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
B_{total}= 10 Log I_{final}/I_{initial} 


Term
Calculate total attenuation if the intensity at a certain depth is decreased to 1/2 of its original value. 

Definition
B_{t}= 10 log I_{f}/I_{i}
= 10 log 1/2 I_{i}/I_{i}
=10 log .5= 10 log .3
=3 dB 


Term
Fill in the blanks
Attenuation I_{final}
3dB _____ _{Iinitial}
6dB _____ _{Iinitial}
9dB _____I_{initial}
10 dB _____ I_{inital} 

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/cm^{2? }
^{(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/cm^{2}) X 2= 10 mW/cm^{2}=Ii 


Term
If I ~ A^{2}, 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


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


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

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


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


Term
Specular, Diffuse, and Rayleigh Scattering are all types of what? 

Definition
Specular, Diffuse, and Rayleigh Scattering are all types of reflection. 

