Development of Subtraction CT Technique for Detection of Lung Nodules on Low-Dose CT

低剂量CT对早期肺癌的检测是敏感的，但大量CT图像的解释对于放射科医生来说是费时的。因此，我们开发了一种减影CT技术，以协助放射科医生检测小肺结节。该方案通过三维形态滤波和线增强滤波得到给定截面的“掩模图像”。将迭代图像翘曲技术得到的翘曲掩模图像与相应的CT图像相减，得到减法CT图像。为了进一步减少由血管引起的伪影，我们采用了线增强滤波器。将目标切片图像中提取的线状图案加入到掩模图像中。这样就可以消除相减图像中由于血管而产生的伪影。CT减影图像能明显增强肺小结节。CT减影对早期肺癌的诊断有一定的指导意义。

Low-dose CT is sensitive in the detection of early lung cancer, however, the interpretation of a large number of CT images is time consuming for radiologists. Therefore, we have developed a subtraction CT technique to assist radiologists for their detection of small lung nodules. In this scheme, the "mask image" for a given section was obtained by a 3 dimensional morphological filtering and line enhancement filtering. The subtraction CT images were obtained by subtracting the warped mask images, which were obtained by iterative image warping technique, from the corresponding CT images. For further reduction of artifacts due to vessels, we employed a line enhancement filter. The extracted line patterns in the target section image were added to the mask image. Thus the artifacts due to vessels in the subtraction image could be eliminated. The subtraction CT images can clearly enhance small lung nodules. The subtraction CT image could be useful for the detection of early lung cancer.