CAREER: Subcellular Nuclear Magnetic Resonance Imaging

德塞里·戴维斯 拟议的研究旨在开发仪器，这将提高核磁共振（NMR）显微镜的分辨率至少一个数量级的（1- 2米）3范围。由于哺乳动物细胞的直径通常为5-10 μ m，这一进展将开辟目前被排除在外的整个亚细胞应用范围。 与其他显微镜技术相比，NMR的固有优势包括能够提供完整的三维信息及其非侵入性特征。NMR显微镜不仅提供空间信息，而且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生物分子物理环境的信息。这项研究的主要创新将是设计和优化直径为100-200 m的射频（RF）微线圈，比以前在NMR显微成像应用中使用的小一个数量级。除了对于给定的体素尺寸的每个体素的信噪比（SNR）的固有增加之外，使用小RF线圈导致较低的采集带宽和相对于较大线圈的进一步SNR改善。这些RF线圈还将允许设计和构造非常小直径的高强度磁场梯度，这对于克服扩散和磁化率效应并实现所需分辨率是必要的。将构建射频微弹簧圈、磁场梯度和微定位器的集成组件。 将使用滤波反投影（FBP）技术采集数据，因为这些技术具有比傅立叶技术更高的固有SNR，并且对于给定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竞争理论、最低可检测的自旋数以及诸如在不可渗透边界处的边缘增强的现象的效应，来实验性地确定最大可能的分辨率。由于射频线圈的灵敏度不够高，因此以前没有对这些进行严格的研究。两个主要的生物应用的研究提出。首先，切除的脊髓组织的高分辨率显微成像。非侵入性MRI显示，信号强度变化是由脊髓损伤和随后的再生引起的。为了充分理解这些变化，有必要观察脊髓内的小结构，而不是整个脊髓的大体积平均信号强度。 其次，我们将使用显微射频和梯度线圈，以确定目前未知的物理环境的蛋白质丰富的囊泡的二维扩散有序光谱，信息，这应该有助于阐明某些神经递质在哺乳动物的行动。 微型核磁共振系统的发展是一个新兴的领域，在成像，应充分融入我们的学术课程。目前，申请人与他的同事一起在电气和计算机工程系内开发了一系列独特的三门磁共振课程。主要的教育重点将是完成基于交互式计算机的学习整合到这三门课程中，并结合磁共振系统实验室课程的准备，以配合研究生水平的系列讲座。拟议的研究有许多方面是相关的电气工程：高频建模和仿真，电路表征，设计优化，以及感兴趣的生物工程师的应用程序。事实上，由于磁共振通常不是电气工程师的活跃领域，我们预计将通过纳入该部门的教师，本科生和研究生研究人员取得重大进展。在过去的两年里，该部门的20多名学生已经选择了这个领域进行本科研究，并与申请人一起进行高级设计项目。

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.