Abstract #0524

Universal Design of Multiphoton Parallel Transmission (MP-pTx) Pulses for Uniform, High-Flip Angle Excitations

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

¹Dept. of Electrical 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, Boston, MA, United States, ⁴Dept. of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA, United States

Synopsis

Keywords: High-Field MRI, Brain

Motivation: Contrast in high-field MRI is complicated by the spatially non-uniform transmission profile of birdcage coils.

Goal(s): We create “universal” pulses for spatially-uniform excitations using multiphoton parallel transmission (MP-pTx).

Approach: MP-pTx operates a $$$B_z$$$ shim array in the kHz range to supplement birdcage excitation. We extend this framework to arbitrary flip angles and a universal design (a population of $$$B_1^+$$$ and $$$\Delta B_0$$$ maps) using spinor-domain, Bloch dynamics representation.

Results: Universal MP-pTx pulses have 11.3%, and 16.3% flip angle NRMSE for 90º and 180º pulses played on test subjects not used for training, compared to 24.5% and 25.3% with conventional birdcage.

Impact: Universal MP-pTx pulses will allow users to mitigate flip angle inhomogeneity present in the brain at 7 T using precomputed pulses without SAR concerns beyond that of a conventional birdcage transmit coil or subject-specific calculations.

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