Spin Lock Adiabatic Correction (SLAC) for B1-insensitive pulse design at 7T

Edward M Green; Yasmin Blunck; Bahman Tahayori; Peter M Farrell; James C Korte; Leigh A Johnston

doi:10.1016/j.jmr.2019.106595

Spin Lock Adiabatic Correction (SLAC) for B₁-insensitive pulse design at 7T

J Magn Reson. 2019 Nov:308:106595. doi: 10.1016/j.jmr.2019.106595. Epub 2019 Sep 11.

Authors

Edward M Green¹, Yasmin Blunck², Bahman Tahayori³, Peter M Farrell⁴, James C Korte⁵, Leigh A Johnston⁶

Affiliations

¹ Melbourne Brain Centre Imaging Unit, The University of Melbourne, Melbourne, VIC, Australia; Department of Biomedical Engineering, The University of Melbourne, Melbourne, VIC, Australia. Electronic address: egreen@student.unimelb.edu.au.
² Melbourne Brain Centre Imaging Unit, The University of Melbourne, Melbourne, VIC, Australia; Department of Biomedical Engineering, The University of Melbourne, Melbourne, VIC, Australia. Electronic address: bluncky@unimelb.edu.au.
³ Department of Biomedical Engineering, The University of Melbourne, Melbourne, VIC, Australia; Department of Medical Physics and Biomedical Engineering, Shiraz University of Medical Sciences, Shiraz, Iran; Center for Neuromodulation and Pain, Shiraz, Iran. Electronic address: tahayori@sums.ac.ir.
⁴ Department of Electrical and Electronic Engineering, The University of Melbourne, Melbourne, VIC, Australia. Electronic address: pfarrell@unimelb.edu.au.
⁵ Department of Biomedical Engineering, The University of Melbourne, Melbourne, VIC, Australia; Department of Physical Sciences, Peter MacCallum Cancer Centre, Melbourne, VIC, Australia. Electronic address: james.korte@petermac.org.
⁶ Melbourne Brain Centre Imaging Unit, The University of Melbourne, Melbourne, VIC, Australia; Department of Biomedical Engineering, The University of Melbourne, Melbourne, VIC, Australia. Electronic address: l.johnston@unimelb.edu.au.

PMID: 31542447
DOI: 10.1016/j.jmr.2019.106595

Abstract

A new framework for B₁ insensitive adiabatic pulse design is proposed, denoted Spin Lock Adiabatic Correction (SLAC), which counteracts deviations from ideal behaviour through inclusion of an additional correction component during pulse design. SLAC pulses are theoretically derived, then applied to the design of enhanced BIR-4 and hyperbolic secant pulses to demonstrate practical utility of the new pulses. At 7T, SLAC pulses are shown to improve the flip angle homogeneity compared to a standard adiabatic pulse with validation in both simulations and phantom experiments, under SAR equivalent experimental conditions. The SLAC framework can be applied to any arbitrary adiabatic pulse to deliver excitation with increased B₁ insensitivity.

Keywords: Adiabatic pulse; B(1) inhomogeneity; Frequency-modulated; MRI; RF excitation.