Ultrasound Therapy
Dr. Amal, & Mr. Chandrasekar.L
PHT 221 – 1st SEM – 1435-1436H
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LECTURE OUTLINE

This lecture deals about the topic ultrasound in
following sub-categories;
1. Basics
principles & production of US
2. Indications & Contraindications of US
3. Physiological & Therapeutic effects of US
4. Methods of application / Treatment procedure – An
overview of clinical application
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LECTURE OBJECTIVE
At the end of the lecture the student should be able to

Understand physics and properties of US

Know different Modes & methods of US

Identify physiologic & therapeutic effects, indications,
contraindications of US

Recognize dangers and precautions with US

Know the difference between US and phonophoresis

Analyze and discuss different cases
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Definition

It is a form of acoustic vibration propagated in the form of longitudinal
compression waves at frequencies too high to be heard by the human ear.

It is a form of MECHANICAL energy

US is used to produce thermal and mechanical (non-thermal) effect in the
tissues.
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peak
Longitudinal Wave
Trough
Transducer head
Compression /
+ Pressure phase
Rarefaction /
- Pressure phase
LONGITUDINAL PROPOGATION OF ULTRASONIC WAVES
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Frequencies of US

Medical frequencies between 1MHz to 15 MHz

Physiotherapy equipment : 0.75 MHz, 0.87MHz, 1MHz,
1.5 MHz, 3.3 MHz.

In clinical setting the commonly used frequencies of US
are 1MHz for deeper penetration(2-5cms) & 3MHz for
superficial penetration(1-2cms)
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Propagation and speed of US

Propagation velocity of US is depends on:
1- density of the medium
2- elasticity of the medium
ACOUSTIC IMPEDANCE:-

It is the term that denotes the relative resistance of a

medium to wave energy, the more dense the molecules, the
greater the impedance. (Greater energy is absorbed)
There is an inverse relationship between absorption &
penetration.
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
Propagation and speed of US
Body

possesses
resistance
against
US
propagation.
Tissues has impedance (Z) is directly proportion

to velocity of propagation (V) and the density (p)
of tissue
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Z= pV
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Absorption of US energy
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Half Value Depth
Depth (cm)
2
4
6
8
3 MHz
50%
25%
1 MHz
50%
25
To achieve a particular US intensity at depth, account must be
taken of the proportion of energy which has been absorbed by
the tissues in the more superficial layers. The table gives an
approximate reduction in energy levels with typical tissues at
two commonly used frequencies
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Absorption of US energy
• Blood – 3%
• Fat – 13%
• Muscle – 24%
• Skin – 39%
• Tendon – 59%
• Cartilage – 68%
• Bone – 96%
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ABSORPTION & PENETRATION
The blood & water has LOWEST IMPEDANCE

POOR ABSORBERS OF SONIC ENERGY / Good penetration
Bone is the MOST DENSE of all tissues has
HIGHEST IMPEDANCE


GOOD ABSORBERS OF SONIC ENERGY/ Poor penetration
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
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
PRINCIPLE OF PRODUCTION OF US
The sonic waves are produced by the VIBRATION OF

A CRYSTAL or some similar material – Under the
influence of electric current.
Most Favored Crystal – QUARTZ CRYSTAL.
Other materials – BARIUM TITANATE &


LEAD ZIRCONATE TITANATE (PZT)
The crystal is cut for suitable size most being
important is THICKNESS


PIEZOELECTRIC EFFECT
A crystal usually vibrates at a natural frequency which

depends largely on its thickness – produce electric
current.
REVERSE PIEZOELECTRIC EFFECT:-

The crystal will contract & deform under the influence of

an electric current – to produce sound waves.
Mostly all US generators are constructed on the Reverse
Piezoelectric effect.

PRODUCTION OF US WAVE
The Ultrasonic Generator – It consists of a high

frequency Alternating Current(HFAC) produced by a valve
Applied to the Quartz Crystal via
COAXIAL CABLE
This HFAC causes the crystal to VIBRATE at the same
frequency – Producing the train of SONIC
COMPRESSION WAVES.


PRODUCTION OF US WAVE
The Crystal is housed inside an applicator called a

TRANSDUCER.
The treatment surface of transducer consists of a

METAL PLATE which acts as an interface between the
VIBRATING CRYSTAL & the Patient tissue.
The sonic wave is effectively transmitted into the patient
tissue through the Coupling Medium.

THERAPEUTIC TRANSDUCER
It is available in a variety of sizes from
1cm² to 10cm²

.1
The 5cm² is the most frequently clinically used
.2
ultrasound transducer.
Transducer Head
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Ultrasound transmission

Ultrasound consists of wave that transmit energy by
alternating compressing and rarefying the material
of the medium, as the particles of the medium
vibrate in its position therefore the energy transmit
from one particle to another and hence propagation
occur.
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Compression and Rarefaction
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Physical phenomena of US

US behaves as rays of light and follows the
laws of optics:
-
Reflection
-
Refraction
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Reflection

Reflection will occur at the interface between the
two media.

The amount of reflection is depend on the difference
of the acoustic impedances of the media.
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Reflection

Reflection at bone periosteum interference

Reflection at tissue-air interference. i.e. transducer
head -skin interference.
AMOUNT OF ULTRASONIC REFLECTION
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Interface
Energy Reflected
Water – Soft tissue
.2%
Soft tissue - Fat
1%
Soft tissue - Bone
15 – 40%
Soft tissue - Air
99.9%
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Refraction

It is the deviation from the original path.
The refraction is proportional to the differences in

acoustic impedance of the boundary materials & to
the incident angle of wave.
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Transmission of ultrasound - Attenuation
The Attenuation describes the rate at which the sonic energy is lost to the
tissues. The higher the tissue H2O content, the less the attenuation. The
higher the tissue protein content, the more the attenuation

Factors affecting attenuation.
-
Absorption, Scatter, Shear waves.
Attenuation of 1 MHz beam
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Tissue
Percentage
Blood
3%
Fat
13%
Muscle
24%
Skin
39%
Tendon
59%
Cartilage
68%
Bone
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96% 3:27 AM

Transmission of ultrasound
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ERA – Effective Radiating Area
ERA is the effective radiating area that corresponds to

the part of the sound head that produces the sound
wave.
The ERA should be close to the size of the sound head

or transducer. If it is smaller than the sound head, it may
be misleading when treating the patient.
The recommended treatment area is only 2 to 3 times
the ERA.
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
BNR – Beam Non-Uniformity Ratio
BNR is the measure of the variability of the ultrasound wave

intensity produced by the machine.
Beam non-uniformity ratio: It is the ratio of the spatial peak to
the spatial average intensity.
The lower the ratio, the more uniform the machine output,
resulting in a more uniform treatment.
BNR should always be between 2 and 6
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

Mode of US application
Continuous
Pulsed
1- Continuous : as there is continuous delivery of US throughout the
treatment period.
2- Pulsed mode: as there is delivery of US during only a portion of
the treatment time.
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TYPES / MODES OF SONIC WAVE
Continuous:

Sound intensity remains the same
Commonly used for thermal effects
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
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TYPES / MODES OF SONIC WAVE
Pulsed:

Intensity periodically interrupted

Average intensity reduced over time
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
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Duty Cycle
Percentage of time that US is actually being emitted from
the head. Ratio between the US’s pulse length & pulse
interval when US is being delivered in the pulsed mode
Pulse length = amount of time from the initial nonzero charge to
the return to a zero charge
Pulse interval – amount of time between ultrasonic pulses

Duty cycle = pulse length/(pulse length + pulse interval) x 100
100% duty cycle indicates a constant US output

Low output produces non thermal effects (20%)

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


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Intensity of US

The unit of intensity is watt/ cm2 .

The limit of the average intensity is 3W/cm2

The intensities can be:
1.
Spatial Average Intensity
2.
Spatial Peak Intensity
3.
Spatial Average Temporal Average (SATA)
4.
Spatial Average Temporal Peak (SATP)
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Intensity of US
Spatial Average Intensity

This is the average intensity of the ultrasound output
over the area of the transducer expressed as W/cm2
Spatial Peak intensity:

The peek intensity of the US output over the area of
the transducer . This intensity is greater at the center
of the beam.
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Intensity of US
Spatial average temporal average intensity (SATA):

It is used when the US is applied by the pulsed mode.

SATA= SATP X duty cycle.
Spatial average temporal peak (SATP):

It is the spatial average intensity during the on time of the
pulse
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Effects of ultrasound
Physical and physiological
Biological
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Physical and physiological effect
Thermal
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Non
thermal
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Preferentially heats collagen-rich tissues
• Increases tissue elasticity of collagen-rich tissue
• Increases blood flow
Thermal
effects
• Increases pain threshold
• Decreases muscle spasm
• Decreases pain and joint stiffness
• Causes a mild inflammatory response
Note: Intensities above approximately 0.3 W/cm2 are considered thermal.
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Non thermal effect of US:
Note: Intensities between 0.1 and 0.3 W/cm2 are
considered non-thermal
Increases cell membrane permeability
• Increases vascular permeability


• Increases blood flow in chronically ischemic tissue
• Stimulates collagen synthesis
• Stimulates phagocytosis


• Promotes tissue regeneration

• Breaks down scar tissue in acute injuries

• Kills bacteria and viruses in chronic situations
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
Non thermal effects
cavitation
Acoustic streaming
Standing waves
Micro massage
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Cavitation

Cavitation is the formation of tiny gas bubbles in the tissues
as a result of ultrasound vibration.

There are two types of cavitation:
1.
Stable :
Bubbles oscillate to & fro within the sonic wave pressure &

remain intact.
2. Transient / Unstable cavitation – It occurs when the

volume of the bubble changes rapidly & then collapse resulting
tissue damage.
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CAVITATION
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Acoustic streaming / Microstreaming

This is the steady circular flow of cellular fluid that stimulate cell
activity & it occur at the boundary of the cell membrane and the
surrounding fluid, which alter membrane permeability and calcium
activity.

This lead to therapeutic advantages for repair:
1.
Increase protein synthesis
2.
Increased secretion from mast cells
3.
Fibroblast mobility change
4.
Increase uptake of the second messenger calcium.
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Non-thermal Effects of Ultrasound
Cavitation
gas buble expansion
gas buble compression
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Microstreaming
bubble rotation &
associated fluid
movement along
cell membranes
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STANDING / STATIONARY WAVES
Assume two sonic waves with the same

amplitude, frequency and wavelength, traveling
in opposite directions in a medium.
It results due to reflection being superimposed

on the incident wave.
This leads to marked local heating.

In order to prevent this it is necessary to keep

moving the transducer head continuously.
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Micro massage

It is the movement that formed by the
compression and rarefaction waves of the US .

This can help in edema reduction.
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Biological effects of US

US is effective in accelerating wound healing. As it enhance
the wound repair phases which are:
1.
Inflammation phase
2.
Proliferation / granulation phase
3.
Remodeling phase.
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Inflammation phase
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Proliferation / granulation phase
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Remodeling phase
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Therapeutic effects and uses of US

Recent injuries and inflammation

Chronic edema

Soft tissues shortening / scar tissue mobilization

Pain control

Dermal ulcer

Surgical skin lesion
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Therapeutic effects and uses of US

Tendons injuries

Resorption of calcium deposition

Bone fracture

Compressive syndrome

Planter warts and herpes zoster
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Recent injuries and inflammation

US with pulsed mode and low intensity help in resolution of
an acute inflammation. US help in removal of exudate and
promotion of tissue repair.
Chronic edema:

Can be done by breaking of adhesion formed between
adjacent layers
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Soft tissues shortening / scar tissue mobilization

US can increase tissue extensibility make stretching is easy, it can
be used in cases of adhesive capsulitis of shoulder.
Pain control:

Continuous ultrasound relief pain via gait control theory as it
enhance tissue extensibility

Pulsed ultrasound by its non thermal effects help in modulating
inflammation as well as reducing the conduction velocity of
transmission of noxious impulses through the nociceptors .

It can be used in pain arc syndrome
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Dermal ulcer:

Ultrasound accelerate the healing of vascular and pressure
ulcer.

It accelerate migration of neutrophil, lymphocytes, and
macrophages that kill the invading organism at the area of
wound.

It assist in enhancement of fibroblasts and production of
wound factors, enhancement of angiogenesis, and wound
contraction.

It can be used in varicose ulcer, pressure ulcer.
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Surgical incision:

It help in reduction of pain associated and enhance the breaking
strength of such wound.

It can be used in cases as episiotomies
Tendon injuries:

Pulsed mode , low intensity US is recommended to be used with
acute cases to accelerate recovery.

Continuous mode and high intensity US assist in the resolution of
chronic tendonitis.

US can be used in cases of tennis elbow.
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Resorption of calcium deposits:

US facilitate the resorption of calcium deposits
as in cases of calcific tendinitis of shoulder.
Bone fractures:

Low dose ultrasound can reduce the time of
healing.
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Compressive syndromes:

Pulsed ultrasound produced greater improvement in
cases of carpal tunnel syndrome due to its antiinflammatory and tissue stimulating effects.
Planter warts and herpes zoster:

It is effective in pain reduction in cases of
herpes.
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Contraindications
Thrombophlebitis:

It cause emboli to be broken off and block circulation in some other parts as
heart or brain.
Acute sepsis:

As it cause spread of infection or breaking off septic emboli.
Pregnancy:

As it may lead to fetal abnormalities
Central nervous system:

As it lead to damage of CNS tissue
Malignancy:

It enhance growth and production of metastasis
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Joint cement:
 As it rapidly heated result in loosening of the prosthesis.
Pacemaker:
 US should not be applied to the chest or upper back as
pacemaker is heated and damaged.
Over the eye
 As the cavitation in the ocular fluid may damage the eyes.
Over the male and female reproductive organ:
 As it affect gamete development.
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Precautions:

Acute inflammation

Epiphyseal plate

Fractures

Breast implants
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Dangers of ultrasound

Burn

Cavitation

Over dose

Damage to equipment
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Burn
Causes :

Using of continuous mode lead to accumulation of heat

Head is not moved continuously during the application
It can be prevented by:

Using pulsed mode

Avoiding bony prominence

Continuous movement of transducer head of ultrasound.
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Cavitation

Unstable cavitation causes local increase in the
temperature lead to pain and discomfort

Cavitation can be prevented by continuous movement of
the head of the ultrasound
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Over dose

Excessive treatment lead to an exacerbation of the
symptoms.
Damage to equipment
Causes:

if the head is held in air where it is switched on
that lead to reflection of wave to the crystal lead
to its damage.
Prevention:

It can be prevented by not switch the head until
contact with the medium
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Phonoporesis
Definition:
It is the migration of drug molecules through the skin under
the influence of the ultrasound
Or it is the therapeutic application of ultrasound with topical
drug. Phonophoresis is also known as Sonophoresis or
Ultrasonophoresis.
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Mechanism of action of
phonophoresis:
Phonophoresis (sonophoresis)
Phonoporesis
Factors affecting the effects of phonophresis:
1.
Frequency of US
2.
Intensity of US
3.
Duty cycle
4.
Treatment duration
5.
The nature of the drug itself.
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Dosimetry of ultrasound
Factors affecting US dose:
1.
2.
3.
Size of the treated area
Depth of the lesion
Nature of the lesion
Parameters of US:
1.
2.
3.
4.
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Mode
Frequency
Intensity
duration
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Mode


Continuous mode: All forms of chronic cases
Pulsed mode: Acute + Sub-acute cases
Frequency


Higher frequency for the superficial lesion e.g.
3MHZ(1-2cms)
Lower frequency for deep lesion, e.g. 1 MHZ(25cms)
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Tissue State
Intensity required at the lesion
(W/cm2)
Acute
0.1 - 0.3
Sub Acute
0.2 - 0.5
Chronic
0.3 - 0.8
Duration of treatment




It depend on the area of injury.
The minimum treatment time 1-2 min and the
maximum treatment time 10-15 min.
Duration is also affected by the nature of the lesion.
For acute lesion the duration 2-3 min, which may
increase to 4-5 min.
In chronic lesion a duration of 4 min is selected can be
increase to 10-15 min.
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Progression and timing

Acute condition is treated once or twice daily.

Chronic cases is treated on alternate days.

Progression is based on the outcome of the
previous treatment
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Principles of application of US
Factors must be considered before using US:
A. choice of the US machine:
Guide lines:

Safety

Beam non uniformity ratio

Frequency

Digital control/ displays

Automatic timer

calibration
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B. Couplant
Characteristic of ideal coupling:
1.
Contains no gas bubbles
2.
Gel like viscosity
3.
Sterile
4.
Hypo allergic
5.
Chemically inert
6.
Perform also as an wound dressing
7.
Transparent
8.
Inexpensive
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C. Testing the machine

Using water path
D. technique of application
1.
Direct contact
2.
Water bath method
3.
water bag method
4.
Gel pad method
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DIRECT METHOD
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)

Effectiveness is  if body part is 
hair, irregular shaped, or unclean
Must maintain firm, constant 
pressure
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DIRECT METHOD
Move the sound head
s-l-o-w-l-y 4 cm/sec 

Moving the head faster
decreases heating

If the patient describes
discomfort, decrease
the output intensity

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Water 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 approximately 1” from 
the body part
Avoid the formation of air bubbles 
Operator’s hand should not be immersed. 
No metal on part or operator’s hand 
Ceramic tub is recommended 
Don’t touch skin except to briefly sweep 
skin when bubbles form
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Water bag application

This technique uses a plastic or rubber bag filled
with water and coated with a coupling gel thus
forming a water cushion between the treatment head
and the skin. The bag is then held in place over the
area to be treated. The treatment head is moved
firmly over the bag.
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Pad Method
A mass of conductive
gel
Commercial pads 
Self-made bladders

Conforms to the 
treatment area
Commercial pads help
limit the size of the
treatment area
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

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