± 273 mm²/second; CCl₄ (9 weeks): 943 ± 132 mm²/second; P = 0.002). An inverse correlation between ADC and liver fibrosis volume density was observed (r = –0.712, P < 0.001). In contrast, these findings were not observed in the rats after they were killed or in the fixated livers.Conclusion: Decreased ADC correlated with increased liver fibrosis in living rats, but not after death. These results suggest that restricted water diffusion cannot be assessed by DWI in liver fibrosis. Other factors, such as a decrease of perfusion, may explain the decrease of the hepatic ADC measured in vivo in rats with liver fibrosis. J. Magn. Reson. Imaging 2007.

To prospectively use transesophageal magnetic resonance (MR) imaging to determine the morphologic and hemodynamic characteristics of esophageal varices.The study was approved by the ethics committee. All patients gave written informed consent. Forty-two patients (29 men, 13 women; mean age, 58 years +/- 11 [standard deviation]) with esophageal varices that were recently demonstrated at endoscopy were included in the study. MR imaging was performed by using a receiver probe that was placed in the esophagus. Black-blood T2-weighted MR images were obtained with cardiac triggering and navigator gating of the right hemidiaphragm. On these images, the maximal diameter, minimal diameter, and surface area of the largest esophageal varix were measured. Periesophageal and paraesophageal varices were recorded. A hemodynamic examination was performed in the last 21 patients to undergo MR imaging, which was used to obtain measurements of flow velocity and rate before and after intravenous injection of 50 mug of octreotide or a placebo. A Kruskal-Wallis test was used to assess differences in the diameter and surface area of the varices according to endoscopic grade. Hemodynamic changes observed after octreotide or placebo injection were compared by using an analysis of variance and a 95% confidence interval.Periesophageal varices were observed in 36 patients, and paraesophageal varices were observed in 32 patients. The minimal diameter, maximal diameter, and surface area of the esophageal varices at MR imaging differed significantly according to endoscopic grade (P < .001). In the periesophageal varices, the velocity and flow changes caused by octreotide differed significantly from those caused by the placebo (P < .001). A decrease in velocity (mean velocity change, -2.766 cm.sec(-1)) and flow (mean flow change, -0.455 mL.sec(-1)) was noted after octreotide injection, but no significant change in velocity (mean velocity change, 0.252 cm.sec(-1)) or flow (mean flow change, 0.018 mL.sec(-1)) was noted after placebo injection. The surface area of the varices did not change significantly after octreotide (mean change, -0.771 mm2) or placebo (mean change, -0.015 mm2) injection.Transesophageal MR imaging is a feasible method to assess the morphologic and hemodynamic characteristics of esophageal varices before and after pharmacologic treatment.