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A 31-channel integrated “AC/DC” B0 shim and radiofrequency receive array coil for improved 7T MRI
{Purpose: To test an integrated "AC/DC" array approach at 7T, where B0 inhomogeneity poses an obstacle for functional imaging, diffusion-weighted MRI, MR spectroscopy, and other applications. Methods: A close-fitting 7T 31-channel (31-ch) brain array was constructed and tested using combined Rx and $\Delta$B0 shim channels driven by a set of rapidly switchable current amplifiers. The coil was compared to a shape-matched 31-ch reference receive-only array for RF safety, signal-to-noise ratio (SNR), and inter-element noise correlation. We characterize the coil array{\textquotesingle}s ability to provide global and dynamic (slice-optimized) shimming using $\Delta$B0 field maps and echo planar imaging (EPI) acquisitions. Results: The SNR and average noise correlation were similar to the 31-ch reference array. Global and slice-optimized shimming provide 11{\textpercent} and 40{\textpercent} improvements respectively compared to baseline second-order spherical harmonic shimming. Birdcage transmit coil efficiency was similar for the reference and AC/DC array setups. Conclusion: Adding $\Delta$B0 shim capability to a 31-ch 7T receive array can significantly boost 7T brain B0 homogeneity without sacrificing the array{\textquotesingle}s rdiofrequency performance, potentially improving ultra-high field neuroimaging applications that are vulnerable to off-resonance effects.}
@article{item_3346014, title = {{A 31-channel integrated {\textquotedblleft}AC/DC{\textquotedblright} B0 shim and radiofrequency receive array coil for improved 7T MRI}}, journal = {{Magnetic Resonance in Medicine}}, abstract = {{Purpose: To test an integrated "AC/DC" array approach at 7T, where B0 inhomogeneity poses an obstacle for functional imaging, diffusion-weighted MRI, MR spectroscopy, and other applications. Methods: A close-fitting 7T 31-channel (31-ch) brain array was constructed and tested using combined Rx and $\Delta$B0 shim channels driven by a set of rapidly switchable current amplifiers. The coil was compared to a shape-matched 31-ch reference receive-only array for RF safety, signal-to-noise ratio (SNR), and inter-element noise correlation. We characterize the coil array{\textquotesingle}s ability to provide global and dynamic (slice-optimized) shimming using $\Delta$B0 field maps and echo planar imaging (EPI) acquisitions. Results: The SNR and average noise correlation were similar to the 31-ch reference array. Global and slice-optimized shimming provide 11{\textpercent} and 40{\textpercent} improvements respectively compared to baseline second-order spherical harmonic shimming. Birdcage transmit coil efficiency was similar for the reference and AC/DC array setups. Conclusion: Adding $\Delta$B0 shim capability to a 31-ch 7T receive array can significantly boost 7T brain B0 homogeneity without sacrificing the array{\textquotesingle}s rdiofrequency performance, potentially improving ultra-high field neuroimaging applications that are vulnerable to off-resonance effects.}}, volume = {87}, number = {2}, pages = {1074--1092}, publisher = {Wiley-Liss}, address = {New York}, year = {2022}, slug = {item_3346014}, author = {Stockmann, JP and Arango, NS and Witzel, T and Mareyam, A and Sappo, C and Zhou, J and Jenkins, L and Craven-Brightman, L and Milshteyn, E and Davids, M and Hoge, WS and Sliwiak, M and Nasr, S and Keil, B and Adalsteinsson, E and Guerin, B and White, JK and Setsompop, K and Polimeni, JR and Wald, LL} }