Correspondence of lung nodules in sequential chest CT images for quantification of the curative effect

Abstract

In this paper, we propose a method to find the corresponding nodules among sequential chest X-ray CT images. To measure the curative effect of lung nodules, it is necessary to find the corresponding nodules between current and previous CT images. Since the lung shape is deformed by the respiration and posture of the patient, it is difficult to determine the correspondence of nodules automatically on exams of different dates. In the proposed method, the position of each nodule is represented as a relative coordinate in the lung region. The circumscribed quadrangles are set to left and right lung regions, respectively, in axial and coronal sections. The distance from quadrangle origin to nodule center is measured along the direction of x-, y- and z-axis. The nodule position is represented by three components as the ratio of the distance and the length of quadrangle edge in each direction. We applied the method to three chest X-ray CT images that were taken by sequential exams of the same patient. One hundred and eighty-eight pairs (188) of corresponding nodules were checked by visual observation, of which, 175 pairs could be found automatically by the proposed method. Thirteen pairs were false correspondence and the correct correspondence rate was 0.93.