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The Development of Transceiver for Magnetic Resonance Imaging Spectrometer

Author: LaiZaiXing
Tutor: GengPing；HeYanFa
School: Northeastern University
Course: Radio Physics
Keywords: MRI spectrometer transmitter receiver
CLC: R318.6
Type: Master's thesis
Year: 2009
Downloads: 69
Quote: 1
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Abstract


The technology of Magnetic Resonance Imaging (MRI) has been widely used in the areas of medical and researching imaging. But the costly instruments of MRI are not affordable for most small hospitals and labs. Therefore, to develop an affordable MRI transceiver which is suitable in low magnetic field for our own lab is valuable and important, and this is the purpose of this thesis.The thesis mainly develops two main parts of transceiver in MRI instrument, one part is a Radio Frequency (RF) transmitter, and the other part is a receiver. The transmitter is designed by adopting the Direct Digital Frequency Synthesis (DDS) technology. The transmitter includes the digital frequency synthesis circuit (DFSC) and the modulate circuit. The DFSC includes three D/A generating devices (AD9851), and the three AD9851s are programmed via a multifunctional card (PCI6229) to generate a 9.8MHz sin signal as the carrier for RF signal. The second signal whose frequency is 20.5MHz generated by the second AD9851 is used as the input of local oscillator (LOIP) to the receiver. The third signal whose frequency is 10.7MHz generated by the third AD9851 is used as quadrature demodulation signal to the receiver. A CLC5523 is the main chip of modulation circuit, which mixes the carrier signal from the AD9851 with the modulation signal from the multifunctional card PCI6229 into the RF signal via the CLC5523.The other main part of this thesis is to develop a receiver for transceiver. The receiver has been designed by adopting the superheterodyne demodulation mode, and is designed based on the chip AD607. The object signal is demodulated via two steps of mixing the object signals with the local oscillating signals. The first demodulation step is that the receiver mixes the object signal with the LOIP signal from the transmitter to demodulate the center frequency of the object signal to an intermediate frequency (10.7MHz). The second demodulated step is that the receiver demodulates the center frequency of the signal from the intermediate frequency (10.7MHz) to the base frequency by mixing the output of the first demodulation step with the local oscillating signal (FDIN) from the transmitter. The receiver could demodulate the object signal into an in-phase signal (I signal) and a quadrature signal (Q signal).Controlled by the multifunctional card PCI6229, the digital frequency synthesis circuit could generate sine waves with the tuning resolution of approximately 0.037Hz, and with max frequency not more than 40MHz. The modulation circuit could generate the main petal of Sinc modulated signals with vary frequency bands. The receiver could demodulate the center frequency of the object signal from radio frequency to the base frequency, and generates I and Q signals.

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CLC: > Medicine, health > Basic Medical > Medical science in general > Biomedical Engineering > Apparatus, equipment
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