Abstract #4416

Multiphoton Parallel Transmission (MP-pTx)

John M Drago^1,2,3, Bastien Guerin^2,3, Stephen F Cauley^2,3, and Lawrence L Wald^2,3,4

¹Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, United States, ²Harvard Medical School, Boston, MA, United States, ³A. A. Martinos Center for Biomedical Imaging, Charlestown, MA, United States, ⁴Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA, United States

Synopsis

Keywords: RF Pulse Design & Fields, Parallel Transmit & MultibandWe introduce multiphoton parallel transmission to mitigate nonuniform excitation in high-field MRI. Following an on-resonance birdcage subpulse, a multiphoton subpulse consisting of a single, off-resonance, high-frequency field from a birdcage coil, is supplemented with low-frequency parallel irradiation from a shim array. RF heating concerns are simplified compared to pTx, because only the birdcage coil produces significant SAR. Using a small-tip forward model, we optimize a nonconvex problem to find the amplitudes/phases of the low-frequency coils. Simulations demonstrate flip angle variation reduction across the brain ROI of 31.5% and NRMSE reduction of 42.0% compared to a conventional 7 T birdcage excitation.

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