Effects of microperfusion in hepatic diffusion weighted imaging

Abstract

ObjectiveClinical hepatic diffusion weighted imaging (DWI) generally relies on mono-exponential diffusion. The aim was to demonstrate that mono-exponential diffusion in the liver is contaminated by microperfusion and that the bi-exponential model is required.MethodsNineteen fasting healthy volunteers were examined with DWI (seven b-values) using fat suppression and respiratory triggering (1.5 T). Five different regions in the liver were analysed regarding the mono-exponentially fitted apparent diffusion coefficient (ADC), and the bi-exponential model: molecular diffusion (Dslow), microperfusion (Dfast) and the respective fractions (fslow/fast). Data were compared using ANOVA and Kruskal–Wallis tests. Simulations were performed by repeating our data analyses, using just the DWI series acquired with b-values approximating those of previous studies.ResultsMedian mono-exponentially fitted ADCs varied significantly (P < 0.001) between 1.107 and 1.423 × 10−3 mm2/s for the five regions. Bi-exponential fitted Dslow varied between 0.923 and 1.062 × 10−3 mm2/s without significant differences (P = 0.140). Dfast varied significantly, between 17.8 and 46.8 × 10−3 mm2/s (P < 0.001). F-tests showed that the diffusion data fitted the bi-exponential model significantly better than the mono-exponential model (F > 21.4, P < 0.010). These results were confirmed by the simulations.ConclusionADCs of normal liver tissue are significantly dependent on the measurement location because of substantial microperfusion contamination; therefore the bi-exponential model should be used.Key PointsDiffusion weighted MR imaging helps clinicians to differentiate tumours by diffusion propertiesFast moving water molecules experience microperfusion, slow molecules diffusionHepatic diffusion should be measured by bi-exponential models to avoid microperfusion contaminationMono-exponential models are contaminated with microperfusion, resulting in apparent regional diffusion differencesBi-exponential models are necessary to measure diffusion and microperfusion in the liver

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