In tissue harmonic imaging, which signal is detected and at what frequency relative to the transmitted frequency?

• A. The fundamental frequency
• B. The second harmonic, at approximately 2f0
• C. The third harmonic, at approximately 3f0
• D. The negative frequency

Answer: (B)

In tissue harmonic imaging, the wave becomes distorted as it propagates through tissue, producing harmonic frequencies of the transmitted tone. The second harmonic—approximately twice the transmitted frequency—is the strongest and is what lip imaging systems mainly detect. The receiver is tuned to pass this 2f0 component while suppressing the fundamental, which improves image quality by reducing near-field clutter and enhancing resolution. Higher harmonics, like the third (around 3f0), exist but are weaker and not used as the primary signal. Negative frequency isn’t a practical factor in this context.