Electromagnet assembly
An electromagnet assembly comprises a first pair of substantially co-planar coils wound in opposite senses to each other. It further comprises a second pair of co-planar coils also wound in opposite senses to each other. The coil pairs are arranged substantially parallel to, and spaced apart from, each other. In use, the field shape and direction produced by the first coil pair are substantially mirrored by those produced by the second coil pair.
1. An MRI machine comprising an electromagnet assembly comprising a first pair of substantially co-planar main field coils and a second pair of co-planar main field coils, the coils of the coil pairs comprising superconducting material and the coil pairs being arranged substantially parallel to and spaced apart from each other to define a target area therebetween, wherein the main field coils in each pair are adjacent to each other, each main field coil including a left hand coil or a right hand coil respectively and are operatively configured so that resultant fields are symmetrical with respect to the target area around a plane of symmetry which lies midway between the plane of the first main field coil pair and the second main field coil pair and directed so as to have opposing polarities with the field shape and direction produced by the first main field coil pair being substantially mirrored about said plane of symmetry by those produced by the second main field coil pair.
2. An MRI machine according to claim 1 , wherein mutually facing parallel coils respectively in the first and second coil pairs are wound with the opposite sense.
3. An MRI machine according to claim 1 , wherein at least one coil in either or both main field coil pairs is associated with one or more satellite coils for enhancing field homogeneity.
4. An MRI machine according to claim 3 , wherein both coils in both main field coil pairs are provided with two satellite coils.
5. An MRI machine according to claim 4 , wherein the two satellite coils of each coil are situated substantially diametrically opposite each other.
6. An MRI machine according to claim 3 wherein each said satellite coil is wound contiguously in series with and with the same sense as the main field coil with which it is associated.
7. An MRI machine according to claim 1 wherein one or more ferromagnetic members and/or permanent magnets is or are located within, or just out of, the plane of one or both main field coil pairs.
8. An MRI machine according to claim 1 , wherein each coil pair has closely physically associated therewith, respective substantially planar x, y and z gradient coils.
9. An MRI machine according to claim 8 , wherein the planes of the gradient coils are substantially parallel to the planes of the coil pairs with which they are associated.
10. An MRI machine according to claim 1 , wherein the main field coils are connected to a main field power supply.
11. An MRI machine according to claim 1 , wherein the main field coil pairs are mounted on metallic mounts and the metallic mounts are arranged to be cooled by a cryocooling system.
12. An MRI machine according to claim 1 wherein the main field coil pairs are independently or together moveable relative to a patient bed.