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Several subsequent A-scans are performed with a time interval $\Delta t , but the individual A-scans are not plotted as curves, but by using colour codes: the higher the value of R is, the lighter patch corresponds to it. The values of the k-th A-scan are placed in the k-th column. This technique can be applied to observe the heart valves, for example.

Figure 3.


Figure 4. M-mode image. The movement of the mitral valve is clearly visible.

When choosing the value of $\Delta t, it is important to consider the maximal depth z_{max} of the examinable area: the next A-scan cannot be performed until the echo of the previously emitted signal arrives from the maximal depth. Therefore, \Delta t \geq 2z_{max}/c .

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