Which imaging technique results in selective reception of frequencies that are 2 times that of the transmitted frequency?

• A. Color Doppler imaging
• B. Tissue harmonic imaging
• C. Pulsed Doppler imaging
• D. Tissue Doppler imaging

Answer: (B)

The concept being tested is harmonic imaging in ultrasound, specifically how tissue harmonic imaging works. In tissue, the ultrasound wave propagates in a nonlinear way, which generates new frequency components called harmonics that are multiples of the transmitted frequency. By transmitting at the fundamental frequency and selectively receiving the second harmonic—two times the transmitted frequency—the system gains image quality advantages. The received harmonic signals come from deeper, more uniform tissue responses and are less affected by near-field clutter and some artifacts, leading to better contrast and resolution.

This is why tissue harmonic imaging is the correct choice: it deliberately uses the doubled frequency component created inside the tissue to form the image. The other imaging modes rely on Doppler shifts or motion signals rather than exploiting harmonic generation; they do not involve selective reception of frequencies at twice the transmitted frequency.