Low leakage, low field, easy access flat hybrid magnets for MRI applications are being investigated. This configuration associates bobbins and ferrite permanent magnets having a Br field equal to 0.4 T. The complete magnet is designed using the laboratory-conceived CALMAG3D code[1] which allows us to simulate, in three dimensions, the various magnetic field producing elements (resistive bobbins, permanent magnets, ferromagnetic pieces) while taking into account their nonlinearity. A full-scale magnet should produce a sufficiently homogeneous field of a few ppm over a 30 cm sphere for whole body imaging purposes. For this reason we have elaborated a configuration of cylindrical [2] form with a revolution symmetry. The realisation of a 1/3 prototype requires some ferrite disks of big dimensions. We propose here a relatively low cost fabrication method with respect to that proposed by the manufacturers.

We propose a novel magnet structure for magnetic resonance imaging. The design made use of the CALMAG3D code which features high precision and high speed calculation and requires relatively small computer memory. The magnetic field at any point in space can be calculated without using the classical methods of finite elements, conformal transform, boundary limit conditions, and matrix inversion.

We present here the principle and structure of a method to calculate the three-dimensional (3-D) static magnetic fields which have already permitted us to study hybrid magnets for magnetic resonance imaging and ion confinement [1], [2], Field sources can be issued from resistive or superconducting coils, permanent magnets, and other magnetic bodies such as soft iron, It can be extended to very low-frequency fields calculation as long as eddy current effects do not intervene, We call this method CALMAG3D.

This paper describes an optimal design of a highly homogeneous resistive coil system for Magnetic Resonance Imaging (MRI). Magnetic material is used to improve field uniformity at the central region and to shield the magnet. The influence of magnetic material is calculated by using a code based on the solution of scalar and vector potentials equations. The obtained result is an axisymmetric coil configuration enveloped by iron whose optimization was made by fixing one of the criteria : the weak stray field near the magnet. It presents a great accessibility to the homogeneous area and satisfies the bore's required dimensions. Dimensions and field charts are given.

A long solenoid is capable of producing, at least theoretically, a B, field that is relatively more homogeneous than other known structures. This paper describes the design of a UHF probe incorporating a one‐turn solenoid associated with a pair of parallel‐plate transmission line feeders and presents a practical example used in a 360‐MHz spectrometer for micro‐imaging experiments. Numerical evaluation of the solenoid inductance using King's method for direct calculation of elliptic integrals is also included. © 1987 Academic press, Inc.

The slotted cylinder, and inductive structure with low self‐inductance, low electric field, has been studied as a probe for NMR imaging applications. A theoretical calculation allows us to map the magnetic field and to evaluate electrical parameters of the structure. Several implementations, including new designs, have been experimentally tested over a wide range of frequencies (4–40 MHz), and compared to a classical coil probe. This study demonstrates the efficiency of the slotted cylinder for NMR imaging. It is optimized for large conductive samples when imaging at high frequencies (for human head, above 20 MHz).

A new design for an axial magnetic field gradient is described. Implemented in a four-coil configuration, it requires far less power than the conventional Maxwell pair, while maintaining the same field linearity. A practical design tool with a set of curves giving coil dimensions is proposed. Two realizations dedicated to NMR imaging are described and compared with the equivalent Maxwell pair. Substantial power reductions are achieved; in these cases, dc power is reduced by a factor of 5 and switching power by a factor of 15.

More than a dozen Nuclear Magnetic Resonance (NMR) imaging methods have been described using different radio-frequency pulse sequences, magnetic field gradient variations, and data processing. In order to have a theoretical understanding in the most general case, we have conceived a computer program for the simulation of NMR imaging techniques. The algorithm uses the solution of the Bloch equations at each point of a simulated object. The direction of every elementary magnetic moment is computed at each instant, and stored in an array giving the global signal to be processed, whatever the pulse and gradient sequence. To test the validity of this program, we have simulated some well-known experimental results. Some applications are presented which contribute to the understanding of image distortions and to techniques such as selective radio-frequency pulse or oscillating gradients. This program can be used to unravel physical and technological causes of image distortions, to have a “microscopic” look at any parameter of an experiment, and to study the contrast given by various NMR imaging techniques as a function of the three NMR parameters, i.e., the hydrogen nuclei density ϱ and the relaxation times T1 and T2.

2014 L'influence de l'inhomogénie spatiale du champ magnétique est étudiée, à l'aide des équations de Bloch, par la déformation produite sur une raie théoriquement lorentzienne.L'étude est effectuée pour un échan- tillon immobile dans différents cas de détection et sur le signal de précession libre dans le cas d'un échantillon tournant.La mise en évidence d'une fonction ne dépendant que de la forme de l'échantillon et que de l'inhomo- génie du champ magnétique principal permet de proposer une méthode d'amélioration de la résolution des spectres de résonance magnétique nucléaire par transformée de Fourier.Cette méthode, valable pour des composés liquides dont les raies sont théoriquement lorentziennes, n'introduit pas de facteur empirique.Quelques exemples per- mettent d'en apprécier l'efficacité.Abstract.-The spatial inhomogeneous magnetic field is studied by means of its effects on a line shape which theoretically would be a lorentzian curve.The Bloch equations permit to solve this problem for a non-spinning sample, in various experiments, and also for a sample rotating around the axis of the field, in the case of a free induction decay signal.We show as an example, how one can theoretically obtain the line shape for some types of inhomogeneous fields.Then, through the definition of a complex function depending only on the inhomogeneity of the magnetic field and on the form of the sample, we propose a new method for the resolution enhancement of Fourier transform nuclear magnetic resonance.This method, suitable for lines with a theoretically lorentzian shape, does not use an empirical parameter.Few examples are presented to demonstrate the potential of this method.