1. Therapeutic Ultrasound
Chapter 7
© 2005 – FA Davis

2. Description
Acoustical energy (sound waves) above the range of human hearing
Therapeutic range: 0.75 to 3.3 MHz
Effects:
Thermal
Nonthermal (mechanical)
© 2005 – FA Davis

3. Uses Calcific bursitis Inflammatory conditions Joint contractures Pain
Acute orthopedic injuries (low pulses, low intensity)
© 2005 – FA Davis

4. Production of Ultrasound
An alternating current is passed through a crystal
The current causes the crystal to vibrate
Electropiezo effect
Vibrating crystal produce high-frequency sound waves
© 2005 – FA Davis

5. Effective Radiating Area (ERA)
Area of the crystal that actually produces sound waves
Produces more than 5% of the energy at 5 mm from the transducer face
ERA is always smaller than the transducer face
Energy is concentrated near the center
ERA
© 2005 – FA Davis

6. Beam Profile Multiple waves emerge from the head
Energy diverges as it moves away from the source
Energy is uniform close to the head
Near zone (Fresnel zone)
Becomes less consistent farther away from the head
Spatial peak intensity
Spatial Peak Intensity
© 2005 – FA Davis

7. Beam Nonuniformity Ratio (BNR)
Spatial Peak Intensity
Describes the amount of variation in the beam
Ratio between:
Spatial peak intensity (SPI)
Average intensity (SAI - metered output)
BNR = SPI/SAI
Perfect beam would have a BNR of 1:1
Minimally acceptable BNR is 8:1
The actual peak output is equal to the SAI * the BNR
10 W total output * 6:1 BNR
60 watt SPI
Spatial Average Intensity (Displayed on the unit)
© 2005 – FA Davis

8. Modes of Application Continuous
Ultrasonic energy is constantly produced
Can produce thermal effects based on:
Output intensity
Treatment duration
Pulsed
Ultrasonic output is regularly interrupted
Produces nonthermal effects
© 2005 – FA Davis

9. Continuous Output (100% Duty Cycle) Pulsed Output (67% Duty Cycle)
Ultrasonic output is cycled “On” and “Off”
On = Pulse length
Off = Pulse interval
Expressed as a Duty Cycle
ON/(ON+OFF) * 100
20mSec/(20mSec+10mSec) * 100
20/30 * 100
67%
Continuous Output (100% Duty Cycle)
Pulsed Output (67% Duty Cycle)
© 2005 – FA Davis

10. Output Frequency Measured in megahertz (MHz)
1 MHz = 1,000,000 waves per second
Determines the depth of effects
1 MHz Output
Penetrates 5 to 7 cm
Thermal effects last longer
More divergent beam
3 MHz Output
Penetrates 2 to 3 cm
Heats 3 times faster than 1 MHz output
More collimated beam
© 2005 – FA Davis

11. Power and Intensity Spatial Average Intensity
Spatial Average Temporal Peak Intensity
Spatial Average Temporal Average Intensity
Half-layer Value
© 2005 – FA Davis

12. Spatial Average Intensity (SAI)
Describes the energy per unit of area
Total output (watts)/area
Watts/effective radiating area (cm2)
W/cm2
15 watts being applied with a 10 cm2 ERA
15 Watts / 10 cm2
1.5 W/cm2
© 2005 – FA Davis

13. Power Measures – Pulsed Output
Spatial Average Temporal Peak Intensity (SATP)
The average energy delivered during the “On” time of the duty cycle.
Spatial Average Temporal Average Intensity (SATA)
Energy delivered over time
Spatial Average Intensity * Duty Cycle
Meaningful only during pulsed output
© 2005 – FA Davis

14. Biophysical Effects
Thermal
© 2005 – FA Davis

15. Thermal Effects Increased sensory nerve conduction velocity
Increased motor nerve conduction velocity
Increased extensibility of collagen-rich
Increased vascular permeability structures
Increased collagen deposition
Increased blood flow
Reduction of muscle spasm
Increased macrophage activity
Enhanced adhesion of leukocytes to damaged endothelial cells
© 2005 – FA Davis

16. Heating Classifications
Increase Used For
Mild 1°C Mild inflammation Accelerate metabolism
Moderate 2° – 3°C Decreasing muscle spasm Decreasing pain Increasing blood flow Chronic inflammation
Vigorous 3° – 4°C Tissue elongation Scar tissue reduction
© 2005 – FA Davis

17. Heating Rate Heating rate and magnitude is based on: Duty cycle
Output frequency
Intensity
Target tissues
Size of the treatment area
© 2005 – FA Davis

18. Thermal Effects Same as other heat modalities
Smaller volume of tissue
Shorter duration of effects
Preheat the skin with a moist heat pack
Decreases the time to reach vigorous heating
Poorly vascularized, collagen-rich tissues are preferentially heated
Fascia, tendon, scar tissue
Tissues containing an increased proportion of fluid do not heat as well
Adipose tissue, articular fluid
© 2005 – FA Davis

19. Biophysical Effects
Nonthermal
© 2005 – FA Davis

20. Nonthermal Effects Increased cell membrane permeability
Altered rates of diffusion across the cell membrane
Increased vascular permeability
Secretion of cytokines
Increased blood flow
Increased fibroblastic activity
Stimulation of phagocytosis
Granulation tissue production
Synthesis of protein
Synthesis of collagen
Reduction of edema
Diffusion of ions
Tissue regeneration
Formation of stronger deformable connective tissue
© 2005 – FA Davis

21. Nonthermal Application
Pulsed output
20 to 25% duty cycle
Nonthermal output intensity
Continuous output
100% duty cycle
Output intensity of less than 0.3 W/cm2
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22. Acoustical Streaming Ultrasound causes interstitial fluids to flow
Fluids strike cell membranes
Produce eddy currents
Eddy currents displace ions and molecules
Alter:
Cell membrane permeability
Cellular function
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23. Effect on Injury Response
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24. Cellular Response Acoustical streaming: Thermal effects:
Increases cell membrane permeability
Alters cell membrane diffusion rate
Increased histamine release
Mast cell degranulation
Increased rate of protein synthesis
Thermal effects:
Increased cell metabolism
Increased rate of inflammation
© 2005 – FA Davis

25. Inflammation May lead to an earlier onset of proliferation
Increased fibroblast proliferation
Release of growth factors and platelets
Increased macrophage activity
Leukocytes bind to damaged endothelial cells
Cell division is increased
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26. Inflammation Frequency Specificity 1 MHz Output 3 MHz Output
Release of preformed fibroblasts
3 MHz Output
Increased synthesis and secretion of fibroblast precursors
Increased in areas of high collagen concentration
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27. Blood and Fluid Dynamics
May increase blood flow for 45 minutes
Thermal effects
Decreased vascular tone
Histamine release
Causes vasodilation
Moist heat application prior to treatment decreases net increase in blood flow
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28. Pain Control Direct Pain Reduction
Increased nerve cell sodium permeability
Alters nerve function
Increases pain threshold
Indirect Pain Reduction
Increased blood flow
Increased capillary permeability
Increased oxygen delivery
Decreased muscle spasm
© 2005 – FA Davis

29. Muscle Spasm Reduced secondary to: Decreased pain
Altered nerve conduction velocity
Increased temperature (counterirritant effect)
Muscle relaxation
© 2005 – FA Davis

30. Tissue Elasticity
Ultrasound preferentially heats collagen-rich tissues (tendon, fascia, scar tissue)
Temperature must be increased 7.2°F
Stretching window lasts approximately 3 minutes following the treatment
Place tissues on stretch during application
Perform stretching/mobilization immediately following the treatment
Multiple treatments are required to gain length
© 2005 – FA Davis

31. Wound Healing Tendon Healing Continuous US application may:
Increase tensile strength
Increase collagen deposition
Skin Ulcers
3 MHz, low-intensity pulsed output may assist the healing process
Cover the wound with an occlusive dressing
© 2005 – FA Davis

32. Fracture Healing Low-intensity pulsed output
Accelerates rate of fracture healing for:
Acute fractures
Nonunion fractures
Stress fractures
Requires specialized unit
Biophysical Effects:
Mechanical (sound) energy strikes bone
Microvibration of bone triggers growth (osteogenesis)
PARAMETERS
Frequency 1.5 MHz
ERA 3.88 cm2
Intensity 30 mW/cm2
Treatment Duration 20 minutes Daily
© 2005 – FA Davis

33. Contraindications Acute conditions (thermal mode) Ischemic areas
Areas of impaired circulation
Over areas of deep vein thrombosis
Anesthetic areas
Over cancerous tumors
Sites of active infection or sepsis
Over the spinal cord or large nerve plexus in high doses
Exposed penetrating metal (eg, external fixation devices)
Around the eyes, heart, skull, or genitals
Over the thorax in the presence of an implanted pacemaker
Pregnancy when used over the pelvic or lumbar areas
Over a fracture site before healing is complete
Stress fracture sites or sites of osteoporosis
Over the pelvic or lumbar area in menstruating female patients
© 2005 – FA Davis