Harmonic imaging

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Harmonic imaging is a technique in ultrasonography that provides images of better quality as compared with conventional ultrasound technique.

Physics

Harmonic imaging exploits non-linear propagation of ultrasound through the body tissues. The high pressure portion of the wave travels faster than the low pressure portion resulting in distortion of the shape of the wave. This change in waveform leads to the generation of harmonics (multiples of the fundamental or transmitted frequency) from a tissue. At present, the 2 harmonic is being used to produce the image because the subsequent harmonics are of decreasing amplitude and insufficient to generate a proper image.

These harmonic waves that are generated within the tissue, increase with depth to a point of maximum intensity and then decrease with further depth due to attenuation. Hence there is an optimum depth below the surface at which maximum intensity is achieved.

Advantages over conventional ultrasound