2012
Zhu, Yudong; Alon, Leeor; Deniz, Cem M; Brown, Ryan; Sodickson, Daniel K
System and SAR characterization in parallel RF transmission Journal Article
In: Magnetic Resonance in Medicine, vol. 67, no. 5, pp. 1367–1378, 2012, ISSN: 07403194.
@article{Zhu2012,
title = {System and SAR characterization in parallel RF transmission},
author = {Yudong Zhu and Leeor Alon and Cem M Deniz and Ryan Brown and Daniel K Sodickson},
url = {http://doi.wiley.com/10.1002/mrm.23126},
doi = {10.1002/mrm.23126},
issn = {07403194},
year = {2012},
date = {2012-05-01},
journal = {Magnetic Resonance in Medicine},
volume = {67},
number = {5},
pages = {1367--1378},
abstract = {The markedly increased degrees of freedom introduced by parallel radiofrequency transmission presents both opportunities and challenges for specific absorption rate (SAR) management. On one hand they enable E-field tailoring and SAR reduction while facilitating excitation profile control. On other hand they increase the complexity of SAR behavior and the risk of inadvertently exacerbating SAR by improper design or playout of radiofrequency pulses. The substantial subject-dependency of SAR in high field magnetic resonance can be a compounding factor. Building upon a linear system concept and a calibration scheme involving a finite number of in situ measurements, this work establishes a clinically applicable method for characterizing global SAR behavior as well as channel-by-channel power transmission. The method offers a unique capability of predicting, for any excitation, the SAR and power consequences that are specific to the subject to be scanned and the MRI hardware. The method was validated in simulation and experimental studies, showing promise as the foundation to a prospective paradigm where power and SAR are not only monitored but, through prediction-guided optimization, proactively managed.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The markedly increased degrees of freedom introduced by parallel radiofrequency transmission presents both opportunities and challenges for specific absorption rate (SAR) management. On one hand they enable E-field tailoring and SAR reduction while facilitating excitation profile control. On other hand they increase the complexity of SAR behavior and the risk of inadvertently exacerbating SAR by improper design or playout of radiofrequency pulses. The substantial subject-dependency of SAR in high field magnetic resonance can be a compounding factor. Building upon a linear system concept and a calibration scheme involving a finite number of in situ measurements, this work establishes a clinically applicable method for characterizing global SAR behavior as well as channel-by-channel power transmission. The method offers a unique capability of predicting, for any excitation, the SAR and power consequences that are specific to the subject to be scanned and the MRI hardware. The method was validated in simulation and experimental studies, showing promise as the foundation to a prospective paradigm where power and SAR are not only monitored but, through prediction-guided optimization, proactively managed.
Deniz, Cem M; Alon, Leeor; Brown, Ryan; Sodickson, Daniel K; Zhu, Yudong
Specific absorption rate benefits of including measured electric field interactions in parallel excitation pulse design Journal Article
In: Magnetic Resonance in Medicine, vol. 67, no. 1, pp. 164–174, 2012, ISSN: 07403194.
@article{Deniz2012,
title = {Specific absorption rate benefits of including measured electric field interactions in parallel excitation pulse design},
author = {Cem M Deniz and Leeor Alon and Ryan Brown and Daniel K Sodickson and Yudong Zhu},
url = {http://doi.wiley.com/10.1002/mrm.23004},
doi = {10.1002/mrm.23004},
issn = {07403194},
year = {2012},
date = {2012-01-01},
journal = {Magnetic Resonance in Medicine},
volume = {67},
number = {1},
pages = {164--174},
abstract = {Specific absorption rate management and excitation fidelity are key aspects of radiofrequency pulse design for parallel transmission at ultra-high magnetic field strength. The design of radiofrequency pulses for multiple channels is often based on the solution of regularized least-squares optimization problems for which a regularization term is typically selected to control the integrated or peak pulse waveform amplitude. Unlike single-channel transmission, the specific absorption rate of parallel transmission is significantly influenced by interferences between the electric fields associated with the individual transmission elements, which a conventional regularization term does not take into account. This work explores the effects upon specific absorption rate of incorporating experimentally measurable electric field interactions into parallel transmission pulse design. Results of numerical simulations and phantom experiments show that the global specific absorption rate during parallel transmission decreases when electric field interactions are incorporated into pulse design optimization. The results also show that knowledge of electric field interactions enables robust prediction of the net power delivered to the sample or subject by parallel radiofrequency pulses before they are played out on a scanner.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Specific absorption rate management and excitation fidelity are key aspects of radiofrequency pulse design for parallel transmission at ultra-high magnetic field strength. The design of radiofrequency pulses for multiple channels is often based on the solution of regularized least-squares optimization problems for which a regularization term is typically selected to control the integrated or peak pulse waveform amplitude. Unlike single-channel transmission, the specific absorption rate of parallel transmission is significantly influenced by interferences between the electric fields associated with the individual transmission elements, which a conventional regularization term does not take into account. This work explores the effects upon specific absorption rate of incorporating experimentally measurable electric field interactions into parallel transmission pulse design. Results of numerical simulations and phantom experiments show that the global specific absorption rate during parallel transmission decreases when electric field interactions are incorporated into pulse design optimization. The results also show that knowledge of electric field interactions enables robust prediction of the net power delivered to the sample or subject by parallel radiofrequency pulses before they are played out on a scanner.