In harmonic imaging, which statement is true?

• A. It uses the fundamental frequency to form the image
• B. It relies on Doppler shifts
• C. It improves contrast resolution
• D. It reduces frame rate

Answer: (C)

Harmonic imaging relies on the tissue’s nonlinear response to ultrasound to generate echoes at twice the transmitted frequency, so the image is formed from these second-harmonic signals rather than the fundamental frequency. This harmonic signal tends to be less affected by near-field clutter and reverberations, which makes tissue borders and contrast between structures more conspicuous. That clearer delineation is what improves contrast resolution. It isn’t based on Doppler shifts, and the image isn’t formed from the fundamental frequency. Frame rate isn’t the main benefit and isn’t the reason harmonic imaging is used.