A new method is introduced able to track the motion of a thin object, e.g. a wall, from a series of digital field data (e.g. images) in order to analyze field information corresponding to the moving position of the object. The method is based on the extraction of M-mode images where the wall can be identified and the wall properties can be extracted and analyzed. The digital implementation of the method into electronic equipments improves the quality of the information that can be extracted from field data and the potential diagnostic capability when applied to echographic medical imaging.