ARTIFACT-FREE CT IMAGING FOR RADIOTHERAPY PLANNING

描述（由申请人提供）：通过开发用于重建无伪影X射线计算机断层扫描（CT）图像的新技术，我们旨在提高患者体内存在异物时放射治疗计划的靶和关键解剖结构描绘的准确性，特别强调在近距离放射治疗中使用的腔内施源器、粒子和针的情况下的成像。我们假设无伪影的图像重建技术将支持足够的定量CT成像，使我们能够通过CT成像解决光子截面的非侵入性测量问题。这将允许基于蒙特-卡罗的剂量计算引擎考虑组织异质性对低能种子植入物和利用低能光子场的其他模态的剂量规格的影响。 在具体目标1中，我们提出了一个基本的理论和实验研究条纹伪影的起源，旨在了解CT探测器读数和扫描对象（包括金属物体）的放射特性之间的关系。我们假设伪影的一个重要原因是CT探测器响应的过于简单的模型和CT信号形成的实际过程之间的不匹配。在具体目标2中，我们建议开发和测试一种新的算法，该算法源自CT信号形成过程（包括噪声、射束硬化、模糊和散射）的严格物理模型，用于从测量和模拟的螺旋透射正弦图重建无伪影CT图像，准确估计患者体内的施源器/金属物体位置。在特定目标3中，我们建议开发和临床测试一个原型系统，该系统能够根据从商用CT扫描仪获得的螺旋透射正弦图离线重建三维（3D）成像研究，包括当前的螺旋和更新的多排探测器扫描仪。最后，在具体目标4中，我们将开发和测试基于模型的图像重建算法的扩展，用于单能量和双能量扫描的光子衰减系数和其他放射学数据的无创测量，目标精度为3%。

DESCRIPTION (provided by applicant): Through the development of novel techniques for reconstructing artifact-free X-ray computed tomographic (CT) images, we aim to enhance the accuracy of target and critical anatomy delineation for radiotherapy treatment planning when foreign metal bodies are present in the patient, with specific emphasis on imaging in the presence of intracavitary applicators, seeds, and needles used in brachytherapy. We hypothesize that artifact-free image-reconstruction technologies will support sufficiently quantitative CT imaging, allowing us to solve the problem of non-invasive measurement of photon cross sections by CT imaging. This will allow Monte-Carlo based dose-calculation engines to account for the influence of tissue heterogeneities on dose specification for low-energy seed implants and other modalities utilizing low-energy photon fields. In Specific Aim 1,we propose a fundamental theoretical and experimental investigation of origin of streaking artifacts, aimed at understanding the relationship between CT detector readings and the radiological properties of the scan subject, including metal objects. We hypothesize that an important cause of artifacts is mismatch between overly simplistic models of CT detector response and the actual process of CT signal formation. In Specific Aim 2, we propose to develop and test a novel algorithms, derived from rigorous physical models of the CT signal formation process (including noise, beam hardening, blur and scatter), for reconstructing artifact-free CT images from measured and simulated spiral transmission sinograms that accurately estimates applicator/metal object locations in the patient. In Specific Aim 3, we propose to develop and clinically test a prototype system capable of off-line reconstruction of a three-dimensional (3D) imaging study from spiral transmission sinograms obtained from commercial CT scanners and including both current spiral and newer multi-row detector scanners. Finally, in Specific Aim 4, we will develop and test extensions of our model-based image-reconstruction algorithms for noninvasive measurement of photon attenuation coefficients and other radiological data from single- and dual-energy scans with a target accuracy of 3%.