Motivation: Generating spatially uniform multiphoton excitation requires a z-directed transmit coil to produce a homogeneous B1,z field. Goal(s): To improve the spatial homogeneity of the B1,z field with a numerically optimized coil. Approach: We compared two coil winding patterns: solenoid vs. numerically optimized. We computed the magnetic field spatial distribution and experimentally measured the B1,z field by adapting the double flip angle method to multiphoton excitation. Results: Our optimized coil demonstrated a 28% improvement in spatial homogeneity, characterized by the diameter with a coefficient of variation (CV) of 20% or less. In simulation, we observed a 20-fold decrease in CV for the optimized coil. Impact: Our numerically optimized z-directed transmit coil provides improved spatial homogeneity and field strength for multiphoton MRI applications. This advancement supports our future experimental requirements as we further explore the applications of multiphoton MRI.
Kempfert et al. (Tue,) studied this question.
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