Ultrasounds are acoustic vibrations that are not perceived by the human ear as their frequency is greater than 20,000 Hz. They are artificially generated by the action of the electric current, whose polarity is periodically reversed, on a quartz crystal, subjecting it, by the action of the electromagnetic field created, to successive contractions and expansions. This alternation of movements generates vibrations, which, transmitted to cellular and intercellular structures, cause collisions and generate heat [1].

The best known and most widespread application of ultrasounds in medicine is diagnostic echography, a reliable, non-invasive and very safe technique for both operators and patients. Echography is a method that allows you to obtain images of the internal organs of the human body using high-frequency ultrasound waves between 2 and 15 Megaherz by means of probes called “ultrasounds probes”. Echoes from ultrasound waves are recorded and displayed on monitors; the images, displayed in real time, show the movement of internal organs and tissues and the blood flow in the vessels. The ultrasounds frequency is chosen keeping in mind that higher frequencies have greater resolving power of the image, but penetrate less deeply into the subject; lower frequency waves are more penetrating. During the exam the probe is kept in direct contact with the patient’s skin with the interposition of a special gel that allows ultrasound to penetrate the anatomical segment to be analyzed [2-5].

The echography allows the visualization of the internal organs, showing position, conformation, dimensions: the superficial structures like muscles, tendons, breast, thyroid, parathyroid are exposed to high frequency ultrasound, 7-18 Mhz, to obtain a better resolution; most internal organs such as liver, kidneys are exposed to low frequency ultrasound, 1-6 MHz, which have a greater penetrating power. High contrast echography is used for the characterization of the formation of metastases, for the characterization of lesions, including the detection of stenosis, aneurysms, fistulas, in case of renal failure or both cystic and solid renal tumors , and is performed by injection of an inert gas, generally sulfur hexafluoride, intravenously. The microbubbles of gases formed increase the echogenicity of the blood allowing the visualization of the microcirculation: this method is particularly suitable for the diagnosis of liver pathologies in which alterations of the parenchyma are visualized by the formation of nodules, very vascularized, compared to a healthy parenchyma. This method has a high diagnostic sensitivity that allows to detect even early stage tumors or small tumors with a diameter of less than 10 mm [6-9].

Elastography, a technique complementary to echography, allows you to evaluate the degree of elasticity of the tissues in a non-invasive way by means of an external electronic stimulation that simulates manual palpation. Many pathologies cause a change in tissue elasticity: benign tissues have elasticity, while rigid tissues are the expression of tumors or chronic inflammatory processes [10]. With this method it is possible to highlight the inflammatory pathologies of the gastrointestinal tract and Crohn’s disease [11,12]; the elastography finds application in the differential diagnosis between benign or malignant nodules in superficial organs such as breast, thyroid, lymph nodes, prostate; it is useful for assessing liver stiffness in the case of liver fibrosis and other liver diseases [13,14].

Echocardiography is the application of ultrasounds to evaluate the size, shape and movement of cardiac structures; it allows to obtain information on the contractility of the heart, on the morphology of its valves and on the flow of blood in its cavities, both at rest and after fisic exercises or taking a drug. This technique is of great importance in the intensive care unit for patients in shock, allowing the accurate measurement of different hemodynamic variables in a non-invasive way. The doctor can evaluate different aspects of shock states, such as cardiac output and fluid reactivity, myocardial contractility, intracavitary pressures, ventricular interactions and the echocardiography is therefore an important diagnostic tool for the treatment of patients with pain chest and respiratory failure. This test proves very useful for understanding the origin of chest pain, a symptom often reported by patients. In fact, if the coronary arteries are stenotic, the blood flow under stress conditions is insufficient and the cardiac musculature contracts to a lesser extent, asynchronously and the beat can also stop. Contraction anomalies can be highlighted already by an electrocardiogram impaired, and are the first sign of heart pain. Echocardiography is used to evaluate the prognosis on people after a heart attack event, to understand the heart condition and, for people with coronary artery disease, to evaluate the advisability of a revascularization intervention by bypass or angioplasty [15-17].

Endoscopic echography is an invasive diagnostic procedure, which integrates the ultrasound system with classical endoscopy, allowing you to study the pathologies of the digestive system, biliary tract and pancreas. With this, it is possible to perform an echography of the abdominal organs by applying a small ultrasound probe on the tip of the endoscope. This examination has a power of resolution superior to other methods in evaluating the wall of the hollow organs of the upper and lower digestive system, in the study of mediastinal lymph nodes and pancreatic parenchyma; it also allows needle biopsies of pancreatic and lymph node lesions [18-21].

The penetration capacity of ultrasounds through the tissues of the human body both at the surface and at the depth, inversely proportional to the frequency of the waves, has determined their use not only in diagnostics, but also to treat orthopedic and muscle diseases, in physiotherapy, and in aesthetic medicine [22,23]. Their activity is carried out with different actions: chemical, thermal and on blood circulation; the choice of the type of frequency varies depending on the organ and tissue to be treated and depending on the therapy required [24]. The main therapeutic effects concern the resolution of muscle contractures which benefit from the thermal effect and micro massage; fibrolytic action on the collagen of fibrous tissues which is of particular importance for the treatment of traumatic hematomas and scar tissues; action on calcifications and skin thickenings [25,26].

The ultrasounds treatment can be performed in two different ways. The direct method consists in the application of a conductive gel on the head of the device which is then placed directly on the area to be treated by performing a slow rotary movement. The indirect method is performed by immersing the area to be treated and the head of the appliance in a basin containing water at 37°C, being the areas to be treated with an irregular shape such as elbows, hands, malleoli, difficult to treat directly. The distance between the head and the application area is 2 cm and the duration of the application varies from 10 to 15 minutes depending on the method and frequency used. In addition to relieving pain, this therapy is antiinflammatory, biostimulating at the cellular level and decontracting on the muscles.

Ultrasounds find applications in ablative therapy, a microsurgery technique that uses high intensity sound waves to necrotize cancer cells present in some organs such as kidneys, prostate, and eliminate them. This ability to release energy in a specific area, better known as shock wave therapy, is used to reduce the size of kidney stones, lithotripsy, or to produce a rise in temperature such as to necrotize the tumor tissues and destroy them as in the case of prostate cancer or uterine fibroids. The patient undergoes anesthesia and the ultrasounds reach the tumor by means of an electrode which destroys the cancerous cells; it is also possible during the surgery to take a sample of organ tissue to perform a biopsy and better understand the type of tumor [27-29].

The lymphatic system is essential for the survival of the body, being the main seat of the interaction between foreign substances that attack the body and the defense mechanisms that are put in place to counter this aggression. The enlargement of a lymph node can be due to inflammation, infection or tumor and only through a biopsy examination can a certain diagnosis be made. Thyroid needle aspiration is a minimally invasive method that is performed by means of a very thin needle connected to a syringe, under echography guidance, and allows only the removal of cells contained in the nodule without affecting the tissue.

The echographic guide allows you to take cells even from clinically non-palpable nodules and to choose, based on the echographic characteristics, on which part of the nodule to perform the sampling for cytological analysis. For biopsy, however, a spring-activated larger gauge needle, called the core needle, is used and the tissue sample is subjected to histological analysis for tumor diagnosis [30].

The aspiration of the transbronchial needle guided by endoscopic echography is very useful in the diagnosis of malignant pleural mesothelioma being based essentially on the analysis of pleural samples [31,32]. The execution procedure is similar to that of a normal endoscopy: in this case, however, the patient is sedated with benzodiazepines and the duration of the examination is slightly longer; if it is then integrated with the Doppler mode, the evaluation can also be extended to the main blood vessels. With the help of echography, a synovial tissue biopsy can also be performed for better understand the pathogenesis of inflammatory arthropathies and evaluate the appropriate treatments [33].

Echography is the most useful, safest, most precise imaging technique for guiding needles in the organs and in the abdominal and pelvic masses, allowing adequate tissue sampling, with constant monitoring over time for biopsy, without patients suffer from consequences [34,35].

Ultrasounds play an important role in medicine for their ability to provide both kinetic and thermal energy. Similarly to sound waves they spread in materials, including biological tissues, without making transformations, but with different intensity depending on the medium they pass through. The attenuation of the intensity while they moving through the human body is linked to the different density of the tissues, bone, fat, muscle, which an ultrasounds beam encounters in our body. The use of ultrasounds in the medical field is very wide: from use to diagnose diseases or the origin of a disorder: echography, flowmetry, doppler; to therapy: ablative surgery using high intensity focused ultrasounds, lithotripsy, used for the treatment of urinary stones, physical therapy used for body rehabilitation.

The most widespread and best-known application of ultrasounds in medicine is diagnostic echography, a method that is risk-free for operators and extremely safe and reliable for patients.

Some therapeutic applications of ultrasounds exploit the possibility of releasing energy at a specific point, as in the case of lithotripsy which is used to reduce the size of kidney stones. In the case of ablative surgery it is possible to focus the ultrasounds in an area to produce a thermal rise such as to necrotize the tumor tissues and destroy them. Using a less intense heating on the tissues,the ultrasounds are used in physiotherapy to repair bone fractures and lesions of tendons or for the treatment of scars.

The author declares no conflict of interest.