Utah Center for Advanced Imaging Research, Department of Radiology, University of Utah, Salt Lake City, UT 84108 USA.
IEEE Trans Med Imaging. 2010 Feb;29(2):523-30. doi: 10.1109/TMI.2009.2037496.
The use of multiple independent simultaneous radio-frequency (RF) transmitters and coils, known as parallel transmission, has the potential to make multidimensional excitation applicable to a wide range of magnetic resonance imaging applications. The sensitivity profile of the RF coils in a parallel transmission system determines the performance of the system. We present a theoretical framework, allowing the evaluation of the performance of a coil array for parallel transmission. We show through theoretical analysis and Monte Carlo simulation that the proposed framework predicts the fidelity of excitation that can be achieved by a given coil configuration in the presence of noise in the measured coil sensitivity profiles. We evaluate the fidelity of excitation achieved by four candidate coil configurations for a four-channel parallel transmission system with noisy coil sensitivity estimates. Theoretical results are confirmed with Monte Carlo simulation. The results give insight into the design of coil configurations for parallel transmission. In particular, optimal fidelity of excitation for subsampled Cartesian excitation k -space is achieved with a coil sensitivity profile having uniform amplitude and increasing linear phase for each channel. Such sensitivity profiles may be achieved with twisted birdcage coil designs.
使用多个独立的同时射频（RF）发射器和线圈，即并行传输，有可能使多维激发适用于广泛的磁共振成像应用。并行传输系统中 RF 线圈的灵敏度分布决定了系统的性能。我们提出了一个理论框架，允许评估并行传输中线圈阵列的性能。我们通过理论分析和蒙特卡罗模拟表明，该框架可以预测在测量的线圈灵敏度分布中存在噪声时给定线圈配置可以实现的激发保真度。我们评估了具有噪声线圈灵敏度估计的四通道并行传输系统的四个候选线圈配置的激发保真度。理论结果得到了蒙特卡罗模拟的验证。结果深入了解了并行传输中线圈配置的设计。特别是，对于欠采样笛卡尔激发 k 空间，通过每个通道的幅度均匀且线性相位递增的线圈灵敏度分布可以实现最佳的激发保真度。这种灵敏度分布可以通过扭绞鸟笼线圈设计来实现。
