Patent ID: 6963200

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 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 conical section of permanent magnetic material and having a narrower end and a wider end connected by inner and outer substantially 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 conical section having a first value and a first orientation of remanence, ii) an inner essentially cylindrical magnetic section of permanent magnetic material and having a longitudinal axis coincident with the common longitudinal axis and adjacent and magnetically coupled to the wider end of the conical section, the inner cylindrical magnetic section extending radially in a direction away from the common longitudinal axis, the inner cylindrical magnetic section having a second value and a second orientation of remanence, iii) transition means for interfacing the wider end of the conical section and the adjacent end of the inner cylindrical magnetic section for at least partially correcting for field distortion in or near the region of interest arising from the magnetic coupling between the wider end of the conical section and the adjacent end of the inner cylindrical magnetic section.