title: Relevance of b-values in evaluating liver fibrosis: a study in healthy and cirrhotic subjects using two single-shot spin-echo echo-planar diffusion-weighted sequences.
abstract: OBJECTIVE
  To investigate the relevance of increasing b-values in evaluating liver fibrosis through the agreement of two diffusion-weighted (DW) sequences.
  
  
  METHODS
  A total of 29 cirrhotic patients and 29 healthy volunteers were studied on a 1.5T system. Two single-shot spin-echo echo-planar sequences were acquired using sets of increasing b-values: 0, 150, 250, and 400 seconds/mm(2) (first sequence: DW1a) and 0, 150, 250, 400, 600, and 800 seconds/mm(2) (second sequence: DW2a). Apparent diffusion coefficients (ADCs) of the hepatic parenchyma were calculated on ADC maps. Noise-scaled single-point ADCs were calculated for each sequence from b = 400 seconds/mm(2).
  
  
  RESULTS
  ADCs resulted significantly lower in cirrhotic patients compared to controls using both DW1a (mean 1.14 +/- 0.20 x 10(-3)mm(2)/second vs. 1.54 +/- 0.12 x 10(-3)mm(2)/second; P < 0.0001) and DW2a (mean 0.91 +/- 0.18 x 10(-3)mm(2)/second vs. 1.04 +/- 0.18 x 10(-3)mm(2)/second; P = 0.0089). DW1 and DW2, respectively significantly differed in diagnostic performance at receiver operating characteristic (ROC) curve analysis (P = 0.003), showing AUCs of 0.93 (sensitivity 89.7%, specificity 100%) and 0.73 (sensitivity 62.1%, specificity 79.3%), respectively. Noise-scaled single-point ADCs showed a progressive convergence to similar values in cirrhotic and healthy livers at b = 800 seconds/mm(2) (1.12 +/- 0.27 x 10(-3)mm(2)/second vs. 1.13 +/- 0.17 x 10(-3)mm(2)/second).
  
  
  CONCLUSIONS
  A DW sequence is accurate in assessing liver fibrosis using intermediate (400 seconds/mm(2)) rather than high (800 seconds/mm(2)) maximum b-values, but after proper recalculation of ADCs the effects of perfusion rather than diffusion should be considered responsible for the higher accuracy at lower b-values.
authors.affiliation: Institute of Radiology, Department of Medical and Morphological Research, University of Udine, Udine, Italy. rgirometti@sirm.org
authors.forename: Rossano
authors.initials: R
authors.lastname: Girometti
authors.forename: Alessandro
authors.initials: A
authors.lastname: Furlan
authors.forename: Gennaro
authors.initials: G
authors.lastname: Esposito
authors.forename: Massimo
authors.initials: M
authors.lastname: Bazzocchi
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Como
authors.forename: Franca
authors.initials: F
authors.lastname: Soldano
authors.forename: Miriam
authors.initials: M
authors.lastname: Isola
authors.forename: Pierluigi
authors.initials: P
authors.lastname: Toniutto
authors.forename: Chiara
authors.initials: C
authors.lastname: Zuiani
mesh_terms: D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D019540:Area Under Curve; D016022:Case-Control Studies; D003287:Contrast Media; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D017352:Echo-Planar Imaging; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D008103:Liver Cirrhosis / Q000473:pathology*; D008297:Male; D008536:Meglumine / Q000031:analogs & derivatives; D008875:Middle Aged; D009942:Organometallic Compounds; D019047:Phantoms, Imaging; D011446:Prospective Studies; D012372:ROC Curve; D012680:Sensitivity and Specificity
chemical_list: D003287:Contrast Media; D009942:Organometallic Compounds; C064572:gadobenic acid; D008536:Meglumine