Ch 5, 6, 7 Flashcards
How long does it take for sound to make a round trip to and from the skin’s surface to a reflector depth of 1 cm in soft tissue?
13 us
In soft tissue, sound travels to a reflector and back to the transducer in 39 us. How deep is the reflector?
39/13 = 3cm
In soft tissue, sound travels to a reflector and back to the Tx in 39us. What is the total distance that the pulse traveled?
39/13= 3cm (x2) = 6cm
One reflector is 5 times deeper than another. The time of flight of sound to the deeper structure is _____ the time of flight of the shallower reflector.
5 times greater than
Time of flight is directly related to depth of reflector.
True or False?
We need one intensity to calculate decibels?
False- decibels measure relative changes, comparison/ratio
-10dB means that the intensity is reduced to ____ of its original value.
One-tenth
What is the log is 10,000?
4
10x10x10x10
Every 3 dB means that the intensity will ____.
Double
A drop in intensity to one-quarter of its original value is ___dB.
-6
If -3dB is half, then -6 dB is one quarter
A wave’s intensity is 2mW/cm^2. There is a change +9 dB. What is the final intensity?
Bc it’s +9dB -every 3 decibels doubles so it would be
2(2)=4(2)=8(2)= 16
break it down
What combination of the following is related to greater attenuation?
Long or short distance
AND
Low or high frequency
Long distance
High frequency
What combination of the following results in the wave with the highest intensity?
Long or short distance
AND
Low or high frequency
Short Distance
Low frequency
Which of the following results in the least attenuation?
A) 4MHz sound, path length 2 cm
B) 4 MHz sound, path length 8 cm
C) 6 MHz sound, path length 8 cm
D) 6 MHz sound, path length 4 cm
4 MHz sound, path length 2 cm
High frequency, short distance
Which of the components of attenuation is the dominant contributor?
Absorption
Rayleigh scattering is proportional to _____.
Frequency^4
Attenuation is measured in ___.
Decibels
____ is an extremely low attenuater.
Water
____ has the highest attenuation.
Air
Bone and lungs have a _____ attenuation.
High
What is the relationship btw propagation speed and attenuation coefficient in soft tissue?
They are unrelated
In soft tissue, attenuation coefficient is directly related to ____.
Frequency
As path length increases, the attenuation coefficient of ultrasound in soft tissue _____.
Remains the same
A sound wave, with an intensity of 50W/cm^2, strikes a boundary and is totally reflected.
What is the IRC?
100%
A sound wave, with an intensity of 50W/cm^2, strikes a boundary and is totally reflected.
What is the reflected intensity?
50W/cm^2
The ITC of sound is 99.9%. What percent of sound is reflected back to the transducer?
0.1%
What is this formula for?
(Z2-Z1 / Z2+Z1) x100
IRC%
ITC% =
(Transmitted intensity/ incident intensity) x 100
Or
ITC%= 1-IRC
What is Snell’s Law?
Quantifies the physics of refraction
Sin(transmission angle)/sin(incident angle) = speed of med 2/ speed of med 1
The angle btw an ultrasound pulse and the boundary btw two media is 56 degrees. This is called _____.
Oblique incidence
With normal incidence, what factors affect refraction?
None
True or false?
Right angle incidence reflections are always generated at a boundary if the propagation speeds of the media are different.
False
What is most likely to create Rayleigh scattering?
Red blood cells
Snell’s law describes physics of ____.
Refraction
The most likely amount of reflection at a boundary btw soft tissue is ____.
1%
Sound is traveling from medium 1 to medium 2. Propagation speeds of M1 and M2 1600 m/s and 1500 m/s respectively. There is normal incidence.
A) incident angle > reflection angle
B) incident angle = reflection angle
C) incident angle < reflection angle
Incident angle = reflection angle
Intensities may be reported in various ways with respect to ___
Time and space
____ measurements are important in the study of ____
Intensity
Bioeffects
What is the measurement for all intensities?
W/cm2
____ is the most relevant intensity with respect to tissue heating
SPTA
Spatial peak temporal average
Bc peak measurements are larger than avg measurements, ____ intensity has the highest value while ____ has the lowest value.
SPTP (spatial peak temporal peak)
SATA (spatial avg temporal avg)
____ is always higher than Spatial avg intensity.
Spatial peak intensity
A number called _____ describes the spread of a beam in space.
Beam uniformity coefficient
- also called SP/SA factor
SP/SA factor is unitless with a value of 1 or greater
____ describes the relationship of the beam intensities with time. A unitless number with a value btw 0 & 1
Duty factor
For a ____ ultrasound, the beam is always “on” and the pulse avg and temporal avg intensities are the same.
Thus, ___ = ____ and ___=____
Continuous wave
SPTA=SPPA
SATA=SAPA
When pulsed and continuous wave sound beams have the same ____ intensities, the continuous wave beam has the higher SPTA intensity.
SPTP
When pulsed and continuous wave sound beams have the same SATP intensities, the continuous wave beam has the higher _____ intensity.
SATA
Itp is the maximum intensity in ____
Time
Im intensity is averaged over the most intense ___
Half-cycle
Ipa is averaged only during the pulse duration ____ time only.
“On”
Ita is averaged during the ___
PRP
both “on” and “off” times
Rank intensity from largest to smallest
SPTP Im SPPA SPTA SATA
Isp is the maximum in ____
Space
Isa is averaged over the _____ of the beam
Cross sectional area
Attenuation is measured in ____ and reported as a ____ change.
Decibels
Relative
10 dB of attenuation means
A decrease in 10dB
-10dB
___ is likely to occur when the dimension of a boundary is large
Reflection
2 types of reflection
Specular
Diffuse (backscatter)
Sound scatters when tissue _____
Interface is small
Scattering is directly related to ____
Frequency
Lung tissue ____ bc aveoli are filled with air.
Scatters
One example of Rayleigh scattering is when there is interaction of ultrasound and ____
RBC
____ is the largest component of attenuation
Absorption- when ultrasound energy is converted to another energy (heat)
Due to ____, high frequency waves attenuate more than lower frequency waves.
Absorption
A tissue’s impedance is ____ not ____.
Calculated not measured for
Sound not reflected must be ____.
Transmitted
With normal incidence, what factors affect refraction?
None
Incidence angle ALWAYS equals ____
Reflection angle
2 physical principles ALWAYS apply to reflection with oblique incidence:
Conservation of energy
Reflection angle = incident angle
Refraction ONLY occurs with ___ and ____
Oblique incidence and different propagation speeds
Whichever medium has the higher speed has the ____ angle.
Greatest
Time of flight is ____ for shallow and ___ for deep reflectors.
Shorter
Longer
Time of flight (go return time/round trip time) is directly related to
Depth of reflector
Time of flight is calculated using
Speed of sound in soft tissue (1.54mm/us) and go return time
A pulse’s time of flight will be twice as long for a reflector that is ____ the depth of another.
Twice
13 microsecond always applies when
Sound travels through soft tissue
Total distance is always ___ the depth.
Twice
____ is the go return time of a sound pulse btw the transducer and the bottom of the image.
PRP
PRP =
imaging depth (cm) x 13 us/cm
If the imaging depth is 10 cm, what is the PRP?
Depth x 13 us/cm
10x13 = 130 us
If there is a depth of 5 cm, what is the PRP?
5cm x 13us/cm = 65us
In one second, sound can travel into tissue AND return from a depth of ____.
77,000 cm (nearly half a mile)
In 1 one second, sound can travel to and from 77 cm a total of ___ times
1,000
In 1 one second, sound can travel to and from 7.7 cm a total of ___ times
10,000
Shallow depth of view = ___ PRF
High (more cycles per second)
Deep depth of view =
Low PRF (less cycles per second)
PRF (Hz) =
77,000 cm/s / imaging depth(cm)
If the depth is 7.7 cm, what is the PRF?
77,000 / 7.7 = 10,000 Hz
*remember PRF is measured in Hz
