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An ultrasound is defined as an acoustic vibration with frequencies above the audible limit (that is, higher than 20,000 Hz).
Ultrasounds for therapeutic use were introduced and studied systematically in the period following the Second World War. In Italy, their use spread immediately and many of our scholars contributed considerably to experimental and clinical research in this field. Ultrasounds are diffused under the form of compression-decompression waves, with a to-and-fro movement of the particles of the transmission media, parallel to the direction of the propagation waves.
Ultrasounds are produced artificially through a piezoelectric effect, exploiting either a quartz or a disc of ceramic material. By applying electrical charges to the faces of a quartz lamina the crystal is compressed; by inverting the direction expansion is obtained. By subjecting the quartz to an alternated electrical field it is therefore possible to obtain alternating compression and expansion of the crystal and the production of a series of vibrations used for therapy. When ultrasonic waves travel through the tissue, they lose a certain amount of their energy; this process is known as attenuation. In the tissues, attenuation is caused by several mechanisms; absorption, ray divergence and deflection. Absorption is the main cause of ultrasound attenuation. Ultrasound energy is absorbed by the tissues and then converted into heat. For most tissues, attenuation increases when frequency increases so that a 1.0 MHz signal would penetrate more deeply than a 3.0 MHz signal due to lower attenuation in the tissue. Divergence of the light is the rate that the ray is dispersed from the transducer. Divergence of the ray decreases as the frequency increases and therefore, a higher frequency signal has a more focused ray. Deflection includes the process of reflection, refraction and dispersion. An ultrasound therapy appliance consists primarily in an alternated current generator (typically 1 MHz and/or 3 MHz) that, via a cable, powers an emitting treatment head in which a transducer is inserted (a piezoelectric disc or quartz lamina) that converts electrical energy into mechanical energy (acoustic vibrations) then transmitted to the tissues.
Available on the following products
Programmes Therapeutic Ultrasound
