碳纤维平板对CT图像均匀性影响的研究

Study on Influence of Carbon Fibre Flat Plates on CT Image Uniformity

目的研究碳纤维平板对CT图像均匀性的影响。方法使用水模体和碳纤维平板(CIVCO CT平板床和ORFIT AIO固定底板)对5种摆放情形进行研究:情形A,水模体悬空放置;情形B,将水模体置于碳纤维CT平板床上;情形C,在水模体与CT平板床之间有1块固定底板;情形D,在水模体与CT平板床之间有2块固定底板;情形E,在水模体与CT平板床之间有3块固定底板。采用6种放疗扫描协议,对上述5种情形扫描获得CT图像,在每张CT图像的3、6、9、12点钟方向距离中心0、5.0(内环)、7.5 cm(外环)处勾画面积为2.34 cm2的圆形感兴趣区域(ROI),得到ROI中平均CT值,计算内外环两种位置情况下的图像均匀性。结果在水模下加入碳纤维平板后,CT图像的均匀性变差;内外环相比,对外环ROI(即图像边缘处)的图像均匀性影响更大,边缘处ROI的平均CT值的影响以图像下方(即6点钟方向)为主。结论碳纤维平板对CT图像的均匀性存在影响,物理师在进行质控时应注意水模体的摆放位置。

Objective To investigate the in？uence of carbon fibre flat plates （including a CIVCO carbon fbre CT ？at tabletop and ORFIT AIO carbon fbre immobilization base plates） on CT image uniformity. Methods The following experimental methods including 5 kinds of water phantom position were utilized to carry out the work. A situation： the water phantom was suspended in the air. B situation： the water phantom was placed on the CT flat tabletop. C situation： a base plate was positioned between the water phantom and the CT flat tabletop. D situation： two base plates were positioned between the water phantom and the CT lat tabletop. E situation： three base plates were positioned between the water phantom and the CT flat tabletop. Six radiotherapeutic scanning protocols had been used to acquire CT images. Nine circular regions of interest （ROIs）, each with area of 2.34 cm2, were selected at the spots that were 0 cm, 5.0 cm （inner ring） and 7.5 cm （outer ring） away from the centroid at 3, 6, 9 and 12 o’clock positions to calculate the CT mean value and image uniformity in two ROI cases. Results The CT image uniformity deteriorated when placing the carbon fbre ？at plates under the water phantom. The in？uence of carbon fbre flat plates on CT image uniformity was greater for ROIs of outer ring than for those of inner ring. The infuence on CT mean value of outer ring focused mainly on the bottom part （6 o’clock direction）. Conclusion Carbon fbre flat plates have in？uence on CT image uniformity. It should be paid attention to the correct position of water phantom when carrying out quality control tests for CT devices.