Computer aided speckle interferometry: a technique for measuring deformation of the surface of the heart

An investigation of the inhomogeneous and anisotropic properties of myocardium necessitates a whole field measurement technique with high spatial resolution. Computer aided speckle interferometry (CASI) may be applied to measuring deformation on the epicardial surface of the heart. Silicone carbide particles (approximately 40 microm in diameter) were sprinkled randomly onto the epicardial surface of isolated rabbit hearts. When illuminated with white light, speckles may be observed with a charge coupled device (CCD) camera. A balloon was placed in the left ventricle to control the intracavitary load on the arrested heart. To compare CASI to the "gold" standard technique of sonomicrometry, two ultrasonic transducers were implanted into the wall of the myocardium. Three hearts were exposed to various loading conditions, and at each condition speckle images were recorded. CASI was used to determine the distribution of displacement vectors (both direction and magnitude) in the region imaged by the CCD camera. Strain along the axis of the implanted transducers was determined with CASI and compared to that obtained with sonomicrometry. Strain determined from CASI and sonomicrometry produced equivalent results. Unlike sonomicrometry, whereby the displacement between two points with a relatively large gauge length is obtained, CASI is able to determine displacement vectors for hundreds of "points" within the same region. In conclusion, CASI produced equivalent results to those obtained from sonomicrometry (although not with the same temporal resolution), but it is a whole field deformation mapping technique that has a spatial resolution three orders of magnitude higher than that of sonomicrometry.