Lecture #44 – Ultrasound
what is sound?
 The transfer of
motion
 The human ear can hear sound waves that
vibrate 16-20,000 times/second
 Above this rate is
 750,000 to 3 million times/second
(Mega Hertz = MHz)
therapeutic ultrasound
 Acoustical energy (sound waves) above the
range of human hearing
 Therapeutic range: 0.75 to 3.3 MHz
 Effects:
 Thermal
 Nonthermal (
)
ultrasound frequencies
anatomy of an ultrasound machine
 Generator
 Crystal
 Transducer - Converts electrical energy
into acoustic energy
 Houses the crystal

 Applicator
soundhead
 Part of the ultrasound unit that contains the
crystal
 Also called transducer or transducer
faceplate
 Ultrasound machines can have dual soundheads
of different sizes
how does it work?
 Generator produces a high-frequency
at 0.75–3
million cycles per second (MHz).
 Current travels through the coaxial cable to the
transducer.
 Transducer converts mechanical vibration by a
reversal of the
effect.
 Crystal in the transducer converts electrical
energy to sound energy.
Notes
 Reverse piezoelectric effect -
modes of application
Continuous
 Ultrasonic energy is
 Can produce thermal effects based on:
 Output intensity
 Treatment duration
Pulsed
 Ultrasonic output is
 Produces non-thermal effects
pulsed output
 Ultrasonic output is cycled “On” and “Off”
 On = Pulse length
 Off = Pulse interval
 Expressed as a
 ON/(ON+OFF) * 100
 20mSec/(20mSec+10mSec) * 100
 20/30 * 100
 67%
output frequency
 Measured in
(MHz)
 1 MHz = 1,000,000 waves per second
 Determines the
of effects
1 MHz output
 Penetrates
 Thermal effects last longer
 More
beam
3 MHz output
 Penetrates

 More collimated beam
power & intensity
Power
 The total amount of ultrasound energy
produced by the generator (
)
Intensity
 Strength of the sound waves over the given
area (
)
 The higher the
, the faster the
 If intensity is increased, treatment time should
be
and vice versa
size of treatment area
 Should be limited to no more than
 If the area is too large, ultrasound won’t heat
the tissues.
Lecture #44 – Ultrasound
transducer movement
 Use slow movement covering about
 Back and forth or circular strokes
 Keep the soundhead
 Keep the soundhead flat on the surface
being treated
coupling
 Ultrasonic energy cannot pass through
 A coupling medium is required
 Medium should be water-based
coupling methods
 Direct coupling – use of a
to deliver US energy
 Immersion coupling – use of
to
deliver US energy
 Best for
body parts
 Bladder coupling – use of a commercial bladder
pad to deliver US energy
thermal effects
 Increased
 sensory nerve conduction velocity
 motor nerve conduction velocity

of collagen-rich tissue
 vascular permeability structures
 collagen deposition
 blood flow
 Reduction of muscle spasm
 Effects are based on
heating classifications
heating rate
 Heating rate and magnitude are based on:
 Duty cycle
 Output frequency ( 1MHz vs. 3MHz)

(W/cm2)
 Target tissue (muscle, ligament, tendon,
etc.)
 Size of the treatment area
non-thermal effects
 Increased cell membrane
 Altered rates of diffusion across the cell
membrane
 Increased vascular permeability
 Increased
Notes
 Reduction of edema
 Diffusion of ions
 Tissue regeneration
 Formation of stronger connective tissue
non-thermal application
 Pulsed output

% duty cycle
 Non-thermal output intensity
 Continuous output
 100% duty cycle
 Low output intensity
(less than 0.3 W/cm2)
how does it work?
 As ultrasound wave exerts pressure against the
cell wall, the membrane deforms slightly
(referred to as micromassage)
 Acoustical Streaming (Microstreaming)

acoustical streaming
 Ultrasound causes fluid between cells to flow
 Fluids strike cell membranes
 Produce
 Eddy currents displace ions and molecules
 Alter:
 Cell membrane permeability
 Cellular function
stable cavitation
 Compression and expansion of
in the blood and tissue
 Cellular effects
○ Increase in cell membrane
diffusion
○ Increase cellular activity
indications
 Bursitis
 Inflammatory conditions (
)
 Joint stiffness
 Pain
 Muscle Spasm
 Acute injuries (non-thermal US)
contraindications
 Acute injuries (
)
 Areas of impaired circulation
 Anesthetic areas
 Over
 Over sites of active infection
 Over the spinal cord or large nerves in high
doses
 Exposed metal that penetrates the skin (e.g.,
external fixation devices)
 Areas around the eyes, heart, skull, or genitals
Lecture #44 – Ultrasound
 Over the thorax in the presence of an implanted
pacemaker
 Pregnancy when used over the pelvic or lumbar
areas

 Stress fracture sites or sites of osteoporosis
 Over the pelvic or lumbar area in menstruating
female patients
precautions
 Symptoms may
after the initial
treatment
 Use caution when applying ultrasound around
the spinal cord
 The use of ultrasound over metal implants is
not contraindicated
 Keep the sound head moving
 Use caution when applying ultrasound over
epiphyseal plates of growing bone
patient preparation
 Establish that no
are
present
 Determine the method and mode of ultrasound
application to be used
 Clean the area to be treated
 Determine the type of coupling method to be
used
 Identify a treatment area that is
 For direct coupling: spread the gel over the area
to be treated
 Explain the sensations to be expected during
the treatment:
 Mild to moderate warmth (but not pain
or burning) for
treatments

for
pulsed ultrasound
 Advise the patient to report any adverse,
unusual, or painful sensations during the
treatment.
Notes
initiation of the treatment
 Reduce the intensity to zero before turning on
the power.
 Select the appropriate mode for the output
(CONTINUOUS or PULSED)
 Set the timer to the appropriate treatment
duration
 Begin slowly moving the sound head over the
medium
 Press the START button to begin the
treatment session
 Slowly increase the intensity

 Move the head at a slow pace (
)
 Use firm, overlapping strokes
 If pain is experienced:
 Move the sound head at a
rate
 Use a
duty cycle
 Use a lower
 If the gel begins to wear away or if the sound
head begins sticking on the skin, press the
PAUSE button and
termination of the treatment
 If the treatment is being terminated
prematurely:
 Reduce the intensity before removing
the transducer
 Clean the remaining gel from the patient’s skin
 Immediately initiate any post-treatment
 To ensure continuity of treatment sessions:
 Record the treatment parameters
○ Output
○ Intensity
○ Duration
○
○ Running count of ultrasound
treatments given for this
condition