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How does M-scan ultrasound record the movement of the heart?

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M-scan (or M-mode) ultrasound records the movement of the heart by directing a narrow, stationary ultrasonic beam along a single line through the cardiac structures.12

As the beam encounters internal structures such as heart valves and muscle walls, it records the echoes reflected from these tissues. Because the beam is fixed, the system captures the amplitude and the rate of motion of these structures with high accuracy over time. This data is then displayed to provide a precise record of how these specific parts of the heart move during the cardiac cycle.132

While M-scan is highly effective for tracking motion along that single line, it does not depict lateral motion—movement perpendicular to the ultrasonic beam—or provide a full cross-sectional view of cardiac shape. For those purposes, real-time, two-dimensional echocardiography is typically used.2