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Therapy Modalities Lecture > Ultrasound > Flashcards

Ultrasound Flashcards

1
Q

What is Ultrasound?

A

Sound energy that’s produced through changes in pressure

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2
Q

Ultrasound: Frequency

A
  • Number of waves per second (Hz)
  • Human ear can hear frequencies from 16-20,000 Hz
  • Ultrasound is at a frequency above the sonic level: 750,000-3,000,000 Hz
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3
Q

Ultrasound: Therapeutic vs. Diagnostic

A
  • Frequency
    ~ Therapeutic: .75-3.3 MHz (low)
    ~ Diagnostic: 2-15 MHz (high)
  • Amplitude
    ~ Measure of the amount of energy/
    pressure of the wave
    ~ Therapeutic: High
    ~ Diagnostic: Low
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4
Q

Production of Ultrasound: Direct Piezoelectric Effect

A
  • Piezoelectric Crystals
    ~ Crystals that produce positive
    and negative charges (voltage)
    when mechanical stress
    (pressure) is applied
  • Deform crystal —-> electricity
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5
Q

Production of Ultrasound: Reverse Piezoelectric Effect

A
  • Crystal contracts and expands in reaction to the application voltage
  • US generator produces alternating current that passes through Piezoelectric crystal located in the transducer
    ~ Expansion and contraction of crystal
    produces changes in pressure/sound
  • Electricity into crystal ——-> Deformed
    crystal
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6
Q

Beam Nonuniformity Ratio (BNR)

A
  • BNR measures the nonuniformity of US waves
  • Indicator of the variability of intensity of an US beam
  • Expressed as a ratio:
    ~ Peak Intensity: Average intensity
    ~ 5:1 = average of 1W/cm2 with peaks
    of 5 W/cm2
    ~ Low ratios are ideal (1:1) in order to
    evenly distribute sound
    ~ High ratios can cause discomfort
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7
Q

Effective Radiating Area

A
  • Surface area of sound head that transmits a sound wave from the crystal into tissues
    ~ ERA is always smaller that the sound
    head
    ~ The best sound head will have an ERA
    that is close to the total area of the
    sound head
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8
Q

Transmission of Ultrasound

A
  • Requires molecular collision for transmission
  • Requires a dense medium for good transmission
    ~ Minimizes displacement
    ~ Maximizes contact with vibrating
    molecules
  • Requires a coupling agent to pass US from the transducer into tissues
    ~ Agent should transmit rather than
    reflect US energy
  • Mediums:
    ~ Water
    ~ US Gel
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9
Q

Coupling Methods: Direct

A
  • Transducer is applied directly to the skin
  • Used in areas at least as large as the transducer head
  • Gel serves as the coupling medium
    ~ Eliminates air between the head and
    skin (reflection)
    ~ Hair an irregularly shaped areas
    increase air pockets and bubbles
    between the head and skin
  • Firm constant pressure should be used
    ~ Too light: Poor coupling
    ~ Too hard: Force medium out of space
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10
Q

Coupling Methods: Water Immersion

A
  • Used for irregularly shaped body parts
  • Head held approximately .5-1cm from the body
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11
Q

Coupling Methods: Bladder Method

A
  • Water filled balloon/plastic bag or gel pad coated with gel and placed over treatment area
  • Used for irregularly shaped or small areas that can not be immersed
  • Must take care to remove all air from bag or balloon
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12
Q

Transmission of Ultrasound Through Tissues

A
  • Sound travels in longitudinal waves
    ~ Movement/oscillation of molecules
    within the wave are in the direction of
    the wave
  • Within the wave are different regions
    ~ Compressions (collection of
    molecules)
    > Area of high pressure
    > Molecules squeezed together
    ~ Rarefactions (spread out molecules)
    > Area of low pressure
    > Molecules spread out
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13
Q

Transmission of Ultrasound Through Tissues: Law of Grotthus-Draper

A
  • As the sound wave moves through the tissues, it’s reflected, refracted, and absorbed, or passed to deeper tissues
  • Absorption is the goal
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14
Q

Reflection/Refraction

A
  • Product of sound energy passing through different mediums
    ~ Different mediums can have different
    acoustic impedance (resistance to
    sound wave flow)
  • When a sound wave encounters a boundary between mediums (tissue layers) some energy will be lost to reflection/refraction
  • The greater the difference in impedance the greater the amount of reflection
  • Reflection is increased when the head is not placed parallel to the body
  • High reflection at
    ~ Soft-tissue/bone interface
    ~ Musculotendinous Junction
    ~ Intermuscular interfaces
    ~ Interface between head and air (can
    cause crystal to become damaged)
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15
Q

Standing Waves

A
  • If a reflected wave meets the incoming wave, a standing wave is created
    ~ Areas of high and low pressure are
    exaggerated, causing greater
    movement of molecules
    ~ Movement (friction) causes a high
    amount of energy (heat)
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16
Q

Absorption

A
  • Sound energy is absorbed by converting mechanical energy to heat energy
  • As a result, the intensity of the sound wave decreases as the distance it travels increases
  • The amount of absorption that takes place depends on how much collagen is contained
    ~ The more collagen the greater the
    absorption
    ~ Tissues with high collagen are denser
    > Tendon
    > Muscle
    > Ligament
    > Bone
17
Q

Transmission of Ultrasound Through the Tissues: As frequency increases…

A
  • Divergence decreases
    ~ Depth decreases
    > 1 MHz = 5cm
    • Deeper but more generalized
    > 3 MHz = 2 cm
    • Superficial but more specific
18
Q

Pulsed vs. Continuous Ultrasound

A
  • Continuous
    ~ US energy is being produced 100% of
    the time during Tx
    ~ Most commonly used when thermal
    effects are desired
    > Heats very effectively
  • Pulsed
    ~ US energy is interrupted with off
    periods
    ~ Utilizes Duty Cycle
    > On time/On time + Off time
    > % of time US energy is being
    produced
    ~ Most commonly used when
    nonthermal effects are desired
    > Heating will still occur but a
    decreased rate
19
Q

Thermal Effects of US

A
  • All due to the absorption of US as it moves through the tissues
    ~ Absorption involves conversion of
    mechanical energy (motion) to heat
    ~ Main advantage over other heating
    modalities is that US is selective for
    tissues containing high amounts of
    collagen
20
Q

Thermal Effects of US: Increased Metabolism

A
  • Results of Increased Metabolism
    ~ Increased Oxygen Consumption
    which can increase secondary
    damage/Low O2
    ~ Increased cellular wastes
    ~ Increased cell activity
    > Good during repair-maturation/
    fibroblasts, but bad during acute/
    WBC
21
Q

Thermal Effects of US: Increased Circulation

A
  • Due to local vasodilation
    ~ How/when can this be used as an
    advantage?
    > Repair-maturation
    ~ How/when can this be a
    disadvantage?
    > Acute
22
Q

Thermal Effects of US: Increased Capillary Permeability and Decreased Tissue Stiffness

A
  • Increased Capillary Permeability
    ~ Increased potential for venous and
    lymphatic drainage
  • Decreased Tissue Stiffness
    ~ Increased elasticity of collagen
    ~ Decreased fluid viscosity
23
Q

Thermal Effects of US: Decreased Pain and Decreased Muscle Tone/Spasm

A
  • Decreased Pain
    ~ Increased blood flow (increased O2)
    ~ Counter Irritant
    ~ Removal of chemical mediators
  • Decreased Muscle Tone/Spasm
    ~ Reduction in pain (pain-spasm-stasis)
    ~ Increased O2 delivery
    ~ Decreased MS sensitivity (more
    relaxation)
24
Q

Nonthermal Effects of US

A
  • Nonthermal US is applied to tissues when a more acute injury is present
  • Mostly used when
    ~ Using pulsed output w/ normal
    intensities
    > 20-25% duty cycle
    ~ When using continuous US w/ low
    intensity
    > .3 W/cm2 intensity
25
Q

Nonthermal Effects of US: Cavitation

A
  • Formation of gas filled bubbles that expand and compress due to pressure changes in tissue fluids
    ~ Compression in high pressure
    ~ Expansion in low pressure
26
Q

Nonthermal Effects of US: Acoustical/Microstreaming

A
  • Unidirectional flow of fluids along cell membranes
  • Also causes movement of gas bubbles (produced by cavitation) along cell membranes
    ~ Micro-massage
27
Q

Nonthermal Effects of US: Cavitation and Microstreaming

A
  • Because cavitation and Microstreaming always occur regardless of the settings used, nonthermal effects will always occur no matter what the goals (thermal/nonthermal) of the US tx are
  • The cavitation and Microstreaming cause a “micro massage” of the cells resulting in the specific non-thermal effects
28
Q

Nonthermal Effects of US: Results

A
  • Increased Cell membrane permeability
  • Fibroblast activity stimulation
  • WBC activity stimulation
  • Osteoblast activity stimulation
29
Q

Thermal and Nonthermal US

A
  • Both produce some heat and nonthermal effects
  • Specific settings can be used to emphasize thermal or nonthermal effects
30
Q

Power vs. Intensity

A
  • Power
    ~ The amount of ultrasound energy in
    the beam/wave.
    ~ Measured in Watts
  • Intensity
    ~ Rate of ultrasound energy delivered
    per unit of ERA area
    > ERA = Area of the transducer
    head that is actually emitting
    energy
    ~ Measured in Watts/cm2
    ~ Must make sure of which units the
    machine is displaying for proper
    treatment.
    > Intend to apply 2.0 Watts/cm2,
    but actually applying 2 Watts
    > Actually putting in .5 Watts/cm2
    (2.0 Warts w/ERA of 4cm2 = .5
    W/cm2)
31
Q

Choosing Proper Intensity

A
  • No hard rules for proper levels
  • Guidelines
    ~ Use the lowest intensity at the
    highest frequency that will transmit
    the energy to the target tissue
    > Low intensity: decreases chance
    of damage or discomfort
    > High frequency: concentrate
    energy in the area being treated
32
Q

Choosing Proper Intensity: Nonthermal Effects

A
  • All US will heat to a certain degree, goal is to minimize this effect
    ~ Continuous US
    > A very low intensity should be
    used: < .3 W/cm2
    ~ Pulsed US
    > Higher intensities can be used
    usually around 1.0 W/cm2
    > Must use a duty cycle (20-25%)
33
Q

Choosing Proper Intensity: Thermal

A
  • Absolute Temperature
    ~ Thermal effects occur when tissues
    are raised to 104-113 degrees
    ~ Body temp: 98 degrees
  • Amount of Temperature Increase
    ~ ^ of 1 degrees increases metabolism
    and healing.
    ~ ^ of 2 - 3 degrees decreases pain and
    muscle spasm.
    ~ ^ of 4 degrees C or more increases
    extensibility of collagen and
    decreases joint stiffness.
34
Q

Choosing Proper Intensity: Thermal Tx Time

A
  • Main factor in choosing intensity is the
    treatment time.
    ~ Most intensities of continuous
    ultrasound will eventually raise
    temperature to therapeutic leveis or
    an absolute temperature
    ~ Lower intensities require more time
    and higher intensities require less
    time.
35
Q

Rate of Heating Per Minute

A

Intensity W/cm2 1MHz 3MHz
.5 .04 C .3 C
1.0 .2 C .6 C
1.5 .3 C .9 C
2.0. .4 C 1.4 C

36
Q

Treatment Area Size

A
  • Tx area should be 2-3 times the size of the transducer (ERA)
    ~ 2 times the ERA is optimal for thermal
    treatments
  • Transducer should be moved at a rate of 4 cm/second
  • If area is too large or head is moved too quickly, optimal healing of tissues won’t occur
37
Q

Timing/Frequency of Treatment

A
  • Acute/Repair/Maturation
  • Start of treatment
    ~ Start as soon as clinically acceptable
    following an injury
  • Later stages
    ~ Continue until no benefit is seen from
    Tx
38
Q

US Indications

A
  • Pain
  • Spasm
  • Scar tissue
  • Connective tissue tightness
  • Bone healing
  • Myositis ossificans
    ~ an increase in circulation causes
    body to flush it out/reabsorb
39
Q

US Contraindications

A
  • Acute inflammation (thermal)
  • Pregnancy
  • Tumor
  • Over spinal cord or superficial nerves
    (ulnar and common peroneal)
    ~ These structures are dense which
    means they heat up very effectively

Therapy Modalities Lecture (9 decks)

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