CAREER: Subcellular Nuclear Magnetic Resonance Imaging

拟议的研究旨在开发将核磁共振显微镜的分辨率提高至少一个数量级到(1-2米)3范围的仪器。由于哺乳动物细胞的直径通常为5-10米，这一进展将打开目前被排除在外的整个亚细胞应用范围。与其他显微技术相比，核磁共振的内在优势包括能够提供完整的三维信息和非侵入性。核磁共振显微镜不仅可以提供空间信息，还可以用于确定化学成分、质子迁移率和分子扩散，后两种测量提供有关感兴趣生物分子的物理环境的信息。这项研究的主要创新将是直径100-200米的射频(RF)微线圈的设计和优化，这比以前用于核磁共振微成像应用的微线圈少了一个数量级。对于给定的体素大小，除了每体素信噪比(SNR)的内在提高之外，使用较小的RF线圈会导致较低的采集带宽，并比较大的线圈进一步提高SNR。这些射频线圈还将允许设计和建造非常小直径、高强度的磁场梯度，这将是克服扩散和磁化率效应并实现所需分辨率所必需的。将构建一个由射频微线圈、磁场梯度和微定位器组成的集成组件。滤波反投影(FBP)技术将被用来获取数据，因为这些技术具有比傅立叶技术更高的内在SNR，并且对于给定的分辨率需要更小的梯度。使用优化的成像系统的第一个实验将是通过比较分子扩散效应的相互竞争的理论、可检测到的最低自旋数量以及非渗透边界上的边缘增强等现象的影响，来实验确定最大可能的分辨率。由于射频线圈的灵敏度不够高，以前没有对这些进行过严格的研究。提出了这项研究的两个主要生物学应用。第一，切除脊髓组织的高分辨率显微成像。无创性核磁共振显示，脊髓损伤和随后的再生都会产生信号强度的变化。为了充分了解这些变化，有必要观察脊髓内的小结构，而不是整个脊髓的大容量平均信号强度。其次，我们将使用显微射频和梯度线圈通过二维扩散有序光谱来确定目前尚不清楚的富含蛋白质的囊泡的物理环境，这一信息将有助于阐明某些神经递质在哺乳动物中的作用。微型核磁共振系统的开发是一个新兴的成像领域，应该完全融入我们的学术课程。目前，申请者和他的同事们已经在电气和计算机工程系内开发了一套独特的三门磁共振课程。主要的教育重点将是完成将以计算机为基础的交互式学习融入这三门课程，并编写一门以实验室为基础的磁共振系统课程，以配合研究生水平的系列讲座。所提出的研究有许多与电气工程相关的方面：高频建模和仿真、电路特性和设计优化，以及生物工程师感兴趣的应用。事实上，由于磁共振通常不是电气工程师的活跃领域，我们预计该系的教职员工、本科生和研究生研究人员的加入将取得重大进展。在过去的两年里，该系的20多名学生已经选择了这个领域作为本科研究和他们与申请者的高级设计项目。

deseree davisdeseree davis The proposed research aims to develop instrumentation which will improve the resolution of nuclear magnetic resonance (NMR) microscopy by at least an order of magnitude to the (1- 2 m)3 range. Since mammalian cells are typically 5-10 m in diameter, this advance would open up a whole range of subcellular applications which are currently precluded. The intrinsic advantages of NMR over other microscopic techniques include the ability to provide full three- dimensional information and its non-invasive character. NMR microscopy not only gives spatial information, but can also be used to determine chemical composition, proton mobility, and molecular diffusion, the latter two measurements giving information on the physical environment of the biological molecules of interest. The major innovation in this research will be the design and optimization of radiofrequency (RF) microcoils of diameter 100-200 m, an order of magnitude less than has previously been used in NMR microimaging applications. In addition to the intrinsic increase in signal-to-noise ratio (SNR) per voxel for a given voxel size, the use of small RF coils results in a lower acquisition bandwidth and further SNR improvements over larger coils. These RF coils will also allow the design and construction of very small diameter, high strength magnetic field gradients, which will be necessary to overcome diffusion and susceptibility effects and achieve the desired resolution. An integrated assembly of RF microcoil, magnetic field gradients, and micropositioner will be constructed. Filtered back projection (FBP) techniques will be used to acquire the data, since these have an intrinsically higher SNR than Fourier techniques, and require smaller gradients for a given resolution. The first experiments using the optimized imaging system will be to determine experimentally the maximum possible resolution by comparing competing theories of effects of molecular diffusion, the lowest detectable number of spins, and the effects of phenomena such as edge enhancement at non- permeable boundaries. These have not been rigorously studied previously since the sensitivity of the radiofrequency coils was not sufficiently high. Two major biological applications of the research are proposed. First, high resolution microimaging of excised spinal cord tissue. Non-invasive MRI has shown that signal intensity changes are produced by both spinal cord damage and subsequent regeneration. In order to understand these changes fully, it is necessary to look at the small structures within the cord, as opposed to a large volume averaged signal intensity from the whole cord. Second, we will use the microscopic radiofrequency and gradient coils to determine the presently unknown physical environment of protein-rich vesicles by two dimensional diffusion-ordered spectroscopy, information which should help to elucidate the action of certain neurotransmitters in mammals. The development of micro-NMR systems is an emerging area in imaging which should be fully integrated into our academic curriculum. Currently the applicant, together with his colleagues, have developed a unique series of three courses in magnetic resonance within the Department of Electrical and Computer Engineering. The major educational thrust will be to complete the integration of interactive computer based learning into these three courses, combined with the preparation of a laboratory based course on magnetic resonance systems to accompany a graduate level lecture series. The proposed research has many aspects which are relevant to electrical engineering: high frequency modelling and simulations, electrical circuit characterization, and design optimization, as well as applications which are of interest to the bioengineer. Indeed, since magnetic resonance is not usually an active area for electrical engineers, we anticipate that significant advances will be made by the inclusion of faculty, underg raduate and graduate researchers from this department. More than twenty students within the department have already chosen this area for undergraduate research and their Senior Design projects with the applicant in the past two years.