Harmonics in ultrasound imaging are created primarily in which medium?

• A. Receiver
• B. Transducer
• C. Tissues
• D. Beam former

Answer: (C)

The key idea is that harmonics come from nonlinear propagation of the ultrasound as it travels through tissue. As the pulse moves, the tissue’s response distorts the waveform, and the pressure-dependent speed of sound generates higher-frequency components (overtones) of the transmitted frequency. This nonlinear interaction occurs primarily in the tissue, so the medium creating the harmonics is the tissue itself. The transducer, beam former, and receiver mainly handle the transmission and detection of the fundamental frequency, with any harmonics arising only as a result of tissue interaction (and only minorly from device nonlinearities). Hence, tissues are the primary source of harmonic content.