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623: Physical Agents & Mech Modalities > Ultrasound > Flashcards

Ultrasound Flashcards

1
Q

Ultrasound with thermal effects is used to treat what?

A

Application to tendons, ligaments, and fascia

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2
Q

How is ultrasound with non-thermal effects used?

A

Facilitates healing, modifies inflammation, and enhances transdermal drug deliver

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3
Q

In order to deliver ultrasound with non-thermal effects, what type should you use?

A

Low-intensity, pulsed US

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4
Q

What is the range of frequency for therapeutic ultrasound?

A

between 0.7-3.3 MHz

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5
Q

Therapeutic US maximizes energy absorption at a depth of _ - _ cm of soft tissue.

A

2-5

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6
Q

US travels through material and decreases in intensity as a result of ________.

A

attenuation

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7
Q

Ultrasound is a high frequency sound wave that can be described by what 5 things?

A
  • Intensity
  • Frequency
  • Duty cycle
  • Effective radiating area (ERA)
  • Beam non-uniformity ratio (BNR)
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8
Q

Ultrasound enters the body and is attenuated in the tissue by ______, ______, and ______.

A
  • absorption
  • reflection
  • refraction
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9
Q

Attenuation is greatest in what types of tissues?

A

In tissues with high collagen content such as tendons, ligaments, muscles, joint capsules, meniscus, and cortical bone.

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10
Q

Attenuation is greatest with the use of ___ frequency ultrasound.

A

high

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11
Q

Continuous ultrasound delivers _____ effects whereas pulsed ultrasound delivers _______ effects.

A

thermal; non-thermal

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12
Q

What is the thermal effect of ultrasound?

A

Increasing tissue temperature

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13
Q

What are the 4 non-thermal effects of ultrasound?

A
  • Acoustic streaming
  • Microstreaming
  • Cavitation
  • May alter cell membrane permeability
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14
Q

Which penetrates deeper ultrasound of a higher (3 MHZ) or lower (1 MHz) frequency? Which is more superficial?

A

1 MHz penetrates deeper with a lower frequency

3 MHz penetrates more superficial with a higher frequency

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15
Q

How is an ultrasound produced?

A

When an alternating electrical current is passed through a piezoelectric crystal, causing the crystal to contract and expand

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16
Q

The contraction and expansion of the crystal occurs from _____ to _______ times per second.

A

750,000 to 3,000,000 times per second

0.75 to 3 MHz frequency

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17
Q

What do ultrasound waves require?

A

a dense medium in which to travel

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18
Q

How does ultrasound travel through human tissue?

A

wave energy is transferred from one molecule to another

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19
Q

There is minimal to no significant temperature increase in what type of tissue?

A

fat and skin

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20
Q

Ultrasound waves have a ____ shape

A

sinusoidal

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21
Q

The peak and trough of ultrasound waves correspond to what two phases?

A

compression and rarefaction phases

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22
Q

Describe the compression phase

A

During the compression (positive pressure) phase tissue molecules in the path of the wave are compressed together

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23
Q

Describe the rarefaction phase

A

During the rarefaction (negative pressure) phase molecules spread out more than before the pressure was applied

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24
Q

When compression and rarefaction occurs in the same direction that the wave is traveling, what type of wave results?

A

longitudinal

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25
Q

Longitudinal waves can travel in what types of substances?

A

in both liquids and solids

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26
Q

When compression and rarefaction occurs in a direction at right angles to the direction that the wave is traveling, what type of wave results?

A

shear

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27
Q

Shear waves can travel in what types of substances?

A

only in solids

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28
Q

In human tissue, shear waves tend to form where?

A

at the surfaces of bone

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29
Q

What does spatial average intensity represent?

A

the amount of energy in a specific area

30
Q

Spatial average intensity is expressed in what?

A

watts per centimeter squared

31
Q

How do you calculate spatial average intensity?

A

by dividing the total output by the effective radiating area (ERA) of the head

32
Q

What is spatial peak intensity?

A

the maximum intensity point in the beam

33
Q

Where is the spatial peak intensity located?

A

in the far field of the beam

34
Q

What is the beam nonuniformity ratio (BNR) a ratio between?

A

the spatial peak intensity and the spatial average intensity

35
Q

What is the ideal BNR of an ultrasound unit? Is this clinically attainable?

A

1:1

No

36
Q

Because an ideal 1:1 ratio is clinically unattainable what do the ratios average between?

A

2:1 to 6:1

although 8:1 are acceptable

37
Q

Frequency is typically delivered at what 2 frequencies?

A

1MHz or 3 MHz

38
Q

A _ MHz beam is more collimated and penetrates deeper than a _ MHz beam

A

1

3

39
Q

7 thermal effects of US

A
  • Acceleration of metabolic rate
  • Control of pain and muscle spasm
  • Alteration of nerve conduction velocity
  • Increased circulation/altered blood flow
  • Increased enzymatic activity
  • Changes in contractile activity of skeletal muscle
  • Increased soft tissue extensibility
40
Q

An ultrasound frequency of 1 MHz is used to heat tissues up to a depth of _ cm

A

5

41
Q

An ultrasound frequency of 3 MHz is used to heat tissues up to a depth of _ - _ cm

A

1- 2

42
Q

In order to increase the total amount of heat delivered to the tissue, what must be increased?

A

the duration and/or the average intensity of US application

43
Q

Factors that affect ultrasound absorption

A
  • Cooling by the circulation of blood
  • Heating by reflected ultrasound waves
  • Conduction from one warmed area of tissue to another
  • Thickness of each tissue layer
  • Amount of circulation
  • Distance to reflecting soft tissue/bone interfaces
44
Q

According to the Law of Grotthus-Draper, as superficial tissues absorb more energy, ___ energy is transmitted to underlying tissues. Therefore if the amount of energy absorbed is sufficient to stimulate the target tissue, some physiological response will occur.

A

less

45
Q

When does heating occur?

A

When the acoustic energy is absorbed and converted into thermal energy. This is the result of frictional forces between molecules as well as cavitation

46
Q

In order to achieve a therapeutic effect through ultrasound heating, tissue temperatures should be maintained between what temperature range for how long?

A

between 40 and 45 degrees Celcius for at least 5 minutes

47
Q

The degree of tissue temperature rise depends on what 5 things?

A
  • Mode of application
  • Intensity and frequency of the output
  • Vascularity of the tissue
  • Type of tissue
  • The speed at which the sound head moves
48
Q

How fast should you move the sound head?

A

4 cm/second

49
Q

What size should the treatment area be?

A

2 times the size of the US head

50
Q

As the intensity of the US is increased, what happens to temperature change?

A

It increases (more so at a frequency of 3 MHz than 1 MHz because it is heating more superficial tissue)

51
Q

For a patient with sub-acute inflammation what type of thermal effect will ultrasound have on them?

A

Mild (approximately 1º C temperature increase)

52
Q

For a patient with chronic inflammation, muscle spasm, or they need pain modulation what type of thermal effect will ultrasound have on them?

A

Moderate (approximately 2º C temperature increase)

53
Q

For a patient with that needs increased blood flow or tissue heating to increase extensibility what type of thermal effect will ultrasound have on them?

A

Vigorous (approximately 3º C temperature increase)

54
Q

What are the 3 mechanical non-thermal ultrasound effects?

A
  • Cavitation (mechanical vibration)
  • Microstreaming
  • Acoustic streaming
55
Q

5 Biological non-thermal effects of ultrasound

A
  • Increased skin and cell membrane permeability
  • Increased mast cell degranulation
  • Increased chemotactic factor and histamine release
  • Increased responsiveness of macrophages
  • Increased rate of proteoglycan synthesis by chondrocytes
56
Q

How does non-thermal ultrasound effect cells?

A

The compression phase of an US wave deforms tissue molecules and also effects gas bubble in the tissue fluids which adds further stress to cell membranes

57
Q

What is cavitation?

A

the formation of gas bubbles, which expand and compress due to ultrasonically induced pressure changes in tissue fluids

58
Q

Stable vs. Unstable cavitation

A

During stable cavitation gas bubbles expand and contract, without growing to critical size

During unstable cavitation gas bubbles expand too far and suddenly collapse, resulting in increased pressure and temperature

59
Q

Cavitation sets up ___ currents in the fluid surrounding the vibrating bubble. What do these currents do?

A

Eddy

They exert a twisting motion on nearby cells

60
Q

The eddy currents caused by cavitation cause fluid movement in and around tissue cells caused by the ultrasound wave, what is this called?

A

Microstreaming

61
Q

What is the primary site for ultrasound interaction?

A

The cell membrane

62
Q

The destabilization of the cell membrane caused by ultrasound leads to what?

A

Increased permeability, which allows various ions and molecules to diffuse into cells, where they precipitate secondary events

63
Q

What two ions/molecules tend to diffuse into the cells have an effect?

A

Calcium and Histamine

64
Q

How does calcium effect cells?

A

Calcium is known as a messenger for other cell functions, including protein synthesis

65
Q

How does histamine effect cells?

A

It plays an influence on circulation and also plays a stimulating effect on protein synthesis

66
Q

Why is the role of histamine controversial?

A

Some studies have shown that it plays a positive effect on tissue healing, whereas other studies show that high intensity US can produce too much histamine, resulting in prolonged inflammation

67
Q

Indications for Ultrasound

A
  • Soft tissue healing and repair
  • Scar tissue
  • Joint contracture
  • Stretching of connective tissue
  • Chronic inflammation
  • Reduction of muscle spasm
  • Bone healing
  • Pain modulation
  • Increase blood flow
  • Soft tissue repair
  • Increase in protein synthesis
  • Tissue regeneration
  • Repair of nonunion fractures
  • Myofascial trigger points
68
Q

Contraindications for Ultrasound

A
  • Areas of decreased sensation/circulation
  • Vascular insufficiency
  • Malignancy
  • Pregnancy
  • CNS tissue
  • Joint cement/total joint replacements
  • Plastic components
  • Pacemaker
  • Thrombophlebitis
  • Eyes
  • Reproductive organs
  • Epiphyseal areas in young children
  • Infection
69
Q

Precautions to Ultrasound

A
  • Acute inflammation
  • Epiphyseal plates
  • Fractures
  • Breast implants
70
Q

3 adverse effects of US

A
  • Burns
  • Blood cell stasis
  • Endothelial damage
71
Q

How should you move the transducer?

A

Slow strokes around 4cm per second in a linear or circular direction ensuring there is good contact/coupling and that the transducer is flat on surface

623: Physical Agents & Mech Modalities (17 decks)

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