New York University

Brk Wireless Company, Inc

Esaote S.p.a.

Philips Medical Systems, Inc.

US Government As Represented by the Secretary of the Army

Esaote Biomedica

Manlio G Abele

Henry Rusinek

Jens Jensen

Norman E Chase

Christopher H Marshall

Herbert A Leupold

Alessandro Trequattrini

Ernest Potenziani, Ii

Stefano Pittaluga

Vincenzo Punzo

Stefano Besio

Franco Bertora

Ramesh Chandra

Gareth A Mair

Anthony M Passalaqua

An MRI apparatus having a magnet structure which delimits a cavity for receiving a body under examination or a part thereof, which includes a mechanism for generating a magnetic field in the cavity, as well as a mechanism for causing the body under examination or the part thereof to emit nuclear magnetic resonance signals, a region defined in the cavity, known as an imaging volume, and a mechanism for receiving the nuclear magnetic resonance signals. The geometric center of the geometric shape of the cavity delimited by the magnet structure is offset in relation to the geometric center of the imaging volume.

MRI apparatus with offset imaging volume

A magnetic structure enclosing a prismatic cavity of regular polygonal cross-section is presented. The structure contains the field within the volume of the magnet without the need of an external ferromagnetic yoke, which makes it suitable for generating fields of several Tesla. The structures presented are designed to generate uniform fields for NMR studies, especially high intensity fields.

High field NMR permanent magnetic structure

An open magnetic structure comprising a conical permanent magnetic structure that generates an MRI imaging field around the body part of a patient in a cavity of the structure. The permanent magnetic sections include a recess over the cavity, with the surface of the structure bounding the recess following a cone angle of the conical permanent magnetic structure. The structure can be configured sufficiently large to accommodate a full patient body.

MRI conical magnet imaging system

An open magnetic structure comprising a conical magnetic structure that generates an NMR imaging field around the head of a patient, and a transition magnetic structure including a cylindrical magnet connected to the conical magnetic structures that extends the uniform field generated in the head magnet cavity to or near the shoulders of the patient. The overall geometry is designed to integrate the magnetic structure in a surgical suite with a minimum interference with surgical procedures, which typically involve surgery on the brain of the patient. A method for improving field uniformity by shimming is also included. Advantages include improved field uniformity, and reduced weight and size.

NMR imaging system with conical permanent magnet

An open magnetic structure comprising a conical magnetic structure including a hollow conical magnet surrounding and contacting an inner pole piece that generates an NMR imaging field around the head of a patient. The annular surface of contact between the conical magnetic structure and the inner pole piece is configured such that that annular surface of contact is maintained as an equipotential surface to maintain a uniform imaging field. An advantage is to integrate as one-piece the various permanent magnetic sections to greatly simplify fabrication. A method for determining the profile of the annular surface of contact is also included.

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.

Superconducting magnet, particularly for MRI imaging apparati and method of using same

An open magnetic structure comprising a conical magnetic structure that generates an NMR imaging field around the head of a patient, and a transition magnetic structure including a cylindrical magnet connected to the conical magnetic structures that extends the uniform field generated in the head magnet cavity to the shoulders of the patient. The overall geometry is designed to integrate the magnetic structure in a surgical suite with a minimum interference with surgical procedures, which typically involve surgery on the brain of the patient.

NMR head imaging system

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.

Open unipolar magnetic structure

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. The magnetic structure is designed assuming a hypothetical high permeability membrane parallel to the single pole piece and located where the open second side of the cavity will be made, the high permeability membrane forming an equipotential surface at the interface with the surrounding medium. This minimizes the fringe field generated in the surrounding medium when the second side of the cavity is opened.

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. An important application for the magnetic structure of the invention is MRI, as it can be configured as an open structure accessible to medical intervention during the MRI.

Generation of highly uniform magnetic fields with magnetized wedges

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. Structures and techniques are also provided for replacing thick, heavy blocks of ferromagnetic material with thin straps and for extending the magnetostatic potential of a component in a magnetic structure by connecting a thin strap thereto and embedding the strap in the magnetic structure along an equipotential surface of the magnetic field generated by the magnetic structure.

Strapped open magnetic structure

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. The second wedge of each pair is magnetized such that the absolute values of components of the magnetization along the first and second axes are equal to components of the magnetization of the first wedge along the first and second axes, respectively, and one of the magnetization components of the second wedge is opposite to the respective magnetization component of the first wedge. The region of interest containing the substantially uniform field is between the first sides of the pair of wedges, the second sides of the pair of wedges, or both. To minimize or eliminate the surface charge density along the third side of each wedge, the third side of each wedge is preferably parallel to the direction in which the wedge is magnetized.

Apparatus for generating uniform magnetic fields with magnetic wedges

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.

Open permanent magnet structure for generating highly uniform field

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. This invention also includes the structure resulting from carrying out the technique of the invention.

Method and apparatus for compensation of field distortion in a magnetic

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. In a method for compensating for field distortion in a magnetic structure that defines a cavity, the magnetic field on a surface is measured to produce a map of the field on the surface. A plurality of points on the surface are projected to corresponding points on a second surface. A dipole is applied at each such point on the second surface that cancels perturbations of the magnetic field of the magnetic structure at the respective first point.

Growing community of inventors

New York, NY, United States of America

Manlio G Abele