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Abstract #4416

The Ritz adjoint method for optimization of arbitrary waveform excitation pulses: Demonstration in slice-selective parallel transmission

John M Drago1,2,3, Georgy Guryev1, Nicolas Arango1, Bastien Guerin2,3, and Lawrence L Wald2,3,4
1Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, United States, 2Harvard Medical School, Boston, MA, United States, 3Dept. of Radiology, Massachusetts General Hospital, A. A. Martinos Center for Biomedical Imaging, Charlestown, MA, United States, 4Harvard-MIT Division of Health Sciences Technology, Cambridge, MA, United States

Synopsis

Keywords: RF Pulse Design & Fields, RF Pulse Design & Fields

Motivation: Optimization of arbitrary RF and gradient waveforms provides considerable degrees-of-freedom to mitigate excitation inhomogeneity at 7 T; however, waveform optimization is a computationally difficult non-convex optimization problem.

Goal(s): We introduce an arbitrary waveform pulse optimization method to enable real-time (~3 min) tailored slice-selective pulse optimization.

Approach: We employ the Ritz adjoint method to efficiently calculate the optimization gradients to optimize waveforms parameterized by global polynomials, while respecting SAR and system constraints.

Results: A 3.5 ms slice-selective, tailored parallel transmission pulse can be designed in 3 minutes with in-plane NRMSE 50% better than an optimized 3-spoke design.

Impact: The Ritz adjoint method efficiently optimized arbitrary waveform universal and tailored parallel transmission slice-selective pulses that respect SAR constraints and system limitations while correcting the flip angle inhomogeneities for high-field excitations.

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