High Performance Gradient and Shim System for a 4T Human MR Scanner

University Of Minnesota, Minneapolis MN

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Abstract

DESCRIPTION (provided by applicant): The aim of this proposal is to upgrade the gradient/shim system on our human 4T/90cm Varian/Siemens MR scanner. This 4T magnet was installed in 1998, its console will be upgraded this year, but the current gradient/shim system will be the limiting factor for the high performance of this human MR scanner. The currently used Siemens Sonata gradient/shim coil was designed for 1.5T and does not meet the requirements for high quality, advanced magnetic resonance spectroscopy (MRS) and imaging (MRI) at 4T. The strength of the second-order shim system is absolutely insufficient to compensate strong non-linear deformations of the static magnetic field (B0). The proposed upgrade of the gradient/shim system with strong second- and third-order shims will guarantee that the B0 inhomogeneities could be minimized in any brain location and over a larger volume of tissue. The high B0 homogeneity will result in high spectral resolution, which is critical for extracting broad and reliable neurochemical information from MRS data beyond the range of NAA, Cr and Cho. The third-order shim set is critical for an efficient B0 field homogeneity adjustment in large volumes of tissue, which is required for MR spectroscopic imaging, 13C MRS and fMRI. A powerful shim system will be extremely important for all clinically oriented projects of neurodegenerative diseases, where the affected brain region is rather often located in areas of poor B0 homogeneity. High performance gradient system (gradient strength, slew rate, duty cycle, gradient linearity) will significantly increase the application range of novel imaging techniques, such as SWIFT and RASER. The new gradient system will have highly beneficial impact on the implementation of advanced imaging methods using non-Cartesian sampling. PUBLIC HEALTH RELEVANCE: Upgrade of the gradient/shim system on the 4T MR scanner is essential for a reliable noninvasive quantification of metabolites in any region of the brain or other parts of the body. In addition, upgraded MR scanner will allow implementation of novel imaging methods providing extended anatomical and pathophysiological information.