What is an Ultrasound? Those interested in sonography will benefit from knowing in greater detail how ultrasound works.
The term itself refers to sound wave frequencies that are beyond 20,000 hertz, which is considered the upper limit of hearing in humans. Medical sonography is the transmission of high-frequency sound waves into the body and the conversion of the resulting reflections or echoes into images of internal structures within the body. The same underlying principle, echolocation, enables certain species such as bats and dolphins to navigate in dark environments by detecting reflected sound waves rather than by relying on vision. While animals use frequencies between 20 and 100 kilohertz, ultrasound technicians use much higher frequencies that vary between one and 20 megahertz.
Frequencies near the lower end of the medical ultrasound range do not provide sharp resolution on images, but they do penetrate deeply into the body and can therefore provide successful imaging of abdominal organs. Many abdominal conditions and diseases that would otherwise be hard to detect are accurately diagnosed using ultrasound. These include gallstones, liver cancer, fatty liver, enlarged spleen and growths or cysts in the pancreas, liver or spleen. Frequencies at the upper end offer less penetration because the body more readily absorbs these sound waves before they travel very far inside. Higher frequencies are thus well suited to creating sharp images of more superficial areas of the body such as the eye and neck.
When ultrasound frequencies enter the body, they encounter tissues of various densities such blood, bone or different organs. At the boundaries between these different tissue densities, some sound waves continue to penetrate while others are reflected back. An ultrasound machine uses the speed of sound in tissue and the time each echo takes to return to calculate distances between these boundaries and map them into images of the inner body.