Beinert T, Behr J, Mehnert F, Kohz P, Seemann M, Rienmüller R, Reiser M
Department of Internal Medicine, Klinikum Grosshadern, University of Munich, Germany.
J Comput Assist Tomogr. 1995 Nov-Dec;19(6):924-31. doi: 10.1097/00004728-199511000-00016.
Assessment of lung attenuation by CT reflects changes in the air-to-tissue ratio of the lung. We have analyzed the interdependence of intrathoracic gas volume, lung morphology, and functional disorder by high resolution CT (HRCT) to assess quantitative disease threshold in obstructive and restrictive diffuse lung disease.
Pulmonary HRCT was performed on 24 healthy volunteers, 11 patients with chronic obstructive pulmonary disease (COPD), and 16 patients with idiopathic lung fibrosis (IPF). HRCT measurement was standardized by taking three scans at the carina +/- 5 cm and by defining inspiration levels by percent vital capacity (VC) via spirometrically gating to the scanner.
The mean lung density at 50% VC (DL50) for healthy subjects was -819 +/- 3.8 (mean +/- SEM) HU. In contrast, COPD DL50 was lower, averaging -861 +/- 6.4 HU, and the IPF DL50 was considerably higher (-731 +/- 17.7 HU), both significantly different (p < 0.001) compared with the control group. The accuracy of quantitative HRCT at different inspiration levels was evaluated by scanning the basal layer at 20, 50, and 80% VC. The control values were -747 +/- 5.6, -816 +/- 3.6, and -855 +/- 3.0 HU, respectively, which were significantly higher (p < 0.001) than those seen in COPD patients at 20 and 50% VC. Again, the IPF patients exhibited increased lung density (p < 0.001) at all inspiratory levels. Discrimination power was best among all cohorts at 20 and 50% VC. Position-dependent artifacts on lung density were quantified by the anteroposterior density gradient (APG). Irrespective of the underlying disease, APG at 50 and 80% VC was similar, but was up to twofold higher at 20% VC, indicating that quantitative estimates near RV may misrepresent mean lung density.
Our data indicate that quantitative HRCT measurements should be performed not near full inspiration or expiration, but at an intermediate degree of lung inflation, e.g., 50% VC, for reasons of accuracy, intra- and intersubjective comparability, and feasibility. We conclude quantitative HRCT to be a sensitive tool for the evaluation of diffuse parenchymal lung disease.
通过CT评估肺实质密度可反映肺内气-组织比的变化。我们通过高分辨率CT（HRCT）分析了胸腔内气体容积、肺形态和功能障碍之间的相互关系，以评估阻塞性和限制性弥漫性肺疾病的定量疾病阈值。
对24名健康志愿者、11名慢性阻塞性肺疾病（COPD）患者和16名特发性肺纤维化（IPF）患者进行了肺部HRCT检查。HRCT测量通过在隆突上下5 cm处进行三次扫描进行标准化，并通过肺活量计门控扫描仪以肺活量百分比（VC）定义吸气水平。
健康受试者在50% VC时的平均肺密度（DL50）为-819±3.8（平均值±标准误）HU。相比之下，COPD患者的DL50较低，平均为-861±6.4 HU，而IPF患者的DL50显著更高（-731±17.7 HU），与对照组相比均有显著差异（p<0.001）。通过在20%、50%和80% VC时扫描基底层来评估不同吸气水平下定量HRCT的准确性。对照组的值分别为-747±5.6、-816±3.6和-855±3.0 HU，在20%和50% VC时显著高于COPD患者（p<0.001）。同样，IPF患者在所有吸气水平下肺密度均增加（p<0.001）。在所有队列中，20%和50% VC时的鉴别能力最佳。通过前后密度梯度（APG）对肺密度的位置依赖性伪影进行量化。无论潜在疾病如何，50%和80% VC时的APG相似，但在20% VC时高达两倍，这表明在接近残气量（RV）时的定量估计可能会错误代表平均肺密度。
我们的数据表明，出于准确性、受试者内和受试者间可比性以及可行性的原因，定量HRCT测量不应在完全吸气或呼气附近进行，而应在肺膨胀的中间程度，例如50% VC时进行。我们得出结论，定量HRCT是评估弥漫性肺实质疾病的敏感工具。
