Interslice current change constrained B₀ shim optimization for accurate high-order dynamic shim updating with...

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Biophysics
• Medical Physics

Background:

• Dynamic B0 shimming in MRI faces challenges like eddy currents, ill-posed optimizations, and high power supply demands.
• Eddy current generation is linked to shim current changes, and B0 inhomogeneity varies smoothly in the slice direction.

Purpose of the Study:

• To develop and implement a novel shim optimization algorithm for dynamic B0 shimming.
• The algorithm aims to limit shim current amplitudes and their temporal variations using constraints and regularization.

Main Methods:

• Implemented a new algorithm that reduces eddy current generation by limiting interslice shim current changes.
• Addressed shim degeneracy and high current amplitudes by penalizing high solution norms.
• Validated the algorithm through simulations, phantom, and in vivo measurements.

Main Results:

• The proposed algorithm substantially reduced absolute shim current amplitudes and their temporal variation.
• Achieved a B0 homogeneity factor of 2.0, comparable to conventional methods (2.1).
• Demonstrated a 14-fold reduction in average maximum shim current changes compared to conventional methods.

Conclusions:

• The novel algorithm effectively reduces shim current amplitudes and temporal variation with minimal impact on B0 homogeneity.
• This approach has the potential to overcome key challenges in dynamic B0 shimming.
• The findings suggest increased availability and applicability of dynamic B0 shimming techniques.