Ultrasound Flashcards
What is sound?
Waves that transmit energy
Why is “ultra” used in ultrasound?
Frequency greater than 20,000 cycles per second is ultra
How is sound transmitted
Waves transmitted by energy alternately compress and rarefy material. You need a medium, otherwise they disperse
Frequency in sound waves is:
of compression/rarefraction cycles per unit of time expressed in cycles/sec or hertz
What measurement is used to describe frequency in ultrasound?
Hertz
At what frequency is therapeutic US used?
> 20,000 cycles/sec.
What determines which frequency is used w US?
How deep Tx needs to go.
What’s the diff between continuous and pulsed US?
Continuous is thermal. Pulsed is nonthermal effects
What is duty cycle?
On off time
Duty cycle for continuous US?
100%
Most common duty cycle for pulsed US
20-80% or 1:5 ratio
In what measurement is the intensity if US registered on the US unit?
Watts/ cm2
What is cavitation?
Formation, growth, and pulsation of gas filled bubbles caused by US
Stable vs unstable cavitation
Stable: bubbles oscillate in size throughout cycles but don’t burst.
Unstable: bubbles grow over # of cycles and then implode
When is unstable cavitation more likely to occur?
Increased temp & increased pressure
What is ERA?
Effective radiating area aka size of a sound head
Contraindications for US
Malignant tumor Pregnancy CNS tissue Joint cement Plastic components Pacemaker Thrombophlebitis Eyes Reproductive organs Shallow or weak bone
Purpose of thermal US
Increase metabolic rate
Decrease pain and mm spasm
Increase circulation
Increase soft tissue extensibility
What should occur immediately after US?
Massage
Stretch
Exercise
Recommended duration for US?
5-10 min for each Tx area that’s twice the size of ERA or transducer head
Pulsed
Nonthermal
20% frequency
Continuous
Thermal
100% frequency
To avoid pain with US
More gel (medium) Avoid over bone Flatten transducer head and don't scoop gel
Rate of transducer head
Slow
4cm/sec
How electrical energy is converted to mechanical in US
Transducer has crystal inside made of piezoelectric properties, causing it to respond to AC by expanding/contracting @ same frequency that current changes polarity.
Crystal expands=compress the material in front of it.
Crystal contracts=thins area in front of it
To penetrate deeper tissues using ultrasound u should:
Use a lower frequency
Desired effects of ultrasound
Increase cell permeability
Mast cell degranulation
Increased collagen synthesis
How are tissues heated using ultrasound
Heat accumulates in tissues by conversion of kinetic energy
Does pulsed ultrasound minimize temp increase?
Yep
The ERA is what size?
Smaller than size of soundhead
Ideal parameters for using ultrasound before stretching shortened soft tissue?
1-2w/cm continuous
Ideal parameters for modulating inflammation during ultrasound
1-3mhz, .5-1w/cm2
Pulsed 20%
