Therapeutic ultrasound uses high frequency sound waves to produce thermal and nonthermal effects in tissues. It selectively heats tissues high in collagen like tendons and ligaments. Key parameters include frequency (1-3 MHz), intensity (0.5-3 W/cm2), and treatment time. Ultrasound increases blood flow, tissue extensibility, and metabolism to enhance soft tissue healing and reduce pain. It is used for conditions like tendinitis, bursitis, and muscle strains.

1. THERAPEUTIC
ULTRASOUND
A COMPLIMENTTO MUSCULOSKELETAL REHABILITATION
THERAPEUTIC EXERCISE, MOBILIZATIONS +
ULTRASOUND

2. THERAPEUTIC ULTRASOUND
Therapeutic ultrasound produces acoustic vibrations of high frequency (not detectable by human ear) that
produce thermal and/or nonthermal effects in the body’s tissues.
Unique advantages over other nonacoustic heating modalities:
• Soundwaves selectively heat tissues high in collagen (e.g., tendons, ligaments, muscles, joint capsules,
menisci, nerve roots, periosteum, and cortical bone) without causing a significant tissue temperature
increase in skin or fat.
• Provides therapeutic benefits by stimulating normal body physiological functions to perform better for
the primary purposes of enhanced soft tissue injury repair and pain relief.
• Greater tissue heating depth penetration: For example: a 4-minute whirlpool @ 105ºF (40.6°C) produces
a temperature increase at 1 cm below the fat tissue of about 2.0°F (1.1ºC).At the same 1 cm depth, 3
MHz ultrasound treatment increases temperature over 10.8°F (6°C).

3. THE ULTRASOUND UNIT: 4 MAIN PARTS
• Generator: a high frequency electric generator linked through an oscillator circuit and
a transformer. Control panel: on-off, power, time, intensity, duty cycle, continuous or
pulsed modes, 1 or 3 MHz frequency, and automatic shut-off in case the crystal
overheats.
• Crystal: a thin synthetic ceramic crystal that is a transducer that converts electric
energy to acoustic energy through mechanical deformation (expands & contracts) of the
crystal that causes the soundhead to vibrate resulting in the mechanical production of
high-frequency sound waves.

4. THE ULTRASOUND UNIT: 4 MAIN PARTS
CONT . . . .
• Soundhead: a ceramic, aluminum, or stainless steel plate attached to the crystal that is a
transmitter that transfers the acoustic sound waves from the crystal to the tissues where
it causes the tissues to vibrate.
• Applicator: this is the housing for the crystal and the soundhead.A handheld device that
facilitates the application of the ultrasound to patients. It should be ergonomically
designed so that when held the wrist is able to be kept in a neutral position where it is
functional strong to withstand the constant motion required to apply the therapy without
succumbing to a repetitive motion injury.

5. HOW DOES ULTRASOUND WORK –THE
PHYSICS
Sound
Sound is created when a force acts upon a molecule causing it to vibrate back and forth
which then sets in motion a cascade of molecular vibrations producing a mechanical wave
(sound wave).
• Ultrasound is a mechanical wave in which energy is passed by the vibrations of the
molecules of a biological medium through which the wave is traveling, concentrating the
energy in a targeted or limited area.

6. HOW DOES ULTRASOUND WORK –
THE PHYSICS, CONT . . . .
Types of sound waves
• Longitudinal waves: these waves travel with vibration (molecular displacement) in
alignment or longitudinally through soft tissues.
• Transverse waves: these waves vibrate in a direction perpendicular to the longitudinal
waves, such as when the sound wave rebounds after hitting bone.

7. HOW DOES ULTRASOUND WORK –
THE PHYSICS, CONT . . . .
Frequency of sound wave transmission
In body tissues, the higher the frequency of soundwave, the greater the amount of
ultrasound energy that is absorbed in the tissues, resulting in less energy that is transmitted
to deeper tissues.
• 3 MHz frequency – these sound waves are absorbed superficially and are only
transmitted to a depth of 2-3 cm.
• 1 MHz frequency – these sound waves are transmitted deeper before being absorbed
to a depth of approx. 6 cm.

8. HOW DOES ULTRASOUND WORK –
THE PHYSICS, CONT . . . .
Attenuation
Attenuation is a decrease in energy as a sound wave passes through body tissues as some of the energy is
absorbed in the tissues.
• Fat tissue: minimal energy absorption
• Muscle tissue: has a high rate of energy transmission
• Dense tissue high in protein: energy is well absorbed in this type of tissue
• Tissue high in water content: the energy penetrates easily to a deeper level
• Superficial bone: energy is easily absorbed
• Peripheral nerves: energy is absorbed at a rate twice that of muscle

9. HOW DOES ULTRASOUND WORK –
THE PHYSICS, CONT . . . .
Characteristics of crystal – also impacts how well ultrasound will penetrate tissues.
The quality of a crystal can affect how well the ultrasound wave penetrates tissues. Crystal
quality is partly determined by:
• Effective Radiating Area (ERA):The surface area of a soundhead that transmits a
sound wave from the crystal to the tissues.
• Beam Nonuniformity Ratio (BNR):A measure of the uniformity of the ultrasound
beam.

10. EFFECTIVE RADIATING AREA (ERA)
ERA is the surface area of a soundhead (faceplate)
that transmits a sound wave from the crystal to
the tissues. Important considerations include:
• The ERA is always smaller than the crystal and
sometimes significantly smaller than the
soundhead.
• The entire surface of the soundhead does not
radiate ultrasound output.
• It is recommended that the total size of the
crystal and soundhead surface match as closely
as possible for ease of application in order to
maintain the most effective contact with the
targeted tissue area.

11. BEAM NONUNIFORMITY RATIO (BNR)
The BNR is an indicator as to variability of intensity within an ultrasound beam
as they are not completely uniform – with some point higher and other points
of lower intensity. The BNR is the ratio of the spatial peak intensity
(highest intensity in the beam), to the spatial average intensity (average
intensity across the beam).
• A good BNR is between 2 to 5.The lower the BNR, the more uniform the
ultrasound output will be and the less likelihood of developing hot spots.
• Hot Spot:An area at tissue interfaces that may become overheated from
too much concentrated energy in one area, resulting in discomfort and
potential tissue damage.
• The higher the BNR ratio, the more important it is to use lower intensities
or move the soundhead faster during treatment to avoid hot spots.

12. ULTRASOUNDTREATMENT
PARAMETERS
The “therapeutic dose” of ultrasound is determined by these parameters:
• Mode
• Frequency
• Intensity
• Treatment Length
• Treatment Area Size

13. ULTRASOUND PARAMETER - MODE
Ultrasound devices produce “continuous” or “pulsed” mode ultrasound.
• Continuous Mode: the ultrasound energy remains constant (100%) throughout the
treatment.
• Pulsed Mode: the ultrasound energy is periodically interrupted so that no ultrasound
energy is being produced during the “off” period.
• Duty Cycle: the percentage of time that ultrasound is generated over one pulse period.
• Pulse Duration (on time) x 100 / Pulse Period (on-time + off-time)
• Example: pulse duration of 10ms & total pulse period of 40ms.The duty cycle would be 25% = the
total amount of energy delivered to the tissues would be only 25% (10 x 100 = 1,000/40 = 25).This
means that the total amount of energy delivered to the tissues would be only 25% of the energy
delivered if a continuous mode was used.

14. ULTRASOUND PARAMETER - FREQUENCY
Therapeutic ultrasound typically has a frequency range of 0.75 to 3.0 MHz.
Ultrasound frequency determines the depth of tissue penetration and the rate of tissue heating.
• 3 MHz frequency soundwaves are absorbed more superficially (2cm-3cm depth) and therefore are best for
treating conditions that are more superficial. For example, medial and lateral epicondylitis, patellar tendinitis,
plantar fasciitis,Achilles tendinitis, radial or ulnar nerve entrapment, hand/finger and foot/toe joints, carpal
tunnel syndrome, muscles close to the body surface, etc.
• At 3 MHz the rate of absorption/attenuation is not only absorbed more superficially but is also absorbed 3 times faster
than at 1 MHz and therefore heats the tissue 3 times faster.
• 1 MHz frequency soundwaves are transmitted through the more superficial tissues and absorbed primarily in
deeper tissues (3cm to 6cm depth). Because of its depth of penetration, it is recommended to use this
frequency on individuals with a high percentage of body fat and when deeper tissues need to be heated. For
example, deeper muscles such as piriformis, soleus, hip internal rotators, supraspinatus, or larger joints, etc.

15. ULTRASOUND PARAMETER - INTENSITY
Intensity is the rate at which energy is being delivered per unit area and is a function of both the pulse
width and pulse frequency, measured in watts (W). Also referred to as spatial average intensity (SAI).
SAI is the intensity of the ultrasound beam averaged over the area of the soundhead.
• SAI = Total watts (W) / Effective radiating area (cm²) = W/cm².
• There are no definitive guidelines for intensity for selecting specific ultrasound intensities during
treatment. A safe range of intensity for a moving soundhead is 0.5 to 3 W/cm².
• Thermal ultrasound treatments should feel slightly warm and adjusted to patient tolerance. If there is a
significant adjustment in intensity it should be countered with an adjustment in the treatment time. If
intensity is increased, treatment time is reduced. If intensity is reduced, treatment time is increased.

16. ULTRASOUND PARAMETER –
TREATMENT LENGTH
The length of treatment time for any individual should be based on:
• Size of the area to be treated should only be about 2x to 3x the size of the sound head,
otherwise the energy will be distributed too broadly, and therapeutic temperature will
not be reached
• Ultrasound frequency (remember, ultrasound at 3 MHz heats tissues 3x faster than 1
MHz)
• Intensity in W/cm² (the lower the intensity the longer the treatment time)
• Desired temperature increase

17. ULTRASOUND PARAMETER –
TREATMENT LENGTH, CONT . . . .
TEMPERATURE INCREASES &
ASSOCIATEDTISSUE EFFECT
• 1.8°F (1°C) = (↑ metabolism, ↓ mild
inflammation)
• 3.6 °F to 5.4°F (2°C-3°C) = (↓ pain &
muscle spasm, ↑ blood flow)
• 7.2°F (4°C) = (↑ ROM & tissue
extensibility)
PER MINUTE RATE OF MUSCLE
HEATING USING ULTRASOUND
Intensity Frequency Frequency
(W/cm²) (1 MHz) (3 MHz)
0.5 0.07°F (0.04°C) 0.54°F (0.3°C)
1.0 0.36°F (0.2°C) 1.08°F (0.6°C)
1.5 0.54°F (0.3°C) 1.62°F (0.9°C)
2.0 0.72°F (0.4°C) 2.52°F (1.4°C)

18. DETERMINING ULTRASOUNDTREATMENT
LENGTH –THE “GUESSTIMATE” METHOD
• Scenario: Patient is experiencing medial epicondylitis. In preparation for massage and
eccentric resistance exercises, you want to heat the origin of the wrist flexor muscle
group. An appropriate approach would be to:
• Heat the muscle tendon junction using 3 MHz frequency at an intensity of 1W/cm². This
would take approx. 7 minutes to reach the 7.2°F (4°C) temperature.
• 1W = 1.08°F (0.6°C)/min x 7 minutes = 7.6°F or 4.2°C
Note: If at some point the patient complains that the temperature is too hot and
uncomfortable, simply decrease the intensity dose and add some additional treatment time.

19. TREATMENT AREA SIZE & SOUNDHEAD
MOTIONS
• Treatment Area Size: Ultrasound is a very effective
tool for heating deep tissues. However, the treatment
should be limited to an area that is two or three times
the size of the ERA of the crystal, or twice the size of
the soundhead surface to ensure proper heating depth.
• Soundhead Motions: Ultrasound head can be moved
in back-and-forth linear strokes or small overlapping
circular motions at a rate of 3-4 cm/second.

20. ULTRASOUND BEAMTRANSMISSION –THE
MEDIUM OF “GEL”
Ultrasound beams must be transmitted from the soundhead to the patient through a coupling medium,
either a gel or emersion in water.The coupling gel serves as a lubricant and fills incongruities between the
soundhead and skin, helping to ensure that the ultrasonic energy enters the target tissue at the desired
intensity. Important considerations include:
• The application of gel to the body surface treatment area should be sufficient in amount to maintain
good contact and lubrication, but not allow air pockets to form from the movement of the soundhead.
• When administering the treatment with a gel medium it is essential that the soundhead’s surface remain
in complete contact with the body surface at all times. Lifting or tilting the soundhead at an angle of
even 15° will result in a significant reflection loss of energy and reduced treatment effects.
• Ultrasound gel should be stored at temperatures above 104°F (40°C) to prevent bacterial growth on the
gel bottle tips.

21. ULTRASOUND BEAMTRANSMISSION –
“IMMERSION OFTHE SOUNDHEAD IN WATER”
The immersion in water of the body part to be treated and the soundhead to deliver the
ultrasonic energy is used for areas of the body like hands/wrist and feet/ankle where irregular
surfaces and body prominences exist. Important considerations include:
• The container of the water should NOT be metal as this will reflect some of the ultrasound.
• The water used for immersion should be at least body core temperature, not room
temperature, to ensure the desired “thermal” effects.
• The soundhead should move parallel to the body treatment surface area at a distance of less
than 1cm.
• If air bubbles form on the soundhead or treatment area, wipe them off immediately.

22. “THERMAL” EFFECTS OFTHERAPEUTIC
ULTRASOUND
• Increased local blood flow – delivering oxygen and nutrition to healing
tissues
• Increased extensibility of connective tissues (tendons, joint capsule,
adhesions, scar tissue) – enhancing the effectiveness of stretching
• Increased metabolism in tissues in which heat is absorbed
• Diminished pain perception – increased blood flow that washes away
metabolic waste products/chemical irritants that cause pain

23. THERAPEUTIC ULTRASOUND – AS AN AID
TO “STRETCHING CONNECTIVETISSUE”
Just as plastic is hard and not pliable when cool, connective tissues have a somewhat similar
characteristic. However, heat up the plastic object and it becomes pliable and can be
stretched. Heat up connective tissues and they become more pliable and extensible and can
more effectively be stretched/elongated.Therefore, to enhance the effectiveness of
stretching, joint mobilizations, friction massage, muscle warm-up, you should stretch these
tissues when they are still warmed, preferably immediately after ultrasound treatment is
terminated.The window of opportunity for this therapeutic benefit is around 5 to 10
minutes.

24. “NONTHERMAL” EFFECTS OFTHERAPEUTIC
ULTRASOUND
• Tissue regeneration
• Facilitating inflammation and wound healing
• Cell membrane alteration – facilitating diffusion of metabolites and promoting protein
and collagen synthesis
• Increased phagocytic activity of macrophages

25. “INDICATIONS” FOR USE OFTHERAPEUTIC
ULTRASOUND
• Soft Tissue Shortening – restoring ROM lost
from contracture and/or scare tissue –
combined with stretching when tissue is still
warmed
• Soft tissue healing and repair
• Diminish pain – increased blood flow that
washes away metabolic waste products/chemical
irritants that cause pain
• “itis” conditions – tendinitis, bursitis, fasciitis,
epicondylitis, arthritis
• Musculoskeletal syndromes/conditions (carpal
tunnel, nerve entrapment,TMJ dysfunction)
• Ligament sprains, muscle/tendon strains
• Trigger points – desensitization
• Muscle spasms – heated tissues have increased
blood flow → eliminates chemical irritants,
alters nerve conduction speed and relaxes
muscle tension (e.g., IT Band tightness)

26. “CONTRAINDICATIONS” FOR USE OF
THERAPEUTIC ULTRASOUND
• Acute and post-acute conditions with continued bleeding
• Over reproductive organs (a gravid uterus) – could potentially damage developing fetus
• Cancer – a local exposure may contribute to metastasizing from increased blood flow
• Over eyes – could cause cavitation in the fluid compartments
• Impaired arterial circulation – sufficiently healthy to meet the increased metabolic demand
• Over spinal cord after laminectomy – cavitation may occur in the cerebrospinal fluid
• Over pacemaker or carotid sinus – could affect normal pacing of heart or baroreceptors
• Thrombophlebitis – potential to cause an emboli
• Presence of infection – heat could accelerate infection

27. “PRECAUTIONS” FOR USE OFTHERAPEUTIC
ULTRASOUND
• Over epiphyses of bones of young children – in high doses may disrupt growth by
affecting early closure
• Over metal implants - potential to heat implant
• Over areas of impaired sensory – could hinder patient feedback on excessive heating
• Excessive exposure to bony prominences – to avoid concentration on periosteum
• Only use intensities considered therapeutically safe – to avoid cavitation and the potential
for tissue damage

28. ULTRASOUND & ELECTROTHERAPY
The combination of ultrasound and electrotherapy (combination therapy) involves the
stimulation of muscle contraction as the ultrasound head serves as an electrode in
delivering the electrotherapy. The benefits of combination therapy are:
• Pain reduction and muscle contraction stimulation
• Effective in the treatment of myofascial trigger points
• Effective in reducing the pain-spasm-pain cycle

29. INSTRUCTIONS FOR USE OF ULTRASOUND –
PREPARATION FOR APPLICATION
• Application of ultrasound should be performed using only calibrated and properly working
ultrasound unit
• Identify specific location for treatment (may consider marking area so stay within 2x to 3x
ERA) and evaluate for any sensory deficit in the skin, for open wounds or rashes
• Explain to patient the procedure – gel medium, soundwaves generate gentle warmth, report if
any feeling of hot, totalTx time, etc.
• Prepare patient – positioned and draped for comfort, modesty, and accessibility to treatment
site, including positioning for access to deeper tissues
• Use appropriate soundhead size
• Apply appropriate amount of gel medium (or immerse part in tepid water)

30. INSTRUCTIONS FOR USE OF ULTRASOUND –
SET APPLICATION DOSAGE
Frequency: 1MHz for mod to deep tissue penetration “or” 3 MHz for superficial tissue heating
Mode:
• Continuous: the ultrasound energy remains constant (100%) throughout the treatment
• Pulsed: the ultrasound energy is periodically interrupted so that no ultrasound energy is being produced during the “off” period.
• Duty Cycle: the percentage of time that ultrasound is generated over one pulse period
Intensity: The lower the intensity the longer the treatment time.Also, adjust the intensity to the patient’s heat perception. If it gets too
hot for the patient, move the applicator faster as you turn down the intensity.
Treatment Duration:
• 1 MHz: 10 to 15 minutes for vigorous heating
• 3 MHz: 3 to 7 minutes for vigorous heating

31. INSTRUCTIONS FOR USE OF ULTRASOUND –
OTHER CONSIDERATIONS
• Frequency of therapy applications: 1x to 2x daily
• Number of treatments: approximately 14 sessions
• If goal is to increase joint ROM, place body part in stretch position during latter part of
ultrasound application and stretch the tissue immediately after termination of ultrasound

32. POSTTHERAPY PROCEDURES
• Clean the soundhead of gel and disinfect
• Wipe any remaining gel from the patient’s skin
• Perform any stretching or mobilization technique of the patient while the tissue is still
warm and pliable
• Documentation of ultrasound treatment dosages: Frequency, intensity, mode and duty
cycle if pulsed, size and location of treatment, treatment length, patient response to
treatment, etc.

33. REFERENCES
• Draper, D.O., Jutte, L.S., Knight, K.L.,Therapeutic Modalities:The Art and Science, 3rd
Edition
• Cameron, M. H., Physical Agents in Rehabilitation: From Research to Practice, 4th Edition