CT能谱成像在胸腔渗出液与漏出液定性鉴别中的作用

The use of spectral CT imaging in characterization of pleural fluid： a new method to differentiate transudates from exudates

目的探讨CT能谱成像定量分析鉴别胸腔积液性质的价值。方法将20例胸腔积液患者经胸腔穿刺术抽出的胸腔积液放在试管中进行能谱CT扫描，同时抽出的胸腔积液做胸水常规和生化检查。根据实验室检查结果，分为渗出液和漏出液。应用能谱分析软件，分析两组数据的常规混合能量140kVp图像的CT值差异，以及两组数据的不同keV水平（40—140keV）的CT值、能谱曲线斜率、有效原子序数、碘-水浓度、钙-水浓度、钙-脂肪浓度等CT能谱成像的定量参数间的差异。对渗出液和漏出液的CT能谱特征参数进行独立样本t检验。结果根据实验室检查结果，20例中11例渗出液、9例漏出液。渗出液组的常规混合能量140kVp的图像CT值[（19．56±4．10）HU]高于漏出液组[（13．44±3．46）HU]，差异有统计学意义（t=3．002，P：0．010）。keV能量越低，其CT值差别越大。在40keV，其CT值差异最大，分别是（47．49±14．60）、（19．76±6．85）HU，差异有统计学意义（t=5．520，P=0．000），渗出液明显高于漏出液；而在140keV，其CT值差异无统计学意义，平均值分别是（9．76±4．16）和（6．22±3．17）HU（t=2．107，P=0．050）。渗出液能谱曲线斜率（0．51±0．23）明显大于漏出液（0．18±0．08），差异有统计学意义（t=4．287，P=0．001）。渗出液的有效原子序数、碘（水）浓度、钙（水）浓度、钙（脂肪）浓度明显高于漏出液组，两组的值分别为7．89±0．16和7．67±0．07、（5．74±1．28）和（1．70±0．95）g／L、（7．89±1．78）和（2．53±1．37）g／L、（25．95±1．74）和（20．82±1．40）g/L，差异均有统计学意义（t值分别为4．080、6．998、6．546、6．301，P值均〈0．05）。结论渗出液与漏出液具有不同的能谱曲线和能谱特征物质含量，低能量keV图像在渗出液的鉴别中起重要作用，能谱CT为鉴别胸腔积液的性质提供了一种多参数的方法。

Objective To assess the feasibility of characterizing pleural fluid on the basis of spectral imaging features utilizing spectral CT imaging. Methods Gemstone spectral imaging （GSI） was used to examine 20 pleural fluids filled tubes （11 exudates and 9 transudates ） following diagnostic thoracentesis. Effusions were classified as transudates or exudates using laboratory markers based on Light criteria. CT values on 140 kVp QC image were compared between two groups. Using GSI viewer, various CT spectral imaging parameters （CT values on different energy level, effective-Z, iodine-water concentration, calcium-water concentration and calcium-fat concentration） were calculated and compared between two groups. The difference of these spectral characteristic parameters was evaluated statistically by independent- samples t test. Results According to Light criteria, the mean CT value on QC image of exudates [ （ 19.56 ± 4. 10） HU ] was higher than that of transudates [ （ 13.44 ± 3.46） HU ] （ t = 3. 002, P = 0. 010 ）. Difference of CT value was found more obvious in the lower keV. On 40 keV images, the difference of CT value of two groups was the largest, the mean value of exudates [ （47.49 ± 14. 60） HU] was significantly higher than that of transudates[ （ 19. 76 ± 6. 85） HU ] （ t = 5. 520, P = 0. 000）. While On 140 keV, the mean CT value were （ 9. 76 ± 4. 16 ） and （ 6. 22 ± 3.17 ） HU and the difference of the two group has no statistically significant difference （t = 2. 107, P = 0. 050）. The mean slope rates of exudates （0. 51 ± 0. 23 ） was significantly larger than that of transudates （ 0. 18 ± 0. 08 ） （ t = 4. 287, P = 0. 001 ）. The effective-Z （7.89 ± 0. 16）, iodine-water concentration [ （ 5.74 ± 1.28 ） g/L ], calcium-water concentration [ （ 7. 89 ± 1.78 ） g/L] and calcium-fat concentration [ （25.95 ± 1.74） giLl of exudates were significantly higher than those of transudates [ 7. 67 ± 0. 07 , （1. 70 ± 0. 95 ） g/L,（2.53 ±1.37） g/L,（20.82±1.40） g/L]（t= 4. 080,6. 998,6. 546,6. 301 ,P 〈 0. 05 ）. Conclusions The spectral curve and spectral imaging parameters of exudates is found to be different from transudates. The low energy spectral imaging plays an important role in the characterization of pleural fluid. Gemstone spectral CT imaging provides a new muhiparameter method to differentiate transudates and exudates.