摘要:
Convenient side access to an image volume located within a two-pole, two-column main magnet of an MRI system is provided by rotating the symmetry axis of the magnet to be non-perpendicular with respect to the longitudinal axis of the patient transport and/or otherwise displacing the two column structures of the magnetic circuit so as to permit open and unobstructed access to the image volume along a direction perpendicular to the longitudinal axis of the patient transport.
摘要:
An open access superconducting MRI magnet includes a ferromagnetic frame open on at least two sides and having upper and lower end plates and at least two support posts. A superconducting coil assembly is mounted to each end plate for generating a magnetic flux field in a patient receiving area located between the end plates. A magnetic flux field shaping means is associated with each end plate. The flux field shaping means includes rose shims, inner rings mounted within the rose shims, and removable segments mounted to the rose shims. Transition plates are located between the support ports and end plates for minimizing flux leakage. In addition the end plates are formed with a varying thickness such that a cross section taken perpendicular to a return path of magnetic flux is substantially constant.
摘要:
A magnet system for providing a localized, substantially homogeneous field for use in medical magnetic resonance imaging and its incorporation into a method of siting. The magnet system includes a vacuum vessel defining a bore for receiving the subject of the imaging and having a first end and a second end. A cryogenic containment vessel is supported within the vacuum vessel and a single coil is disposed within the containment vessel for providing the magnetic field. The magnetic system also includes a shield assembly of ferromagnetic material positioned closely adjacent the outside of the vacuum vessel and including first and second end assemblies and a plurality of axially extending beam-like members interconnecting the end assemblies. The coil comprises a winding made up of thousands of turns of small superconductive wire and which is configured to compensate for the effect of the presence of the shield to provide the substantially homogeneous field at a predetermined location in the bore. The components of the shield assembly are adapted for mounting to said vacuum vessel after siting. This permits simplified siting of the magnet system in that the vacuum vessel with the components inside of it can be sited first and the components of the shield assembly thereafter mounted on the vacuum vessel. A method of manufacturing the magnet system is also disclosed.
摘要:
A sleeve assembly for thermally interconnecting a pulse tube, two stage cryocooler with a superconducting device includes a heat transfer cylinder, a heat transfer receptacle and a wall extending therebetween to define a passageway. The heat transfer receptacle is formed with a tapered recess wherein a tapered cooling probe of the cryocooler is urged against the heat transfer receptacle to establish thermal communication therebetween. A cooling element of the cryocooler is disposed in the heat transfer cylinder to establish thermal communication therebetween. In operation, the cryocooler moves relative to the sleeve assembly between a first configuration wherein the cryocooler is engaged with the sleeve assembly to establish thermal communication therebetween and a second configuration wherein the cryocooler is disengaged with the sleeve assembly. An expandable bellows which interconnects the cryocooler with the sleeve assembly will maintain thermal insulation therebetween when the cryocooler is disengaged from the sleeve assembly.
摘要:
A magnet system, having permanently installed power leads, for providing a magnetic field. The system includes a vacuum vessel and a cryogenic containment vessel supported within the vacuum vessel. The containment vessel holds a main coil formed of superconductive wire, along with a quantity of liquid helium to maintain the wire below its critical temperature. The power leads, which supply energy to the coil from a power supply outside the vacuum vessel, also take energy from the coil to a load resistor outside the vacuum vessel when the coil is discharged, each include an elongate metallic tube. The magnet system also includes a solenoid controlled valve which is responsive to the passage of electric current through the tubes of the power leads to cause helium gas resulting from the boiling of liquid helium in the containment vessel to be vented to atmosphere through the tube thereby cooling them.
摘要:
An improvement in cooling apparatus in a magnet system for providing a localized, substantially homogeneous magnetic field for use in magnetic resonance imaging. The magnet system includes a vacuum vessel, a cryogenic containment vessel inside the vacuum vessel and having a coil of superconductive wire along with a quantity of liquid helium to maintain the wire below its critical temperature. The system also includes an inner thermal radiation shield between the containment vessel and the vacuum vessel and an outer thermal radiation shield between the inner shield and the vacuum vessel. A cryogenic refrigerator is supported by the vacuum vessel and extends inside. This refrigerator has a first-stage heat station cooling the outer shield and second-stage heat station for cooling the inner shield. The improvement includes the provision of a tank holding a quantity of liquid nitrogen. This tank is supported in good heat transfer relationship with the first-stage heat station between the vacuum vessel and the outer shield and is spaced from the outer shield. Tubing is provided for transferring the liquid nitrogen from the tank so that it boils in good heat transfer relationship with the outer shield and also returns gas resulting from the boiling of the liquid nitrogen back to the tank where the refrigerator condenses it in the tank. A method of using the cooling apparatus in the event the refrigerator is not functional, is also disclosed.
摘要:
A magnetic resonance imaging (MRI) system magnet includes at least one main electromagnet winding disposed within a first radius of the magnet and at least one bucking electromagnet winding disposed within a second radius, larger than the first radius of the magnet and configured to provide self-shielding magnetic fields that substantially reduce fringe magnetic fields outside the magnet produced by the main electromagnet winding. The combination of magnetic fields produced by both the main and bucking electromagnet windings inside the magnet conform to MRI requirements within at least an imaging volume. The main and bucking electro-magnet windings are configured so as to create a net fringe field outside the magnet within the range of 50-100 gauss at a distance within a range of 3-5 meters axially and 2-3 meters radially from a center of the magnet.
摘要:
A magnetic resonance imaging (MRI) system magnet includes at least one main electromagnet winding disposed within a first radius of the magnet and at least one bucking electromagnet winding disposed within a second radius, larger than the first radius of the magnet and configured to provide self-shielding magnetic fields that substantially reduce fringe magnetic fields outside the magnet produced by the main electromagnet winding. The combination of magnetic fields produced by both the main and bucking electromagnet windings inside the magnet conform to MRI requirements within at least an imaging volume. The main and bucking electro-magnet windings are configured so as to create a net fringe field outside the magnet within the range of 50-100 gauss at a distance within a range of 3-5 meters axially and 2-3 meters radially from a center of the magnet.
摘要:
An open access MRI magnet includes a ferromagnetic frame open on at least two sides and having upper and lower end plates and at least two support columns. A superconducting coil assembly is mounted to each end plate for generating a magnetic flux field in a patient receiving area located between the end plates. Each superconducting coil assembly includes a toroidal vacuum tight vessel, insulation, and one or more temperature shields mounted within the vacuum tight vessel. One or more coils of superconducting wire is wound within the vacuum vessel, and is coupled to a power source and to a persistent switch for maintaining a constant flow of current with no power consumption. A return path for the flux is provided by the end plates and support posts of the frame. The superconducting coils, the thermal shields, and the persistent switch are cooled by a cryocooler, by means of conduction through solid thermal conductors or by a combination of conduction and convection, through a fluid cooling circuit, without the consumption of a liquid cryogen.
摘要:
Ferromagnetic pieces are mounted on a plurality of nonmagnetic radial rods located at desired locations parallel to a pole face of a permanent magnet used in a magnetic resonance imaging apparatus. The pieces comprise plates which are translatable radially along each rod. Each rod carrying the plates are each rotatable about the rod axis to produce an error field cancelling environmentally induced, low order perturbations. A method for accomplishing same is also included. In a preferred embodiment, the plates are mounted on radial rods positioned at equal angles from one another, preferably thirty degrees (30.degree.) apart and arranged as spokes of a wheel.