1. (Abstract Noun) An imaging technique that uses high frequency sound waves to visualize the image of an internal body structure or a developing fetus; underwater surfaces, boundaries, objects, and currents.Ultrasonography is also called sonography, diagnostic sonography, and echocardiography when it is used to image the heart.Sound waves are a form of energy called longitudinal pressure waves that result when molecules are pushed together and then become rarified (less dense). The molecules through which the wave passes are not transported by the wave; rather, they vibrate back and forth around a neutral position. The number of times that a molecule moves through a compression and rarification cycle in one second is called the frequency of the wave. The unit of the frequency of a sound wave is the Hertz (Hz). Frequencies between about 20 Hz and 20,000 Hz are audible to the human ear and the greater the frequency, the higher a sound wave sounds. Frequencies above 20,000 Hz are called ultrasonic and the human ear cannot detect these sound waves. The frequencies of sound waves used in ultrasonography are between about one million and 15 million Hz (or one and 15 MHz).

English: ultrasonography,
Assamese: আল্ট্ৰাচাউণ্ড