DIGITAL IMAGE SUBTRACTION OF TEMPORALLY SEQUENTIAL CHEST IMAGES FOR DETECTION OF INTERVAL CHANGE

An automated digital image subtraction technique for temporally sequen tial chest images has been developed in order to aid radiologists in t he detection of interval changes. A number of small regions of interes t (ROIs) are selected automatically in the lung areas of two temporall y sequential chest images. A local matching, based on a cross-correlat ion method, is performed on each pair of corresponding ROIs in order t o determine shift values for the coordinates of two images. A proper w arping of xy coordinates is obtained by fitting two-dimensional polyno mials to the distributions of shift values. One of the images is warpe d and then subtracted from the other. Forty six pairs of chest images (42 with interval changes and 4 without interval change) were processe d using this method. The subtraction images were able to enhance vario us important interval changes, such as differences in the size of tumo r masses, changes in heart size, and changes in pulmonary infiltrates or pleural effusions. Approximately 70% of the pairs showed reasonably good registration.