Optimization of region-of-interest imaging with penetrating radiation

穿透辐射成像是现代社会的一种常见特征。X射线成像的医疗和安全用途是众所周知的，而工业射线照相被广泛用于金属部件和焊缝的检查。此外，计算机断层扫描(CT)现在是一种可行的医疗诊断工具，并在一些机场用作爆炸物检测设备。这种技术依赖于对暴露在辐射(X射线、伽马射线或中子)下的物体的整个部分(在CT的情况下是横截面)进行成像。这样的“整体”成像过程虽然有用，但代价是降低了某些可能特别感兴趣的位置的精细细节的清晰度。尝试增强图像清晰度需要提高整个图像中所有位置的图像分辨率；这反过来又需要增加辐射暴露，并且通常伴随着更高水平的噪声和波动。因此，需要一种“感兴趣区域”成像过程，其可以“聚焦”在物体的特定部分上，以获得空间分辨率和/或材料对比度方面的更精细的细节。这种成像过程还可以用作整体成像的后续处理，以在例如高应力区域、乘客行李中的可疑材料或身体中的肿瘤处提供更精细的细节。拟议工作的目标是以实用和灵活的方式优化成像系统，以提高某些感兴趣区域的图像质量，从而能够利用现有设备进行实地应用。据笔者所知，还没有采取系统的方法来获得最佳的感兴趣区域成像。将对所开发的安排进行实验验证。这项工作将涉及辐射传输计算、数学优化、反问题求解、成像系统设计和成像概念的实验验证。这些技能对培养无损检测和成像系统工程方面的高素质人才非常有益。

Imaging with penetrating radiation is a common feature of modern day society. Medical and security uses of x-ray imaging are well known, while industrial radiography is widely employed for inspection of metal parts and welds. Moreover, computed tomography (CT) is nowadays a viable tool in medical diagnostics, and is used at some airports as an explosive detection device. Such techniques rely on imaging the entire portion (a cross section in the case of CT) of the object exposed to radiation (x-ray, gamma-rays, or neutrons).  Such an "overall" imaging process though useful, comes at the expense of reduced definition of finer details at some locations that may be of particular interest. Attempting to enhance image definition requires increasing the image resolution everywhere in the overall image; which necessitates in turn increased radiation exposure, and is typically accompanied by a higher level of noise and fluctuations. There is therefore a need for a "region-of-interest" imaging process that can "focus" on a particular portion of an object to obtain finer details in terms of spatial resolution and/or material contrast. Such imaging process can also be utilized as a follow-up to overall imaging to provide finer details at, for example, an area of high stress, a suspect material in a passenger luggage, or a tumor in a body. The objective of the proposed work is to optimize imaging systems to enhance image quality at certain regions of interest, in a practical and flexible manner that enables field application with commonly available equipment. To the author's knowledge, no systematic approach has been undertaken to achieve best region-of-interest imaging. Experimental validation of developed arrangements will be performed. This work will involve radiation transport calculations, mathematical optimization, inverse problem solution, imaging system design and experimental validation of imaging concepts. Such skills are quite beneficial for the training of highly qualified personnel in the engineering of non-destructive examination and imaging systems.