UltraSound Flashcards
(32 cards)
Production of US
Application of hi-freq ele currect to a piezoelectric transducer creates cycles of compression and rarefaction waves directed at the tissue
Force creates voltage
the crystal transducer converts ele energy INTO mechanical energy (sound waves) (distorts and springs back to NL of the crystal = waves)
US Collimates
doesn’t spread out but stays in 1 direct path
if not calibrated correctly can cause some serious damage/burns
ERA
Effective radiating area - area of the transducer from which the US energy radiates; just smaller than the head of the US machine
Do NOT treat an area bigger than 2x the ERA
Treatment time
8-10 minutes dont want to do for much longer
Transmission
Beam 1st converges then diverges
1mHz = depth of 3cm
3mHz = depth of 1-2 cm (superficial and preferred method)
Applicator
ALWAYS moving - most E in the middle of the applicator - easy way to burn
ALWAYS flat against the skin!
Scattering
reflected and refracted waves
needs a medium (gel) to travel in
Absorption
Tissues absorb sound energy liquids absorb very little sound waves varies w tissue type (collagen abs lots of E) tendon> muscle for absorption dependent upon US frequency
Attenuation
decrease in US intensity as it travels thru the tissue
50% is due to absorption
superficial bone if hit will start to have a deep ache
Attenuation of 1mHz of various tissues
Mm - 24% skin - 39% Tendon - 59% Cartilage - 68% Bone* - 96% - bone can get painful quickly w US
BNR***
beam nonuniformity ratio
beam is not uniform and therefore center is most intense
depends on the quality of the piesoelectric transducer
BNR = peak intensity/ average intensity
2:1 to 8:1 - want it to be LOW - more even distribution
Standing Waves
reflecting surface in exact multiple of the US wavelength - reflects back on the original and doubles the intensity; hence dynamic technique used at 4cm/sec to not produce huge waves
Continuous US
greater thermal effects
duty cycle = on time/ total x 100 = 100%
acute injury at 0.5 intensity
Pulsed US
appropriate for acute injury bc no heat effecs at 20-50% duty cycle
Intensity
rate of E delivered per unit area W/cm(^squared) acute = 0.5 subacute = 0.5 - 1.5 chronic = 1.0 - 3.0
Ways to control E delivered
Intensity Treatment duratioln frequency duty cycle area size
Thermal Effects
higher dose = more thermal more collagen = more thermal ~4-5 cm deep inc tissue extensibility (4 min post) dec pain/inc pain threshold promote resorption of Ca deposits may promote bone healing inc local BF inc enzyme activity
NonThermal Effects Cavitation
formation of tiny gas bubbles in tissues bc on US vibration - thins membrane bc scrub-brush like
unstable cav = bubbles burst and kills cell
Microstreaming
flow of fluid near the vibrating bubbles
“surf” on waves and around membrane to also thin and inc permeability of membrane
allows garbage to get out easier and promote healing
Theorized Effects
- Cavitation and microstreaming may alter membrane permeability and promote soft tissue healing
- Inc rate of PRO syn
- Inc intracellular Ca
- Inc skin permeability –> sonoporation helps phonophoresis
Frequency Response Hypothesis
inc Stress = lay down collagen to withstand stress
MECHANICAL stress
in vitro
US fires up fibroblasts to inc collagen spewage = stronger tissue
Direct Contact
sound head makes direct contact with gel medium
Water immersion
treated immersed in water
parallel to skin
plastic container and Not metal
