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ULTRASOUND A Deep Thermal & Non-thermal Mechanical Modality 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

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A Deep Thermal & Non-thermal Mechanical Modality

what is ultrasound
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)
  • 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
  • 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
types of current
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
longitudinal vs transverse waves
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)
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
  • 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)
  • 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 @ 1540 m/sec and 4000 m/sec through compact bone
influences on the transmission of energy
Influences on the Transmission of Energy
  • Reflection – occurs when the wave can’t 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 wave’s energy
  • Decrease in a wave’s 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
attenuation acoustic impedance
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 @ m. interface
  • Soft-tissue: bone interfaced = much reflected
  • As US energy is reflected @ tissue interfaces with different impedances, intensity is increased creating a Standing Wave (hot spot)
Effective Radiating Area (ERA): area of the sound head that produces ultrasonic waves; expressed in square centimeters (cm2)
    • Represents the portion of the head’s 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
intensity output power
Intensity Output & Power
  • Power: measured in watts (W);
    • amount of energy being produced by the transducer
  • Intensity:strength of sound waves @ a given location within the tissues being treated
  • Spatial Average Intensity (SAI):amount of US energy passing through the US head’s 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
intensity output power15
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
beam nonuniformity ratio bnr
Beam Nonuniformity Ratio (BNR)
  • Ratio between the spatial peak intensity (SPI) to the average output as reported on the unit’s meter
    • The lower the BNR, the more uniform the beam is
    • A BNR greater than 8:1 is unsafe
    • Because of the existence of high-intensity areas in the beam (hot spots), it is necessary to keep the US head moving


duty cycle
Duty Cycle
  • Percentage of time that US is actually being emitted from the head
  • Ratio between the US’s 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%)
movement of the transducer
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
coupling agents
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
direct coupling
Direct Coupling
  • Effectiveness is  if body part is hair, irregular shaped, or unclean
  • Must maintain firm, constant pressure
  • Various gels utilized
water immersion
Water Immersion
  • Used for odd shaped parts
  • Place head approx. 1” away from part
  • Operator’s hand should not be immersed No metal on part or operator’s hand
  • Ceramic tub is recommended
  • If nondistilled H20 is used, intensity can be  .5 w/cm2 because of air & minerals
  • Don’t touch skin except to briefly sweep skin when bubbles form
  • 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
  • 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)
  • 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
thermal effects
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
nonthermal effects
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
pulsed ultrasound
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!)
pulsed ultrasound29
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
clinical applications soft tissue
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
clinical applications soft tissue plantar warts
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.
clinical applications scar tissue joint contracture pain reduction
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
clinical applications
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
treatment duration area
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
treatment goal duration
Treatment Goal & Duration
  • Adjust the intensity & time according to specific outcome
  • Desired temp.   /min. = treatment min.
    • Ex. For 1.5 W/cm2: 2°C  .3°C = 6.67 min.
  • 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
  • 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