1. A method for defining a Region Of Interest (ROI) of a carotid artery comprising: providing at least one image including a portion of the carotid artery; slicing the image into vertical slices; selecting a stripe which corresponds to the Common Carotid Artery (CCA), within each of the slices; computing a size of each selected stripe; comparing the sizes of the selected stripes; identifying a base of a bulb of the carotid artery as corresponding to the stripe having at least a minimum increase in size compared to stripes in lower slices; and positioning the ROI below the base of the bulb.