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Abstract

PURPOSE: Shear wave elastography (SWE) is an emerging tool for estimating passive muscle stiffness via shear wave velocity (SWV). However, the lack of standardized collection and processing methods limits its clinical utility. One key factor in SWV analyses is the region of interest (ROI), which varies in size across the literature. Individuals post-anterior cruciate ligament reconstruction (ACLR) show changes in muscle quality, making it plausible that ROI size could influence SWE measurements in this population. METHODS: Twenty individuals post-ACLR participated (11M/9F, age = 19 ± 2 years, time since surgery = 5 ± 5 months, body mass index = 26.4 ± 4.4 kg/m2). Participants were positioned supine with legs flexed to 30° and rested for 5 minutes before data collection. Shear wave velocity was measured using a GE Logic Fortis ultrasound unit with a 50 mm linear-array transducer, placed over the mid-belly of the vastus lateralis. The on-unit ROI was centered in the image, with a width of at least 95 mm and the height spanning the full muscle thickness. Once the image stabilized, 10-20 frames were captured. Data were exported as DICOM files, and SWV was analyzed using a custom-built MATLAB application. SWV measurements were taken across the 3 most consistent consecutive images in the following ROI sizes: 4x4 mm, 6x6 mm, and 8x8 mm. To assess the reliability of SWV across the different ROI sizes, intraclass correlation coefficients (ICCs) for absolute agreement were calculated with a two-way mixed effects model for single measures. To determine the effect of ROI size on SWV, a repeated measures analysis of variance (ANOVA) was performed. RESULTS: ICCs for average and standard deviation of SWV across ROI sizes were 0.959 (95% CI: 0.917–0.982) and 0.806 (95% CI: 0.649–0.908), respectively, indicating good-to-excellent reliability (p<0.001). Repeated measures ANOVA showed no significant effect of ROI size on average (p=0.080) or standard deviation of SWV (p=0.197). CONCLUSION: ROI size did not significantly impact SWV post-ACLR. Further research is needed to explore the effects of ROI size and other methodological factors on SWV. Shear wave elastography is a novel, non-invasive modality to enhance assessments of muscle quality, but the field would benefit from establishing standardized methodology.

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