Ultrasound is sound with a frequency greater than the upper limit of human hearing, approximately 20 kilohertz/20,000 Hertz. Some animals, such as dogs, dolphins, bats, and mice have an upper limit that is greater than that of the human ear and thus can hear ultrasound.
Ultrasound has industrial and medical applications. Medical Sonography (also called ultrasonography) can visualize muscle and soft tissue, making them useful for scanning the organs, and obstetric sonography is commonly used during pregnancy. The use of microbubble contrast media in medical sonography to improve ultrasound signal backscatter is known as contrast enhanced ultrasound. This technique is currently used in echocardiography, and may have future applications in molecular imaging and drug delivery.
Diagnostic Sonography is often incorrectly referred to as "ultrasound"; however, ultrasound is a term of physics meaning acoustic energy with a frequency above human hearing. To call a sonogram an "ultrasound" is analogous to calling a photograph a "light". There are other uses of ultrasound in medicine that are not imaging or sonography. These include heating tissue in physical therapy, cleaning teeth in dental hygiene. Ultrasound is also used by iron workers for nondestructive testing of metals and welds, and jewelers use ultrasound to clean rings and watches. These other uses are not included in the definition of Diagnostic Sonography.
In medical ultrasonography, a sound wave is produced by creating short, strong pulses of sound from a phased array of piezoelectric transducers. The sound wave, which is able to penetrate bodily fluids, but not solids, bounces off the solid object and returns to the Transducer, this return is an echo.
The return of the sound wave to the Transducer results in the same process that it took to send the sound wave, just in reverse. The return sound wave vibrates the Transducer and turns that vibration into an electrical pulse that is sent through the probe and into sonographers computer where it can be interpreted and transformed into a digital image.