Patent ID: 6236203
Filing Date: 2001-05-22
Classification: G01R

Abstract:
A method of designing an active shield for substantially zeroing a magnetic field on one side of a predetermined boundary in an open magnetic resonance imaging system, the method comprising:(a) defining a finite length cylindrical geometry for a primary coil which carries a first current distribution on its surface;(b) defining a finite length cylindrical geometry for a secondary coil which carries a second current distribution on its surface, the secondary coil being coaxial with the primary coil and the primary coil being inside the secondary coil;(c) constraining a total magnetic field resulting from a combination of the first and second current distributions such that normal components thereof substantially vanish at the surface and beyond of one of the primary and secondary coils;(d) constraining the first current distribution to the surface of the primary coil;(e) constraining the second current distribution to the surface of the secondary coil; and,(f) calculating the first and second current distributions concurrently allowing both the first and second current distributions to vary while observing the constraints such that a predetermined magnetic field is achieved in a first region and a magnetic field on one side of a predetermined boundary is substantially zeroed.