title: Reproducibility of aortic intima-media thickness in infants using edge-detection software and manual caliper measurements.
abstract: BACKGROUND
  Aortic intima-media thickness measured by transabdominal ultrasound (aIMT) is an intermediate phenotype of cardiovascular risk. We aimed to (1) investigate the reproducibility of aIMT in a population-derived cohort of infants; (2) establish the distribution of aIMT in early infancy; (3) compare measurement by edge-detection software to that by manual sonographic calipers; and (4) assess the effect of individual and environmental variables on image quality.
  
  
  METHODS
  Participants were term infants recruited to a population-derived birth cohort study. Transabdominal ultrasound was performed at six weeks of age by one of two trained operators. Thirty participants had ultrasounds performed by both operators on the same day. Data were collected on environmental (infant sleeping, presence of a sibling, use of sucrose, timing during study visit) and individual (post-conception age, weight, gender) variables. Two readers assessed image quality and measured aIMT by edge-detection software and a subset by manual sonographic calipers. Measurements were repeated by the same reader and between readers to obtain intra-observer and inter-observer reliability.
  
  
  RESULTS
  Aortic IMT was measured successfully using edge-detection in 814 infants, and 290 of these infants also had aIMT measured using manual sonographic calipers. The intra-reader intra-class correlation (ICC) (n = 20) was 0.90 (95% CI 0.76, 0.96), mean difference 1.5 μm (95% LOA -39, 59). The between reader ICC using edge-detection (n = 20) was 0.92 (95% CI 0.82, 0.97) mean difference 2 μm (95% LOA -45.0, 49.0) and with manual caliper measurement (n = 290) the ICC was 0.84 (95% CI 0.80, 0.87) mean difference 5 μm (95% LOA -51.8, 61.8). Edge-detection measurements were greater than those from manual sonographic calipers (mean aIMT 618 μm (50) versus mean aIMT 563 μm (49) respectively; p < 0.001, mean difference 44 μm, 95% LOA -54, 142). With the exception of infant crying (p = 0.001), no associations were observed between individual and environmental variables and image quality.
  
  
  CONCLUSIONS
  In a population-derived cohort of term infants, aIMT measurement has a high level of intra and inter-reader reproducibility. Measurement of aIMT using edge-detection software gives higher inter-reader ICC than manual sonographic calipers. Image quality is not substantially affected by individual and environmental factors.
authors.forename: Kate
authors.initials: K
authors.lastname: McCloskey
authors.forename: Anne-Louise
authors.initials: AL
authors.lastname: Ponsonby
authors.forename: John B
authors.initials: JB
authors.lastname: Carlin
authors.forename: Kim
authors.initials: K
authors.lastname: Jachno
authors.forename: Michael
authors.initials: M
authors.lastname: Cheung
authors.forename: Michael R
authors.initials: MR
authors.lastname: Skilton
authors.forename: Jane
authors.initials: J
authors.lastname: Koleff
authors.affiliation: Murdoch Childrens Research Institute, Royal Children's Hospital, Parkville, Australia. peter.vuillermin@deakin.edu.au.
authors.forename: Peter
authors.initials: P
authors.lastname: Vuillermin
authors.forename: David
authors.initials: D
authors.lastname: Burgner
mesh_terms: D001011:Aorta / Q000000981:diagnostic imaging*; D050197:Atherosclerosis / Q000000981:diagnostic imaging; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods / Q000592:standards / Q000706:statistics & numerical data; D007223:Infant; D008297:Male; D015588:Observer Variation; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects / Q000000981:diagnostic imaging; D015203:Reproducibility of Results; D012984:Software; D017539:Tunica Intima / Q000000981:diagnostic imaging; D017540:Tunica Media / Q000000981:diagnostic imaging; D014463:Ultrasonography / Q000379:methods* / Q000592:standards* / Q000706:statistics & numerical data