(6) TEST-RETEST RELIABILITY OF A 3-D PRINTED GUIDE FOR VASTUS LATERALIS MUSCLE VOLUME

Purpose: The purpose of this study was to compare the test-retest reliability between a custom-built ultrasound probe guide and manual ultrasound imaging for the vastus lateralis. Methods: 40 participants (mean ± SD: age = 21 ± 3 yrs; BMI = 24.5 ± 4.2 kg/m²) completed one visit to the laboratory where each participant underwent non-invasive ultrasound imaging on their vastus lateralis (VL) across four separate image acquisition sessions, each separated by 10 minutes. Two trials utilized the custom-built, 3-D printed probe guide (PGT) while the other two trials did not use a probe guide (TRAD). The PGT consisted of a customized cradle which was printed to fit the exact dimensions of the ultrasound probe used in this study. To acquire images, the cradle, which controlled the pitch and yaw of the probe, was then placed on custom-designed tracks while it glided on tracks during a cross-sectional plane ultrasound scan. Anatomical cross-sectional area (ACSA) was quantified every 1.5 cm along the length of the vastus lateralis, which was standardized based off of the capabilities of the PGT. During the TRAD trials, scans occurred in the same locations as the aforementioned trials. ACSA was quantified by an experienced investigator carefully selecting the muscle fascia of the vastus lateralis using open-source software. Muscle volume was estimated using a cubic spline interpolation for the ACSA scans. Test-retest reliability statistics (i.e., interclass correlation coefficients [icc] model 2,1, standard error of measure expressed as a percent [sem%], and the minimal difference [md] values needed to be considered real) were quantified. Furthermore, paired sample t-test were employed to assess efficiency of imaging during PGT and TRAD trials. Results: The PGT and TRAD method indicated good reliability (icc_2,1 = 0.97, sem% = 4.67, md = 9.16 cm³, p = 0.85; icc_2,1 = 0.99, sem% = 2.96, md = 5.81 cm³, p = 0.77), but the TRAD method has less marginal error and within variability. Conclusions: The findings from the present investigation suggest that both PGT and TRAD methods are reliable when quantifying muscle volume, but the TRAD may have less error between repeated scans compared to the PGT. Future studies should assess the utility of this approach with other muscles and with technicians of varying experience levels. Practical Applications: The PGT method is as reliable as the TRAD method for ultrasound scanning. While they are both reliable, this tool may be useful for novice practitioners or researchers who aim to have reliable imaging practices. Acknowledgements: None