Tissue Characterization by Low-Frequency Acoustic Waves Generated by a Single High-Frequency Focused Ultrasound Beam

Area of Science:

• Biomedical Engineering
• Medical Imaging
• Acoustics

Background:

• Mechanical properties of biological tissues are crucial indicators of pathologic processes.
• Conventional ultrasound methods for inducing and detecting kilohertz-frequency mechanical vibrations often require complex, high-power systems.
• Existing techniques face limitations in non-invasively assessing tissue mechanical characteristics.

Purpose of the Study:

• To propose and demonstrate a novel ultrasound-based method for observing kilohertz-frequency mechanical responses in biological tissues.
• To establish a correlation between acoustic signals and microstructural properties of bone.
• To evaluate the technique's efficacy in soft tissue stiffness measurements and imaging challenging inclusions.

Main Methods:

• Irradiation of mouse femoral bones (healthy and osteoporotic) with short, focused megahertz-frequency acoustic radiation pulses (3.1 MHz, 15 μs).
• Acquisition of low-frequency acoustic responses (1-100 kHz) using a hydrophone.
• Micro-computed tomography (μCT) to determine bone structural parameters (porosity, trabecular number, etc.).
• Assessment of soft tissue stiffness using a phantom with varying densities and Young's moduli.

Main Results:

• A strong correlation was identified between spectral maps of acquired acoustic signals and μCT data of bone structure.
• The novel technique successfully imaged inclusions in a tissue-mimicking phantom that were undetectable by conventional B-mode ultrasound.
• Demonstrated good image contrast for soft tissue stiffness variations.

Conclusions:

• The proposed method utilizing megahertz-frequency acoustic radiation bursts provides a simpler and effective approach for analyzing kilohertz-frequency mechanical responses in biological tissues.
• This technique shows promise for non-invasive assessment of bone properties and soft tissue characterization.
• The findings suggest a potential advancement in ultrasound-based diagnostic tools for various medical applications.