Purpose: Integrated parallel reception, excitation, and shimming (iPRES) coil arrays allow radio-frequency currents and direct currents to flow in the same coils, which enables excitation/reception and localized B0 shimming with a single coil array. The purpose of this work was to improve their shimming performance by adding the capability to shim higher-order local B0 inhomogeneities that are smaller than the radio-frequency coil elements.
Methods: A novel design was proposed in which each radio-frequency/shim coil element is divided into multiple direct current loops, each using an independent direct current current, to increase the number of magnetic fields available for shimming while maintaining the signal-to-noise ratio of the coil. This new design is termed iPRES(N), where N represents the number of direct current loops per radio-frequency coil element. Proof-of-concept phantom and human experiments were performed with an 8-channel body coil array to demonstrate its advantages over the original iPRES(1) design.
Results: The average B0 homogeneity in various organs before shimming and after shimming with the iPRES(1) or iPRES(3) coil arrays was 0.24, 0.11, and 0.05 ppm, respectively. iPRES(3) thus reduced the B0 inhomogeneity by 53% and further reduced distortions in echo-planar images of the abdomen when compared with iPRES(1).
Conclusion: iPRES(N) can correct for localized B0 inhomogeneities more effectively than iPRES(1) with no signal-to-noise ratio loss, resulting in a significant improvement in image quality.
Citation: Darnell, D., Truong, T. K., & Song, A. W. (2017). Integrated parallel reception, excitation, and shimming (iPRES) with multiple shim loops per radio-frequency coil element for improved B0 shimming. Magnetic resonance in medicine, 77(5), 2077–2086. https://doi.org/10.1002/mrm.26267