Test 2 Flashcards
If the intensity of the beam is 20 mW/cm^2
3dB
What are three names for normal incidence?
Right angle
Orthogonal
Perpendicular
Note: Not 45 degrees
What is the property of a medium that provides a measure of resistance to sound passing through the medium?
Acoustic impedance
What causes refraction at a tissue interface?
Change in propagation speed
What happens to the intensity if the amplitude is increased by a factor of 3?
Intensity is increased by a factor of 9.
Note: amplitude multiplied by itself = the amount of intensity
The intensity of an ultrasound beam is 1000 mW/cm^2. You increase the power by 40 dB. What is the new intensity of the beam?
10,000,000 mW/cm^2
With absorption, acoustic energy is converted to:
Heat
Acoustic impedance is expressed in which unit?
Rayl
What is the amount of transmission expected from a soft tissue / air interface
1% or less.
If the intensity transmitted at a boundary 40% what is the intensity reflection coefficient?
0.6
What is something that would cause a strong echo at an interface?
A great change in impedance
True/False
Lower frequency transducers perform better when using harmonics
True
What is the angle at which there is a 100% internal reflection and no transmission?
Critical angle
Which interaction is responsible for the internal texture of organs in the ultrasound image?
Scattering
What is the best estimate of how much a 8 MHz beam will be reduced if it travels a total of 5 cm in soft tissue?
20 dB
Determine the percentage of transmitted power at an interface between the two media if the acoustic impedance of the first medium in 3 MRayls and the acoustic impedance of the second medium is 2 MRayls
96%
(Typed)
One advantage of using harmonics is that the (blank) resolution is improved.
Lateral
What is the expected attenuation of a 5 MHz sound beam that has returned from a soft tissue target 6cm away?
30 dB
True/False:
Frequency and propagation speed are indirectly related
False
Note: there is NO relationship between frequency and propagation speed
Which of the following has the correct relationship to an increase in stiffness?
Increased propagation speed
An increase in the frequency from 2MHz to 4MHz will have the greatest effect on which type of interface?
Rayleigh scatterer
True/False:
Attenuation always results in a decibel loss
True
How are frequency and attenuation related?
Directly related
What is the attenuation coefficient of a 6MHz probe traveling 2cm?
3 dB/cm
What is the half value layer for a 12MHz transducer?
0.5 cm
You had an initial intensity of 10,000 mW/cm^2. You are scanning with a 4 MHz transducer and the beam had a total path length of 10 cm. What is the final intensity of your beam?
100mW/cm^2
What term describes the distance between the compression zones?
Wavelength
What does Snell’s law predict?
Beam direction transmitted through an interface
With a specular reflector, the angle of reflection equals:
Angle incident
The angle of incidence is equal to 90 degree. The acoustic impedance of medium one equals four rayls and the propagation speed of medium one equals 1.54 mm/microseconds. The acoustic impedance of medium two equals four rayls and the propagation speed of medium two equals 1.45 mm/microseconds. What is the IRC? (%)
0%
In DMS, what will happen to the wavelength if the frequency doubles?
It will be halved
True/False:
Scattering reflectors are angle dependent
False
Note: Scattering reflectors (non-specular) are frequency dependent; not angle dependent.
Rank the propagation speeds of the following mediums from fastest to slowest:
fast, blood, soft tissue
Blood, Soft tissue, Fat
True/False:
Tissue harmonics are present at the transducer face and near field so artifacts are reduced in these areas
False
List all the components that go into beam attenuation. (What are the different things that happen to the beam?) You must list all of them to get credit.
Reflection
Refraction
Transmission
Absorption
