Burk L, Lee Y, Lu J, Zhou O
University of North Carolina at Chapel Hill.
Med Phys. 2012 Jun;39(6Part27):3949-3950. doi: 10.1118/1.4736119.
Micro-CT is commonly employed for lung imaging of mice; prospective gating allows for in-vivo imaging of free-breathing subjects. While this technique is successfully executed for healthy animals, results are less consistent for some disease models whose symptoms include irregular or unstable respiration. The purpose of this work is to repair the quality of high-blur images that arise from respiration instability using a retrospective method of motion reduction which identifies the individual x-ray projection images contributing most to the motion blur. Reconstructions were performed after the exclusion of these projections (the so-called restricted set).
Sixteen mice were imaged using field emission cone beam micro-CT and prospective gating with a bellows-type respiration sensor. The scanner was operated in step-and-shoot mode; 400 projection images were acquired per scan. An algorithm was developed to analyze the respiration trace file and segment the individual breath corresponding to each projection image. We tested three different criteria to define a bad breath shape (correlation, mean breath height, or mode breath height), and restricted data set reconstructions were performed using each of these criteria to exclude projections corresponding to bad breaths. Each restricted set was compared against the full unrestricted data set image; the slope perpendicular to the diaphragm was used as a quantitative assessment of motion blur.
All image sets saw a reduction in motion blur with at least one restriction technique. In 22 of 27 images, improvement was measured regardless of the removal criterion. Five percent total projection removal is optimal; a more aggressive correction increases the likelihood of under-sampling artifacts.
Removing a subset of bad projections from otherwise complete image sets measurably decreases motion blur in respiratory-gated imaging. An approach based on breath height generally provides the best results. The technique is applicable to a variety of imaging modalities.
微型计算机断层扫描（Micro-CT）常用于小鼠肺部成像；前瞻性门控技术可实现对自由呼吸的实验对象进行活体成像。虽然该技术在健康动物成像中取得了成功，但对于一些症状包括呼吸不规则或不稳定的疾病模型，成像结果的一致性较差。本研究的目的是采用一种回顾性运动减少方法来修复因呼吸不稳定而产生的高模糊图像质量，该方法可识别对运动模糊贡献最大的个体X射线投影图像。在排除这些投影（即所谓的受限集）后进行重建。
使用场发射锥形束微型计算机断层扫描和带有波纹管式呼吸传感器的前瞻性门控技术对16只小鼠进行成像。扫描仪以步进扫描模式运行；每次扫描采集400幅投影图像。开发了一种算法来分析呼吸轨迹文件，并分割与每个投影图像对应的个体呼吸。我们测试了三种不同的标准来定义不良呼吸形状（相关性、平均呼吸高度或模式呼吸高度），并使用这些标准中的每一种进行受限数据集重建，以排除与不良呼吸对应的投影。将每个受限集与完整的非受限数据集图像进行比较；垂直于膈肌的斜率用作运动模糊的定量评估。
所有图像集在至少一种限制技术下运动模糊都有所减少。在27幅图像中的22幅中，无论采用何种去除标准，均测量到图像有所改善。去除5%的总投影是最佳的；更激进的校正会增加欠采样伪影的可能性。
从完整的图像集中去除一部分不良投影可显著减少呼吸门控成像中的运动模糊。基于呼吸高度的方法通常能提供最佳结果。该技术适用于多种成像模式。
