Microsoft Word - ISMRM2005-000291.DOC
نویسندگان
چکیده
B. Wu, P. Qu, J. Yuan, G. X. Shen MRI Lab, Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong INTRODUCTION Minimizing the mutual coupling among array elements is necessary for parallel MRI. Preamplifiers with extremely low input-impedance [1] and capacitive decoupling networks [2, 3] have become the primary techniques for decoupling arbitrarily placed coil array elements. However, the low input-impedance preamplifier is not suitable in transmit mode, and capacitive decoupling networks may cause design difficulties for large number of elements [4]. In this paper, we show that the tunable loop microstrip (TLM) coil array [5, 6] with decoupling circuit can achieve more than -20dB element isolation. The decouple circuit in our design is quite simple, only n decoupling capacitors are needed for n elements. Thus, it is suitable for arrays with large number of coils and for transceivers. METHOD The TLM coil array shown in Fig.1 is a series of TLM coils linked by decoupling capacitors. Each TLM coil consists of a conductive loop and ground plane separated by low loss dielectric material. The section in the square box of Fig.1 illustrates the decoupling method, where CT and CD are tuning and decoupling capacitors, M and L denote the mutual inductance and equivalent self-inductance of each coil respectively. According to even/odd mode analysis, when two resonant mode frequencies fe = fo, the mutual inductive coupling of adjacent elements diminishes [7]. Then, the required CD can be calculated as: ) /( 2 M L M C C T D − = (1).
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