108 Chapter 6 Figure 3. Achilles tendon thickness measurement with the UTC procedure of the midportion of the tendon. After identifying the thickest part of the tendon in the longitudinal plane the maximum AP diameter perpendicular to the latero-medial width (white solid line) was measured in the transversal plane. The yellow line identifies the periphery of the tendon. For intra-rater reliability, a single researcher (TSV) performed thickness measurements in a consecutive order on all UTC scans a second time with an average time interval of 43 (SD; 1) days. This researcher was unaware of previous measurements (both his own and of the other rater). Statistical analysis A total of 100 participants were recruited. Descriptive statistics comprising mean and standard deviations were computed for the participants' characteristics and tendon thickness (maximum AP diameter in mm). During the measurement phase, both researchers also assessed whether data collection errors were present which refrained them from properly obtaining the outcome measurement. In case both researchers independently agreed that a UTC scan was not suitable to obtain the outcome measurement, we decided to exclude the scan in the analysis. If only one of both researchers assessed the scan as unsuitable for performing measurements, this was discussed between the two. In case there was no consensus, we decided to ask a third reviewer with experience in US data collection and analysis (SO) to assess the suitability of the UTC images. To determine inter- and intra-rater reliabilities, the intraclass correlation coefficient (ICC) was used. For both asymptomatic participants and those diagnosed with AT, the ICC ± 95% confidence interval (CI) was calculated for the maximum thickness in the midportion area and insertional area, using two-way random, single measurement on UTC scans. The reliability between conventional US and UTC measurements was also calculated for maximum thickness in the midportion and insertional region, using a two-way mixed, single measurement for
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