Electron spin resonance imaging: a functional imaging tool for biomedical science

现代医学依赖于各种身体扫描仪来可视化我们身体的内部结构。研究科学家使用类似的仪器来研究整个生物和医学科学领域的重要材料。然而，对于许多目的，解剖或其他结构信息是不够的：我们寻求功能成像方法，报告正在发生的过程。我们的项目是关注这样一个功能成像方法的发展异常广泛的适用性：电子自旋共振成像。正是离原子核最远的电子，即所谓的“价”电子，赋予原子、离子、分子和材料大部分的化学和物理性质，因为正是这些电子与环境的相互作用最强烈。当存在奇数个价电子（或在某些特殊情况下为偶数个价电子）时，电子将净磁矩传递给原子/分子/材料。电子自旋共振是测量这种磁性的一种灵敏而精确的方法。可以将这些测量与价电子的环境联系起来，从而使用它来报告化学结构和动力学，并最终提供化学和其他动力学过程的功能信息。电子自旋共振通过测量允许微波辐射的共振吸收所需的外加磁场来确定电子的磁性。空间信息是通过将不同的磁场施加到被调查对象的不同部分来获得的。如果在大量的磁场梯度中测量微波吸收，则可以计算物体的磁特性的三维图像。这种总体方法类似于核磁共振成像（MRI）中采用的方法。然而，电子自旋共振成像在技术上更具挑战性，因为价电子与环境的相互作用比原子核强得多。这一重要差异意味着需要新的、极其灵敏和高效的微波吸收测量方法。我们的项目专注于必要的技术。电子自旋共振成像仪器的灵敏度应该适当地表示为在给定时间内在空间分辨体积元中可以检测到的电子的数量。因此，具有显著提高的灵敏度的仪器也将能够进行更高分辨率的图像和/或更快的测量。分辨率和速度不足一直是早期方法的限制因素。我们的项目背后的动机是ESR成像可以潜在地应用于非常广泛的重要应用。这项工作将使我们对心血管疾病，癌症，糖尿病和感染性休克等主要人类疾病的理解取得实质性进展，并允许评估这些疾病的新疗法的疗效。

Modern medicine relies upon a variety of body scanners with which to visualise the internal structures of our bodies. Similar instruments are used by research scientists to study materials of significance across the whole range of the biological and medical sciences. For many purposes, however, anatomical or other structural information is not enough: we seek functional imaging methods that report on the processes that are taking place. Our project is concerned with the development of such a functional imaging method of exceptionally broad applicability: electron spin resonance imaging. It is the electrons furthest away from the atomic nucleus, the so-call 'valence' electrons, which confer most of the chemical and physical properties on atoms, ions, molecules and materials, since it is these electrons that interact most strongly with the environment. When an odd number of valence electrons are present (or in some special cases an even number) the electrons impart a net magnetic moment onto the atom/molecule/material. Electron spin resonance is a sensitive and precise method of measuring this magnetism. It is possible to relate these measurements to the environment of the valence electrons and hence use it to report on chemical structure and dynamics, and ultimately to provide functional information on chemical and other dynamical processes. Electron spin resonance determines the magnetic properties of electrons by measuring the applied magnetic field that is required to allow resonant absorption of microwave radiation. Spatial information is obtained by applying different magnetic fields to different parts of the object under investigation. If the microwave absorption is measured in a large number of magnetic field gradients a three-dimensional image of the magnetic properties of the object can be calculated. This overall approach is similar to that employed in nuclear magnetic resonance imaging (MRI). However, electron spin resonance imaging is technically much more challenging because valence electrons interact much more strongly with their environment than do nuclei. This important difference means that new, extremely sensitive and efficient, methods of measuring microwave absorption are required. Our project is focused on the necessary technologies. The sensitivity of an electron spin resonance imaging instrument should properly be expressed as the number of electrons that can be detected in a spatially resolved volume element in a given time. Thus an instrument with substantially improved sensitivity will also be able to make higher resolution images and/or faster measurements. Insufficient resolution and speed have been limiting factors in earlier approaches. The motivation behind our project is the extraordinary range of important applications to which ESR imaging can potentially be put. This work will enable substantial advances in our understanding of major human diseases such as cardio-vascular disease, cancer, diabetes, and septic shock, and also allow the efficacy of new therapies for these conditions to be assessed.