低管电压低管电流联合全模型迭代重建在颈动脉CT血管造影的应用

Combined application of low kV,low mAs,and iterative model reconstruction （IMR） in carotid CT angiography

目的 探讨低管电压低管电流联合全模型迭代重建（IMR）在颈动脉CT血管造影（CTA）的应用价值。方法 将40例行颈动脉CTA的患者（BMI 20~25 kg/m^2）按随机数字表法分为常规剂量组和低剂量组，每组20例。常规剂量组管电压120 kV，自动mAs，应用滤波反投影法（FBP）重建；低剂量组管电压80 kV，自动mAs并限制最大值为150 mAs，应用FBP和IMR重建。两组病例对比剂均采用碘帕醇（370 mg I/100 ml），用量32 ml，注射速率4 ml/s，注射完毕后以同等速率注射生理盐水50 ml。以画感兴趣区域（ROI）的方式分别测量主动脉弓、左颈总动脉分叉处、右颈动脉颅内岩骨段3段血管CT值、SD值（图像噪声）和同层面邻近肌肉CT值、SD值（背景噪声），计算信噪比（SNR）、对比噪声比（CNR）。运用多平面重组（MPR）、最大密度投影（MIP）、容积再现（VR）等技术重建图像，采用四分法对各图像质量进行主观评价。记录每例患者的容积CT剂量指数（CTDIvol）和剂量长度乘积（DLP），并计算有效剂量（E）。结果 低剂量组图像主动脉弓、左颈总动脉分叉处和右颈动脉颅内岩骨段CT值分别为（479.87±70.28）、（514.78±82.69）和（436.50±89.87） HU，高于常规剂量组图像CT值（295.63±34.75）、（325.09±37.81）和（286.93±36.46） HU （t=-6.47、-5.76、-3.66，P〈0.05）；低剂量组IMR重建主动脉弓、左颈总动脉分叉处、右颈动脉颅内岩骨段3段颈动脉的SNR和CNR均高于常规剂量组FBP重建图像（t=-7.54、-3.55、-5.31、-7.13、-5.28、-8.35，P〈0.05）。常规剂量组FBP重建和低剂量组IMR重建颈动脉图像质量、血管边缘形态整体满意，低剂量组FBP重建图像质量差于常规组FBP重建和低剂量组IMR重建（Z=-2.87、-3.69，P〈0.05）。低剂量组有效剂量（0.57±0.13） mSv较常规组（2.22±0.36） mSv降低73.0%。结论 采用低管电压低管电流扫描联合IMR，可使颈动脉CTA获得良好图像质量并大幅降低受检者辐射剂量。

Objective To evaluate the application value of combination of low kV,low mAs,and iterative model reconstruction （IMR） in carotid CT angiography. Methods Forty patients （BMI 20-25 kg/m^2） were enrolled and randomly divided into routine dose group （20） and low dose group （20）,The parameters in routine dose group were 120 kV,automatic mAs,and filter back projection （FBP）;and that in low dose group were 80 kV,automatic mAs but upper limit 150 mAs,and FBP or IMR.All patients received the injection of 32 ml of iopamidol （370 mg I/100 ml） at a flow rate of 4 ml/s,followed by 50 ml normal saline at the same rate.The CT value and image noise （SD） of the aortic arch,left carotid artery bifurcation,and right carotid artery of rock bone were measured with region of interest （ROI） method,and then signal to noise ratios （SNR） and contrast to noise ratio （CNR） of image were calculated.The image quality was evaluated by two radiologists using a subjective four points scale on multiplanar reformated （MPR）,maximum density projected （MIP） and volume rendered （VR） images.Volume CT dose index （CTDIvol）,dose length product （DLP）,and the effective dose （E） of each patient were recorded. Results CT values of carotid artery[（479.87±70.28）,（514.78±82.69）,（436.50±89.87） HU]in low dose group were significantly higher than those in routine dose group[（295.63±34.75）,（325.09±37.81）,（286.93±36.46） HU]（t=-6.47,-5.76,-3.66,P〈0.05）.The SNR and CNR of IMR reconstructed image in low dose group were significantly higher than those of FBP reconstructed image in routine dose group （t=-7.54,-3.55,-5.31,-7.13,-5.28,-8.35,P〈0.05）.The image quality of FBP reconstructed images in routine dose group and IMR reconstructed images in low dose group were all enough for diagnosis.The image quality of FBP reconstructed images in low dose group was significantly poorer than that in routine dose group and IMR reconstructed images in low dose group （Z=-2.87,-3.69,P〈0.05）.The effective dose in low dose group （0.57±0.13） mSv was 73% less than that in routine dose group （2.22±0.36） mSv. Conclusions Using low kV,low mAs,and IMR would help to obtain good carotid CT angiographic images and low radiation dose.