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