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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 determine the feasibility of iterative reconstruction of low-dose computed tomography (CT) scan parameters by using current-mode tube current-noise and tube current-radiation dose curves. Methods Several pairs of different parameters were used to scan water phantom on Siemens second-generation dual-source CT. The CT images were reconstructed with FBP and SAFIRE (3) respectively, and the image noise was measured. The radiation dose was recorded and the tube voltage was drawn to be 120 kV. Reference tube current-noise curves for different reconstruction methods and reference tube current-radiation dose curves for different scanning methods at 100 kV, 80 kV. Eighty patients who underwent enhanced CT scan of abdomen were randomly divided into control group and experimental group. The control group was scanned by routine scanning and reconstruction method. The scanning conditions of experimental group were read from SAFIRE curve (3), and its noise level was compared with that of control Group similar radiation dose at the same time the lowest. Two radiologists used the blind method to subjectively score the two groups of images and measured the image noise (SD), signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) Group volume CT dose index (CTDIvol), dose length product (DLP), calculated effective radiation dose (ED). Two independent samples t test and non-parametric test were used to analyze the two groups of patients’ evaluation indexes. Results There was no significant difference in subjective image quality score, SD, SNR, and CNR of each ROI between the experimental group and the control group (P> 0.05). The CTDIvol in the experimental group was significantly lower than that in the control group [(9.38 ± 2.12) m Gy vs (16.29 ± 2.85) m Gy, P <0.05]. Conclusion The current-noise and tube current-radiation dose curves of water phantom can be used to accurately and effectively determine the scanning conditions of low-dose CT for abdominal reconstruction.