Apparatus and method for reducing spurious currents in NMR imaging apparatus induced by pulsed gradient fields

摘要

NMR imaging apparatus having at least one pulsed magnetic field gradient coil generating pulsed magnetic gradient fields and having at least one other coil structure magnetically linked thereto (and therefore subject to induced pulsed currents which create opposing magnetic fields if permitted to flow) includes apparatus connected in circuit with the other coil structure for suppressing such induced currents. The suppression is effected by causing the other coil structure to have increased electrical impedance with respect to such induced currents. Where the other coil structure is a radio frequency transmit/receive coil having plural parallel connected turns, the suppression apparatus includes at least one capacitor in series with at least some of the turns so as to present a substantially open circuit condition at the relatively lower frequencies of the unwanted induced currents. Where the other coil is a static field profiling or "shimming" coil, it is driven with a wide-band current source so as to counteract the unwanted induced currents.