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USAHS Methods II > Unit 4: Ultrasound > Flashcards

Unit 4: Ultrasound Flashcards

1
Q

Ultrasound

A

-Inaudible, acoustic, mechanical vibrations of high frequency that produce thermal and non-thermal physiological effects.
-Therapeutic US is typically 1.0-3.3 MHz.
-Ultrasound waves are produced by “running” an alternating current across a piezoelectric crystal in the sound head.
-A mechanical pressure (sound wave)
Sound waves with a frequency between 20 to 20,000 Hz are audible
-Ultrasound is defined as sound above 20 KHz.

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2
Q

Transducer

A

-Part of the ultrasound unit that contains a crystal.
-The crystal converts electrical energy to sound waves.

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3
Q

Piezoelectric Effect

A

Ability of a material to generate electricity when mechanically deformed

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4
Q

Reverse Piezoelectric Effect

A

-Electrical input causes a mechanical deformation (contraction and expansion of crystal, quartz or ceramic)
-Crystal in US head vibrates in response to electricity

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5
Q

Attenuation

A

Loss of energy in the US beam due to scattering (reflection and refraction) and absorption

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6
Q

Absorption

A

-Causes the thermal effects of US as Us is converted to heat in the tissues
-Different types of tissues absorb energy and “heat up” at different rates (tendon vs. muscle)

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7
Q

Less Absorption > More Absorption

A

Fat > Water > Blood > Muscle > Nerve > Skin > Tendon> Bone

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8
Q

Frequency Ranges for Ultrasound

A

-1 MHz = 1 million cycles per second; 5 cm depth
-3 MHz = 3 million cycles per
second; 2 cm depth
-3 Mhz heats up 3-4x faster than 1 Mhz*
-High frequencies are absorbed more quickly

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9
Q

Frequency Indicator (Hz):

A

-The number of compression/ rarefaction cycles per unit of time. Expressed in cycles per second – hertz (Hz).
-Increased frequency causes a decrease in the depth of penetration and concentration of US on superficial tissues
-3Mhz US heats tissues 3-4x’s Faster!!

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10
Q

Power (Acoustic Power: Intensity)

A

Amount of acoustic energy per unit of time
-Expressed in Watts (W)

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11
Q

Intensity (Acoustic Power: Intensity)

A

-Spatial Average (SA) intensity: W/cm2
-Watts (power) per unit area (ERA in cm) of the sound head
-Influences the rate of heating, strength of US

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12
Q

Intensity does NOT influence… (ultrasound)

A

Depth of penetration

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13
Q

Intensity usually creates in the… (ultrasound)

A

Center of the beam

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14
Q

Intensity lowest at… (ultrasound)

A

The edges

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15
Q

Intensity and BNR (ultrasound)

A

-High intensity areas within the ultrasound beam are a primary cause for “hot spots”.
-“Hot Spots” are prevented in part by keeping the sound head moving throughout the treatment
-Caution should be taken with using higher intensities with units that have poor BNR

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16
Q

Beam Nonuniformity Ratio (BNR)

A

-Refers to the uniformity of the US output ratio
-The ratio of the highest intensity (spatial peak intensity) found in the US beam to the spatial average intensity
-The smaller/lower the BNR the more homogeneous the beam produced by the transducer and the safer and more effective the treatment

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17
Q

A poor BNR

A

> 6:1 = Potential to create hot spots
-If you are doing an US set at 1.0 W/cm2, there will be an area of the beam as intense as 6 W/cm2
(8:1 max permitted)

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18
Q

Cliniacal Relevance of BNR

A

-BNR of 2:1 to 5:1 move ultrasound head 1cm/sec
-BNR of 6:1 to 9:1 move ultrasound head 4cm/sec
(indicated on unit by manufacturer)

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19
Q

Ultrasound Coupling

A

US attenuates quickly in air, and is reflected at the
air-tissue interface
-KEEP SOUND HEAD MOVING AND IN CONTACT WITH PATIENT’S SKIN!
-You will need a coupling agent (Ultrasound gel) to get the ultrasound energy into the desired tissue
-If you use other agents such as Vaseline, eucerin cream, hydrocortisone cream=no US energy is transmitted
-Ultrasound head should be kept in a consistent flat plane in relation to the skin

20
Q

Effective Radiating Area (ERA) sq.cm

A

-Area of the ultrasound from which the energy radiates
-The crystal does not vibrate uniformly which causes the ERA to be smaller than area of the ultrasound head
-Treatment area should be 2*-3 times the size of the ERA (This is not 2x’s the diameter of the sound head)
-Physical size of sound head should match body part being treated

21
Q

Duty Cycle

A

The amount of Time sound waves are penetrating tissue …Expressed in on/off cycle of time
-Continuous Ultrasound: US on all of the time 100% duty cycle
-Pulsed Ultrasound: 20% 50% on/off
-Duty Cycle: 2 ms on, 8 ms off: 2ms on/10ms total=20%
-Delivery of the ultrasound during a segment of time: 20% duty cycle (Minimizes thermal effect and serves primarily as mechanical effect)

22
Q

Continuous Ultrasound

A

US on all of the time 100% duty cycle
-Increase in peripheral blood flow
-Increase in metabolic rate
-Increase in oxygen uptake
-Increased temperature in tissues with local hyperemia
-Elevated pain threshold
-Changes sensory and motor nerve conduction (research inconclusive)
-Increased skin temperature, if applied over sympathetic nerves
-Increased collagen tissue extensibility (why??)
-Increased heating at interfaces (especially bone-muscle interface; bone absorbs 10 x’s more than soft tissue)

23
Q

Pulsed Ultrasound

A

20% 50% on/off
-Effects occur at the cell membrane due to mechanical vibration causing:
-Acoustic Streaming, Micro Massage, Cavitation

24
Q

Acoustic Streaming:

A

-Unidirectional movement of fluid within the pressure field that causes structural changes in cell membrane
(Increased cell permeability and ionic exchange)

25
Q

Acoustic Streaming (pulsed ultasound)

A

-Unidirectional movement of fluid within the pressure field that causes structural changes in cell membrane
(Increased cell permeability and ionic exchange)

26
Q

Micro Massage (pulsed ultrasound)

A

Force which occurs during compression phase of pulsed ultrasound that deforms the cell membrane and massages the cell

27
Q

Caviation (pulsed ultrasound)

A

-Formation, growth and pulsation of gas or vapor filled bubbles caused by ultrasound bean
-Stable: Changes in cellular diffusion
-Unstable: Tissue Death
(Pulsed US reduces risk of unstable caviation)

28
Q

Physiological Effects of Pulsed Ultrasound

A

Increases cell and vascular wall permeability to calcium and sodium ions
-Resulting in less leakage from the capillaries into the interstitial spaces (decreases edema)
-Increases extensibility of connective tissue (collagen rich tissue)
-Stimulation of tissue regeneration (fibroblast activity)
-Promotes soft tissue and bone repair
-Increase circulation
-Stimulate the release of histamine from mast cells by degranulation. especially within the first few hours of the injury, thus accelerating the healing process
-Decreases inflammatory phase (inhibits the release of inflammatory mediators)
-Stimulates fibroblasts to secrete collagen (increases tensile strength)
-Accelerates wound contraction and healing of the dermis
-Decreases pain

29
Q

1 MHz (ultrasound)

A

-5cm
-Increased depth
-Slow heating
-Increased treatment time with increased intensity
-Pulsed: 0.5-1.0 W/cm2
-Continuous: 1.5-2.0 W/cm2

30
Q

3 MHz (ultrasound)

A

-1-2cm
-Decreased depth
-Quick heating
-Decreased treatment time with decreased intensity
-Pulsed: 0.5-1.0 W/cm2
-Continuous: 1.0-1.5 W/cm2

31
Q

Patient Response: Intensity too high

A

Deep ache from overheating the bone periosteum

32
Q

Patient Response: Intensity too low

A

No increased temperature

33
Q

Clinical Ultrasound Uses

A

-Sub-acute and chronic soft tissue inflammation (thermal)
-Joint contractures
-Muscle spasm
-Neuroma (thickening of nerve tissue due to compression or irritation of the nerve)
-Loosen scar tissue
-Trigger point areas
-Acute injuries (non-thermal only)
-Bone healing (non-thermal only)
-Tissue repair

34
Q

Soft Tissue Shortening

A

-Can penetrate depths of most joint capsules, tendons, ligaments, scar tissue
-Collagen content (high absorption coefficient)
-Increased extensibility of tissue with reducing risk of damaging tissues
-US is more effective when stretch applied to tissue

35
Q

Thermal Effects (pain control)

A

-Stimulation of cutaneous thermal recpetors
-Increased soft tissue extensibility
-Change with nerve conduction

36
Q

Nonthermal Effects (Pain Control)

A

Modulation of inflammation

37
Q

Therapeutic Usage

A

-Surgical Incision
-Healing Fracture
-Tendon Injuries (tendonitis, tendon laceration s/p repair)
-Phonophoresis

38
Q

Surgical Incision (therapeutic uses)

A

-Accelerates the development of new blood vessels
-Reestablishes circulation and facilitates wound healing
-Relieves pain from scars
-Accelerates hematoma resolution

39
Q

Healing Fracture (therapeutic uses)

A

-Thermal US not used over unhealed fractures
-Low dose pulsed ultrasound can reduce fracture healing time
-Can be painful? Why?

40
Q

Tendonitis

A

-Acute Phase: Low intensity pulsed US (non-thermal)
-Chronic Phase: High intensity continuous, if shortening of tissue has occurred (thermal)

41
Q

Tendon Laceration s/p Repair

A

-Minimum of 6 weeks post repair (ongoing research)
-Increases extensibility of tissue
-Preparatory method for tendon gliding

42
Q

Phonophoresis

A

-Application of ultrasound in conjunction with topical drug
-Enhance delivery of the drug
-Inconsistencies in regard to effectiveness
-MD prescription required for medication

43
Q

Contraindications

A

-Over pacemaker or implanted electrical device
-Do not apply after cold pack/ice
-Over the heart, eyes, reproductive areas
-Over CNS tissue (spinal cord post laminectomy)
-Sites of insulin injections
-Over fracture sites before healing, demineralize the bone (thermal setting only)
-Ischemic areas
-Areas with limited sensation
-Do not apply over heart, eye, pregnant uterus, reproductive, organs, children’s growth plates, breast implants

44
Q

Ultrasound Precautions

A

-Cognitive/communication impairment
-Impaired pain or temperature sensation
-Reduced circulation
-Acute inflammation
-Joint implants
-Main peripheral nerve branches (controversial)

45
Q

Ultrasound Contraindications (controversial areas)

A

-Plastic implants
-Joint cement
-Metal implants
-Peripheral nerve branches
-Epiphyseal growth plates

46
Q

Ultrasound Documentation

A

-Area of body treated
-Ultrasound Parameters: Frequency, Intensity, Duty cycle, Treatment duration, Delivery, Patients response to treatment

47
Q

Guidelines

A

-Correctly position your patient
-Describe advantages and disadvantages of modality
-Recall precautions and contraindications
-Explain procedure and what the patient should feel
-Select appropriate US settings
-Clean skin with alcohol and/or soap
-Apply gel and position head of US correctly
-Move the US head slowly (pain-free); If pain, decrease intensity
-Ask the patient to describe what they are feeling
-Remove gel and clean transducer
-Inspect
-Document

USAHS Methods II (5 decks)

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