ULTRASOUND

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ULTRASOUND

• A Deep Thermal Non-thermal Mechanical Modality

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What is Ultrasound?

• Located in the Acoustical Spectrum
• May be used for diagnostic imaging, therapeutic
  tissue healing, or tissue destruction
• Thermal Non-thermal effects
• We use it for therapeutic effects
• Can deliver medicine to subcutaneous tissues
  (phonophoresis)

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Ultrasound

• Sinusoidal waveform
• Therapeutic ultrasound waves range from 750,000
  to 3,000,000 Hz (0.75 to 3 MHz)
• Displays properties of
• wavelength,
• frequency,
• Amplitude

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Transducer

• A device that converts one form of energy to
  another
• Piezoelectric crystal a crystal that produces
  () and (-) electrical charges when it
  contracts or expands
• Crystal of quartz, barium titanate, lead
  zirconate, or titanate housed within transducer
• Reverse (indirect) piezoelectric effect occurs
  when an alternating current is passed through a
  crystal resulting in contraction expansion of
  the crystal
• US is produced through the reverse piezoelectric
  effect
• Vibration of crystal results in high-frequency
  sound waves
• Fresnal zone (near field) area of the
  ultrasound beam on the transducer used for
  therapeutic purposes

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Types of Current

• Direct Current the uninterrupted unidirectional
  flow of electrons
• Alternating Current the uninterrupted
  bidirectional flow of electrons
• Ultrasound is produced by this type of current
  flowing through a piezoelectric crystal
• Pulsed Current the flow of electrons interrupted
  by discrete periods of noncurrent flow

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Longitudinal vs. Transverse Waves

• Longitudinal waves molecular displacement is
  along direction in which waves travel (bungee
  cord)
• Compression regions of high molecular density
  (molecules in high pressure areas compress)
• Rarefraction regions of low molecular density
  (molecules in low pressure areas expand)
• Transverse waves molecular displacement in
  direction perpendicular to wave (guitar string)

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• Longitudinal waves travel in solids liquids
• Soft tissue more like liquids
• US primarily travels as longitudinal wave
• Transverse waves cannot pass through fluids
  found in the body only when ultrasound strikes
  bone

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Frequency

• Frequency number of times an event occurs in 1
  second expressed in Hertz or pulses per second
• Hertz cycles per second
• Megahertz 1,000,000 cycles per second
• In the U.S., we mainly use ultrasound frequencies
  of 1, 2 and 3 MHz
• 1 low frequency 3 high frequency
• ? frequency ? depth of penetration
• ? frequency sound waves are absorbed in more
  superficial tissues (3 MHz)

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Velocity

• The speed of sound wave is directly related to
  the density (? velocity ? density)
• Denser more rigid materials have a higher
  velocity of transmission
• At 1 MHz, sound travels through soft tissue _at_
  1540 m/sec and 4000 m/sec through compact bone

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Influences on the Transmission of Energy

• Reflection occurs when the wave cant pass
  through the next density
• Refraction is the bending of waves as a result
  of a change in the speed of a wave as it enters a
  medium with a different density
• Absorption occurs by the tissue collecting the
  waves energy

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Attenuation

• Decrease in a waves intensity resulting from
  absorption, reflection, refraction
• ? as the frequency of US is ? because of
  molecular friction the waves must overcome in
  order to pass through tissues
• US penetrates through tissue high in water
  content is absorbed in dense tissues high in
  protein
• ? Absorption ? Frequency (3 MHz) , and
• ? Penetration ? Absorption (1 MHz) , so
• ? Penetration ? Frequency ? Absorption (1
  MHz)
• Tissues ? water content low absorption rate
  (fat)
• Tissues ? protein content high absorption rate
  (peripheral nerve, bone)
• Muscle is in between both

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Attenuation Acoustic Impedance

• Determines amount of US energy reflected at
  tissue interfaces
• If acoustic impedance of the 2 materials forming
  the interface is the same, all sound will be
  transmitted
• The larger the difference, the more energy is
  reflected the less energy that can enter the
  2nd medium
• US passing through air almost all reflected
  (99)
• US through fat 1 reflected
• Both reflected/refracted _at_ m. interface
• Soft-tissue bone interfaced much reflected
• As US energy is reflected _at_ tissue interfaces
  with different impedances, intensity is increased
  creating a Standing Wave (hot spot)

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• Effective Radiating Area (ERA) area of the sound
  head that produces ultrasonic waves expressed in
  square centimeters (cm2)
• Represents the portion of the heads surface area
  that produces US waves
• Measured 5 mm from face of sound head represents
  all areas producing more than 5 of max. power
  output
• Always lesser area than actual size of sound head
• Large diameter heads column beam
• Small diameter heads more divergent beam
• Low frequency (1 MHz) diverge more than 3 MHz
• Treatment Duration time for total treatment

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Intensity Output Power

• Power measured in watts (W)
• amount of energy being produced by the transducer
• Intensity strength of sound waves _at_ a given
  location within the tissues being treated
• Spatial Average Intensity (SAI) amount of US
  energy passing through the US heads ERA
• expressed in watts per square centimeter (W/cm2)
  (power/ERA)
• Changing head size affects power density (larger
  head results in lower density)
• Limited to 3.0 W/cm2 of maximum output

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Intensity Output Power

• Spatial Average Temporal Peak Intensity (SATP)
  average intensity during the on time of the
  pulse
• Output meter displays the SATP intensity
• Spatial Peak Intensity (SPI) max. output (power)
  produced within an ultrasound beam
• Spatial Average Temporal Average Intensity (SATA)
  or Temporal (time) Average Intensity
• Power of US energy delivered to tissues over a
  given period of time
• Only meaningful for Pulsed US
• SAI x Duty Cycles

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Beam Nonuniformity Ratio (BNR)

• Ratio between the spatial peak intensity (SPI) to
  the average output as reported on the units
  meter
• The lower the BNR, the more uniform the beam is
• A BNR greater than 81 is unsafe
• Because of the existence of high-intensity areas
  in the beam (hot spots), it is necessary to keep
  the US head moving

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BNR
SPI
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Duty Cycle

• Percentage of time that US is actually being
  emitted from the head
• Ratio between the USs pulse length pulse
  interval when US is being delivered in the pulsed
  mode
• Pulse length amount of time from the initial
  nonzero charge to the return to a zero charge
• Pulse interval amount of time between
  ultrasonic pulses
• Duty cycle pulse length/(pulse length pulse
  interval) x 100
• 100 duty cycle indicates a constant US output
• Low output produces nonthermal effects (20)

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Movement of the Transducer

• 4 cm2/sec
• Remaining stationary can cause problems
• Moving too rapidly decreases the total amount of
  energy absorbed per unit area
• May cause clinician to treat larger area and the
  desired temps. May not be attained
• Slower strokes can be easier maintained
• If patient complains of pain or excessive heat,
  then decrease intensity but increase time
• Apply constant pressure not too much not too
  little

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Coupling Agents

• Optimal agent distilled H20 (.2 reflection)
• Modern units have a shut down mechanism if sound
  head becomes too hot (Dynatron beeps red lights
  on Chattanoogas)
• Improperly coupled head causes ? temp.
• Types of agents
• Direct
• H20 immersion
• Bladder
• Reduce amount of air bubbles

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Direct Coupling

• Effectiveness is ? if body part is hair,
  irregular shaped, or unclean
• Must maintain firm, constant pressure
• Various gels utilized

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Water Immersion

• Used for odd shaped parts
• Place head approx. 1 away from part
• Operators hand should not be immersed No metal
  on part or operators hand
• Ceramic tub is recommended
• If nondistilled H20 is used, intensity can be ?
  .5 w/cm2 because of air minerals
• Dont touch skin except to briefly sweep skin
  when bubbles form

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Bladder

• H20 filled balloon or plastic bag coated with
  coupling gel
• Use on irregular shape part
• Place gel on skin, then place the bladder on the
  part, and then place gel on bladder
• Make sure all air pockets are removed from bladder

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Indications

• Soft tissue healing repair
• Joint contractures scar tissue
• Muscle spasm
• Neuroma
• Trigger areas
• Warts
• Sympathetic nervous system disorders
• Postacute reduction of myositis ossificans
• Acute inflammatory conditions (pulsed)
• Has been shown to be ok to use following the
  stopping of bleeding with an acute injury (pulsed)

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Contraindications

• Acute conditions (continous output)
• Ischemic areas or impaired circulation areas
• Tendency to hemorrhage
• Around eyes, heart, skull, or genitals
• Over pelvic or lumbar areas in pregnant or
  menstruating females
• Cancerous tumors
• Spinal cord or large nerve plexus in high doses
• Anesthetic areas
• Stress fracture sites or over fracture site
  before healing is complete (continuous)
  epiphysis
• Acute infection

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Thermal Effects

• ? blood flow
• ? sensory motor nerve conduction velocity
• ? extensibility of structures (collagen) ? joint
  stiffness
• ? collagen deposition
• ? macrophage activity
• Mild inflammatory response which may enhance
  adhesion of leukocytes to damaged endothelial
  cells
• ? muscle spasm
• ? pain
• all Nonthermal effects

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Nonthermal Effects

• ? cell membrane permeability
• ? vascular permeability
• ? blood flow
• ? fibroblastic activity
• Altered rates of diffusion across cell membrane
• Secretion of chemotactics
• Stimulation of phagocytosis
• Production of granulation tissue
• Synthesis of protein
• ? edema
• Diffusion of ions
• Tissue regeneration
• Formation of stronger CT

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Pulsed Ultrasound

• Stimulates phagocytosis (assists w/ ? of chronic
  inflammation) increases of free radicals (?
  ionic conductance on cell membrane)
• Cavitation formation of gas bubbles that expand
  compress due to pressure changes in tissue
  fluids
• Stable occurs when bubbles compress during the
  ?-press. peaks followed expansion of bubbles
  during ?-press. troughs
• Unstable (transient) compression of bubbles
  during ?-press. Peaks, but is followed by total
  collapse during trough (BAD!)

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Pulsed Ultrasound

• Acoustical Streaming stable cavitation leads
  this one-directional flow of tissue fluids, is
  most marked around cell membranes
• Facilitates passage of calcium potassium other
  ions, etc. in/out of cells
• Collagen synthesis, chemotactics secretion, ?
  update of calcium in fibroblasts, ? fibroblastic
  activity
• Eddies (Eddy) circular current of fluid often
  moving against the main flow
• Flows around the cell membranes its organelles
• Flow of bubbles in stream cause change in cell
  membrane permeability

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Clinical Applications Soft Tissue

• Stimulates release of histamine from mast cells
• May be due to cavitation streaming
• ? transport of calcium ions across membrane that
  stimulates histamine release
• Histamine attracts leukocytes, that clean up
  debris, monocytes that release chemotactic
  agens growth factors that stimulate fibroblasts
  endothelial cells to form a collagen-rich,
  well-vascularized tissue

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Clinical Applications Soft Tissue Plantar
Warts

• Pitting edema - ? temp. makes thick edema liquefy
  thus promoting lymphatic drainage
• ? fibroblasts stimulation of collagen
  production gives CT more strength
• Plantar Warts - 0.6 W/cm2 for 7-15 min.

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Clinical Applications Scar Tissue, Joint
Contracture, Pain Reduction

• ? mobility of mature scar
• ? tissue extensibility
• Softens scar tissue
• ? pain threshold
• Stimulates large-diameter myelinated n. fibers
• ? n. conduction velocity

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Clinical Applications

• Chronic Inflammation - Pulsed US has been shown
  to be effective with ? pain ? ROM
• 1.0 to 2.0 W/cm2 at 20 duty cycle
• Bone Healing Pulsed US has been shown to
  accelerate fracture repair
• 0.5 W/cm2 at 20 duty cycle for 5 min., 4x/wk
• Caution over epiphysis may cause premature
  closure

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Treatment Duration Area

• Length of time depends on the
• Size of area
• Output intensity
• Goals of treatment
• Frequency
• Area should be no larger than 2-3 times the
  surface area of the sound head ERA
• If the area is large, it can divided into smaller
  treatment zones
• When vigorous heating is desired, duration should
  be 10-12 min. for 1 MHz 3-4 min. for 3 MHz
• Generally a 10-14 day treatment period

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Thermal Applications
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Treatment Goal Duration

• Adjust the intensity time according to specific
  outcome
• Desired temp. ? ? ?/min. treatment min.
• Ex. For 1.5 W/cm2 2C ? .3C 6.67 min.

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Phonophoresis

• US is used to deliver a medication via a safe,
  painless, noninvasive technique
• Opens pathways to drive molecules into the
  tissues
• Not likely to damage or burn skin as with
  iontophoresis
• Usually introduces an anti-inflammatory drug
• Preheating the area may enhance delivery of
  medication
• Encourages vascular absorption distribution of
  meds.
• Some medications are poor conductors

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Phonophoresis

• Factors affecting rate of medication diffusion
• Hydration higher water content skin more
  penetrable
• Age better with younger ages
• Composition better near hair follicles,
  sebaceous glands sweat ducts
• Vasularity higher vascular areas are better
• Thickness thinner skin is better
• Types of medications
• Corticosteroids hydrocortisone, dexamethasone
• Salicylates -
• Anesthetics - lidocaine