Ultrasound Flashcards
Is US audible to the human ear
No
How is US generated
High frequency electrical generator that is part of an oscillatory circuit which puts energy through a crystal causing it to vibrate emitting sound waves
What is the crystal made of and it’s thickness
Synthetic ceramic 2-3 mm
What does the crystal convert electrical energy to
Mechanical acoustic energy
True or False:
US creates a reverse piezoelectric effect
True
What is the reverse piezoelectric effect
Voltage creating a mechanical compression to the crystal
What is the soundhead made of (3)
Ceramic, aluminum, or stainless steel plate
Is the soundhead interchangeable and why or why not
No because it generally matches the frequency of the crystal
What does the applicator house (2)
- Crystal
2. Soundhead
What is the applicator made out of
Hard insulated plastic
What type of wave do photons move along the wave
Electromagnetic
What type of wave do molecules bump into their neighbor resulting in propagation of energy
Mechanical
What are the 2 types of therapeutic ultrasound waves
- Longitudinal waves
2. Transverse waves
Can sound waves travel through a vacuum why or why not
No because they need to be able to bump into something
True or False:
US creates a wave that goes positive and negative
True
What wave type do the molecules move in the direction the wave travels and perpendicular to the direction the wave travels
Transverse waves
What wave type do molecules move along the direction the wave travels
Longitudinal waves
What is the molecular flow occurring in the same direction as the wave known as
Microstreaming
What is the near field
Area of the US beam closest to transducer
What is another name for the near field
Fresnel zone
What is the far field
Area of the US beam where wave begins to diverge
What is another name for the far field
Fraunhofer zone
What does the near field look like
Sound waves are transmitted in a straight line
What does the far field look like
Sound wave begins to diverge or scatter
What are rarefactions
Dispersion of molecules
When do rarefactions occur during US
The peak of the wave
When does compression occur during US
The valley of the wave
What is power
Amount of energy per unit of time
1W equals what
1 joule/sec
What is 1 joule equal to
The energy expended in 1 second by an electric current of 1 ampere in a resistance of 1 ohm
What is a joule equal to in foot pounds
0.738 foot pounds
What is the effective radiating area (ERA)
The size of the area of the transducer that radiates the US beam
What is the ERA dependent on
The size of the crystal
Is the ERA generally larger or smaller than the size of the transducer cover
Smaller
What is the ERA measured in
cm2
What are the 2 variables that pertain to intensity of US
- Spatial
2. Temporal
What is spatial intensity variable
Relates to the size of transducer ERA
What is temporal intensity variable
Relates to time transducer is on
How do you determine the spatial average intensity
Power/ERA
What is spatial peak intensity
The peak intensity of the US beam over the area of the transducer
Where is the spatial peak intensity the greatest
The center of the US beam
How do you determine the spatial average temporal average (SATA) intensity
Spatial average temporal peak (SATP) * Duty cycle
What does SATA measure
The amount of energy delivered to tissue
What is beam nonuniformity ratio (BNR) technical terms
Ratio of spatial peak intensity to spatial average intensity
What is beam nonuniformity ratio (BNR) dumby terms
Ratio of the intensity of the highest peak to that of the average of all peaks
What does a lower BNR mean
There is a lower probability that the patient will feel any undesirable hot spots
What is the recommended range for BNR values
2:1 and 8:1
What is the duty cycle
The percent of time the US beam is on
What does a continuous duty cycle mean
The US beam is always on
What does a pulsed duty cycle mean
The US beam is on 10%, 20%, or 50% of the time
What duty cycle should be used for the acute phase of healing
Pulse
What duty cycle should be used for the subacute phase of healing
Continuous
What duty cycle should be used for the chronic phase of healing
Continuous
What does the pulse duty cycle do
Limits the amount of energy put in the patient
What is the frequency equivalent to for US
The number of compression-rarefaction cycles per unit of time
What is the frequency range for TUS
0.75 MHz to 3.3 MHz
How deep does 1 MHz US penetrate
Up to 5 cm
How deep does 3 MHz US penetrate
1-2 cm
True or False:
Absorption decreases as frequency increases
False
How much quicker does absorption occur for 3 MHz US compared to 1 MHz US
1/3 the time
What is absorption considered
Conversion of mechanical energy of US wave into kinetic or heat energy
What types of tissues absorb US the best
Tissues high in collagen
What is reflection
Redirection of the US beam away from the surface
How much does the soft tissue bone interface reflect US
35%
How much does the skin air interface reflect US
100%
How much does the skin air interface reflect US with a couplant
0.1%
What is refraction
Wave enters tissue at one angle and continues through at another angle
What does attenuation measure
The decrease in US intensity as the wave travels through tissues
What causes the intensity of US to decrease (2)
- Absorption of US wave by tissue
2. Dispersion of US wave due to reflection and refraction
What types of tissues have higher attenuation coefficients
Tissues with higher collagen content
True or False:
Penetration and absorption of the US beam are inversely proportional to one another
True
What happens to absorption as frequency increases
Absorption increases
True or False:
Reflected US waves interact with the wave moving in the opposite direction potentially making the wave more intense if both waves are in phase
True
How do you minimize standing waves
Keep the sound head moving
What is cavitation
Formation, growth, and pulsation of bubbles exposed to US beam
What is the compression phase
The bubbles compress
What is the rarefaction phase
The bubbles expand
True or False:
Cavitation can be stable or unstable
True
True or False:
Stable cavitation is thought to produce a thermal effect of US
False
Does true unstable cavitation occur at the therapeutic level
NOOOOOO!!!!!!!
What is microstreaming
The minute unidirectional flow of fluid in the vicinity of pulsating bubbles
What is microstreaming a result of
Pressure of the sound wave that moves ions or small molecules
True or False:
The US waves that bounce off of bone can great a double heating effect to tissues between the bone and applicator
True
What is the velocity of the sound wave dependent on
The physical properties of the medium it travels through
How fast does the sound wave move through bone
3360 m/sec
How fast does the sound wave move through water
1500 m/sec
How fast does the sound wave move through air
300 m/sec
What is a couplant
Any agent that allows for smooth transmission of US from sound head to tissue
What percent of the US does degassed water transmit
100%
What percent of the US does mineral oil transmit
97%
What percent of the US does US gel (ultraphonic) transmit
96%
What percent of the US does US lotion (polysonic) transmit
90%
What does non thermal US do
Alters cell membrane permeability
True or False:
It may not be the cavitation that causes the effects it may be the frequency (resonant frequency)
True
True or False:
Higher intensities and more continuous beam produces more vigorous vibration
True
What is the absorption coefficient
The amount of absorption of US energy that occurs in a tissue type at a specific frequency
True or False:
Absorption coefficient increases proportionally with US frequency
True
What are the thermal effects of US (7)
- Increased extensibility of collagen fibers
- Reduced viscosity of fluid elements in tissues
- Decreased joint stiffness
- Reduced muscle spasm
- Diminished pain perception
- Increased metabolism
- Increased blood flow
What is considered mild heating of tissue
1 C
What is considered moderate heating of tissue
2-3 C
What is considered vigorous heating of tissue
4 C
What is the effect of mild heating (2)
- Increased metabolism
2. Reduces mild swelling
What is the effect of moderate heating (2)
- Reduces pain and muscle spasm
2. Increases blood flow
What is the effect of vigorous heating (1)
- Increases ROM and tissue extensibility
How much does 1 MHz and 3 MHz increase tissue temperature per minute at 0.5 W/cm2
1 MHz: 0.04 C
3 MHz: 0.3 C
How much does 1 MHz and 3 MHz increase tissue temperature per minute at 1.0 W/cm2
1 MHz: 0.2 C
3 MHz: 0.6 C
How much does 1 MHz and 3 MHz increase tissue temperature per minute at 1.5 W/cm2
1 MHz: 0.3 C
3 MHz: 0.9 C
How much does 1 MHz and 3 MHz increase tissue temperature per minute at 2.o W/cm2
1 MHz: 0.4 C
3 MHz: 1.4 C
How long does the temperature change last for 1 MHz at 2.5 cm depth and 5 cm depth and 3 MHz 1.2 cm depth when temperature is raised 1 C
1 MHz 2.5 cm: 2:34
1 MHz 5 cm: 2:31
3 MHz 1.2 cm: 1:20
How long does the temperature change last for 1 MHz at 2.5 cm depth and 5 cm depth and 3 MHz 1.2 cm depth when temperature is raised 2 C
1 MHz 2.5 cm: 6:35
1 MHz 5 cm: 6:50
3 MHz 1.2 cm: 3:22
How long does the temperature change last for 1 MHz at 2.5 cm depth and 5 cm depth and 3 MHz 1.2 cm depth when temperature is raised 3 C
1 MHz 2.5 cm: 12:10
1 MHz 5 cm: 14:32
3 MHz 1.2 cm: 5:50
How long does the temperature change last for 1 MHz at 2.5 cm depth and 5 cm depth and 3 MHz 1.2 cm depth when temperature is raised 4 C
1 MHz 2.5 cm: 21:14
1 MHz 5 cm: 27:49
3 MHz 1.2 cm: 9:13
What are the non thermal effects of US (11)
- Increased histamine release
- Influx of Ca++
- Increased phagocytosis of macrophages
- Increased protein synthesis
- Increased capillary density of ischemic tissue
- Tissue regeneration
- Wound healing
- Cell membrane alteration
- Attraction of immune cells to injured tissues
- Increased fibroblast activity
- Vascular regeneration
How do non thermal effects of US occur (3)
- Membrane deforms slightly due o pressure against cell wall
- frequency response theory
- Micromassage, microstreaming, and cavitation
Where do most of the non thermal effect of US take place
The cell membrane
What is the frequency response theory
Specific frequency will cause specific tissue resonance
