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KMID : 1137820080290020099
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의공학회지
2008 Volume.29 No. 2 p.99 ~ p.106
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Time-Multiplexed RF Transmission to Improve Homogeneity in High Field MRI
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Han Byung-Hee
Seo Jeung-Hun
Heo Hye-Young
Lee Soo-Yeol
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Abstract
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To improve B₁homogeneity 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 B₁homogeneities 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 B₁inhomogeneity 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 B₁improving 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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KEYWORD
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B₁, homogeneity, time-multiplexed transmission, transmit array coil, high field, dielectric effect
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