Velocity-selective RF pulses in MRI
Velocity-selective RF pulses in MRI
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DOI：
10.1002/mrm.20751
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发表时间：
2006-01-01
影响因子：
3.3
通讯作者：
Durand, E
中科院分区：
文献类型：
--
作者：
de Rochefort, L;Maître, X;Durand, E
设计了一系列速度选择脉冲，由一系列射频硬脉冲和随后的双极梯度组成。使用 k 空间方法在小顶角近似内推导出所需的脉冲序列。所需速度激励的傅里叶变换确定了翻转角级数，并且广义 k 空间中的相应位置确定了双极梯度一阶矩。可以选择任何速度等级的旋转。为了说明这种方法，我们设计并实验测试了速度切片选择，该选择类似于标准空间切片选择，但涉及以选定速度（速度切片中心）和给定间隔（速度切片厚度）内移动的自旋的激励。假设的近似值并不将设计限制为小角度，因为速度选择对于高达 90 度的角度仍然适用。速度切片是通过实验选择的，以速度范围为-1 m s(-1)至1 m s(-1)为中心，速度切片厚度为0.4 m s(-1)。评估了实验速度切片剖面并对流量进行了量化。
A family of velocity-selective pulses consisting of a series of RF hard pulses followed by bipolar gradients was designed. The succession of required pulses was deduced using a k-space approach within a small tip-angle approximation. Fourier transform of the desired velocity excitation determined the flip-angle series, and the corresponding position in the generalized k-space identified the bipolar-gradient first moments. Spins from any velocity class can be selected. To illustrate this approach we designed and experimentally tested a velocity-slice selection that is analogous to standard spatial-slice selection but involves excitation of spins moving at a chosen velocity (velocity-slice center) and within a given interval (velocity-slice thickness). The assumed approximation does not limit the design to small angles, because velocity selection still holds for angles up to 90 degrees. Velocity slices were experimentally selected, centered on velocities ranging from -1 m s(-1) to 1 m s(-1) with a velocity-slice thickness of 0.4 m s(-1). The experimental velocity-slice profile was assessed and the flow was quantified.