title: MR-diffusion weighted imaging of healthy liver parenchyma: repeatability and reproducibility of apparent diffusion coefficient measurement.
abstract: OBJECTIVE
  To compare repeatability and reproducibility of four different methods of apparent diffusion coefficient (ADC) evaluation of liver parenchyma. In fact, repeatability and reproducibility assessment is mandatory in quantitative evaluations, however, these have not been accurately investigated in liver MR-diffusion-weighted studies.
  
  
  METHODS
  Diffusion-weighted sequences, b-value = 0-1000 s/mm(2), were acquired on 30 healthy volunteers by a 1.5T scanner whose reliability has been validated by a phantom study. Four sampling methods, evaluating various parenchyma percentages by different-sized region-of-interests (ROIs), were compared by two observers: 70% and 30% of the volume, 4%-one-ROI-per-segment, and 4%-one-ROI-per-slice in the right-lobe. Ninety-five percent limits of agreement and intraclass correlation coefficient (ICC) were calculated.
  
  
  RESULTS
  Complete measurements on the left lobe could be obtained in less than half of patients. The 4%-one-ROI-per-slice and 4%-one-ROI-per-segment yielded lower mean values compared with 30-70% volume methods (1343-1373 versus 1463-1560.10(-6) mm(2)/s, respectively). Repeatability was acceptable (ICCs approximately 0.80) whereas reproducibility was low (ICCs <or= 0.45) for all methods. Averaging at least 3 measurements in middle-lower sections of the right lobe improved both repeatability (ICCs to >or=0.87) and reproducibility (ICCs to 0.82) for 30-70% V methods.
  
  
  CONCLUSIONS
  ADC measurements were repeatable but not reproducible in our study. Reproducibility could be improved by taking averages on the right lobe with large ROI methods. Studies on procedures that standardize ADC measurements using more than two observers are needed.
authors.affiliation: Department of Clinical Physiopathology, University of Florence, Azienda Ospedaliero-Universitaria Careggi, Florence, Italy. stefano.colagrande@unifi.it
authors.forename: Stefano
authors.initials: S
authors.lastname: Colagrande
authors.forename: Filippo
authors.initials: F
authors.lastname: Pasquinelli
authors.forename: Lorenzo Nicola
authors.initials: LN
authors.lastname: Mazzoni
authors.forename: Giacomo
authors.initials: G
authors.lastname: Belli
authors.forename: Gianni
authors.initials: G
authors.lastname: Virgili
mesh_terms: D000328:Adult; D000368:Aged; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D008099:Liver / Q000033:anatomy & histology / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D019047:Phantoms, Imaging; D011446:Prospective Studies; D011786:Quality Control; D015203:Reproducibility of Results; D014867:Water / Q000737:chemistry
chemical_list: D014867:Water