A Novel Magnetic Resonance Radio-Frequency Coil Array that Eliminates Inductive Coupling

Parallel magnetic resonance imaging (MRI) techniques employ RF coil arrays for faster data acquisition, and have been shown to reduce the overall length of MRI procedures, improve signal-to–noise ratio (SNR) and image quality, thus making MRI more attractive and less costly. Elimination of inductive coupling is an essential step in designing RF coil arrays for parallel MRI. If mutual inductance remains among coils in the RF coil array, the MR signal obtained from one coil may disturb the flux in another coil, making it difficult to match the impedance of each individual element to the input impedance its preamplifier. This non-optimal matching can lead to degradation of MR signal thereby yielding images with low quality. The most common strategy for inductive decoupling involves the use of preamplifiers with very low input impedance and decoupling networks with lumped elements. However, the construction of preamplifiers with low input impedance is not easy to accomplish, and these preamplifiers impose technical restrictions on coil design, requiring the use of overlapping loops to further minimize the amount of mutual inductance between the coils.

The present invention describes a novel RF coil circuitry scheme to remove inductive coupling and to overcome the limitations of having to use overlapping geometries and low-impedance preamplifiers. The coil array employs a transformer to match the input impedance of the preamplifier. The signal that reaches the preamplifier is coupled in an inductive fashion to the RF coil decoupling network through the transformer’s primary coil. Because primary and secondary coils in the transformer are isolated, the preamplifier circuit (and the MRI scanner electronics) is electrically isolated from the MR pickup coil. This arrangement provides a perfect electrical balance and isolation between the array channels, thus making it unnecessary to use traps and balluns in the circuit. At 7T, a 4-channel small animal coil array implementing the novel circuitry provided images with excellent SNR and demonstrated isolation of all individual RF coils and immunity to standing waves and other parasitic signals.