1. ULTRASOUND
Chapter 7

2. What is Ultrasound?
US is a type of sound wave that transmits energy by alternately compressing and decompressing (rarefying) material.

3. How does US transfer thermal energy?
Heat is transferred by conversion of soundwaves. Mechanical energy is converted into heat.

4. When using US energy is absorbed 2 to 5 cm
As US travels thru tissue it decreases in intensity

5. Generation of US
US is generated by applying high freq AC (plug in the wall) to the crystal in the transducer.
The crystal is made of material with piezoelectric properties .

6. The AC current causes the crystal to expand (compress molecules) and contract (molecules rarefy or spread apart)
Compression >>rarefaction = complete cycle of a soundwave (fig 7-3, p 178)

7. Ultrasound
US can produce a variety of physical effects. They can be classified as thermal and nonthermal.
Thermal Effects: caused by vibration of molecules that bounce into each other cause a release in energy and an increase in tissue temperature.

8. US
Nonthermal Effects: do not generate an increase in tissue temperature, due to less movement of molecules.
Acoustic streaming, microstreaming, and cavitation which may alter cell membrane permeability are nonthermal effects of US.

9. Cavitation (page 199)
Formation, growth, and pulsation of gas-filled bubbles caused by US.
Cavitation can be stable or unstable.

10. Microstreaming (p 200)
Micoscale eddying that takes place near any small, vibrating objects.
Microstreaming occurs around the gas bubbles set into oscillation by cavitation.

11. Acoustic Streaming (p 199)
Steady current in a fluid driven by the absorption of ultrasound waves.
The flow is larger the microstreaming and is thought to alter cellular activity by transporting material from one part of the ultrasound field to another.

12. US waves will be transmitted, absorbed , reflected or refracted.
Review terms on pp

13. Effects of Ultrasound

14. Thermal Effects
Page 179

15. Tissue Affected
Ultrasound can reach deeper tissue than superficial thermal agents
The thermal effects of US can :
Accelerate metabolic rate
Modify pain
Modify mm spasm
Alter nerve conduction velocity
Increase circulation
Increase soft tissue extensibility

16. Ultrasound will heat tissue with high ultrasound coefficients (see page 199). This would be tissue with high collagen content.
i.e. tendons, ligaments, joint capsules and fascia

17. Factors Affecting the Amount of Temperature Increase
Tissue of application
Frequency
Average intensity
Duration of application

18. Frequency Unit of measure = megahertz (MHz)
Frequency is the parameter that affects depth of penetration of US waves.
US can penetrate as deep as 5 cm.

19. Frequency
The depth of penetration if a sound wave is inversely related to frequency, therefore the lower the freq. the deeper the penetration.

20. Frequency
As the freq. increases there is more scattering of US energy and less energy is available for penetration into deeper tissue.
1 MHz will penetrate deeper than 3.3 MHz

21. Mode of Application Continuous vs. Pulsed Modes
Continuous mode – acoustic energy that flows w/o interruption
Allow for a build up of thermal energy

22. Intensity (spatial average intensity)
Intensity of US is the rate at which sound energy is applied or the strength of the acoustic energy.
Unit of measure is watts per centimeter squared (w/cm2).

23. Pulsed Mode Interrupted flow of acoustic energy.
Duty Cycle – ratio of pulse duration; on and off time of US flow

24. Pulsed Mode
The amount of “on” time will determine how much thermal energy is created.
If the duty cycle is high (i.e. 80% or 50%) some thermal energy will be generated.
If the If the duty cycle is low (i.e. 20%) no thermal energy will be generated and will result in non themal effect

25. Thermal Effects of US Can be used to increase tissue temp
Can reach deeper and heat smaller areas compared to superficial heat modalities.
Can heat tissue with high collagen content (ie. Tendon ligament, jt. Capsule, fascia)

26. Thermal Effects of US
The amount of tissue temp increase will depend on the type of tissue being heated, frequency, intensity and duration of US.

27. What are the physiological effects from thermal US?
Metabolic rate
Pain
Mm spasm/tone
Nerve conduction
Circulation
Soft tissue extensibility

28. Nonthermal Effects of US
Micromassage – due to microstreaming (pg 192) and acoustic streaming(pg 192).
Increased cell permeability – US causes a “stirring” effect in fluid near biomembrane which can increase the rate of ion diffusion across the membrane.
Cavitation (pg 192)

29. Methods of Application
Coupling agent (gel, mineral oil, glycerin, degassed water) must be used to enhance transmission of US waves.
Direct Contact on area of treatment.

30. Immersion – body part of Rx can be immersed in water
Immersion – body part of Rx can be immersed in water. Useful in treating superficial areas, small irregular surfaces, sensitive areas and wounds (no direct contact).

31. Clinical Applications of US Page 181
Soft Tissue Shortening
Pain Control
Dermal Ulcers
Surgical Skin Incisions
Tendon Repairs
Resorption of Ca+ Deposits

32. Clinical Applications of US
Bone Fractures
Carpal Tunnel Syndrome (CTS)
Phonophoresis
Plantar Warts
Herpes Zoster Infection

33. How Do I Decide What Parameters to Use?
Paramters for US depend on desired effect (thermal vs non-thermal), state on condition (acute vs chronic), Size of treatment area, type of target tissue, initial Rx vs follow up Rx.

34. Considerations for Duration of US Rx
The 1st Rx is generally shorter in duration compared to follow up Rx. Once response is assessed then time can be increased.
Acute conditions require less time.
Smaller areas require less time

35. Effective Radiating Area (ERA) of the sound head can be used to determine US duration.
ERA is found in the manual of the US machine.
Rx time = 2 x ERA
If area is 20 cm2 and the ERA is 10cm2 the Rx time would be 5 – 10 minutes

36. Considerations for Intensity of US Rx
Intensity is documented in W/cm2
Set according to Rx goal
Superficial lesions should be treated with lower intensity (I.e. hand v. back)
Acute condition should be Rx’s with lower intensities.

37. Considerations for Duty Cycle of US Rx
Duty Cycle selected according to Rx goal
Duty cycle can be 100%, 50% (pulsed), or 20%
(this refers to the “on” time of the US)
To increase tissue temp (generate heat) use 100%.
If nonthermal effect is desired used 50% or 20%

38. PHONOPHORESIS
US using meds ( hydrocortisone, dextamethasone, lidocaine).
Meds are RX by MD.
Cream is applied to skin, then US gel

39. Theories of Phonophoresis
1. Heating superficially increases vasodilation and absorption through circulation
2. Increase in cell permeability enhances diffusion of meds across the cell membrane
3. Pressure of US drives the drug into skin.

40. Contraindication (pg 189)
Malignant Tumor
Pregnancy
CNS tissue
Joint Cement
Plastic components
Pacemaker
Thrombophlebitis
Eyes
Reproductive Organs

41. Precautions for US (page 191)
Acute inflammation
Epiphyseal Growth Plate
Fractures
Beast Implants

42. Adverse Effects of US Burns – especially if superficial
Cavitation can cause tissue damage
Pain – 3 reasons
1. Sharp pain = sign of periosteal over heating caused by sound head moving over bony prominence or moving too slow over bone

43. Pain with US Dull ache = intensity is too high
Prickling/stinging = not enough coupling medium

44. Documentation for US In the objective document:
- Specific location of RX
- Intensity (w/cm2)
- Duty Cycle/ Mode (pulsed 20% vs. continuous)
- Freq ( 1 MHz or 3 MHz)
- Duration ( always put a time measure I.e. minutes)

45. Guideline For Selecting Ultrasound Intervention Parameters
Intensity
Greater than 1.0 w/cm2 for thermal effects
Less than 1.0 w/cm2 for nonthermal effects
Frequency
1 MHz for targeting deep tissue
3 MHz for targeting superficial tissue
Duty Cycle
100% (continuous) for thermal effects (elevate tissue temperature)
20% for nonthermal effects (prevent build up of heat)
Treatment Time
Longer treatment time to get maximal heating.
.4 X ERA
Shorter times for more acute and smaller areas
.67 x ERA