Dual polarity encoded MRI using high bandwidth radiofrequency pulses for robust imaging with large field inhomogeneity

Research output: Contribution to journalArticlepeer-review

Abstract

Purpose: The ability to use dual polarity encoded MRI with the missing pulse steady-state free precession (MP-SSFP) sequence is demonstrated to perform robust MRI with low radiofrequency (RF) amplitude, where the field is distorted by embedding metallic screws in an agar phantom. Image-based estimation of the 3D ΔB0 map and image distortion correction is shown to require ~1 minute to perform. Theory and methods: Dual polarity encoded MP-SSFP was implemented at 1.5T and used to image agar phantoms with one stainless steel and one titanium screw embedded inside. A multispectral fast spin-echo acquisition was performed for comparison. Self-consistent ΔB0 estimation is performed iteratively using a 3D B-spline basis, which is compared to the ΔB0 estimate generated by the multispectral sequence. Results: Dual polarity encoded MP-SSFP yields image quality similar to the multispectral sequence used with substantially less imaging time, provided the MP-SSFP experimental parameters are chosen well. The multispectral sequence appears to visualize modestly closer in proximity to the metallic screws used, despite the spectral bins covering the same bandwidth as the pulses used in MP-SSFP. However, MP-SSFP avoids ripple artifacts characteristic of the multispectral sequence. The ΔB0 estimate generated by MP-SSFP is qualitatively similar to that generated by the multispectral sequence but larger in magnitude. Conclusion: Despite longer processing time compared to multispectral imaging, MP-SSFP yields similar image quality with significantly lower acquisition times in the absence of parallel imaging. The work herein demonstrates the ability to perform 3D ΔB0 estimation and image correction within a reasonable amount of time, ~1 minute.

Original languageEnglish (US)
JournalMagnetic resonance in medicine
Early online dateMar 29 2021
DOIs
StateE-pub ahead of print - Mar 29 2021

Bibliographical note

Funding Information:
This work was supported by the National Institutes of Health grants U01 EB025153 and P41 EB025144‐01. The authors thank Dr. Casey Johnson for providing the screws to embed in the phantom, Dr. Jutta Ellermann for helpful advice and discussions, and the referees for providing comments to improve the clarity of this work.

Publisher Copyright:
© 2021 International Society for Magnetic Resonance in Medicine

Keywords

  • accessible MRI
  • dual polarity
  • MP-SSFP
  • portable MRI
  • reverse encoding

PubMed: MeSH publication types

  • Journal Article

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