​Therapeutic ultrasound has its roots in the US military, where sonar machines heated the water around the submarine so much that they were baking the marine life (fish filet, anyone?).  Today, it is another modality used to heat tissues and promote healing of wounds and fractures.  

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​​Therapeutic ultrasound uses high frequency sound waves at 0.7 to 3.3 MHz and transmits these into various tissues within the body. As the waves attenuate (aka go through) the gel and transfer into the body, thermal and non-thermal effects occur.  This is due to the reverse piezoelectric effect.  The Piezoelectric Effect says that mechanical deformation can create energy.  With ultrasound, we do the opposite of this- by using energy, we are attempting to make a mechanical change within the tissue (you rock, science).  

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​Contraindications (DON'T DO IT!): Over carotid sinus, directly over pacemaker, in area of active bleeding or infection, over malignancies, eyes or testes, on top of DVT or thrombophlebitis, directly over the heart, stellate or cervical ganglia, or other CNS tissue, nor directly over plastic joint replacements or adhesive cement.

 

​Precautions (be careful, ask more questions. When in doubt, leave it out):​ Pregnancy (don't do it around the baby), acute inflammation (careful with the settings), breast implants (they'll explode), limited sensation (as they won't be able to tell if they are getting burned) and epiphyseal plates (try to avoid those areas).​





​Thermal effects are thought to occur when the machine emits energy at a continuous duty cycle.  Some of these awesome thermal effects include: 

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Acceleration of metabolic rate, reduced pain/spasm, change in nerve conduction, increase blood circulation, & increase in soft tissue extensibility.

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The amount of temperature increase is important for various effects to take place.  According to current research:



1 degree C change: increases metabolic rate

2-3 deg °C change: reduces muscle spasm/pain & increases blood flow

>4 deg °C change: increases collagen extensibility & inhibits sympathetic activity.

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Draper et al studied how long you need to perform ultrasound at two different intensities to get the desired temperature rise of 4 deg C.  The chart to the left shows what they found.

Basically, if you want to treat someone at 1MHz (say, for a superficial target tissue), you need to make sure you treat them for at least 10 minutes to achieve appropriate tissue heating.  At 3MHz, you need to be especially careful you don't burn them!​



Non-thermal effects are thought to occur at a 20% duty cycle. These effects are caused by creation of a stable cavitation, which leads to microcurrents and acoustic streaming. In turn, this creates benefits for wound healing. Some awesome non-thermal effects include:

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Increase intracellular calcium, increase in cell permeability, promotes normal cellular function with increased fibroblast, macrophage, and mast cell activity, and increased mast cell and histamine release.



​Procedure: Put patient in a comfortable position with the target area exposed. Check area for skin breakdown and cleanliness. Put gel on skin (or on transducer head... or both if you like).  



If tissue is superficial (1-2cm), use the high frequency.

If tissue is deep (up to 5cm), use the low frequency.

If injury is acute (so you want non-thermal effects), use pulsed ultrasound by 20% duty cycle.

If it is chronic (and you want thermal effects), use continuous setting.

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The area treated should be 2 times that of the effective radiating area (ERA) of the transducer face (the ERA is shown in the picture to the left).  This stuff gets hot, so KEEP THE HEAD MOVING to prevent burns or blood stasis.  Always communicate with your patient to verify it isn't too hot to handle.  If any irritation occurs, stop the treatment.  Also a good idea to check the area afterward, to make sure everything is peachy keen. 

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Normal procedure is 5-10 minutes for 2 times the area of the ERA.



Treatment time for thermal effects is based on the type of tissue, as different tissues absorb the ultrasound waves at different rates (those that absorb more= less time needed for treatment). Check out the cool chart!

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Suggested Parameters:

 

• Pain Control: Continuous at 0.5-3.0 W/cm2, 1-3 Mhz freq, 3-10 minutes
• Dermal Ulcers: 20% duty cycle, 8-1.0 W/cm2, 3 Mhz, 5-10 minutes, Treat wound perimeter, or cover with coupling sheet, or place in water
• Tendon Injuries: .5-1.5 W/cm2, continuous, 3-5 minutes, lower intensities recommended to avoid heating acutely inflamed tissue post operatively
• Ligamentous Injuries: Low dose 0.5 – 1.0 W/cm2, pulsed US
• Fracture Healing: 0.15 W/cm2 at 20% duty cycle at 1.5 Mhz for 15-20 minutes daily
• Phonophoresis: 3 MHz, Pulsed 20% duty cycle at 0.5-0.75 W/cm2 for 5-10 minutes