Sensitivity and uniformity improvement of phased array MR images using inductive coupling and RF detuning circuits

To improve sensitivity and uniformity of MR images obtained using a phased array RF coil, an inductively coupled secondary resonator with RF detuning circuits at 300 MHz was designed.

A secondary resonator having detuning circuits to turn off the resonator during the transmit mode was constructed. The secondary resonator was located at the opposite side of the four-channel phased array to improve sensitivity and uniformity of the acquired MR images. Numerical simulations along with phantom and in vivo experiments were conducted to evaluate the designed secondary resonator.

The numerical simulation results of |B₁⁺| in a transmit mode showed that magnetic field uniformity would be decreased with a secondary resonator having no detuning circuits because of unwanted interferences between the transmit birdcage coil and the secondary resonator. The standard deviation (SD) of |B₁⁺| was decreased 57% with a secondary resonator containing detuning circuits. The sensitivity and uniformity of |B₁^-| in the receive mode using a four-channel phased array were improved with the secondary resonator. Phantom experiments using a uniform saline phantom had 20% improvement of the mean signal intensity and 50% decrease in the SD with the secondary resonator. Mice with excess adipose tissue were imaged to demonstrate the utility of the secondary resonator.

The designed secondary resonator having detuning circuits improved sensitivity and uniformity of mouse MR images acquired using the four-channel phased array.