Exam 1 Flashcards
what is the relationship of wavelength and frequency?
inversely related
what is the relationship between velocity, wavelength, and frequency?
Velocity = wavelength x frequency
(V= distance over time)
( V = 𝛌 / T or V = 𝛌 / (1/T) —> V = 𝛌f )
Velocity and frequency are directly related when 𝛌 is constant. vice versa
What is attenuation?
Units?
Determined by?
Directly related to?
The decrease in intensity, power, and amplitude of a sound wave as it goes through a medium.
Measured in: decibels
Determined by: path length and frequency
Is directly related to distance and frequency
What are the four types of attentuation?
1) Scattering
2) Absorption
3) Reflection
4) Refraction
what is scattering?
directly related to?
occurs when?
is the random redirection of sound in many directions. Occurs when the tissue interface is small; that is, equal to or less than the wavelength of the incident sound beam.
directly related to frequency
what is absorption?
directly related to?
occurs when ultrasonic energy is converted into another energy form, such as heat.
Directly related to frequency (like scattering)
what is reflection?
A portion of the wave’s energy is redirected or reflected back to the sound source.
Reflection weakens the portion of the sound wave that continues forward.
Two forms: specular and diffuse
what is refraction?
is a change in direction of wave propagation when traveling from one medium to another. Occurs only with oblique incidence (not normal) and different propagation speeds of the two media.
Energy per unit area of a sound beam is called what?
intensity
what is intensity?
Formula?
units?
range?
determined by?
is it adjustable?
-Is the concentration of energy in a sound beam
-Divide the beam’s power by the beam’s cross-sectional area.
-Describes brightness of a wave
-Intensity depends on both power of the beam and the area over which the power is applied.
-Units: Watts/cm^2
-Ranges: 0.01 to 300 W/cm^2
-Determined by: sound source
-Adjustable
Intensity = Power (W) / Area (cm^2)
Define Power
describes what?
proportional to?
determined by?
is it adjustable?
Units?
Typical values?
-the rate of energy transfer or rate at which work is performed.
-Like amplitude, it describes the size of a wave or magnitude of a wave
-Is proportional to amplitude^2
-If power increases so does amplitude
-Determined by sound source
-Adjustable
-Units: Watts
-Typical ranges: .004 to 0.09 W
Define amplitude
units?
determined by?
rate at which it decreases depends on?
adjustable?
-bigness of a wave. difference between the maximum value and the average value of an acoustic variable.
-Units: can have any of the acoustic variables Decibels (dB) (one Melinda’s slide not in book), Pressure- Pascals (Pa), Density- g/cm^3, Distance- cm, mm, um
-Determined by sound source
-The rate at which it decreases depends on the characteristics of both the sound wave and the medium.
-Adjustable
Define Sensitivity
the ability of a system to display low-level echoes
What is the relationship between Power, Amplitude, and Intensity?
-describe the strength of a wave.
-They are directly related
-Power increases so does amplitude and intensity
-Power is related to amplitude ^2
-Intensity is related to amplitude
what is the peak pressure or height of the wave known as?
Amplitude
What is B-mode?
-appears as a line of dots of vary brightness
-Also called B-scan
-Brightness of the dot indicates the strength of the reflection
-Basis for all types of gray scale
-Weaker reflections appear as darker gray dots, whereas stronger reflections appear as brighter white dots.
(brightness mode)
Define Frequency
units?
typical values?
determined by?
adjustable?
-The number of cycles that occurs in one second
-Units: 1/second, Hertz (Hz)
Ex: 1 cycle/second = 1 Hertz
1,000 cycles / second = 1 kHz
1,000,000 cycles / second = MHz
-Typical values: 2 MHz - 15 MHz
-Determined by sound source only
-Not adjustable- Sonographer must change the frequency on the machine (only goes ½) or transducer to adjust the depth or resolution of the scan
Define Temporal Average
refers to all time, transmit (pulse duration) and receive.
a pulsed beam does not have the same intensity at different times
averaging the intensity during the entire pulse repetition period (both transmit and receive)
Define Time of Flight or Go Return Time
directly related to?
formula
is the time it takes a pulse to go to an interface and return to the receiver
-It is directly related to depth
Smaller depths short time-in-flight
Deeper depths large time-in-flight
-Time of flight equals depth multiplied by 13 us
A sound wave is created by a transducer, reflects off an object, and returns to the transducer. The depth of the reflector is 10 cm in soft tissue. What is the go-return time?
a) 13 us
b) 1.3 us
c) 65 us
d) 130 us
D. Time of flight equals depth multiplied by 13 us. 10cm x 13 us = 130 us
A sound wave is created by a transducer, reflects off an object, and returns to the transducer. The go-return time is 26 us. What is the depth of the reflector?
a) 1 cm
b) 2 cm
c) 3 cm
d) 4 cm
B. the reflector depth is 2 cm. 2cm x 13 us = 26 us
what is SPTA?
units?
taken where?
is always?
Spatial Peak, Temporal Average
-the most relevant method for measuring intensity with respect to tissue heating
Units: watts/cm^3
-Is where a measurement is taken at a location where the intensity is maximum and averaged over all time, both transmit and received.
-is ALWAYS higher than the spatial average intensity
Rank Intensities from Largest to Smallest
SPTP –> Im –> SPPA –> SPTA –> SATA
Which has the highest velocity?
Bone
Air
Water
Soft tissue
Sound travels the fastest in solids, liquids then gasses.
Bone (3,500 m/s)
Soft tissue (1,540 m/s)
Water (1,480 m/s)
Air (330 m/s)
Define Spatial Pulse Length
units?
typical values ?
determined by ?
equals ?
adjustable?
-is the distance that a pulse occupies in space from the start to the end of a pulse.
-Units: mm
-Typical values: in soft tissue 0.1 to 1.0 mm
-Determined by: both the source and medium
-It equals the number of cycles in each pulse times the wavelength of each cycle.
Since wavelength is determined by both, so is the spatial pulse length.
-NOT adjustable
Spatial pulse length formula
directly proportional to?
inversely proportional to?
SPL = # cycles x wavelength
Directly proportional to the number of cycles in the pulse
Inversely proportional to frequency.
Arrange in increasing order of ultrasound velocity
Bone
Air
Liver
Water
Bone (3,500 m/s)
Liver (1,560 m/s)
Water (1,480 m/s)
Air (330 m/s)
Define Propagation Speed
units?
typical values?
adjustable?
-Is the rate at which a sound wave travels through a medium.
-Units: meters per second, mm/us, or any distance divided by time.
-Typical values: 500 m/s to 4000 m/s depending on the tissue through which it travels.
-Not adjustable by sonographer, just by traveling from one medium to a different medium.
If you have 2 identical mediums, and the beam is sent and strikes an interface at 90 degrees or perpendicular in between the two mediums. What happens to the beam?
If both mediums are identical and the incidence was normal then only transmission occurs because the impedances of the media are the same.
If you have 2 mediums, and one has one impedance, what happens to the beam when they strike the interface between those two mediums?
If both mediums are different with a normal incidence and different impedance, both reflection and transmission occur.
Refraction occurs only if what two conditions are meet?
Oblique incidence (not normal)
Different propagation speeds of the two media
When increasing pulse repetition period what does it do to resolution imaging depth? or refraction?
Pulse repetition period and imaging depth are directly related
As depth of view increases, the pulse repetition period increases.
With deeper imaging the listening time and the pulse repetition period ________.
With shallower imaging, the listening time and the pulse repetition period ________.
lengthen
shorten
Definition of Period?
units?
typical values?
determined by?
adjustable?
Is the time it takes a wave to vibrate a single cycle, of the time from the start of one cycle to the start of the next cycle
Units: microseconds (um), seconds
Typical values: 0.06 to 0.5 microseconds (us)
Determined by: sound source only
Not adjustable by sonographer.
What is the least obstacle to the transmission of ultrasound in the body?
Blood
Product of the period and number of cycles in a pulse is called what?
frequency
Define Pulse Repetition Frequency
units
typical values
determined by
adjustable
not related to
is the number of pulses that an ultrasound system transmits into the body each second.
Units: Hertz (Hz) or per second
Typical values: 1,000 or 10,000 hertz or one to ten thousand pulses per second.
Determined by
Sound source only and maximum imaging depth
Yes adjustable by sonographer by adjusting depth of view
NOT related to frequency
Define Continuous wave
transducer has 2 crystals, one for sending and one from receiving. It does this at the same time. It never stops. It is unable to produce a picture. It will average all velocities scanned.
Define Pulse Duration
typical contain
units
determined by
adjustable
is the actual time from the start of a pulse to the end of that pulse. Is a single transmit, talking, or “on” time.
Typically contain 2 to 4 cycles
Shorter duration pulses are desirable for imaging because they create images of greater accuracy.
Units: microseconds (us)
Typical values: 0.3 to 2.0 us
Determined by: sound source only
NOT adjustable
Define Pulse Repetition Period
units
typical
determined by
adjustable
not related to
is the time from the start of one pulse to the start of the next pulse.
Includes one pulse duration plus one listening time
Units: milliseconds, seconds, etc
Typical values: 100 microseconds (us) to 1 millisecond (ms)
Generally about 100 to 1000 times longer than pulse duration.
Determined by: sound source only and imaging depth
Adjustable by sonographer (adjust depth of view PRP also adjusted).
NOT related to period
Define Fresnel
(near field, Fresnel zone) is the region from the transducer to the focus (blue arrow). The beam gradually narrows, or converges, within the near zone.
For a continuous wave, disc-shaped crystal, the diameter of the sound beam as it leaves the transducer is the same as the diameter of the active element.
At the end of the near zone, the beam narrows to only one-half the width of the active element. The focus is located at the end of the near zone.
Define Fraunhofer
(far field) the far zone is the region that starts at the focus and extends deeper (purple arrow). Within the far zone, the beam diverges, or spreads out.
At the beginning of the far zone, the beam is only one-half as wide as it is at the transducer. From the focus, the beam continues to diverge. When the beam is two near zone lengths from the transducer, the beam is again the same size as the active element. At depths more than two near zone lengths, the beam is wider than the active element.
What does the near and far zone do in the sound beam?
They both help form the focal zone which is a region around the focus where the beam is relatively narrow. Reflections arising from the focal zone create images that are more accurate than those from other depths.
what the difference between near vs far zone?
Near zone is closer to the transducer and starts off the same width as it then narrows, while the far zone is further from the transducer starts off narrow and ends at the same width as the transducer.
Particles in a medium that are moving, attenuation will primarily occur in??
Absorption
(Most sizeable component of attenuation)
Define Acoustic Impedance
units
typical
determined by
also called
Is the acoustic resistance to sound traveling in a medium.
Calculated by multiplying the density of a medium by the speed at which sound travels in the medium.
Reflection of an ultrasound wave depends on the difference in acoustic impedances of the two media at a boundary.
Units: rayls (Z)
Typical values: 1,250,000 to 1,750,000(1.25 to 1.75 Mrayls)
Determined by: medium only
Also called Characteristic impedance
There are two mediums: one is equal to the other, what happens to the sound when it starts to penetrate? Is it absorbed, refracted, reflected or does it go right through the medium?
right through it
What is the Fraunhofer zone explaining ?
(far field) the far zone is the region that starts at the focus and extends deeper (purple arrow). Within the far zone, the beam diverges, or spreads out.
At the beginning of the far zone, the beam is only one-half as wide as it is at the transducer. From the focus, the beam continues to diverge. When the beam is two near zone lengths from the transducer, the beam is again the same size as the active element. At depths more than two near zone lengths, the beam is wider than the active element.
Ultrasound waves are called what in tissues?
Longitudinal waves (particles moves in the same direction that the wave propagates)
Mechanical waves
What area of the wave has the most and least particles?
Compression (most)
Rarefaction (less)
Infrasound
less than 20 Hz
(0.02 kHz or 0.0002 MHz)
Audible sound
Between 20 Hz and 20 kHz
(0.02 kHz- 20 kHz
20 Hz - 20,000 Hz
0.0002 MHz - 0.02 MHz)
Ultrasound
Greater than 20 kHz
(0.02 MHz ro 20,000 Hz)
what does Hertz mean?
Some people believe that hertz means “cycles per second”
Hertz are actually a two part process:
Hertz means events per second
To which event are we referring?
what is the focal zone?
a region around the focus or focal point where the beam is relatively narrow and an area where the image detail is superior.
Reflections arising from the focal zone create images that are more accurate than those from other depths.
what is the focal length?
the focal length is the distance from the transducer to the focus (narrowest part of the beam).
focus location can be changed
adjustable
what is the focus?
is the location where the beam is the narrowest (red arrow) for a disc shaped crystal, the width of the sound beam at the focus is one-half the width of the beam as it leaves the transducer.
Located at the end of the near zone, the beginning of the far zone, or the middle of the focal zone.
between 20 Hz to 20,000 Hz, is it audible?
Yes
higher than 20,000 Hz ( 20 kHz), is it audible?
Ultrasound, no
Less than 20 Hz, is it audible?
Infrasound, No
what is the time from the start of a pulse to the end of it?
Pulse duration
“on” time or talking
determined by sound source
not adjustable
units: microseconds
What are the three acoustic variables? Define them?
1) Pressure: concentration of force in an area
Units: pascals (Pa)
2) Density: concentration of mass in a volume
Units: kg/cm^3
3) Distance: measure of particle motion
Units: cm, mm, um, feet, mile
what is the velocity of sound in human soft tissue @ 37 degrees celsius?
Soft tissue average 1540 m/s
Online: 1565 m/s
Define Compression
function of the receiver that is performed twice.
First compression: keeps the electrical signal levels within the accuracy range of the system’s electronics.
Second compression: keeps an image’s gray scale content within the range of the detection by the human eye.
Define Rarefraction
is a change in direction of wave propagation when traveling from one medium to another.
what is wavelength a measurement of?
units?
typical ranges?
determined by?
Adjustable?
is the distance or length of one complete cycle
Units: mm, meters, any other length
Typical ranges: 0.1-0.8 mm
Determined by both the source and medium
Not Adjustable
what is inversely proportional to Period (T) ?
Frequency (1/T)
Define Density
units
inversely related to
concentration of mass in a volume.
Describes the relative weight of a material
Characteristics of a medium that affects the speed of sound
When equal volumes of two materials are compared, the dense material weighs a lot, whereas the non-dense material weighs little.
Steel is dense, aluminum is not
Inversely related to speed
Units: kg/cm^3
Define Propagation Speed
units
determined by?
typical values ?
adjustable?
is the rate at which a sound wave travels through a medium.
Units: meters per second, mm/us, or any distance divided by time
Typical values: 500 m/s to 4000 m/s depending on the tissue
Is determined only by the medium through which the sound is traveling.
All sound, regardless of the frequency, travels at the same speed through any specific medium.
Ex: sound with a frequency of 5 MHz and sound with a frequency of 3 MHz travel at the same propagation speed in the same medium.
Not adjustable by sonographer, just by change of medium
Define Duty Factor
units
determined by
inversely related
adjustable
formula
is the percentage or fraction of time that the system transmits a pulse
Units: none
Determined by sound source only
Inversely related to imaging depth
Is higher at shallow depths, and lower at greater depths.
Adjustable by changing depth of view
Duty factor (%) = ( Pulse duration / pulse rep. period ) x 100
Define sound
(6)
is a mechanical wave in which particles in the medium move
The molecules in the medium vibrate back and forth from a fixed position.
Cannot travel thru a vacuum, must travel through a medium
Where molecules are alternatively compressed and rarefied
Travels in a straight line
Are longitudinal waves
Define Stiffness
directly related to
also called
describes the ability of an object to resist compression.
Characteristics of a medium that affects the speed of sound.
Directly related to speed
Also called Bulk modulus
Elasticity and Compressibility are the opposite
what is the duty factor of a continuous wave vs pulse wave?
is 1.0 (100%) for continuous wave sound, because the system is always transmitting.
Pulse wave duty factor is somewhere in between 0 and 100%
which one is the only one determined by the medium?
Intensity
Period
Propagation speed
Amplitude
Propagation Speed
Name all the acoustic variables
Pressure
Density
Distance
Temperature
Particle motion
*vary with location and time
Power is the rate of _______?
energy
Define Destructive Interference
The interference of a pair of out-of-phase waves results in the formation of a single wave of lesser amplitude than at least one of its components.
Define Axial resolution
units
determined by
adjustable
It measures the ability of a system to display two structures that are very close together when the structures are parallel to the sound beam’s main axis.
Units: mm or any other distance unit
Determined by spatial pulse length (spatial pulse is determined by both sound source and medium)
Not adjustable
How do you improve axial resolution?
Shorter pulses improve axial resolution.
Define Lateral Resolution
units
determined by
the ability to distinctly identify two structures that are very close together when they are side by side, or perpendicular to the sound beam’s main axis.
Units: mm, cm, or any unit of distance (smaller numbers are preferable)
Determined by: width of the sound beam
How to improve lateral resolution?
narrower beams have better resolution
