Harmonic imaging can be considered as a breakthrough in the
ultrasound imaging history. It is as important as Doppler or color flow
imaging. The principle of this method is to filter out the second harmonic
signal and reconstruct the image.

The second harmonic image has greater clarity, contrast, and details
than the fundamental frequency image. Although its scientific basis has
only been explained partially, it is quickly adopted by the ultrasound
imaging manufacturers.