Improvement of CT-Based PET Attenuation Correction

描述(由申请人提供)： 将正电子发射断层扫描(PET)和X射线计算机断层扫描(CT)集成到一台仪器中，可以获取空间配准的功能和结构图像。这提供了使用组合扫描的CT数据对PET数据进行衰减校正的机会。将CT图像(表示CT能量的平均衰减)转换为511 keV衰减图的算法通常会产生高质量的衰减校正。然而，在基于CT的衰减校正中，已经观察到了几种类型的不准确，从而导致校正后的发射图像不准确。缺陷的一个原因是静脉注射或口服造影剂以增强CT扫描。含有造影剂的区域通常会导致511keV图中的衰减值被严重高估。在产生的衰减校正发射图像中观察到类似于病变组织的焦点对比伪影。由于CT和PET采集时呼吸时相的不同，校正后的发射图像中可能会出现另一种伪影。一般来说，PET采集将在多个呼吸周期内平均，而CT将仅在一个周期的一部分或屏气时采集。这项研究计划的假设是，测量的发射正弦曲线包含足够数量的衰减信息，以允许对一些观察到的伪影进行校正。这项工作的目标是开发、实施和测试通过使用这些信息恢复原本理想的衰减图的有限缺陷区域的方法。对于仅从排放数据中提取完整的衰减图这一普遍问题，有几种方法仅取得了有限的成功，并将作为本项目的起点。重要的一点是，目前的研究旨在仅恢复衰减图的有限区域。这比一般情况下的问题简单得多。拟议研究的结果将为制定优化使用PET/CT数据的综合战略提供基本工具和经验。

DESCRIPTION (provided by applicant): The integration of positron emission tomography (PET) and X-ray computed tomography (CT) into a single instrument allows acquisition of functional and structural images that are spatially registered. This provides the opportunity to use the CT data from a combined scan for attenuation correction of the PET data. Algorithms for transforming the CT image, which represents average attenuation at CT energies, to a 511 keV attenuation map generally produce a high quality attenuation correction. However, several types of inaccuracies in CT-based attenuation correction have been observed that result in inaccurate corrected emission images. One cause of deficiencies is the presence of IV or oral contrast agent administered to enhance the CT scan. Regions containing contrast agent often result in significantly overestimated attenuation values in the 511 keV map. Focal contrast artifacts in the resulting attenuation corrected emission images have been observed that resemble diseased tissue. Another type of artifact can occur in corrected emission images due to differences in respiration phase at the time of CT and PET acquisition. Generally, a PET acquisition will be averaged over many respiration cycles while the CT will be acquired over only part of a cycle or with a breath hold. The hypothesis of this research program is that the measured emission sinograms contain a sufficient amount of attenuation information to allow correction of some of the observed artifacts. The goal of the work is to develop, implement, and test methods for recovering limited defective regions of an otherwise ideal attenuation map by using this information. There exist several methods that have been used with only limited success for the general problem of extracting a complete attenuation map from emission data alone and which will serve as the starting point for this project. An important point is that the current research is aimed at recovering only limited regions of the attenuation map. This is a far simpler problem than the general case. The results of the proposed research will provide basic tools and experience for developing a comprehensive strategy for optimizing the use of PET/CT data.