1. A method of operating a diagnostic ultrasound system comprising: measuring, via a probe, a cross-section region of a subject; determining displacement of tissue in the cross-section; determining an elastic information of the tissue in the cross-section region on the basis of the displacement; generating an elastic image of the cross-section region on the basis of the elastic information and displaying the elastic image on a display device; setting at least one of a stress line of interest and a region of interest on the elastic image displayed on the display device, applying different levels of pressure with the probe to generate corresponding compression states for the subject; determining a change of compression state over time by the compression states generated for the subject; displaying the change of the compression state as compression state information together with the elastic image on the display device; evaluating the compression state on the tissue in the cross-section region on the basis of the compression state information; and displaying the compression state information together with the elastic image on the display device, wherein the compression state information includes a stress change distribution for at least one of along the stress line of interest and in the region of interest of the change in one frame of at least one of a stress and a stress distribution applied to the subject, in a pressure range of interest.