Effect of myofibril length and tissue constituents on acoustic propagation properties of muscle
The ultrasonic speed and attenuation coefficient of three muscle samples were measured in-vitro as a function of temperature and frequency. The sarcomere length of each of these samples was also determined. The three muscle groups were bovine longissimus dorsi, psoas major and lobster extensor. These were chosen to separately determine the effects of physical components (% water, % fat and % protein) and structural components (sarcomere length) on the ultrasonic propagation properties. The scanning laser acoustic microscope (SLAM) was used to measure the attenuation coefficient, speed and heterogeneity index of all three samples at 100 MHz. The Daedal exposimetry system (DES) was used to determine both of these quantities as a function of frequency over a range 2-7 MHz. In addition, measurements were made at three temperatures, 4, 20 and 37$\sp\circ$C. The chemical composition of the muscle groups was determined using wet/dry techniques (% water), ether extraction (% fat) and nitric acid digestion (% protein). The sarcomere length for individual samples was determined using light microscopy of suitable stained slides. Finally, the effect of the sarcomere structure was determined by homogenizing the tissue samples, and measuring ultrasonic propagation. The destruction of the regular myofibril architecture showed that the muscle structure plays a critical role in the propagation of ultrasound through tissue. Using the results from these studies a series of multiple linear regression models was determined, which allowed the physical and structural determination of a fourth muscle type (bovine semitendinosus) based solely on the acoustic properties. Subsequent measurement of the physical and structural properties were made to test the accuracy of the developed models. The prediction model for estimating tissue constituents and sarcomere lengths at 100 MHz is remarkably accurate, with very low errors in estimating the tissue constituents within 5% and sarcomere lengths with an accuracy of less than half a micron. Overall, the empirical model developed using the DES was not as accurate as that of the SLAM. Results at the lower temperature of 4$\sp\circ$C were consistently better than those at higher temperatures, with all parameters being predicted within 10% of the measured values.
Engineering, Biomedical, Engineering, Electronics and Electrical, Health Sciences, Radiology, Biophysics, General
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign