Current density mapping approach for design of clinical magnetic resonance imaging magnets

Abstract

Novel current density mapping (CDM) schemes are developed for the design of new actively shielded, clinical magnetic resonance imaging (MRI) magnets. This is an extended inverse method in which the entire potential solution space for the superconductors has been considered, rather than single current density layers. The solution provides an insight into the required superconducting coil pattern for a desired magnet configuration. This information is then used as an initial set of parameters for the magnet structure, and a previously developed hybrid numerical optimization technique is used to obtain the final geometry of the magnet. The CDM scheme is applied to the design of compact symmetric, asymmetric, and open architecture 1.0 -1.5 T MRI magnet systems of novel geometry and utility. A new symmetric 1.0-T system that is just 1 m in length with a full 50-cm diameter of the active, or sensitive, volume (DSV) is detailed, as well as an asymmetric system in which a 50-cm DSV begins just 14 cm from the end of the coil structure. Finally a 1.0-T open magnet system with a full 50-cm DSV is presented. These new designs provide clinically useful homogeneous regions and have appropriately restricted stray fields but, in some of the designs, the DSV is much closer to the end of the magnet system than in conventional designs. These new designs have the potential to reduce patient claustrophobia and improve physician access to patients undergoing scans. KEY WORDS: magnetic resonance imaging magnet; symmetric design; asymmetric design; open magnet design; current density mapping method

A Simple Relationship for High Efficiency–Gradient Uniformity Tradeoff in Multilayer Asymmetric Gradient Coils for Magnetic Resonance Imaging

“…In order to calculate forces and torques, the coil system was placed theoretically in the bore of an ultrashort 1.5 T superconducting magnet [1]. The resulting torque was 0.753 N m A and the remaining force 0.194 N/A.…”

“…The main magnet must produce a very homogenous and stable magnetic field in a relatively large diameter spherical volume (DSV) of 40 to 50 cm. It becomes more difficult to satisfy all the required constraints as the length of the magnet is reduced [1], [2]. One of the first trials to study the relationship between cost and magnet length was presented by H. Xu et al [3].…”

A design method for superconducting MRI magnets with ferromagnetic material

“…The initial layout of the superconducting coils was determined by the current density mapping method (CDM) [12]. This information then is used as an initial set of parameters for the superconducting coils in the mixed material system.…”

Design of actively shielded main magnets: an improved functional method

“…The current distribution of a design at this stage is called a continuous solution. We note that a recent publication also takes a similar stage in the design of MR magnets [11]. Due to the cylindrical symmetry and mirror reflection around the mid-plane of a magnet design, in the quest to cancel even internal moments, only a quadrant of the ρ-z (radial-axial) plane solution needs to be discussed throughout this paper.…”

“…In recent years, the trends in industry have been toward shorter cylindrical MRI machines, in order to increase patient comfort [1,2]. Previous design work has included a Monte Carlo method [3,4], functional (or inverse) methods [5,6], annealing methods [7,8], "hybrid" methods [9,10,11], and a genetic algorithm approach [12,13]. In general, the Monte Carlo, annealing, and genetic algorithm methods need extensive computing power in order to search through a larger parameter space.…”