FLOW COMPENSATED SPECTRAL SPATIAL EXCITATION PULSES

流量补偿光谱空间激励脉冲

• 批准号: 6282981
• 负责人: JILL O FREDRICKSON
• 金额: $ 2.21万
• 依托单位: STANFORD UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-01-01 至 1998-12-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6282981
• 关键词: bioengineering /biomedical engineering; biomedical resource; cardiovascular system; magnetic resonance imaging; radiology; technology /technique

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.

简介：快速螺旋的采集非常有用 由于扫描时间短，定量流量应用。 在 这些序列，光谱空间激发脉冲通常是 用于减少脂质的模糊。 这些脉冲仅激发 切片内的水质子，导致脂质信号最少 质子。 但是，移动质子在期间经历相位调制 光谱空间激发，导致信号下降和 流量量化问题。 我们设计了补偿流量 光谱空间脉冲作为解决此问题的解决方案。 使用这些新 脉冲，以恒定速度移动的质子经历相同的 激发曲线作为静态质子，而脂质信号仍然是 大幅下降。 方法和结果：实现流量 在光谱空间激发期间的补偿，应用RF能量 只有当振荡梯度的零点和第一瞬间是 重新聚焦或无效。 这些脉冲的设计受到 系统的最大梯度振幅和振荡速率。 使用标准 梯度参数，流量补偿的设计以维持光谱 选择性仅适用于相对较厚的空间平板激发。 随着我们较新的梯度系统（较高的梯度振幅，更快 降低率），可以保持光谱选择性，同时达到 较宽的切片厚度。 用于整个平面流 测量值，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， 还缩短了序列的最小TE和TR。 摘要和 结论：流量补偿光谱空间脉冲设计是 具有更强的梯度子系统可行。 这些脉冲产生 以恒定速度移动的质子的所需激发曲线 在激发期间，保持光谱和空间 选择性。 与非流量补偿设计相比，较高的信号 通过移动旋转可更好地可视化更快的移动 血管中的流动，并可能更准确地确定 定量流量应用中的平面流量测量。