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Analysis of RF transmit performance for a 7T dual row multichannel MRI loop array.

Mikhail Kozlov¹, Robert Turner

¹Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig D-04103, Germany. kozlov@cbs.mpg.de

Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual International Conference

|January 19, 2012

Summary

Dual-row loop arrays improve radiofrequency (RF) field homogeneity in the human brain when combined with RF shimming. This dual-row array strategy enhances coverage and reduces power deposition in the brain, though peak SAR may increase.

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Area of Science:

Magnetic Resonance Imaging (MRI)
Radiofrequency (RF) Engineering
Biomedical Engineering

Background:

Optimizing radiofrequency (RF) field distribution (B(1)+ homogeneity) is crucial for effective Magnetic Resonance Imaging (MRI) of the human brain.
Single-row loop arrays have limitations in achieving uniform excitation across the entire brain volume.
Dual-row loop arrays offer potential for improved RF field performance.

Purpose of the Study:

To numerically investigate the RF field generation inside the human head using single and dual-row loop arrays.
To evaluate the performance of dual-row arrays with and without static RF shimming for brain excitation.
To assess the impact on B(1)+ homogeneity, coverage, power deposition, and specific absorption rate (SAR).

Main Methods:

Numerical simulations were performed to model RF field propagation within a human head model.
Investigated single and dual-row loop array configurations.
Analyzed excitation in uniform circular polarization (CP) mode and a dual-row configuration with a +90° phase shift between rows.

Main Results:

A dual-row array alone offers no advantage over a single-row array for uniform CP mode brain excitation.
Combining a dual-row array with static RF shimming (CP mode, +90° phase shift) significantly improves B(1)+ homogeneity and axial coverage.
This optimized dual-row configuration maintains excitation efficiency, reduces brain power deposition, but may moderately increase peak SAR(10 g) on the nose skin.

Conclusions:

Dual-row loop arrays, when utilized with specific RF shimming techniques, provide superior B(1)+ homogeneity and coverage for brain MRI.
The improved B(1)+ distribution leads to more efficient energy deposition within the brain.
Further research is needed to explore dual-row array performance in transmit SENSE applications.