The goal of this project is the technical and clinical development of magnetic resonance imaging for the analysis of the cardiovascular system. The complex anatomy and motion of the heart presents special technical challenges which are not found in other organ systems. Research has focused primarily on the heart, including myocardial perfusion, regional function, and coronary artery anatomy. Over the last year we have developed a new MRI pulse sequence which has permitted the evaluation of myocardial perfusion using commercially available MRI contrast agents. Image acquisition speed is high enough to enable the assessment of the entire heart during a single breathhold as the contrast agent passes through the myocardium. This technique is currently being evaluated in patients and compared to conventional nuclear medicine perfusion studies. In addition, we have studied perfusion in animal models using a new intravascular MRI contrast agent that can provide more information and less image artifacts than conventional agents which leak into the interstitial space. Using our recently developed methods of determining high resolution strain maps of the myocardium, we have evaluated the """"""""border zone"""""""" around myocardial infarcts in an animal model. These studies have revealed a pattern of abnormal contraction in this zone which may contribute to myocardial remodeling and eventual heart failure. Longitudinal studies are now underway to evaluate this hypothesis. Another goal of the program is to assess the potential of MRI for imaging the coronary arteries. Toward this end, we have implemented new MRI pulse sequences that can image the coronary arteries during a breathhold and contrast bolus. The results show a significant improvement in signal-to-noise and contrast-to-noise ratios as compared with noncontrast images. In addition, we have developed techniques that can image coronary arteries during free-breathing (i.e. without breathholding). In one of these methods the MRI scanner is used to assess the diaphragmatic position during image acquisition. Images of the coronary arteries have been acquired in about 5 minutes. Other methods that may be superior for following cardiac position as a function of respiratory cycle are being evaluated. These include information from a number of non-MR modalities such as the ECG, accelerometers, thoracic impedance, and bellows. These alternative methods may prove more accurate in the assessment of myocardial position as a function of respiratory cycle. In addition to the projects described above, MRI has been shown to be useful in assessing a number of other aspects of the cardiovascular system. These include valve function and valve leaflet visualization, arterial compliance, and wall shear rate. Studies are underway to assess the efficacy of MRI with regard to assessing these parameters and evaluating how the results compare to conventional techniques.
