Multimodal Magnetic Resonance Methods for Metabolic Research

Nuclear magnetic resonance imaging (MRI) is a medical routine diagnostic tool that provides images from the human body non-invasively, fast and safely, without exposing the patient to ionising radiation. Beyond that, nuclear magnetic resonance (NMR) can also be employed as a more elaborate tool for investigating metabolism in vivo, when the modality is used to perform magnetic resonance spectroscopy (MRS). Although NMR of hydrogen is most frequently used, other intrinsically less sensitive nuclei may be measured. This so-called X- nuclear NMR offers a wider view on the metabolism and the state of tissue under investigation. Taken together, NMR modalities offer an impressive versatility: a multitude of different examinations is possible with the same scanner hardware. An interesting property of MR with different nuclei is that, in principle, two or more independent examinations can be performed at the same time, without creating interference. Practical advantages to such an approach are improvement of time efficiency, and reduction of patient time in the magnet. Beyond this, there are major scientific benefits from confronting data collected simultaneously during a single stress test and pertaining to different aspects of the same physiological or pathological states. However, it remains technically challenging to interleave multi-nuclear NMR, and this has only been performed by a minority of groups, as somewhat specific spectrometer configurations are required for each modality. On modern standard clinical MR scanners it is currently technically impossible to concurrently collect signals with frequencies several tens of Megahertz apart. The current project is a joint effort of two groups who have used interleaved multi-nuclear NMR on more open experimental MR systems in the past. Their primary objectives to implement this tool is to combine arterial spin labelled MRI measurements of perfusion and dynamic 31P MRS measurements of oxidative phosphorylation on their respective systems, corresponding to two generations of scanners from a common clinical MR manufacturer. Beyond this first step, the overall ambition of the project is to translate the interleaved NMR approach from specialised applications, restricted to a small community of technically skilled research laboratories and open research scanners to conventional clinical MR scanners, in order to facilitate its large-scale application. From a hardware perspective, multinuclear interleaving should be possible without modification on the future vendor platform, or by bringing a hardware addition to scanners using the current platform. Thereafter, developments of RF pulse-programming for acquisition, data extraction, reconstruction and post-processing will be essentially common to both the current and the upcoming generation of clinical MR scanners at the two sites. This project should open a whole set of new research perspectives, whether relating to physiological applications which will become available with the interleaved NMR possibilities on clinical platforms, or whether extending technical developments towards further integrated modalities.

Nuclear magnetic resonance imaging (MRI) is a medical routine diagnostic tool that provides images from the human body non-invasively, fast and safely, without exposing the patient to ionising radiation. Beyond that, nuclear magnetic resonance (NMR) can also be employed as a tool for investigating metabolism without physically taking probes from the tissue, when the machine is used to perform magnetic resonance spectroscopy (MRS). Although NMR of hydrogen (H) is most frequently used, other nuclei (for example phosphorus, P) may be employed to generate signal. This so-called "X-nuclear" NMR offers a wider view on the metabolism and the state of tissue under investigation. Taken together, different NMR methods offer an impressive versatility: a multitude of different examinations is possible with the same scanner hardware. An interesting property of MR with different nuclei is that, in principle, two or more independent examinations can be performed at the same time, without disturbing each other. This is advantageous, because the measurement time is used better, and a patient may need to stay in the scanner less long. Beyond this, there are major scientific benefits from confronting data collected simultaneously during a single stress test and pertaining to different aspects of the same physiological or pathological states. However, it remains technically challenging to interleave multi-nuclear NMR, and this has only been performed by a minority of groups, as somewhat specific spectrometer configurations are required for each modality. This project was a joint effort of two research groups, one in Austria, one in France, to implement this technique. The main task was to combine H MRI which can give information about blood perfusion and P MRS measurements, revealing information on oxidative energy turnover in the muscle, which is obviously connected. Beyond this, a motivation for the project was a translation of the interleaved NMR approach from specialised applications, restricted to a small community of technically skilled research laboratories and open research scanners to conventional clinical MR scanners, to facilitate its large-scale application. All developed methodologies were published and both groups have started actively helping interested research sites with their implementations. The hardware adaptations necessary for some scanners were developed in the project, and beyond that, multi-nuclear interleaving is possible without modification on the latest MR scanner platforms of major vendors. The results of this project open a set of new possible research perspectives. Some of these relate to physiological applications which will become available with the interleaved NMR possibilities on clinical platforms, others are extending technical developments towards further integration of different multi-nuclear MR methods.