Ch. 6 Physics: Interaction of sound and media Flashcards
The intensity, power, and amplitude of the sound wave weakens as it passes through tissue
Attenuation
What creates the images?
Reflections
Weak reflections are often created as a sound strikes a ______ between two different media.
Boundary
Sound wave that is sent out is 100%, what is the sound wave when it returns?
20%
What determines the attenuation?
Path length and frequency
Distance and frequency are __________ related to attenuation
Directly related
What are the units for attenuation?
dB (decibels)
What processes contribute to attenuation?
Absorption
reflection
scattering
What processes is the primary component of attenuation?
Absorption
Whats the relationship for absorption and frequency>
Directly
True or false:
Higher frequency waves attenuate more than lower frequency waves
True
What is it called when the boundary is smooth, the sound is reflected in only one direction in an organized manner?
Specular reflection
What is another name for backscatter?
Diffuse reflection
When the sound beam strikes an irregular surface, reflections radiate in multiple directions
Diffuse reflection
True or false
Backscattered signals have a higher strength than specular reflections in diffuse refelction.
False
They have lower strength
Whats the random redirection of sound from the primary path into many directions?
Scattering
What occurs when the tissue interface is smaller than or equal to the wavelength of the primary beam?
Scattering
______ allows us to see the tissue interface.
Scattering
Scattering is _______ related to frequency
Directly
What is a redirection of the sound wave equally in all directions?
Rayleigh Scattering
True or false
Rayleigh scattering is organized scattering
True
Occurs when the structure is much smaller than the beams wavelength
Rayleigh Scattering
A blood cell is considered a _______
Rayleigh scatterer
Rayleigh scattering is related to frequency
True or false
True
Rayleigh scattering is equal to __________
Frequency^4
Doubling the frequency = Rayleigh scattering that is ________.
16 times greater
What frequency sound waves have longer pulses and do not attenuate as fast?
Lower frequency sound wave
What frequency sound wave can travel deeper, but the image quality is not as good?
Lower frequency sound wave
What frequency sound wave have shorter pulses and have better image quality?
Shorter frequency sound wave
What frequency sound wave attenuate more and are less capable of traveling deep?
Shorter frequency sound wave
What are methods of rating numbers or values?
Logarithms
The _______________ is the number of 10s multiplied to create the original number.
Log of a number
What is the log of 1000?
3(10 x 10 x 10)
What is the log of 100,000?
5(10 x 10 x 10 x 10 x 10)
As the logarithm increases by 1, the number value increases by ___________.
10 times
What is an example of a logarithmic scale?
The Richter scale
What measures the strength of the sound beam created by the transducer as it travels through the body?
Dcibels (dB)
What compares the final strength to the initial strength of the decibles?
Logarithmic scale
What two intensities does decibels require?
The reference (starting point- transmission)
The level at the time of measurement (reception)
True or false
Decibels are a ratio
True
When a wave’s intensity doubles, a relative change of +3dB is called_____
A positive decibel
A positive decibel, when increased 10- fold, will create a change of
+10dB
Decibel increase/ decrease will be reported in factors of ____ or ____
3 or 10
When a decrease in signal strength or getting smaller is called
A negative decibel
A negative decibel, if intensity is reduced in half, a relative change of ____ occurs
-3dB
When the intensity is reduced by 1/10, a change of ____ occurs
-10dB
The number of decibels of attenuation that occurs when sound travels one centimeter.
Attenuation coefficient
Attenuation occurs as a result of
Absorption
Scattering
Reflection
Attenuation is dependent on
Frequency
the medium
distance
The reporting of a waves _________________ is a process simplified by the attenuation coefficient.
total attenuation
Attenuation coefficient is measured in _____
dB/cm
True or false
Attenuation coefficient remains fluctuates no matter how far it travels
False
It stays the same
Once the attenuation coefficient has been determined, the distance is the only factor that will change a wave’s ____________
Total attenuation
How do you determine the attenuation coefficient in soft tissue?
1/2 the frequency(MHz)= attenuation coefficient dB/cm
Scattering and frequency are ______ related
Directly
Attenuation and coefficient are measuring the ___________________.
loss of energy
You are scanning soft tissue with a 6 MHz transducer. Your depth of view is 5 cm.
What is your attenuation coefficient?
What is your total attenuation?
Atten. Coef. = 3 dB/cm
Total atten= 15 dB
atten coef (dB/cm)= frequency (MHz)/ 2
Total atten (dB)= atten coef (dB/cm) X distance (cm)
6MHz / 2 = 3 dB/cm
3dB/cm x 5 cm = 15 dB
True or False
To determine the attenuation coefficient in soft tissue, you just need to half the operating frequency.
True
What is the total attenuation of 12 MHz of sound traveling in soft tissue to reflectors that are 7 cm deep?
42 dB
Which medium has extremely high attenuation?
Air
Which medium has extremely low attenuation?
Water
