【作者】 宁立波；

【导师】 邱庆春； 吴仁华；

【作者基本信息】 汕头大学 ， 材料物理与化学， 2010， 硕士

【摘要】 人体组织病变多伴随细胞内外酸碱平衡(pH)紊乱,如脑卒中,肾衰竭,肿瘤及一些炎症。快速准确地检测人体病变组织酸碱环境对疾病的早期诊断以及后续治疗意义重大,然而,当前在体测定人体内环境pH值的手段十分有限。近来发现磁共振技术可以无损地测定组织的pH值。早期多用磁共振频谱测定动物组织细胞内外pH值,但其分辨率较低,难以应用于临床。新近发现的化学交换饱和转移(Chemical exchange saturation transfer,CEST)技术有可能获得组织pH的高分辨空间分布信息。本研究的目的是通过修改MT序列激发三池模型,以获得pH依赖的化学交换饱和转移效应(CEST),探讨临床1.5 T场强下磁共振pH成像的可行性。本研究主要包括三方面内容:第一,探讨化学交换饱和转移理论,分析其与pH值之间的关系。主要探讨三池模型的布洛赫方程唯象理论,分析化学交换速率与pH值的关系,并综述了最新的APT pH成像技术。上述问题的的深入讨论将对序列设计工作具有理论指导意义。第二,脉冲序列设计原理及其实现。研究射频脉冲和梯度场脉冲成像原理,针对CEST pH成像遇到的困难,修改磁化传递脉冲并在EPIC平台上编程实现。第三,扫描模型实验。使用MT-SE序列扫描三池模型,验证三池模型化学交换饱和转移理论,并对比了MT SE序列与常规SE序列在检测pH值方面的差异。结果显示MT SE序列较常规SE序列具有更大的pH敏感性,认为在临床1.5 T场强具有磁共振pH成像的可行性。本课题属于前沿课题。国内未见“基于CEST的pH成像研究”方面的研究报道,国外仅有少数小组将其应用于pH成像方面,目前该研究仍处于探索阶段。本文在编译平台上成功地模拟了MT脉冲序列。本文对CEST的理论描述及MRI脉冲序列成像原理的研究可为后续工作者理解、开发新的pH特异的脉冲序列提供借鉴意义。更多还原

【Abstract】 Acid-based balance is altered in a variety of common pathologies, including ischemia, renal failure, cancer and inflammation. It is of importance to rapidly and accurately detect the acid-base environment of human lesions in early disease diagnosis and follow-up treatment.However, It is known that there are few effective tools available to evaluate pH values in vivo.Recently the Magnetic Resonance is found to provide a non-invasive tool of estimating pH value. MRS was first introduced to measure intra- and extracellular pH, but the inherent low resolution of spectroscopy makes it difficult to be applied to clinic. A new technique known as Chemical Exchange Saturation Transfer (CEST) may provide an high-resolution image of the spatial distribution of pH values in humans. In this research, we used the modified MT-SE sequence to scan the tissue-like pH phantom on 1.5T scanner, with the purpose of exploring the feasibility of CEST MR pH imaging on a clinical scanner.This study includes three aspects. Firstly, investigate chemical exchange saturation transfer theory and its relationship with pH value. It is mainly to investigate the Bloch equations of the three-pool model modified, the relationship between pH value and chemical exchange rate, and review the progress of APT pH imaging. Detailed study of on this issue will be of theoretical significance for the design of pulse sequence. Secondly, the pulse sequence design theory and its programming. It is to study the RF pulse and gradient pulse imaging principle. For CEST pH imaging difficulties, the MR pulse sequence program workstation is used to accomplish the magnetization transfer pulse program on the platform of EPIC. Thirdly, the scanning model experiment. The MT-SE sequence scanning three pool model is performed to verify its CEST effect, and the results were compared with the routine SE in the detection of pH value. Ourresults show that MT SE sequence has a greater pH sensitivity than the routine SE sequence. We concluded that it is feasible to get pH imaging map in 1.5T MRI scanner.This subject is a global problem. No "based on CEST pH imaging" related work was reported in China, and there are only a few pH imaging groups abroad, whose studies on pH imaging are still at an initial stage. We successfully implemented MT pulse sequence programming andsimulation in EPIC workstation. In addition, the theoretical description of CEST and the principle of MRI pulse sequence in this thesis will help the follow-up workers to understand and design the new pH-specific pulse sequences.更多还原