Advanced Clinical Cardiovascular MR Imaging and Spectroscopy at 7 Tesla

Magnetic Resonance Imaging (MRI) allows us to image the inside of the human body non-invasively. Pioneered in the brain this technique has become invaluable over the last 5-10 years for imaging the heart in the clinic. MRI scanners operate at a magnetic field strength of 1.5 Tesla. Increasing the magnetic field strength can provide higher image quality and we have pioneered the use of 3 Tesla scanners. The highest commercially available human field strength is 7 Tesla, which is our next step.

Imaging at higher field strength results in more signal, and thus, the images are obtained quicker, or with higher spatial resolution. The areas that we will develop are those that are limited by low SNR (signal-to-noise ratio) at 1.5 and 3 Tesla. These include imaging the coronary arteries and the energy-rich metabolites in the human heart. Coronary artery imaging is important as these vessels are critical to supplying blood to the heart (blockages cause ?heart attack?). The higher SNR of 7T will allow us to image the blood and walls of these vessels at higher resolution than has previously been possible with MRI enabling us to visualise small plaques and subtle damage. The metabolic condition of the heart is another important area of research where we in Oxford are world leaders. A technique called MRS (magnetic resonance spectroscopy) shows the biochemistry of the heart. Levels of phosphocreatine and adenosine triphosphate, which are essential energy-providing metabolites, can give an indication of damage even before functional changes become apparent. At 7T, the higher spatial resolution enables the MRS examination of small regions in the heart, equivalent to those presently required in clinical examination (this is impossible at lower field). Additional projects will build on these methods to look at oxygen supply, the degree of fibrous scar tissue, and the blood supply from small vessels in the heart.

Clinically these developments have the potential to transform MR imaging of cardiac metabolism, oxygenation, and coronary plaque biology from a niche research tool into a mainstream diagnostic measure that can treat the patient as an individual, enabling doctors to monitor the progress of a disease or the response to therapy over time. These techniques would contribute significantly to improving cardiovascular health and to relieving the burden of cardiovascular disease. Our plans are highly novel, and we would be the first site in the UK, and probably in Europe, developing cardiac MR at 7T.

MR imaging of the cardiovascular system (CMR imaging) has made a huge clinical and scientific impact. Currently, CMR is performed at field strengths of either 1.5 or 3 Tesla (T). Here, CMR allows analysis of cardiac anatomy, function, viability and perfusion. CMR can offer much deeper insight into cardiac pathophysiology, as it is capable of providing accurate information about cardiac metabolism and oxygenation, coronary lumen anatomy and atherosclerotic plaque. However, these advanced CMR applications currently are severely limited by their low resolution and reproducibility. While 3T, compared to 1.5T, provides resolution gains in the right direction, these are insufficient. Our understanding of the major epidemic diseases in Cardiology, ischemic heart disease and heart failure, would benefit greatly from reliable and highly reproducible non-invasive characterisation of these advanced parameters. This would allow fundamentally novel insights into disease mechanisms and treatment effects. We aim to be at the leading edge of this new development by obtaining a high-field (7T) imaging system as a platform from which these highly desirable goals can be made a reality. In a collaborative effort (with local, national and international MR Physics partners), we will develop CMR methods at 7T, the first such effort in the UK (and probably in Europe). MR physics research will initially focus on coil design, SAR and B1 management, RF pulse optimisation, regional shimming. High resolution quantitative MR spectroscopy (MRS) will be developed, to measure cardiac high-energy phosphates and the novel parameters CK flux and free energy change, regionally resolved, with high reproducibility, making true metabolic imaging of the heart by MRS a reality for the first time. Clinical research applications will include ischemic heart disease, heart failure and hypertrophic cardiomyopathy. Coronary lumen and wall imaging will be developed with unprecedented resolution, allowing reliable non-invasive serial assessment of coronary artery disease in application studies. The BOLD effect is greatly enhanced at 7T, and we will develop robust imaging of myocardial oxygenation, allowing assessment of the interrelations amongst cardiac function, perfusion, oxygenation and metabolism in patients. Such a development has the potential to transform CMR imaging of cardiac metabolism, oxygenation, and coronary plaque from a niche research tool into a mainstream diagnostic measure that can treat the patient as an individual, enabling doctors to monitor the progress of a disease or the response to therapy. Such new MR techniques would contribute significantly to improving cardiovascular health and to relieving the burden of cardiovascular disease.