Résumé : Physicians often perform diagnoses based on the evolution of lesions, tumors or anatomical structures through time. The objective of this report is to automatically detect regions with apparent local volume variation with a vector field operator applied to the local displacement field obtained after a non-rigid registration between successive temporal images. In studying the information of apparent shrinking areas in the direct and reverse displacement fields between images, we are able to segment evolving lesions. Then we propose a method to segment lesions in a whole temporal series of images. In this report we apply this approach to the automatic detection and segmentation of multiple sclerosis lesions in time series of MRI images of the brain.