Mishima M, Hirai T, Jin Z, Oku Y, Sakai N, Nakano Y, Sakai H, Chin K, Ohi M, Kawakami K, Shimada K, Itoh H, Yamaguchi K, Sawa T, Kuno K
Department of Clinical Physiology, Kyoto University, Japan.
Front Med Biol Eng. 1997;8(2):79-86.
We examined the methods for measuring the LAA% (100 x low attenuation area/total lung area) on thoracic X-ray CT scans in order to develop a useful indicator of chronic pulmonary emphysema (CPE). First, we modified the method for calculating the LAA% to be applicable by the programming tool installed in a commercially available CT machine in order to minimize manual procedures. This new method proved to be applicable in all CT machines produced after 1987. Second, we examined the difference in the Hounsfield Unit (HU) between different CT machines using two kinds of phantoms. One phantom was composed of Styrofoam, which has a density similar to the low attenuation areas. The other phantom was composed of Styrofoam and water, which has a density similar to the lung. We proved that the difference of LAA% with the correct value was 5% at maximum among four different CT machines. Thus, the phantom developed in the present study may play an important role in the standardization of HU. Finally, the possibility of decreasing the X-ray levels was examined. Twenty-five percent of the standard electrical current provided the same LAA% in cases where the subject was an established CPE patient, whereas the LAA% was overestimated in subjects with a normal LAA% value. However, a correction using a linear regression equation may be possible in the latter cases. It may be concluded that LAA% analysis can easily be performed in many city hospital, without much investment of manual procedures or any corrections to the HU levels between different CT machines. This method may be useful as a routine follow up for CPE patients because of the smaller irradiated dose given when using a CT machine.
为了开发一种有用的慢性肺气肿（CPE）指标，我们研究了在胸部X线CT扫描上测量LAA%（100×低衰减面积/全肺面积）的方法。首先，我们修改了计算LAA%的方法，使其适用于商用CT机中安装的编程工具，以尽量减少人工操作。这种新方法被证明适用于1987年以后生产的所有CT机。其次，我们使用两种体模研究了不同CT机之间亨氏单位（HU）的差异。一种体模由密度与低衰减区域相似的聚苯乙烯泡沫塑料组成。另一种体模由密度与肺相似的聚苯乙烯泡沫塑料和水组成。我们证明，在四台不同的CT机中，LAA%与正确值的最大差异为5%。因此，本研究中开发的体模可能在HU标准化中发挥重要作用。最后，研究了降低X线水平的可能性。在受试者为确诊的CPE患者的情况下，25%的标准电流可提供相同的LAA%，而在LAA%值正常的受试者中，LAA%被高估。然而，在后一种情况下，使用线性回归方程进行校正可能是可行的。可以得出结论，LAA%分析在许多城市医院都可以轻松进行，无需大量人工操作或对不同CT机之间的HU水平进行任何校正。由于使用CT机时辐射剂量较小，这种方法可能作为CPE患者的常规随访很有用。
