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Coronary Artery Imaging
The goal of the project is to develop MRI techniques for non-invasive detection of coronary artery stenosis. Our major contributions include:
- the original development of the three-dimensional imaging technique, which allowed the visualization of the entire coronary artery tree with high resolution;
- the early development and continued improvement of respiratory motion compensation methods, which allowed the images to be acquired without corruptions from respiratory motion;
- the development of imaging techniques to improve image signal intensity and tissue contrast, which allowed clear visualization of coronary arteries;
- the reduction of imaging time to the range that patients can tolerate. These developments laid the foundation for coronary MR imaging techniques widely used today.
Recently, we performed clinical studies using coronary MRI and showed that it has the potential to rule out significant coronary artery disease reliably and eliminate the need for unnecessary, costly, and invasive conventional angiographic procedure in some subjects. Our group is widely recognized as a leader in coronary MRI in international MR research community. We have two active R01 grants to support this research and have been funded by NIH on this research continuously since 1996.
High-Resolution Myocardial Perfusion Assessment
Myocardial perfusion and perfusion reserve are crucial physiological parameters in assessing ischemic heart disease. The decision to enhance myocardial blood flow either by angioplasty or surgery is often made on the assumption that regional flow is compromised by a coronary stenosis and can be partially or wholly reversed by treatment. The decision to revascularize is frequently based on invasive coronary angiography with left ventriculography or on the basis of nuclear techniques and evaluation of contractile reserve by dobutamine echocardiography. Recently, first-pass perfusion MRI using gadolinium-based contrast has demonstrated utility for direct visualization of myocardial blood flow in animal models and in patients. Because first-pass techniques require high temporal resolution, image artifacts may occur, mimicking perfusion defects. In particular, the technique must be carefully designed to balance conflicting requirements, such as spatial resolution, temporal resolution, signal-to-noise ratio, and spatial coverage of the entire heart. These requirements are crucial for wide clinical application of the technique.
Our group made major progress in addressing these needs by improving spatial resolution by a factor of 4 and imaging speed by a factor of 8. In particular, we developed a novel data acquisition approach to eliminate common image artifacts that have plagued the technique for years, and motion correction techniques to allow images to be acquired without ECG gating and during free breathing. These improvements will make major impacts on the clinical application of myocardial perfusion MRI. We have close collaboration with Noel Bairey Merz, MD and Daniel Berman, MD in using this new technique for evaluating women's heart disease. Behzad Sharif, PhD, made an oral presentation on the recent Society for Magnetic Resonance in Medicine Annual Meeting (Feb. 1-3, 2013) on this work and was awarded the Early Career Investigator Award.
MRI of Atherosclerosis
Atherosclerosis is a systematic disease underlying the majority of the cardiovascular disease, including myocardial infarction, stroke, aortic aneurysm, and peripheral vascular disease. We are developing MRI techniques to detect the presence and characterize the composition of atherosclerosis. Potential significance of the research includes:
- individualized risk stratification such as identifying asymptomatic subjects at high risk for atherosclerosis progression, who might benefit from drug therapy and lifestyle modifications in early stages of the disease, and identifying patients at high risk of a cardiovascular event in the near future who are in most urgent need of intervention;
- serving as surrogate outcomes for clinical trials evaluating therapeutic response. We have developed techniques to enable visualization of arterial wall and atherosclerosis in 3D with isotropic resolution, efficient coverage of the entire region, and adequate contrast between the lumen and vessel wall.
Our group played a key role in several subclinical studies to establish the correlation between atherosclerosis and cardiovascular disease risks in coronary and peripheral arteries. We are currently collaborating with P.K. Shah, MD and Moshe Ariditi, MD on imaging atherosclerotic mouse models to evaluate the effects of various therapies. We are also working with Dr. Tony Conte on atherosclerotic imaging of HIV patients.
Non-Contrast MR Angiography
This project aims at developing MR angiographic techniques without the use of MR contrast media. Contrast-enhanced imaging is the clinically accepted conventional method for MR angiography. However, patients with renal insufficiency who receive gadolinium-based agents are at risk of developing a debilitating and a potentially fatal disease known as nephrogenic systemic fibrosis. Therefore, MR angiographic methods which don't require contrast agents will have vital importance for patients with renal insufficiency. Our group developed a novel MR angiography method that doesn't require MR contrast media and is particularly effective in areas with slow or complex flow such as in peripheral arteries or distal to stenosis. This method is currently undergoing preliminary clinical evaluation in several centers. We are working with Rola Saouaf, MD to evaluate the effectiveness of the technique in patients with peripheral arterial diseases.