Myocardial passive shear wave detection
We studied the mechanical waves after mitral and aortic valve closure in the septal wall of 34 pigs (18 diabetic for heart failure and 16 controls), using high frame rate imaging on a programmable commercial ultrasound machine. The wave pattern was extracted from the data through a local tissue velocity estimator based on phase correlation. The wave propagation velocity was determined by manual estimates, cross-correlation, and Radon and Fourier transforms resulting in waves propagation velocities between 1.5 and 9 m/s, with spectral contents in the audible range of the heart tones. The Fourier analysis showed that the propagation velocity increases with frequency, which is consistent with asymmetric Lamb waves as can be expected from the geometry of the septal wall surrounded by blood.