Elliptical Halbach magnet and gradient modules for low-field portable magnetic resonance imaging

Area of Science:

• Medical Imaging
• Magnetics Engineering
• Biophysics

Background:

• Portable MRI scanners offer potential for point-of-care diagnostics.
• Existing low-weight MRI configurations face limitations in field homogeneity and gradient performance.
• Halbach magnet configurations are explored for their efficiency in generating strong magnetic fields.

Purpose of the Study:

• To design a complete magnetic system for a truly portable MRI scanner for neurological and musculoskeletal (MSK) applications.
• To optimize field homogeneity, field of view (FoV), and gradient performance in a lightweight configuration.
• To explore optimal elliptic-bore Halbach configurations using discrete permanent magnet arrays.

Main Methods:

• Optimized tightly packed Nd2Fe14B cube arrays using differential evolution algorithms.
• Designed shimming magnet arrays with interior point and differential evolution methods.
• Developed and optimized elliptical gradient coils using a target field method, considering heat dissipation.

Main Results:

• Constructed a portable MRI scanner with an elliptical Halbach bore (10 and 14 cm semi-axes).
• Achieved an 87 mT field with homogeneity down to 5700 ppm in a 20 cm FoV, weighing 216 kg.
• Gradient efficiencies reached 0.8 mT/m/A, with a 28 cm lobe separation, and heat dissipation of ~25 W.

Conclusions:

• Elliptic-bore Halbach magnets significantly enhance the ergonomicity and field distribution of portable MRI scanners.
• The design allows for full-length gradient support, increasing the field of view (FoV).
• This geometry shows potential for adaptation into prospective low-cost, whole-body MRI technology.