Patent ID: 8410777
Filing Date: 2013-04-02
Classification: G01R

Abstract:
1. A magnetic resonance imaging system with reduced cryogenic losses and acoustic noise, the system including superconducting windings for creating an intense main magnetic field {right arrow over (B 0 )} in a usable interior space in the form of a tunnel with axis Z, means for radio-frequency excitation and processing of radio-frequency signals emitted in response by a body or object placed in said usable interior space, a set of solenoid gradient windings for superposing on the intense main magnetic field {right arrow over (B 0 )} components of an additional magnetic field, said gradient windings being placed in a cylindrical annular space situated between an exterior cryogenic enclosure containing said superconducting windings for creating an intense main magnetic field {right arrow over (B 0 )} and said usable interior space, and electronic control circuits, the toroidal exterior cryogenic enclosure defining said usable interior space at room temperature in the form of a tunnel with axis Z in which there is placed the set of solenoid gradient windings, said exterior cryogenic enclosure successively comprising from said usable interior space a vacuum enclosure, at least one first thermal screen maintained at a temperature in the range 20 K to 80 K, a helium reservoir at a temperature less than 5 K, and a former for supporting the superconducting windings for creating an intense main magnetic field {right arrow over (B 0 )}, wherein the exterior cryogenic enclosure further includes at least one additional envelope placed between the set of solenoid gradient windings and the vacuum enclosure, the additional envelope being made of a conductive material with electrical resistivity greater than or equal to 7×10 −8 Ω·m and having a characteristic frequency of purely radial vibration less than or equal to the characteristic frequencies of each of the other components of the exterior cryogenic enclosure, and wherein said conductive material of said additional envelope is made of one of the following materials: lead, tin, tin alloy, alloy of lead and at least one of the following elements: tin, bismuth, cadmium.