水模管电流-噪声与管电流-辐射剂量曲线对确定腹部迭代重建低剂量CT扫描参数的价值

The Value of the Tube Current-Noise Curve and Tube Current-Radiation Dose Curve in Selecting Scanning Parameters of Low-Dose Abdomen CT with Iterative Reconstruction

目的探讨应用水模管电流-噪声与管电流-辐射剂量曲线确定腹部迭代重建低剂量CT扫描参数的可行性。方法在西门子二代双源CT上用多组不同的参数扫描水模,分别用FBP和SAFIRE(3)重建CT图像,测量图像噪声,记录各组的辐射剂量,绘制管电压为120 k V、100 k V、80 k V时不同重建方法的参考管电流-噪声曲线与不同扫描方法的参考管电流-辐射剂量曲线。搜集80例拟行腹部CT增强扫描的患者,随机纳入对照组和实验组,对照组采用常规扫描和重建方法,实验组扫描条件从上述SAFIRE(3)曲线上读取,要求其噪声水平与对照组相近的同时辐射剂量最低。由两名放射科医师采用盲法对所得两组图像质量进行主观评分,并测量兴趣区(ROI)的图像噪声(SD)、信噪比(SNR)及对比噪声比(CNR),记录两组的容积CT剂量指数(CTDIvol)、剂量长度乘积(DLP),计算有效辐射剂量(ED)。用两个独立样本t检验和非参数检验对两组患者各评价指标进行统计学分析。结果实验组与对照组相比,主观图像质量评分、各ROI的SD、SNR、和CNR均无统计学差异(P>0.05)。实验组CTDIvol显著低于对照组[(9.38±2.12)m Gy比(16.29±2.85)m Gy,P<0.05]。结论应用水模管电流-噪声与管电流-辐射剂量曲线可以准确、有效地确定腹部迭代重建低剂量CT的扫描条件。

Objective To evaluate the feasibility of selecting scanning parameters of low-dose abdomen CT combined with iterative reconstruction by the tube current-noise curve and tube current-radiation dose curve. Methods The water phantom was scanned using different level parameters on the Dual-source 128 MDCT and the CT images were reconstructed with FBP and SAFIRE （3）. One radiologist measured the image noise（SD） of ROI and recorded the radiation dose of dif- ferent parameters. The reference tube current-noise curve and reference tube current-radiation dose curve of different tube voltage were drawn with Excel. Then, eighty patients who underwent the enhanced abdomen CT were randomly assigned into the control group using normal abdomen scanning parameters and experimental group of which scanning parameters that bad the same image noise and lower radiation dose were selected in the above SAFIRE （3） standard curves. Two radiologists blindly evaluated the subjective image quality score of each group. Image noise of ROI were measured on the syngo MMWP VE 36A . CTDIvol and DLP were recorded. Signal to noise ratio （SNR）, contrast to noise ratio（CNR） and effective radia- tion dose（ED） were calculated subsequently, t test and nonparametric tests were used for statistical analysis. Results There was no statistical difference in subjective image quality scores,image noise, SNR and CNR of every RO[ between con- trol and experimental group （ P 〉 0.05 ）. Compared with the control group, CTDIvol of experimental group was significantly lower [（9.38 ±2.12）mGy vs. （16.29 ±2.85）mGy ,P〈0.05]. Conclusion It is accurate and effective to select the scanning parameters of low-dose abdomen CT with iterative reconstruction by the tube current-noise curve and tube current-radiation dose curve.