Patent ID: 8710843

Claim:
A magnetic resonance imaging (MRI) apparatus suitable for radiotherapy, the apparatus comprising: two sets of coil pairs, each set having at least one coil pair, each coil pair comprising two individual coils having different polarities, superimposed over each other and sharing a common axis of rotation; the coil pairs in each set of coil pairs sharing a common transverse plane; the two sets of coil pairs sharing the common transverse plane and being parallel to and spaced apart from each other, the two sets of coil pairs having opposing polarities, and defining a common plane of symmetry and an imaging area between the two sets of coil pairs; the two sets of coil pairs being configured to generate a substantially homogenous electromagnetic field in a first transverse direction in the common transverse plane, in the imaging area between the two sets of coil pairs; the two sets of coil pairs also being configured to generate peripheral electromagnetic fields in a second transverse direction opposite to the first transverse direction in a peripheral area outside of the imaging area; and at least one focusing magnet positioned in the peripheral areas, substantially parallel to the first transverse direction, the at least one focusing magnet being configured to generate a focusing electromagnetic field in a focusing area, in a direction substantially the same as the first transverse direction; wherein at least a portion of the peripheral electromagnetic fields is maintained in a defocusing area between the focusing area and the imaging area.