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[The second tissue harmonic signal: from physics principles to clinical application].
1Dipartimento Clinico-Sperimentale di Medicina e Farmacologia, Università degli Studi, Messina. scipione2@interfree.it
Summary
Harmonic tissue imaging utilizes nonlinear tissue properties to generate clearer ultrasound images by filtering out fundamental frequencies, reducing artifacts and improving visualization for better diagnostic accuracy.
Area of Science:
- Ultrasound physics
- Biomedical imaging technologies
Context:
- Ultrasound wave propagation in biological tissues exhibits nonlinear behavior.
- Tissue density variations affect ultrasound velocity, causing waveform distortion.
- Harmonic generation arises from nonlinear tissue properties, shifting energy from fundamental to harmonic frequencies.
Purpose:
- To explain the physical principles behind harmonic generation in ultrasound imaging.
- To elucidate how harmonic imaging enhances signal-to-noise ratio and reduces artifacts.
- To highlight the clinical utility of harmonic tissue imaging in various echocardiographic applications.
Summary:
- Second harmonic signals in ultrasound are generated by nonlinear tissue properties causing waveform distortion, not primary harmonic transmission.
- Ultrasound velocity changes with tissue density, leading to compression phases overtaking rarefaction phases and waveform distortion.
- Harmonic imaging improves signal-to-noise ratio by filtering fundamental frequencies, reducing haze and reverberations, and offers narrower beams with lower side-lobe levels.
Impact:
- Enhanced endocardial border definition improves left ventricular function assessment.
- Improved visualization aids in delineating cardiac structures like the left atrial appendage.
- Reduced artifacts and clutter facilitate accurate detection of intracardiac shunts and spontaneous echo contrast.