Ultrasounds are acoustic vibrations with a frequency higher than 20,000 Hz and therefore not perceptible to the human ear, which spread in the form of compression-decompression waves accompanied by a “return” movement of the particles that constitute the transmission medium
Applying electric charges on the faces of a quartz or ceramic material, the compression of the crystal is obtained, inverting its direction, on the contrary an expansion of the crystal is obtained (piezoelectric effect)
The succession of compressions and decompressions will determine the establishment of a series of vibrations that can be used for therapeutic purposes.
Ultrasound is therefore obtained artificially, using a physical principle
An ultrasound therapy device consists of an alternating current generator (generally from 1 MHz to 3 MHz), which feeds, through a cable, an emitting head in which a transducer is inserted, consisting precisely of a piezoelectric disk or a foil quartz, which has the task of converting electrical energy into mechanical energy, that is, into acoustic vibrations that are transmitted to the tissues.
According to the “concept of attenuation”, when ultrasound waves travel through the tissue, they lose a certain portion of their energy due to 3 mechanisms
1. Absorption (+++)
2. Divergence of the ray
The attenuation increases as the frequency increases, so a 1 MHz signal has a lower attenuation (therefore it penetrates more deeply) of a 3 MHz signal
Another physical concept applied to ultrasound is that of “divergence”, that is, the degree in which the beam disperses from the transducer; it decreases as the frequency increases, so the higher the frequency, the more focused the beam is … but also the attenuation!
The “deflation” is finally the last concept and includes in itself the processes of
The interaction between ultrasounds and biological tissues basically creates four types of effects:
the mechanical action is to be charged to the movement of the particles belonging to the tissues crossed by the ultrasonic wave. In this way, pressure variations are produced which determine a movement of liquids and an increase in membrane permeability, in addition to a tissue disruption due to the separation of the collagen fibers.
The thermal effect is related to the propagation of the ultrasonic energy within the tissues and depends on the absorption characteristics of the biological medium and on the reflection of energy; the sum of the reflected wave and of the incident wave generates a heat increase that is greater at the level of the bone tissue where about 30% of the energy is reflected;
The increase in skin temperature is therefore modest, especially if compared with other forms of diathermy, but there is good penetration and simultaneous heating at the muscular level and of the deep structures.
The chemical effect determines changes in the local pH and the permeability of the cell membrane, accompanied by molecular changes induced by the considerable accelerating forces to which the molecules of the tissues crossed by the ultrasonic wave are subjected.
The term cavitation means the ability of the ultrasound to generate, within a fluid, small bubbles of the dissolved gas, accompanied by a subsequent dimensional increase and a consequent possible explosion of the latter. This last principle has no therapeutic application in physiotherapy but rather in human aesthetic medicine
How to apply ultrasound
Direct contact mode
use of the movable head with direct massage method on the skin using the presence of a conductive gel (which eliminates the air between the head and the tissue). A slow displacement pressure of 2-3 cm per second is carried out on a total surface not exceeding 50 cm²
use of the fixed head with direct skin contact through the gel interposition maintained on site during the entire treatment
• Immersion mode
it is usually used when the area to be treated is small or irregular or so painful as to prevent direct contact with the head. The distance of the head, lowered in water together with the part to be treated, from the skin in this case must not exceed 2-3 cm
Ultrasounds find their therapeutic application in all the pathologies of the musculoskeletal system in which an antalgic, anti-inflammatory and muscle relaxant effect is sought; in particular, through ultrasound therapy it is possible to obtain:
An analgesic effect due to the thermal rise and direct action of ultrasound on sensitive nerve endings.
A vasodilatory effect, resulting from thermal elevation, which accelerates the repair of tissue damage and the resolution of inflammatory processes.
A fibrolytic action induced by the oscillation of the tissue particles produced by the ultrasounds, and which determines the disruption of the collagen fibers of the fibrotic tissues.
A muscle relaxant effect linked both to the thermal effect and to the tissue micromassage action induced by the ultrasounds.
In everyday practice the main diseases treated with ultrasound are:
- Organized hematomas and scar tissues
- Muscular contractions
- The achievable goals
- Increase extensibility of collagen to improve ROM
- Decreased spasms (contractures)
- Decreased pain (osteoarthritis)
- Increased blood flow (repair)
If we want to summarize in a simple box the parameters and the variables of an ultrasound instrument, we can say that:
In continuous mode we have the maximum thermal effect
In 20% pulsed mode we have the maximum mechanical effect
In pulsed mode at 50% we find both effects in an equivalent way
At a frequency of 1 Mhz the ultrasound reaches a depth of 3-5 cm
At a frequency of 3 Mhz the ultrasound reaches a depth of 1-3 cm
The intensity indicates the total energy radiated, expressed in Watts.
Depending on the probe used, we talk about W / cm2 to consider the amount of energy.
For example 5 W and 5 cm2 probe = 1W / cm2
It varies according to the area to be treated, depending on the concentration of soft tissues
1.5- 2 W / cm2 if moderate-abundant soft tissues
1-1.5 W / cm2 if moderate
0.5-1 W / cm2 if scarce (eg carp)
Acute inflammatory processes
Skin lesions and changes in sensitivity
The application of ultrasounds must be avoided, even at therapeutic dosages, in correspondence with the ocular globes and the gravid uterus, in order to avoid the phenomenon of cavitation.
It is not recommended for use in the presence of metal synthesis and / or joint prostheses, given their greater absorption power than the surrounding tissues, which can lead to overheating and separation due to the vibratory effect induced by u.s.
The contraindications in the case of osteoporosis do not seem to be more relevant, given that the piezoelectric effect induced by the ultrasounds could have an even positive effect on the osteogenesis.
Particular attention must be paid to the treatment of areas located near the spinal cord after laminectomy
It is necessary to avoid direct application to the cardiac area due to the possibility of interference on the conduction and the cardiac contraction itself.
Avoid direct exposure of pacemakers and other implanted equipment to possible permanent damage that may result