6 107 Ultrasonographic Achilles Tendon Thickness: Insertional vs. Midportion Reliability Ultrasound Tissue Characterization We utilized the UTC Imaging version 2020 (UTC Imaging, Stein, The Netherlands) for the standardized ultrasound assessment. This system involves a tracking device and conventional US equipment. The UTC scan was carried out following a standardized protocol. Participants were positioned in an identical manner to the conventional US procedure, prone on an examination table with a maximum passive dorsiflexion angle of the ankle obtained and then maintained by the researchers knee (Supplementary File 1). The same multi-frequency 5-16 MHz linear-array transducer (Terason, Burlington, United States) was used in a transverse and perpendicular position, moving automatically from proximal to distal over a distance of 12 cm to obtain a three-dimensional data block. The UTC tracking and data-collection device facilitated the collection of ‘raw’ digital transverse images at regular intervals of 0.2 mm. The exact working mechanisms of the UTC procedure have been described in detail in previous literature.9,23,24 All scans were collected in a database and pseudonymized before initiating the measurements. The maximum AP distance was measured manually by two independent researchers (RJDV and TSV) using a standardized procedure (Figure 2 and 3). First, the thickest part of both the midportion and insertion region of the tendon were estimated by the researchers in the longitudinal plane. Then, these regions of the tendon were assessed in the transversal plane and subsequently the maximum diameters of the tendon were measured. Measurements were performed using pixel size (rounded to one decimal), with 1 pixel corresponding to 0.062 millimeters (mm). Both raters were blinded to the conventional US measurements and each other’s measurements. Both raters were aware of the disease condition (symptomatic vs. asymptomatic) but were blinded to clinical information such as localized tendon thickening and additional cues (e.g., age, height, symptom duration, gender, etc.). Measurements were performed in a consecutive order as varying the order of subjects was impractical. Figure 2. UTC image of the Achilles tendon. In the longitudinal plane (B), the thickest part of both the midportion and insertional region of the tendon were estimated. Subsequently, those regions were assessed in the transversal plane (A).
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