Ultrasound

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Author:
jpowell22
ID:
135651
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Ultrasound
Updated:
2012-02-27 22:15:28
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lecture
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maureen lecture
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  1. What are the types of ultrasound?
    • diagnostic
    • surgical
    • therapeutic
  2. We use therapeutic US, what is the frequency and intensity range for it?
    freq - 1-3 (.7-3.3)MHz

    int - 0.1-2.5 (5) W/cm2
  3. Superficial temp elevation to a depth of 1cm targets what tissue?
    skin and subcutaneous


    HP, paraffin, hydrotherapy, infrared, fluido, moist air cabinet
  4. How many cm is the deep temp elevation and what tissues does it target?
    2-5

    deeper subcutaneous tissues and superficial musculature
  5. Which MHz penetrates deeper, 1 or 3?
    1
  6. How are sound waves generated?
    the high frequency alternating current (.75 to 3 MHz) travels thru the coaxial cable to the transducer

    it is then converted into mechanical vibrations by a reversal of the piezoelectric effect

    when the current passes thru the crystal head, it vibrates and molecules are compressed and released
  7. When using non-thermal components, what type of effects do you get?
    • separation of collagen fibers (increases tissue extensibility)
    • increased permeability of cell membranes
  8. When using thermal components, what effects do you see?
    all those of non thermal, plus increased tissue temp and all those of heating
  9. What are advantages of US?
    • can produce temp changes deep within tissue
    • local-few generalized responses
    • short application times
  10. What are disadvantages of US?
    • difficult to monitor disage (pt feels little sensation)
    • pressure on body part (tenderness)
  11. What are indications?
    • soft tissue shortening (joint contractures, scarring)
    • subacute and chronic inflammation
    • can treat acute conditions if using pulsed mode
    • painful conditions-muscle guarding, neuroma, trigger areas
    • warts
    • phonophoresis (delivers meds locally to tissues)
  12. What are contraindications?
    • arterial circulation unable to meet increased metabolic demand
    • if bleeding is present it will increase
    • pregnant uterus-cavitation
    • cancer
    • spinal cord after laminectomy-cavitation
    • infection
    • carotid sinus or cervical ganglia
    • possible increased destruction of articular cartilage in acute inflammatory joint pathologies
    • some plastics used in implant joints
    • DVT
    • anesthetized areas
  13. What are precautions for US?
    • maintain constant energy transfer-if not>BURNS...keep sound head moving, even contact, remove air bubbles, keep off bony prominences
    • dont hold sound head in air
    • avoid higher intensities than those therapeutic
    • careful over anesthesized skin
  14. What is the depth of penetration dependent on?
    the absorption and scattering of the US beam as it travels thru tissue
  15. What type of tissue has greater absorption?
    denser tissue - with more protein content
  16. What is absorption?
    uptake of heat converted from acoustic (sound) energy by propagation of US through the tissues
  17. What is the absorption of US in direct proportion to?
    protein content of the tissues sonated
  18. What tissues are selectively heated by US?
    • superficial bone
    • joint capsules
    • tendon
    • scar tissue
    • peripheral nerves
    • myofasical interface
    • cell membranes
  19. How do you need to stay with the US head to be sure the energy is being absorbed?
    perpendicular
  20. What is the diffuse reflection or refraction of US from irregular surfaces or inhomogeneities within the tissue?
    scattering
  21. What happens if you do now stay perpendicular to the body part while performing an US?
    reflection/refraction is worse and you lose energy
  22. What is the reversal of the direction of propagation of the US wave?
    reflection

    occurs when there is a mismatch of acoustic impedence between two tissue levels

    the greater the acoustical impedance, the greater the reflection

    interfaces are heated more (tendon/muscle, ligament/muscle, periosteum)
  23. What is refraction?
    reflection of energy from a straight path when passing obliquely from one medium to another

    increases as the transducer head becomes less perpendicular to the tx area

    lead to concentration of US energy at the point of refraction (where tendon joins bone)
  24. What is the rate at which energy is delivered per unit area and is expressed in watts per square centimeter?
    intensity
  25. What is power?
    • total output of transducer and is expressed in watts
    • measured on an US power meter
  26. What is the equation for average intensity?
    w/cm2 = total power output (W)/transducers ERA (cm2)
  27. What is the available intensity for therapeutic US? What intensity is most commonly used?
    available - 0-5 w/cm2

    most common - 0.5-2 w/cm2
  28. Can you use US for acute conditions?
    yes...pulsed mode is nonthermal
  29. What is frequency?
    • number of oscillations in one second
    • expressed in megahertz (MHz)
  30. What are the frequencies we use for US?
    • 1MHz - deep
    • 3MHz - superficial
  31. What type of beam is used for deeper penetration (1MHz)?
    diverging (gradually gets bigger)
  32. What type of beam is used for superficial penetration (3MHz)?
    collimating (stays same size)
  33. What must you use when your performing an US, and why?
    a coupling medium

    US energy will not pass thru the air or skin without the presence of a coupling medium

    aqueous gels
  34. What qualitites should a good coupling medium possess?
    • high transmission and low absorption of US
    • exclude air
    • minimal air entrapment
    • good impedance match with transducer/skin
    • low drag coefficient
    • good viscosity
    • low salt content
    • economical cost
    • easy to use
  35. What is a hydrogel sterile wound dressing?
    3.3mm thick transparent polyscrylamide agar gel, containing 96% water

    can be used as a coupling medium for US and then left on as a sterile wound dressing

    sterile saline must be appiled below and on top of the dressing to eliminate air trapped between the dressing and underlying tissues and to improve the drag coefficient to transducer head
  36. Why do you use an underwater US?
    when tissue depth and surface topography is irregular or sensitive to pressure

    hands, ankles
  37. How do you prepare for an underwater US?
    room temp degassed (get bubbles off side of tub) water in a plastic tank

    helps decrease reflection

    move transducer as close as possible while remaining perpendicular to area
  38. What is another option to use if the hydrogel sterile dressings are not necessary and if direct contact or immersion techinique are not possible?
    water cushions - transparent, resealable, rigid, small
  39. A duty factor of 100% is needed to elevate tissue temps to physiologically significant temps of what?
    • 40-45C
    • 104-112F
  40. How long does US need to be performed to reach a tru therapeutic effect?
    5 mins
  41. What should a patient feel while receiving an US (is anything at all)?
    mild sensation of warmth
  42. What are the effects of thermal US?
    • increased local metabolism and perspiration
    • local vasodilation with hyperemia
    • muscle relaxation
    • sensory nerve endings sedated
    • ..long tx times- increased body temp, resp, pulse, decreased BP
  43. What is the duty factor?
    what fraction of time the sound is present over one pulse period

    duty factor= duration of pulsed time on/total pulsed time
  44. What are the most common pulsed modes?
    • 20% (1:4)
    • 50% (1:1)
    • 10% (1:9)

    (1:4)=1 min on, 4 mins off
  45. What duty factors should you select for acute and subacute conditions?
    • acute- 5-15%
    • subacute- 20-50%
  46. What do nonthermal effects help with?
    • edema reduction
    • pain and muscle spasms
    • improved blood flow
    • induction of non-union bone repair
    • tissue regeneration and soft tissue repair
  47. When using a pulsed setting for US, what should a patient feel?
    NOTHING at all..subsensory
  48. Nonthermal effects are due to mechanical vibrations resulting in what?
    • acoustic streaming
    • cavitation
    • micromassage
  49. What is acoustic streaming?
    unidirectional flow of tissue components, which occurs at the cell membrane

    • increased cell membrane and vascular wall permeability
    • increased ion flexes and cellular activity
    • increased capillary density and improved blood flow
    • increased protein synthesis with increased wound healing
  50. What is cavitation?
    US vibrations cause compression and expansion of small gas bubbles in the blood and tissue fluids. the pulsation of the bubbles can cause changes in the cellular activity..sufficiently intense can cause tissue damage
  51. What type of cavitation do we want?
    stable cavitation - increased cellular activity, results in diffusional changes along cell membrane
  52. What type of cavitation do we not want?
    unstable/transient cavitiation - violent collapse of bubbles with tissue damage (blood vessel damage)....sends a shock wave thru the tissues
  53. What is micromassage?
    oscillatory movement of tissue and cells

    effects intercellular fluids thus reducing edema (milks out edema)

    stimulation of mechanoreceptor and autonomic nervous system - stimulates sensory nerves, somewhat works with gate theory, relaxation
  54. What does BNR stand for?
    beam non-uniformity ratio
  55. What is the beam non-uniformity ratio?
    ratio of highest intensity (w/cm2) found in the near field to the average intensity (w/cm2)
  56. Do you want a large or small BNR? Why?
    smaller..more homeogenous

    results in greater pt comfort, focused tx areas, slower head movement (will produce consistent therapeutic dose throughout target tissues)
  57. What happens with greater BNR ratio differences?
    less homeogenous the US beam...causes hot spots of increased wattage
  58. What does ERA stand for, and what is it?
    effective radiating area

    the area of the transducer head that is effective...always smaller than the actual head.
  59. Should you do US before or after cooling/heating modalities?
    before...cooling/heating alters the patients perception of pain and warmth
  60. What technique should you avoid at all times?
    stationary....casues selective heating and hot spots which can burn and damage tissue
  61. What two types of techniques should you use for US?
    • overlapping circles
    • parallel stroking technique

    *cover half of previous area
  62. What is the rate of stroking?
    4 inches per second
  63. What is dosage governed by and what does it change?
    by power and time

    sonation can change the nerve conduction velocities
  64. What intensity increases velocity? Decreases?
    • low and high increases (0.5 or 3.0 w/cm2)
    • moderate decreases (1 to 2 w/cm2)

    1.5 is like perfect
  65. What are some considerations for treatment (to determine power)?
    • goal of treatment
    • site of lesion
    • acuteness
  66. What is phonophoresis and its advantage?
    medicinal molecules that are driven across the skin into deeper muscle and nerves by US

    no invasion of skin like injections
  67. What are some indications for phonophoresis?
    • subacute inflammatory conditions with antiinflammatory drugs
    • use low intensity, long duration


    10% hydrocortisone cream, cortisol, salicylates, dexamethasome in glycerol, cream, oil, or water
  68. For what reason would you terminate US treatment?
    • 1. complete relief of signs/symptoms or restoration of function
    • 2. find no beneficial effects after 3-4 treatments
    • 3. after course of 12-15 treatments- no proof of further US benefits
    • 4. modify tx is symptoms get worse

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