title: Reproducibility of ultrasonographically determined intima-media thickness is dependent on arterial wall thickness. The Tromsø Study.
abstract: OBJECTIVE
  We compared the reproducibility of B-mode ultrasonographic measurements of intima-media thickness (IMT) in various segments of the right carotid artery and examined whether measurement error was associated with IMT or cardiovascular risk factor levels.
  
  
  METHODS
  In 1994/1995 a total of 6676 participants in the Tromsø Study underwent ultrasound examination of common carotid artery IMT. Reproducibility of measurements was assessed by inviting 111 participants to a second ultrasound scan within 3 weeks of the first scan. On each occasion the subjects were examined by three sonographers.
  
  
  RESULTS
  The mean between-observer absolute differences in IMT in the far wall of the bifurcation and the near and far walls of the common carotid-artery were 0.15, 0.10, and 0.08 mm, respectively. The corresponding within-observer differences were 0.15, 0.10, and 0.06 mm, respectively. Approximately 70% to 80% of total measurement variability was due to differences among sonographers; the rest was attributable to within-reader variability. Measurement error increased significantly with increasing IMT: the increase was more than twofold over the range of measurements. Cardiovascular risk factor levels were not associated with measurement variability when we controlled for IMT.
  
  
  CONCLUSIONS
  We conclude that B-mode ultrasound provides reproducible estimates of the IMT in both the near and far walls of the carotid artery. Although measurement error is generally small, it increases proportionally with the level of IMT.
authors.affiliation: Institute of Community Medicine, University of Tromsø, Norway. eva.stensland-bugge@ism.uit.no
authors.forename: E
authors.initials: E
authors.lastname: Stensland-Bugge
authors.forename: K H
authors.initials: KH
authors.lastname: Bønaa
authors.forename: O
authors.initials: O
authors.lastname: Joakimsen
mesh_terms: D000368:Aged; D002318:Cardiovascular Diseases; D017536:Carotid Artery, Common / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D015203:Reproducibility of Results; D012307:Risk Factors; D017539:Tunica Intima / Q000000981:diagnostic imaging*; D017540:Tunica Media / Q000000981:diagnostic imaging*; D014463:Ultrasonography