Optimal echo times for multi-gradient echo-based B0 field-mapping

Yasmin Geiger, Assaf Tal

Research output: Contribution to journalArticlepeer-review


B0 field maps are used ubiquitously in neuroimaging, in disciplines ranging from magnetic resonance spectroscopy to temperature mapping and susceptibility-weighted imaging. Most B0 maps are acquired using standard gradient-echo–based vendor-provided sequences, often comprised of two echoes spaced a few milliseconds apart. Herein, we analyze the optimal spacing of echo times, defined as those maximizing precision—minimizing the standard deviation—for a fixed total acquisition time. Field estimation is carried out using a weighted least squares estimator. The standard deviation is shown to be approximately inversely proportional to the total acquisition time, suggesting a law of diminishing returns, whereby substantial gains are obtained up to a certain point, with little improvement beyond that point. Validations are provided in a phantom and a group of volunteers. Multi-gradient echo sequences are readily available on all manufacturer platforms, making our recommendations straightforward to implement on any modern scanner.

Original languageEnglish
Article numbere4316
JournalNMR in Biomedicine
Issue number7
StatePublished - 1 Jul 2020
Externally publishedYes

Bibliographical note

Funding Information:
Assaf Tal acknowledges the support of the Monroy‐Marks Career Development Fund, the Carolito Stiftung Fund, the Leona M. and Harry B. Helmsley Charitable Trust and the historic generosity of the Harold Perlman Family. This work was funded by the Minerva Foundation.

Publisher Copyright:
© 2020 John Wiley & Sons, Ltd.


  • B0 mapping
  • field mapping
  • geometric distortion
  • multi-gradient echo
  • quantitative susceptibility mapping
  • shimming


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