Eye-tracking technology has become a widely used means to understand how radiologists perceive and interpret medical images, providing useful information that can help improve diagnostic accuracy. However, existing eye-tracking studies in medical imaging remain limited due to the small number of stimuli and/or of subjects involved, and the lack of quantitative metrics to fully reveal readers' gaze behaviour. In this paper, we present the conduct of a larger scale eye-tracking study, where seven expert radiologists were asked to read 196 mammogram images. Furthermore, we carry out an analyse various gaze metrics including fixation duration, saccade amplitude, as well as gaze deployment, which quantify radiologists' gaze behaviour.