Gradient-modulated SWIFT

Research output: Contribution to journalArticlepeer-review

13 Scopus citations


Purpose Methods designed to image fast-relaxing spins, such as sweep imaging with Fourier transformation (SWIFT), often utilize high excitation bandwidth and duty cycle, and in some applications the optimal flip angle cannot be used without exceeding safe specific absorption rate (SAR) levels. The aim is to reduce SAR and increase the flexibility of SWIFT by applying time-varying gradient-modulation (GM). The modified sequence is called GM-SWIFT. Theory and Methods The method known as gradient-modulated offset independent adiabaticity was used to modulate the radiofrequency (RF) pulse and gradients. An expanded correlation algorithm was developed for GM-SWIFT to correct the phase and scale effects. Simulations and phantom and in vivo human experiments were performed to verify the correlation algorithm and to evaluate imaging performance. Results GM-SWIFT reduces SAR, RF amplitude, and acquisition time by up to 90%, 70%, and 45%, respectively, while maintaining image quality. The choice of GM parameter influences the lower limit of short T2 sensitivity, which can be exploited to suppress unwanted image haze from unresolvable ultrashort T2 signals originating from plastic materials in the coil housing and fixatives. Conclusions GM-SWIFT reduces peak and total RF power requirements and provides additional flexibility for optimizing SAR, RF amplitude, scan time, and image quality.

Original languageEnglish (US)
Pages (from-to)537-546
Number of pages10
JournalMagnetic resonance in medicine
Issue number2
StatePublished - Feb 1 2016

Bibliographical note

Publisher Copyright:
© 2015 Wiley Periodicals, Inc.


  • GOIA
  • SAR
  • fast relaxing spins
  • frequency sweep
  • gradient modulation
  • ultrashort T


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