What is the primary clinical use of M-mode in cardiology?

• A. Detecting liver disease
• B. Assessing motion of cardiac walls and structures
• C. Evaluating bone density
• D. Assessing lung ventilation

Answer: (B)

M-mode echocardiography provides a one-dimensional, time-based trace along a single ultrasound line with very high temporal resolution. This setup makes it ideal for precisely watching how cardiac walls and structures move throughout the heartbeat and for measuring their dimensions as they change in systole and diastole. Clinically, therefore, it’s used to assess motion of the heart walls and valves and to track exact movements and sizes of cardiac structures over time. The other options refer to processes outside this imaging modality—liver disease, bone density, and lung ventilation—so they don’t reflect M-mode’s primary clinical purpose.