In tissue harmonic imaging, the receiver selectively 'listens' to the harmonic frequencies that were generated as the sound traveled through the tissue.

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

Answer: (C)

Harmonics produced by tissue as the sound travels are the key idea. In tissue harmonic imaging, the system transmits at the basic frequency but the receiver is tuned to detect the higher harmonic frequencies that tissue generates, while filtering out the fundamental. This selective listening makes the image clearer because those harmonics have shorter wavelengths, enhancing spatial resolution and contrast, and it also reduces artifacts from the near field and from side lobes. The other modes rely on different principles—Color Doppler and Pulsed Doppler use Doppler shifts to assess flow, and M-mode tracks motion along a single line for anatomy over time—so they don’t hinge on listening for tissue-generated harmonics.