Calibrated decoupling of tightly coupled concentric surface coils

Claim 1

Apparatus for controlling the shape and magnitude of the RF field applied to a body through active decoupling of a plurality of RF coils comprising, an RF source for providing RF energy having a power spectrum including a frequency component ω₀; a plurality of resonant circuits, first said resonant circuit comprising a first coil and a second said resonant circuit comprising a second coil, said first and second coils proximally disposed, each said resonant circuit capable of exhibiting resonant behavior at frequency ω₀, said second resonant circuit comprising a plurality of frequency dependent reactive portions, at least one said reactive portion including means for receiving control information and capable of exhibiting very different frequency dependence in accord with said control information; RF coupling means for applying said RF energy in common to each said resonant circuit, circuit means for supplying said control information to said second resonant circuit whereby the resonant behavior of said second resonant circuit is altered in a first sense of frequency offset with respect to ω₀, to cause induction of RF current having a phase φ in said first coil due to said second coil and for altering the resonant behavior of said second resonant circuit in a second sense of frequency offset relative to ω₀ to cause induction of an RF current having a phase -φ in said first coil, whereby the combined RF field due to both said coils is selectively controllable in magnitude and spatial distribution.