Measurements are reported on the propagation velocity of ultrasound in muscle tissue. This appears to be dependent on fiber direction for various muscle types (in vitro). Typical results are 1550 m/s perpendicular and 1557 m/s parallel to fiber direction (20 degrees C). A model is drawn up to relate such data to the elastic properties of muscle. It is shown that the assumptions: linear elastic behavior, homogeneity, and anisotropy with cylindrical symmetry, do not harmonize with the experimental results. A more elaborate model is suggested. Contraction dependence of the ultrasound velocity was investigated on human biceps muscle (in vivo) and frog gastrognemius muscle (in vitro). The measured velocity increase in biceps muscle during contraction--up to 3 m/s--is attributed to a varying blood content of the muscle. In (in vitro) frog muscle contraction is not accompanied by a change in ultrasound velocity. This suggests that increased muscle stiffness is not appreciably reflected in ultrasound velocity.

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Evaluation of the function of implanted prosthetic valves is important in early diagnosis of valve dysfunction. Bjork-Shiley valves contain two radiopaque rings, which are projected as ellipses in cineradiography. From these ellipses the actual valve opening angle can be calculated. A computer-aided method was developed that enables measurement of ellipse characteristics reliably, independent of projection angle and valve opening. It is demonstrated that calculated and real opening angles differ fess than 2" with this method. Using the same technique the tilting angle of the valve ring during the cardiac cycle is computed for evaluation of progression of valve dehiscense in case of a paravalvular leak. Application of the method to patient data is illustrated by three cases. The method is suitable for use by technicians. It can be implemented on a small microprocessor system. The method proved to be a powerful tool in the evaluation of patients with implanted Bjork-Shiley valves.