Journal of Biomedical Engineering Research (대한의용생체공학회:의공학회지)

The Korean Society of Medical and Biological Engineering (대한의용생체공학회)
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Time-Multiplexed RF Transmission to Improve $B_1$ Homogeneity in High Field MRI

  • Han, Byung-Hee (Dept. of Biomedical Engineering, Kyung Hee University) ;
  • Seo, Jeung-Hun (Dept. of Biomedical Engineering, Kyung Hee University) ;
  • Heo, Hye-Young (Dept. of Biomedical Engineering, Kyung Hee University) ;
  • Lee, Soo-Yeol (Dept. of Biomedical Engineering, Kyung Hee University)
  • Published : 2008.04.30
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Abstract

To improve $B_1$ homogeneity in high field MRI, the RF power is applied to the transmit array coil elements sequentially in the time-multiplexed way. Since only a single coil element is activated in a time-multiplexing slot, the global standing wave formation in the human body is greatly suppressed. The time-multiplexing slot width is on the order of micro seconds, hence, high-order-harmonic slices can be placed far from the transmit coil and simultaneous multiple slice selection can be avoided. The $B_1$ homogeneities of a birdcage coil and an eight-channel transmit array coil have been compared through finite difference time domain simulations. The simulation results indicate that the proposed technique can reduce the peak-to-peak $B_1$ inhomogeneity down to one fourth of the transmission with a birdcage coil on the central plane of the human head model at 3 T. The mimicking experiments at 3 T, eight separate experiments with a single coil element activated and image reconstruction by combining the eight images, also show promising results. It is expected that the proposed technique has some advantages over other $B_1$ improving methods in real practice since simple RF switching circuitries are only necessary and electromagnetic coupling between the coil elements is out of concern in its realization.

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References

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