M-mode
Ultrasound acquisition along a single sample line, plotted over time. The result is a 1D position × time strip — high temporal resolution along that line. Used primarily for cardiac wall motion measurements (LV septal / posterior-wall thickness, mitral-valve excursion, aortic-root timing).
Why it matters to buyers: Standard echocardiography mode on every cardiac-capable platform.
Why it matters to engineers: Output is 1D × time, not a 2D image. Frame-rate is effectively very high; useful where temporal resolution matters more than spatial coverage.