• Ultrasound is a type of sound, and all forms of sound consist
of waves that transmit energy by alternately compressing and
• It is sound with a frequency greater than 20,000 cycles per
• Human can hear sound with a frequency of 16 to 20,000 Hz,
sound with a frequency greater than this is known as
• Therapeutic ultrasound has a frequency between 0.7 and 3.3
megahertz to maximize energy absorption at a depth of 2 to 5
cm soft tissue.
3. • As ultrasound travels through material ,it gradually decreases
in intensity as a result of attenuation , in the same way that
the sound we hear becomes quieter as we move farther from
• Ultrasound cause a slight circular motion of material as they
are transmitted , but they do not carry the material along with
• Ultrasound has a variety of physical effects that can be
classified as thermal or non-thermal .Increasing tissue
temperature is its thermal effect.
• Acoustic streaming, microstreaming and cavitation , which
may alter cell membrane permeability , are its non-thermal
• Ultrasound is a high frequency, duty cycle, effective radiating
area [ERA], and beam non-uniformity ratio [BNR]
4. ACOUSTIC STREAMING
• This effect produced by the ultrasonic beam in unidirectional
flow of tissue components which occurs particularly at the cell
• Streaming has been shown to produce changes in the rate of
protein synthesis and could thus have a role in the stimulation
• Is a common condition in which a bubble gas is produced in
the tissues as a result of insonation.
• Stable cavitation is not dangerous to the tissues, as the
bubbles remain intact and oscillate harmlessly in he ultrasonic
• Transient cavitation is dangerous to the tissues , a the bubble
grows and collapses rapidly in the ultrasonic beam and this is
thought to cause very great increase in the temperature.
• When the gas bubbles pulsate in response to the ultrasound
they act on surrounding media by unique forms of radiation
• The streaming flow of fluid around an oscillating object such
as gas bubble.
• It enters the body and attenuated in the tissue by absorption
,reflection and rare-fraction.
• Attenuation is greatest in tissues with high collagen content
and with the use of high ultrasound frequencies.
• Attenuation is the result of absorption, reflection and
refraction , with absorption accounting for about one-half of
6. • Attenuation co-efficient are tissue-specific and frequency –
• They are higher for tissues with higher collagen content and
increase in proportion to the frequency of the ultrasound.
• Continuous ultrasound is generally used to produce thermal
effects, whereas pulsed ultrasound is used for non-thermal
• Both thermal and non thermal effects of ultrasound can be
used to accelerate the achievement of treatment goals when
ultrasound is applied to the appropriate pathological
condition at the appropriate time.
FREQUENCY OF ULTRASOUND
• Ultrasonic energy generated at 1 MHz is transmitted through
the more superficial tissue and absorbed primarily in the
deeper tissues at depths of 3 to 5 cm
7. • A 1mhz frequency is most useful in individuals with a high
percentage of cutaneous body fat and whenever the desired
effects are in the deeper structures.
• At 3 MHz the energy is absorbed in the more superficial
tissues with a depth of penetration between 1 and 2 cm.
PROPERTIES OF ULTRASOUND
• Sonic waves are a series of mechanical compression and
rarefactions in the direction of travel of the wave , hence they
are called longitudinal waves
• The passage of these waves of compression through matter is,
of course , invisible because in the molecules that vibrate
about their average position as a result of the sonic wave.
8. • The velocity of a wave is the speed at which wave moves
through the medium and it varies depending upon the
physical nature of the medium .
• Sound waves will pass more rapidly material in which the
molecules are closed together , thus their velocity is higher in
solids and liquids than in gases.
• The velocities of sound in some media are-
• Air – 44 m/s
• Water – 1410m/s
• Muscle - 1540m/s
• Bone – 3500m/s
9. PRODUCTION OF ULTRASOUND
• Ultrasound is generated by applying a high frequemcy
alternating electrical current to the crystal in the transducer
of an ultrasound unit.
• The crystal is made of material with piezoelectric properties,
causing it to expand and contract at the same frequency that
the current changes polarity
• When the crystal expands, it compresses the material in front
of it and when it contracts, it rarefies the material in front of
• This alternating compression-rarefaction is the ultrasound
CHRISTINA JANE MARY K
11. • There is a source of high frequency current, which is
conveyed by a coaxial cable to a transducer circuit or
treatment head or applicator or sound head.
• Inside the transducer circuit high frequency current is applied
to the crystal being fused to the metal front plate of the
• Any change in the shape of the crystal cause a movement of
the metal front plate which in turn produces ultrasonic waves.
12. • The property of piezoelectricity- the ability to generate
electricity in response to a mechanical force or to change
shape in response to an electric current- was first discovered
by Paul – Jacques and Pierre Curie in the 1880s.
• A variety of materials are piezoelectric, including bone,
natural quartz, synthetic plumbium zirconium titanate
(PZT)and barium titanate.
• Ultrasound transducers are usually made of PZT because this
is presently the least costly and most efficient piezoelectric
• To obtain a pure single frequency of ultrasound, a single
frequency of alternating current is applied to a piezoelectric
crystal whose thickness resonates at this frequency.
• Thinner crystals are used to generate higher frequencies of
13. • All ultrasound crystals, particularly those used for higher
frequencies ultrasound are fragile and should be handled with
• Multifrequency transducers used to be made with single
uniform crystal whose thickness was optimized for one of the
frequencies but that could vibrate at other frequencies by
applying tjose frequencies of alternating electrical currents
• Multifrequency transducers now use composite materials that
can deliver multiple frequencies of ultrasound more
accurately and efficiently.
• Pulsed ultrasound is produced when high-frequency
alternating electrical currents is delivered to the transducer
for only a limited proportion of treatment time.
• Ultrasound waves, when they strike a medium, cause
expansion and compression of the medium.
14. COUPLING MEDIA
• Ultrasonic waves are not transmitted by air, thus some
couplant which does transmit them must be interposed
between the treatment head (transducer) and the patient’s
• Unfortunately, no couplant affords perfect transmission and
only a percentage of the original intensity is transmitted to
the patient. Even most efficient couplant reduces the applied
dose by a quarter.
• Consequently, the treatment head is never left switched on
when not in contact with a transmitting medium.
DIRECT CONTACT METHOD
If the surface to be treated is fairly regular then a coupling
medium is applied to the skin in order to eliminate air between
the skin and the treatment head and transmit the ultrasonic
beam from the treatment head to the tissues.
17. • The treatment head is moved in small concentric circles over
the skin in order to avoid concentration at any one point,
keeping the whole of the front plate in contact with the
• This technique is suitable for areas up to threetimes the size
of the treatment head. Large area should be divided and each
area treated separately.
• The size of the area and its exact location should be specified
on the treatment
18. WATER BATH METHOD
• When direct contact is not possible because of irregular shape
of part or because of tenderness, a water bath may be used.
As the part to be treated is immersed in water this can only
reasonably be applied to the hand, ankle and foot.
• A water bath filled with degassed water is used if possible.
Ordinary tap water presents
• the problem that gas bubbles dissociate out from the water,
accumulate on the patient skin
• and the treatment head, and reflect the US beam. If tap water
has to be used then the gas
• bubbles must be wiped from these surfaces frequently.
19. • The patient is seated and part is put in water of a comfortable
temperature in such a position that itis suitably supported The
treatment head is placed in the waterand held 1 cm from the
skin and moved in small concentric circles, keeping the front
parallel to the skin surface to reduce reflection to a minimum.
• If the patient’s hand is to be immersed in the bath while the
application is active, care should be taken to minimize
exposure to any reflected or scattered ultrasound. This can be
done by wearing a dry knitted glove inside a water-proof
rubber or plastic glove.
20. WATER BAG METHOD
• Another method of applying ultrasound therapy to irregular
surface which cannot
• conventionally be placed in a water bath is treated with a
plastic or rubber bag filledwithwater forming a water cushion
between the treatment head and the skin.
• Rubber bag filled with degassed water can be used.
• All visible air bubbles should besqueezed out before knotting
the neck of the bag to seal it. A coupling medium has to
beplaced both between the rubber bag and skin and between
the rubber bag and the treatment head to eliminate any air
• The bag placed on irregular surface is then held with the help
of patient or others. Treatment head pressed firmly on to the
bag so that a layer of water about 1 cm thick separates it from
the surface (body)
21. • Inevitably, some bubbles will form and it is important to
ensure that these are in the sides of the bag and not in the
region transmitting the ultrasound. The treatment head is
then moved over the surface of the bag. It does, however
present problems in terms of attenuation as many more
interfaces have to be crossed by the ultrasound and rubber
absorbs much of ultrasonic energy. To minimize the problem,
condoms or thin balloons are more satisfactory because these
are thin, cheap and easy touse.
22. PROCEDURE AND TECHNIQUES OF
PREPARATION OF PATIENT
● Skin should be washed and hairs should be removed.
● The nature of the treatment, need for a couplant and
stability of the area are all needs to be explained to the
● The duration of the treatment as well as any particular
cooperation required is indicated
EXAMINATION AND TESTING
● Skin surface to be treated should be inspected; inflammatory
skin conditions should be avoided.
PREPARATION OF THE PART TO BE RELAXED
● The couplant should be applied to the skin surface.
23. SETTING UP
● The patient should be in a comfortable position as skill is
needed to apply efficient ultrasound therapy, ensuring close
contact, appropriate movement and correct angle of the
transducer at all times.
● The treatment head is placed on the skin before the output is
● This is to avoid damage to the transducer which can occur if
the energy is reflected back into the transducer.
● Some machines have a monitoring system. If the ultrasound
energy reaching the tissues becomes much less than the set
intensity, the output is greatly reduced, the timer stops and
the operation is alerted in some way.
24. INSTRUCTIONS AND WARNINGS
● The patient is asked to keep the part still and relaxed and to
report if any increase of pain or other sensations
● The treatment head is moved continuously over the surface
while even pressure is maintained in order to iron out
irregularities in the sonic field.
● The emitting surface must be kept parallel to the skin surface
to reduce reflection and pressed sufficiently firmly to exclude
25. • The rate of movement must be slow enough to allow the
tissues to deform and thus remain in complete contact with
rigid treatment head but fast enough to prevent ‘hot spots’
developing when using a high intensity treatment.
The pattern of movement can be a series of overlapping
parallel strokes, circles or figures of eight
Three factors which determine ultrasound dosage are as follows:
1. size of the treatment area
2. depth of the lesion from the surface
3. nature of lesion.
The treatment parameters depends on the desired effects of
ultrasound therapy (thermal or non thermal)
5. Duration of treatment
• Continuous mode produces more heat so it is used for
musculoskeletal conditions such as muscular spasm, joint
stiffness, pain, etc.
29. • Pulsed mode produces less heat so it is used for soft tissue
repair, e.g. tendinitis
• For example, 0.5 W/cm2 pulsed at 1 : 4 deliver the same
energy as 0.1 W/cm2 on a continuous mode
• 3MHZ:- Higher the frequency lesser the depth of penetration
and more absorption in superficial tissue.Its more approriate
for superficial lesions(2-3cm)
• 1MHZ:-Lower the frequency greater the depth of
penetration and greater the depth of penetration into deeper
tissue. It's more effective for deeper lesion(3-5cm)
30. • Intensity:
It is a measure of the rate at which energy is being
delivered per unit area. Since power and intensity are unevenly
distributed in the beam, several varying types of intensities must
• Spatial-averaged intensity:-It is average intensity US Output
over the area of tranducer
• Spatial peak intensity:-It is the highest value of US output
occuring within the beam over time(0.25-3w/cm2)
• Spatial Average Temporal-averaged intensity(SATA):-It is the
average intensity of US during on and off period
• Spatial-averaged temporal peak (SATP):-It is spatial average
intensity during on Time in pulsed mode US
32. • Duty Cycle
• Each pulse has thermal and nonthermal properties. The net
effects of these properties in the body are based on the duty
cycle. A continuous (100% duty cycle) output causes primarily
thermal effects. A pulsed (e.g., 25% duty cycle) output
produces primarily nonthermal(mechanical) effects.
• The decision to use thermal or non-thermal ultrasound
depends on the stage of healing and the treatment goals.
• Non-thermal ultrasound can be used during acute
inflammation and thermal ultrasound is used later in the
• Duration of Treatment:- Dependance on interaction of
frequency ,dose, and effects
• Amount of energy depends on intensity and duration of
treatment. Size of area determine the treatment time
33. • 1–2 minutes for every cm2
• Many transducer heads have an area of 5 cm2 and the palm
of the small hand is about 50 cm2
• Minimum — 1–2 minutes
• Maximum — 8 minutes
• Average — 5 minutes
• For chronic — Longer treatment time
• For acute — Lesser treatment time
• Beam non uniformity ratio(BNR):-The BNR describes the
consistency (uniformity) of the ultrasound output as a ratio
between the spatial peak intensity and the spatial average
intensity. The lower the ratio, the more uniform the beam. A
BNR greater than 8:1 is unsafe
35. THERMAL EFFECT
• As the ultrasound waves are absorbed by the tissues they are
converted into heat. The amount of heat developed depends
• Absorption of the tissues, e.g. protein absorbs ultrasound
more effectively and therefore produces much heat.
• The number of times the treatment head passes over the
• The efficiency of circulation through the insonated tissues.
• When using continuous ultrasound, the amount of heat
developed is directly proportional to the intensity and
duration of insonation.
• When using pulsed ultrasound there is less thermal effect
than with continuous and a mark : space ratio 1 : 4 produces
less heat than 1 : 1.
36. • Reflection of ultrasound at a tissue interface produces a
concentration of heating effect at a specific point. This is
particularly likely at the interface between periosteum and
bone. As reflection from bone occurs there is double
intensity of ultrasound in the periosteal region, which may
cause localized over heating and can manifest itself as
periosteal pain. In practical terms this means that it is best to
avoid passing the ultrasound treatment head over the
subcutaneous bony points if possible.
37. USES OF THERMAL EFFECT:
• The local rise in temperature could be used to accelerate
healing. The extensibility of collagen is increased by rise in
temperature and so stretching of scars or adhesions is easier
following ultrasound. The thermal effect may also help
• In the past ultrasound was classified as a heat treatment, but
recent work has shown that there are many nonthermal
effects of ultrasound which may be of use in treatment.
• These effects are all associated with one another, and arise
because of considerable
• force generated within the tissues by the ultrasound. The
nonthermal effects are as follows:
This is the oscillatory activity of highly compressible bodies
within the tissues such as gas or vapor filled voids.
Cavitation may be stable or unstable cavitation.
Stable cavitation: Stable cavitation occurs when bubbles
oscillate to and fro within the ultrasonic pressure waves but
remain intact. It is not dangerous and could be of benefit as it
modifies the ultrasonic beam in such a way as to cause
Microstreaming is the unidirectional movement of fluids along
the boundaries of the cell. Due to microstreaming, permeability
of cell membrane and direction of movement of molecules into
the cells is influenced
39. Unstable or Transient Cavitation: This occurs when the volume
of the bubbles changes rapidly and then collapse. It is potentially
dangerous to the tissues as the collapse of the bubbles cause a
great local rise in temperature. It is avoided by moving the
treatment head (to prevent standing waves) using a low intensity
(below 3 watt/cm2)and using a high frequency.
40. MECHANICAL EFFECTS OR MICROMASSAGE
This occurs where the longitudinal compression waves of the
ultrasound beam produces compression and rarefaction of cells,
and affect the movement of tissue fluid in interstitial spaces. This
can help in reducing edema. Combined with the thermal effect
the extensibility of scars and adhesions could be affected in such
a way to make stretching them easier. It is also possible that the
mechanical effect could help reduce pain.
41. BIOLOGICAL EFFECTS
Ultrasound can have some useful effects in all three stages of repair.
1. Inflammatory: Ultrasound probably increases the fragility of
lysosome membrane, and thus enhances the release of their
contained enzymes. These enzymes will help to clear the area of
debris and allow the next stage to occur.
2. Proliferative: Fibroblasts and myofibroblasts may have Ca++ ions
driven into them by the ultrasound. This increases their mobility and
encourages their movement toward the area of repair. The
fibroblasts are stimulated to produce the collagen fibers to form scar
and myofibroblasts contract to pull the edges together.
3. Remodeling: Ultrasound has been shown to increase the tensile
strength of the scar by affecting the direction, strength and elasticity
of fibers which make up the scar easier.