Coil Array Optimization and Wireless Transceiver Design for MRI

This dissertation, "Coil Array Optimization and Wireless Transceiver Design for MRI" by Juan, Wei, 魏娟, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled Coil Array Optimization and Wireless Transceiver Design for MRI submitted by Wei Juan for the degree of Doctor of Philosophy at The University of Hong Kong in February 2007 In recent years, parallel imaging has revolutionized the field of fast MRI. Array coils with independent receivers and the use of the additional spatial encoding enable parallel imaging techniques much more efficiently. Recently, due to the cost reduction of RF receivers, the number of array channels has risen to 96. This thesis presents the author's investigations into the optimization of RF coil array for ultra high field MRI and the design of a wireless RF transceiver for MRI signal transmission. On the optimization of RF coil array, the author emphasizes the parallel imaging performance which is closely related to the uniqueness of each element sensitivity pattern. For such applications, the design process begins by choosing the number, shape and arrangement of the elements. Then the electromagnetic field modeling is applied to predict sensitivity patterns and the noise covariance matrix to calculate parameters such as G-factor and SNR dedicated to the evaluation of parallel imaging performance. However, the mutual coupling of coil array causes the shift of the resonant frequency of the elements and degrades their sensitivity. There are some decoupling techniques, such as the "geometric," "preamplifier" and "reactive" methods, but they make the coil array design much more complicated. An investigation into the intrinsic coupling characteristics of array elements is also presented in this thesis to provide a simple guidance to minimize the mutual coupling for array design. In recent years, there has been a trend to dramatically increase the number of receive channels of coil array to shorten imaging time without sacrificing much of their SNR. However, with many elements, the cable crosstalk and RF burn become the serious problem. Wireless transmission is a promising alternative to coaxial cables for the MRI coil array to avoid this problem. Although wireless links have been widely used in the field of telecommunications, some special critical issues for MRI are highly imposed in order to maintain the image quality. In this thesis, the wireless transmission system based on IEEE 802.11b standard is implemented. With this new technique the MR images of both phantom and human head are successfully obtained from XinaoMDT 0.3T MRI system (Langfang, China). In summary, the author optimizes the different RF coil arrays based on the simulations and bench tests to present guidelines for future coil array design. The implementation of digital wireless transmission and the MR images obtained have demonstrated the potential of wireless multi-channel transmission for MRI array. DOI: 10.5353/th_b3858302 Subjects: Imaging systems Signal detection Magnetic resonance imaging