The first major aim of the project was to design new and efficient algorithms for being able to calculate how dielectric materials could be tailored in three dimensions to produce specific signal intensities within the image. In a paper entitled "High-Permittivity Pad Design for Dielectric Shimming in Magnetic Resonance Imaging using Projection Based Model Reduction and a 3D Nonlinear Inversion Scheme" which has been submitted to IEEE Transactions on Medical Imaging, we presented a fast and efficient method for designing dielectric pads. The domain decomposition method of our previous work was taken as a starting point, and we showed that the order of this model can be reduced to a great extent by employing a projection based model order reduction technique, and can subsequently be used to construct an automated optimization method. For the specific problem of imaging the cerebellum at 7T which was considered in this paper, the previously presented domain decomposition based model with an order of approximately 27,000 was successfully reduced to a system of order 500, thereby reducing the model order by a factor of 54. Having these reduced-order models available, B+ field responses can now be evaluated in only a fraction of a second for each pad realization at the cost of a very small reduction in accuracy. We showed how this approach could very rapidly produce convergence on a pad designed to image the cerebellum on a commercial 7 T scanner.
The second major aim was to investigate new materials with very high permittivities, and to assess their use in improving clinical MRI. In this area major progress has been made using blocks of lead zirconate titanate with a relative permittivity of 1070 to improve the quality of spinal cord imaging on a commercial 3 Tesla scanner. This work was recently published in Magnetic Resonance in Medicine, the most commonly read technical MRI journal. Electromagnetic simulations and the in vivo data acquired in this study confirm that very high permittivity ceramic blocks, made of lead zirconate titanate, improve the transmit efficiency in the spine. No adverse effects on the receive sensitivity of the array were found in this study. The locally enhanced receive sensitivity in combination with the focused transmit profile results in highersignal-to-noise in the spine region, leading to an increased image quality. Importantly, with regard to the overall aim of the project of enabling quality enhancement on systems which are not state-of-the-art, this study showed the feasibility of “upgrading” single channel transmit hardware at 3T with high permittivity PZT blocks to support spine applications. Image quality is significantly improved and power deposition is reduced with respect to a basic quadrature setup.
An interesting new project and collaboration was formed in mid-2016 with the ceramics group at ITMO University in Russia. They are able to form ceramics with very high permittivities and relatively low losses. In collaboration we were able to produce radiofrequency coils for very high frequency high resolution microimaging at 17 Tesla. This work was presented at the PIERS Conference in Paris in late 2016.
The final aim of the project is to investigate new types of detectors for MRI which use plasmas rather than the conventional copper conductors. Progress in this work has been achieved in collaboration with new partners at the University of Wurzburg in Germany. A paper has been submitted on this work, in which we have shown the first demonstration of plasma-based antennas for MR imaging on a commercial 3 Tesla system. The measured B1+ field of the single monopole antenna show similar behavior as a conventional metal antenna.
New materials developed during this project so far have been provided to many sites around the world. In 2016 and 2017 these include the University of Cardiff Imaging Center, King's College London, and the new 7 Tesla facility in Glasgow.
