title: Shear wave elastography for liver stiffness measurement in clinical sonographic examinations: evaluation of intraobserver reproducibility, technical failure, and unreliable stiffness measurements.
abstract: OBJECTIVE
  The purpose of this study was to determine the optimal minimum number of liver stiffness measurements on shear wave elastography (SWE) and to evaluate the frequency of technical failures and unreliable stiffness measurements and the intraobserver reproducibility of SWE.
  
  
  METHODS
  This retrospective study was approved by our Institutional Review Board, and informed consent was waived. From August 2011 to January 2013, 540 patients underwent abdominal sonography, including SWE. In 86 patients (group 1), the minimum number of examinations was determined by comparing the intraclass correlation coefficient (ICC) of subsets of the first 2 to 14 measurements with that from 15 measurements. In 454 patients (group 2), 2 SWE sessions were performed in the right lobe within 1 day. Technical failure was defined as when no or little signal was obtained in the elastogram during the first 5 acquisitions; unreliable SWE results were defined as when the interquartile range/median liver stiffness value exceeded 30%. Intraobserver reproducibility was assessed using ICCs and Bland-Altman plots.
  
  
  RESULTS
  In group 1, the ICCs did not significantly increase after the first 6 measurements. In group 2, there were technical failures and unreliable results in 47 patients (10.35%) and 74 patients (16.29%), respectively. In 407 patients, after excluding technical failures, there was no significant difference in the median liver stiffness values between the 2 sessions (6.95 versus 6.86 kPa; P > .05). The overall intraobserver reproducibility was excellent (ICC, 0.95).
  
  
  CONCLUSIONS
  In this study, the optimal minimum number of SWE measurements was 6, and SWE using 6 measurements showed excellent intraobserver reproducibility.
authors.affiliation: Department of Radiology and Institute of Radiation Medicine, Seoul National University College of Medicine, 101 Daehak-ro, Jongno-gu, Seoul 110-744, Korea. jmsh@snu.ac.kr.
authors.forename: Jeong Hee
authors.initials: JH
authors.lastname: Yoon
authors.forename: Jeong Min
authors.initials: JM
authors.lastname: Lee
authors.forename: Joon Koo
authors.initials: JK
authors.lastname: Han
authors.forename: Byung Ihn
authors.initials: BI
authors.lastname: Choi
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D055119:Elastic Modulus; D054459:Elasticity Imaging Techniques / Q000379:methods*; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008099:Liver / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D008103:Liver Cirrhosis / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D033081:Shear Strength; D055815:Young Adult
keywords: elastography; gastrointestinal ultrasound; reproducibility; shear wave elastography; ultrasound-based elastography