Magnetic resonance imaging of myocardial viability and cardiac function in humans: Physiologic mechanisms and technical feasibility

Cardiovascular disease (CVD) is the most common cause of death in the Western world. Its diagnosis and treatment are therefore of significant interest. Two important aspects of cardiovascular disease are cardiac contractile function and viability. Contractile function, defined as the ability of the heart muscle to move and therefore pump blood, is a distinctly different physiologic issue compared to viability, defined as whether heart cells (myocytes) are alive or dead. Circumstances in which contractile function and viability are dissociated are often those for which intervention may be expected to be most beneficial. For example, the blood supply to a region that does not contract but remains viable can be surgically reestablished resulting in patient improvement (coronary artery bypass grafting or angioplasty). Therefore both contraction and viability are important considerations in the choice of patient treatment. In principle, magnetic resonance imaging (MRI) can address both issues in one exam. Cine MRI could reveal abnormalities in the cardiac contraction pattern, and contrast enhanced MRI (ceMRI) could determine viability. However, the physiological significance of images obtained with ceMRI has not been fully established, and the quality of cine MR images is limited by the requirement that all image data be acquired within a breathhold. The first part of this dissertation examines the physiological information portrayed by contrast enhanced images and compares this to the information portrayed by direct imaging of myocardial sodium and potassium. The data demonstrate that regional differences in MRI contrast agent concentrations directly relate to myocyte viability. The second part is concerned with the development of more efficient image acquisition schemes for cine MRI, improving image quality while maintaining or shortening acquisition time. A new technique described for the first time in this dissertation, the Selective Line Acquisition Mode (SLAM) allows cutting the scan time in half. Six-fold savings in time are obtained with a second new technique called Reconstruction by Estimation of Lines and Inhibition of Fold-In (RELIF). The dissertation proposes a combination of ceMRI and fast cine MRI as comprehensive cardiac MRI examination.