Ultrasound Flashcards
1
Q
What is Ultrasound?
A
Sound energy that’s produced through changes in pressure
2
Q
Ultrasound: Frequency
A
- Number of waves per second (Hz)
- Human ear can hear frequencies from 16-20,000 Hz
- Ultrasound is at a frequency above the sonic level: 750,000-3,000,000 Hz
3
Q
Ultrasound: Therapeutic vs. Diagnostic
A
- Frequency
~ Therapeutic: .75-3.3 MHz (low)
~ Diagnostic: 2-15 MHz (high) - Amplitude
~ Measure of the amount of energy/
pressure of the wave
~ Therapeutic: High
~ Diagnostic: Low
4
Q
Production of Ultrasound: Direct Piezoelectric Effect
A
- Piezoelectric Crystals
~ Crystals that produce positive
and negative charges (voltage)
when mechanical stress
(pressure) is applied - Deform crystal —-> electricity
5
Q
Production of Ultrasound: Reverse Piezoelectric Effect
A
- Crystal contracts and expands in reaction to the application voltage
- US generator produces alternating current that passes through Piezoelectric crystal located in the transducer
~ Expansion and contraction of crystal
produces changes in pressure/sound - Electricity into crystal ——-> Deformed
crystal
6
Q
Beam Nonuniformity Ratio (BNR)
A
- BNR measures the nonuniformity of US waves
- Indicator of the variability of intensity of an US beam
- Expressed as a ratio:
~ Peak Intensity: Average intensity
~ 5:1 = average of 1W/cm2 with peaks
of 5 W/cm2
~ Low ratios are ideal (1:1) in order to
evenly distribute sound
~ High ratios can cause discomfort
7
Q
Effective Radiating Area
A
- Surface area of sound head that transmits a sound wave from the crystal into tissues
~ ERA is always smaller that the sound
head
~ The best sound head will have an ERA
that is close to the total area of the
sound head
8
Q
Transmission of Ultrasound
A
- Requires molecular collision for transmission
- Requires a dense medium for good transmission
~ Minimizes displacement
~ Maximizes contact with vibrating
molecules - Requires a coupling agent to pass US from the transducer into tissues
~ Agent should transmit rather than
reflect US energy - Mediums:
~ Water
~ US Gel
9
Q
Coupling Methods: Direct
A
- Transducer is applied directly to the skin
- Used in areas at least as large as the transducer head
- Gel serves as the coupling medium
~ Eliminates air between the head and
skin (reflection)
~ Hair an irregularly shaped areas
increase air pockets and bubbles
between the head and skin - Firm constant pressure should be used
~ Too light: Poor coupling
~ Too hard: Force medium out of space
10
Q
Coupling Methods: Water Immersion
A
- Used for irregularly shaped body parts
- Head held approximately .5-1cm from the body
11
Q
Coupling Methods: Bladder Method
A
- Water filled balloon/plastic bag or gel pad coated with gel and placed over treatment area
- Used for irregularly shaped or small areas that can not be immersed
- Must take care to remove all air from bag or balloon
12
Q
Transmission of Ultrasound Through Tissues
A
- Sound travels in longitudinal waves
~ Movement/oscillation of molecules
within the wave are in the direction of
the wave - Within the wave are different regions
~ Compressions (collection of
molecules)
> Area of high pressure
> Molecules squeezed together
~ Rarefactions (spread out molecules)
> Area of low pressure
> Molecules spread out
13
Q
Transmission of Ultrasound Through Tissues: Law of Grotthus-Draper
A
- As the sound wave moves through the tissues, it’s reflected, refracted, and absorbed, or passed to deeper tissues
- Absorption is the goal
14
Q
Reflection/Refraction
A
- Product of sound energy passing through different mediums
~ Different mediums can have different
acoustic impedance (resistance to
sound wave flow) - When a sound wave encounters a boundary between mediums (tissue layers) some energy will be lost to reflection/refraction
- The greater the difference in impedance the greater the amount of reflection
- Reflection is increased when the head is not placed parallel to the body
- High reflection at
~ Soft-tissue/bone interface
~ Musculotendinous Junction
~ Intermuscular interfaces
~ Interface between head and air (can
cause crystal to become damaged)
15
Q
Standing Waves
A
- If a reflected wave meets the incoming wave, a standing wave is created
~ Areas of high and low pressure are
exaggerated, causing greater
movement of molecules
~ Movement (friction) causes a high
amount of energy (heat)
16
Q
Absorption
A
- Sound energy is absorbed by converting mechanical energy to heat energy
- As a result, the intensity of the sound wave decreases as the distance it travels increases
- The amount of absorption that takes place depends on how much collagen is contained
~ The more collagen the greater the
absorption
~ Tissues with high collagen are denser
> Tendon
> Muscle
> Ligament
> Bone
17
Q
Transmission of Ultrasound Through the Tissues: As frequency increases…
A
- Divergence decreases
~ Depth decreases
> 1 MHz = 5cm
• Deeper but more generalized
> 3 MHz = 2 cm
• Superficial but more specific
18
Q
Pulsed vs. Continuous Ultrasound
A
- Continuous
~ US energy is being produced 100% of
the time during Tx
~ Most commonly used when thermal
effects are desired
> Heats very effectively - Pulsed
~ US energy is interrupted with off
periods
~ Utilizes Duty Cycle
> On time/On time + Off time
> % of time US energy is being
produced
~ Most commonly used when
nonthermal effects are desired
> Heating will still occur but a
decreased rate
19
Q
Thermal Effects of US
A
- All due to the absorption of US as it moves through the tissues
~ Absorption involves conversion of
mechanical energy (motion) to heat
~ Main advantage over other heating
modalities is that US is selective for
tissues containing high amounts of
collagen
20
Q
Thermal Effects of US: Increased Metabolism
A
- Results of Increased Metabolism
~ Increased Oxygen Consumption
which can increase secondary
damage/Low O2
~ Increased cellular wastes
~ Increased cell activity
> Good during repair-maturation/
fibroblasts, but bad during acute/
WBC
21
Q
Thermal Effects of US: Increased Circulation
A
- Due to local vasodilation
~ How/when can this be used as an
advantage?
> Repair-maturation
~ How/when can this be a
disadvantage?
> Acute
22
Q
Thermal Effects of US: Increased Capillary Permeability and Decreased Tissue Stiffness
A
- Increased Capillary Permeability
~ Increased potential for venous and
lymphatic drainage - Decreased Tissue Stiffness
~ Increased elasticity of collagen
~ Decreased fluid viscosity
23
Q
Thermal Effects of US: Decreased Pain and Decreased Muscle Tone/Spasm
A
- Decreased Pain
~ Increased blood flow (increased O2)
~ Counter Irritant
~ Removal of chemical mediators - Decreased Muscle Tone/Spasm
~ Reduction in pain (pain-spasm-stasis)
~ Increased O2 delivery
~ Decreased MS sensitivity (more
relaxation)
24
Q
Nonthermal Effects of US
A
- Nonthermal US is applied to tissues when a more acute injury is present
- Mostly used when
~ Using pulsed output w/ normal
intensities
> 20-25% duty cycle
~ When using continuous US w/ low
intensity
> .3 W/cm2 intensity
25
Nonthermal Effects of US: Cavitation
- Formation of gas filled bubbles that expand and compress due to pressure changes in tissue fluids
~ Compression in high pressure
~ Expansion in low pressure
26
Nonthermal Effects of US: Acoustical/Microstreaming
- Unidirectional flow of fluids along cell membranes
- Also causes movement of gas bubbles (produced by cavitation) along cell membranes
~ Micro-massage
27
Nonthermal Effects of US: Cavitation and Microstreaming
- Because cavitation and Microstreaming always occur regardless of the settings used, nonthermal effects will always occur no matter what the goals (thermal/nonthermal) of the US tx are
- The cavitation and Microstreaming cause a “micro massage” of the cells resulting in the specific non-thermal effects
28
Nonthermal Effects of US: Results
- Increased Cell membrane permeability
- Fibroblast activity stimulation
- WBC activity stimulation
- Osteoblast activity stimulation
29
Thermal and Nonthermal US
- Both produce some heat and nonthermal effects
- Specific settings can be used to emphasize thermal or nonthermal effects
30
Power vs. Intensity
- Power
~ The amount of ultrasound energy in
the beam/wave.
~ Measured in Watts
- Intensity
~ Rate of ultrasound energy delivered
per unit of ERA area
> ERA = Area of the transducer
head that is actually emitting
energy
~ Measured in Watts/cm2
~ Must make sure of which units the
machine is displaying for proper
treatment.
> Intend to apply 2.0 Watts/cm2,
but actually applying 2 Watts
> Actually putting in .5 Watts/cm2
(2.0 Warts w/ERA of 4cm2 = .5
W/cm2)
31
Choosing Proper Intensity
- No hard rules for proper levels
- Guidelines
~ Use the lowest intensity at the
highest frequency that will transmit
the energy to the target tissue
> Low intensity: decreases chance
of damage or discomfort
> High frequency: concentrate
energy in the area being treated
32
Choosing Proper Intensity: Nonthermal Effects
- All US will heat to a certain degree, goal is to minimize this effect
~ Continuous US
> A very low intensity should be
used: < .3 W/cm2
~ Pulsed US
> Higher intensities can be used
usually around 1.0 W/cm2
> Must use a duty cycle (20-25%)
33
Choosing Proper Intensity: Thermal
- Absolute Temperature
~ Thermal effects occur when tissues
are raised to 104-113 degrees
~ Body temp: 98 degrees
- Amount of Temperature Increase
~ ^ of 1 degrees increases metabolism
and healing.
~ ^ of 2 - 3 degrees decreases pain and
muscle spasm.
~ ^ of 4 degrees C or more increases
extensibility of collagen and
decreases joint stiffness.
34
Choosing Proper Intensity: Thermal Tx Time
- Main factor in choosing intensity is the
treatment time.
~ Most intensities of continuous
ultrasound will eventually raise
temperature to therapeutic leveis or
an absolute temperature
~ Lower intensities require more time
and higher intensities require less
time.
35
Rate of Heating Per Minute
Intensity W/cm2 1MHz 3MHz
.5 .04 C .3 C
1.0 .2 C .6 C
1.5 .3 C .9 C
2.0. .4 C 1.4 C
36
Treatment Area Size
- Tx area should be 2-3 times the size of the transducer (ERA)
~ 2 times the ERA is optimal for thermal
treatments
- Transducer should be moved at a rate of 4 cm/second
- If area is too large or head is moved too quickly, optimal healing of tissues won’t occur
37
Timing/Frequency of Treatment
- Acute/Repair/Maturation
- Start of treatment
~ Start as soon as clinically acceptable
following an injury
- Later stages
~ Continue until no benefit is seen from
Tx
38
US Indications
- Pain
- Spasm
- Scar tissue
- Connective tissue tightness
- Bone healing
- Myositis ossificans
~ an increase in circulation causes
body to flush it out/reabsorb
39
US Contraindications
- Acute inflammation (thermal)
- Pregnancy
- Tumor
- Over spinal cord or superficial nerves
(ulnar and common peroneal)
~ These structures are dense which
means they heat up very effectively
