A design method for superconducting MRI magnets with ferromagnetic material

Abstract

The emphasis of this work is on the optimal design of MRI magnets with both superconducting coils and ferromagnetic rings. The work is directed to the automated design of MRI magnet systems containing superconducting wire and both ‘cold’ and ‘warm’ iron. Details of the optimization procedure are given and the results show combined superconducting and iron material MRI magnets with excellent field characteristics. Strong, homogeneous central magnetic fields are produced with little stray or external field leakage. The field calculations are performed using a semi-analytical method for both current coil and iron material sources. Design examples for symmetric, open and asymmetric clinical MRI magnets containing both superconducting coils and ferromagnetic material are presented.

Globally optimal superconducting magnets Part II: Symmetric MSE coil arrangement

“…A number of advancements in design have seen the development of improved and cheaper technologies in magnet construction and performance [2][3][4][5][6][7][8][9], which provide clear benefits to the community in the form of more accurate and insightful diagnostic and preventative healthcare. Recent emerging technologies have provided practitioners with the ability to obtain higher resolution images, and perform faster scans, resulting in greater patient throughput and improved patient comfort.…”

“…Attempts have been made to address the concerns of weight, size and magnetic field nonlinearity [2][3][4] in these magnet systems, with the hope of manufacturing less costly systems.…”

Comprehensive Analysis of Lenz Effect on the Artificial Heart Valves During Magnetic Resonance Imaging

“…In the former case, the stray field may reach more than 100 gauss(G) and it needs a special room for the magnet to protect the electronic equipment from adverse effects. Next generation magnets came with the concept of active shielding where the stray field is less than 4 G (in regions at least 4 m away from the iso-center) either by using ferromagnetic materials [11] or using coaxial coils carrying current in the opposite direction [12]. Different methods are used to design magnets of highly homogeneous field, based on stochastic optimization [20], matrix subset selection [21], inverse approach [22], hybrid numerical methods [23] and methods for permanent magnet design [24].…”

Formulation of the spherical harmonic coefficients of the entire magnetic field components generated by magnetic moment and current for shimming

“…13 Subsequently, methods of configuring small pieces of ferromagnetic material were proposed. 14,15 They employed the expressing of spherical harmonics and a magnetization computation as well as an optimization method. I proposed a method of passive shimming in addition to magnetic shielding.…”

“…[4][5][6][7][8][9][10][11][12][13][14][15][16][17] The z-component of the magnetic field, parallel to the axis of the symmetry, is homogenized, and the others (radial and azimuthal components) are ignored. axially asymmetric configuration of a magnet or a return yoke, without shimming.…”