Speed and contrast in magnetic resonance imaging
The four main projects presented in this thesis investigate different aspects of speed and contrast in MRL Firstly, a new method called SPENT is described that is used to investigate the homogeneity of tissue. The resulting images appear bright in regions where pixel's underlying magnetisation is non-uniform and dark in regions where it is uniform. The aim of this section is to investigate the contrast produced using SPENT images and evaluate their potential for obtaining structural information beyond that normally available. Secondly, the structure and strength of bone as predicted using MRI is compared to Young's Modulus, a measure of biomechanical strength, and bone mineral density measured by DEXA. Direct MR-image based structural assessment of excised trabecular bone samples is compared to the relaxation parameters (R2 / R2') and SPENT for the determination of bone strength. Thirdly, a 200MHz/4.7 T multiple receiver coil is evaluated for its Signal to Noise Ratio (SNR) performance both for standard and parallel imaging. This entails the development of software for accurate mapping of coil sensitivity, SNR estimation and for combining the images from each array coil element. The software and coil developed are shown to enable a reduction in imaging time using the SENSE (SENSitivity Encoding) technique. Fast Spin Echo (FSE) images are presented demonstrating the array coil used at 4.7 T obtains in vivo images of humans with improved quality. Finally, new pulse sequences are presented that produce multiple images in rapid succession. These multiple images are acquired with a reduced data matrix that corresponds to several shorter periods of data acquisition. The multiple images are combined to produce full matrix images. The most promising application for these techniques is in improving the performance of Gradient Echo-Echo Planar Imaging (GE-EPI) at high field. Segmenting the acquisition in this way provides an increase in image quality without many of the problems associated with other methods to segment the EPI acquisition.