B 0 concomitant field compensation for MRI systems employing asymmetric transverse gradient coils

Paul T. Weavers, Shengzhen Tao, Joshua D. Trzasko, Louis M. Frigo, Yunhong Shu, Matthew A. Frick, Seung Kyun Lee, Thomas K.F. Foo, Matt A. Bernstein

Research output: Contribution to journalArticle

13 Scopus citations

Abstract

Purpose: Imaging gradients result in the generation of concomitant fields, or Maxwell fields, which are of increasing importance at higher gradient amplitudes. These time-varying fields cause additional phase accumulation, which must be compensated for to avoid image artifacts. In the case of gradient systems employing symmetric design, the concomitant fields are well described with second-order spatial variation. Gradient systems employing asymmetric design additionally generate concomitant fields with global (zeroth-order or B 0 ) and linear (first-order) spatial dependence. Methods: This work demonstrates a general solution to eliminate the zeroth-order concomitant field by applying the correct B 0 frequency shift in real time to counteract the concomitant fields. Results are demonstrated for phase contrast, spiral, echo-planar imaging (EPI), and fast spin-echo imaging. Results: A global phase offset is reduced in the phase-contrast exam, and blurring is virtually eliminated in spiral images. The bulk image shift in the phase-encode direction is compensated for in EPI, whereas signal loss, ghosting, and blurring are corrected in the fast-spin echo images. Conclusion: A user-transparent method to compensate the zeroth-order concomitant field term by center frequency shifting is proposed and implemented. This solution allows all the existing pulse sequences—both product and research—to be retained without any modifications. Magn Reson Med 79:1538–1544, 2018.

Original languageEnglish (US)
Pages (from-to)1538-1544
Number of pages7
JournalMagnetic Resonance in Medicine
Volume79
Issue number3
DOIs
StatePublished - Mar 2018

Keywords

  • B
  • asymmetric gradients
  • frequency shifting
  • real-time correction

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging

Fingerprint Dive into the research topics of 'B <sub>0</sub> concomitant field compensation for MRI systems employing asymmetric transverse gradient coils'. Together they form a unique fingerprint.

  • Cite this