Study on the decoupling of stacked phased array coils for magnetic resonance imaging

Abstract

It has been suggested that multi-coil solenoids, which consist of an array of stacked surface coils, can be used in magnetic resonance imaging (MRI) applications to increase the signal-to-noise ratio (SNR) and consequently improve the image quality. However, due to the physical stacked design, mutual coupling effect occurs and distorts the array signals. A new compensation method has been proposed to remove the mutual coupling effect. It employs a set of newly defined mutual impedances to establish a compensation matrix through which the decoupled signals can be obtained. In this paper, the design of stacked phased array coils for MRI is described in details, and the decoupling method between the coil elements is clearly explained. Moreover, workbench experiments were conducted in a mimic MRI system with a cylindrical phantom acting for the loading purpose. A two-element stacked phased coil array has been designed as the receive-only coils under the radiation of a source coil placed above the cylindrical phantom. With the scattering parameters measured by a network analyzer, the new mutual impedances and compensation matrix were determined, and thereby decoupled signals were obtained. To demonstrate the robustness of the decoupling method, measurements were performed over a power deviation from-10 dBm to 10dBm, a frequency deviation from 84.9 MHz to 85.1 MHz, and a deviation of the distance between the two coil elements from 0.5cm to 3cm. In each case, the derived decoupled signals were then compared with the ideally measured coupling free signals. From the comparison results, it is concluded that the new decoupling method can decouple the coupled signals effectively. Because of the robustness and flexibility in all the different experimental scenarios, the stacked phased array coil design together with the new decoupling method is proved to have a potential application in MRI.