title: Design and validation of a novel method to measure cross-sectional area of neck muscles included during routine MR brain volume imaging.
abstract: BACKGROUND
  Low muscle mass secondary to disease and ageing is an important cause of excess mortality and morbidity. Many studies include a MR brain scan but no peripheral measure of muscle mass. We developed a technique to measure posterior neck muscle cross-sectional area (CSA) on volumetric MR brain scans enabling brain and muscle size to be measured simultaneously.
  
  
  METHODS
  We performed four studies to develop and test: feasibility, inter-rater reliability, repeatability and external validity. We used T1-weighted MR brain imaging from young and older subjects, obtained on different scanners, and collected mid-thigh MR data.
  
  
  RESULTS
  After developing the technique and demonstrating feasibility, we tested it for inter-rater reliability in 40 subjects. Intraclass correlation coefficients (ICC) between raters were 0.99 (95% confidence intervals (CI) 0.98-1.00) for the combined group (trapezius, splenius and semispinalis), 0.92 (CI 0.85-0.96) for obliquus and 0.92 (CI 0.85-0.96) for sternocleidomastoid. The first unrotated principal component explained 72.2% of total neck muscle CSA variance and correlated positively with both right (r = 0.52, p = .001) and left (r = 0.50, p = .002) grip strength. The 14 subjects in the repeatability study had had two MR brain scans on three different scanners. The ICC for between scanner variation for total neck muscle CSA was high at 0.94 (CI 0.86-0.98). The ICCs for within scanner variations were also high, with values of 0.95 (CI 0.86-0.98), 0.97 (CI 0.92-0.99) and 0.96 (CI 0.86-0.99) for the three scanners. The external validity study found a correlation coefficient for total thigh CSA and total neck CSA of 0.88.
  
  
  CONCLUSIONS
  We present a feasible, valid and reliable method for measuring neck muscle CSA on T1-weighted MR brain scans. Larger studies are needed to validate and apply our technique with subjects differing in age, ethnicity and geographical location.
authors.affiliation: Geriatric Medicine Unit, Centre for Cognitive Ageing and Cognitive Epidemiology, University of Edinburgh, Edinburgh, United Kingdom. ahmkilgour@doctors.org.uk
authors.forename: Alixe H M
authors.initials: AH
authors.lastname: Kilgour
authors.forename: Deepak
authors.initials: D
authors.lastname: Subedi
authors.forename: Calum D
authors.initials: CD
authors.lastname: Gray
authors.forename: Ian J
authors.initials: IJ
authors.lastname: Deary
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Lawrie
authors.forename: Joanna M
authors.initials: JM
authors.lastname: Wardlaw
authors.forename: John M
authors.initials: JM
authors.lastname: Starr
mesh_terms: D000328:Adult; D000368:Aged; D019412:Anatomy, Cross-Sectional / Q000379:methods*; D001921:Brain / Q000033:anatomy & histology*; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009334:Neck Muscles / Q000033:anatomy & histology*; D015588:Observer Variation; D009929:Organ Size; D015203:Reproducibility of Results