Ultrasound Flashcards
What is frequency in US?
Number of vibrations/second
One million vibrations per second = 1 MegaHertz or 1 MHz
Use 1 to 3 in treatment
What is inside an US? What does it do?
Piezoelectric Crystals
Compressed mechanically, produce voltage
If voltage is passed through the crystal, it will compress or expand
US Trans contain such a crystal ,when plugged in, voltage causes the crystal to compress and expand
How is energy transmitted to tissue?
Sound energy is transmitted by vibration of molecules in the transducer via a medium (gel or water)
When is 1 MHz used?
Used for targets deeper than 2 cm (Up to 5 cm (2.5 inches) deep)
When is 3 MHz used?
Used for targets 1 to 2 cm deep
What are the two mode for ultrasound?
Continuous wave mode
Delivered w/o interruption
Pulsed wave mode
Interrupted by periods of no ultrasound wave transmission
Involves Duty Cycle
What is duty cycle?
Duty cycle is expressed as a percentage of sound wave transmission over time
Ex: time on/time on + time off
Duty cycle= On time/Total time
10 ms/20 ms = 50% duty cycle
(10ms/10ms+10ms)
What is wave intensity?
Intensity = amount of energy delievered to tissue and is measured in watts/cm2
Also known as the amplitude of the wave
Different areas of the crystal vibrate at different rates and therefore intensity is not uniform in the beam due to how is attached
Spatial Peak Intensity
Power of the beam at its greatest, located at center of soundhead
ERA = Effective Radiating Area; Sound is actually delivered in ERA
Size of sound head is slightly larger than ERA.
Spatial Average Intensity
Expression of the average power of the entire beam.
What you are actually putting on your patient
Beam Non-Uniformity Ratio
Ratio of spatial peak intensity/spatial average intensity
Smaller is better (and more expensive)
More even the energy disruption
Determined by the quality of the crystal and how transducer is structured
Ratios of 6:1 and less are acceptable ratios
Which of these two is a bad BNR?
The left! Bad Ratio, very high concentration in one spot
ERA – Effective Radiating Area
Actual cross sectional area of the US beam coming out of the US head
Treatment area should be maximum of about 2x the ERA (10 cm2)
Acoustic Impedance
Sound travels different through different mediums
Low impedance allows good transmission and little absorption
Blood and fluids have low impedance, bone has high impedance
Reflection and Refraction
If there is heterogeneity in tissue, reflection and refraction of sound waves will occur
Example: Boundary of muscle and bone will lead to significant reflection and refraction
Waves can interact with other waves due to reflection
What is a standing wave?
Sum and increase the energy at the interface.
Standing waves can be minimized by continuous movement of the sound head
Can be used to show sensitivity in stress fractures
Attenuation
Refers to a decrease in sound energy as it travels through tissue
Can be reflected, refracted, or absorbed
Physiologic Effects of Ultrasound
Thermal
Non Thermal
Thermal Effects from US
Sound energy from US is absorbed by tissue causes friction at the molecular level which will produce heat
Pain modulation
Vasodilation
Decrease muscle tone
Decrease tissue viscosity
Known as a deep heating modality
Continuous mode for thermal effects
3 MHz heats up superficial quickly (5 min) while 1 MHz is longer more tissues (10 minutes)
Maximum of 4 degrees to increase extensibility
Non Thermal Effects from US
- Delivery of energy wihtout a significant rise in tissue temperature, typically requires a pulsed mode operation with a duty cycle equal to or less than 50%
- Microstreaming or acoustic streaming
- Cavitation
- Unstable cavitation
What is microstreaming?
Ions undergo small magnitude movement
Suggested that this alters permeability of cell membrane thereby facilitating cellular processes and promoting healing and growth
Gunk can be disrupted around other membrane and allow for tissue healing to occur as now things aren’t in the way
Limited research in support that it works
What is cavitation?
Small gas bubbles that MIGHT be present in tissue fluid MAY undergo compression and expansion
Be very skeptical
What is Unstable cavitation
Violent implosion and explosion of gas bubbles in tissue causing tissue destruction
May happen at high levels of US with no healing
Would never see in clinic
US and Effect on Tissue Healing
Evidence is still lacking :/
When you perform Thermal US on a patient do they receive both thermal and non thermal effects?
Yes
Indications for US
- Promotion of local tissue mobility (small or deep tissue)
- Temporary pain relief (less pain signals going through)
- Promotion of tissue healing
- Thermal effects for vasodialation
- Non-thermal effects for acute injuries, wounds, fractures
Contraindications for US
- Neither continuous nor pulsed US
- Pregnancy (Low back or abdomen)
- Cancer
- Over electronic devices
- Actively bleeding tissues or untreated hemorrhaging disorder
- Deep Vein Thrombosis
- Recent radiated tissues
- myosisits ossificans
- eyes
- Anteriro neck/carotid sinus
- reproductive organs
- tissues with TB
- Continuous
- Cognitive impairment
- infected tissues
- Acute or exacerbation of chronic injury
- Impaired circulation
- Impaired sensation
- Heat sensitive skin
- Over implants containing cement or plastic components
How large of an area should you do US on?
2x size of ERA
What intensity is a good starting point for US
1.5
How do you determine how long to US?
Time is based on how much time it will take for tissues to heat up
- Factors:
- Frequency
- Tendon vs muscle
How fast should you move the US head?
Slow, 4 cm/sec (approximately 1.5 inches
Phonophoresis
Physically drive medication into tissue
No evidence to back this
Precautions for US
- Pulsed or continuous
- Spinal cord or superficial peripheral nerves
- Regenerating nerves
- Active epiphysis (growing adolescents)
- Fragile skin
- Pulsed
- Cement or plastic implants
- impaired sensation
- Impaired congition
- Impaired circulation
- heat sensitivity
- infected tissues with drainage
- Regenerating nerves
- Acute or exacerbation of chronic injury
