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2022 Deep Thermal Lecture covering Ultrasound and Diathermy

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2022 Deep Thermal_Lecture

2022 Deep Thermal Lecture covering Ultrasound and Diathermy


Deep Thermal Modalities

Before proceeding with the presentation on ultrasound, you should first be
familiar with the information in the corresponding chapter of the textbook on
Physical Agent Modalities by Dr. Alfred G. Bracciano.


Learning Objectives
After completing this lesson, you should be able to:

• Discuss the theory and rationale for the application of therapeutic

• Outline and differentiate between the parameters for
• therapeutic ultrasound
• Outline current research trends in the utilization of
• ultrasound
• Demonstrate clinical decision making in the
• determination of the appropriate treatment parameters for ultrasound
• Discuss the clinical procedures for the application of
• ultrasound
• Present guidelines for the safe use of ultrasound,
• contraindications and precautions for treatment


Ultrasound is a type of sound or acoustic energy, but is inaudible to the human
ear because the frequency is beyond the parameters of human hearing.
The normal sound frequency audible to humans occurs between 16 to 20,000
hertz, and any sound frequency beyond 20,000 hertz is considered ultrasound.

- It is used in medicine for diagnosing by imaging the internal structures, for
tissue destruction, and with surgery and hyperthermia for tumor

Ultrasound is also used in physical medicine and rehabilitation to facilitate
restoration and healing soft tissue.

Not this:

But this:


Therapeutic Uses

The frequency band of medical ultrasound is 800,000 to 3,300,000 hertz (or 0.8 to
3.3 megahertz) and sound can be absorbed to a depth of 1 to 5 centimeters in
soft tissue.
This sound energy is a deep penetrating modality that produces changes in the
tissue through a thermal, non-thermal, or mechanical mechanism.
It is important to remember that energy produced by ultrasound is not an
electromagnetic spectrum, but rather it is acoustical.
In medicine, the lowest intensity of sound spectrum is used for diagnostic
procedures and imaging, while higher intensities are used for tissue destruction.



Thermal agents are classified as superficial and deep.
• Superficial thermal modalities penetrate to a depth of approximately 1 to 2
centimeters, while ultrasound may penetrate to a depth of 5 centimeters.

The biophysiological effects of ultrasound will depend on the output of the
therapeutic parameters but will produce greater changes when the ultrasound
energy can penetrate deep into the tissue.

The two purposes of therapeutic ultrasound include elevating the tissue
temperature and providing non-thermal secondary cellular effects.
• Depending on the output
parameters, ultrasound can facilitate
tissue repair and wound healing, increase
vascularization and tissue extensibility,
alter nerve conduction velocities, deliver
medication, and assist in fracture healing.

When ultrasound is used for
rehabilitation, it is primarily for tissue

The development of ultrasound as an acoustic energy began with the work of Paul
Jacques and Pierre Curies in the 1800’s.
• They found that certain crystals, such as quartz, lithium sulfate, and zinc
oxide could generate an electrical charge when mechanically compressed.

They also discovered that voltage polarization will change across electrodes and
can cause a corresponding change in the direction of crystal distortion.
• Curies concluded that crystals could produce positive and negative
electrical charges when they expand and contract, known as the piezoelectric

In essence, when the polarity changes, it causes the crystal to oscillate and


deform in response to the electrical current.

• The voltage of ultrasonic frequency likewise causes the crystal to oscillate
at the same frequency.
• The piezoelectric effect occurs when electrical current is applied to the
crystal which then vibrates and resonates, and consequently produces a sound

The military use of ultrasound began
in the early part of the 20th century
with the advent of submarine
warfare. Crude transducers were
built and placed in the water to send
short pulses of sound energy
through the water that could receive
echoes as the energy “bounced off”
the steel hull of the submarines.
The duration of time it took for the
sound to travel from the transducer
to the submarine and then return


was used to calculate the distance to a submarine. Researchers discovered that
not only was the sound navigation and ranging (or SONAR) effective to locate
submarines, but the amplitude of the acoustic wave was also strong enough to kill
marine animals and small fish. As research on pulse-echo technology continued,
adaptations were developed for use in medicine.

Ultrasound Equipment

Ultrasound occurs when alternating electrical current is applied to the
piezoelectric crystal located in the transducer. Originally, natural crystals such as
quartz, barium titanate, or lead zirconate were used. However, it was later
discovered that synthetic crystals such as plumbium zirconium titanate (PZT)
could produce a more consistent and cost effective acoustic wave.

The standard ultrasound unit consists of a power supply, oscillator circuit,
transformer, coaxial cable transducer and ultrasound applicator. The power
supply is a generator that uses common household current (or alternating
current) to convert electrical energy into
ultrasonic energy.

As the electrical current is applied to the
crystal, it begins to respond by expanding and
contracting at the same frequency which the
current changes polarity.

The crystal in the transducer subsequently
deforms in response to the change in the
direction of flow of the current and is
proportional to the amount of voltage applied
to the crystal.

Each crystal in an ultrasound unit has a unique
vibrating frequency that is matched to the
internal electronics. However, most
transducers are not interchangeable due to


the electronics, and therefore, some manufacturers have produced
interchangeable sound heads.
A multi-frequency transducer uses a single crystal, but is optimal only at one
frequency level.
• Although the crystal in this type of transducer can vibrate at other
frequencies when alternating current is applied, it is less efficient and can cause a
greater variability in output frequency, will decrease the effective radiating area
(ERA), and will result in an increase in the beam n on-uniform ratio (BNR).

Modern ultrasound units are equipped with an ultrasound transmission sensor
that shuts off the sound output and will indicate the loss of conductivity through a
light, meter, or bell.
These safety sensors can also shut off a unit if there is an inefficient conduction
medium being used or if the contact between the sound head and the patient is
All modern ultrasound units provide continuous ultrasound and most can also
produce pulsed ultrasound.
• Continuous ultrasound will cause a thermal effect, while
• Pulsed ultrasound is required for non-thermal applications.


At a minimum, ultrasound units should have a continuous (100%) duty cycle,
although some units have duty cycles that range from 100% down to 50%, and a
20% pulsed cycle.


Biophysical Principles

When the crystal begins to deform with the application of alternating current, the
voltage polarization will oscillate across the electrodes and generate pressure
waves that will transmit to a small volume of tissue and cause the molecules to

However, ultrasound travels poorly through the air because of the high
frequencies and a dense medium is needed such as a lubricant to allow the
energy to be dispersed into the tissue.


Sound Propagation

The sound waves that are created by ultrasound are analogous to the waves
created when a stone is tossed into the middle of a pond.
In essence, the sound waves produced by a transducer are generated in rapid
succession and the displaced molecules in the waves then move longitudinal or
parallel to the sound.

• As the crystal expands and contracts, the molecules are pushed back and
forth by the alternating phases of successive waves until the waves run out
of energy.

• The peak and trough of the sound waves mirror the phases of compression
and rarefaction of the crystal.

The compression and rarefaction of the crystal will cause alterations of high and
low pressure and produce areas of high particle density during compression and
areas of low particle density during rarefaction along the path of the sound wave
within the tissue.
When this type of molecular flow moves in one direction, it is known as a
longitudinal wave.


As the ultrasound wave leaves the transducer, it transmits in a straight line and
will diverge as the energy travels farther away from the source.

• Low-frequency sound waves such as human speech diverge in all directions
through the air.

• The rate in which the sound wave travels is dependent, in part, on the
density of the molecules of the specific tissue.

When the particle movement occurs at a right angle to the propagation of the
wave, a shear or transverse wave will be created.
Shear waves occur in solid substances whereas longitudinal wave occur in liquids
and gases since they have weaker intramolecular bonds.

As the frequency of ultrasound increases, the sound beam divergence decreases.
• Due to the higher frequencies of ultrasound beams, they are well
collimated and similar to a piercing beam of light emitting from a spotlight.
• As the sound energy reaches the bone, a shear wave is generated along the
periosteum and offers therapeutic heating within the bone (or periosteal).

However, the shear wave does
not transmit ultrasound
energy or produce
significant heating in soft

Each ultrasound
transducer is labeled with its frequency, effective radiating,
area, and the beam nonuniformity ratio.

Smaller ultrasound heads have more divergent beams with low-frequency (1
MHz) than high-frequency (3MHz) sound heads.


Absorption and Penetration

Sound waves are transferred from an ultrasound beam into surrounding tissue
through the conversion of mechanical energy into thermal energy.

Sound waves, though, will collide quicker in a medium when the molecules are
closer to each other.

Furthermore, the extent of acoustic impedance to wave energy will depend on the
density of the medium and how heavy the molecules are.

However, as the distance increases away from the medium, the gas molecules of
the wave tend to disperse in the air since ultrasound travels at a low velocity.

When the wave energy does pass through various tissues of the body, it will
acquire kinetic energy and cause cellular vibration.


Human Tissue

Human tissue is not a homogenous medium since it consists of interspersed layers
and compartments of different density.
Consequently, each tissue layer transmits and absorbs ultrasound according to its
acoustical properties.

• Fluid elements in the body such as blood and water have the lowest
impedance values and the lowest acoustic absorption because they are
“poor” absorbers of sound energy.

• Conversely, bone matter has the highest impedance value and the highest
acoustic absorption coefficient because it is the most dense tissue, and
therefore, is a “good” absorber of ultrasound energy.

Thus, as sound waves are absorbed and subsequently transferred to kinetic
energy within the tissues, it will lead to physiologic changes.

• It should be noted that when there are higher energy levels, tissue heating
will also occur.

Acoustic Impedance Level

The intensity of ultrasound energy will decrease as it travels through tissue.

However, ultrasound is not greatly affected by adipose or fat tissue and will pass
through it rather easily in route to the underlying tissue.


Reflection & Refraction

As sound waves cross a boundary, the beam
will lose some energy from the reflection off
the medium.
• Yet, for such acoustic properties as
skin, fat, blood vessels, and muscle, the
amount of reflection will be insignificant to
the therapeutic outcome.
• However, reflection of sound energy
will increase in proportion to the difference
in acoustic impedance of the materials on
either side of a boundary.

When a sound beam strikes an acoustical
interface with differing tissue layers, some of
the energy will be reflected or refracted; but,
the refraction at the interface will be small
between the soft tissue and bone.

The amount of reflection at the metal-air interface of the transducer is almost
99%, and therefore, a coupling medium is needed to minimize the loss of
ultrasound when it is transmitted in the air.

Also, when a reflected wave meets an incoming wave, a “standing wave” will be
created that causes an increase in the intensity of the energy due to the creation
of areas of high and low pressure.

This collection of intense energy in a small space will increase the risk of tissue

• However, standing waves can be prevented by keeping the ultrasound
transducer moving.




The frequency of the ultrasound refers to the number of complete wave cycles
that are generated each second.

• The duration of each wave cycle and the wavelength will decrease as the
number of cycles per second increase.

• Therapeutic ultrasound operates in a range of 0.75 million cycles per
second (MHz) to 3 MHz.

• However, frequencies up to 5 MHz are available in Europe.
Since the frequency of ultrasound is a primary influence for the amount of energy
that will be absorbed by the tissues, higher frequencies with faster molecule
oscillation will cause greater amounts of energy absorption.



Absorption is the conversion of the mechanical energy of ultrasound into heat.
• The amount of absorption that occurs in tissue at a specific frequency is
expressed by its absorption coefficient.

However, the absorption and attenuation of sound energy are inversely related
and higher frequencies can limit penetration.

Therefore, treatments with a frequency of 3 MHz will result in more superficial
effects than treatments with a frequency of 1 MHz.

Furthermore, tissue impedance will influence the depth of penetration of the
sound energy and this penetration is described as the distance which 50% of the
original intensity remains within the beam (termed the half-value depth of

Energy that is not reflected or absorbed will pass into the next layer of tissue and
the intensity will decrease as it moves through the tissue.

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. This gives an approximate reduction in energy levels with
typical tissues at two commonly used frequencies:

2 cm 50%
4 cm 25% 50%
8 cm 25%



Intensity is a term used to describe the magnitude of force in a sound wave and
describes the strength of acoustic energy at the site of application.

• As the intensity of the wave increases, so does the excursion of the
molecules in the wave field.

The intensity is the most significant factor in determining the tissue response and
is reported in “watts per square centimeter (W/cm2).

• This is obtained through the transducer that measures the total power it
emits in “watts” (or units of electrical power), and the emitting surface area
of the transducer is measured in square centimeters.


Energy Distribution

• Spatial Peak Intensity (SPI) – maximum intensity appearing at any point in
the beam

• Spatial Average Intensity (SAI) – average intensity over the beam of energy
• Beam Non-uniformity Ratio (BNR) – relationship between SPI and SAI
• Hot spots – caused by high intensity areas within the beam

Variations of energy will occur within the sound wave and are caused by a
number of mechanisms, including peaks and troughs of the sound wave in the
near and far fields.
• The spatial peak intensity (SPI) is the maximum intensity appearing at any
point in the beam, and the spatial average intensity (SAI) is the average intensity
over the area of the beam of energy.


However, the intensity will be higher in some areas of the ultrasound beam than
others. The relationship between the SPI and the SAI is called the beam
nonuniformity ratio (BNR), and the maximum BNR must be specified on each
ultrasound transducer according to the FDA.

The BNR (Beam Non-uniformity Ratio) is
a figure showing the uniformity of
ultrasonic radiated from the probe. As
the smaller the BNR is, the more
uniform the ultrasonic being radiated
are, we can see that this is an excellent
probe. Generally, if it is a BNR ≤ 5, it is
considered to be good. Also, the higher
intensity areas within the ultrasound
beam are a primary cause for “hot
spots” which may occur during application but can be prevented by moving the
sound head throughout the treatment.


Biophysical Effects

The therapeutic use of ultrasound will cause biophysiological changes that include
thermal and non-thermal effects.
• The thermal effects of ultrasound include an increased metabolic rate,
alteration of the nerve conduction velocity, increased circulation, decreased pain
and muscle spasms, and increased soft tissue extensibility.
o The advantages of ultrasound to heat tissue include its greater depth
penetration capability than superficial thermal agents and it can be used for more
localized applications.
• The non-thermal effects of ultrasound are due to changes within the tissue
that result from the mechanical effects of the sound energy.

Although there are two distinct classifications, thermal and non-thermal effects
are not mutually exclusive of each other.
• Physiological changes will occur for both within the body, but the
magnitude and proportion are based on the duty cycle selected and the intensity
of the output.


Thermal effects

The physiological effects of tissue heating are the same, regardless how the heat
is applied.

• When the duty cycle is high, the thermal effects will be significant; and
when the output intensity is high, the magnitude of the effects will be

• Therefore, tissues that possess a high ultrasound absorption coefficient can
be heated more readily than those with a low absorption coefficient.

Furthermore, tissues with a high collagen content such as scar tissue, joint
capsules, ligaments, and tendons, will accumulate or absorb sound energy and be
heated through the conversion of kinetic energy.

• Because protein dense structures will absorb ultrasound, therapists can
also use ultrasound to heat deep, lying tissues.

• Muscle tissue, though, has a relatively low absorption coefficient due to the
extensive capillary network and size of the tissue.

• Therefore, ultrasound will not be an effective heating modality for muscle
tissue since it tends to lose heat quickly.


Thermal Effects

As the sound wave is delivered to the tissue, the cells and molecules in the beam’s
path will begin to oscillate in a cyclical manner proportionate to the output

These oscillations will facilitate the development of gas-filled bubbles that
increase in activity as the wave intensity increases.

Consequently, stable cavitation will occur when the bubbles expand and contract
during high and low pressure peaks and troughs.

However, unstable cavitation will occur when the bubbles collapse and release
energy into the surrounding tissue.

• This will cause an increase in the temperature that may damage the tissue
and blood cells located within the sound wave.

• A treatment application
using continuous, thermal
parameters at a frequency
of 1 MHz is more prone to
unstable cavitation than a
frequency of 3 MHz. This is
due to the signal being more
intensely applied, the non-
stopped sound application
(100% duty cycle), and the
higher intensity (greater
than 1.0 watts/cm2).


Biophysical Effects

The general principles of heat transfer will
involve both convection and conduction.

• Conduction occurs in the periosteum,
while convection occurs through the
circulating blood, lymph, air and water

However, dense protein rich tissue such as
scar tissue, capsule, ligament, tendons, and
bone will accumulate and retain heat better
than vascular tissue.

• Although muscles are rich in capillary
network, they will release heat more readily due to convection and
conduction, but loose heat when ultrasound is applied in water.

To increase the total amount of heat that is delivered to any tissue, the duration
of the ultrasound application and/or the intensity must be increased.

One MHz frequency should be used for deeper tissues as it heats to
5 cm, and 3 MHz should be used for superficial tissue since it will heat only to a
depth of 1-2 cm.
• Because tissue temperature
will increase approximately 0.2
degrees C per minute at 1 W/cm2 at
1MHz, 3MHz ultrasound will
increase tissue temperature more
readily than 1 MHz ultrasound, and
therefore, the intensity should be
approximately 3 to 4 times lower
than 1 MHz of ultrasound.

Since the temperature will also vary
because of BNR, the sound head needs to be moved during the application to
help distribute the heat more equally and prevent hot or cold areas.


Duty Cycle

The process of interrupting the delivery of sound wave so that periods of sound
wave emission are separated with periods of interruption.

a) Pulsed ultrasound (10%, 20%, or 50% duty cycle) demonstrating the on time
and off time. Duty cycle is determined by the ratio of “on” time to pulse with
the off time to rest. In this case, a 50% duty cycle

b) Continuous ultrasound (100% Duty Cycle) is shown


Thermal Effects

Biophysiological changes that occur with thermal ultrasound include
• increased metabolic rate of tissue,
• increased blood flow and tissue permeability which may assist in resolution
of swelling and edema,
• increased viscoelasticity of connective tissue along with a decrease in the
viscosity of fluid elements in the tissue,
• elevated pain threshold, and
• increased enzymatic reactivity to stimulate the immune system.


Non-thermal Ultrasound

When the thermal effects of ultrasound are reduced by applying low intensity
ultrasound or by pulsing the sound wave, cellular or mechanical changes will

The results will be non-thermal ultrasound that include cavitation, micro-
streaming or acoustic streaming.

• Non-thermal ultrasound can cause increased cellular permeability and a
cascade of second-order effects.

• The clinical use of pulsed or non-thermal ultrasound, therefore, can help to
facilitate tissue repair.

Non-thermal or Mechanical Ultrasound

Cells and molecules located within the ultrasound beam’s path will oscillate in a
cyclical manner in direct proportion to the ultrasound’s intensity.

Since the cell membrane is sensitive to distortions in an ultrasound field, the
effects of non-thermal ultrasound will initially occur at the cell membrane.

• When the sound wave reaches the cell membrane, the deformation is
called a micro-

• During the
compression and
rarefaction of the
sound wave,
stable cavitation
will occur and
cause a unit-
directional flow
of the tissue

• These eddy
currents in the fluid will then surround and exert a twisting motion on the
nearby cell membranes. This fluid movement within the sound field is
known as acoustic streaming or micro streaming.


The heat that is generated when delivering ultrasound in a pulsed mode with a
20% duty cycle or lower will be dispersed during the off time and will result in no
measurable increase of tissue temperature.

• Therefore, the setting that is most frequently used to evaluate the effects
of non-thermal ultrasound is the 20% duty cycle.

The role of cavitation must also be considered for both thermal and non- thermal
mechanisms of ultrasound.
Stable cavitation will occur when pulsed ultrasound is used because it restricts the
number of successive cycles of bubble growth.

• However, the risk of unstable cavitation can be decreased during a
treatment by using 3 MHz of pulsed, low intensity ultrasound.


Second-Order Effects

The use of pulsed ultrasound has produced a number of positive second-order
effects that include increases in intracellular calcium, skin and cell membrane
permeability, mast cell degranulation, chemotactic factor and histamine release,
macrophage responsiveness, and protein synthesis by fibroblasts.

The benefits of using non- thermal ultrasound occur in the healing processes of
inflammation, proliferation, and maturation.

Basically, destabilization of the cell membranes will lead to increased cell
permeability that allows ions and molecules to diffuse into the cells which
precipitates the secondary events.

The acoustic streaming or flow of bubbles within the tissue will subsequently
cause changes in the cell membrane permeability and diffusion rates.

• The net effect is that ultrasound will facilitate the passage of calcium,
potassium and other ions and metabolites into and out of the cell.

• These changes are non-thermal and have been attributed to cavitation,
acoustic streaming and micro-streaming.

Ultrasound has a number of non-thermal or second-order effects on the
biophysiological processes.

• The second-order effects are not due to any increase in tissue temperature,
but rather are the result of the mechanical events produced by ultrasound,
including micro- streaming, cavitation, and acoustic streaming.

• When ultrasound is administered in a pulsed mode with a 20% duty cycle, it
is usually done to produce non-thermal effects.

• Pulsed ultrasound will elevate the inflammatory response of histamine and
vasoactive substances that are released from the mast cells and circulating
platelets and will cause an increase in vascular permeability and phagocytic
activity of the macrophages.

• Additionally, the number of fibroblasts and their motility will rise with an
increase of fibroplasia and also enhance angiogenesis, which is the process
of endothelial cell budding and the growth of newly formed collagen that
form blood vessels. This will then expedite the wound contractions
because of the centralized pulling at the wound edges.


Cellular-level processes are essential components of tissue healing and will be
responsive when applying ultrasound for a variety of pathologies and conditions.

Because of the positive effect on macrophage motility, ultrasound can be an
effective modality during the inflammatory phase of tissue repair.

Also, pulsed ultrasound at a 20% duty cycle with intensities less than 0.75 W/cm2
is more effective on cell membrane permeability than continuous or thermal
ultrasound delivered at the same intensity.


Therapeutic Applications

Since ultrasound can be used to treat a variety of conditions and is also utilized
during various stages of healing, the application choice should be based on which
one is the most appropriate.
The thermal effects of ultrasound will stretch the shortened soft tissue and assist
in pain reduction so the patient can engage in an occupation or activity, whereas
non-thermal effects will alter cell permeability and facilitate tissue healing.
Ultrasound will also aid in healing dermal ulcers, surgical skin incisions, tendon
injuries and bone fractures, and it can be used to promote transdermal drug
penetration through both thermal and non-thermal effects.


Soft Tissue Extensibility

There are a several factors that influence soft tissue extensibility and may lead to
the shortening of joint capsules, surrounding tendons and/or ligaments. These

• immobilization,
• adhesions or scarring,
• disuse atrophy or deconditioning, and
• pain.

They will result in functional occupational limitations and are clinically manifested
as decreased joint range-of-motion, pain, weakness, and loss of function.

• Stretching the soft tissues can help to regain the normal length and
facilitate the return of function.

• However, there is only a short window of opportunity of approximately 5
to 10 minutes after the soft tissue is heated to lengthened it and still have
minimal risk of tissue damage.

The soft tissue length
can also be maintained
if the stretch force is
applied while the
tissue is elevated.


Utilizing a positional stretch or dynamic splinting after employing ultrasound may
help to facilitate the outcome.
Since “stress” will alter the viscoelasticity and matrix of the collagen fibers, the
joint capsules, tendons, and ligaments can be effectively heated with ultrasound
by initially administering a selective absorption rate prior to stretching.
Applying heat at a frequency of 1 or 3 MHz with continuous ultrasound at an
intensity between 1.0 and 2.5 W/cm2 for 5 to 10 minutes, can be very effective
therapy when combined with stretching prior to performing any activity or
Fracture Healing
Before ultrasound was accepted within the medical community as a way to
promote bone growth stimulation and to help slow healing fractures, pulsed
ultrasound was found to be beneficial in the development of callus formation in

• Studies, though, eventually substantiated that when human subjects
received pulsed ultrasound with a 20% duty cycle, 0.15 W/cm2 intensity, and 1.5
MHz frequency, the outcomes were effective in accelerating the biomechanical
healing of Colles’ and tibial fractures when it was administered for 20 minutes on
the first postoperative day and continued daily for 14 to 28 days.


There is now an approved FDA device that can be used in the home which will
provide low doses of ultrasound to help facilitate fracture healing.

• The device is preset so it can be used 15 to 20 minutes daily and has
treatment parameters of 0.15 W/cm2 intensity, a 20% duty cycle, and a 1.5
MHz frequency.

Skin Incisions and Dermal Ulcers

Pulsed ultrasound can be used to facilitate wound healing, particularly dermal
ulcers when the treatment parameters consist of
20% duty cycle, 0.8 to 1.0 W/cm2 intensity, and 3 MHz frequency for 5 to 10

• However, the most effective treatment parameters involve 0.5 to 0.8
W/cm2 intensity and 20% duty cycle for 3 to 5 minutes, 3 to 5 times per

Dermal ulcers or open incisions can be treated by applying transmission gel to the
intact skin, circling the wound, and then treating the outer edges.
Furthermore, lesions or wounds can be covered with a coupling sheet before
beginning the treatment.
Ultrasound can also be applied underwater when it is necessary to submerge an
extremity or lesion in the water.


It has been hypothesized that ultrasound can accelerate angiogenesis by altering
the cell membrane permeability and influence the macrophages.

Ultrasound can also be used to heal surgical incisions, relieve pain associated with
surgical procedures, and promote stronger tissue repair.

• For example, ultrasound has been used effectively to treat painful,
thickened episiotomy scars and gynecological surgical wounds, even years
after the incisions had been completed.

Ultrasound can decrease the pain after a procedure by administering it during the
first or second postoperative day and by accelerating the resolution of

Decrease Pain

Since cellular changes can alter the electrical activity of the nerve fiber and
elevate the pain threshold, ultrasound can also decrease pain as a counterirritant
when the nerve conduction velocity is increased.
With an application of continuous ultrasound at 0.5 to 2.0 W/cm2 intensity and
1.0 MHz within 48 hours of an injury, it has been effective in decreasing the pain
from soft tissue injuries.

Furthermore, ultrasound is more effective than exercise alone in decreasing pain
when it is applied at 1.5 W/cm2 for 3
to 5 minutes for 10 treatments over
a 3-week period and can also
improve the range of motion for
patients who have shoulder pain.
Therefore, in order for ultrasound to
be an effective tool to decrease pain,
the application parameters should
be 1 or 3 MHz of frequency
(depending on the targeted tissue
depth) with an intensity of 0.5 to 2.0
W/cm2 for 3 to 10 minutes.



Phonophoresis involves administering a topical drug with ultrasound in which the
ultrasound delivers or drives the medication through the skin into the underlying
tissue for either a systemic or localized effect.
The ultrasound energy will open the pathways in the skin and allow the
transdermal medication to pass through the enzymatic barrier of the epidermis
and stratum corneum into the deeper tissues.

• The stratum corneum is the superficial layer of the skin that acts as the
protective barrier that prevents foreign materials from entering the body.

• Also, the ultrasound can modify the permeability of the stratum corneum
by both thermal and mechanical methods.

An advantage of using transcutaneous delivery rather than by oral means is there
will be a higher concentration of the medication at the delivery site.
Although this application is non-invasive and the medications are anti-
inflammatory, it effectiveness is still questionable because of the variability of the
treatment parameters.


Factors that will affect the transdermal passage of medications include
• skin composition
• hydration,
• vascularity, and
• skin thickness.

Although the medication will be locally concentrated at the targeted area, it will
also diffuse across the stratum corneum and disperse systemically by vascular

• The diffusion rates of the medication may also be enhanced by acoustic

• Research has indicated that passage of medication may be due to increased
tissue permeability from the heat of the ultrasound.

The radiation pressure of ultrasound may also be a contributing factor that will
force the medication away from the transducer into the body.

• However, medications should not be administered by phonophoresis if the
patient is receiving oral medications since this may increase the potential of
adverse effects.


Transmissivity of Ultrasound

Hydrocortisone is commonly used for phonophoresis and a physician’s

prescription may be required when a medication gel or cream is used as a

coupling agent.

There are a variety of commercially available gels that can transmit ultrasound
into the tissue, but topical gel-mixed media and transmission gels are good

conductors of sound energy and will reflect most of the ultrasound back into the


Medication mixtures not designed for

phonophoresis should be avoided and Anti-inflammatory medications

corticosteroid creams are poor conductors that are used in the application

of ultrasound. of phonophoresis include, but

Although the actual amount of medication are not limited to:
that can penetrate into the targeted • Hydrocortisone
tissue is unknown, drug penetration can • Dexamethasone
be increased with the application of • Salicylates

conductive heating and ultrasound.

• Thus, preheating the treatment area with a moist hot pack can enhance the

delivery of the drug into the tissue.

• However, leaving the remaining mixture on the occlusive dressing may

facilitate diffusion of the medication.

Ultrasound Transmission by Phonophoresis
According to Media

Transmission Relative Product that Transmits

to Water (%) US Well

97% Lidex gel, fluocinonide 0.05%

97% Theragesic cream

97% Mineral Oil

96% Ultrasound gel or lotion

90% Betamethasone 0.05% in gel

88% Diprolene, betamethasone .05%

36% Hydrocortisone (HC) powder in 1% US gel

29% HC powder in US gel


Although the utilization of phonophoresis is still controversial, recent studies have
indicated that it can be successful when following the treatment parameters of
0.6 to 0.8 W/cm2 intensity and a continuous mode of 7 to 15 minutes for 2 to 15
The effectiveness may also be enhanced by using an approved ultrasound
transmission gel or media and ensuring the patient’s skin is well hydrated.



• Malignant tumors
• Pregnancy
• Central nervous system tissue
• Joint cement
• Plastic components
• Pacemakers
• Thrombophlebitis
• Eyes
• Reproductive organs
• Ultrasound should not be applied over cemented prosthesis or plastic

components since such materials can heat quickly

Ultrasound is a safe and effective intervention. However, if the patient’s
condition does not improve within 3 or 4 treatments or worsens, a reevaluation
of the treatment approach and intervention should be considered.
Contraindications for the use of ultrasound include malignant tumors, pregnancy,
central nervous system tissue, joint cement, plastic components, pacemaker,
thrombophlebitis, over the eyes, and over reproductive organs.
Ultrasound may be used over areas with metal implants such as screws, plates, or
all-metal joint replacements since metal will not heat rapidly by ultrasound and it
will not loosen screws or plates.
But, ultrasound should not be applied over a cemented prosthesis or where there
are plastic components since such materials can heat quickly.


Since thermal ultrasound will produce heat, it may exacerbate the inflammatory
process, bleeding, pain, swelling, and impair healing in areas of acute
Care should also be used over growing epiphyseal plates when administering high
dosage levels.
Additionally, high intensity ultrasound may impact fracture healing and increase
pain, whereas low-dose ultrasound should only be applied over fractures.
Precaution should also be taken over breast implants since high intensity
ultrasound may cause increased pressure inside the implant and result in rupture.


Clinical Application

The decision whether to use ultrasound should be based on
• a thorough knowledge and understanding of the healing process or stage of
• the type of tissues involved,
• the depth of the trauma or targeted tissue,
• the nature and inflammatory state of the injury, and
• consideration of the skin and superficial tissues overlying the specific region
to be treated.

Ultrasound may be applied before or after other treatment interventions, unless
the therapeutic goal is to heat the tissue.

Ultrasound should be not applied after any intervention that may impair
sensation such as with cryotherapy.

Before administering an application, the ultrasound head should always be
cleaned with 0.5% alcoholic chlorohexidine or other approved antimicrobial agent
to prevent cross-infection.

• The frequency of treatments is dependent on the level of ultrasound and
the state of healing, but non-thermal ultrasound may be applied at earlier
stages of healing and administered daily.

• However, thermal-level ultrasound should be is applied 3 times per week
during the subacute or chronic phase of healing.


Implications of Treatment

The area of tissue that can be realistically heated using ultrasound should be
equivalent to twice the size of the radiating area of the transducer.

However, water-immersion techniques can considerably diminish the therapeutic
effect of ultrasound heat when the skin and subcutaneous tissues are submerged
more than 3 centimeters since water can quickly absorb heat.

Patients, though, will experience minimal sensation of warmth during underwater


To increase the temperature level 4 to 6 degrees near the bone, the treatment
parameters should be set at 1 MHz frequency with 1.0 W/cm2 intensity using a
stroking technique rate of 3.2 cm/s.

A therapeutic temperature of 40o C can be achieved with 8 to 15 minutes of
ultrasound treatment using dosage levels between 1 to 1.5 W/cm2.


Questions to Ask

Has a tissue problem been clearly identified?
• The therapists needs to determine the specific treatment goals.

Is stimulation of tissue repair indicated?
• Acute and subacute inflammation from strains and sprains, bruising, muscle
tears, burns, superficial and deep skin wounds, crush injuries, and other
similar types of conditions will have a positive response from low-intensity
pulsed ultrasound

Are heat and stretch indicated?
• Restriction of movement, with or without pain, muscle spasms, chronic
edema, fibrosis, connective tissue contracture, adhesions, unresolved
hematoma, and similar conditions of a chronic inflammatory nature are
indications to use high intensity, continuous-mode ultrasound.

Is ultrasound a time-effective approach to the problem?
• Ultrasound is indicated for treatment of well-defined localized tissue areas
and usually will require more than 12-15 minutes to be effective. The
clinician should remain for the duration of the treatment to monitor the
patient’s condition.

Is the target tissue accessible?
• Since ultrasound is best absorbed by dense tissue, bone and joint structures
should not lie between the treatment area and the path of the ultrasound
beam. An alternative modality should be selected if swelling occurs inside a
joint, whereas swelling outside a joint may be an indication for ultrasound.


Is the delivery of ultrasound practical?
• Although administering ultrasound through direct contact or by water-
immersion are both effective modalities, skin breakdown, risk of infection,
tenderness, and presence of dressings, casts, and splints may preclude the
use of ultrasound.

Does the treatment goal involve delivery of a topical medication?
• If difficult tissue contours preclude the use of ultrasound, delivery through
iontophoresis (over the lateral epicondyle of the humerus) may be an
effective alternative.

Is ultrasound medically safe for the patient?
• Since there are contraindications that can preclude the use of ultrasound as
the choice of treatment, it is essential that all patients be properly


Case Study
History and Assessment: MR is a 65 y/o female with 3 months of post-closed
reduction from a colles’ fracture to the right wrist due to a fall on the ice. She has
been referred to occupational therapy to improve strength and ROM of the right
wrist. Since the removal of the cast, MR has had difficulty dressing, opening
doors and jars, although the patient had been active prior to the fracture. An
objective exam revealed a decreased passive ROM in the flexion and an extension
at the right wrist. The patient guards the right hand and wrist and displays
limitation of movement of the supination and pronation. Her grip and pinch
strength have also decreased and she complains of “spasms” in the forearm, and
pain during passive and active movement. All other objective measures are within
normal limits.


According to the History and Assessment, the patient is a 65-year-old female with
3 months of post-closed reduction from a colles’ fracture to the right wrist due to
a fall on the ice. She has been referred to occupational therapy to improve
strength and range of motion of the right wrist. Since the removal of the cast, the
patient has had difficulty dressing, opening doors and jars, although the patient
had been active prior to the fracture. An objective exam revealed a decreased
passive range of motion in the flexion and an extension at the right wrist. The
patient guards the right hand and wrist and displays limitation of movement of
the supination and pronation. Her grip and pinch strength have also decreased
and she complains of “spasms” in the forearm and pain during passive and active
movement. All other objective measures are within normal limits.

Analysis of Clinical Findings

Patient manifests impairments of pain in the right wrist with movements of
flexion/extension and pronation/ supination. She displays shortening and
tightness of the right wrist joint capsule and has decreased functional abilities and
fine motor control.

Goals of Treatment
▪ Decrease pain
▪ Improve range of motion and functional
• use of the right hand
▪ Improve fine motor prehension patterns
▪ Return of functional ADL and IADL
• independence


Determination of Appropriateness of Ultrasound

Therapeutic ultrasound is indicated for the treatment of pain and for soft tissue
extensibility. A superficial heating agent could be used but would not penetrate
to the depth needed to increase the extensibility of the soft tissue. Manual
therapy techniques or positional stretch and engaging in occupational activities
should be pursued after the application of the ultrasound.

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