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ULTRASOUND

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  1. ULTRASOUND A Deep Thermal & Non-thermal Mechanical Modality

  2. 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)

  3. 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

  4. 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

  5. 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

  6. 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)

  7. 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

  8. 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)

  9. 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 @ 1540 m/sec and 4000 m/sec through compact bone

  10. 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

  11. Attenuation • 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

  12. 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)

  13. 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

  14. 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

  15. 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

  16. 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

  17. BNR SPI

  18. 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%)

  19. 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

  20. 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

  21. Direct Coupling • Effectiveness is  if body part is hair, irregular shaped, or unclean • Must maintain firm, constant pressure • Various gels utilized

  22. 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

  23. 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

  24. 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)

  25. 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

  26. 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

  27. 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

  28. 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!)

  29. 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

  30. 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

  31. 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.

  32. 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

  33. 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

  34. 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

  35. Thermal Applications

  36. 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.

  37. 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

  38. 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