Author Box
Articles Categories
All Categories
Articles Resources

How Does Ultrasound Therapy Work?

April 13, 2012 | Comments: 0 | Views: 147

Ultrasound Therapy:

Definition Ultrasound; sound waves vibrating at frequencies above those that the human ear can hear, greater than 20,000cycles per second (hertz, Hz). Therapeutic ultrasound is that which is used for therapeutic (rather than diagnostic) purposes and is usually produced at 1 million cycles per second or 1 megacycle (MHz). Generally US frequency is between 0.7 and 3.3 MHz.

Introduction Ultrasound was first researched in Europe and was introduced to the United States in the early 1950`s, since this time, the use of ultrasound has grown, and it remains a very popular modality today.

Mechanism of action US is produced by a high-frequency alternating current being applied to a crystal made of quartz or a synthetic (i.e. barium titanate or lead zirconate). The current causes the crystal to bend, first in one direction and then the other, as the current alternates. This deformation of the crystal creates what is called piezoelectric energy. The vibration energy is transferred to a metal plate, usually nickel-plated brass, and then the patient's tissue. The crystal and metal plate are housed in the transducer or sound head of the unit.

Physical properties It is not transmitted through a vacuum It is transmitted poorly through gases It is transmitted best through gas-free liquids and high-density solids

The console Similar to a radio transmitter. Has an oscillator that produces electromagnetic wave at high frequencies. Transducer head Converts electromagnetic waves into sound waves. Larger transducer surface is better (7-13cm*), but small enough to maintain skin contact. Waves are emitted in a cylindrical beam perpendicular to traducer surface. Therefore hold the transducer head parallel to tissue surface. Never allow the beam to shoot straight into the air without gel or water as this may damage the crystal.

To test crystal: water on the head, turn up the intensity the water should stream.

Coupling agents Air does not conduct well, must use a coupling medium. Use a commercial gels, not mineral oil and some gels will contain substances that can promote healing such as, vit E, aloe.

Attenuation As US travels through human tissue, it gradually decreases in intensity due to attenuation. Attenuation is the result of absorption, reflection and refraction, with absorption accounting for about half of attenuation.

- Proteins are the major absorbers of US - Increase protein content increase absorption - Tissues with high water content decrease absorption (waves pass through) - Homogenous tissues decrease absorption (fat) - Heterogeneous tissues, fascia planes increase absorption e.g. bone\ periosteum, fat \ muscle, diff muscle groups. - Bone reflects waves, which meet incoming waves: resonance therefore heat production (periosteal burning) - Metal artefacts reflects waves but absorb heat therefore caution

Absorption Conversion of the mechanical energy of US into heat is expressed as an absorption coefficient and is dependent on tissue type and frequency. This coefficient is expressed in decibels/cm and is highest for tissues with the highest collagen content and increase in proportion to the US frequency.

Absorption coefficients in decibels/cm at 1 and 3 MHz Half depth The depth of tissue at which the US intensity is half its initial intensity is frequency and tissue type dependent Half depths in mm at 1 and 3 MHz

Reflection Is the redirection of an incident beam away from a reflecting surface at an angle equal and opposite to the angle of incidence. US waves are reflected at tissue interfaces with most reflection occurring where there is the greatest difference between the acoustic impedance of adjacent tissues.

There is 100% reflection of US at an air-skin interface and only a 0.1% reflection at couple medium- skin interface. In the body most reflection approx 35% occurs at soft tissue-bone interface.

Refraction The redirection of a wave at an interface When refraction occurs, the US wave enters the tissue at one angle and continues through the tissue at a different angle.

Frequency The number of compressions-rarefactions cycles per unit of time expressed as (hertz). Increasing the frequency decreases the depth of penetration. Use 1 MHz for tissue up to 5 cm deep and 3 MHz for tissue 1 to 2 cm deep.

Dosage There is no certain way of exactly calculating how much energy is absorbed in any particular tissue, the decision about dosage is a matter of judgement to some extent. This judgement must be based on the known factors governing ultrasound absorption and is based on the following:

Mode of delivery: - Continuous output Continuous delivery of US throughout the treatment period Used sub acute and chronic stages

- Pulsed output Sound on and off alternately (variable ratio) I.e. 20% or 1:5 duty cycle is on 20% of the time off 80% of the time: on for 2ms off for 8ms

When ultrasound is delivered in at pulse mode, with a 20% duty cycle or lower the heat generated during the time on is dispersed during the off time. Used more for acute and sub-acute stage where heat is not desirable. Also pulsed US has been shown to increase cellular permeability more the constant US (see below) especially at 1:5 at an intensity of 0.5-0.75 W/cm.

Power The amount of acoustic energy per unit time (Watts)

Intensity The power per unit area of the transducer head expressed in Watts/cm and is limited to 3W/cm

The intensity applied should be altered in accordance with the nature of the lesion (chronic higher than acute) tissue type (see above) lower intensities for higher absorbers.

When applying US for non-thermal effects rules of thumb, use 0.5 to 1.0 W/cm. For thermal effects when using a frequency of 1 MHz use an intensity of between 1.5 to 2.0 W/cm, at a 3MHz frequency usually an intensity of 0.5 W/cm is sufficient due to the energy being absorbed in a smaller more superficial volume of tissue. When looking to achieve thermal effects you expect the patient to feel a mild warming after 2 to 3 minutes of treatment, if this does not take place increase the intensity.

Time The amount of energy applied to the tissues and hence the effects is dependent not only the intensity but also the length of time applied. In general, treatment duration should be increased when lower intensities or lower frequencies are used.

Minimum treatment times are considered to be 1-2 min, maximum 10-15 min. It is also suggested that chronic lesions benefit from longer treatment times.

Effects of US on human tissue

Thermal effects

The friction caused by the vibration of the molecules within the patient's tissues will produce heat. Therefore US can be used as a thermal agent to increase the temperature of deep tissues on average soft tissue temperature has been shown

to increase by 0.02C per minute at 1 W/cm at 1MHz. The thermal effects are similar to thermotherapy (see thermotherapy notes) however US can heat deeper structures and can be applied more accurately then superficial heating agents. US is also selective and will heat tissues with a higher absorption coefficient (bone, tendons, ligaments, joint capsules, fascia) more than those with low coefficients (fat, muscle).

To increase heat being delivered the duration and/or intensity can be increased. Frequency will effect penetration with 3MHz will heat tissue up to 1 to 2 cm deep, whereas 1MHz will heat tissue up to 5cm

Note that with 3MHz the max temperature is higher, but the depth of penetration is lower.

Non Thermal effects

Cavitation Cavitation is the formation of tiny gas or vapour filed bubbles in the tissues as a result of ultrasound. During the compression phase bubbles are compressed and during rarefaction phase they expand.

Stable cavitation: occurs when the bubbles oscillate in size within the ultrasound pressure waves but remain intact and when associated with acoustic steaming, is considered to have therapeutic value. See below

Transient cavitation: occurs when the volume of bubble changes rapidly and than collapse causing high-pressures and temperature changes, resulting in gross tissue damage and free radical release. This happens at high intensities

Micro-streaming As a result of cavitation there is a localised, unidirectional fluid movement around the vibrating bubble. These very small fluid movements around cells called micro-streaming and are believed to play a significant role in the therapeutic effect of US by altering the permeability of cell membranes so increase the diffusion rate of ions across the membrane, e.g. Ca which act as a second messenger, may stimulate the repair process. Na, which alters electrical activity in nerves, therefore could be involved in pain relief. Also associated with increase mast cell degranulation, increase chemotactic factors, histamine release increase macrophage responsiveness and increase the rate of protein synthesis by fibroblasts. All of which is thought to enhance healing.

Acoustic streaming This is a steady circulatory flow due to radiation torque and is thought to alter cellular activity by transporting martial from one part of the US field to another.

Micro-massage The waves of compression and rarefaction may produce a form of micro-massage which could reduce oedema and break down adhesion at high intensities.

Phonophoresis Is the application of US in connection with a topical drug preparation as a couple medium as US pulsation's increase skin absorption of chemical substances i.e. counter irritants, vitamins, salicylates etc.

Pain control US is believed to control pain by altering its transition or perception or by modifying the underlying condition. Stimulation of cutaneous thermal receptors Changes in nerve conduction by thermal changes or non-thermal effects Modulation of inflammation Placebo

Warrington Chiropractic

Source: EzineArticles
Was this Helpful ?

Rate this Article

Article Tags:



Ultrasound Therapy






Sports Injury


Sure Health

Teenage rebellion is easier to tolerate in book or film form. Take a look back at some of the most well known and loved "coming of age" stories set in boarding schools.

By: Harvey McEwan l Arts & Entertainment l July 10, 2012 lViews: 445

An important thing you have to consider before working out is having a pair of great training shoes. You cannot immediately undergo any physical training wearing inappropriate footwear. If you do so,

By: Steve Hill l Recreation & Sports l July 10, 2012 lViews: 349

Granite is one natural stone that is used for several purposes from dimension stone to countertops to sculptures. The use of granite for building the temples and monuments was initiated millions

By: Steve L Patterson l Arts & Entertainment l July 10, 2012 lViews: 298

Up to 65,000 H-1B visas for new employment may be issued each fiscal year (FY) for professional workers, including medical providers. In general, a person who already has an H-1B and applies for

By: Ann Badmus l Arts & Entertainment l July 10, 2012 lViews: 308

Beside coin shooting, gold detecting or the many other things you can do with your metal detector. There is a large group of people who take their metal detector out looking for old stuff. Not just

By: Candy L Lindsey l Recreation & Sports l July 07, 2012 lViews: 293

Many people want to be writers and you may be one of them. In order to make your dream occupation a reality, you need to have a plan. You also need to work on this plan constantly. These tips from a

By: Harriet Hodgson l Writing & Speaking l July 06, 2012 lViews: 439

In our fast-paced world, we could hurt ourselves while doing even the simplest tasks. Being trained in first-aid but not having a kit around would be quite pointless. A simple first-aid kit can be

By: Greg Garnerl Health & Fitnessl April 20, 2012 lViews: 153

A walk in clinic is an important business that you may need at some point. Visit one of the clinics if you need emergency care when your doctor's office is closed.

By: A Aaronsonl Health & Fitnessl April 20, 2012 lViews: 125

Whether this is your first or fifth child, there are decisions to be made when it comes to an obstetrics office. You want to feel confident and comfortable through the entire experience.

By: Anna Woodwardl Health & Fitnessl April 20, 2012 lViews: 130

First aid is the procedure for providing immediate assistance in case of injuries or illnesses to stabilize the person till a more advanced medical help takes over treatment or until the person

By: Greg Garnerl Health & Fitnessl April 20, 2012 lViews: 156

Bloodborne pathogens are known to cause many contagious diseases including some that do not have any definitive cure, thus making them one of the biggest threats in the healthcare field. Realizing

By: Greg Garnerl Health & Fitnessl April 20, 2012 lViews: 150

I'm amazed that more trainers and gym owners don't know what motivates their clients. When asked why people come in, most give generic answers like "Oh well, most of my clients want to lose weight,

By: Curtis Mockl Health & Fitnessl April 18, 2012 lViews: 111

Discuss this Article

comments powered by Disqus