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 0.18μm
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.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-3159 |
| Date | 15 May 2009 |
| Creators | Liu, Xiaoqun |
| Contributors | Wright, Steven M., Zourntos, Takis |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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