Improvement of CT-Based PET Attenuation Correction

描述（由申请人提供）： 正电子发射断层扫描（PET）和X射线计算机断层扫描（CT）集成到一个单一的仪器允许采集功能和结构的图像，空间配准。这提供了将来自组合扫描的CT数据用于PET数据的衰减校正的机会。用于将表示CT能量处的平均衰减的CT图像变换为511 keV衰减图的算法通常产生高质量的衰减校正。然而，已经观察到基于CT的衰减校正中的几种类型的不准确性，其导致不准确的校正发射图像。缺陷的一个原因是存在IV或口服造影剂以增强CT扫描。包含造影剂的区域通常导致511 keV图中的衰减值被显著高估。在所得到的衰减校正的发射图像中已经观察到类似于患病组织的焦对比伪影。另一种类型的伪影可能由于CT和PET采集时呼吸相位的差异而出现在校正的发射图像中。通常，PET采集将在多个呼吸周期上取平均值，而CT将仅在一个周期的一部分上或在屏气的情况下采集。本研究计划的假设是，测量的发射正弦图包含足够量的衰减信息，以允许校正一些观察到的伪影。这项工作的目标是开发，实施和测试方法，用于恢复有限的缺陷区域，否则理想的衰减图，通过使用这些信息。有几种方法，已被用于从发射数据单独提取一个完整的衰减图的一般性问题，只有有限的成功，这将作为本项目的起点。重要的一点是，目前的研究旨在恢复衰减图的有限区域。这是一个比一般情况简单得多的问题。拟议研究的结果将为制定优化PET/CT数据使用的综合策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.