Novel methodologies for functional Magnetic Resonance Imaging incorporating multiple refocusing pulses and parallel data acquisition
10 / 2004 - 10 / 2007
Functional magnetic resonance imaging (fMRI) is an important technique in diagnostic imaging and cognitive neuroscience. It is used for such applications as pre-operative treatment planning and mapping brain activation. Despite its great success in the last decade the most commonly employed approach, use of T2*-weighted echo planar imaging (EPI), suffers from some grave disadvantages. These are limited spatial resolution, image distortion and, in some areas, signal voids due to inhomogeneities in the main magnetic field that arise from susceptibility gradients caused by the object itself. These problems increase with main magnetic field strength, and are hence of particular relevance as there is a shift in neurological imaging from 1.5 T to the new generation of 3 T scanners. This proposal aims to provide significant improvements in the quality of fMR investigations at both of these field strengths, so that image artefacts are eliminated, and the spatial resolution is determined by the extent of measurable physiological changes. The novelty of this proposal lies in the combination of multiple spin-echo based imaging sequences (which do not suffer from image distortion) with the newly developed methodology of parallel imaging. The latter can reduce the level of radio frequency power deposition and long echo-train lengths (ETLs) that are traditionally associated with spin-echo sequences. A primary aim is to develop a spinecho sequence with a minimum number of 180ø refocusing pulses that is suitable for use in a T2*-weighted experiment at both 1.5 and 3 T. Residual signal voids should be eliminated by developing a single-shot 3D variant of this approach. At 3 T functional T2-contrast is sufficiently strong to use for cognitive experiments, in addition to the more commonly used T2*-contrast. T2-contrast has the advantage of intrinsically better spatial resolution at the cost of some reduction in sensitivity. T2-weighted sequences can be both free of signal voids and distortions. Hence, at 3 T a set of specific experiments that combine these desirable characteristics with low power deposition and a single-shot imaging capability, will be developed for both 2D and 3D imaging. These methods will be extensively investigated for functional imaging of regions of the brain such as the hippocampus that are difficult to examine with current methodology and in radiological practice, including surgical treatment planning.