Flashcards in Ultrasound Deck (68):
What is ultrasound?
Inaudible acoustical energy caused by acoustic vibrations with high frequency
What does ultrasound produce?
Thermal and non thermal effects
What are the parts of the basic flow chart algorithm?
- Electrical output
- Mechanical vibration
- Acoustic soundwave
- Absorbed in the tissues
What is ionizing radiation?
Radiation of sufficient energy to dissociate atoms or molecules into electrically charged atoms or radicals in the irradiated material
What is diagnostic ultrasounds?
A method of obtaining images from inside the human body through the use of high frequency sound waves
What is ultrasound imaging also known as?
What is the difference between acoustical and electromagnetic energy?
- Requires a medium to be transported
- Does not travel through a vacuum
- Travels most efficiently through dense tissue
What is the energy output for high frequency?
75,000-3.3 million Hz (.75-3.3 MHz)
What is the piezoelectric effect?
The ability of certain materials like crystals, somer ceramics and bone to generate an electric potential in response to applied mechanical stress
What are different types of piezoelectric crystals used?
- Lead zirconate or titanate
- Barium titanate
- Nickel cobalt
How does the crystal convert electrical energy to sound energy?
Through mechanical deformation
What is crystal deformation?
When an alternating current is passed through a crystal it will expand and compress
What is the reverse piezoelectric effect?
Occurs when an alternating electrical current passes through the crystal causing the crystal to contract and expand creating an acoustical sound wave
What is the effective radiating area (ERA)?
The total surface area of the sound head which emits acoustic energy
What are the typical sound head sizes?
- 2.5 cm
- 5 cm
- 10 cm
What is the beam non-uniformity ratio (BNR)?
Indicates the amount of variability in intensity within the beam
What is the ratio of the BNR?
The highest intensity found in the beam relative to the average intensity of the transducer
What is the ideal BNR and what is the typical BNR?
How does the BNR affect the intensity?
The lower the BNR the more even the intensity
What frequency do most generators produce?
1.0 or 3.0 MHz
What is the depth of penetration dependent on?
What depth is 1 MHz absorbed at?
What depth is 3 MHz absorbed at?
What occurs in the near field?
Distribution of energy is non uniform due to the manner in which waves are generated and differences in acoustic pressure
What is the point of maximum acoustic intensity?
Waves are indistinguishable and basically arrive simultaneously
What occurs in the far field?
Energy is more evenly distributed and the beam becomes more divergent
How does absorption increase?
As the frequency is increased
What happens with penetration and absorption in tissues high in water content?
Decreased absorption, energy penetrates easily
What happens with penetration and absorption in adipose tissue?
Decreased absorption, energy penetrates easily to deeper tissues
What happens with penetration and absorption in tissues high in protein content?
Increased energy absorption
What happens with penetration and absorption in peripheral nerves?
Energy is absorbed 2X that of muscle
What are the different ways the intensity of the sound wave can be decreased?
What is a longitudinal wave?
The molecular displacement is in the direction of wave propagation.
There are regions go high and low molecular density (compression and rarefaction) as the wave travels through alternating regions
What can longitudinal waves travel through?
Liquids and solids (soft tissue)
What is a transverse wave?
Displacement is perpendicular to direction of propagation
What can transverse waves travel through?
Solids (bone) and it rebounds when it hits
What is rarefaction?
The lessening in the density of something
What are standing waves (hot spots)?
When an ultrasound wave hits the interface between two tissues of different acoustic impedance a reflection of a percentage of the waves will occur.
What can occur in standing waves?
Achieve peak intensity and pressure which can create increased pain and tissue destruction through excess NRG and gas bubble formation
What is power?
The total amount of ultrasound NRG in the beam and is expressed in watts
What is intensity?
The rate at which energy is being delivered per unit area
What is spatial average intensity?
Intensity of the beam average over the area of the transducer
What is the usual rage for intensity?
0.1 - 3.0 W/cm2
What is the recommendation for intensity?
The lowest intensity at the highest frequency which transmits energy to a specific tissue to achieve a desired therapeutic effect
What are the thermal effects of ultrasound?
- Increased collagen extensibility
- Increased blood flow
- Decreased pain
- Reduction of muscle spams
- Decreased joint stiffness
- Reduction of chronic inflammation
For thermal effects to occur how much does the temperature need to rise and for how long?
Temp raised 40-50 degrees for a minimum of 5 minutes
What occur during mild, moderate and vigorous heating?
- Mild: increase of 1 degree C, accelerators metabolic rate in tissue
- Moderate: increase of 1-2 degrees C, reduces pain, muscle spams, chronic inflammation, increases blood flow
- Vigorous: increase of 3-4 degrees C, viscoelastic properties of collagen
What are the non-thermal effects of ultrasound?
- Increased fibroblastic activity
- Increased protein synthesis
- Tissue regeneration
- Reduction of edema
- Bone healing
- Pain modulation
What is micro-streaming?
Unidirectional flow of fluid and tissue components along the cell membrane interface resulting in mechanical pressure waves in an ultrasonic field
What does micro-streaming do?
Alters cell membrane permeability to sodium and calcium ions important in the healing process
What does the movement if air bubbles within the interstitial tissue do?
Enhances the permeability of cell membranes, increasing diffusion rates
What is cavitation?
The formation of gas filled bubbles that expand and compress due to pressure changes in fluid
What is stable cavitation?
Results in an increased fluid flow around these bubbles. The resultant movement of interstitial fluids in essence promotes acoustical streaming
What is unstable cavitation?
Results in violent large excursions in bubble volume with collapse, creating increased pressure and temperatures that can cause tissue damage
What does cavitation and streaming do during the inflammatory stage?
Increases transport of calcium across cell membrane releasing histamine which stimulates leukocytes to 'clean-up', leading to the stimulation of fibroblasts to produce collagen
What are some application considerations?
- Size of the area being treated
- What are you trying to accomplish
- Intensity of treatment
- Treatment area should be no larger than 2-3 times the size of the ERA
- If you decrease intensity then you should increase treatment duration
What are some different coupling mediums that can be used?
- Mineral oil
- Distilled water
- Analgesic creams
What should you consider when getting started?
- Apply to clean skin
- If too hairy, consider shaving
- Use appropriate conducting medium
- Select appropriate sound head size/frequency
- Ensure sound head is in contact with the skin before turing machine on
- Adjust intensity
- Move sound head (2.5 cm per second)
What are some different ultrasound techniques?
- Direct contact
How/when is the immersion technique used?
- When treating irregular surfaces
- Use a plastic, ceramic or rubber basin
- Can us tap water as a culling medium
- Transducer should not be in contact with the skin
- Wipe air bubbles away
How/when is the bladder technique used?
- Treating irregular surfaces
- Uses a balloon filled with water
- Coat both sides of the balloon with gel
What should the patient be told to pay attention for?
If the patient says something doesn't feel right what should be done?
- Switch to pulse mode
- Decrease intensity
- Discontinue treatment
What is the continuous mode?
The transmission on NRG is on throughout the treatment and the intensity remains constant
What is the pulsed mode?
The transmission of ultrasound is pulsed on and off, the intensity is interrupted therefore the average intensity of output is low over time
What is the duty cycle?
The percentage of on:off time (20%, 50%)
What are some contraindication for ultrasound?
- Acute injury
- Over bone
- Over exposed spinal cord
- Over the eyes
- Over the carotid artery
- Pregnancy/pelvic area during menstruation
- Active infection
- Fracture site
- Decrease skin sensation