钆增强双能量CT诊断肺栓塞的实验研究

Detection of pulmonary embolism with gadolinium-enhanced dual energy CT： an experimental study

目的评价含钆的MR对比剂进行双源双能量cT肺动脉成像（CTPA）用于诊断肺栓塞的可行性。方法（1）用不同稀释浓度的碘对比剂和钆对比剂进行体外双源双能量CT成像，测量不同管电压条件下各样本的cT值。（2）10只新西兰大白兔以3和5ml／kg分2组注射含钆对比剂进行双能量CT扫描，测量不同管电压下肺动脉的强化值。6只家兔在次日经股静脉注射明胶海绵栓子制作急性肺栓塞模型，2h后行双能量CT扫描。分别于2次扫描前经耳缘静脉或股静脉抽血2～3ml行肾功能检查。方差分析和独立样本t检验用于分析不同组别肺动脉强化值的差别。结果（1）同含碘对比剂相似，80kV管电压条件下含钆对比剂的CT值高于140kV和平均加权120kV。（2）在管电压分别为140、80、平均加权120kV时，双能量cT定量测量显示5ml／kg组家兔主肺动脉[cT值分别为（463，1±118．0）、（664．2±188．0）、（522．9±137．7）HU]和肺动脉1级分支[CT值分别为（445．1±82．3）、（606．7±207．2）、（493．4±117．3）HU]CT值均高于3ml／kg组[主肺动脉CT值分别为（258．1±55．1）、（384．0±92．3）、（295．4±73．6）HU，肺动脉1级分支CT值分别为（245．0±73．2）、（309．1±94．2）、（263．8±78．5）HU；P值均〈0．05]。80kV图像肺动脉主干和1级分支的CT值明显高于140kV和平均加权120kV（肺动脉主干：F=6．004，P=0．005；1级分支：F=4．374，P=0．018）。6只栓塞组家兔CTPA显示两下肺动脉强化突然截断，对应的钆图显示钆含量降低，表现为蓝色伪彩色，正常非栓塞肺组织表现为红黄色伪彩色。3和5ml／kg组肌酐增加率分别为6．7％和20．6％。结论含钆MR对比剂具有与含碘对比剂相似的X线衰减特征，可用于对比增强的双能量CT肺成像中，同时提取出的CTPA以及显示肺灌注信息的钆图能够用于肺栓塞的诊断。

Objective To evaluate the feasibility of gadolinium-enhanced dual energy CT pulmonary angiography （CTPA） in detecting pulmonary embolism （PE）. Methods In vitro dual energy CT of phantoms of gadolinium and iodinated contrast agents with different diluted ratio was performed, and CT values were measured at different tube voltages. Ten rabbits which were grouped into 3 ml/kg and 5 mUkg groups underwent dual energy CT scan. CT values of pulmonary artery trunk and the first branch of pulmonary artery were measured. Sponge gelatin were injected into the femoral vein of 6 rabbits to make PE model next day, then lungs were re-imaged with dual energy CT 2 h after embolization. Creatinine was repeatedly measured before and one day after injection of gadolinium via ear marginal vein or femoral vein sampling. One-way ANOVA test and independent student t test were used to analyze the difference of pulmonary artery enhancement between different groups. Results （1）Compared with iodinated contrast agent, CT value of gadolinium-based contrast agent at 80 kV was higher than those at 140 kV and average- weighted 120 kV. （2） At 140, 80, and average weighted 120 kV, CT values of pulmonary artery trunk [CT values were （463.1 ±118.0）, （664. 2 _＋ 188. 0）, （522. 9 ＋ 137.7） HU] and of the first branch of pulmonary artery [CT values were （445. 1 ±82. 3）, （606. 7 ±207.2）, （493.4 ± 117. 3） HU] were higher than those at 3 ml/kg [ CT value of pulmonary artery trunk was （ 258.1 ±55.1 ）, （ 384. 0 ± 92. 3 ）, （295. 4 ± 73.6） HU, CT value of the first branch of pulmonary artery （245.0 ± 73.2）, （309. 1 ±94. 2）, （263.8 ±78.5） HU;all P 〈0.05）. CT values of pulmonary artery trunk and the first branch of pulmonaryartery at 80 kV were higher than those at 140 kV and average-weighted 120 kV （pnlmonary artery trunk： F = 6. 004, P = 0. 005 ; the first branch of pulmonary artery ： F = 4. 374, P = 0. 018 ）. In 6 rabbits, CTPA showed the enhancement cut-off of bilateral pulmonary arteries, gadolinium mapping showed decreased perfusion in the corresponding lung ｜obes, manifested as blue on color-coded map, while normal lung was color coded as red or yellow. Creatinine was higher by 6. 7% and 20. 6% for group 3 ml/kg and 5 ml/kg. Conclusions With similar X-ray attenuation characteristics as iodine, gadolinium-based contrast agent can be used to pulmonary contrast-enhanced dual energy CT imaging, simultaneously providing both CTPA and gadolinium maps to detect PE.