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目的研究螺距变化对影像质量影响,为优化扫描方案提供理论依据。方法使用腹部螺旋扫描类型,准直器宽度16×1.5mm,获取螺距分别为0.563、1.063的两组影像资料。按照双盲法的原则,由三位经验丰富的放射科医师以三个等级标准对图像质量和伪影进行主观评价,得到的数据做Ridit非参数检验的统计分析。记录所有病例的CTDIv;测量门静脉分叉平面的主动脉CT值,以标准差表示图像噪声;测量6点钟方向的空气背景噪声,求得组织信噪比;CTDIv、组织信噪比进行两个独立样本t检验统计分析。结果图像质量优、良、差,0.563螺距为23例、18例、3例;1.063螺距为20例、16例、3例。伪影方面优、良、差,0.563螺距为25例、15例、4例;1.063螺距为19例、17例、13例。螺距0.563、1.063的CTDI均值为16.03、16.01,信噪比均值为2.26、2.70。统计结果显示两组资料的图像质量、伪影、CTDI、信噪比差异没有统计学意义。结论在一定范围内螺距加大,图像质量保持稳定,不影响病灶的可探测性。
Objective To study the effect of pitch variation on image quality and to provide a theoretical basis for optimizing the scanning scheme. Methods The type of abdominal spiral scan was used. The width of the collimator was 16 × 1.5 mm. Two groups of images with the pitch of 0.563 and 1.063 respectively were obtained. According to the principle of double-blindness, three experienced radiologists subjectively evaluated the image quality and artifacts with three grading criteria. The data obtained were used for statistical analysis of Ridit’s nonparametric test. CTDIv was recorded in all cases; CT value of the aorta in portal vein bifurcation plane was measured to represent image noise with standard deviation; air background noise at 6 o’clock was measured to obtain tissue signal to noise ratio; CTDIv, Independent sample t test statistical analysis. Results The results showed excellent image quality, good and poor, 0.563 pitch was 23 cases, 18 cases, 3 cases; 1.063 pitch was 20 cases, 16 cases, 3 cases. In terms of artifacts, excellent, good, poor, 0.563 pitch is 25 cases, 15 cases, 4 cases; 1.063 pitch is 19 cases, 17 cases, 13 cases. The mean CTDI of pitch 0.563,1.063 was 16.03,16.01, the average SNR was 2.26,2.70. The statistical results show that there is no significant difference in image quality, artifacts, CTDI and signal-to-noise ratio between the two groups of data. Conclusion In a certain range of pitch increases, the image quality remained stable, does not affect the detectability of lesions.