Optimization of asymmetric MRI-magnets

The basic field-forming elements in a conventional homogenization procedure of MRI-magnets are active current loops coaxial to the patient axis. An alternative way uses ferromagnetic loops as field-forming structures and hence allows the design of very compact magnets with additional free access to the volume of interest. The principle of ferromagnetic homogenization can be used to find asymmetric magnet configurations that are useful for dedicated MRI applications. The asymmetric concept improves the access to the patient and/or the access for the patient. Consequently the concept has a potential for surgical intervention or screening applications of magnetic resonance imaging. This paper reports the most recent results on homogeneity improvements of asymmetric magnets. Due to the non-linear B-H-curve of the ferromagnetic rings, the homogeneity depends on the field strength. This dependence, which is especially important for superconducting magnets, is investigated in detail.