Approaching ultimate intrinsic specific absorption rate in radiofrequency shimming using high-permittivity materials at 7 Tesla

Gillian G. Haemer, Manushka Vaidya, Christopher M. Collins, Daniel K. Sodickson, Graham C. Wiggins, Riccardo Lattanzi

    Research output: Contribution to journalArticlepeer-review

    Abstract

    Purpose: The aim of this study was to evaluate the effect of integrated high-permittivity materials (HPMs) on excitation homogeneity and global specific absorption rate (SAR) for transmit arrays at 7T. Methods: A rapid electrodynamic simulation framework was used to calculate L-curves associated with excitation of a uniform 2D profile in a dielectric sphere. We used ultimate intrinsic SAR as an absolute performance reference to compare different transmit arrays in the presence and absence of a layer of HPM. We investigated the optimal permittivity for the HPM as a function of its thickness, the sample size, and the number of array elements. Results: Adding a layer of HPM can improve the performance of a 24-element array to match that of a 48-element array without HPM, whereas a 48-element array with HPM can perform as well as a 64-element array without HPM. Optimal relative permittivity values changed based on sample and coil geometry, but were always within a range obtainable with readily available materials (εr = 100–200). Conclusion: Integration of HPMs could be a practical method to improve RF shimming performance, alternative to increasing the number of coils. The proposed simulation framework could be used to explore the design of novel transmit arrays for head imaging at ultra-high field strength. Magn Reson Med 80:391–399, 2018.

    Original languageEnglish (US)
    Pages (from-to)391-399
    Number of pages9
    JournalMagnetic resonance in medicine
    Volume80
    Issue number1
    DOIs
    StatePublished - Jul 2018

    Keywords

    • RF shimming
    • Ultimate intrinsic SAR
    • global SAR
    • high permittivity material
    • transmit array

    ASJC Scopus subject areas

    • Radiology Nuclear Medicine and imaging

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