1
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2
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- Inaudible , acoustic vibrations of high frequency that produce either
thermal or non-thermal physiologic effects
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3
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- Relies on molecular collision for transmission
- Collisions cause molecule displacement and a wave of vibration
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4
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- Longitudinal Wave
- Displacement is in the direction of wave propagation
- Travels in both liquids and solids (Soft tissue)
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5
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- Transverse Wave
- Displacement is perpendicular to direction of propagation
- Travels only in solids (Bone)
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6
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- Audible sound = 16-20 kHz
- Ultrasound > 20 kHz
- Therapeutic Ultrasound = 0.75-3 MHz (1,000,000 cycles/sec)
- Lower frequencies have greater depth of penetration
- Higher frequencies more superficial absorption
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7
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- Directly related to tissue density (the higher the density the greater
the velocity)
- At 1 MHz ultrasound travels through soft tissue at 1540 m/sec
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8
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- Decrease in energy intensity
- Decrease is due to absorption, dispersion, or scattering resulting from
reflection and refraction
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9
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- Inverse relationship
- Absorption increases as frequency increases
- Tissues high in water content decrease absorption
- Tissues high in protein content increase absorption
- Highest absorption rate in bone, nerve, muscle, fat
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10
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- Some energy scatters due to reflection and refraction
- Acoustic impedance (tissue density X speed of transmission) determines
the amount reflected vs. transmitted
- The most energy will the transmitted if the acoustic impedance is the
same
- The larger the difference in acoustic impedance the more energy
reflected
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11
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- 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”
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12
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- High frequency electrical generator connected through an oscillator
circuit and a transformer via a coaxial cable to a transducer housed
within an applicator
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13
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14
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- Timer
- Power meter
- Intensity control ( watts or W/cm2)
- Duty cycle switch (Determines On/Off time)
- Selector switch for continuous or pulsed
- Automatic shutoff if transducer overheats
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15
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- Matched to individual units and not interchangeable
- Houses a piezoelectric crystal
- Quartz
- Lead zirconate or titanate
- Barium titanate
- Nickel cobalt
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16
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- Crystal converts electrical energy to sound energy through mechanical
deformation
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17
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- When an alternating current is passed through a crystal it will expand
and compress
- Direct Effect - An electrical voltage is generated when the crystal
expands and compresses
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18
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- Indirect or Reverse Effect - As alternating current reverses polarity
the crystal expands and contracts producing ultrasound
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19
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- That portion of the surface of the transducer that actually produces the
sound wave
- Should be only slightly smaller than transducer surface
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20
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- Frequency range of therapeutic ultrasound is 0.75 to 3.0 MHz
- Most generators produce either 1.0 or 3.0 MHz
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21
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- 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
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22
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- Concentrates energy in a limited
area
- Larger head- more collimated beam
- Smaller head- more divergent beam
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23
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- Near field
- Distribution of energy is nonuniform due to the manner in which waves
are generated and differences in acoustic pressure
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24
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- Point of Maximum Acoustic Intensity
- Waves are indistinguishable and arrive simultaneously
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25
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- Far Field
- Energy is more evenly distributed and the beam becomes more divergent
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26
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- Indicates the amount of variability in intensity within the beam
- Ratio - Highest intensity found in the beam relative to the average
intensity of the transducer
- Ideal BNR would be 1:1
- Typical BNR 6:1
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27
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- If intensity is 1.5 W/cm2 the peak intensity in the field would be 9
W/cm2
- The lower the BNR the more even the intensity
- Manufacturers must include the BNR on their generators
- Better generators have a low BNR thus provide more even intensity
throughout the field
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28
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- Continuous Ultrasound
- Ultrasound intensity remains constant over time
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29
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- Pulsed
- Intensity is interrupted thus average intensity of output over time is
low
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30
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- Duty Cycle (mark space ratio)
- Duration of pulse / Pulse period X 100
- Duty Cycle may be set to 20% or 50%
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31
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- Rate at which energy is delivered per unit area
- Spatial Average Intensity - W/cm2
- Power output in watts ERA of transducer in cm2
- Example
- 6 watts = 1.5 W/cm2
4 cm2
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32
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- 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
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33
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34
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- Thermal effects
- 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
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35
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- Increased collagen extensibility
- Increased blood flow
- Decreased pain
- Reduction of muscle spasm
- Decreased Joint stiffness
- Reduction of chronic inflammation
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36
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- Set at 1.5 W/cm2 with 1MHz ultrasound would require a minimum
of 10 minutes to reach vigorous heating
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37
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- Set at 1.5 W/cm2 with 3 MHz ultrasound would require only
slightly more than 3 minutes to reach vigorous heating
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38
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- 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
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39
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- Increased fibroblastic activity
- Increased protein synthesis
- Tissue regeneration
- Reduction of edema
- Bone healing
- Pain modulation
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40
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41
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- Unidirectional flow of fluid
and tissue components along
the cell membrane
interface resulting in
mechanical pressure
waves in an ultrasonic field
- Alters cell membrane permeability to sodium and calcium ions important
in the healing process
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42
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- Formation of gas filled bubbles that expand and compress due to pressure
changes in fluid
- Stable Cavitation
- Stable cavitation results in an increased fluid flow around these
bubbles
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43
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- Unstable Cavitation
- Unstable cavitation results in violent large excursions in bubble
volume with collapse creating increased pressure and temperatures that
can cause tissue damage
- Therapeutic benefits are derived only from stable cavitation
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44
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- Can be maximized while minimizing the thermal effects by:
- Using a spatial average intensity of 0.1-0.2 W/cm2 with
continuous ultrasound
- Setting duty cycle at 20% at 1 W/cm2
- Setting duty cycle at 50% at 0.4 W/cm2
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45
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46
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- Acute conditions require more treatment over a shorter period of time (2
X/day for 6-8 days)
- Chronic conditions require fewer treatments over a longer period (
alternating days for 10-12 treatments)
- Limit treatments to a total of 14
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47
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- Size of the area to be treated
- What exactly are you trying to accomplish
- Thermal vs. non-thermal effects
- Intensity of treatment
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48
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- 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
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49
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50
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- Recommendations for specific intensities make little sense
- Ultrasound intensity should be adjusted to patient tolerance
- Increase to the point where there is warmth and then back down until
there is general heating
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51
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- If you decrease intensity during treatment you should increase treatment
duration
- Ultrasound treatments should be temperature dependent not time dependent
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52
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- Energy reflection is great at the air-tissue interface
- Purpose is to minimize air and maximize contact with the tissue
- Include gel, water, mineral oil, distilled water, glycerin, analgesic
creams
- Gel seems to be the best coupling medium
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53
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- Transducer should be small enough
to treat the injured area
- Gel should be applied liberally
- Heating of gel does not increase the effectiveness of the treatment
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54
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- 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
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55
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- Good for treating irregular surfaces
- Uses a balloon filled with water
- Both sides of the balloon should be liberally coated with gel
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56
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- Stationary technique no longer recommended
- Applicator should be moved at about
4 cm/sec
- Low BNR allows for slower movement
- High BNR may cause cavitation and periosteal irritation
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57
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- Cooling the tissues does not facilitate an increase in temperature (Remmington
1994, Draper, 1995)
- Analgesic effects of ice can interfere with perception of heating
- Ultrasound and EMS is effective in treating myofascial trigger points
when used in combination with stretching (Girardi, et al. 1984)
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58
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- Ultrasound is recognized clinically as an effective and widely used
modality in the treatment of soft tissue and boney lesions
- There is relatively little documented, data-based evidence concerning
its efficacy
- Most of the available data-based research is unequivocal
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59
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- During inflammatory stage cavitation and streaming increases transport
of calcium across cell membrane releasing histamine
- Histamine stimulate leukocytes to
“clean up”
- Stimulates fibroblasts to produce collagen (Dyson, 1985, 1987)
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60
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- Increased temperature causes an increase in elasticity and a decrease in
viscocity of collagen fibers (Ziskin, 1984)
- Increases mobility in mature scar (Gann, 1991)
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61
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- Few clinical or experimental studies
- Ultrasound does seem to be effective for increasing blood flow for
healing and reduction of pain (Downing,
1986)
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62
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- Ultrasound accelerates fracture repair (Dyson, 1982, Pilla et al.,
1990)
- Ultrasound given to an unstable fracture during cartilage formation may
cause cartilage proliferation and delay union (Dyson, 1989)
- Ultrasound has no effect on myositis ossificans but may help reduce
surrounding inflammation (Ziskin, 1990)
- Ultrasound not effective in detecting stress fractures
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63
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- Ultrasound not used specifically for decreasing pain
- Ultrasound may increase threshold for activation of free nerve
endings (McDiarmid, 1987)
- Superficial heating may effect gating (Williams et al. 1987)
- Increased nerve conduction velocity creates a counterirritant effect (Kitchen,
1990)
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64
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- A number of studies have demonstrated a placebo effect in patients using
ultrasound (Lundeberg, 1988, Dyson, 1987, Hashish et al., 1986)
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65
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- Ultrasound used to drive topical application of selected medication into
the tissues
- Antiinflammatories
- Cortisol
- Salicylates
- Dexamethasone
- Analgesics
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66
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- Non-thermal effects increase tissue permeability and acoustic pressure
drives molecules into the tissue
- Effectiveness of phonophoresis is debatable
- Early studies demonstrated effective penetration (Griffin, 1982,
Kleinkort, 1975)
- More recent studies show ineffectiveness (Oziomek et al, 1991, Benson et
al., 1989)
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67
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