Ultrasound
(US) is a mechanical (not electrical) form of energy, and therefore, strictly
speaking, it is not really electrotherapy at all, but it falls into
electrotherapy. Ultrasound is applied using the head of an ultrasound probe
that is placed in direct contact with your skin via a transmission coupling
gel. this probe is having electricity as a basic source of energy, which is being converted into mechanical forms into sound or we can say waveforms energy. The sound energy is known as mechanical vibration at increasing
frequencies.
The normal range of human sound is from 16 Hz to something close
to 15-20,000 Hz (in kids and young adults). Beyond that upper limit, the
ultrasound is known as the mechanical vibration. Usually, the frequencies used
in therapy vary from 1.0 and 3.0 MHz (1 MHz= 1 million cycles per second).
Sound
waves are longitudinal waves consisting of compression and rarefaction zones.
Particles of material will oscillate about a fixed point when exposed to a
sound wave, rather than move along with the wave itself. As the energy is
passed on to the material within the sound wave it will cause the particles of
that material to oscillate. Clearly, any increase in molecular vibration in the
tissue can result in heat generation, and ultrasound can be used to produce
tissue thermal changes, although current therapy usage is not focused on this
phenomenon.
In
addition to thermal modifications, tissue vibration tends to have effects that
are generally considered to be non-thermal in nature, but, as with other
modalities (e.g. Pulsed Shortwave), however small, there must be a thermal
component. As the US wave passes through a substance (the tissues), the wave's
energy levels will decrease when energy is transferred to the material.
Waves in Ultrasound
Ultrasound
waveform with compression and rarefaction,
- FREQUENCY, the number of times a particle experiences a complete compression/rarefaction cycle in 1 second. Typically 1 or 3 MHz.
- WAVELENGTH, the distance between two equivalent points on the waveform in the particular medium. In an ‘average tissue,’ the wavelength at 1MHz would be 1.5mm and at 3 MHz would be 0.5 mm.
- VELOCITY, the velocity at which the wave (disturbance) travels through the medium. In a saline solution, the velocity of the US is approximately 1500 m sec-1 compared with approximately 350 m sec-1 in the air (sound waves can travel more rapidly in a more dense medium). The velocity of the US in most tissues is thought to be similar to that in saline.
These
three factors are related to each other but not constant for all tissue types.
Most commonly, average figures are used to represent US passage through the
tissues. Typical US therapeutic equipment frequencies are 1 and 3 MHz although
some devices produce additional frequencies (e.g. 0.75 and 1.5 MHz) and the'
Longwave' ultrasound equipment works at several 10's of kHz (typically
40-50,000Hz–a frequency far lower than' standard US' but still beyond human
hearing range.
CONTRAINDICATIONS:
- Do not expose the embryo or the fetus to clinical ultrasound levels by treating the uterus during pregnancy
- with malignancy (the history of malignancy is NOT a contraindication – DO NOT treat tissue that is or is considered malignant)
- The tissue in which bleeding occurs or could reasonably be expected (usually within 4-6 hours of injury but may be longer in some conditions).
PRECAUTIONS taken during US care are,
- Always use the lowest intensity generating a therapeutic response.
- Ensure that the applicator is moved throughout the procedure (speed and direction not an issue).
- Ensure that the patient is aware of the nature of the procedure and its anticipated result If a thermal dosage is intended.
- Ensure that any contraindications that exist are considered Caution is recommended in the vicinity of a cardiac pacemaker or other electronic devices that have been implanted. Continuous ultrasonography over metal implants is considered unwise.
Therapeutic Ultrasound & Tissue Healing
One of the
therapeutic effects concerning tissue healing for which ultrasound was
being used. It is proposed that U.S. application to damaged tissues would
accelerate the rate of healing and enhance the quality of repair among other
things. The following information is intended to provide a summary of some of
the essential research in this area along with some possible mechanisms by
which US treatments can achieve these changes.
It is not
intended to be a complete explanation of these phenomena or a comprehensive
review of the current literature. It may, none the less, provide some useful
basic information for clinical application.
The
therapeutic effects of US are generally divided into:
THERMAL
& NON‑THERMAL.
In thermal
mode, the US will be most efficient in heating the dense collagenous tissues
and will need a relatively high intensity to achieve this effect, ideally in
continuous mode.
Non-thermal
US non-thermal effects are now attributed primarily to a combination of
CAVITATION and ACOUSTIC STREAMING. Little evidence appears to support the MICROMASSAGE, although it sounds rather appealing.
In its
The simplest sense, CAVITATION refers to the creation of gas-filled voids within
the tissues & body fluids. There is STABLE & UNSTABLE
cavitation which have very different effects.
STABLE CAVITATION does appear to
be taking place at US therapeutic doses. This is gas bubbles forming &
growing by accumulating dissolved gas in the medium. They're getting approx.1000
Cycles to get to its maximum size. The' cavity' works to improve the trend of
acoustic streaming & as such would seem to be of benefit.
ACOUSTIC
STREAMING is portrayed as a little scale eddying of liquids almost a vibrating
structure, for example, cell layers and the outside of stable cavitation gas
bubble This wonder is known to influence dissemination rates and film
porousness.
MICROMASSAGE
is a mechanical impact which seems to have been ascribed less significance as
of late. Generally, the sound wave going through the medium is professed to
make particles vibrate, potentially improving tissue liquid exchange and
influencing tissue portability. There is close to nothing if any hard proof
for this regularly referred to the guideline.
How Much safer is it?
Ultrasound treatment is a safe and harmless method of
treatment. However, there are situations when therapy with ultrasound is
not appropriate. Your professional physiotherapist will make sure it's the
right approach for you and will discuss it with you. Some reasons where it
certainly would not be used are; parts of the body with cancer, in pregnant
women and in babies. Studies have shown that ultrasound therapy in different
soft tissue conditions can enhance symptoms and healing but the quality of the
evidence is often low.
Ultrasound-treated typical injuries are Bursitis, Tendonitis, Muscle Strain and tears, Osteoarthritis, Ligament and tendon injuries.
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