UltraSound (US)
High-frequency ultrasound imaging works by generating harmless sound waves in tissue through transducers. As the sound waves travel through the tissue, they are partially reflected and received again by the transducer. A 2D, 3D or even 4D image can then be calculated from this echo. Micro-ultrasound was specially developed by VisualSonics for examinations on small animals, with frequencies between 15 MHz and 80 MHz. In comparison, clinical ultrasound systems operate in a range of 3-15 MHz.
- Advantages:
Micro-ultrasound is the only true real-time imaging method with up to 1000 images per second. It can be used to study high-speed events such as blood flow and cardiac function in mice. Resolutions of up to 30 µm are possible. This allows the imaging of very small vessels in tumor angiogenesis. To visualize capillaries, this resolution can be increased to 3-5 µm by injecting microbubbles as a contrast agent. To visualize molecular correlations, it is possible to couple such bubbles with specific markers. - Limitations:
Unlike micro-MRI, micro-CT, micro-PET and micro-SPECT, ultrasound only has a limited penetration depth. As the frequency increases, the maximum depth imaging decreases. Typically, ultrasound can visualize tissue up to 3 cm under the skin, which is sufficient for rats and mice. The quality of the ultrasound examination will usually depend heavily on the experience and skill of the examiner.