What type of sound has frequencies greater than 20,000 Hz and is utilized in medical imaging?

Ultrasound refers to sound waves with frequencies that exceed 20,000 Hz, which is beyond the upper limit of human hearing. This type of sound waves is particularly useful in medical imaging applications, such as ultrasound scans.

In medical imaging, ultrasound is employed to visualize internal structures of the body, such as organs and developing fetuses. The high-frequency sound waves generated by the ultrasound machine travel through the body and reflect off different tissues. The echoes are then captured and translated into images that can be interpreted by healthcare professionals. This non-invasive technique offers a safe way to obtain real-time imaging without harmful effects, making it a preferred choice in many diagnostic situations.

The other types of sound mentioned do not fit this context. Infrasound consists of frequencies below 20 Hz, which are not used for imaging. Audio sound relates to the range audible to humans (approximately 20 Hz to 20,000 Hz) and therefore does not expand into the ultrasound range. Subsonic sound also pertains to sound waves below human hearing capabilities and is not used in medical applications like ultrasound. Hence, ultrasound is the only correct answer here, as it encompasses the high frequencies required for effective medical imaging.