Ultrasound is a sound wave whose frequency exceeds the limit detectable by the human ear (that is, the sound cannot be perceived by people because it is located around the spectrum of 20,000 Hz).
There are several ultrasound applications. At an industrial level, it allows measuring distances or developing non-destructive tests, for example. Another very frequent use occurs in the medical field. Ultrasound is one of the most popular ultrasound-related procedures. The emission of this type of sounds directed at a body makes it possible to form an image that serves diagnostic purposes. A device known as a transducer sends the ultrasound waves towards the mass under study and then receives their echo. A computer is responsible for converting this echo into an image displayed on the screen.
Because it does not use any type of radiation, ultrasound is used to visualize the fetus that is forming in the mother’s uterus. The application of the gel on the skin helps in the correct transmission of the ultrasound. Ultrasound is also useful as an insect repellent. Some computers or cell phones are capable of reproducing an acoustic wave that annoys insects and drives them away. Species like bats and dolphins use ultrasound as a kind of radar. The phenomenon, known as echolocation , occurs when the sound waves emitted by these animals “rebound” off the objects around them and allow them to create a kind of “image”. When a liquid is subjected to ultrasound, certain cavities are generated which, once collapsed, reach temperatures of 30,000 degrees Celsius and the phenomenon called sonoluminescence occurs, during which light emission occurs. Some research attempts to show that cold fusion can occur in these cavities, a nuclear fusion reaction that takes place at temperatures well below those needed to produce a thermonuclear reaction. During a physical therapy treatment, ultrasound is used very often. Among its benefits in relation to the use of heat or cold is the fact that it does not produce any physical effect perceptible by the patient, it does not generate any immediate sensation. However, it is not a placebo: its healing effects have been scientifically proven. As for its work on the body, it uses equipment capable of transferring mechanical waves of a frequency higher than sound through a gel, which allows it to propagate and transmit energy (heat) due to the vibrations produced by the waves.
The vibrations make the cells move, improving healing and, at the same time, increasing the temperature of the region where the ultrasound is applied. However, as noted above, patients do not notice this thermal change; the reason is that there are very few heat receptors deep in the tissues. Regarding the criteria for the application of ultrasound in physiotherapeutic treatments, the time, the dimensions of the surface to be treated and the head are counted (the first of these parameters depends on the remaining two). In general, applications are made that last between 2 and 6 minutes and only during the first sessions, as the main objective is to reduce inflammation, which usually does not last more than 5 days, and contribute to fibroplasia (generation of fibrous tissue during healing), which does not exceed 3 weeks. Depending on the healing time of each patient, among other personal factors, the number of ultrasound sessions varies. On average, however, it is estimated that its use does not exceed 8 applications over 3 weeks.