VARIATION IN ULTRASONIC BACKSCATTERING FROM SKELETAL-MUSCLE DURING PASSIVE STRETCHING

The purpose of this study was to further validate the scattering mecha nism of ultrasound in the skeletal muscle tissue. It was hypothesized that the endomysial collagen fibers are a major determinant of ultraso nic scattering in the skeletal muscle. Previous studies have found tha t the ultrasonic backscattering from avian skeletal muscle changed as it was passively stretched from 0 to 40%. In this study, ultrasonic ba ckscattering was measured from chicken breast muscles as they were str etched passively in increments of 10% of original length up to 60%. Th e integrated backscatter was found to reach a peak as the specimen was stretched to 40% and leveled off as it was further stretched from 40 to 60%. This finding was supported by results from scanning electron m icroscopy (SEM) of the specimens. SEM images showed that the orientati on of the endomysial collagen fibers surrounding muscle fibers became approximately parallel to the axis of the muscle fiber when the muscle was stretched up to 40% of its original length, yielding maximal ultr asonic backscatter and as the muscle was further stretched, no apparen t alteration of fiber orientation could be observed.