A New Decoupling Method for Quadrature Coils in Magnetic Resonance Imaging

School of Information Technology and Electrical Engineering, University of Queensland, Brisbane QLD 4072, Australia.
IEEE Transactions on Biomedical Engineering (Impact Factor: 2.35). 11/2006; 53(10):2114-6. DOI: 10.1109/TBME.2006.881783
Source: PubMed


A powerful decoupling method is introduced to obtain decoupled signal voltages from quadrature coils in magnetic resonance imaging (MRI). The new method uses the knowledge of the position of the signal source in MRI, the active slice, to define a new mutual impedance which accurately quantifies the coupling voltages and enables them to be removed almost completely. Results show that by using the new decoupling method, the percentage errors in the decoupled voltages are of the order of 10(-7) % and isolations between two coils are more than 170 dB.

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    • "In [12] it is claimed that by using this method, only the transmitting array is properly modelled to compensate the MC effect, and it fails to correctly model the receiving array. Here, we use a new concept of the mutual coupling modeling, called receiving mutual coupling impedance method [14] [15] [16] which has been shown to have a better performance than the conventional method in several antenna array applications such as direction finding [13] [15], adaptive nulling [17], and in magnetic resonance imaging [16]. Recent works [2] [5] [7] have shown that using a simple matching network at the receive side can give a significant improvement for MIMO performance in the presence of MC. "
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    ABSTRACT: Applying MIMO technology in small wireless devices leads to closely spaced antennas, which results in antenna mutual coupling (MC) and highly correlated signals. In this paper, we investigate the effect of the terminal load impedance of the antennas on the MIMO capacity in the presence of the mutual coupling. We use a new concept of receiving mutual impedances to model the MC effect, which has been shown to have a much better performance than the conventional open-circuit voltage method in different applications of array antennas. Simulation results for a 2×2 MIMO system with half-wavelength dipoles in different scattering distribution scenarios, show that in our proposed method, an optimum value of the terminal load impedance ZL of the antennas can be obtained to maximise the capacity for all scattering distributions, whereas the conventional methods need to different ZL in different scattering scenarios.
    Full-text · Conference Paper · Jan 2010
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    • "Hence the position information of the active slice is available and can be used to determine the receiving mutual impedance. Theoretical studies using this method have been found in MRI surface coil arrays [12] and MRI quadrature coils [13]. It was shown in these studies that mutual coupling could be almost totally removed and nearly coupling-free array signals can be obtained. "
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    ABSTRACT: A new decoupling method for magnetic resonance imaging (MRI) phased arrays is studied by experimental measurements. A laboratory measurement setup is built to characterise the signal coupling paths and their coupling strengths. A new concept, the receiving mutual impedance, is introduced to measure the coupled signals between the phased array elements. Measured values of the receiving mutual impedances for a typical two-element surface-coil array are obtained and used in other experiments to find the uncoupled voltages from the received voltages. Results show that the new decoupling method is both accurate and robust over a wide frequency range. Comparison of the uncoupled voltages with the actual ideal uncoupled voltages confirms that if the position of the signal source is known, almost error-free uncoupled voltages can be obtained. The errors resulted from a change of the position of the signal source are also measured and it is found that they generally increase with the deviation of the signal source from its position where the receiving mutual impedances are measured. The maximum % error of the uncoupled voltages is found to be below 10% when the signal source changes its position over a distance of half the length of a surface coil. Over this distance change, the signal isolation between the two surface coils is found to be at least 20 dB, whereas the maximum is more than 300 dB. The results demonstrate the effectiveness and the feasibility of the new decoupling method for use in MRI phased arrays.
    Preview · Article · Oct 2008 · IET Science Measurement ? Technology
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    ABSTRACT: Mutual coupling is a common problem in the applications of antenna arrays. It significantly affects the operation of almost all types of antenna arrays. Over the past years, there have been many different kinds of methods suggested to decouple (or to compensate for) the mutual coupling effect in antenna arrays. The effectiveness of these methods varied and depended upon the types of antenna arrays being considered and the applications in which the antenna arrays were used. In this paper, a brief review of the decoupling methods for the mutual coupling effect in antenna arrays is presented. These include patented and non-patented methods. The methods are grouped under seven categories for antenna arrays in communications and four categories for antenna arrays in magnetic resonance imaging (MRI). The various methods will be first briefly described and their operation principles will be explained. Then some comments on their scopes of application and their comparisons or relations to other methods will be given. The problems associated with these methods will also be analysed. This is the first review on this topic and we believe that it helps to give an overview of the decoupling methods which have been so far proposed in the literature. We also believe that this review will help clarify some main differences and relations between the various decoupling methods and provide some information for future research on the problem of mutual coupling.
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