1. Therapeutic UltrasoundBy
Beverly Nelson

2. Purpose of Presentation
To provide a basic foundation of the physics involved in therapeutic ultrasound(US)
Analyse the transmission of sound energy in biologic tissue
Explain the thermal and non thermal effects of US
Choose the most appropriate and clinically effective uses for US

3. What is ultrasound ?
Sound waves with a Frequency above 20,000 Hz

4. What is Frequency ?
The number of oscillations a molecule undergoes in one second defines the frequency of sound waves.
Frequency is expressed in Hertz (Hz)
1MHz – deep penetration/deep heating/ 1-5cm
3MHz– Superficial penetration/superficial heating/1-3cm

5. Generation of ultrasound
Ultrasound can be generated with special crystals that possess the property of piezoelectricity and are able to vibrate very rapidly
There are 2 forms of piezoelectric effect, direct and indirect or reverse

6. Piezoelectric property
The direct piezoelectric effect is the generation of an electric voltage across a crystal when the crystal is compressed
The reverse piezoelectric effect is the contraction or expansion of a crystal to a voltage applied across its face. Thus ,the reverse piezoelectric effect is used to generate ultrasound at a desired frequency

7. Biologic effects of Ultrasound
2 classifications;
(1) Thermal effects
(2) non thermal effects-

8. Thermal effects
Increase temperature by 1 ̊C , increases metabolism & healing
2- 3 ̊C decreases pain and muscle spasm
4 ̊C -- greater increase in extensibility of collagen and decreases joint stiffness
Greater than 4 ̊C temperature elevation, damage the tissues

9. Non thermal effects Results from cavitation and microstreaming
Modifies the inflammatory response
Enhance the healing of injured tissues

10. Effective Radiating Area(ERA)
The total area of the surface of the Transducer that actually produces the sound wave

11. Pulsed versus Continuous wave
When continuous wave ultrasound is used, the sound intensity remains constant throughout the treatment
When pulsed ultrasound wave is used , the intensity is periodically interrupted with no ultrasound energy being produced during the off period.

12. Duty cycle Is selected according to treatment goal
To increase tissue temperature a 100% (continuous) duty cycle is used
When non thermal effects are the goal, pulsed ultrasound with a 20% or 50% duty cycle should be used

13. Attenuation
Energy contained within a sound beam decreases as it travels through the tissue

14. Intensity
The strength of the sound beam is determined by its intensity
Intensity is expressed in units of watts per square centimetre(w/cm²)
Intensities employed in PT range from 0.25w/cm² w/cm²
Higher intensities results in greater tissue temperature increase

15. Clinical implications of Ultrasound
Soft tissue healing and repairs
Scar tissue and joint contracture
Stretching of connective tissue
Absorption of calcium deposits
Bone healing
Pain reduction
Assessing stress fracture
Chronic inflammation

16. Phonophoresis
A technique in which ultrasound is used to enhance delivery of selected medication into the tissues
Most common medications used are anti-inflammatory drugs ,e.g. hydrocortisone 1% or 10% , dexamethasone

17. Treatment parameters Frequency of treatment Duty cycle Intensity
Area to be treated
Duration of Treatment
Coupling methods
Number & frequency of treatments
Moving the sound head

18. Frequency Is selected according to the depth of tissue to be treated
Tissue at a depth of 5cm- 1MHz is used
Superficial tissue to a depth of 1-2cm- 3MHz is used
Acute conditions may use low intensity pulsed US ,daily

19. Duty cycle
Selected according to the goal of treatment

20. Intensity Selected according to the goal of treatment
To increase tissue temperature, the patient should feel mild warmth within 2-3 minutes of starting application

21. Treatment area
Recommended that area to be treated be roughly twice the size of the sound head for minutes
Larger areas will need longer time
Higher intensity applied in w/cm – shorter time and vice versa

22. Duration of treatment Selected based on size of area to be treated
The ERA of the sound head
Whether thermal or non-thermal application
5 – 10 minutes duration for an area twice the size of the sound head
Little research defining the duration

23. Coupling medium
Purpose of the medium is to exclude air from the region between the patient and the transducer so that the sound waves get to the targeted area
Transfer of sound energy by conversion requires an intervening material to be a good transmitter of sound energy
Reflection is reduced at the air-tissue interface

24. Coupling medium
Should be viscous enough to act as a lubricant as the transducer moves over the surface of the skin
Should be applied to the skin surface and the transducer should be in contact with the coupling medium before the power is turned on
If the transducer is not in contact with the skin & coupling medium , the piezoelectric crystal may be damaged and the transducer can overheat

25. Coupling medium Water is an effective coupling medium
Water – soluble gels have the most desirable properties for a good coupling medium
Salts in the gel may damage the metal face of the transducer with improper cleaning

26. Moving the transducer/sound head
Due to the nonuniformity of the ultrasound beam ,energy distribution is uneven in the tissue
Potential for creating tissue- damaging “hot spots”
Moving the transducer during treatment leads to a more even distribution of the energy

27. Moving the transducer/sound head
Overlapping circular motions or longitudinal stroking pattern can be used
Slow movement of the transducer is recommended

28. Number & frequency of treatments
Depends on goals of treatment and patient’s response
An effect should be detectable within 1 to 3 treatments
If no improvement after 3 or 4 applications, US should be discontinued or the parameters adjusted

29. Contraindications & precautions
Physical Agents in Rehabilitation – Chapter 7/page 189

30. Suggested Readings
Physical Agents in Rehabilitation by Michelle H. Cameron
Thermal Agents in Rehabilitation by Susan L. Michlovitz
Therapeutic Modalities in Rehabilitation by William E.Prentice

31. Number & frequency of treatments
It is recommended that US be limited to 14 treatments.
Not documented ,scientifically

32. Method of application
Direct contact
Immersion
Bladder technique

33. Recording Ultrasound treatment
Area of the body treated
Ultrasound frequency
Ultrasound intensity
Duty cycle
Treatment duration
Technique of application
(Read documentation on page 194)