Questions and Answers
Ultrasound - ANS -sound waves with a frequency greater than 20,000 hertz
-has a thermal/nonthermal effects when applied to the body
sound waves enter the body and are attenuated by? - ANS -absorption
-reflection
-refraction
attenuation - ANS gradual decrease in intensity as ultrasound travels through tissue
absorption - ANS -some tissues are capable of greater absorption of ultrasound than others
-tissue and frequency specific
-higher absorption occurs in tissue with a high collagen rate and with higher us frequencies
ultrasound energy absorption - ANS best in tendon, ligament, fascia joint capsule and scar
tissue
reflection of a sound wave - ANS occurs when the wave passes between two tissues and a
fraction of the wave "bounces" back
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, refraction - ANS occurs when the US signal is deflected from a straight path and the angle of
deflection is away from the transducer
coupling agents - ANS gel and water
US parameters - ANS -effective radiating area (ERA) -cm2
-beam nonuniformity ratio (BNR)- ratio
-intensity- w.cm2
-frequency- MHZ
-duty cycle-%
effective radiating area (ERA) - ANS -area of the crystal that actually produces sound waves
-energy is concentrated near the center
-era is always smaller than the total size of the transducer head
beam profile - ANS -multiple ways to emerge from the head
-energy diverges as it moves away from the source
-energy is uniform close to the head (fresnel zone)
-becomes less consistent farther away from the head (spatial peak intensity)
beam nonuniformity ration (BNR) - ANS -describes amount of variation in the beam
-perfect beam would have a BNR of 1:1
ration is between the spatial peak intensity and spatial averaged intensity
-high the quality of the crystal, the lower the BMR
-lower BNR is more favorable since patients will be less likely to experience hot spots and
discomfort during treatment
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