FAMASITO: FASTMAP Shim Tool towards user-friendly single-step B₀ homogenization

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Neuroimaging Physics

Background:

• B0 shimming is crucial for high-resolution MRI, aiming to achieve optimal magnetic field homogeneity.
• Traditional shimming methods often require multistep iterative adjustments due to implementation complexities.
• The FASTMAP (Fast, Automatic Shimming by Mapping Along Projections) method offers a theoretical framework for B0 field quantification.

Purpose of the Study:

• To develop and validate a software package, FAMASITO, for efficient and automated B0 shimming.
• To address the limitations of applying the FASTMAP concept in practical MRI sequence implementation and shim hardware.
• To demonstrate single-step optimal adjustment of first- and second-order B0 field terms.

Main Methods:

• Implementation of a FASTMAP pulse sequence within the FAMASITO software package.
• Development of automated calibration and analysis routines for B0 field mapping.
• Creation of a script for automated experimental execution and data processing.
• Testing FAMASITO on the prefrontal cortex, a known difficult-to-shim brain region, in seven human volunteers.

Main Results:

• FAMASITO enables optimal single-step adjustment of first- and second-order spherical harmonic terms for B0 shimming.
• The method achieved a mean refinement of linear terms below 1% in the prefrontal cortex.
• Demonstrated efficient shimming in a challenging anatomical location, reducing the need for iterative adjustments.

Conclusions:

• FAMASITO provides an effective solution for rapid and automated B0 shimming, overcoming practical implementation challenges.
• The software package significantly improves the efficiency of achieving optimal magnetic field homogeneity.
• Single-step shimming with FAMASITO is feasible and highly effective, particularly in difficult-to-shim brain regions.