Multi-Turn Transmit Coil to Increase B1 Efficiency in Current Source Amplification

Authors

  • N. Gudino,

    1. Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, USA
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  • M. A. Griswold

    Corresponding author
    1. Department of Radiology, University Hospitals of Cleveland, Cleveland, Ohio, USA
    • Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, USA
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Correspondence to: Mark A. Griswold, Ph.D., Case Western Reserve University, 11100 Euclid Ave., Bolwell Bld., Room B-124, Cleveland, OH 44106. E-mail: mag46@case.edu

Abstract

Purpose

A multi-turn transmit surface coil design was presented to improve B1 efficiency when used with current source amplification.

Methods

Three different coil designs driven by an on-coil current-mode class-D amplifier with current envelope feedback were tested on the benchtop and through imaging in a 1.5 T scanner. Case temperature of the power field-effect transistor at the amplifier output stage was measured to evaluate heat dissipation for the different current levels and coil configurations. In addition, a lower power rated device was tested to exploit the potential gain in B1 obtained with the multi-turn coil.

Results

As shown both on the benchtop and in a 1.5 T scanner, B1 was increased by almost 3-fold without increasing heat dissipation on the power device at the amplifier's output using a multi-turn surface coil. Similar gain was obtained when connecting a lower power rated field-effect transistor to the multi-turn coil.

Conclusion

In addition to reduce heat dissipation per B1 in the device, higher B1 per current efficiency allows the use of field-effect transistors with lower current ratings and lower port capacitances, which could improve the overall performance of the on-coil current source transmit system. Magn Reson Med 69:1180–1185, 2013. © 2013 Wiley Periodicals, Inc.

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