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ULTRASOUND

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SOUND & ULTRASOUND Periodic mechanical disturbance of an elastic medium

such as air.

Ultrasound refers to mechanical vibrations of a higher frequency, beyond the range of human hearing

Frequency -     Typically 1 or 3 MHz

Wavelength - @ 1MHz would be 1.5mm and @ 3 MHz would be 0.5 mm.

velocity of ultrasound - Sound waves can travel more rapidly in a more dense medium.  The velocity varies from

331 m/sec in air 1450 m/sec in fat, 1570 m/sec in blood

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Transducer (sound head): A crystal that converts electrical energy into sound

Power: The amount of acoustic energy per unit time. This is usually expressed in Watts.

Intensity: The power per unit area of the sound head. This is usually expressed in Watts/centimeter2.

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Spatial Peak Intensity: The peak intensity of the ultrasound output over the area of the transducer. The intensity is usually greatest in the centre of the beam and lowest at the edges of the beam.

Spatial Average Intensity: The average intensity of the ultrasound output over the area of the transducer.

Beam Nonuniformity Ratio (BNR) : The ratio of the spatial peak intensity to the spatial average intensity .

For most units this is usually between 5:1 and 6:1,

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Continuous Ultrasound:

Pulsed Ultrasound: Pulsing the ultrasound minimizes its thermal effect.

Duty Cycle: The proportion of the total treatment time that the ultrasound is on. This can be expressed either as a percentage or a ratio.

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Spatial Average Temporal Peak (SATP) Intensity: The spatial average intensity of the ultrasound during the on time of the pulse.

Spatial Average Temporal Average (SATA) Intensity: The spatial average intensity of the Ultrasound averaged over both the on time and the off time of the pulse.

SATP x duty cycle = SATA

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Effective Radiating Area (ERA) area of the sound head that

produces ultrasonic waves; expressed in square

centimeters (cm2) Always lesser area than

actual size of sound head Large diameter heads –

column beam Small diameter heads –

more divergent beam Low frequency (1 MHz) –

diverge more than 3 MHz

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Near Field/Far Field: The near field, also

known as the Fresnel zone is the convergent region and

the far field, also known as the Fraunhofer zone, is the divergent region

Length of near field = Radius of transduce2 / Wavelength of ultrasound (r2 /λ)

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Acoustic Impedance

It is a measure of the resistance of particles of medium to mechanical vibrations

This resistance increases in proportion to the density of medium and

velocity of ultrasound in the medium

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Reflection most reflection occurring where there is the

greatest difference between the acoustic impedance of adjacent tissues.

In the body, most reflection i.e. 1% in soft tissue / fat interface about 35%, occurs at soft tissue-bone

interfaces there is 100% reflection of ultrasound at

the air skin interface and only 0.1% reflection at the transmission

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Standing Wave

When reflected ultrasound meets further waves being transmitted, a standing wave (hot spot) may be created, which has potential adverse effects upon tissue.

Such effects can be minimized by ensuring that

the apparatus delivers a uniform wave, using pulsed waves and moving the transducer during treatment

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Standing Wave

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Absorption Absorption

coefficients are tissue and frequency specific.

They are highest for Tissues with highest collagen content and

Increase in proportion to the ultrasound frequency

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Refraction

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Attenuation Attenuation is the result of

absorption, reflection, and refraction, with absorption accounting for about one-half of attenuation.

Attenuation coefficients are tissue and Frequency specific.

They are higher for tissues with a higher collagen content and

increase in proportion to the frequency of the ultrasound

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Half value depth this is the tissue depth

at which 50% of the ultrasound delivered at the surface has been absorbed.

The average 1/2 value depth of

3MHz ultrasound is at 2.5 cm and

1MHz ultrasound as 4.0 cm

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  1 MHz 3 MHz

Muscle   9.0  mm   3.0  mm

Fat 50.0  mm 16.5  mm

Tendon   6.2  mm   2.0  mm

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Quantity of

Ultrasound(fraction of beam being

further propagated)

1.0

.5

.25

.125

1st HalfValue

2nd HalfValue

3rd HalfValue

4th HalfValue

Tissue depth

The quantity of the ultrasound beam decreases as the depth of the medium (tissue) increases.

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Generation of UltrasoundGeneration of Ultrasound Pizoelectric effect - generated by pizoelectric crystalsPizoelectric effect - generated by pizoelectric crystals

occurs when an electric current is passed through the crystaloccurs when an electric current is passed through the crystal crystal expands & contracts at frequencies that produce crystal expands & contracts at frequencies that produce ultrasoundultrasound

pizoelectric crystal in transducer head Wavelength

ultrasound transducer

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Production

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Ultrasound Machine & Coupling Agent

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Types of Ultrasound BeamsTypes of Ultrasound Beams

Continuous WaveContinuous Wave - no interruption of beam: - no interruption of beam: best for best for maximummaximum heat buildup heat buildup

Pulsed WavePulsed Wave - intermittent “on-off” beam - intermittent “on-off” beam modulationmodulation builds up less heat in tissues used for builds up less heat in tissues used for post post

acuteacute injuries injuries

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Pulsed Wave

Mark Space ratio

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Physiological Effects of UltrasoundPhysiological Effects of Ultrasound

Thermal effectsThermal effects (minimum 10 min - 2.0 watts - 1 MHz) (minimum 10 min - 2.0 watts - 1 MHz) ▲▲ blood flowblood flow

▼▼ inflammation and inflammation and ▼▼ hematoma (remains controversial?) hematoma (remains controversial?)

▲▲enzyme activityenzyme activity ▲▲sensory and motor nerve conduction velocitysensory and motor nerve conduction velocity ▲▲extensibility of connective tissue & possibly scar tissueextensibility of connective tissue & possibly scar tissue ▼▼ joint stiffnessjoint stiffness ▼▼ muscle spasmmuscle spasm ▼▼painpain

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Non-thermal effectsNon-thermal effects cavitations

alternating expansion & compression of small gas bubbles

may cause ▲ cell membrane & vascular wall permeability (▲ nutrient and oxygen

delivery) unstable cavitations may cause

tissue damage unstable cavitations – large,

violent changes in bubble volume

Micro streaming bubble rotation of fluid

movement along cell membrane boundaries (▲ nutrient and oxygen delivery)

changes in cell permeability & ion flux reduces healing time

gas buble expansion

gas buble compression

bubble rotation & associated fluid movement alongcell membranes

Cavitation Microstreaming

Non-thermal Effects of Ultrasound

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Non-thermal effectsNon-thermal effects

Possible therapeutic benefits of non-thermal effects

difficult to make distinction from thermal benefits

▲ capillary density & ▲ cell permeability ▲ fibroblastic activity and associated

collagen production ▲ cortisol production around nerve bundles

reduce inflammation

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Output FrequencyDurationDuty CycleOutput Intensity

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Output Frequency Determines the treatment depth 1 MHz Output

Deep (5 to 7 cm) tissues○ Rotator cuff, vastus intermedius, gastroc

3 MHz OutputSuperficial (up to 3cm deep) tissues

○ Patellar tendon, MCL, brachialis

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Treatment Duration Depends on:

Size of the treatment areaOutput intensityTherapeutic goals

Vigorous heating1 MHz output

○ 8 to 10 minutes3 MHz output

○ 3 to 4 minutes

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Direct CouplingImmersion MethodPad/Bladder Method

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Coupling Methods Ultrasonic energy cannot pass through

the air A coupling medium is required Medium should be water-based Coupling method should confirm to the

body area The body area should be clean and

relatively hair-free

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Direct Coupling Gel or Creams Only use approved

coupling agents Apply liberally to area Remove air bubbles

by passing sound head over area (before power is increased)

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Direct Coupling

Move the sound head s-l-o-w-l-y4 cm/sec

Moving the head faster decreases heating

If the patient describes discomfort, decrease the output intensity

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Coupling Ability of Various MediaSubstance

Transmission Saran Wrap 98 Lidex ge, fluocinonide (.05%) 97 Thera-Gesic 97 Mineral oil 97 US Transmission gel 96 US Transmission lotion 90 Chempad-L 68 Hydrocortisone powder (1%) 29 Hydrocortisone powder (10%) 7 Eucerin cream 0 Myoflex 0 White petrolatum gel 0

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Immersion Technique Used to treat irregularly

shaped areas The limb is immersed in a

tub of degassed water If tap water is used,

increase the output intensity by 0.5 w/cm2

Transducer is held appx. 1” from the body part

Avoid the formation of air bubbles

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Pad (Bladder) Method

A mass of conductive gelCommercial padsSelf-made bladders

Conforms to the treatment area

Commercial pads help limit the size of the treatment area

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Contraindications Acute injuries (100% duty

cycle) Ischemic areas Areas of impaired

circulation including arterial disease

Over areas of deep vein thrombosis

Anesthetic areas Over cancerous tumors Over sites of active

infection or sepsis Over the spinal cord or

large nerve plexus in high doses

Exposed metal that penetrates the skin (e.g., external fixation devices)

Areas around the eyes, heart, skull, or genitals

Over the thorax in the presence of an implanted pacemaker

Pregnancy when used over the pelvic or lumbar areas

Over a fracture site before healing is complete

Stress fracture sites or sites of osteoporosis

Over the pelvic or lumbar area in menstruating female patients

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Precautions Symptoms may increase after the initial

treatments. Use caution when applying ultrasound around

the spinal cord, especially after laminectomy. The use of ultrasound over metal implants is

not contraindicated Keep the sound head moving

Use caution when applying ultrasound over epiphyseal plates of growing bone

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PHONOPHORESIS

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PHONOPHORESIS

It is the movement of drugs through skin into the subcutaneous tissues under the influence of ultrasound

Also known as sonophoresis or ultrasonophoresis

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Pathways of drug penetration

1.Through stratum corneum

2.Transfollicular

3.Through sweat gland

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Advantages

Avoid risk and inconvenience of IV therapy

Bypass liver in terms of elimination Less chance of overdose or underdose Allow easy termination Permit both local and systemic

treatment effects

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Effectiveness Depends upon Anatomical area treated Hydration of the skin Health or pathological condition of the skin State of cutaneous and systemic

metabolism Patient’s age

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Methods of application Adequate quantity of drug rubbed into the

skin over the target area Same gel mixed with standard ultrasound

gel placed over transducer head as coupling medium

US is then applied as a direct contact method

Standard intensity is 1 to 2 w/cm² Standard duration is 5 to 10 minutes Lower ultrasonic frequencies and pulsing

lead to deeper penetration

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Phonophoretic agentsDrug Indication Reactions/

contraindications

Hydrocortison Anti inflammatory Skin rashes

Lidocaine/xyclocaine Acute pain

Methyle salicylate Chronic painfull MS disorders

Sensitivity to aspirin

Zinc oxide/siloderm Open wounds Allergy to metals

Iodine Adhesion,calcification,adhessive capsulitis

Allergic to sea food

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