Patent ID: 6954070

Claim:
A magnetic structure for generating a uniform magnetic field capable of implementing NMR imaging of the head of a patient within a region of interest, comprising: a) first and second magnetic structures defining a first cavity having the region of interest and configured to accommodate the head of a patient and defining adjacent the first cavity a second cavity, larger than the first cavity, configured to accommodate the shoulders of the patient when the latter's head is positioned in the first cavity, the first and second magnetic structures being positioned on opposite sides of the first and second cavities and defining a common longitudinal axis through the centers of the first and second magnetic structures and providing access if desired from the outside for surgical intervention to the head of the patient when positioned within the first cavity, b) each of the first and second magnetic structures comprising a magnetic structure including: i) an annular section of permanent magnetic material and having a conical portion having a narrower end and a wider end and substantially inner and outer conical surfaces and a conical axis coincident with the common longitudinal axis, the narrower end being positioned closer to the region of interest than the wider end, the permanent magnetic section having a first value and a first orientation of remanence, ii) a pole piece member of ferromagnetic material and positioned within the conical section adjacent and bordering its inner conical surface and having an axis also coincident with the common longitudinal axis, the annular surface of contact between the inner conical surface of the permanent magnetic section and the bordering pole piece member being slightly curved, c) the permanent magnetic sections and the pole piece members of the first and second magnetic structures cooperating to produce within the first cavity a substantially uniform magnetic field capable of supporting NMR imaging, d) the shape of the annular curved surface of contact being configured so as to form at that surface an equipotential surface, whereby distortion of the substantially uniform magnetic field is minimized.