title: Inter-reader differences in common carotid artery intima-media thickness: implications for cardiovascular risk assessment and vascular age determination.
abstract: OBJECTIVE
  Far wall common carotid artery intima-media thickness, a surrogate measure of atherosclerosis, requires the tracing of two carotid wall interfaces on ultrasound images: the lumen-intima and media-adventitia. Vascular age is derived from intima-media thickness measurements. We studied how tracing the wall interfaces affects intima-media thickness measurements and estimates of vascular age.
  
  
  METHODS
  Five readers made far-wall common carotid intima-media thickness measurements on 26 carotid artery images. Each reader traced lines at the lumen-intima and media-adventitia interfaces. An observer, blinded to reader identity and intima-media thickness values, reviewed the images and estimated the relative location of these lines compared to his judgment of the interface location: +1 for 1 pixel above the interface, 0 at the interface, and -1 if below. The significance of differences was evaluated by analysis of variance.
  
  
  RESULTS
  Mean intima-media thickness measurements ranged between 0.57 and 0.78 mm and showed significant differences between readers (P < .009). Differences in carotid intima-media thickness measurements made by the readers were significantly associated with the location of the media-adventitia interfaces (P < .0001) but not the lumen-intima interfaces (P = .07). The intima-media thickness differences corresponded to mean differences in estimated vascular age ranging from 14 to 21 years.
  
  
  CONCLUSIONS
  Inter-reader differences in common carotid intima-media thickness measurements are mostly seen for the media-adventitia wall interface and are detectable by an experienced observer. These inter-reader differences affect the use of intima-media thickness measurements for cardiovascular risk evaluation, can cause substantial errors in vascular age estimates, and might be correctable by performing replicate readings of standard image sets.
authors.affiliation: Department of Radiology, Tufts Medical Center, 800 Washington St, Box 299, Boston, MA 02111, USA. jpolak@tuftsmedicalcenter.org
authors.forename: Joseph F
authors.initials: JF
authors.lastname: Polak
authors.forename: Laurie C
authors.initials: LC
authors.lastname: Funk
authors.forename: Daniel H
authors.initials: DH
authors.lastname: O'Leary
mesh_terms: D000704:Analysis of Variance; D050197:Atherosclerosis / Q000000981:diagnostic imaging*; D002340:Carotid Artery Diseases / Q000000981:diagnostic imaging*; D017536:Carotid Artery, Common / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D015203:Reproducibility of Results; D018570:Risk Assessment; D017539:Tunica Intima / Q000000981:diagnostic imaging*; D017540:Tunica Media / Q000000981:diagnostic imaging*; D014463:Ultrasonography