High-field Magnetic Resonance
Modern medical diagnostics would be unthinkable without magnetic resonance imaging (MRI). In addition to traditional imaging, which reveals anatomical structures, functional MRI (fMRI) has become a valuable tool for brain research. It comes close to allowing us to watch the brain at work and has contributed considerably to the advances in human cognitive neuroscience. The special advantage of MRI is that experiments, unlike X-ray diagnostics, computer tomography (CT) and positron emission tomography (PET), can be carried out without putting any strain on the health of the person being examined. In particular, it can create outstanding images of soft tissue in the biological organism, which means, especially at high magnetic fields, that for the first time it is possible to explore human brain processes non-invasively with good spatial resolution.
Our primary goal is to develop new magnetic resonance techniques that are able to specifically probe the structural and biochemical composition of living tissue. This is closely linked with our interest to understand the details of magnetic resonance signal formation within a living environment, as nuclear magnetization is continuously influenced by different processes during its live time between excitation and relaxation. This is a simple, eventually computationally demanding task, since we just have to forward the tiny fluctuating magnetic fields, which are sensed by the water during its random or oriented walk through tissue, to the Bloch or similar equations. A prominent example is the detection of neuronal activation with magnetic resonance, often called functional MRI or fMRI: increased neuronal activation increases the observed magnetic resonance signal, and sometimes vice versa. This BOLD effect is the working horse of numerous applications in cognitive neurosciences, however, a detailed understanding of this effect on a microscopic or mesoscopic scale is missing.
Besides functional MRI, which measures nerve cell activity indirectly via the blood flow and blood oxygenation response, magnetic resonance is also very useful for mapping neurochemical and neurobiological brain processes directly. However, a magnetic field stronger than that of clinical instruments is necessary for these advanced measurements. To provide optimal research opportunities, two ultra high-field magnetic resonance imaging systems were acquired - an MR system with a field strength of 9.4 Tesla and a usable volume of 60 cm diameter for human studies and a 14.1 Tesla MR system for small animal studies are available. In comparison, the strength of the earth’s magnetic field in Central Europe is around 0.00005 Tesla. In addition to the two large magnets, there is a clinical 3.0 Tesla MR system available, which will be used for neuroscience applications and joint ventures.
Research on these three systems is focused on detection of neuronal activity and connectivity, as well as on the neurochemistry of the brain. This requires the development of new methods, which permit highly specific and quantitative mapping of neuronal activity and bioenergetic processes in nerve cells. Faster image acquisition and better image quality also form part of the research objective. The high magnetic field strengths provide the possibility to apply high resolution spectroscopic MR methods. These techniques permit to obtain more precise insights in the chemical processes in the brain. For example, the function of neurotransmitters such as GABA or glutamate can be revealed in greater detail. In addition to hydrogen, the most frequently used nucleus in MRI, it is possible to use the signal from other MR active elements such as carbon, oxygen, fluorine, sodium or phosphorus. Such investigations are less feasible in devices with low magnetic fields, because of the much lower sensitivity and concentration of these nuclei compared to hydrogen.