耦合自旋体系下空间选择性脉冲的优化控制及其应用

Localized manipulation of spin systems can be accurately achieved by spatial-selective radio-frequency pulses, which plays a key role in the field of magnetic resonance imaging and in vivo magnetic resonance spectroscopy. The existing spatial-selective pulses optimization methods are based on the Bloch equation described by classical mechanics, and thus adapted to simple, uncoupled spin systems, but unable to optimize the experiments for complex, coupled spin systems, such as metabolites. In response to this problem, based on spin dynamics and the optimal control theory, our project aims at studying the numerical optimization of spatial-selective pulses for coupled spin systems. The localized experimental quality thus can be improved since the complex spin systems will be deeply manipulated. Then, we will reveal the underlying mode of action of optimized spatial-selective pulses. Furthermore, to verify the above optimal pulses, optimized localized metabolite quantification experiment in vivo is demonstrated. Compared with the conventional method, the approach proposed in this project would efficiently increase both sensitivity and accuracy for scans with a higher degree of automation. The study would be a beneficial extension for the spatial-selective technology of coupled spin systems. Moreover, it is conducive to the understanding of localized manipulation mechanism for complex and coupled spin systems, and also provides scientific basis for further application of optimized spatial-selective pulses in relevant areas of in vivo magnetic resonance spectroscopy.

空间选择性射频脉冲可实现定域内自旋体系的精确操纵，在磁共振成像和活体谱等领域扮演重要角色。现有选择性脉冲的优化设计理论一般建立在经典力学的Bloch方程基础上，因而适应于简单自旋体系，无法直接应用于复杂、耦合自旋体系如代谢物分子体系。针对这一问题，本项目拟基于自旋动力学和优化控制原理，利用数值计算方法开展适应于复杂耦合自旋体系的多维空间选择性脉冲的优化控制研究，实现复杂自旋体系的深度操控，从而改善实验质量；在此基础上，揭示优化选择性脉冲对耦合自旋体系的定域作用机理；进一步地，通过活体小鼠的定域代谢物浓度定量的优化实验来验证优化脉冲的有效性。与传统方法相比，本项目的研究方法将有效提高定域实验的灵敏度、准确性和自动化程度。该研究是磁共振优化脉冲对耦合体系下空间选择性技术的补充和拓展，有助于加强对复杂耦合自旋体系的定域操控机制的认识，同时为优化选择性脉冲在定域活体谱等领域的推广应用提供科学依据。

空间选择性射频脉冲可实现定域内自旋体系的精确操纵，在磁共振成像和活体谱等领域扮演重要角色。现有脉冲的优化设计理论一般建立在经典力学的Bloch方程基础上,因而适应于简单自旋体系，无法直接应用于复杂、耦合自旋体系如代谢物分子体系。本项目基于自旋动力学和优化控制原理，利用数值计算方法系统地开展适应于复杂耦合自旋体系的脉冲优化控制研究，阐明脉冲之间的缺陷补偿规律，揭示脉冲作用机理，并探索优化脉冲性能的物理极限。进一步地，通过代谢混合物定量实验验证优化脉冲的有效性。项目提出一种通用的单次扫描协作脉冲优化方法，可对整个序列或序列片段进行全局性优化，并且对子脉冲数量、子脉冲持续时间、子脉冲片段数没有限制。利用上述单次扫描协作脉冲技术，针对INEPT序列设计开发了适用于J耦合宽带的COOP-INEPT转移协作脉冲，实现$1H-13C耦合自旋体系在120 - 250 Hz的J耦合常数范围内高均匀相干转移，并与常规INEPT、J45+90A-INEPT等方法作了对比。在此基础上，进一步形成可用于代谢混合物浓度定量的高精度COOP-HSQC序列，并利用自主开发的Spin-Scenario波谱成像模拟平台开展了模拟波谱实验，验证了COOP-HSQC在大范围J耦合常数条件下的定量准确性。此外，项目开发的Spin-Scenario模拟实验平台可通过直观统一的编程环境完成自旋体系构建、脉冲序列设计和优化、各类实验任务仿真和数据分析，从而为新技术研发提供高度统一、即插即用的实用化可编程环境。