Dataset Information

Bench to bore ramifications of inter-subject head differences on RF shimming and specific absorption rates at 7T.

ABSTRACT:

Purpose

This study shows how inter-subject variation over a dataset of 72 head models results in specific absorption rate (SAR) and B₁⁺ field homogeneity differences using common shim scenarios.

Methods

MR-CT datasets were used to segment 71 head models into 10 tissue compartments. These head models were affixed to the shoulders and neck of the virtual family Duke model and placed within an 8 channel transmit surface-loop array to simulate the electromagnetic fields of a 7T imaging experiment. Radio frequency (RF) shimming using the Gerchberg-Saxton algorithm and Circularly Polarized shim weights over the entire brain and select slices of each model was simulated. Various SAR metrics and B₁⁺ maps were calculated to demonstrate the contribution of head variation to transmit inhomogeneity and SAR variability.

Results

With varying head geometries the loading for each transmit loop changes as evidenced by changes in S-parameters. The varying shim conditions and head geometries are shown to affect excitation uniformity, spatial distributions of local SAR, and SAR averaging over different pulse sequences. The Gerchberg-Saxton RF shimming algorithm outperforms circularly polarized shimming for all head models. Peak local SAR within the coil most often occurs nearest the coil on the periphery of the body. Shim conditions vary the spatial distribution of SAR.

Conclusion

The work gives further support to the need for fast and more subject specific SAR calculations to maintain safety. Local SAR_10g is shown to vary spatially given shim conditions, subject geometry and composition, and position within the coil.

SUBMITTER: Hardy BM

PROVIDER: S-EPMC9376015 | biostudies-literature | 2022 Oct

REPOSITORIES: biostudies-literature

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Publications

Bench to bore ramifications of inter-subject head differences on RF shimming and specific absorption rates at 7T.

Hardy Benjamin M BM Banik Rana R Yan Xinqiang X Anderson Adam W AW

Magnetic resonance imaging 20220713

<h4>Purpose</h4>This study shows how inter-subject variation over a dataset of 72 head models results in specific absorption rate (SAR) and B<sub>1</sub><sup>+</sup> field homogeneity differences using common shim scenarios.<h4>Methods</h4>MR-CT datasets were used to segment 71 head models into 10 tissue compartments. These head models were affixed to the shoulders and neck of the virtual family Duke model and placed within an 8 channel transmit surface-loop array to simulate the electromagnetic ...[more]

PMID: 35842192

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Dataset Information

Bench to bore ramifications of inter-subject head differences on RF shimming and specific absorption rates at 7T.

Purpose

Methods

Results

Conclusion

Publications

Bench to bore ramifications of inter-subject head differences on RF shimming and specific absorption rates at 7T.

Similar Datasets

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