Continuous Wave Electron Paramagnetic Resonance Imaging

项目3：连续波电子顺磁共振成像。摘要：由于氮氧化物在动物体内以及在人类应用中都被用作治疗剂，监测氮氧化物的分布、代谢和消除是一个重要的目标。该项目的主要动机是开发仪器和图像数据收集策略，以提供成像顺磁探针的能力，如氮氧化物自由基，这些能力是其他方法无法满足的。为了实现这些目标，我们进行了仪器的开发以及新的数据采集策略，并给出了这些方面的进展如下。仪器：连续波EPR成像中的数字信号处理：我们实验室和其他实验室的连续波EPR成像光谱仪实现了使用模拟设备检测顺磁物种的能力。在数字信号处理(DSP)技术出现之前，这一直是唯一的选择。我们已经开始努力开发一种使用DSP技术的EPR光谱仪，希望实现显著提高检测感兴趣物种的灵敏度。通过剔除通常对噪声有影响的模拟元件，我们成功地设计、测试并实现了第一台基于DSP概念的EPR光谱仪。我们现在正在优化光谱仪，为常规操作做好准备。快速扫描EPR成像：CW EPR成像方法是一种固有的缓慢成像方式，因此在活体成像中容易出现伪影，在活体成像中，动物运动(如心跳、呼吸)可能会导致噪声和图像伪影。我们借用了核磁共振光谱学中开发的概念，并开发了快速扫描功能的仪器，其中扫描图像的时间已从几分钟减少到几秒。在这种图像数据采集模式中，使图像花费不到毫秒的单个投影将运动伪影降至最低。第一个版本的扫描仪已经完成，我们还介绍了一种通过旋转梯度来收集图像数据的有效方法。初步可行性研究已经完成，目前，我们正在优化扫描仪以实现自动操作。用于EPR成像的同轴线圈：目前在EPR成像中对动物的研究要求我们将动物放置在垂直于磁轴的谐振器线圈中以进行信号检测。然而，这使得监测生命体征、维持核心体温、维持麻醉以及在动物体内静脉注射造影剂变得困难。与磁轴同轴的谐振器线圈避免了这些困难。我们已经测试了满足这一需求的谐振器线圈，并与以前的版本进行了比较。我们已经发现，我们能够非常容易地进行活体实验，并实现增强的检测灵敏度。用于pO2映射的T1加权成像：顺磁物种的EPR谱容易出现称为“功率饱和”的伪像，其中信号强度在较高的射频功率下丢失，特别是在依赖氧的线宽明显低于常氧条件下存在的区域。利用这种人工产物，我们开发了一种新的图像数据收集/图像重建程序，其中与当前使用的方法相比，可以快速收集图像数据并获得pO2的定量地图。

Project 3: Continuous Wave Electron Paramagnetic Resonance Imaging.Summary: Since nitroxides are used as therapeutic agents in vivo in animal models as well as in human applications, monitoring the distribution, metabolism, and elimination, non-invasively is an important goal. This project's main motivation is develop instrumentation and image data collection strategies to provide the capabilities of imaging paramagnetic probes such as the nitroxide radicals, which are not amenable by other means. To accomplish the goals, we have undertaken development of instrumentation as well as novel data acquisition strategies, and the progress on these aspects is given below.Instrumentation:Digital Signal processing in CW EPR imaging: The CW EPR Imaging spectrometer in our laboratory and other labs implements the capability of detecting the paramagnetic species using analog devices. This has been the only option until the advent of digital signal processing (DSP) technology. We have initiated efforts to develop an EPR Spectrometer using DSP technology with hope of realizing significant enhancements in sensitivity of detecting the species of interest. By eliminating analog components, which contribute to noise in general, we have designed, tested and implemented successfully the first EPR spectrometer based on DSP concepts. We are now optimizing the spectrometer and have it ready for routine operation.Rapid-scan EPR imaging: The CW EPR imaging method is an intrinsically slow modality for imaging and therefore is prone to artifacts in in vivo imaging where animal motion such as heart beat, breathing can contribute to noise and image artifacts. We have borrowed concepts developed in NMR Spectroscopy and developed instrumentation for rapid scan capabilities where the scan times have been reduced from several minutes to a few seconds for image. In this mode of image data collection, individual projections which make the image take less than millisecond minimizing motional artifacts. The first version of the scanner is complete and we also introduced an efficient way of image data collection by rotating the gradients. Initial feasibility studies are complete and currently, we are optimizing the scanner for automated operation.Co-axial coil for EPR Imaging: Current studies in animals in EPR Imaging require us to have the animal placed in a resonator coil which is perpendicular to the magnet axis for signal detection. However, this makes causes difficulty in monitoring the vital signs, maintain core body temperature, maintain anesthesia and have i.v lines in the animal for contrast agent delivery. A resonator coil co-axial with the magnet axis avoids these difficulties. We have tested a resonator coil which satisfies this need and compared with the previous versions. We have found that we are able to carry out in vivo experiments with great ease and also realized enhanced sensitivity in detection.T1-weighted imaging for pO2 mapping: EPR spectra of paramagnetic species are prone to an artifact called "power saturation" where signal intensity is lost at higher RF powers, especially in regions where the oxygen-dependent line width is significantly lower than when in the presence of normoxic conditions. Utilizing this artifact, we have developed a novel image data collection/image reconstruction procedure where it was possible to collect image data rapidly compared to currently used methods and obtain quantitative maps of pO2.