Feedback Control of the Nuclear Magnetization State (SGER Award)

本研究的目的是应用反馈控制的概念来改善现有的核磁成像和光谱学方法的性能。这些方法是基于观察射频脉冲序列产生的核磁化波动，在成像的情况下，应用磁场梯度。传统的成像和光谱学技术是开环过程，通过测量磁化状态来优化连续射频脉冲之间的脉冲参数。本项目特别关注磁共振成像中的对比度增强。开发了一种自动调整脉冲参数以增强特定化学物质之间对比度的反馈策略。该控制设计在商用成像仪上使用水和油样品进行了实验验证。自适应控制算法调整脉冲参数，使水和油磁化信号之间的差异最大化。这项研究的意义是双重的。首先，介绍了成像和光谱学领域使用反馈所带来的优势。其次，为进一步考虑反馈概念在核磁成像和光谱学中的应用提供了基础。

The objective of this research is to improve the performance of existing nuclear magnetic imaging and spectroscopy methods of applying the concepts of feedback control. These methods are based on observing the fluctuations in nuclear magnetization produced by sequences of RF pulses and, in the case of imaging, applied magnetic field gradients. Conventional imaging and spectroscopy techniques are open-loop processes in that measurements of the magnetization state are used to optimize the pulse parameters between successive RF pulses. This project focuses specifically on contrast enhancement in magnetic resonance imaging. A feedback strategy that automatically adjusts pulse parameters to enhance the contrast between specified chemical species is developed. The control design is verified experimentally on a commercial imager using a sample of water and oil. An adaptive control algorithm tunes the pulse parameters so that the difference between the water and oil magnetization signals is maximized. The significance of this research is twofold. First, it introduces the imaging and spectroscopy communities to the advantages afforded by using feedback. Second, it provides a foundation on which to consider further applications of feedback concepts to nuclear magnetic imaging and spectroscopy.