Detection of MR signal during RF excitation using a transmit array system

Most of conventional MRI applications are based on a time interleaved approach for RF excitation and signal detection. The idea of concurrent RF excitation and reception was implemented in a few recent studies using sideband excitation [1, 2] and swift [3] techniques. In sideband excitation technique, the necessary decoupling between MR signal and RF pulse is achieved by filtering out the excitation frequency band. In the continuous swift technique, partial decoupling is achieved using mechanical adjustment of receiver and transmitter coils. The remainder of signal was separated using a series of signal processing technique. According to our simulations (MATLAB: Mathworks, Natick, MA), voltage induced on a receiver coil due to RF excitation pulse from the transmit coils must be reduced by at least 80dB to make this voltage comparable to the voltage induced from the spins. Note that more decoupling is needed to bring coupling to the noise level depending on the required SNR. In this study, magnetic field decoupling of 75dB is achieved between transmitter and receiver. This method of transmit/receive isolation enables detection of MR signal during RF excitation which is significant for imaging species with ultra short T2 values, and measurement of spin properties during excitation.