Transcript Therapeutic Ultrasound

Therapeutic Ultrasound
By
Beverly Nelson
Purpose of Presentation
• To provide a basic foundation of the physics
involved in therapeutic ultrasound(US)
• Analyse the transmission of sound energy in
biologic tissue
• Explain the thermal and non thermal effects
of US
• Choose the most appropriate and clinically
effective uses for US
What is ultrasound ?
• Sound waves with a Frequency above 20,000
Hz
What is Frequency ?
• The number of oscillations a molecule
undergoes in one second defines the
frequency of sound waves.
• Frequency is expressed in Hertz (Hz)
• 1MHz – deep penetration/deep heating/ 15cm
• 3MHz– Superficial penetration/superficial
heating/1-3cm
Generation of ultrasound
• Ultrasound can be generated with special
crystals that possess the property of
piezoelectricity and are able to vibrate very
rapidly
• There are 2 forms of piezoelectric effect,
direct and indirect or reverse
Piezoelectric property
• The direct piezoelectric effect is the
generation of an electric voltage across a
crystal when the crystal is compressed
• The reverse piezoelectric effect is the
contraction or expansion of a crystal to a
voltage applied across its face. Thus ,the
reverse piezoelectric effect is used to generate
ultrasound at a desired frequency
Biologic effects of Ultrasound
• 2 classifications;
• (1) Thermal effects
• (2) non thermal effects-
Thermal effects
• Increase temperature by 1 ̊C , increases
metabolism & healing
• 2- 3 ̊C decreases pain and muscle spasm
• 4 ̊C -- greater increase in extensibility of
collagen and decreases joint stiffness
• Greater than 4 ̊C temperature elevation,
damage the tissues
Non thermal effects
• Results from cavitation and microstreaming
• Modifies the inflammatory response
• Enhance the healing of injured tissues
Effective Radiating Area(ERA)
• The total area of the surface of the Transducer
that actually produces the sound wave
Pulsed versus Continuous wave
• When continuous wave ultrasound is used,
the sound intensity remains constant
throughout the treatment
• When pulsed ultrasound wave is used , the
intensity is periodically interrupted with no
ultrasound energy being produced during the
off period.
Duty cycle
• Is selected according to treatment goal
• To increase tissue temperature a 100%
(continuous) duty cycle is used
• When non thermal effects are the goal, pulsed
ultrasound with a 20% or 50% duty cycle
should be used
Attenuation
• Energy contained within a sound beam
decreases as it travels through the tissue
Intensity
• The strength of the sound beam is determined
by its intensity
• Intensity is expressed in units of watts per
square centimetre(w/cm²)
• Intensities employed in PT range from
0.25w/cm² - 1.5w/cm²
• Higher intensities results in greater tissue
temperature increase
Clinical implications of Ultrasound
•
•
•
•
•
•
•
•
Soft tissue healing and repairs
Scar tissue and joint contracture
Stretching of connective tissue
Absorption of calcium deposits
Bone healing
Pain reduction
Assessing stress fracture
Chronic inflammation
Phonophoresis
• A technique in which ultrasound is used to
enhance delivery of selected medication into
the tissues
• Most common medications used are antiinflammatory drugs ,e.g. hydrocortisone 1% or
10% , dexamethasone
Treatment parameters
•
•
•
•
•
•
•
•
Frequency of treatment
Duty cycle
Intensity
Area to be treated
Duration of Treatment
Coupling methods
Number & frequency of treatments
Moving the sound head
Frequency
• Is selected according to the depth of tissue to
be treated
• Tissue at a depth of 5cm- 1MHz is used
• Superficial tissue to a depth of 1-2cm- 3MHz is
used
• Acute conditions may use low intensity pulsed
US ,daily
Duty cycle
• Selected according to the goal of treatment
Intensity
• Selected according to the goal of treatment
• To increase tissue temperature, the patient
should feel mild warmth within 2-3 minutes of
starting application
Treatment area
• Recommended that area to be treated be
roughly twice the size of the sound head for 510 minutes
• Larger areas will need longer time
• Higher intensity applied in w/cm – shorter
time and vice versa
Duration of treatment
•
•
•
•
Selected based on size of area to be treated
The ERA of the sound head
Whether thermal or non-thermal application
5 – 10 minutes duration for an area twice the
size of the sound head
• Little research defining the duration
Coupling medium
• Purpose of the medium is to exclude air from
the region between the patient and the
transducer so that the sound waves get to the
targeted area
• Transfer of sound energy by conversion
requires an intervening material to be a good
transmitter of sound energy
• Reflection is reduced at the air-tissue interface
Coupling medium
• Should be viscous enough to act as a lubricant as
the transducer moves over the surface of the skin
• Should be applied to the skin surface and the
transducer should be in contact with the coupling
medium before the power is turned on
• If the transducer is not in contact with the skin &
coupling medium , the piezoelectric crystal may
be damaged and the transducer can overheat
Coupling medium
• Water is an effective coupling medium
• Water – soluble gels have the most desirable
properties for a good coupling medium
• Salts in the gel may damage the metal face of
the transducer with improper cleaning
Moving the transducer/sound head
• Due to the nonuniformity of the ultrasound
beam ,energy distribution is uneven in the
tissue
• Potential for creating tissue- damaging “hot
spots”
• Moving the transducer during treatment leads
to a more even distribution of the energy
Moving the transducer/sound head
• Overlapping circular motions or longitudinal
stroking pattern can be used
• Slow movement of the transducer is
recommended
Number & frequency of treatments
• Depends on goals of treatment and patient’s
response
• An effect should be detectable within 1 to 3
treatments
• If no improvement after 3 or 4 applications,
US should be discontinued or the parameters
adjusted
Contraindications & precautions
• Physical Agents in Rehabilitation – Chapter
7/page 189
Suggested Readings
• Physical Agents in Rehabilitation by Michelle
H. Cameron
• Thermal Agents in Rehabilitation by Susan L.
Michlovitz
• Therapeutic Modalities in Rehabilitation by
William E.Prentice
Number & frequency of treatments
• It is recommended that US be limited to 14
treatments.
• Not documented ,scientifically
Method of application
• Direct contact
• Immersion
• Bladder technique
Recording Ultrasound treatment
•
•
•
•
•
•
•
Area of the body treated
Ultrasound frequency
Ultrasound intensity
Duty cycle
Treatment duration
Technique of application
(Read documentation on page 194)