Abstract: A superconducting magnet, in which a static magnetic filed is generated in a region of interest, i.e. a predetermined volume in which the part under examination has to be placed for imaging characterised in that it is provided with means for generating a uniform annular distribution of electric currents enclosing the polyhedral cavity.

Abstract: A superconducting magnet, in which a static magnetic filed is generated in a region of interest, i.e. a predetermined volume in which the part under examination has to be placed for imaging characterised in that it is provided with means for generating a uniform annular distribution of electric currents enclosing the polyhedral cavity.

Abstract: An open unipolar magnetic structure allowing an arbitrary location of a region of interest which will contain a uniform magnetic field within a cavity. In a preferred embodiment, a yoked magnetic structure is modified to reduce the field perturbations in the region of interest when the latter is arbitrarily located within the cavity. The modification includes the provision of supplemental permanent magnetic members at the opening, the configuration of the supplemental permanent magnetic members being related to the configuration of some of the permanent magnetic members of the magnetic structure that provides the uniform magnetic field.

Abstract: A magnetic structure generating a uniform magnetic field within a region of interest using permanently magnetized prism-shaped blocks of magnetic material positioned around a cavity and which constitute the predominant generator of the uniform magnetic field in the desired region of interest. The magnetic structure has a plane surface comprising a high permeability ferromagnetic member interfacing with a first side of the cavity and forming a single pole piece of the magnetic structure. The magnetic structure produces within the cavity adjacent the single pole piece the uniform magnetic field and collects the magnetic flux flowing through the single pole piece and through the cavity, with the region of interest being located adjacent the single pole piece. A second side of the cavity generally opposite to the first side is open to a surrounding medium and forms an interface with the surrounding medium but not with a magnetic member.

Abstract: A magnetic structure generating a substantially uniform magnetic field within a region of interest using permanently magnetized wedge-shaped blocks of magnetic material. In a preferred embodiment, the permanently magnetized wedge-shaped blocks are provided in pairs positioned on opposite sides of the x z plane of an arbitrary x,y,z coordinate system, and each of the blocks are magnetized in certain directions. The uniform field is created in the vicinity of the z axis. In another embodiment, the parts of the structure below the x-axis are replaced by a high-permeability, soft magnetic plate to form a so-called mirror system. In still another embodiment, permanently magnetized blocks positioned outside of the wedge-shaped blocks are employed as the main compensation means for field distortions arising from the practical need to truncate the wedge-shaped blocks to a practical size.

Abstract: Strapped open magnetic structure, particularly useful in nuclear magnetic resonance imaging applications, which provides a substantially uniform magnetic field within a region of interest while allowing access by a surgeon to a patient via an opening at the top of the magnetic structure. The magnetic structure comprises nested inner and outer magnetic structures separated by ferromagnetic material or pole pieces and surrounded by a ferromagnetic yoke. The structure contains one or more thin layers or straps of high magnetic permeability material aligned substantially along equipotential surface(s) of an associated closed magnetic structure of ideal properties.

Abstract: A magnetic structure generating a substantially uniform magnetic field within a region of interest comprising at least one pair of magnetic wedges of substantially identical shape arranged symmetrically about a first axis and abutting one another along a common edge. Each magnetic wedge has a first side and a second side which terminate at the common edge. The first wedge of each pair is positioned to define a first angle between the first side and the first axis and a second angle between the second side and the first axis, and is uniformly magnetized in a direction relative to a second axis (perpendicular to the first axis) which is a function of the sum of the first and second angles.

Abstract: A hybrid permanent magnet structure for providing a uniform magnetic field within a region of interest while allowing access via open ends by a patient for NMR scanning and by a surgeon to the patient via a large opening at the top. The magnet structure comprises nested inner and outer magnetic structures separated by ferromagnetic material and surrounded by a ferromagnetic yoke. The inner magnetic sections comprise end blocks of triangular cross-section, and the outer magnetic sections comprise end blocks of trapezoidal cross-section. Field distortion compensating means is provided by a primary filter structure to the ferromagnetic material and by magnetic insertions or a secondary filter structure.

Abstract: A technique is provided for improving the homogeneity of the magnetic field within a cavity disposed inside a magnetic structure that has an opening to permit convenient access to an imaging region. The technique is based upon the step of inserting layers of magnetized material between plates of high magnetic permeability material. The layers are inserted at the boundary of the cavity. The technique includes the step of (1) computing the surface charges on the plates as used to derive the distribution of the magnetostatic potential, (2) analyzing the uniformity of the magnetic field within the imaging region as effected by the opening in the magnetic structure by expanding the magnetostatic potential in a spatial harmonic series, and (3) determining the geometry and the composition of the inserted layers based on the successive elimination of increasing orders of spatial harmonics in the potential expansion within the imaging region.

Abstract: A magnetic structure is provided having a pair of spaced apart magnetized elements having surfaces in a common plane that defines a wall of a cavity. The space between the first and second magnetized elements is formed with at least one slit extending perpendicularly to the common plane. In order to compensate for field distortion in the cavity, a magnetized element is provided in at least one of the slits, the material in the slit having a remanence that is different from the remanences of the spaced apart magnetized elements that define the structure. In modifications of the invention, the field distortion is compensated by including at least one component in the cavity that has a high magnetic permeability. This component, has a variable thickness. It may be formed of a single component, or of a plurality of plates. In a still further embodiment, for a yokeless magnetic structure, field distortion compensation is effected by positioning magnetized elements outside of the magnetic structure.

Abstract: A high field strength permanent magnet has a plurality of layers, with at least two of the layers being formed of materials of different remanence. The remanence of the material of each layer is no greater than that of the layers thereunder, and is preferably less than the remanence of all underlying layers.The inner layer may be formed of a magnetic structure in which all or part of a basic yoke has been replaced by a shunt of active material. Such a shunt may alternatively be employed in a single layer magnetic structure.

Abstract: The invention is directed to a method for determining the fields of permanent magnet structures with a surface or boundary solution method for the magnetic material with linear characteristics with small susceptibility and large permeabilities of the ferromagnetic materials.

Abstract: A magnetic structure defining a cavity includes a first member of high-permeability material having a flat surface defining a first wall of the cavity, and a member of permanent magnetic material spaced from the flat surface and producing a uniform magnetic field in the cavity. The permanent magnetic material member may have two or more layers, with the layers outward of the cavity being of a material having a remanence that is no greater than the adjacent inner layers.

Abstract: A yoked magnetic structure has a pair of spaced magnetized members defining a cavity, and an end ferromagnetic structure closing said cavity and abutting an end of the magnetized members. The end structure comprising at least a first element of triangular cross section having one side abutting an end of one of said magnetized member and a second element of triangular cross section having one side abutting the adjacent side of said cavity. The first and second elements have second sides away from the magnetized member and cavity defining at least part of an equipotential line whereby the flux density on the side of the equipotential line away from the magnetized structure is zero. A region of .mu.=.infin. material is provided adjacent the magnetized member to minimize the effect of perturbations.

Abstract: A permanent magnetic structure comprising a cylindrical body (15) and a termination structure (14, 12, 10). The cylindrical body (15) is composed of magnetic material causing a magnetic field and flux of magnetic induction. The cylindrical body (15) is oriented such that the interface between the cylindrical body 15 and the termination (14, 12, 10) is parallel to the magnetic induction and the cylindrical body (15).

Abstract: A permanent magnet structure having at least one loop of circulating flux comprises a first and second plurality of uniformly magnetized prismatic magnetic material sections forming a polygonal shaped cavity and having a point F positioned along a zero equipotential base line joining two vertices within the cavity, that point being the reference for a figure of merit M corresponding to a maximum field strength and a minimum ratio of the value of the area of magnetized material to the area of the cavity. The first plurality of sections totally define the cavity and have their respective remanences aligned to result in a flux passing orthogonally through the base line. The second plurality of section is oriented with respect to their respective remanences and the first sections so as to confine the flux within the cavity. A third plurality of nonmagnetized magnetic sections encloses the base line and borders the first sections for providing an inductive path to channel the flux and close the loop.

Abstract: Magnetized transition elements are provided between the magnetized elements that define the cavity of the structure. The magnitudes and directions of the fields of these transition elements are arranged so that the external boundary of the transition elements are equipotential surfaces, and the induction in the transition elements is zero. Separate return yokes are provided for the magnetized elements adjacent the transition elements, that do not contact the transition elements.

Abstract: A permanent magnet structure comprising a longitudinally extending flux sce fabricated of magnetically rigid material. The flux source comprises a central cavity with a magnetic field being produced therein. Magnetic dipoles having predetermined magnitude and orientation for compensating nonuniformities in the magnetic field are symmetrically located within the plane of the flux source.

Abstract: The construction of a yokeless permanent magnet structure with a cavity, which structure comprises a single layer of abutted magnetic prisms, is performed by first utilizing a reference point "F" for the construction such that point F lies on a equipotential line of zero potential. The point F must, furthermore, be selected so that it lies on a line which divides the magnetic flux within the cavity into two separate loops or parts. Beginning from point F, the magnet structure is then constructed from a series of precisely abutted prisms of magnetic material which form a cavity with a predetermined, uniform polygonal cross section. Using well known boundary value conditions between the cavity and the various prisms of the magnetic material, as well as the restriction that the exterior surface of the permanent magnetic must be an equipotential surface of zero potential, each prism, in turn, is constructed, until the entire permanent magnet is completed.

Abstract: A method and apparatus for computed axial tomography (CAT) image reconstruction applicable to X-ray scanning of the human body. Successive series of calculations determine the values of a characteristic in defined segmented areas of an examination plane. A reduction in the time and equipment requirements for reconstruction calculations may thereby be effected.Images representative of the difference between the value of the characteristic at a reconstruction point and the average value of the characteristic in adjacent regions (.DELTA..mu.) may be calculated and displayed from measurements taken within a localized contiguous region of the examination plane. Radiation dose to patients and computation time in X-ray computerized axial tomography scanning systems is thus reduced. Differential displays of the type described may be adjusted to image boundaries, in which case they do not suffer from gray scale resolution problems which are typical of prior art displays.