Ultrasound

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Ultrasound

• Veronica Southard PT MS GCS

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Ultrasound general considerations

• Commonly used
• Indicated for tissue repair and pain relief
• Acoustic rather than electromagnetic
• For heating Deep heat like Daithermy I.e.
  raises tissue temperature

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Ultrasound defined

• Inaudible, acoustic vibrations of high frequency
  that may produce either thermal or non-thermal
  physiologic effects.
• As a clinician you need to know what your trying
  to accomplish

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Transmission of Acoustic Energy

• Use molecular collision. A coupling medium is
  used to enhance absorption, cause vibration.
• Through the medium a minimum amount of
  displacement occurs to the surrounding issues,
  allowing the molecules to vibrate.
• Eventually this wave of vibration has propagated
  through the entire medium.
• Biologic vibration

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Wave transmission

• Two types of waves travel through a solid medium
• 1. Longitudinal Molecules are displaced in the
  direction the wave travels. In this wave, areas
  of high molecular density are called
  compressions, molecules get squeezed together.
  Travel in solids and liquids. Rarefaction lower
  molecular density molecules spread out.
• 2. Transverse waves molecules become displaced
  perpendicular to the direction in which the wave
  is moving. Solids such as bone interfaces.

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Frequency of wave transmission

• Audible sound is transmitted bet 16kHz and20 kHz.
• Therapeutic US is between .75- 3MHz.
• The gt the frequency the more focused the beam of
  sound produced
• In humans the lower the frequency the greater the
  depth of penetration.

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Velocity

• Velocity of US propagation is directly related to
  the density. The more dense and rigid materials
  have a higher velocity of transmission.

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Attenuation

• Transmitting through various tissues reduces the
  intensity of the US energy.
• Decreased energy may be due to absorption,
• Dispersion,or scattering of the sound wave after
  reflection or refraction.
• Therefore penetration and absorption are
  inversely related.
• As the frequency increases, the absorption
  increases, thus less energy is transmitted to
  deeper tissues

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Acoustic Impedance

• DEF reflection or refraction of a sound wave
  when it encounters a boundary or an interface
  between 2 tissues.
• If the acoustic impedance is the same for both
  structures, all the the sound will be transmitted
  and none will be reflected.
• Standing waves or hot spots develop when the
  energy reflected at the tissue interfaces meets
  new energy being transmitted. This new energy
  can cause tissue damage.

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Components of an Ultrasound Generator

• US generator is made up of a High Frequency
  electrical generator and transformer.
• A frequency of 1MHz means the crystal deforms 1
  million times / second

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Transducer

• Aka APPLICATOR OR SOUNDHEAD
• Composed of piezoelectric crystal such as quartz,
  or synthetic ceramic.
• The crystal in the transducer converts the
  electrical energy to acoustic energy through
  mechanical deformation of the piezoelectric
  crystal

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Piezoelectric Effect

• Created by generating an AC current at the same
  frequency as the crystal. The piezoelectric
  effect is the expansion and contraction of the
  crystal in response to the passage of current.
• 1. Direct piezoelectric effect
• 2. Indirect (Reverse) piezoelectric effect

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Effective Radiating Area

• Def surface of the transducer producing the
  sound wave.
• Dependent on the surface area of the crystal.
• Experiments have shown when treating 10 using
• 2 ERA will increase temperature 3.6C( vigorous)
• 6 ERA 1.1C increase (mild heating)

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Frequency of Therapeutic US

• Frequency is the of wave cycles/second.
• Clinically use 1 and 3MHz.
• 1 MHz less energy is absorbed in the
  superficial tissues and thus there is greater
  penetration.
• 3 MHz Newer units. More superficial heating
  then 1 MHz.
• Clearly, the intensity of US does not determine
  penetration depths, the frequency does.

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The Ultrasound Beam

• The larger the sound head the more focused or
  collimated the US beam.
• Beams generated at 1 MHz are more divergent than
  US at 3 MHz.

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BNR Beam Nonuniformity Ratio

• Variability of the ultrasound beam intensity.
• FDA acceptable between 2 and 6. Labeled.
• The lower the BNR, the more uniform the output of
  the machine.

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Pulsed vs. Continuous Wave US

• 1. Continuous sound intensity is constant
  throughout treatment. US energy is produced
  100 of the time.
• 2. Pulsed interrupted intensity. No US energy
  is produced during the off period. In this case
  the average intensity over time is reduced. Duty
  cycle refers to on time.

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Amplitude, Power and Intensity

• Amplitude magnitude of the vibration from a
  point of equilibrium. Cm or cm2
• Power Watts. Total US energy in the beam .
• Intensity Rate of energy delivery per unit area.
• Spatial averaged intensity
• Spatial Peak intensity
• Temporal peak intensity
• Temporal averaged intensity
• Spatial averaged temporal peak

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Physiologic Effects of US

• Thermal and non thermal
• Thermal Attenuation is caused by the conversion
  of US energy to heat through absorption and to a
  lesser degree by scattering and beam deflection

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Clinical Effects of Thermal US

• 1.Increased extensibility of collagen in jt.
  Capsules and tendons.
• 2. Decreased joint stiffness.
• 3. Decreased m spasm

• 4. Modulation of pain
• 5. Increased bl fl
• 6. Mild inflamm response that may reduce chronic
  inflamm

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Advantages of Thermal US

• Tissues with high concentrations of collagen such
  as ligs, m ,tendons, jt. Capsules, jt. Menisci,
  intermuscular interfaces, NR, periosteum,
  cortical bone, and other deep tissues which may
  be selectively heated to the therapeutic range
  without causing a significant tissue temp
  increase in the skin or fat.

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Effects of Non Thermal US

• Cavitation formation of gas filled bubbles that
  expand and compress because of ultrasonically
  induced pressure changes in tissue fluids
• 1. Stable cav. Occurs 2ary to regularly repeated
  pressure changes over many acoustic cycles.
• 2. Unstable cav. Violent large swings before
  implosion and collapse occurs. High intensities
  at low frequencies.
• 3. Acoustic microstreaming- unidirectional
  movement of fluids along the boundaries of cell
  membranes resulting from mechanical pressure
  waves in an US field

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Non thermal Therapeutic Effects

• 1. Stimulation of fibroblast activity
• 2. Bone healing and repair of non union fracture

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Techniques of Application

• 1. Frequency Acute low intensity or pulsed OD
  to BIW 6-8 days until acute sx subside.
• Chronic seen alternating days, continue until
  improvement. Without improvement following 3-4
  tx, D/c or change parameters
• 2. Duration
• Size of area to be tx
• Intensity in w/cm2
• Frequency
• Desired temperature increase

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Summary of Effects of US
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Coupling Medium/Methods

• Decreases impedance at the air skin juncture.
  Eliminates air from body part bet US head and tx
  surface.
• For optimal tx effects, the sound head should be
  ll and perpendicular to tx surface.

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Exposure Techniques

• Direct contact surface must be larger than the
  transducer
• Immersion can be used when the treatment area
  is smaller than the transducer. Treatment area
  is irregular.
• Plastic, ceramic, rubber basin should be used
• Tap water
• Move transducer ll to surface you are txing. _at_ .5
  1 cm away. Wipe away air bubbles. Intensity
  should be increased up to 50

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Indications Ultrasound
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Contraindications
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Phonophoresis

• US used to drove in whole molecules of topical
  meds. Safe painless, noninvasive. Active
  transport as a result of increased membrane
  permeability during sonation.

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US in Combination with other Modalities

• There is no proof that US in combination with
  other modalities is more beneficial. In fact a
  HP may increase superficial attenuation therefore
  decreasing the depth of penetration.
• Pulsed US and cold should however be a choice to
  promote soft tissue healing.

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Documentation

• Record specific parameters in order to reproduce
  or change treatments.
• Include Frequency, Intensity, Pulsed/continuous,
  Duration, pt. position,
• Direct/immersion. Pt response to modality.