CT扫描不同层厚及范围对扫描靶点的影响研究

Research on effects on the targets due to changing slice thickness or scanner field of CT scanning

目的:分析不同扫描厚度和范围对扫描靶点位置、形状的影响,为肿瘤治疗中CT扫描精确定位提供参考。方法:采用双源CT对TLD-T1型头模进行扫描,将头模水平放置扫描床行定位图扫描后取最大直径5 mm扫描,扫描厚度分别设置为2 mm、3 mm、5 mm及10 mm,分析扫描厚度变化对扫描直径、形状和噪声值的影响。取扫描厚度5 mm,改变扫描视野,分析不同扫描视野在200 mm、300 mm和250 mm下靶点偏移位置。结果:12 mm和3 mm扫描厚度靶区最大直径均为6 mm,依照人体视觉分析,靶点直径从大到小依次为2 mm、3 mm、5 mm和10 mm;2改变扫描厚度,靶点形状出现变化,随着扫描厚度的增加,图像形状变化逐渐规律,2 mm图像评分显著高于10 mm图像评分,差异有统计学意义(t=27.080,P<0.05);3噪声测量值逐渐减少,10 mm噪声测量值(3.52 HU)低于2 mm噪声测量值(9.06 HU),差异有统计学意义(t=8.646;P<0.05)。以扫描视野200 mm为基准,250 mm和300 mm扫描视野靶点位置沿着X轴正方面偏移分别为1.5 mm和2.0 mm。结论:不同扫描厚度和扫描范围均会影响靶点位置,对放射治疗精确定位具有很大影响,随着扫描厚度的增加,图像质量降低,噪声测量值逐渐减少,故在CT扫描中应正确掌握变化规律并采取相应的措施。

Objective： To analyze the effects on the size and shape of targets due to changing slice thickness or scanning field of CT scanner, and to provide reference for the accuracy of scanning location and accurate therapy of tumors. Methods： TLD-T1 type head mold was scanned by dual source CT Type head was scanned with max diameter 5 mm after horizontal positioning and scanning. Scanning thickness is set to 2 ram, 3 mm, 5 mm and 10 mm. The effect of scanning diameter, shape and noise with different scanning thickness.The slice thick was 5 mm, scanner fields were taken 200 mm, 250mm and 300 mm, respectively, target offset position was analyzed. Results： ①The maximum diameter of the 2 mm and 3 mm scan thickness target area were 6mm,the target point diameter from the big to the small sequence was 2 mm, 3 mm, 5 mm, 10 mm according to human vision. ②The scan thickness, the shape of the target was changed, the shape of the image was changes gradually with the increase of the scan thickness, 2ram noise measurements （3.52 HU） were significantly lower than the 10 mm noise measurements （9.06 HU）, P〈0.05. ③The noise measurement value was gradually reduced, 10 mm noise measurements （3.52 HU） were significantly lower than the 2 nun noise measurements （9.06 HU）, t=8.646, P〈0.05. To scan the 200 mm as the baseline, the 250 mm scanning field of vision target position along the X axis is in the direction of the 1.5 mm, the 300 mm scan field of view point position along the X axis was 2.0 mm. Conclusion： Different scanning thickness and scanning range willinfluence the location of the target, on radiotherapy of accurate positioning has great influence, image quality decreased with the increase of thickness scan, noise measurement value decreased gradually, in CT scanning should correctly grasp the changes and take corresponding measures.