Ultrasonic examination of mammalian tendon with acoustic microscopy in various media

Abstract

Fresh mammalian tendon threads (diameter ≃110 μm) were examined using the scanning laser acoustic microscope (Sonomicroscope 100R, Sonoscan, Inc., Bensonville, IL) at 100 MHz to make quantitative ultrasonic velocity and impedance measurements. Tendon is high in collagen (about 30% wet weight, 50%–90% dry weight), a structural protein which is believed to be important in the ultrasonic visualization of tissues. Ultrasonic velocity measurements are made by measuring a shift in the phase front of the sound as it propagates through the tissue as compared with the surrounding medium. Ultrasonic impedance measurements are made by comparing the acoustic contrast of the specimen with respect to that of the surrounding medium. The use of different media provides the opportunity to match velocity and impedance of the medium with that of the collagen threads thus yielding quantitative values of these ultrasonic characterization parameters. The use of different media also allows examination of the possibility that the medium itself is affecting the collagen thread. Two reference media at various concentrations were used, viz., aqueous solutions of sodium chloride or glycerine. Initial results using the different media indicate that the velocity of tendon is similar to that of pure glycerine (velocity ≃ 1926 m/s). This is almost 30% greater than the ultrasonic velocity of soft tissues. An impedance match has not been obtained using the reference media of the present study. This result suggests that the collagen thread may not be homogeneous with respect to its ultrasonic properties. This result when considered with the high velocity of the tendon, indicate that there is a marked difference in the ultrasonic characteristics of this tissue and other biological tissue. [This work was supported in part by grants from NIH and a Biomedical Research grant from University of Illinois, Urbana‐Champaign.]