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Ultrasound 3

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  • Think of how a stone can skip through the water creating waves or ripples. Or think of a boat with an outboard motor. Look at the wake even at slow speeds. Ultrasound is a mechanical wave in which energy is transmitted by the vibrations of the molecules of the biologic medium through which the wave is traveling.
  • Since soft tissues are mostly like liquids, therefore US travels primarily as a longitudinal wave, except when in contact with bone, a transverse wave results.
  • US has a frequency of >20KHz
  • In our bodies structures naturally have different densities. For example the US will travel at 1540 m/s through soft tissue. Through bone it travels at 4000m/s
  • Tissues with high fluid content such as blood plasma US penetrates. Tissues with high protein contents such as skeletal m, peripheral n the US will have its greatest absorption and greatest heating potential
  • Sound passing from the transducer to air will be almost completely reflected. Never hold the transducer in the air because it will damage the crystal. The possibility of standing waves is minimized by assuring that you either use pulsed wave US or continually move the sound head.
  • High frequency generator that is connected via an oscillator circuit. Transformer is attached via a coaxial cable to a transducer housed in a type of insulated applicator. The oscillator circuit produces a sound beam at a specific frequency. Frequency is reached by the transformation of household current of 60Hz/100v Acto 500v or more by electronic components in the US apparatus. The higher voltage is then applied to oscillators or vibrators that boost the household frequencies to the desired level of 1 or 3 MHz. DEMONSTRATION
  • Two types of piezoelectric effects: 1. Direct the generation of an electric voltage across the crystal when it is compressed or expanded. 2. Reverse piezoelectric effect or indirect. This occurs when the AC moves through the crystal producing compression or expansion. This change in voltage polarity causes the crystal to expand and contract and thus vibrate at the frequency of the electrical oscillation. The reverse piezoelectric effect is used to generate US at a desired frequency
  • Ideally matches the diameter of the transducer faceplate. The acoustic energy is contained w/I a focused cylindrical beam that is ~ the same diameter as the sound head. This will assure the maintenance of the best coupling. The appropriate size of area to be treated using US is 2-3 x the size of the ERA of the crystal.
  • AT 1Mhz US is transmitted through superficial tissues and absorbed primarily at 2-5 cm. 1 Mhz is beneficial for fatter pts., and whenever the desired effects are in deeper tissues. I.e.. Piriformis, Soleus At 3 MHz energy is absorbed in superficial tissues and absorbed with a depth of penetration between 1-2 cm. Ideal for plantar fascitis, patella tendonitis, and epicondylitis. As the frequency of the US increases, the rate of absorption and attenuation increases. 3 MHz frequency US is absorbed more superficially and 3x faster than 1 MHz US. Faster absorption causes faster peak heating. 3Mhz US heats human m 3x faster than 1 MHz
  • Collimated means the beam is focused, less divergent and generally produced by a large diameter transducer. As the beam moves away from the transducer the waves eventually become indistinguishable and arrive at a certain point simultaneously. This creates a point of highest acoustic intensity. Maximum Acoustic intensity can e determined by calculating the distance L from the surface of the transducer. L = D2/ 4 W Where D squared is the diameter of the transducer and w is the wavelength.
  • Some units are as high as 8 to 1. Peak intensities of 8w/cm2 have been shown to damage tissue. Therefore the pt. runs the risk of tissue damage at intensities > 1w/cm2 are used. Lower BNR’s allow you to lower the chance of developing “Hot Spots” of concentrated energy
  • If during a 40 ms time period the US was on for 10ms and off for 30 ms you would say that this is a 25% duty cycle. Formula for Duty Cycle: on time x 100 on time + off time Another example if the pulse duration = 1 ms and the total pulse period is 5 msec. The duty cycle is 20%. Take home message: Continuous US is used most for thermal effects. Pulsed US causes decreased heating. At a low intensity, US pulsed and continuous will produce nonthermal mechanical effects that are desirable for soft tissue healing.
  • Spatial averaged intensity: Intensity if the US beam averaged over the area of the transducer Spatial peak intensity: Highest beam value over time range bet 2.5-3.0 w/cm2 Temporal peak- pulsed US, max intensity during on phase w/cm2 Temporal averaged intensity: only pulsed US,average power of both on and off periods Spatial averaged temporal peak- max intensity occurring in time of the spatial averaged intensity. Spatial average during a single pulse. - Regardless of whether the US is pulsed or continuous if the spatial averaged temporal intensity is in the .1 to .2 w/cm2 range the intensity is too w to produce tissue temperature increase and only nonthermal effects will occur
  • Some say that tissue temp Increases of 1C increase metabolism and healing, Increases of 2-3 C decrease pain and m spasm, Increases of 4 C or > increase the extensibility of collagen and decrease joint stiffness. Temperatures greater than 45C may damage tissues, pt will experience pain prior to extreme temps
  • Acoustic microstreaming may cause high viscous stresses, which may in turn alter cell permeability to Na+ and Ca++ ions– important for the healing process
  • Tx area ~ sound head. Larger areas Increase time. The > intensity the less time Frequency determines depth of penetration, and rate of healing. # Mhz is absorbed 3x faster than 1 which means faster healing.
  • Coupling agents should not absorb US energy. Medium should be free of air bubbles. Medium shuld act like a lubricant, the transducer should have coupling medium on it before the unit is turned on. If the head is held away from the body part the crystal may be damaged and the transducer may overhead. Water soluble gels are most desirable.
  • Move the transducer slowly @ ~4cm/sec cover an area ~ 2-3 x greater than the ERA of the transducer. Overlapping circular motions or longitudinal are acceptable. The higher the BNR the more important it becomes to move the head faster. If the pt c/o pain, decrease the output but increase the duration
  • Meds anti inflamm., cortisol, salicates, dexamethosone, analgesics, lidocaine. Thermal effects will increase permeability and the acoustic pressure the us beam creates, will drive the meds in. So the medication will follow the path of the beam. When you do phonophoresis, Us can be pulsed or cont. Potential depth of phonophoresis is > than Ionto

Transcript

  • 1. Ultrasound
  • 2. 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
  • 3. 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
  • 4. 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
  • 5. 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.
  • 6. Frequency of wave transmission
    • Audible sound is transmitted bet 16kHz and20 kHz.
    • Therapeutic US is between .75- 3MHz.
    • The > the frequency the more focused the beam of sound produced
    • In humans the lower the frequency the greater the depth of penetration.
  • 7. Velocity
    • Velocity of US propagation is directly related to the density . The more dense and rigid materials have a higher velocity of transmission.
  • 8. 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
  • 9. 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.
  • 10. 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
  • 11. 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
  • 12. 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
  • 13. 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)
  • 14. 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 .
  • 15. 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.
  • 16. 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.
  • 17. 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.
    • +++ +++ +++
  • 18. 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
  • 19. 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
  • 20. 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
  • 21. 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.
  • 22. 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
  • 23. Non thermal Therapeutic Effects
    • 1. Stimulation of fibroblast activity
    • 2. Bone healing and repair of non union fracture
  • 24. 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
  • 25. Summary of Effects of US Effect Temperature inc Application Non thermal None 37.5 baseline Acute inj, edema, healing Mild thermal 1C Subacute inj, hematoma Mod thermal 2C Chronic itis,pain, TP Vigorous 4C Stretch collagen
  • 26. 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.
  • 27. 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. @ .5 – 1 cm away. Wipe away air bubbles. Intensity should be increased up to 50%
  • 28. Indications Ultrasound Acute/subacute cond Soft tiss heal/repair Scar tissue Jt.contracture Chr itis Inc collagen extensibility Dec m spasm Pain Inc bl fl Soft tiss repair Inc Pr- syn Tiss regen Bone healing Repair non-union fx Inflamm assoc Myos. Ossificans Plantar warts Myofascial trigger points
  • 29. Contraindications Acute/post acute cond.(Thermal) Areas of decreased temp sensation Areas dec circ Vasc. Insuff Thrombophleb Eyes Reproductive organs Pelvis immed after menses Pregnancy PPM Malignancy Growing epiphysis TJR Precaution not directly over Infection tumors
  • 30. 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.
  • 31. 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.
  • 32. 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.