Advanced measurement of human cardiac metabolism by interleaved 31P and 1H 7T MR

Cardiovascular diseases are the most frequent cause of morbidity and mortality in the western world. Coronary heart disease or cardiomyopathies often lead to impaired energy metabolism, which is a primary cause of function and tissue loss. Non-invasive phosphorus (31P) magnetic-resonance spectroscopy (MRS) can measure human energy metabolism directly via concentrations and kinetics of adenosine tri-phosphate (ATP) and phospho-creatine (PCr). Their concentrations as well as their ratio are markers of tissue function and integrity, and excellent predictors of disease progression. In this project, by developing the necessary techniques and methods, high field (7 T) cardiac 31P MRS will be raised to its full potential. The first step to further increase the accuracy in metabolite quantification using 7 T 31P MRS is an efficient, sensitive and robust radio frequency (RF) coil. This dual-frequency coil, also usable for conventional proton (MRI) will be constructed, using phased arrays of transmission-line resonators (TLR), a recent innovation from our lab. TLRs are flexible, monolithic structures, i.e. they do not require capacitors, and were shown to have favourable parallel imaging properties when used in phased arrays. 31 P MRS pulse sequences will be developed and optimised with the goal of accurately localised, time- resolved quantification of cardiac metabolites. Susceptibility to respiratory motion, which would limit localisation accuracy, will be corrected using rapidly acquired proton MRI navigator images. Voxel positions will be updated using information extracted from these navigator images. The aim is to achieve a localisation quality that is sufficient to allow clear distinction of signals from different anatomical regions, e.g. anterior wall, interventricular septum, or focal lesions. At the end of this project, dynamic (time-resolved) localised 31P MRS and spectroscopic imaging measurement protocols using navigator-based pre-emptive motion correction will be delivered. The expected gain in accuracy and sensitivity will lift the diagnostic value and scientific utility of cardiac 31P MRS to a completely new level. In summary, innovative new technologies, developed in our lab, will be used to create non-invasive metabolic imaging technology ready for future clinical research and diagnostics in cardiac disorders.

Cardiovascular diseases are the most frequent cause of morbidity and mortality in the western world. Coronary heart disease or cardiomyopathies often lead to impaired energy metabolism, which is a primary cause of function and tissue loss. Non-invasive phosphorus (31P) magnetic-resonance spectroscopy (MRS) can measure human energy metabolism directly via concentrations and kinetics of adenosine tri-phosphate (ATP) and phospho-creatine (PCr). Their concentrations as well as their ratio are markers of tissue function and integrity, and excellent predictors of disease progression. In this project 31P MRS pulse sequences were developed and optimised with the goal of accurately localised, time-resolved quantification of cardiac metabolites. Cardiac 31P MRS can now provide in situ quantification of myocardial pH and Gibbs' free energy. To further increase the accuracy in metabolite quantification of 7 T 31P MRS, a more sensitive radio frequency (RF) coil array was developed. We addressed the susceptibility to breathing motion, which would limit localisation accuracy by employing so-called navigators. We used several fast MR images and computer vision object tracking to detect and correct shifts in the heart fully automatically. 31P RMS voxel positions will be updated in real time. We have developed single voxel and spectroscopic imaging 31P MRS measurement protocols using this navigator-based prospective motion correction. The system is modular and can be used in any other MRI or MRS sequence, with only limited development effort. The accuracy and sensitivity of 31P MRS has significantly increased due to this project. In summary, innovative new technologies, developed in our lab, were used to create non-invasive metabolic imaging technology ready for future clinical research and diagnostics in cardiac disorders.