In a M-mode representation in Fig b, pixels along the white vertical line in (a) are repeated parallel to each other over time. Figure 13b shows 5 s of repeated scans. For each heart beat a pulsatile wave travels through the arterial blood pool locally expanding the blood vessels. This expansion can be seen in B-mode as well as in M-mode representation. However, in B-mode (x ray protection) it is an event in time occurring over several image frames, whereas in M-mode this event is plotted as the horizontal axis and therefore easy to detect. White arrows in Fig. 13b indicate the temporal expansion of the blood vessel. Figure 13c shows a much more pronounced motion. The transducer was pointed toward the heart and is therefore either imaging the heart wall or one of the heart valves, showing the typical cardiac pattern.