title: Magnetic resonance imaging of the liver: apparent diffusion coefficients from multiexponential analysis of b values greater than 50 s/mm2 do not respond to caloric intake despite increased portal-venous blood flow.
abstract: OBJECTIVE
  The purpose of this study was to measure potential changes of the apparent diffusion coefficient (ADC) in diffusion-weighted imaging of the liver before and after caloric challenge in correlation to the induced changes in portal vein flow.
  
  
  METHODS
  The study was approved by the local ethics committee. Each of 10 healthy volunteers underwent 4 measurements in a 1.5-T whole-body magnetic resonance scanner on 2 different days: a first scan after fasting for at least 8 hours and a second scan 30 minutes after intake of a standardized caloric either a protein- or carbohydrate-rich meal. Diffusion-weighted spin-echo echo-planar magnetic resonance images were acquired at b values of 0, 50, 150, 250, 500, 750, and 1000 s/mm. In addition, portal vein flow was quantified with 2-dimensional phase-contrast imaging (velocity encoding parallel to flow direction, 60 cm/s). Mean ADC values for regions of interest in 3 different slices were measured from b50 to b250 and from b500 to b1000 images.
  
  
  RESULTS
  Carbohydrate- and protein-rich food intake both resulted in a substantial increase in the portal vein flow (fasting state, 638.6 ± 202.3 mL/min; after protein intake, 1322 ± 266.8; after carbohydrate intake, 1767 ± 421.6). The signal decay with increasingly strong diffusion weighting (b values from 0 to 1000 s/mm2) exhibited a triexponential characteristic, implying fast, intermediate, and slow-moving water-molecule proton-spin ensembles in the liver parenchyma. Mean ADC for high b values (b500-b1000) after fasting was 0.93 ± 0.09 × 10 mm/s; that after protein intake, 0.93 ± 0.11 × 10; and that after carbohydrate intake, 0.93 ± 0.08 × 10. For intermediate b values (b50-b250), the signal-decay constants were 1.27 ± 0.14 × 10 mm/s, 1.28 ± 0.15 × 10, and 1.31 ± 0.09 × 10, respectively. There was no statistically significant difference between fasting and caloric challenge.
  
  
  CONCLUSIONS
  The postprandial increase in portal vein flow is not accompanied by a change of liver parenchymal ADC values. In clinical diffusion imaging, patients may be scanned without prescan food-intake preparations. To minimize interference of perfusion effects, liver-tissue molecular water diffusion should be quantified using high b values (≥500 s/mm) only.
authors.affiliation: From the *Department of Diagnostic and Interventional Radiology, University Hospital of Zürich; †Department of Medicine, Stadtspital Triemli, Zürich, Switzerland; and ‡Section of Experimental Radiology, Department of Diagnostic and Interventional Radiology, University Hospital of Tübingen, Tübingen, Germany.
authors.forename: Shila
authors.initials: S
authors.lastname: Pazahr
authors.forename: Daniel
authors.initials: D
authors.lastname: Nanz
authors.forename: Cristina
authors.initials: C
authors.lastname: Rossi
authors.forename: Natalie
authors.initials: N
authors.lastname: Chuck
authors.forename: Ingo
authors.initials: I
authors.lastname: Stenger
authors.forename: Moritz C
authors.initials: MC
authors.lastname: Wurnig
authors.forename: Fritz
authors.initials: F
authors.lastname: Schick
authors.forename: Andreas
authors.initials: A
authors.lastname: Boss
mesh_terms: D000328:Adult; D000465:Algorithms; D001783:Blood Flow Velocity / Q000502:physiology; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D002149:Energy Intake / Q000502:physiology*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D008099:Liver / Q000033:anatomy & histology* / Q000098:blood supply / Q000502:physiology*; D008102:Liver Circulation / Q000502:physiology; D008297:Male; D011169:Portal Vein / Q000033:anatomy & histology* / Q000502:physiology*; D019518:Postprandial Period / Q000502:physiology*; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D055815:Young Adult