Transverse Strains in Muscle Fascicles during Voluntary Contraction: A 2D Frequency Decomposition of B-Mode Ultrasound Images

Figure 1

The Analysis Method. Coordinates on the superficial and deep aponeuroses and a representative fascicle were manually digitized (red points) for each ultrasound image (a) and used to calculate the fascicle length and inclination angle relative to the -axis (b). Fascicles were enhanced using multiscale vessel enhancement filters and the region of interest was determined between the aponeuroses (c). The repeating fascicular nature is described by its transverse wavelength , which can be resolved into wavelengths and that are in the - and -directions, respectively (d). The spatial frequencies and were determined using a discrete Fourier transform, and the major spatial frequencies characterized by the moment of frequency () (e). The inclination angle was were determined from the major spatial frequencies (f), and the wavelengths and were calculated from these frequencies.