Overhauser Enhanced Magnetic Resonance Imaging (OMRI)

项目二：检修用户增强磁共振成像。（OMRI）总结：这是一种低磁场MRI模式，与通常在1 T或更高磁场下工作的传统MRI扫描仪相比，它依赖于使用造影剂在低磁场（10 mT）下提供增强强度和分辨率的图像。我们现在正在研究体内影响图像强度的基本因素，这是用这种方法测定pO2的核心。由于Overhauser增强取决于造影剂的浓度、本征质子T1、肿瘤微血管密度，我们将三种不同的肿瘤植入小鼠体内，它们具有不同的微血管密度和血流特征，我们检测了增强谱，并测定了除pO2和浓度外的固有T1。我们还利用动态核极化过程的固有优势，探索了OMRI在肿瘤生理学研究中的其他应用。与用于肿瘤灌注研究的动态对比增强MRI不同，OMRI方法从根本上具有优势，因为它依赖于通过动态核极化增强而不是通过对比机制增强。早期MRI研究表明，在稳定输注钆造影剂的情况下，在造影剂的流入和流出达到平衡后，稳态条件下的浓度与肿瘤间质液压力呈负相关。使用OMRI和在OMRI中使用的造影剂，连续输注是不必要的，因此在无创提取这些信息方面可能具有优势。仪器的一个主要挑战是尽量减少射频沉积到组织中，同时不显著影响OMRI的图像强度增强。为了实现这一目标，我们一直在探索几种策略，包括表面结构，可以将射频聚焦到感兴趣的区域，同时最大限度地减少射频沉积在该区域之外。我们正在研究的另一种方法是开发正交谐振结构，这种结构比以前使用的结构更有效地利用射频。这涉及到在两个独立的射频频率上使用正交线圈，这既增加了灵敏度，又更优化地利用了射频功率。这种谐振器配置需要两个检测通道和相关的放大链。这两个方面都完成了，谐振器结构在设计和组装方面也完成了。

Project 2: Overhauser enhanced Magnetic Resonance Imaging. (OMRI)Summary: This is a low field MRI modality which relies on the use of a contrast agent to provide images with enhanced intensity and resolution at low magnetic fields ( 10 mT) compared to the conventional MRI scanners which typically operate at fields 1 T or higher. We are now examining the fundamental factors in vivo which influence the image intensity, which is central to pO2 determination by this method. Since the Overhauser enhancement is dependent on concentration of the contrast media, the intrinsic proton T1, the microvessel density in tumors, we have taken mice implanted with three different tumors with different microvessel density and flow characteristics and examined the enhancement profile as well as determine the intrinsic T1 in addition to pO2 and concentration We are also exploring additional applications for OMRI in studying tumor physiology taking advantage of the inherent advantage of the process of dynamic nuclear polarization. Unlike Dynamic contrast Enhanced MRI which is used in tumor perfusion studies, where contrast in MRI intensity is probed, the OMRI method is fundamentally advantageous since it relies on enhancement via dynamic nuclear polarization rather than enhancement via contrast mechanisms. Early studies with MRI showed that, a with a steady state infusion of Gadolinium contrast agents, after an equilibrium of in-flow and out-flow of the contrast media is attained, the concentration under steady state conditions can be inversely correlated to the tumor interstitial fluid pressure. With OMRI and the contrast media used in OMRI, it is net necessary for the continuous infusion and therefore may have advantage in extracting such information non-invasively.One major instrumentation challenge is to minimize the RF deposition into the tissue while not significantly compromising the image intensity enhancement in OMRI. Towards this goal, we have been exploring several strategies including surface structures which can focus the RF to the region of interest while minimizing the RF deposition outside this. Another approach we are pursuing and have made some progress is the development of quadrature resonant structures which utilize the RF more efficiently than the previously used configurations. This involves using quadrature coils for two seprate RF frequencies which increase both sensitivity as well as utilizing the RF power more optimally. Such resonator configurations need two detection channels and the associated amplification chains. Both these aspects are completed and the resonator structures are completed in terms of design and assembly.