The main purpose of this paper is to compare clustering (region growing) and gradient based techniques for detecting regions of interest in digital mammograms. Such regions of interest form the basis of applying shape and texture techniques for detecting cancerous masses. In addition, the paper proposes a two-stage method, in which gradient based techniques are applied first, followed by a region growing method that will yield lesser numbers of regions for analysis. For this purpose, we first use histogram equalization and fuzzy enhancement techniques to improve the quality of the images and to compare their utility on our mammogram data. Image-enhanced mammograms are then subjected to clustering or to gradient operations (masking) for segmentation purposes. The segmented image is then analyzed for estimating the regions of interest, and the results are compared against the previously known diagnosis of the radiologist. A total of 30 mammograms from the University of South Florida database were used, for which the radiologist's hand-sketched boundaries of the masses were known. The results show that when compared with histogram equalization, fuzzy enhancement techniques are better suited for mammogram analysis, and when compared with gradient based segmentation, region growing segmentation will give a lesser number of regions for analysis without compromising on quality.