T1-Nonlinearity Corrections for Fast Transmit-Array B1+-Mapping of the Human Brain in the Small-Tip-Angle Regime

Martijn Anton Cloos^1,2, Nicolas Boulant¹, Guillaume Ferrand², Michel Luong², Christopher J. Wiggins¹, Denis Le Bihan¹, Alexis Amadon¹

Currently, B₁⁺-mapping is particularly difficult due to the combination of time and conservative specific absorption rate (SAR) constraints applicable to parallel transmission studies involving human subjects. Measuring relative B₁⁺-maps in the low-tip-angle regime provides a low SAR solution. Inherently, this method requires a relatively long TR (0.2-1.0s) to remain in the domain where the signal intensity is linearly dependent for a large range of flip-angles. Considering 3D tailored excitation pulses, such TR values require too much time for transmit-array B₁⁺-mapping and pulse validation. To tackle the aforementioned problems, an optimized version of this method for the quantification of non-selective excitation pulses is presented.