Ultrasound is high frequency sound which is not detectable by human ear. Ultrasound has high frequency above 20000MHz (Megahertz). Human ear can hear up to 16000 MHz, as our ear membrane cannot resonate and move so quick to transfer sound vibrations further inside the ear. Cats, Dogs, Horses, Dolphins, Whales and Bats are among animals that can hear Ultrasound and use it in communication or image creation
Ultrasound is not similar to X-rays or other radiation techniques, so no absorbed radiation dose will apply to human body. It is essentially just a sound wave.
Diagnostic Ultrasound has been widely used in clinical medicine for few decades with no proven ill effects to human body or foetuses (unborn babies). However, if used imprudently, diagnostic ultrasound is capable of causing harmful effects.
Diagnostic Ultrasound examinations should only be performed by competent personnel who are trained and updated in safety matters. It is also important that ultrasound devices are appropriately maintained.
Ultrasound produces heating, pressure changes and mechanical disturbances in tissue. Diagnostic levels of ultrasound can produce temperature rises that are hazardous to sensitive organs and the embryo/foetus. Biological effect of non-thermal origin have been reported in animals but to date, no such effects have been demonstrated in humans, except when a microbubble contrast agent is present.