Local in vivo shimming using adaptive passive shim positioning

Area of Science:

• Medical Physics
• Neuroimaging
• Magnetic Resonance Imaging

Background:

• Achieving optimal magnetic field homogeneity is crucial for high-resolution in vivo Magnetic Resonance Imaging (MRI).
• Passive shimming, using physical shim pieces, is a common method to improve field homogeneity, but optimal configurations can vary significantly between individuals.

Purpose of the Study:

• To propose and validate a subject-specific local in vivo passive shimming method.
• To demonstrate the existence of intersubject variability in optimal passive shim positions.
• To show the efficacy of the proposed method in overcoming individual differences for improved field homogeneity.

Main Methods:

• Development of a novel shimming structure with millimeter-resolution adjustment capabilities for passive shims.
• Computation of optimal shim positions for each subject using a convex optimization algorithm applied to field map data.
• Comparison of MRI field homogeneity using predetermined fixed shim positions versus individually optimized shim positions.

Main Results:

• Significant intersubject variability in optimal passive shim positions was observed.
• The proposed location-sensitive, subject-specific shimming method demonstrated improved main field homogeneity in vivo.
• Individually adjusted shim positions led to superior field homogeneity compared to fixed, predetermined positions.

Conclusions:

• Subject-specific passive shimming is essential for optimizing in vivo MRI field homogeneity.
• The developed method effectively addresses intersubject variability in passive shim requirements.
• This approach holds promise for enhancing the quality and reliability of neuroimaging studies.