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Geometry-Based Shim Coil Design Applied on an Ultralow-Field MRI System | IEEE Journals & Magazine | IEEE Xplore

Geometry-Based Shim Coil Design Applied on an Ultralow-Field MRI System


Abstract:

In an ultralow-field magnetic resonance imaging (ULF-MRI) system, the uniformity of static magnetic field B_{0} is essential for maintaining good imaging quality. How...Show More

Abstract:

In an ultralow-field magnetic resonance imaging (ULF-MRI) system, the uniformity of static magnetic field B_{0} is essential for maintaining good imaging quality. However, achieving high B_{0} homogeneity is difficult due to the low magnitude. This article proposes a flexible active shimming approach for ULF B_{0} optimization, where an original geometry-based method is presented for first- and second-order shim coil designs. Different types of shim coils are approximated by combinatorial geometric curves, where no additional wire is needed for overall connection. An optimization problem is established to ensure that each shim coil generates a high-purity harmonic magnetic field, which is comparable to the optimization results obtained using the conventional stream function method. A computer-controlled multichannel current source is designed to drive the second-order shim coils, where the current output reaches an accuracy of 1 mA. The performance of optimized coils is verified by imaging experiments. It is demonstrated that B_{0} homogeneity is improved from 157 to 111 ppm following the implementation of second-order shimming. The in vivo experiment shows that imaging quality is improved after shimming with the local signal-to-noise ratio increasing 1.16–1.92 folds.
Article Sequence Number: 4010511
Date of Publication: 01 September 2023

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