Fascicle orientation is one of the most widely used parameters for quantifying muscle function in mechanical analysis, clinical diagnosis, and rehabilitation assessment. Ultrasonography has frequently been used as a reliable way to measure the changes in fascicle orientation of human muscles non-invasively. Conventionally, most such measurements are conducted by a manual analysis of ultrasound images. This manual approach is time consuming, subjective and not suitable for measuring dynamic changes. In this study, we developed an automated tracking method based on a frequency domain Radon transform. The goal of the study was to evaluate the performance of the proposed method by comparing it with the manual approach and by determining its repeatability. A real-time B-mode ultrasound scanner was used to examine the medial gastrocnemius muscle during contraction. The coefficient of multiple correlation (CMC) was used to quantify the level of agreement between the two methods and the repeatability of the proposed method. The two methods were also compared by linear regression and a Bland–Altman analysis. The findings indicated that the results obtained using the proposed method were in good agreement with those obtained using the manual approach (CMC=0.94±0.03, difference=−0.23±0.68°) and were highly repeatable (CMC=0.91±0.04). In conclusion, the new method presented here may provide an accurate, highly repeatable, and efficient approach for estimating fascicle orientation during muscle contraction. 
Continuous fascicle orientation measurement of medial gastrocnemius muscle in ultrasonography using frequency domain Radon transform