Calibrated uncoupling of tightly coupled concentric surface coils for in vivo NMR

Three known active methods of detuning rf coils have been tested by determining the efficiency of uncoupling two concentric transmit surface coils in a double-coil probe. In a comparison at 80 MHz, the method based on the use of lambda/4 cables was found to have advantages. These methods utilize the introduction of an additional resonance at the frequency of interest to completely detune a coil. By offsetting the detuning of the coil (by offsetting the additional resonance) a calibrated fraction of the rf field of the detuned coil can be added to or substracted from the rf field of the neighboring coil.