Imaging Meningiomas

Abstract

In this thesis the first application of Magnetic Resonance Rheology (MRR) to patients with known brain lesions was presented.<br /> MRR is a novel approach to image the mechanical properties of brain tissue in vivo. It utilizes a short fall of the head of approximately 1 mm to create a global excitation of the brain tissue. The resulting deformations of the tissue are measured by means of Magnetic Resonance Imaging (MRI) and motion sensitive phase imaging techniques.<br /> Numerical simulations were used to predict the signals MRR yields for volume elements following specific trajectories during the experiment. A post-procession pipeline was developed and implemented to analyze the measured phase data and to reconstruct the induced falling motion based on the optically measured position of the lifting device.<br /> The influence of mechanical properties of the investigated material (stiffness and density) was presented on the basis of exemplary measurements on inhomogeneous phantoms. These consisted of two layers of different agar hydrogel manufactured with either different stiffness but similar density, or of similar stiffness but different density. The application of the method in vivo was shown by means of exemplary measurements on a healthy volunteer.<br /> The measured data was analyzed by visual inspection of the resulting phase images depicting deflection of the material and of computed phase strain images depicting the principle strain in the direction of the falling motion. The dynamics of the material was further investigated using the temporal evolution of the phase over the progression of the falling motion.<br /> The results confirmed a global oscillation of the material in response to the excitation. Particularly useful for visual inspection proved the temporal integration of the phase strain. Here, local differences in the mechanical properties of the phantom material respectively the brain tissue were depicted best.<br /> The presented methods have been used in a study on four patients diagnosed with meningiomas, which are benign tumors originating from the meninges surrounding the brain. Manual palpation by the neurosurgeons that resected the tumors after the MRR measurements showed an increased stiffness of the tumor tissue compared to healthy tissue. The tumor regions showed well defined signatures in the obtained images. Comparing the strain in the tumor regions with the one in healthy parts of the corresponding brains showed a trend of lower strains with increased tumor stiffness.<br /> These results can be considered a proof of concept of the feasibility of MRR to depict local alterations of the mechanical properties of brain tissue in vivo.