Analysis of Speckle Pattern Quality and Uncertainty for Cardiac Strain Measurements Using 3D Digital Image Correlation

Measurement of full-field cardiac strain using optical methods has potential application to validate ultrasound measurements ex vivo, confirming their suitability for accurate in vivo strain imaging. This study describes the use of an effective technique to create a speckle pattern over the surface of a porcine heart for ex vivo experiments with the 3D digital image correlation (DIC) method. We characterised the quality of the speckle pattern applied on the cardiac surface by analysis of speckle size and evaluated the baseline uncertainty of 3D-DIC technique using a zero-strain test, applying rigid-body motion to position the marked sample at four locations. Strain errors were reported at a high spatial resolution (~128 µm) and were evaluated over a range of subset sizes. For subset size greater than 29 pixels the strain error was less than 1% making the baseline uncertainty of the 3D-DIC system acceptable to measure strains on the cardiac surface of the order 10%.