# Shared Flashcard Set

## Details

Physics- 1/30
flashcards for physics for the week of 1/30
26
Physics
01/30/2012

Term
 Attenuation is a decrease of what as US travels through a medium?
Definition
 Attenuation is a decrease in amplitude and intensity.
Term
 True or False, depending on the type of attenuation the number may be positive or negative.
Definition
 FALSE! Attenuation is ALWAYS negative.
Term
 Write the equation for total attenuation or Intensity loss.
Definition
 Btotal= 10 Log Ifinal/Iinitial
Term
 Calculate total attenuation if the intensity at a certain depth is decreased to 1/2 of its original value.
Definition
 Bt= 10 log If/Ii = 10 log 1/2 Ii/Ii =10 log .5= 10 log .3 =-3 dB
Term
 Fill in the blanks Attenuation                                     Ifinal          -3dB                                       _____ Iinitial          -6dB                                         _____ Iinitial           -9dB                                          _____Iinitial         -10 dB                                     _____ Iinital
Definition
 -3 dB.........1/2 Iinitial -6dB.............1/4Iinitial -9dB.........1/8Iinitial -10dB.........1/10Iinitial
Term
 Calculate total attenuation if the intensity at a certain depth is decreased to 1/10,000 if its original value.
Definition
 Bt= 10 log If/Ii = 10 log 10-4 Ii/Ii = 10 log 10-4 =10 X (-4) X 1 =-40 dB
Term
 Intensity of the ultrasound is reduced by 20 dB. What is the ratio of intensities?
Definition
 Bt= 10 log If/Ii -20dB=10 log If/Ii -2= log If/Ii 10-2=If/If= .01
Term
 Intensity of the Ultrasound is decreased by 3dB. What is the initial intensity, if the final intensity was 5 mW/cm2? (hint, looking for Ii and If/Ii)
Definition
 -3dB= 10 log If/Ii -.3=Log If/Ii 10-.3=If/Ii=.5   Ii=If/.5=IfX2 =(5mW/cm2) X 2= 10 mW/cm2=Ii
Term
 If I ~ A2, then what is the equation for amplitude?
Definition
 B= 20 log Afinal/Ainitial
Term
 Calculate total attenuation if the amplitude of an ultrasound wave at a certain depth is decreased to 1/2 of its original value.
Definition
 B=20 log Afinal/Ainitial 20 log .5 Ai/Ai 20 log .5 -6dB
Term
 Name three causes of attenuation.
Definition
 Absorption, Diffraction, and Reflection are all causes of attenuation.
Term
 When does absorption occur in US?
Definition
 Absorption occurs when US energy is converted into a different type of energy (heat, vibration)
Term
 What cause of attenuation is responsible for up to 80% of attenuation in soft tissue?
Definition
 Absorption
Term
 What three factors affect absorption? What type of relationship is it?
Definition
 Freqency- increase in F=increase in absorption Depth- increase in depth=increase in absorption Viscosity (medium)- increase in viscosity=increase in absorption
Term
 Explain relaxation time. what does it play a role in?
Definition
 Relaxation time is the time it takes for the molecules to return to their original postion. Relaxation time plays a role in absorption.
Term
 What is the equation for attenuation due to absorption?
Definition
 [image]
Term
 Calculate the intensity loss due to absorption for the 7.5 MHz ultrasound beam that traveled 5 cm in soft tissue.
Definition
 (.5dB/cm*MHz)(5cm)(7.5MHz)= 18.8 dB drop
Term
 Calculate the intensity loss due to absorption for the echo recieved from a depth of 12 cm using a 2.5 MHz transducer.
Definition
 (.5 dB/cm*MHz)(2.5 MHz)(24cm) = 20 dB drop   (also can be written -20 dB)
Term
 Define Half Value Layer.
Definition
 Half Value layer is the distance sound waves need to travel to decrease by 1/2.
Term
 What factors do Half Value Layer depend on?
Definition
 -frequency of the US -the medium through which US travels
Term
 How many HVL did the ultrasound travel if the original intensity is reduced by 9 dB?
Definition
 Ii...(HVL)...3dB...(HVL)...6dB...(HVL)...9dB   The ultrasound traveled through 3 HVL
Term
 caluclate the intensity loss due to absorption for the echo received from a depth of 12 cm using a 2.5 MHz transducer.
Definition
 -30 db
Term
 Waves can bend around obstacles, what is this ability called?
Definition
 The ability for waves to bend aroubd obstacles are called diffraction.
Term
 Reflection is:   a) the thickness of a material that will reduce intensity to .5 original value. b) the amount of resistance of the medium to the sound wave c) the redirection of the sound beam
Definition
 Reflection is the redirection of the sound beam (c)
Term
 Although ___ attributes to attenuation, it is also a key phenomenon that allows US imaging.
Definition
 Reflection
Term
 Specular, Diffuse, and Rayleigh Scattering are all types of what?
Definition
 Specular, Diffuse, and Rayleigh Scattering are all types of reflection.
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