Transcript Ultrasound - You Can Do It! | Physical Therapy Students

Ultrasound
History:
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Available in 19th century.
Was for sonar (SONAR  Sound Navigation
and Ranging)
Sonar  development of clinical U.S. devices.
Heating of biological tissues.
Used for the past 20 years US  non thermal
effects.
What is Ultrasound?
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Type of sound.
Transmits energy by compressing and rarefying
materials.
Defined as sound with frequency of > 20,000 Hz
(beyond the limits of human hearing).
Therapeutic U.S. frequency is 0.7-3.3 MHz 
depth of absorption 2-5 cm.
Like audible sound.
Intensity decrease when travel through material.
Cause circular motion of material.
Terminology:
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Transducer (Sound Head):
The part that contains the crystals that convert Electrical
energy into sound.
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Power:
Acoustic energy / unit time
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(in watt)
Intensity:
Power / unit area of soundhead
watt/cm2)
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(in watt/cm2) (range : 3
Spatial average intensity:
Average intensity of U.S. / area of transducer
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Spatial peak intensity:
Peak intensity / area of transducer
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Beam Non Uniformity Ratio (BNR):
Spatial peak intensity : Spatial average intensity
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Continuous U.S.:
Continuous delivery of US throughout the treatment.
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Pulsed U.S.:
Delivery of US in portion of the treatment time (period).
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Duty Cycle:
The proportion of total treatment time that US is on.
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Frequency:
The number of compression – rarefaction.
Cycles/unit of time (Hz)
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Effective Radiating Area (ERA):
Area of transducer from which US energy radiates.
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Near Field / Far Field:
Near field  the fresnel zone is the convergent region.
Far field  the fraunhofer zone is the divergent region.
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Absorption:
Conversion of mechanical energy into heat.
Amount of absorption are tissue and frequency specific.
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Reflection:
35% at soft tissue-bone interface.
100% at air-skin interface.
0.1% at medium-skin interface.
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Refraction:
US waves enter the tissue at one angle and continue throughout the tissue
at a different angle.
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Attenuation:
Intensity decreases as U.S. travels through the tissue.
Attenuation is tissue and frequency specific.
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Half depth:
Depth of tissue at which U.S. intensity is half its initial intensity.
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Standing wave:
Avoid by moving the sound head throughout the treatment.
Effects of non thermal U.S. on
tissue:
1. Cavitations:
Formation, growth, and pulsation of gas or vapor filled bubbles caused
by U.S.
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Stable cavitations
Unstable cavitations
2. Micro Streaming:
Micro scale eddying takes place near any small vibrating object.
3. Acoustic Streaming:
The steady circular flow of cellular fluids induced by U.S..
4. Phonophoresis:
Application of U.S. with a topical drug in order to facilitate transdermal
drug delivery.
Generation of U.S.:
~Piezoelectrical Transducer~
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Applying high frequency and an alternating electrical current to the
crystals in the transducer.
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Crystals resonate at a frequency to achieve maximum vibrations.
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Single frequency of alternating current  single frequency of U.S.
from crystals.
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Resonance occur when the U.S. frequency and crystal thickness
conform to:
F = C / 2t
F = Frequency , C = Speed of sound
Metal electrode fixing to crystals
Circuit
Power supply
Switches
Meter
,
t = Thickness of crystal
U.S. parameters:
* Intensity
* Frequency
* Size of transducer
* Medium (gel, water...)
* Mode (pulsed + continuous)
* Time of application
Effects of U.S.: Physiological and therapeutic.
Effects of thermal U.S.:
Physiological effects:
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Increase temperature of deep tissue
Increase circulation
Increase soft tissue extensibility
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Increase tissue healing
Increase Ca+ binding to protein
Decrease pain
Decrease muscle spasm
Decrease joint stiffness
Alternation of N.C.V.
It heats deep and small areas.
It heats tissue with high absorption coefficient (high collagen).
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 Good Luck To You All 