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APPLICATIONS OF GALLIUM NITRIDE FETS TO RF ARRAYS FOR MAGNETIC RESONANCE IMAGING

Twieg, Michael D.
http://orcid.org/0000-0001-6198-0581
http://rave.ohiolink.edu/etdc/view?acc_num=case1459253932

Abstract Details

2016, Doctor of Philosophy, Case Western Reserve University, EECS - Electrical Engineering.
Magnetic resonance imaging (MRI) is an imaging technique with incredible utility for medical applications, along with incredible technical complexity. Two of the primary subsystems of an MRI scanner are the RF transmit and receive chains, containing coils, switches, and amplifiers. The RF chains’ fundamental architecture has changed little since its inception, with Silicon transistors dominating the roles of switches and amplifiers. Recent trends have pushed the RF chains toward parallelized design in order to increase image quality, reduce scan time, and/or improve patient safety. Parallel RF chains face technical challenges due to the density of electronics and cables required. For receive chains the challenge is modest; clinical scanners with 128 receive channels are already available. For transmit chains, the challenge is severe due to the large amount of power dissipation and transmission required. Currently commercial systems are limited to 8 transmit channels, and at very high cost. Here we advocate for the replacement of older circuits with more efficient versions based on high performance transistors. In particular, we demonstrate eGaN FETs as a replacement for PIN diodes for active detuning circuits in receive coils. Unlike PIN diodes, FETs can be controlled with voltage, and require almost no bias current, which drastically simplifies the design and construction of large receive arrays. We also demonstrate eGaN FETs for RF power amplifier (RFPA) modules aimed towards parallel transmit (pTX) chains with high channel counts. The eGaN RFPA modules demonstrate far higher power efficiency and density than linear RFPAs based on Si LDMOS FETs, and can operate within the scanner bore. Since our RFPAs are built on switchmode topologies, we explore the nonlinear and time-varying behavior of coupled amplifiers using experimental and numerical methods. Our results show that pTX chains based on these modules have higher efficiency and lower coupling than pTX chains built with linear RFPAs terminated with isolators, and that these benefits increase with the number of channels in the array. We anticipate that the low cost and high performance of the modules will drastically reduce the cost of pTX chains, greatly increasing the value of MRI to millions of patients.
Mark Griswold, Dr. (Advisor)
Kenneth Loparo, Dr. (Committee Member)
Soumyajit Mandal, Dr. (Committee Member)
Nicole Seiberlich, Dr. (Committee Member)
210 p.
Biomedical Engineering; Electrical Engineering; Medical Imaging
MRI; pTX; GaN; Gallium Nitride; FETs; CMCD; RFPA; RF switch; detuning; parallel transmit

Recommended Citations

Citations

  • Twieg, M. D. (2016). APPLICATIONS OF GALLIUM NITRIDE FETS TO RF ARRAYS FOR MAGNETIC RESONANCE IMAGING [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1459253932

    APA Style (7th edition)

  • Twieg, Michael. APPLICATIONS OF GALLIUM NITRIDE FETS TO RF ARRAYS FOR MAGNETIC RESONANCE IMAGING. 2016. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1459253932.

    MLA Style (8th edition)

  • Twieg, Michael. "APPLICATIONS OF GALLIUM NITRIDE FETS TO RF ARRAYS FOR MAGNETIC RESONANCE IMAGING." Doctoral dissertation, Case Western Reserve University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=case1459253932

    Chicago Manual of Style (17th edition)

case1459253932
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© 2016, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.