title: Effects of microperfusion in hepatic diffusion weighted imaging.
abstract: OBJECTIVE
  Clinical 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.
  
  
  METHODS
  Nineteen 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 (D (slow)), microperfusion (D (fast)) and the respective fractions (f (slow/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.
  
  
  RESULTS
  Median mono-exponentially fitted ADCs varied significantly (P < 0.001) between 1.107 and 1.423 × 10(-3) mm(2)/s for the five regions. Bi-exponential fitted D(slow) varied between 0.923 and 1.062 × 10(-3) mm(2)/s without significant differences (P = 0.140). D (fast) varied significantly, between 17.8 and 46.8 × 10(-3) mm(2)/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.
  
  
  CONCLUSIONS
  ADCs of normal liver tissue are significantly dependent on the measurement location because of substantial microperfusion contamination; therefore the bi-exponential model should be used.
  
  
  CONCLUSIONS
  Diffusion weighted MR imaging helps clinicians to differentiate tumours by diffusion properties. Fast moving water molecules experience microperfusion, slow molecules diffusion. Hepatic diffusion should be measured by bi-exponential models to avoid microperfusion contamination. Mono-exponential models are contaminated with microperfusion, resulting in apparent regional diffusion differences. Bi-exponential models are necessary to measure diffusion and microperfusion in the liver.
authors.affiliation: Center for Medical Imaging - North East Netherlands, Department of Radiology, University of Groningen, University Medical Center Groningen, EB44, PO Box 30001, 9700 RB, Groningen, The Netherlands. h.dijkstra01@umcg.nl
authors.forename: Hildebrand
authors.initials: H
authors.lastname: Dijkstra
authors.forename: Paul
authors.initials: P
authors.lastname: Baron
authors.forename: Peter
authors.initials: P
authors.lastname: Kappert
authors.forename: Matthijs
authors.initials: M
authors.lastname: Oudkerk
authors.forename: Paul E
authors.initials: PE
authors.lastname: Sijens
mesh_terms: D000328:Adult; D000465:Algorithms; D016477:Artifacts; D001783:Blood Flow Velocity / Q000502:physiology; D003198:Computer Simulation; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008099:Liver / Q000033:anatomy & histology* / Q000502:physiology*; D008102:Liver Circulation / Q000502:physiology*; D008297:Male; D008833:Microcirculation / Q000502:physiology*; D008875:Middle Aged; D008954:Models, Biological; D015203:Reproducibility of Results; D055425:Respiratory-Gated Imaging Techniques / Q000379:methods; D012680:Sensitivity and Specificity
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