A device that converts one form of energy to another
Piezoelectric crystal: a crystal that produces (+) and (-) electrical charges when it contracts or expands
Crystal of quartz, barium titanate, lead zirconate, or titanate housed within transducer
Reverse (indirect) piezoelectric effect: occurs when an alternating current is passed through a crystal resulting in contraction & expansion of the crystal
US is produced through the reverse piezoelectric effect
Vibration of crystal results in high-frequency sound waves
Fresnal zone (near field) – area of the ultrasound beam on the transducer used for therapeutic purposes
Longitudinal waves – molecular displacement is along direction in which waves travel (bungee cord)
Compression – regions of high molecular density (molecules in high pressure areas compress)
Rarefraction – regions of low molecular density (molecules in low pressure areas expand)
Transverse waves – molecular displacement in direction perpendicular to wave (guitar string)
Influences on the Transmission of Energy:-
Reflection – occurs when the wave can’t pass through the next density
Refraction – is the bending of waves as a result of a change in the speed of a wave as it enters a medium with a different density
Absorption – occurs by the tissue collecting the wave’s energy
Decrease in a wave’s intensity resulting from absorption, reflection, & refraction
as the frequency of US is because of molecular friction the waves must overcome in order to pass through tissues
US penetrates through tissue high in water content & is absorbed in dense tissues high in protein
Absorption = Frequency (3 MHz) , and
Penetration = Absorption (1 MHz) , so
Penetration = Frequency + Absorption (1 MHz)
Tissues water content = low absorption rate (fat)
Tissues protein content = high absorption rate (peripheral nerve, bone)
Muscle is in between both
Spatial Average Temporal Peak Intensity (SATP): average intensity during the “on” time of the pulse
Output meter displays the SATP intensity
Spatial Peak Intensity (SPI): max. output (power) produced within an ultrasound beam
Spatial Average Temporal Average Intensity (SATA) or Temporal (time) Average Intensity:
Power of US energy delivered to tissues over a given period of time
Only meaningful for Pulsed US
SAI x Duty Cycles
Ratio between the spatial peak intensity (SPI) to the average output as reported on the unit’s meter
The lower the BNR, the more uniform the beam is
A BNR greater than 8:1 is unsafe
Because of the existence of high-intensity areas in the beam (hot spots), it is necessary to keep the US head moving
Soft tissue healing & repair
Joint contractures & scar tissue
Muscle spasm,Neuroma,Trigger areas,Warts
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