Low-frequency vibrations, typically in the ultrasound range (2 to 20 megahertz), are used in ultrasound imaging, also known as sonography, for several reasons:
Penetration: Low-frequency ultrasound waves can penetrate deep into the body tissues. They have longer wavelengths, which allows them to travel through soft tissues, muscles, and organs more effectively. This makes them suitable for imaging structures that are located deeper within the body, such as organs like the liver, kidneys, or uterus.
Attenuation: Ultrasound waves tend to attenuate, or weaken, as they pass through different tissues. Higher frequency ultrasound waves are more easily absorbed and scattered by tissues, resulting in reduced penetration depth. Low-frequency ultrasound waves experience less attenuation, allowing them to maintain their energy and travel deeper into the body.
Image resolution: While higher frequency ultrasound waves provide better image resolution for superficial structures, low-frequency ultrasound waves sacrifice some resolution for increased penetration. This trade-off is necessary to visualize structures that are located deeper in the body. Low-frequency vibrations allow sonographers to obtain images of organs and structures that might otherwise be difficult to visualize with higher frequency ultrasound waves.
Abdominal imaging: In particular, low-frequency ultrasound waves are commonly used for abdominal imaging. The abdomen contains several organs, such as the liver, spleen, and pancreas, which are relatively deep-seated. Using lower frequencies helps to overcome the challenges of imaging through the layers of the abdominal wall and the presence of gas or fat, enabling clearer visualization of these organs.
It's worth noting that the choice of ultrasound frequency depends on the specific imaging requirements, target organ, and the depth at which the structures of interest are located. Higher frequency ultrasound waves are used for more superficial imaging, such as imaging blood vessels near the skin surface or the thyroid gland. The selection of frequency is optimized based on the desired balance between penetration depth and image resolution.