How does ultrasound work for mice? - briefly
Ultrasound imaging for mice uses high‑frequency sound waves (30–70 MHz) that penetrate tissue, reflect off anatomical boundaries, and are detected by a transducer to generate real‑time visual representations. The high frequency provides sub‑millimeter resolution, enabling detailed observation of small‑scale structures in live rodents.
How does ultrasound work for mice? - in detail
Ultrasound generates mechanical waves at frequencies above 20 MHz that propagate through biological tissue with minimal attenuation. The wave’s wavelength, defined by the ratio of sound speed in tissue (~1540 m·s⁻¹) to frequency, determines spatial resolution; higher frequencies produce finer detail but reduce penetration depth, a trade‑off suited to the small size of a mouse.
A transducer converts electrical energy into acoustic pressure using a piezoelectric element. When a voltage pulse is applied, the crystal expands, emitting a short burst of sound. The same crystal detects returning echoes; the received signal is amplified, digitized, and processed to reconstruct an image. Precise timing of emission and reception yields depth information through the speed‑of‑sound calculation.
In mouse tissue, acoustic energy encounters heterogeneous structures that cause reflection, refraction, and scattering. Absorption converts part of the energy into heat, while rapid pressure changes can induce cavitation—formation and collapse of microbubbles—if the mechanical index exceeds safe thresholds. Both thermal and mechanical effects are monitored to avoid tissue damage.
Typical experimental setups include a small animal platform with a temperature‑controlled stage, a thin layer of acoustic coupling gel, and a stereotaxic holder to maintain consistent orientation. Imaging modes employed are:
- B‑mode (brightness) for structural visualization.
- Doppler (color or spectral) for blood flow quantification.
- High‑frequency micro‑sonography for detailed organ morphology.
Data acquisition runs at frame rates of 200–500 fps, delivering axial resolution of 30–50 µm and lateral resolution of 50–100 µm. Post‑processing extracts measurements such as ventricular dimensions, vessel diameters, or tumor volume, often using automated segmentation algorithms.
Safety parameters are expressed as Mechanical Index (MI) and Thermal Index (TI). Recommended limits for rodent studies are MI ≤ 0.5 and TI ≤ 1.0, ensuring that acoustic pressure and temperature rise remain within physiological tolerances. Continuous monitoring of these indices prevents inadvertent injury.
Research applications include:
- Cardiac function assessment—ejection fraction, wall motion.
- Developmental studies—embryonic heart and brain imaging.
- Oncology—tumor growth tracking, vascularization analysis.
- Targeted therapy—ultrasound‑mediated drug or gene delivery via microbubble cavitation.
The combination of high frequency, precise transducer control, and rigorous safety monitoring enables reliable, non‑invasive interrogation of mouse physiology and pathology.