In this paper a linear transformation, the spiral method, is introduced; this transformation maps an image represented in a 3-D space into a signal in a 2-D space. Some features of the spiral are presented: for instance the topologic information of the objects in the image, their contours, areas and the shape of the objects themselves, Two different case-study are presented: the use of spiral method in order to evaluate the number, the size, the shape and the location of the microcalcifications by the use of signals related to the mammograms; entropy is proposed as a measure of the degree of the parenchyma disorder of the mammograms and its use for a system CAD. © Springer-Verlag Berlin Heidelberg 2005.