Design of multi-channel radio-frequency front-end for 200mhz parallel magnetic resonance imaging

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Title: Design of multi-channel radio-frequency front-end for 200mhz parallel magnetic resonance imaging
Author: Liu, Xiaoqun
Abstract: 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 .18 ?m 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 .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -3159
Date: 2009-05-15

Citation

Design of multi-channel radio-frequency front-end for 200mhz parallel magnetic resonance imaging. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -3159 .

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