Development and Validation of 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 1.5Tesla (T). We have pioneered the use of 3T scanners, and have most recently purchased the highest field strength commercially available human scanner (7Tesla). 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 at 7T are those that are limited by low SNR (signal-to-noise ratio) at 1.5 and 3T. These include imaging the coronary arteries, imaging the oxygenation of the blood, and using magnetic resonance spectroscopy to measure the energy-rich metabolites in the human heart.
Coronary artery imaging is particularly important as these vessels are critical to supplying blood to the heart (blockages cause heart attack). The higher SNR of 7T will show 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 magnetic resonance spectroscopy reveals 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 a clinical examination (impossible at lower field strength). 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 one of an elite group world-wide developing cardiac MR at 7T.

This programme of work develops the tools and methodology for clinical cardiac MRI at 7 Tesla, from building the hardware right through to running studies with our clinical researchers. Existing grants have funded the equipment for 7Tesla whole body imaging in Oxford (the only UK cardiac capable ultra-high-field imaging system). The present proposal builds on this technology with sufficient man-power to allow our group to lead in this field. Owing to the challenges of cardiac imaging at 7Tesla and the expense of such a system, longer term Programme Grant funding is sought, this will enable a small but focused team to transition these techniques from being ?theoretically valuable? to actually being present on clinical systems, providing new, useful tools for research and clinical practice. The objective of our work is to develop tools that improve our ability to evaluate the heart in humans. The 7T scanner provides substantially increased signal to noise ratio (SNR) over present technology. We will investigate three areas where 7T shows great promise but is limited due to insufficient SNR at lower field strengths; 1) Coronary Magnetic Resonance Angiography (MRA). 2) BOLD imaging of the heart. 3) Phosphorus spectroscopy of the heart. There are several technical challenges in this work that are mostly related to the transmission of radiofrequency (RF) pulses. The first goal will be to translate the state-of-the-art proton RF coil designs developed by our collaborators (T.Vaughan, Minnesota University) onto our 7T system. To achieve this, we have invested time working in Minnesota, and they will provide hardware and support as part of our research collaboration. Enabling routine proton imaging of the heart at 7T is essential, and once in place will allow us to investigate coronary imaging at 7T with our expert collaborator (D.Li, Northwestern University, Chicago), and will provide the platform for our cardiac BOLD imaging methods. The second goal is to implement Phosphorus spectroscopy at high resolution for regional metabolic imaging of the heart. We will re-engineer a 3Tesla 32-channel proton coil to operate at 7T for 31P, and build a transmit coil. High quality coronary MRA without ionizing radiation; fast regional metabolic imaging; and localised measurements of cardiac oxygenation deficits would all have direct clinical and scientific impact, and are within the scope of this project. With an MRC programme grant, we would have the technical ability and infrastructure to be a world leading 7T cardiac imaging centre.