摘要:
A Magnetic Resonance apparatus includes a 3D structure having a cavity for receiving a body under examination, a mechanism for generating a static magnetic field in the patient receiving cavity, a mechanism for generating variable magnetic fields in the cavity, an antenna for transmitting electromagnetic nuclear spin excitation pulses, an antenna for receiving the electromagnetic signals generated by nuclear spin relaxation, a plate for locating and fixing magnetic dipoles for fine correction of magnetic field homogeneity, and a compartment for the magnetic correction dipole locating and fixing plate, the compartment being adapted to be opened for direct access to the magnetic correction dipole locating and fixing plate from the outside. The compartment may be opened either by removal of an end plate of the magnetic field generating mechanism, or via a lateral slot for insertion and removal of the magnetic correction dipole locating and fixing plate.
摘要:
A Magnetic Resonance apparatus includes a 3D structure having a cavity for receiving a body under examination, a mechanism for generating a static magnetic field in the patient receiving cavity, a mechanism for generating variable magnetic fields in the cavity, an antenna for transmitting electromagnetic nuclear spin excitation pulses, an antenna for receiving the electromagnetic signals generated by nuclear spin relaxation, a plate for locating and fixing magnetic dipoles for fine correction of magnetic field homogeneity, and a compartment for the magnetic correction dipole locating and fixing plate, the compartment being adapted to be opened for direct access to the magnetic correction dipole locating and fixing plate from the outside. The compartment may be opened either by removal of an end plate of the magnetic field generating mechanism, or via a lateral slot for insertion and removal of the magnetic correction dipole locating and fixing plate.
摘要:
An MRI apparatus comprising a magnet structure which delimits a cavity for receiving a body under examination or a part thereof, and which includes means for generating a magnetic field in said cavity, as well as means for causing the body under examination or the part thereof to emit nuclear magnetic resonance signals, a region being defined in the cavity, known as imaging volume, and means for receiving the nuclear magnetic resonance signals. The MRI apparatus also comprises an electronic processing unit with which the means for receiving the nuclear magnetic resonance signals are electrically connected; the cavity has an access opening for receiving a body under examination or part thereof.The geometric center of the geometric shape of the cavity delimited by the magnet structure is in offset relation to the geometric center of the imaging volume.
摘要:
An MRI apparatus including a magnetic structure defining a cavity for receiving a body under examination or a part thereof, a mechanism for generating a magnetic field inside the cavity, a mechanism for causing the body under examination or a part thereof to emit nuclear magnetic resonance signals, and a mechanism for receiving the nuclear magnetic resonance signals. The mechanism for generating the magnetic field includes one or more elements made of permanently magnetized material of the so-called superconducting bulk material type and, in combination therewith, a mechanism for keeping the magnetization condition of the superconducting bulk material which includes mechanisms for maintaining the temperature of the permanently magnetized material below the critical temperature thereof and for restoring the magnetization of the superconducting bulk material upon a complete or partial demagnetization.
摘要:
A method for determining construction parameters of magnet structures designed to generate magnetic fields in predetermined volumes of space, comprising the steps of: a) defining a predetermined volume of space in which a static magnetic field is to be generated; b) defining the nominal strength and profile of the magnetic field in said predetermined volume of space; c) mathematically describing the nominal magnetic field on the surface of and/or in said predetermined volume of space by using a polynomial expansion of the magnetic field-describing function, which provides a series of coefficients; d) determining the size, geometry and relative position in space of the means for generating said nominal magnetic field, with respect to the volume of space in and on which the desired, i.e. nominal magnetic field, is defined. According to the invention, the predetermined volume of space is delimited by an ideal ellipsoidal closed surface and the magnetic field is expressed by coefficients of a polynomial ellipsoidal harmonic expansion. The method may be also used as a shimming method in volumes of space ideally delimited by ellipsoidal closed surfaces, to be implemented whether or not the predetermined volume of space defined by the magnet structure is also delimited by an ideal closed surface, with an ellipsoidal or other shape.
摘要:
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.
摘要:
An MRI apparatus including a magnetic structure defining a cavity for receiving a body under examination or a part thereof, a mechanism for generating a magnetic field inside the cavity, a mechanism for causing the body under examination or a part thereof to emit nuclear magnetic resonance signals, and a mechanism for receiving the nuclear magnetic resonance signals. The mechanism for generating the magnetic field includes one or more elements made of permanently magnetized material of the so-called superconducting bulk material type and, in combination therewith, a mechanism for keeping the magnetization condition of the superconducting bulk material which includes mechanisms for maintaining the temperature of the permanently magnetized material below the critical temperature thereof and for restoring the magnetization of the superconducting bulk material upon a complete or partial demagnetization.
摘要:
Method for making magnets particularly for the use in MRI scanners, which magnets are three-dimensional and have a tubular wall made of magnetized material, with a closed or open annular shaped cross-section, the tubular wall being composed of individual elements made of magnetized material, the magnetization of each element made of magnetized material having a predetermined direction in the transverse section plane and said directions being determined such to generate a uniform static magnetic field in the cavity of the tubular wall. The invention provides the following steps: determining the modulus and direction of the magnetization of elements necessary for generating a predetermined magnetic field in said cavity in a theoretical two-dimensional magnet model, extruding the two-dimensional model to a three-dimensional model and at least partially compensating aberrations, distortions or inhomogeneites of the magnetic field generated in the three-dimensional model by modifying the magnetization orientation in the individual elements and in the plane of the two-dimensional model such to minimize differences between the magnetic field in the two-dimensional model and the magnetic field in the three-dimensional model above all as regards its homogeneity level. The invention relates also to a magnet made by said method and particularly a small magnet.
摘要:
Method for making magnets particularly for the use in MRI scanners, which magnets are three-dimensional and have a tubular wall made of magnetized material, with a closed or open annular shaped cross-section, the tubular wall being composed of individual elements made of magnetized material, the magnetization of each element made of magnetized material having a predetermined direction in the transverse section plane and said directions being determined such to generate a uniform static magnetic field in the cavity of the tubular wall. The invention provides the following steps: determining the modulus and direction of the magnetization of elements necessary for generating a predetermined magnetic field in said cavity in a theoretical two-dimensional magnet model, extruding the two-dimensional model to a three-dimensional model and at least partially compensating aberrations, distortions or inhomogeneites of the magnetic field generated in the three-dimensional model by modifying the magnetization orientation in the individual elements and in the plane of the two-dimensional model such to minimize differences between the magnetic field in the two-dimensional model and the magnetic field in the three-dimensional model above all as regards its homogeneity level. The invention relates also to a magnet made by said method and particularly a small magnet.
摘要:
A method for determining construction parameters of magnet structures designed to generate magnetic fields in predetermined volumes of space, comprising the steps of: a) defining a predetermined volume of space in which a static magnetic field is to be generated; b) defining the nominal strength and profile of the magnetic field in said predetermined volume of space; c) mathematically describing the nominal magnetic field on the surface of and/or in said predetermined volume of space by using a polynomial expansion of the magnetic field-describing function, which provides a series of coefficients; d) determining the size, geometry and relative position in space of the means for generating said nominal magnetic field, with respect to the volume of space in and on which the desired, i.e. nominal magnetic field, is defined. According to the invention, the predetermined volume of space is delimited by an ideal ellipsoidal closed surface and the magnetic field is expressed by coefficients of a polynomial ellipsoidal harmonic expansion. The method may be also used as a shimming method in volumes of space ideally delimited by ellipsoidal closed surfaces, to be implemented whether or not the predetermined volume of space defined by the magnet structure is also delimited by an ideal closed surface, with an ellipsoidal or other shape.