title: Liver apparent diffusion coefficient repeatability with individually predetermined optimal cardiac timing and artifact elimination by signal filtering.
abstract: OBJECTIVE
  To prospectively assess liver ADC (apparent diffusion coefficient) repeatability from cardiac-triggered diffusion-weighted images obtained with an individually predetermined optimal cardiac time window minimizing cardiac-related effects and to evaluate a signal filtering method aimed at artifact elimination.
  
  
  METHODS
  After Institutional Review Board approval and written informed consent, eight healthy volunteers underwent four repetitions of respiratory-triggered diffusion-weighted sequences (3T, b: 0,150,500 s/mm(2) ) without (RTnoCT, 51 sec) and with individually optimized cardiac triggering (RTCT, 306 sec). The optimal cardiac delay was individually predetermined using a 5-second breath-hold sequence. Monoexponential liver ADC and left-to-right-liver ADC ratio were computed from region of interest (ROI) signal measurements (two independent readers). A filtering method, excluding signal intensities lower than the mean intensity at fixed b-value, provided ADC recalculation. Limits-of-agreement (LOAs) from 95% confidence intervals for differences across the four repetitions provided the variability range.
  
  
  RESULTS
  For Reader 1 (Reader 2), left-to-right-liver ADC ratios were significantly higher in RTnoCT 1.51 (1.52) than in RTCT 1.12 (1.15), P = 0.012 (P = 0.017). Respectively for RTnoCT and RTCT: left liver LOAs were ±835 (±775), ± 315 (±369) 10(-6) mm(2) /s; right liver LOAs were ±392 (±445), ± 172 (±140) 10(-6) mm(2) /s: LOAs were larger in the left than in the right lobe (both P < 0.001). After filtering, left liver ADC LOAs narrowed to ±650 (±367) 10(-6) mm(2) /s, P = 0.17 (P < 0.001); ± 152 (±208) 10(-6) mm(2) /s (both P < 0.002) and left-to-right-liver ADC ratio decreased to 1.28 (1.20), P = 0.017 (P = 0.012); 1.09 (1.08), P = 0.106 (P = 0.105).
  
  
  CONCLUSIONS
  Compared to noncardiac-triggered acquisitions, individually optimized cardiac-triggered acquisitions improved ADC repeatability in both liver lobes and reduced ADC differences between left and right liver. Left liver ADC repeatability was further improved after signal filtering.
authors.affiliation: MRI Clinics, Department of Radiology, Hopital Erasme, Universite Libre de Bruxelles, Bruxelles, Belgium.
authors.forename: Thierry
authors.initials: T
authors.lastname: Metens
authors.affiliation: MRI Clinics, Department of Radiology, Hopital Erasme, Universite Libre de Bruxelles, Bruxelles, Belgium.
authors.forename: Julie
authors.initials: J
authors.lastname: Absil
authors.affiliation: Philips Healthcare, Bruxelles, Belgium.
authors.forename: Vincent
authors.initials: V
authors.lastname: Denolin
authors.affiliation: MRI Clinics, Department of Radiology, Hopital Erasme, Universite Libre de Bruxelles, Bruxelles, Belgium.
authors.forename: Maria Antonietta
authors.initials: MA
authors.lastname: Bali
authors.affiliation: MRI Clinics, Department of Radiology, Hopital Erasme, Universite Libre de Bruxelles, Bruxelles, Belgium.
authors.forename: Celso
authors.initials: C
authors.lastname: Matos
mesh_terms: D000328:Adult; D016477:Artifacts; D038524:Diffusion Magnetic Resonance Imaging; D005260:Female; D064368:Healthy Volunteers; D006321:Heart / Q000000981:diagnostic imaging*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008099:Liver / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D011446:Prospective Studies; D015203:Reproducibility of Results; D012815:Signal Processing, Computer-Assisted
keywords: cardiac triggering; diffusion-weighted MRI; liver; quantification; repeatability; reproducibility