Adaptive distortion correction techniques for high-field magnetic resonance neuroimaging

In diesem Projekt werden Methoden für die dynamische Erfassung von Magnetfeldverteilungen während einer MRT Messung entwickelt. Anhand dieser werden die bei EPI entstehenden geometrischen Verzerrungen korrigiert und somit die Vergleichabrkeit mit anatomischen Aufnahmen erhöht (Details siehe engl. Zusammenfassung).

The use of single-shot echo-planar imaging (EPI) has grown dramatically over recent years. A number of advanced brain imaging applications in functional neuroimaging, e.g. functional MRI (fMRI) and diffusion tensor imaging (DTI), use EPI as the imaging module. EPI, however, is susceptible to a number of imaging artefacts and geometric image distortions due to inhomogeneities of the main magnetic field within the sample. These inhomogeneities induced by magnetic susceptibility differences in the sample or by main field inhomogeneities are often regarded as inherently constant in time. Especially for long time-series acquisitions with continuous and repetitive scans, system instabilities, ferro-shim heating or subject s motion and respiration can introduce time dependant changes in the field homogeneity. These result in time variant changes in image distortions leading to degradation and to artefacts in time-series analyses. These effects become increasingly important at high field strengths of 3 Tesla and above, and can become a significant obstacle for EPI applications at 7T. In this project we propose an approach to dynamically measure, characterise and compensate for geometric image distortions in EPI. The project covers various EPI applications ranging from functional MRI to diffusion tensor imaging. The methods, which are to be developed, will be evaluated at various field strengths ranging from 1.5T to 7T. They will significantly improve stability and imaging properties of EPI to allow more sensitive experimental results and higher positional accuracy.