What is the imaging mode called that uses the harmonic of the transmitted frequency to create the image?

• A. Doppler imaging
• B. B-mode imaging
• C. Tissue harmonics
• D. Elastography

Answer: (C)

Tissue harmonic imaging works by using the fact that ultrasound waves become nonlinear as they travel through tissue, generating frequencies that are multiples of the transmitted (fundamental) frequency. In this mode, the system transmits at the base frequency but listens for the harmonic (usually the second harmonic) and constructs the image from that signal, while largely rejecting the fundamental. This produces a crisper image with better boundary definition and reduced near-field clutter, because the harmonic signal tends to originate deeper in the tissue and has higher frequency content that improves spatial resolution. Penetration is somewhat reduced compared to using the fundamental, but the overall image quality near the transducer and in many clinical scenarios is enhanced. The other options describe different techniques—Doppler uses frequency shifts from motion, B-mode uses the fundamental for grayscale, and elastography assesses tissue stiffness—so they don’t describe the harmonic-based imaging method.