Design Of Multi Channel Radio Frequency Front End For 200mhz Parallel Magnetic Resonance Imaging

Design of Multi-channel Radio-frequency Front-end for 200mhz Parallel Magnetic Resonance Imaging

The increasing demands for improving magnetic resonance imaging (MRI) quality, especially reducing the imaging time have been driving the channel number of parallel magnetic resonance imaging (Parallel MRI) to increase. When the channel number increases to 64 or even 128, the traditional method of stacking the same number of radio-frequency (RF) receivers with very low level of integration becomes expensive and cumbersome. However, the cost, size, power consumption of the Parallel MRI receivers can be dramatically reduced by designing a whole receiver front-end even multiple receiver front-ends on a single chip using CMOS technology, and multiplexing the output signal of each receiver front-end into one channel so that as much hardware resource can be shared by as many channels as possible, especially the digitizer. The main object of this research is focused on the analysis and design of fully integrated multi-channel RF receiver and multiplexing technology. First, different architectures of RF receiver and different multiplexing method are analyzed. After comparing the advantages and the disadvantages of these architectures, an architecture of receiver front-end which is most suitable for fully on-chip multi-channel design is proposed and a multiplexing method is selected. According to this proposed architecture, a four-channel receiver front-end was designed and fabricated using TSMC 0.18Bm technology on a single chip and methods of testing in the MRI system using parallel planar coil array and phase coil array respectively as target coils were presented. Each channel of the receiver front-end includes an ultra low noise amplifier (LNA), a quadrature image rejection down-converter, a buffer, and a low-pass filter (LPF) which also acts as a variable gain amplifier (VGA). The quadrature image rejection downconverter consists of a quadrature generator, a passive mixer with a transimpedance amplifier which converts the output current signal of the passive mixer into voltage signal while acts as a LPF, and a polyphase filter after the TIA. The receiver has an over NF of 0.935dB, variable gain from about 80dB to 90dB, power consumption of 30.8mW, and chip area of 6mm2. Next, a prototype of 4-channel RF receiver with Time Domain Multiplexing (TDM) on a single printed circuit board (PCB) was designed and bench-tested. Then Parallel MRI experiment was carried out and images were acquired using this prototype. The testing results verify the proposed concepts.

Development of Multi-channel Radio Frequency Technology for Sodium and Potassium Magnetic Resonance Imaging at 7.0 Tesla: Design and Clinical Application

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