分类： 生物学 >> 生物物理学 提交时间： 2016-05-12
Yan, Xinqiang
Yan, Xinqiang
Yan, Xinqiang
Xie, Zhentian
Zhang, Xiaoliang
Pedersen, Jan Ole
Zhang, Xiaoliang
摘要： Radiative antenna techniques, e.g., dipole and monopole, have been proposed for radiofrequency (RF) coil array designs in ultrahigh field MRI to obtain stronger B-1 field and higher signal-to-noise ratio (SNR) gain in the areas deep inside human head or body. It is known that element decoupling performance is crucial to SNR and parallel imaging ability of array coil and has been a challenging issue in radiative antenna array designs for MR imaging. Magnetic wall or induced current elimination (ICE) technique has proven to be a simple and effective way of achieving sufficient decoupling for radiative array coils experimentally. In this study, this decoupling technique for radiative coil array was analyzed theoretically and verified by a simulation study. The decoupling conditions were derived and obtained from the theory. By applying the predicated decoupling conditions, the isolation of two radiative elements could be improved from about -8 dB to better than -35 dB. The decoupling performance has also been validated by current distribution along the radiative elements and magnetic field profiles in a water phantom. (c) 2015 Wiley Periodicals, Inc.
分类： 生物学 >> 生物物理学 >> 影像医学与生物医学工程 提交时间： 2016-05-12
摘要： Objective: In microstrip transmission line (MTL) transmit/receive (transceive) arrays used for ultrahigh field MRI, the array length is often constrained by the required resonant frequency, limiting the image coverage. The purpose of this study is to increase the imaging coverage and also improve its parallel imaging capability by utilizing a double-row design. Methods: A 16-channel double-row MTL transceive array was designed, constructed, and tested for human head imaging at 7 T. Array elements between two rows were decoupled by using the induced current elimination or magnetic wall decoupling technique. In vivo human head images were acquired, and g-factor results were calculated to evaluate the performance of this double-row array. Results: Testing results showed that all coil elements were well decoupled with a better than -18 dB transmission coefficient between any two elements. The double-row array improves the imaging quality of the lower portion of the human head, and has low g-factors even at high acceleration rates. Conclusion: Compared with a regular single-row MTL array, the double-row array demonstrated a larger imaging coverage along the z-direction with improved parallel imaging capability. Significance: The proposed technique is particularly suitable for the design of large-sized transceive arrays with large channel counts, which ultimately benefits the imaging performance in human MRI.
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