Direct control of the temperature rise in parallel transmission by means of temperature virtual observation points: Simulations at 10.5 tesla

Nicolas Boulant, Xiaoping Wu, Gregor Adriany, Sebastian Schmitter, Kamil Uğurbil, Pierre François Van de Moortele

Research output: Contribution to journalArticlepeer-review

26 Scopus citations

Abstract

Purpose A method using parallel transmission to mitigate B1+ inhomogeneity while explicitly constraining the temperature rise is reported and compared with a more traditional SAR-constrained pulse design. Methods Finite difference time domain simulations are performed on a numerical human head model and for a 16-channel coil at 10.5 Tesla. Based on a set of presimulations, a virtual observation point compression model for the temperature rise is derived. This compact representation is then used in a nonlinear programming algorithm for pulse design under explicit temperature rise constraints. Results In the example of a time-of-flight sequence, radiofrequency pulse performance in some cases is increased by a factor of two compared with SAR-constrained pulses, while temperature rise is directly and efficiently controlled. Pulse performance can be gained by relaxing the SAR constraints, but at the expense of a loss of direct control on temperature. Conclusion Given the importance of accurate safety control at ultrahigh field and the lack of direct correspondence between SAR and temperature, this work motivates the need for thorough thermal studies in normal in vivo conditions. The tools presented here will possibly contribute to safer and more efficient MR exams.

Original languageEnglish (US)
Pages (from-to)249-256
Number of pages8
JournalMagnetic resonance in medicine
Volume75
Issue number1
DOIs
StatePublished - Jan 1 2016

Bibliographical note

Publisher Copyright:
© 2015 Wiley Periodicals, Inc.

Keywords

  • optimization
  • parallel transmission
  • temperature
  • ultrahigh field
  • virtual observation points

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