SUBTRACTION METHOD FOR DETECTING TEMPORAL CHANGE FROM TWO TEMPORALLY SERIAL CHEST X-RAY IMAGES

PROBLEM TO BE SOLVED: To provide a method for creating an image with emphasized pathological change with time by the subtraction between two chest X-ray images (a past image and a present image). SOLUTION: For positioning the images, an image with the emphasized edge of the apex of the lower edge of ribs is created from an original image. Then, the inclination of the center axis of the thoracic cage is computed from the correlation between the left lung field and the right lung field, and the image is rotated so that the center axis is parallel to the vertical line. Next, an image with the emphasized edge of the outside from the apex of the lower edge of the ribs is created from the original image, and the position of the center axis of the thoracic cage in the horizontal direction is computed from the correlation between the left lung field and the right lung field. Then, the image is moved parallel in the horizontal direction so that the center axis of the thoracic cage matches the center axis of the image. After that, the value of mutual correlation is calculated while a partial image inside the thoracic cage of the past image as a template is moved on the present image in the vertical direction with the center axes of the past and present images of the thoracic cage matching each other to find a position where the value of mutual correlation is maximum. Then, the past image and the present image are superimposed on each other at this position and the difference between the images is taken. COPYRIGHT: (C)2008,JPO&INPIT