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Precision of Lunar Achilles+ bone quality measurements: time dependency and multiple machine use in field studies

¹ Tufts University, Gerald J and Dorothy R Friedman School of Nutrition Science and Policy, 150 Harrison Avenue, Boston, MA 02111, ² GE Healthcare, 726 Heartland Trail, Madison, WI 53717, ³ Division of Public Health and Family Medicine, Tufts University School of Medicine, 136 Harrison Avenue, Boston, MA 02111, USA

View larger version (15K): [in this window] [in a new window]   Figure 1. Schematic diagram of the study design. Two Lunar Achilles+ ultrasound machines were assessed over different time periods. Six same-day trials (D1 and D2s) took place over the period of 1 year. Each trial day consisted of six consecutive measurements: three on Lunar1 (L1) and three on Lunar2 (L2). These within-day measurements took place at the beginning or end of a week, such that there were three week-long trials. The three testing weeks were scheduled at 6 month intervals yielding two 6-month examination periods. Finally, these two 6-month time periods constituted one 1-year test period. Subjects were scheduled for testing on as many D1s and D2s as possible throughout this 1-year testing period. n = number of measurements during each trial period. Trial days are shaded in grey.

View larger version (20K): [in this window] [in a new window]   Figure 2. Box-plots representing all 258 measurements of the stiffness index subdivided by subject and Lunar Achilles+ QUS machine. Dotted box-plots represent measurements from Lunar1; open box-plots represent measurements from Lunar2. Subject no. corresponds to subject no. in Table 1.

View larger version (24K): [in this window] [in a new window]   Figure 3. Bland–Altman plot of time-dependent differences between Lunar1 and Lunar2 relative to the average stiffness index. 129 measurements were taken on each machine. Solid and dashed lines represent the mean difference±2 standard deviations (SDs), respectively, of all values (–1.37±3.9).