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首页> 外文期刊>Journal of magnetic resonance >An MRI-based switched gradient impulse response characterization method with uniform eigenmode excitation
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An MRI-based switched gradient impulse response characterization method with uniform eigenmode excitation

机译：基于MRI的交换梯度脉冲响应响应方法，具有统一的特征模型激励

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Switching gradients generate eddy currents and mechanical vibrations of the gradient assembly causing errors in the gradient time integrals. This results in image distortions in k-space and inaccuracies in q-space imaging. The purpose of this work is to develop an MRI based unbiased measurement of the switched gradient impulse response function (sGIRF). A new gradient pattern, called the Tukey windowed Shifted Sine-Integral (Tw-SSI) pulse, is introduced to excite the gradient eigenmodes uniformly over a user-defined bandwidth. A 3D MRI-based method with Hadamard encoding was developed to map the spatiotemporal magnetic field generated after the excitation pulse to obtain the sGIRF for all the three gradient axes simultaneously. Compared to an energy-equivalent traditional trapezoidal pulse, the Tw-SSI pulse is able to excite the weak bandlimited cross-terms of the sGIRF by uniformly distributing the energy across eigenmodes. The developed field mapping method is sensitive enough to capture both the direct and cross-terms in the sGIRF. The various mechanical resonant modes of the gradient coils are also revealed, which were found to last longer than eddy currents in the shielded gradient coil studied. Tunable Tw-SSI pulse offers the flexibility to perform unbiased sGIRF measurements over a bandwidth of interest. Rapid MRI field mapping can be easily implemented in any MRI system. The method may be used to perform gradient pre-emphasis, to evaluate new gradient coil designs, and to characterize higher order shims. Published by Elsevier Inc.
机译：切换梯度产生渐变组件的涡流和机械振动，导致梯度时间积分中的错误。这导致Q空间成像中的k空间和不准确的图像扭曲。这项工作的目的是开发基于MRI的基于MRI的切换梯度脉冲响应函数（SGIRF）的测量。引入了一种新的梯度模式，称为Tukey窗口移位的正弦积分（TW-SSI）脉冲，以在用户定义的带宽上均匀地激发梯度特征范围。开发了一种基于HATAMARD编码的3D MRI的方法，用于映射激发脉冲后产生的时空磁场，同时获得所有三个梯度轴的SGIRF。与能量相同的传统梯形脉冲相比，TW-SSI脉冲能够通过均匀地分布能量来激发SGIRF的弱带状交叉术。开发的字段映射方法足够敏感，以捕获SGIRF中的直接和跨术语。还揭示了梯度线圈的各种机械谐振模式，其发现在研究的屏蔽梯度线圈中持续比涡流更长。可调调谐TW-SSI脉冲提供了在感兴趣的带宽上进行无偏见的SGIRF测量的灵活性。在任何MRI系统中都可以轻松实现快速MRI现场映射。该方法可用于执行梯度预加重，以评估新的梯度线圈设计，并表征更高阶垫片。 elsevier公司发布

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