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：快速螺旋采集在以下方面非常有用： 由于扫描时间短，因此可用于定量流应用。 在 这些序列，光谱空间激励脉冲通常是 用于减少脂质模糊。 这些脉冲仅激发 切片内的水质子，导致脂质信号最小 质子。 然而，移动质子在过程中经历相位调制 光谱空间激发，导致信号减弱和 流量量化问题。 我们设计了流量补偿 光谱空间脉冲作为这个问题的解决方案。 有了这些新 脉冲，以恒定速度运动的质子经历相同的 激发曲线为静态质子，而脂质信号仍然是 显着下降。 方法和结果：实现流程 光谱空间激励期间的补偿，应用射频能量 仅当振荡梯度的零阶矩和一阶矩为 重新聚焦，或归零。 这些脉冲的设计受到以下限制 系统的最大梯度幅度和转换速率。 与标准 梯度参数，保持光谱的流量补偿设计 选择性仅适用于相对较厚的空间板激励。 借助我们更新的梯度系统（更高的梯度幅度和更快的速度） 转换速率），可以保持光谱选择性，同时实现 切片厚度范围更广。 对于穿过平面的流动 测量、速度编码也可以合并到流量中 补偿脉冲。 这进一步减少了梯度占空比，并且 还缩短了序列的最小TE和TR。 总结和 结论：流量补偿光谱空间脉冲设计是 使用更强的梯度子系统是可行的。 这些脉冲产生 质子以恒定速度运动所需的激发曲线 在激发期间，同时保持光谱和空间 选择性。 与非流量补偿设计相比，信号更高 通过移动旋转可以更好地可视化更快的移动 血管中的流量，并可能更准确地确定 定量流量应用中的平面流量测量。