PHILIPS大孔径CT模拟定位机影像质量控制方法研究

Study of image quality control for PHILIPS large bore CT-Simulator

目的通过对CT模拟定位机质量控制模体的测试,对CT模拟定位机的各项指标进行质量控制,分析影响图像质量的因素,保证图像质量。方法利用PHILIPS大孔径CT模拟定位机分别对Catphan504模体四大部分进行头部标准质量控制方案轴向扫描,测试其层厚、CT值线性、均匀性、噪声、空间分辨率、密度分辨率。层厚测试扫描条件为120 kV,280 mAs,层厚9.0、6.0、3.0、1.5 mm,旋转时间0.75 s,算法采用EB;CT值线性扫描条件为120 kV,280 mAs,层厚9.0 mm,旋转时间0.75 s,算法EB、B;均匀性、噪声、空间分辨率扫描条件均为120 kV,280 mAs,层厚9.0 mm,旋转时间0.75 s,算法EB;密度分辨率扫描条件为120 kV,220 mAs、240 mAs、260 mAs、280 mAs,层厚9.0 mm,旋转时间0.75 s,算法EB。结果 9.0 mm、6.0 mm、3.0 mm、1.5 mm标称层厚的测试结果分别为8.82 mm、5.80 mm、2.95 mm、1.55 mm;对于CT值线性,EB、B两种算法的对比度标度分别为1.79×10^(-4) cmHu^(-1)、1.93×10^(-4) cmHu^(-1);均匀性为3.9 Hu;噪声水平为0.34%;空间分辨率为6 LP/cm;220 mAs、240 mAs、260 mAs、280 mAs条件下,密度分辨率分别为4 mm@1%、3 mm@1%、2 mm@1%、2 mm@1%。CT值线性在EB算法条件下,对比度标度近似等于参考值下限值,密度分辨率在220 mAs、240 mAs条件下,其测量值低于参考值,其他测试项目结果均符合要求。结论通过对各项目的检测可保证影像质量最优化,进而保证精确放射治疗的实施。

Objective To analyze the influencing factors and ensure image quality by testing quality control（QC） phantom and indexes for CT-Simulator. Methods The PHILIPS large bore CT-Simulator was performed head standard QC method at axial scan in four parts of Catphan504, and the slice thickness, CT number linearity, uniformity, noise, spatial resolution and density resolution were tested. The scan conditions for testing slice thickness was 120 kV, 280 mAs, with thickness of 9.0 mm, 6.0 mm,3.0 mm and 1.5 mm, rotation time was 0.75-second and algorithm was EB; The scan conditions for testing CT number linearity was 120 kV, 280 mAs, 9.0 mm of slice thickness, rotation time of 0.75-second and algorithms were EB and B; The scan conditions for uniformity, noise and spatial resolution were 120 kV, 280 mAs, 9.0 mm of slice thickness, rotation time of 0.75-second and algorithm was EB; The scan conditions for testing density resolution was 120 kV, 220 mAs, 240 mAs, 260 mAs and 280 mAs, 9.0 mm of slice thickness, rotation time of 0.75-second and algorithm was EB. Results The testing slice thickness results of 9.0 mm, 6.0 mm, 3.0 mm and 1.5 mm were 8.82 mm, 5.80 mm, 2.95 mm and 1.55 mm, respectively. For CT number linearity, the contrast scale of algorithm EB and B were 1.79 ×10^-4 cmHu^-1, 1.93 ×10^-4 cmHu^-1, respectively; The uniformity was 3.9 Hu, noise level was 0.34 %, and spatial resolution was 6 LP/cm. The density resolution of 220 mAs, 240 mAs,260 mAs and 280 mAs were 4 mm@1 %, 3 mm@1 %, 2 mm@1 % and 2 mm@1 %, respectively. For CT number linearity of algorithm EB, the contrast scale was approximately equal to the lower limit of reference value. The test result of density resolu-tion under 220 mAs and 240 mAs was lower than that of reference result, while other test results were in line with the require-ments. Conclusion The indices measurement results demonstrated that it can guarantee the image quality optimization and assure accurate location of radiotherapy.