Deformation imaging by ultrasound for the assessment of regional myocardial function

Assessment of regional myocardial function, i.e. regional myocardial force development, remains an important goal in clinical cardiology as it gives important diagnostic and therapeutic information. Currently, a direct non-invasive measurement of regional force development is not feasible. However, regional function can be approximated by regional myocardial deformation as local force development and local deformation are closely linked. Instantaneous tissue deformation is measured by ultrasound as the spatial gradient in local tissue motion between two acquisitions. Tissue motion can be estimated using several techniques such as the auto- and cross-correlation methodologies. Normalization of the instantaneous deformation to time gives a measure of the regional rate of deformation, i.e. strain rate. Integration of the strain rate curve over the cardiac cycle results in the total tissue strain. In our laboratory, the application of ultrasonic strain and strain rate imaging in cardiology has been studied extensively. Different methodologies towards ultrasound based strain (rate) estimation have been developed and validated by prototyping on simulated ultrasound data sets and subsequently testing these methodologies in gel phantoms and animals using modified ultrasound scanners. Moreover, the clinical use of these techniques has been evaluated in a wide range of pathologies. In this paper, an overview of this work will be given. Different methodologies towards cardiac strain (rate) estimation by ultrasound will be described. Clinical examples of the practical use of the current technique will be shown together with typical image artifacts and their potential solutions. Finally, it will be demonstrated that the combination of ultrasound cardiac deformation data with mechanical models of the left ventricle provides a way to actually estimate regional myocardial force development, i.e. true regional myocardial function.