Mitigation of B1+ inhomogeneity using spatially selective excitation with jointly designed quadratic spatial encoding magnetic fields and RF shimming

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Mitigation of B1+ inhomogeneity using spatially selective excitation with jointly designed quadratic spatial encoding magnetic fields and RF shimming. / Hsu, Yi Cheng; Lattanzi, Riccardo; Chu, Ying Hua; Cloos, Martijn A.; Sodickson, Daniel K.; Lin, Fa Hsuan.

In: Magnetic Resonance in Medicine, Vol. 78, No. 2, 08.2017, p. 577–587 .

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Hsu, Yi Cheng ; Lattanzi, Riccardo ; Chu, Ying Hua ; Cloos, Martijn A. ; Sodickson, Daniel K. ; Lin, Fa Hsuan. / Mitigation of B1+ inhomogeneity using spatially selective excitation with jointly designed quadratic spatial encoding magnetic fields and RF shimming. In: Magnetic Resonance in Medicine. 2017 ; Vol. 78, No. 2. pp. 577–587 .

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@article{d401fccd1a094445a7ca2c3d11a1f0b3,
title = "Mitigation of B1+ inhomogeneity using spatially selective excitation with jointly designed quadratic spatial encoding magnetic fields and RF shimming",
abstract = "Purpose: The inhomogeneity of flip angle distribution is a major challenge impeding the application of high-field MRI. We report a method combining spatially selective excitation using generalized spatial encoding magnetic fields (SAGS) with radiofrequency (RF) shimming to achieve homogeneous excitation. This method can be an alternative approach to address the challenge of inhomogeneity using nonlinear gradients. Methods: We proposed a two-step algorithm that jointly optimizes the combination of nonlinear spatial encoding magnetic fields and the combination of multiple RF transmitter coils and then optimizes the locations, RF amplitudes, and phases of the spokes. Results: Our results show that jointly designed SAGS and RF shimming can provide a more homogeneous flip angle distribution than using SAGS or RF shimming alone. Compared with RF shimming alone, our approach can reduce the relative standard deviation of flip angle by 56{\%} and 52{\%} using phantom and human head data, respectively. Conclusion: The jointly designed SAGS and RF shimming method can be used to achieve homogeneous flip angle distributions when fully parallel RF transmission is not available. Magn Reson Med 78:577–587, 2017.",
keywords = "7T, Fast imaging, Nonlinear gradient, RF inhomogeneity, RF shimming, SAR",
author = "Hsu, {Yi Cheng} and Riccardo Lattanzi and Chu, {Ying Hua} and Cloos, {Martijn A.} and Sodickson, {Daniel K.} and Lin, {Fa Hsuan}",
year = "2017",
month = "8",
doi = "10.1002/mrm.26397",
language = "English",
volume = "78",
pages = "577–587",
journal = "Magnetic Resonance in Medicine",
issn = "0740-3194",
publisher = "Wiley",
number = "2",

}

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TY - JOUR

T1 - Mitigation of B1+ inhomogeneity using spatially selective excitation with jointly designed quadratic spatial encoding magnetic fields and RF shimming

AU - Hsu, Yi Cheng

AU - Lattanzi, Riccardo

AU - Chu, Ying Hua

AU - Cloos, Martijn A.

AU - Sodickson, Daniel K.

AU - Lin, Fa Hsuan

PY - 2017/8

Y1 - 2017/8

N2 - Purpose: The inhomogeneity of flip angle distribution is a major challenge impeding the application of high-field MRI. We report a method combining spatially selective excitation using generalized spatial encoding magnetic fields (SAGS) with radiofrequency (RF) shimming to achieve homogeneous excitation. This method can be an alternative approach to address the challenge of inhomogeneity using nonlinear gradients. Methods: We proposed a two-step algorithm that jointly optimizes the combination of nonlinear spatial encoding magnetic fields and the combination of multiple RF transmitter coils and then optimizes the locations, RF amplitudes, and phases of the spokes. Results: Our results show that jointly designed SAGS and RF shimming can provide a more homogeneous flip angle distribution than using SAGS or RF shimming alone. Compared with RF shimming alone, our approach can reduce the relative standard deviation of flip angle by 56% and 52% using phantom and human head data, respectively. Conclusion: The jointly designed SAGS and RF shimming method can be used to achieve homogeneous flip angle distributions when fully parallel RF transmission is not available. Magn Reson Med 78:577–587, 2017.

AB - Purpose: The inhomogeneity of flip angle distribution is a major challenge impeding the application of high-field MRI. We report a method combining spatially selective excitation using generalized spatial encoding magnetic fields (SAGS) with radiofrequency (RF) shimming to achieve homogeneous excitation. This method can be an alternative approach to address the challenge of inhomogeneity using nonlinear gradients. Methods: We proposed a two-step algorithm that jointly optimizes the combination of nonlinear spatial encoding magnetic fields and the combination of multiple RF transmitter coils and then optimizes the locations, RF amplitudes, and phases of the spokes. Results: Our results show that jointly designed SAGS and RF shimming can provide a more homogeneous flip angle distribution than using SAGS or RF shimming alone. Compared with RF shimming alone, our approach can reduce the relative standard deviation of flip angle by 56% and 52% using phantom and human head data, respectively. Conclusion: The jointly designed SAGS and RF shimming method can be used to achieve homogeneous flip angle distributions when fully parallel RF transmission is not available. Magn Reson Med 78:577–587, 2017.

KW - 7T

KW - Fast imaging

KW - Nonlinear gradient

KW - RF inhomogeneity

KW - RF shimming

KW - SAR

UR - http://www.scopus.com/inward/record.url?scp=84990194342&partnerID=8YFLogxK

U2 - 10.1002/mrm.26397

DO - 10.1002/mrm.26397

M3 - Article

VL - 78

SP - 577

EP - 587

JO - Magnetic Resonance in Medicine

JF - Magnetic Resonance in Medicine

SN - 0740-3194

IS - 2

ER -

ID: 9103237