Which method filters out the transmitted frequency and leaves harmonic frequencies for display?

Which method filters out the transmitted frequency and leaves harmonic frequencies for display?

• A. Harmonic imaging
• B. Doppler imaging
• C. Pulse inversion harmonics
• D. Compound imaging

Answer: (D)

Harmonic imaging relies on the fact that tissue generates frequencies at multiples of the transmitted sound due to nonlinear propagation. The system then filters out the fundamental (transmitted) frequency and displays only the harmonic frequencies, which enhances contrast and reduces clutter from the near field. A common way to strengthen the harmonic signal is pulse inversion, where pairs of pulses with opposite phase cancel the linear response while preserving the nonlinear harmonic response, making harmonics easier to visualize. Compound imaging, by contrast, combines data from multiple angles to reduce speckle and improve resolution, but it does not inherently filter out the transmitted frequency to isolate harmonics. So the method described is harmonic imaging, often implemented with techniques like pulse inversion to boost the harmonic signal.

Harmonic imaging relies on the fact that tissue generates frequencies at multiples of the transmitted sound due to nonlinear propagation. The system then filters out the fundamental (transmitted) frequency and displays only the harmonic frequencies, which enhances contrast and reduces clutter from the near field. A common way to strengthen the harmonic signal is pulse inversion, where pairs of pulses with opposite phase cancel the linear response while preserving the nonlinear harmonic response, making harmonics easier to visualize. Compound imaging, by contrast, combines data from multiple angles to reduce speckle and improve resolution, but it does not inherently filter out the transmitted frequency to isolate harmonics. So the method described is harmonic imaging, often implemented with techniques like pulse inversion to boost the harmonic signal.