Reliability of measurements of a reflection coefficient index to indicate spinal bone strength on adolescents with idiopathic scoliosis (AIS): a pilot study

Purpose To investigate the test-retest, intra- and inter-rater reliabilities of an ultrasound (US) reflection coefficient (RC) index measured in a lumbar vertebra to reflect bone strength on children with AIS. Methods Fifty-eight participants (47F; 11M) were scanned by an US imager in standing position. Twenty-four were scanned twice for a test-retest study. The RC index measures the US signal reflected from L5 to indicate bone strength. Five measurements were obtained using three different methods: (i) the maximum RC (MRC) values on the left and right sides, (ii) the average RC (ARC) values on left and right sides, and (iii) the combined average RC (CARC) from both sides. Only rater 1 measured the 24 repeated US scans once. Raters 1 and 2 measured the RC index twice on all 58 images in 1 week apart. The intraclass correlation coefficient ICC [3, 1] for test-retest and ICC [2, 1] for intra- and inter-rater reliabilities as well as the standard error of measurements (SEM) were reported. Results The means of scan 1 versus scan 2 were 0.16 +/- 0.08 versus 0.16 +/- 0.07 for left-MRC, 0.17 +/- 0.11 versus 0.18 +/- 0.11 for right-MRC, 0.08 +/- 0.04 versus 0.09 +/- 0.04 for left-ARC, 0.09 +/- 0.04 versus 0.09 +/- 0.05 for right-ARC and 0.08 +/- 0.04 versus 0.09 +/- 0.03 for CARC and all ICC[3, 1] >= 0.77. Among these 5 approaches, the CARC provided the best intra-rater and inter-rater reliabilities with ICC [2, 1] >= 0.84 and SEM <= 0.01. Conclusions The RC index could be measured repeatably and reliably. The high RC value may reduce the risk of progression of scoliosis.