Permanent Magnet System for MRI with Constant Gradient mechanically adjustable in Direction and Strength

TL;DR

This paper introduces a permanent magnet MRI system that produces adjustable, homogeneous magnetic field gradients without gradient coils, using superimposed Halbach arrays and mechanical rotation for imaging and gradient control.

Contribution

It presents a novel permanent magnet design combining Halbach dipole and quadrupole arrays, enabling adjustable gradients and MRI imaging without traditional gradient coils.

Findings

Design achieves spatially homogeneous, adjustable magnetic gradients.

Analytical and FEM-simulation results validate the concept.

Gradient can be scaled or nullified by rotating quadrupoles.

Abstract

A design for a permanent magnet system is proposed that generates spatially homogeneous, constant magnetic field gradients, thus creating conditions suitable for MRI without gradient coils and amplifiers. This is achieved by superimposing a weak Halbach quadrupole on a strong Halbach dipole. Rotation of either the quadrupole or the entire magnet assembly can be used to generate 2D images via filtered back-projection. Additionally, the mutual rotation of two quadrupoles can be used to scale the resulting gradient. If both gradients have identical strength the gradient can even be made to vanish. The concept is demonstrated by analytical considerations and FEM-simulations.