Harmonic-mapping-based design of gradient coils on irregular MRI surfaces

Area of Science:

• Medical Imaging
• Biophysics
• Electrical Engineering

Background:

• Designing head-mounted gradient coils for brain imaging presents challenges due to irregular head surfaces.
• Existing methods like the stream function and boundary element methods struggle with optimization on these complex geometries.

Purpose of the Study:

• To develop a novel gradient coil design method with reduced variables for irregular surfaces.
• To successfully design gradient coils for brain imaging applications on a semi-ellipsoidal surface.

Main Methods:

• Harmonic mapping of triangular meshes from the target irregular surface to a rectangle.
• Establishing a link between the rectangular stream function and the coil shape on the original surface via inverse harmonic mapping.
• Utilizing particle swarm optimization for basis function coefficients to finalize coil design.

Main Results:

• Designed and manufactured Gy and Gz gradient coils for a semi-ellipsoidal surface.
• Simulated and measured results demonstrate more linear magnetic fields compared to a reference method.
• Maximum magnetic field deviation for the Gy coil was 4.02% (simulated) and 15.78% (measured), significantly lower than the reference (33.3%).
• Maximum magnetic field deviation for the Gz coil was 2.57% (simulated) and 7.20% (measured), compared to the reference (27.8%).

Conclusions:

• A new, efficient coil design method for irregular 2D surfaces has been established.
• The method yields gradient coils with superior magnetic field linearity and uniformity.
• The designed coils show significant advantages over the boundary element method, with measured deviations well below reference designs.