自适应迭代重建算法在低对比剂肾动脉CTA扫描中的应用

Application of adaptive statistical iterative reconstruction in renal CTA with low-dose contrast medium

目的:探索自适应迭代重建算法(ASIR)在降低肾动脉CTA对比剂用量的应用价值。方法:对40例行肾动脉CTA的患者随机分成两组:常规组(A组)20例,对比剂用量为600 mgI/kg;低对比剂用量组(B组)20例,对比剂用量为300 mgI/kg。采用GSI扫描模式,智能mA,噪声指数为10 HU,螺距为1.375∶1,转速为0.6 s/r,40 s时采集动脉期图像。对所得数据进行重建,常规组用40%ASIR 70 keV进行图像重建,低对比剂用量组用40%ASIR 40～70 keV间隔5 keV进行图像重建(40、45、50、55、60、65、70 keV)。测量每组图像的平扫和动脉期肾动脉的CT值(CT1,CT2)和标准差(SD1,SD2),动脉期图像的竖脊肌的CT值(CT3)和标准差(SD3)。计算每组图像肾动脉的强化幅度(ΔCT=CT2-CT1),信噪比SNR=CT2/SD2,对比噪声比CNR=(CT2-CT3)/SD3,对以上数据进行单因素方差分析。两名经验丰富的医生使用5分系统对每组图像进行盲法主观评分,评分的一致性采用Kappa检验,组间主观评分采用Wilcoxon检验。结果:600 mgI/kg 70 keV组和300 mgI/kg 45 keV组的主观评分医生1和医生2分别是3.90±0.55和4.00±0.65,3.55±0.83和3.70±0.80,其差异无统计学意义(P>0.05),客观参数ΔCT、SNR值和CNR差异亦无统计学意义(P>0.05)。结论:当对比剂的用量降低50%时,ASIR在肾动脉CTA中可以获得满足诊断的图像质量。

Objective： To evaluate the application value of adaptive statistical iterative reconstruction（ASIR） in reducing the dosage of CTA contrast agent in renal artery. Methods： Forty patients with renal artery CTA were randomly divided into two groups： routine group 20 cases（group A） with 600 mgI/kg and low contrast medium dose group 20 cases（group B） with 300 mgI/kg.The scan protocol was： Discovery CT750 HD, smart mA, noise index of 10 HU, pitch 1.375：1, rotating speed 0.6 s/r. Images of the artery phase were reconstructed at 0.625 mm thickness with 40%ASIR, group A reconstructed monochromatic images at70 keV, group B reconstructed monochromatic images from 40～70 keV by interval 5 keV. The CT values and standard deviation（SD） values of the renal artery in plain scan（CT1, SD1） and the arterial phase（CT2, SD2）, and the erector muscle of spine in the arterial phase（CT3, SD3） were measured. The enhancement degree of the renal artery（ΔCT=CT2-CT1）, the signal to noise ratio（SNR=CT2/SD2） and contrast to noise ratio（CNR=（CT2-CT3）/SD3） were calculated. Single factor analysis of variance was used.The subjective image scores of the groups were assessed blindly by two experienced physicians using a 5-point system and the score consistency was compared by the Kappa test. Results： The subjective scores of the 600 mgI/kg 70 keV group and the 300 mgI/kg 45 keV group were 3.90±0.55 and 4.00±0.65, 3.55±0.83 and 3.70±0.80, and the difference was not statistically significant（P〉0.05）, and there was no significant difference in the objective parameters（ΔCT, SNR and CNR）（P〉0.05）. Conclusion： When the dosage of contrast medium is reduced by 50%, the ASIR can get the image quality satisfying the diagnosis in the renal artery CTA.