Department of Radiation Oncology, Beaumont Health, Royal Oak, MI, United States of America. Wayne State University School of Medicine, Detroit, MI 48201, United States of America.
Phys Med Biol. 2019 Feb 18;64(4):045014. doi: 10.1088/1361-6560/aaff7b.
We previously reported that apparent lung mass varies across the phases of 4D computed tomography (4DCT) images. We hypothesize that these variations correspond to the physiologic changes in pulmonary perfusion induced during normal tidal breathing, and should therefore be present in every breathing patient. In this study, we characterize and quantify the respiratory induced variation in pulmonary blood mass (▵PBM) on 89 patients treated with stereotactic body radiotherapy. ▵PBM was computed from the treatment planning helical 4DCT images of each patient. Conversion from Hounsfield Units (HU) to density and mass per voxel was made using the density calibration curve, applied to the lung parenchyma volume within each phase. A difference in the lung mass with breathing was found for all cases, as was a substantial individual variation in lung volume. We found that the ▵PBM increased during inhalation, and decreased during exhalation. A significant correlation between the individual ▵PBM and tidal volume was observed; ▵PBM increased with tidal volume. We further evaluated the anatomic distribution of ▵PBM variation comparing the central versus peripheral lung, cranial versus caudal, dependent versus non-dependent lung. Our observations regarding spatial distribution of the ▵PBM agree with previously reported differences among similar regions for the supine patient. These results show that a variation in pulmonary mass during respiration is apparent on 4DCT and suggest that these variations reflect respiratory induced changes in the pulmonary perfusion. Therefore, the 4DCT derived respiratory induced ▵PBM signal can provide further insight into the pulmonary circulation and advance the overall understanding and diagnosis of human health and disease.
我们之前曾报道过，4DCT 图像的各个时相中肺部的表观质量会发生变化。我们假设这些变化与正常潮式呼吸过程中肺灌注的生理变化相对应，因此在每个呼吸患者中都应该存在。在这项研究中，我们对 89 例接受立体定向体部放疗的患者的呼吸引起的肺血质量变化（▵PBM）进行了特征描述和量化。▵PBM 是从每位患者的治疗计划螺旋 4DCT 图像中计算得出的。通过将密度校准曲线应用于每个时相的肺实质体积，将 Hounsfield 单位（HU）转换为密度和每个体素的质量。所有病例都发现了与呼吸相关的肺质量变化，以及肺容积的个体差异很大。我们发现，在吸气过程中，肺质量增加，而在呼气过程中，肺质量减少。观察到个体▵PBM 与潮气量之间存在显著相关性；▵PBM 随潮气量增加而增加。我们进一步通过比较中心与外周肺、颅侧与尾侧、依赖与非依赖肺，评估了▵PBM 变化的解剖分布。我们对▵PBM 空间分布的观察结果与仰卧位患者类似区域的先前报道结果一致。这些结果表明，4DCT 上的呼吸期间肺质量存在变化，并且这些变化可能反映了肺灌注的呼吸诱导变化。因此，4DCT 衍生的呼吸诱导▵PBM 信号可以提供对肺循环的进一步了解，并推进对人类健康和疾病的整体理解和诊断。
