FLOW COMPENSATED SPECTRAL SPATIAL EXCITATION PULSES

快速螺旋收购是非常有用的 定量流动应用，因为它们的扫描时间很短。在……里面 这些序列、频谱-空间激励脉冲通常是 用来减少因脂质造成的模糊。这些脉冲只会激发 切片中的水质子，导致来自脂质的最小信号 质子。然而，运动的质子在过程中经历一种位相调制 光谱-空间激发，导致信号和 流量量化中的问题。我们设计了流量补偿装置 光谱-空间脉冲作为这个问题的解决方案。有了这些新的 以恒定速度运动的脉冲、质子经历了同样的过程 激发谱为静态质子，而脂类信号仍为 显著下降。方法和结果：实现流畅 在频谱-空间激励过程中，应用射频能量进行补偿 仅当振荡梯度的零阶矩和一阶矩为 重新聚焦，或归零。这些脉冲的设计受 系统的最大梯度幅值和摆率。带标准 保持光谱的梯度参数、流动补偿设计 选择性只对较厚的空间板激励起作用。 使用我们较新的梯度系统(更高的梯度幅度和更快 转换率)，可以保持光谱选择性，同时实现 更大范围的切片厚度。对于贯穿平面的流动 测量、速度编码也可以合并到流中 补偿脉冲。这进一步降低了梯度占空比，并且 还缩短了序列的最小TE和TR。摘要和 结论：流量补偿频谱-空间脉冲设计是 对于更强的梯度子系统是可行的。这些脉冲产生 匀速运动质子的期望激发轮廓 在激发期间，在保持光谱和空间的同时 选择性。与无流量补偿设计相比，信号更高 从移动自旋可以更好地可视化更快的移动 容器中的流动，以及可能更准确地确定 定量流动应用中的贯通平面流动测量。

Introduction: Fast spiral acquisitions are very useful in quantitative flow applications because of their short scan times. In these sequences, spectral-spatial excitation pulses are typically employed to reduce blurring from lipids. These pulses excite only water protons within a slice, resulting in minimal signal from lipid protons. However, moving protons experience a phase modulation during spectral-spatial excitation, resulting in decreased signal and problems in flow quantification. We have designed flow compensated spectral-spatial pulses as a solution to this problem. With these new pulses, protons moving at constant velocities experience the same excitation profile as static protons, while lipid signal is still significantly decreased. Methods and Results: To achieve flow compensation during spectral-spatial excitations, rf energy is applied only when the zeroth and first moments of the oscillating gradient are refocused, or nulled. The design of these pulses is limited by the maximum gradient amplitude and slew rate of the system. With standard gradient parameters, flow compensated designs that maintain spectral selectivity only work for relatively thick spatial slab excitations. With our newer gradient system (higher gradient amplitude and faster slew rates), spectral selectivity can be maintained, while achieving a wider range of slice thicknesses. For through-plane flow measurements, velocity encoding can also be incorporated into the flow compensated pulses. This further reduces the gradient duty cycle, and also shortens the minimum TE and TR of the sequence. Summary and Conclusions: Flow compensated spectral-spatial pulse designs are feasible with stronger gradient subsystems. These pulses produce desired excitation profiles for protons moving at constant velocities during the excitation period, while maintaining spectral and spatial selectivity. Compared to non-flow compensated designs, higher signal from moving spins results in better visualization of faster moving flow in vessels, and potentially more accurate determination of through-plane flow measurements in quantitative flow applications.