迭代重建技术在前门控结合体质量调节管电压管电流心脏CT成像的研究——降低辐射剂量及控制图像质量

Iterative reconstruction in prospective electrocardiogram-gated heart computed tomography combined with weight adjusting tube voltage and current:an experimental study-reducing radiation dose and controlling image quality

目的探讨迭代重建技术(iDose4)在前瞻性心电门控结合体质量调节管电压管电流心脏螺旋计算机断层扫描(computerized tomography,CT)成像中降低辐射剂量及控制图像质量的应用价值。方法选取实验猪10只,每只猪均进行以体质量调节管电压管电流为基础的常规剂量(A组)及在此基础上降低管电流[分别降低30%(B组)、50%(C组)、70%(D组)]的256层前瞻性心电门控心脏CT扫描,所有数据均分别采用滤波反投影(filtered back projection,FBP)和iDose4重建,计算猪接受的辐射剂量,测量升主动脉根部及左心室腔噪声、信噪比(SNR)、对比噪声比(CNR),分别对总体图像质量和冠状动脉图像质量进行评分(5分法评分),3分及以上为图像质量可满足诊断,并对两种重建方法处理后所得结果进行比较。结果 A、B、C、D组的有效辐射剂量(ED)分别为(3.13±0.63)mSv、(2.26±0.51)mSv、(1.61±0.36)mSv、(1.01±0.23)mSv。随着X线剂量降低,图像噪声增加,信噪比、对比噪声比降低,图像质量下降。各组内比较,iDose4重建的图像噪声均较FBP重建者明显降低,而信噪比及对比噪声明显提高,差异均有统计学意义(P均=0.000)。A、B、C、D各组内经FBP/iDose4重建后总体图像质量评分分别为(3.80±0.42)分/(4.60±0.52)分、(3.60±0.52)分/(4.40±0.52)分、(3.00±0.67)分/(3.80±0.42)分、(2.00±0.67)分/(3.40±0.52)分,各组内比较差异均有统计学意义(P<0.05)。用FBP重建,A、B、C、D组近、远端冠状动脉的可诊断率分别为100%、95%、70%、20%和92%、72%、36%、0;经iDose4重建后,A、B、C组近、远端冠状动脉的可诊断率均大于经FBP重建后A组的可诊断率或与其相当(P>0.05),而D组的可诊断率明显低于FBP重建后A组的可诊断率,差异有统计学意义(P<0.05)。结论在前门控结合体质量调节管电压管电流心脏CT成像中,应用iDose4较FBP可显著降低图像噪声,提高信噪比及对比噪声比,提高图像质量;用iDose4重建可以在现有辐射剂量基础上降低50%的剂量进行扫描而图像质量保持不变。

Objectives To evaluate the application of iterative reconstruction （iDose4） for reducing radiation dose and controlling image quality in prospective electrocardiogram （ECG）-gated computed tomography （CT） combined with weight adjusting tube voltage and current.Methods Ten pigs were included.All the pigs were scanned on a 256-slice prospective ECG-gated multilayer spiral CT system utilizing routine dose （group A） based on weight adjusting tube voltage and current and tube current reduced by 30％ （group B）,50％ （group C） and 70％ （group D） respectively.Filtered back-projection （FBP） and iDose4 were used for reconstruction respectively for all data.Radiation dose were calculated and noise,signal-to-noise ratio （SNR）,contrast-to-noise rate （CNR） of ascending aortic root and left ventricle were measured,while general image quality and coronary artery image quality were graded （scale：1-5）.All results reconstructed by FBP and iDose4 were compared.Results The effective radiation doses for group A,B,C,D were （3.1 3-±0.63） mSv,（2.26 ±0.51） mSv,（1.61 ±0.36） mSv,（1.01 ±0.23） mSv.The image noise increased as well as SNR,CNR and image quality decreased with the X-ray dose decreased.Image noise significantly decreased,while SNR and CNR obviously increased with iDose4 reconstruction in each group （all P=0.000）.For FBP/iDose4 reconstruction,there were evident differences of image quality in group A （3.80±0.42 vs.4.60±0.52,P＜0.05）,group B （3.60±0.52 vs.4.40±0.52,P＜0.05）,group C （3.00±0.67 vs.3.80±0.42,P＜0.05） and group D （2.00±0.67 vs.3.40±0.52,P＜ 0.05）.The diagnosed rates of proximal,distal coronary artery in group A,B,C,D with FBP reconstruction were 100％,95％,70％,20％ and 92％,72％,36％,0 respectively,while the diagnosed rates of proximal,distal coronary artery in group A,B,C with iDose4 were not lower than those in group A with FBP （P＞0.05）,whereas the diagnosed rates in group D with iDose4 were significantly lower than those in group A with FBP （P＜0.05）.Conclusions IDose4 can sharply reduce image noise,improve SNR,CNR and image quality compared with FBP in prospective ECG-gated coronary CT combined with weight adjusting tube voltage and current.It＇s workable with a 50％ reduction in radiation dose,while the image quality remains the same.