Combined mri and radiation therapy equipment

Abstract

In a combined MRI and radiation therapy system, a magnet structure and radiation therapy equipment are provided. The magnet structure comprises a single substantially cylindrical field coil structure comprising a number of superconducting coils joined by a support structure and extending axially of a central region. An outer vacuum chamber encloses the field coil structure in an evacuated volume. A cooling arrangement comprising cooling tubes is in thermal contact with the superconducting coils and receives a cryogen flowing through the cooling tubes. The radiation therapy equipment comprises a gamma radiation source rotatable about an axis of the field coil structure to direct a radiation beam substantially radially through the field coil structure. Parts of the field coil structure and the outer vacuum chamber are transparent to radiation emitted by the gamma radiation source whereby the radiation beam is directed through the field coil structure and the outer vacuum chamber without substantial interference.

I claim as my invention: 
     
         1 . A cylindrical superconducting magnet comprising:
 an inner coil and an outer coil, aligned along an axis and housed within a generally cylindrical outer vacuum container, and a thermosyphon cooling arrangement;   thermosyphon cooling arrangement comprising a cryogen tank that is smaller than the inner coil and the outer coil, and a thermosyphon tube extending around the outer coil in thermal contact with its surface, the thermosyphon tube comprising a bore connected to the cryogen tank at its two ends, one end of the bore entering the cryogen tank at an upper location, above a maximum liquid cryogen level, the other end of the bore entering the cryogen tank at a lower location below a minimum liquid cryogen level, and the cryogen tank is positioned within the generally cylindrical shape of the OVC, and a portion of the outer coil is not in thermal contact with the thermosyphon tube below the minimum liquid cryogen level over a length of the portion.   
     
     
         2 . A cylindrical superconducting magnet according to  claim 1  wherein the portion subtends an angle at the axis wherein the angle lies in the range of 40°-120°. 
     
     
         3 . A cylindrical superconducting magnet according to  claim 1  wherein a higher pressure of cryogen is provided at the end of the bore entering the cryogen tank at the lower location than the cryogen pressure at the end of the bore entering the cryogen tank at the upper location. 
     
     
         4 . A cylindrical superconducting magnet according to  claim 1 , further comprising a further thermosyphon tube extending around the inner coil in thermal contact with its surface, the thermosyphon tube comprising a bore connected to the cryogen tank at its two ends, one end of the bore entering the cryogen tank at an upper location, above a maximum liquid cryogen level, the other end of the bore entering the cryogen tank at a lower location below a minimum liquid cryogen level. 
     
     
         5 . A cylindrical superconducting magnet according to  claim 1 , comprising a plurality of inner coils and a plurality of outer coils, each provided with a thermosyphon tube each extending around the respective coil in thermal contact with its surface, wherein the thermosyphon tubes are connected to the cryogen tank though manifolds, a single tube extending from each manifold to the cryogen tank at respective upper and lower locations. 
     
     
         6 . A cylindrical superconducting magnet according to  claim 1 , wherein a thermally conductive cooling strap or thermally conductive member is provided, extending around the outer coil, extending at least over the portion of the outer coil which is not in thermal contact with the thermosyphon tube below the minimum liquid cryogen level over a length of the portion.