Magnetic resonance imaging (MRI) has developed into a powerful tool in both medical diagnosis and cognitive neuroimaging. In the latter it is primarily used to perform activation studies. This is because some MRI experiments can be made sensitive to changes in the concentration of the endogenous paramagnetic contrast agent, deoxyhaemoglobin, which arise as an indirect consequence of increased local neuronal activity. Specifically, activation can result in an increase in the local rate of oxygen consumption and increased synaptic input causes changes in the local blood flow and consequently in the blood volume. In healthy adults the net effect of these changes is to washout the deoxyhaemoglobin, reducing its concentration in tissue and leading to a local increase in the MR signal intensity. These experiments are generally termed functional MRI (fMRI), and have the advantages over competing modalities in that the experiments are harmless, may easily be repeated, and have a spatial resolution of about 3 mm or better. The acquisition of activation maps is but one example of the wealth of information which may potentially be obtained from MRI experiments. Another exciting possibility is the ability to examine the orientation of myelinated nerve fibres using diffusion tensor imaging (DTI).
The research activities of the PI-group MR Techniques in Brain Function concentrate on three topics:
1.Improving fMRI techniques. Here we are looking at using parallel imaging methods which have the ability to reduce image distortion (in EPI) and power deposition (in Fast Spin Echo sequences) in combination with multi-echo gradient-echo EPI and spin echo based techniques. The ultimate aim is to develop methods which represent a clear improvement on the commonly used gradient echo EPI technique.
2.Very high resolution fMRI. Here we are exploring the use of 3D gradient echo methods to obtain isotropic pixel resolutions for fMRI that are under a millimetre and have no distortion.
3.Diffusion tensor and connectivity. We are developing diffusion tensor techniques to give us semi-quantitative measures of anatomical connectivity between brain regions that are independent of the distance between them, and can follow paths through regions of the brain where fibres cross. Parallel to this we are looking at low frequency BOLD fluctuations as a measure of functional connectivity. These projects involve collaborations with Utrecht University and the departments of Neurology and Psychiatry at the UMC St. Radboud in Nijmegen.
Prof. David Norris
Dr. Markus Barth, Youri Bicker, Rasim Boyacioglu, Prof. Jan Buitelaar, Eelco van Dongen, Prof. Jan van der Eerden, Harm van de Haar, Liesbeth Hoekstra, Ronald Janssen, Michiel Kleinnijenhuis , Peter Koopmans, Dr. Ali Mazaheri, Matthias Meyer, Emily van Mierlo, Jeanette Mostert, Emil Nijhuis, Erik van Oort , Mike Sellis, Dr. Elena Shumskaya, Eelke Visser, Huadong Xiang, Dr. Marcel Zwiers.