Characterization of Time-Varying Properties and Regional Strains in Myocardial Ischemia

Abstract

Mechanical dysfunction plays an important role in the pathological progress of myocardial ischemia and is directly related to the prognosis of the patient. The crucial index of myocardial mechanics, regional time-varying elastance, and stress, however, could not be measured directly in clinical practice. This review outlines the steps to deduct myocardial mechanical performance from medical imaging modalities and modeling. The first step is to reconstruct three-dimensional cardiac motion by combining image data and geometric model of the heart. SPAMM-MRI (spatial modulation of magnetization) image, because of its high spatial–temporal resolution and ability to track material point of moving myocardium, is an ideal image modality for such a task. Several geometry models focused on SPAMM-MRI data analysis are discussed in detail, including some that assume cardiac shapes and some that extract the motion information from the tagging and subsequent model building by interpolation. Once the geometry of the heart at different time point is established, the second step is to calculate motion index from it. While different indices have been proposed, such as endocardium excursion, heart wall thickening, cardiac torsion, regional myocardial strain has the advantage of less affected by global heart motion and neighborhood myocardium. It is a key index to bridge cardiac MRI image and regional myocardial mechanical model. Finally, the three-dimensional strain distribution is used to compute myocardium stress and marterial property. Animal experiment, however, has shown that myocardial elastance changes throughout the cardiac cycle. The use of time-varying elastance model instead of elastic solid continuum model can thus provide a more accurate description of regional myocardium mechanics.