Harmonic imaging utilizes harmonics derived from the fundamental frequency; which of the following best describes a characteristic of harmonic imaging?

• A. Even and odd multiples of the fundamental frequency generated in the highest intensity region of the beam
• B. Only the fundamental frequency is used
• C. Harmonics increase grating lobes
• D. Harmonics are generated in the far field only

Answer: (A)

Harmonic imaging relies on nonlinear propagation in tissue, which generates frequency components that are multiples of the transmitted frequency. These harmonics arise most strongly in regions where the beam’s intensity is highest, so the tissue itself becomes the source of the higher-frequency signals, not the transducer alone. The imaging system then listens for these higher-frequency components to form the image.

This means harmonics include both even and odd multiples of the fundamental, with the second harmonic (twice the fundamental) typically being the strongest and most utilized. That’s why this choice best describes harmonic imaging: the harmonics originate in the high-intensity region and consist of multiple multiples of the fundamental frequency, not just the original frequency.