Therapeutic ultrasound uses inaudible, high-frequency sound waves to produce both thermal and non-thermal effects in tissues. It is classified as a deep heating modality capable of rapidly heating tissues. Ultrasound penetrates water-rich tissues and is absorbed by protein-rich tissues, with bone, nerve, and muscle absorbing the most. Reflection and scattering occur at tissue interfaces based on differences in acoustic impedance. Therapeutic ultrasound generators produce ultrasound waves via a transducer applied to the skin. It is used clinically to treat soft tissue injuries, increase range of motion, reduce inflammation and muscle spasms, and promote tissue healing and bone repair.

1. Therapeutic Ultrasound

2. Therapeutic Ultrasound
Inaudible, acoustic vibrations of high
frequency that produce can produce both
non-thermal and non-thermal physiologic
effects
Classified as a deep heating modality
with the ability to heat tissues to a greater
degree in less time as compared to other
superficial heating modalities

3. Penetration vs. Absorption
Ultrasound penetrates through tissue high in
water content and is absorbed by tissues with
high protein content
Tissues with high protein content possess
the greatest potential for heating
Inverse relationship

4. Penetration vs. Absorption
Absorption increases as frequency increases
Tissues high in water content decrease absorption
Tissues high in protein content increase absorption
Tissue absorption rates in descending order
Bone
Nerve
Muscle
Fat

5. Ultrasound At Tissue Interfaces
Some energy scatters due to reflection and
refraction
Acoustic impedance determines the amount
reflected vs. transmitted
Acoustic impedance = tissue density X speed of transmission
The most energy will the transmitted if the
acoustic impedance is the same
↑ difference in acoustic impedance = ↑ reflected energy

6. Reflection vs. Transmission
Transducer to air - Completely reflected
Through fat - Transmitted
Muscle/Fat Interface - Reflected and refracted
Soft tissue/Bone Interface - Reflected
Creates “standing waves” or “hot spots”

7. Therapeutic
Ultrasound
Generators
High frequency
electrical generator
connected through an
oscillator circuit and a
transformer via a
coaxial cable to a
transducer housed
within an applicator

8. Therapeutic Ultrasound Generator
Control Panel
Timer
Power meter
Intensity control ( watts or W/cm2)
Duty cycle switch (Determines On/Off time)
Selector switch for continuous or pulsed
*All units should be calibrated and checked
regularly.

9. Transducer or
Applicator
Matched to individual units
and not interchangeable
Houses a piezoelectric
crystal
Quartz
Lead zirconate or titanate
Barium titanate
Nickel cobalt

10. Transducer or
Applicator
Crystal converts electrical
energy to sound energy
through mechanical
deformation

11. When an alternating current is passed
through a crystal it will expand and
contract
Piezoelectric Effect

12. Piezoelectric Effect
Indirect or Reverse Effect - As
alternating current reverses polarity the
crystal expands and contracts producing
ultrasound
Crystal vibrates at a selected frequency 
sound wave generated and passed to tissues

13. Effective Radiating Area (ERA)
That portion of the surface of the transducer
that actually produces the sound wave
Should be only slightly smaller than transducer
surface
Acoustic energy is contained in a focused
cylinder
Energy output and temperature are significantly
greater at center as compared to periphery

14. Treatment Area Size
Should be 2-3 times larger than the ERA of
the crystal in the transducer
Research has shown that treating too large an
area will not result in the desired increase in
tissue heating
Best if used on smaller treatment areas

15. Frequency of Therapeutic
Ultrasound
Frequency range of therapeutic
ultrasound is 1 to 3.3 MHz
Frequency is the number of wave cycles
per second
Most generators produce either 1.0 or
3.0 MHz

16. The Ultrasound
Beam
Depth of penetration is
frequency dependent not
intensity dependent
1 MHz transmitted through
superficial layer and absorbed
at 3-5 cm
3 MHz absorbed superficially
at 1-2 cm

17. Amplitude, Power, & Intensity
Amplitude
Magnitude of the vibrations in a wave
Power
Total amount of US energy in the beam
(expressed in watts)
Intensity
Rate at which energy is delivered per unit area

18. Thermal vs. Non-Thermal Effects
Thermal effects
Tissue heating
Non-Thermal effects
Tissue repair at the cellular level
Thermal effects occur whenever the spatial
average intensity is > 0.2 W/cm2
Whenever there is a thermal effect there will
always be a non-thermal effect

19. Thermal Effects of Ultrasound
Increased collagen extensibility
Increased blood flow
Decreased pain
Reduction of muscle spasm
Decreased joint stiffness
Reduction of chronic inflammation

20. Set at 1.5 W/cm2 with 1MHz ultrasound
would require a minimum of 10 minutes to
reach vigorous heating
Ultrasound Rate of Heating Per Minute
Intensity W/cm2 1MHz 3MHz
0.5 .04°C .3°C
1.0 .2°C .6°C
1.5 .3°C .9°C
2.0 .4°C 1.4°C

21. There are no specific guidelines which dictate
specific intensities that should be used during
treatment
Recommendation is to use the lowest intensity at the
highest frequency which transmits energy to a specific
tissue to achieve a desired therapeutic effect
Everyone’s tolerance to heat is different – get
feedback from patient during treatment
Adjust settings to patient tolerance
Treatment should be temperature dependent

22. Set at 1.5 W/cm2 with 3 MHz ultrasound would require
only slightly more than 3 minutes to reach vigorous
heating
Intensity W/cm2 1MHz 3MHz
0.5 .04°C .3°C
1.0 .2°C .6°C
1.5 .3°C .9°C
2.0 .4°C 1.4°C

23. Thermal Effects
Baseline muscle temperature is 36-37°C
Mild heating
Increase of 1°C accelerates metabolic rate in
tissue
Moderate heating
Increase of 2-3°C reduces muscle spasm, pain,
chronic inflammation, increases blood flow
Vigorous heating
Increase of 3-4°C decreases viscoelastic
properties of collagen

24. Non-Thermal Effects of
Ultrasound
Increased fibroblastic activity
Increased protein synthesis
Tissue regeneration
Reduction of edema
Bone healing
Pain modulation

25. Literature indicates that non-thermal ultrasound
may modify cellular function
Modulate membrane properties
Alter cellular proliferation
Produce increases in proteins associated with
inflammation and repair
Could modify inflammatory response
Impact protein function
Induce conformational shift  change function
Dissociate multimolecular complex  change function

26. Frequency of Treatment
Acute conditions
Require more treatment over a shorter period of time
(2 X/day for 6-8 days)
Consider pulsed ultrasound
Can begin using within 48 hours
Chronic conditions
Require fewer treatments over a longer period
(alternating days for 10-12 treatments)
Treatment should continue as long as there is
progress

27. Duration of Treatment
Size of the area to be treated
What exactly are you trying to accomplish
Thermal vs. non-thermal effects
Intensity of treatment
What is the desired effect?
Size of the Treatment Area
Should be 2-3 times larger than the ERA of the
crystal in the transducer
If the area to be treated is larger use shortwave
diathermy, superficial hot packs or hot whirlpool

28. Numbers Represent °C Increase Following Treatment
Intramuscular Temp 1 cm below fat layer
at 3 cm after 10 min. after 4 minutes
Hydrocollator Pack 0.8°C -----
1 MHz Ultrasound 4.0 °C -----
Hot Whirlpool (40.6°C) ----- 1.1°C
3 MHz Ultrasound ----- 4.0°C
Ultrasound As A Heating Modality
(Smith, et al., 1995)
(Meyrer et al., 1994)

29. Direct Contact
Transducer should be small
enough to treat the injured
area
Gel should be applied
liberally
Area to be treated should be
larger than transducer
Heating of gel does not
increase the effectiveness of
the treatment

30. Immersion
Technique
Good for treating irregular
surfaces
A plastic, ceramic, or rubber
basin should be used
Tap water is useful as a
coupling medium
Transducer should move
parallel to the surface at .3-5 cm
Air bubbles should be wiped
away

31. Bladder Technique
Good for treating irregular surfaces
when body part cannot be submerged
in water
Uses a balloon filled with water
Both sides of the balloon should be
liberally coated with gel

32. Moving The Transducer
Stationary technique no longer recommended
 could result in hot spots
Applicator should be moved at about 4
cm/sec
Low BNR(Beam Nonuniformity Ratio) allows
for slower movement
High BNR may cause cavitation and periosteal
irritation
Moving the transducer too rapidly decreases the
total amount of energy absorbed per unit area

33. Rapid movement may also cause the athletic
trainer to treat too large an area, reducing the
ability to achieve the desired treatment
temperature
Lower BNR tends to allow for more slow
movement of the transducer
If the patient complains of pain the intensity
should be lowered and the treatment time should
be adjusted
Too much transducer pressure could impact
acoustic transmissivity

34. Clinical Applications For
Ultrasound
Ultrasound is recognized clinically as an
effective and widely used modality in the
treatment of soft tissue and bony lesions
There is relatively little documented, data-
based evidence concerning its efficacy
Most of the available data-based research is
unequivocal

35. Soft Tissue Healing and Repair
Effects on inflammation process
Cavitation and streaming increases transport of
calcium across cell membrane releasing histamine
Histamine stimulate leukocytes to “clean up”
Stimulates fibroblasts to produce collagen
Will liquefy gel-like cellular debris
Heating collagen will increase extensibility in
the tissue

36. Scar Tissue and Joint
Contracture
Increased temperature causes an increase
in elasticity and a decrease in viscosity of
collagen fibers
Increases mobility in mature scar
When vigorous heating is achieved heated
tissues become more extensible

37. Collagen tissue becomes more
yielding when heated
Active exercise is more effective than
ultrasound in increasing intramuscular
temperature
Temperature increase does not appear to influence
range of motion
Stretching window
Time period of vigorous heating when tissue will
undergo greatest extensibility and elongation
Stretching Connective Tissue

38. Tissue heated with ultrasound cools at a
very rapid rate
Joint mobilizations and friction massage
should be performed shortly after heating due
to the elevated cooling rate
Stretching should be done immediately
following ultrasound heating

39. Acute and post-acute
conditions (non-thermal)
Soft tissue healing and repair
Scar tissue
Joint contracture
Chronic inflammation
Increase extensibility of
collagen
Reduction of muscle spasms
Pain modulation
Increase blood flow
Increase protein synthesis
Tissue regeneration
Bone healing
Repair of nonunion fx
Inflammation associated
with myositis ossificans
Plantar warts
Myofascial trigger points
Indications

40. Acute & post-acute
conditions (thermal)
Areas of decreased
temperature sensation
Areas of decreased
circulation
Vascular insufficiency
Thrombophlebitis
Eyes
Reproductive organs
Pelvis immediately
following menses
Pregnancy
Pacemaker
Malignancy
Epiphyseal areas in children
Total joint replacements
Infection
Contraindications