Functional cardiovascular ultrasound imaging: Quantification of plaque vulnerability and cardiac function

With ultrasound strain imaging, the function of tissue and organs can be identified. The technique uses multiple images, acquired from tissue under different degrees of deformation. We developed techniques for cardiovascular applications. The displacement of tissue can be determined at micrometer scale using the raw (i.e., radio frequency, RF-) ultrasound data, containing the amplitude as well as the phase information. A 2D/3D cross-correlation based coarse-to-fine strain estimation strategy is used to quantify the strain. The maximum value of the cross-correlation function is also used for automated segmentation. Furthermore, strain estimation is improved by strain compounding, a technique that combines data acquired at multiple beam-steered angles. Validation experiments in phantoms demonstrated that accurate strain images can be determined using the proposed technique and that strain compounding improves the strain estimate in directions perpendicular to the ultrasound beam. Evaluation using cardiac data in animals showed that automated segmentation provides accurate quantification of the cardiac output and that the strain in the heart walls can be estimated in three dimensions. Segmentation based on combining temporal correlation and filtered echo level outperforms segmentation based on echo level alone.