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目的探讨影响CT值测量的因素及对策。方法通过固定扫描条件对机器自带水模进行扫描,然后在其它条件不变的情况下,改变其中1个扫描条件(层厚、曝光量、重建函数、仟伏、FOV、机器)再对水模各扫描1次,测量CT图像一定兴趣区(ROI)的CT值(x±SD)与固定扫描条件的图像相对应ROI的CT值(x±SD)进行比较。结果相对应ROI的平均CT值:层厚为5mm及曝光量为150mAs与10mm、300mAs比较接近;重建函数为Fc80较Fc10略低;仟伏为130kV(因很少用未作校正)较120kV有明显的增加。相对应ROI的SD(噪声):层厚为5mm和曝光量为150mAs比较接近,较10mm、300mAs有明显增加;重建函数为Fc80较Fc10增加更明显;仟伏为130kV较120kV略有降低。在单纯小场水模的小场和中场CT图像中,相对应ROI的平均CT值和噪声:小场都大于中场。在单纯检测不同机器水模的CT图像中,相对应ROI的平均CT值及噪声:东芝旧CT机均高于GE新CT机。结论CT值不是恒定的,在诊断中只能作为参考,而不能作为诊断的依据。
Objective To explore the factors that affect CT value measurement and countermeasures. The method scans the built-in water model by fixed scanning conditions, and then changes one of the scanning conditions (layer thickness, exposure, reconstruction function, thousand volts, FOV, machine) The modalities were scanned once and the CT values (x ± SD) of a region of interest (ROI) of the CT image were measured and the CT values (x ± SD) of the ROI corresponding to the image of a fixed scan condition were compared. The results corresponded to the average CT values of the ROI: the thickness of 5mm and the exposure of 150mAs and 10mm, 300mAs closer; reconstruction function of Fc80 slightly lower than Fc10; thousand volts of 130kV (due to rarely used uncorrected) than 120kV Obvious increase. SD (noise) corresponding to the ROI: the layer thickness of 5mm and the exposure of 150mAs are relatively close, compared with 10mm, 300mAs significantly increased; reconstruction function of Fc80 increased more significantly than Fc10; 1000kV 130kV slightly lower than 120kV. In small field and midfield CT images of purely small field water modes, the average CT value and noise of the corresponding ROI are: the smaller fields are larger than the midfield. In the simple detection of different machine water-based CT images, the average CT value of the corresponding ROI and noise: Toshiba old CT machine are higher than GE’s new CT machine. Conclusion CT value is not constant, the diagnosis can only be used as a reference, but not as a basis for diagnosis.