Which gain will increase the risk of bioeffects?
a. transmit
b. receive
c. gain
d. overall gain
a. transmit
Which of the following is considered the memory of an ultrasound instrument?
a. pulser
b. transducer
c. receiver
d. beam former
e. digital scan converter
f. display monitor
e. digital scan converter
Spectral broadening suggest:
a. laminar flow
b. turbulent flow
c. flow away from the transducer
d. flow towards the transducer
b. turbulent flow
With pulse wave Doppler axial resolution:
degrades
What color is usually use in color flow Doppler variance map to indicate turbulent flow?
green
Doppler high pass filter eliminates:
high amplitude signals; low velocity flow
The Doppler wall filter is considered a:
high pass filter
The Nyquist Limit is equal to:
a. propagation speed x frequency
b. propagation speed/ wavelength
c. PRF/2
d. 4xV^2
c. PRF/2
Multiple echoes, equally spaced originating from a gas bubble is called:
a. comet tail
b. ring down
c. slice thickness artifact
d. multipath
b. ring down
An increase in red blood cell velocity will_____ the Doppler Shift:
a. increase
b. decrease
c. not change
d. cannot be predicted
a. increase
The primary advantage of CW Doppler is:
a. range resolution
b. range discrimination
c. range ambiguity
d. range gating
e. absence of sampling rate
e. absence of sampling rate
The range for ultrasound begins:
a. 20 Hz
b. 20,000 Hz
c. 2 MHz
d. 15 MHz
b. 20,000 Hz (useful frequency range for clinical imaging is 2MHz-10MHz)
Which instrument control affects the amplitude (dB) of the outgoing signal:
a. gain
b. receiver gain
c. TGC
d. transmit gain
e. overall gain
d. transmit gain; amplitude can be affected by the sonographer
Which of the following is used to convert Doppler shift information into color:
a. high PRF
b. fast Fourier transform
c. autocorrelation
d. time interval histogram
c. autocorrelation
b is incorrect because fast Fourier transform is the method used to process conventional Doppler shift information but is too slow a method for color Doppler
Pulse repetition frequency
Number of pulses that an ultrasound system transmits into the body each second. Hz. Typically 4-15 KHz. PRF and depth of a view are inversely related: When system is imaging deeper, the pulse repetition frequency is lower.
Also the number of pulses created each second
The best way to increase the near field length of an ultrasound beam is to:
increase transducer diameter
The range of frequencies produced by a damped PZT element is called:
a. fundamental frequencies
b. Q Factor
c. near field
d. bandwith
d. bandwidth
The percentage of time that the ultrasound instrument is emitting ultrasound is called:
a. PRF
b. pulse duration
c. pulse repetition period
d. duty factor
d. duty factor; the maximum value is 1, the minimum is 0
The unit of duty factor is:
a. Hz
b. mm
c. ms
d. unitless
d. unitless
Quality Factor= Fundamental frequency/ bandwidth
This allows doses of different types of radiation to be compared for their biological effects.
Clinical imaging transducers are:
wide bandwidth; low q factor
Power/area=
Intensity
Increasing wavelength will _ frequency.
a. increase
b. decrease
c. not change
d. cannot be predicted.
b. decrease
All of the following directly affect frame rate except:
a. depth of penetration
b. field of view
c. number of focuses
d. line density
e. beam width
e. beam width
A reflection will occur at the boundary of two media if the acoustic impedences of the two media are:
a. equal
b. different
c. unchanged
d. cannot be predicted
b. different
A mechanical transducer utilizes:
a. transmit focus
b. receive focus
c. fixed focus
d. dynamic aperture focusing
c. fixed focus; sonographer cannot determine the location of # of foci. mechanical transducer uses cross sectional imaging, rotating wheel, wobbler, oscillating mirror
The transducer frequency is primarily determined by the transducer element:
a. diameter
b. thickness
c. propagation speed
d. type
b. thickness
A strongly focused transducer implies a:
a. short focal length; decreased beam divergence
b. medium focal length; increased beam divergence
c. long focal length; no beam divergenc
d. short focal length; increased beam divergence
d. short focal length; increased beam divergence
B-mode displays reflector:
a. amplitude and distance
b. amplitude and velocity
c. power and direction
d. depth and speed
a. amplitude and distance
An increase in the number of pixels on the display will improve:
detail resolution
Propagation speed is determined by:
a. frequency
b. harmonics
c. bandwidth
d. bulk modulus
d. bulk modulus
Increasing transmit gain increases everything except:
frequency
The correct depth placement of reflectors depends primarily upon:
a. frequency
b. period
c. power
d. propagation speed
d. propagation speed
Which of the following will increase the color flow jet area displayed?
a. increase color gain
b. increase velocity scale
c. increase frequency
a. increase color gain
Increasing propagation speed:
air, soft tissue, bone
The most common type of transducer used in echo is:
sector phased array
Decibels are the units for all of the following except:
a. amplitude
b. transmit gain
c. gain
d. attenuation
e. TGC
f. dynamic range
e. intensity
e. intensity= mW/cm2
What are the four acoustic variables:
- temperature, density, particle motion, pressure
Frequency is
Cycles per second (Hz)
not affected by sonographer
increase frequency; decrease depth
Pulse duration
period (ms) x # of cycles in a pulse
Wavelength
the length of one cycle
wavelength= propagation speed/ frequency
1.54/3MHz= .5mm
An increase in packet size will _ the frame rate
Decrease
The range for audible sound is:
20 Hz- 20kHz
The wavelength of a 1MHz transducer is:
1.54/1= 1.54mm
The average speed of sound in soft tissue is:
1540m/s; 1.54km/s; 1.54mm/us
An increase in overall gain will result in all of the following except:
a. increase in image brightness
b. increase in output power
c. increase in amplification of the returning signal
d. decrease risk in bioeffects
b. increase in power
Reject eliminates:
low amplitude signals
There have been no proven biological effects for unfocused transducers for intensities below:
100mW/cm2 SPTA
The primary cause of attenuation of ultrasound in soft tissue is caused by:
absorption
Resolution artifact
When two structures parallel to the ultrasound beam are displayed as one reflector.
Damping does not decrease:
bandwidth
Spectral Broadening
The widening of the doppler shift spectrum. Meaning the increase of the range of doppler shift frequencies present, owing to a broader range of flow speeds encountered by the sound beam.
Refraction
Change in direction of a wave when it changs speed as in travels from one material to another. The change in the direction of sound as it crosses a boundary.
autocorrelation
used to convert Doppler shift information into color.
PRF
Pulse Repetition Frequency. The rate at which pulses are transmitted, given in hertz or pulses per second; reciprocal of pulse-repetition time.
Period
the time per cycle
1-10usec
Period Calculation
1/frequency
1/5MHz= .2
How do you decrease period?
Increase frequency
Impedance
the opposition of sound propagation
The unit for impedance?
Rayls
what is the doppler shift frequency?
A.recieved ultrasound frequency multiplied by the transmitted ultrasound frequency
B.difference between the transmitted ultrasound frequency and the received ultrasound frequency
C.sum of the transmitted and received ultrasound frequencies
D.ratio of the transmitted ultrasound frequency to the received ultrasound frequency
In this image, which target group is used to evaluate dead zone?
how is lateral resolution determined for a pulsed-echo system using a tissue-mimicking test object?
A.by observing spaces between reflectors perpendicular to the beam
B.by observing spaces between reflectors along the beam path
C.by observing position of deepest visible reflector along the beam path
D.by observing position of deepest visible reflector perpendicular to the beam path
what is the distance to the interface if the round trip time for a sound wave is 39 microseconds?
which signals are eliminated by the wall filter in a spectral Doppler display?
two images demonstrating the same pathology from different scan planes
at minimum, what is required when documenting a pathology discovered during an examination?
If the diameter of the sound beam is halved by focusing, what happens to the intensity
What is the period of a 5 MHz ultrasound wave?
A. 0.02 ms
B. 0.2 ms
C. .5mc
D. 5ms
what is the most appropriate action for the sonographer to take when receiving a verbal order for an exam?
a) Deny performance of the exam until a written request is received
b) Seek approval from supervisor
c) Verbally repeat the request back to the referrer to verify correctness
d) Document two forms of ID of the patient
what is a benefit of using contrast agents?
a) Output power can be increased after contrast administration to improve visualization
b) Increased amplitude of the returning doppler signals
c) Harmonic signals produced by contrast agents are weaker than those produced by tissue
d) Frame rate is improved when interrogating contrast with power doppler
a sound wave propagates fastest through which substance?
a) Bone
b) Muscle
c) Fat
d) Gas
What is this artifact?
A. Shadowing
B. Side lobe
C. Reverberation
D. Mirror image
Which way is the blood flowing?
A. Right to left
B. Left to right
C. Bidirectional
D. Cannot tell
The horizontal axis, or x-axis
Runs side to side
The vertical axis, or y-axis
Runs up and down
Unrelated
Two items that are not associated
Related or Proportional
Two items that are associated or affiliated
However, the relationship between the items does not have to be specified
Directly related or Directly proportional
Two items that are associated such that when one item increases, the other increases
Inversely related or inversely proportional
Two items are associated such that when one item increases, the other decreases
Reciprocal Relationship
When two numbers with a reciprocal relationship are multiplied together, the result is one
Reciprocal numbers are inverse because when one increases, the other decreases
For a numerical answer to a question to be comprehensive, it requires a
Unit
“Increase by a factor” means
To multiply by that number
“Decrease by a factor” means
To divide by that number
Scientific or engineering notation is a shorthand manner to represent what types of numbers?
Very large or very small numbers
A number in scientific notation form with a positive exponent has a value
Greater than 10
A number in scientific notation form with an exponent of zero has a value
Between 1 and 10
A number in scientific notation form with a negative exponent has a value
Less than 1
10⌃9
Prefix: giga
Symbol: G
Meaning: billion
10⌃6
Prefix: mega
Symbol: M
Meaning: million
10⌃3
Prefix: kilo
Symbol: k
Meaning: thousand
10⌃2
Prefix: hecto
Symbol: h
Meaning: hundred
10⌃1
Prefix: deca
Symbol: da
Meaning: ten
10⌃-1
Prefix: deci
Symbol: d
Meaning: tenth
10⌃-2
Prefix: centi
Symbol: c
Meaning: hundredth
10⌃-3
Prefix: milli
Symbol: m
Meaning: thousandth
10^-6
Prefix: micro
Symbol: μ
Meaning: millionth
10^-9
Prefix: nano
Symbol: n
Meaning: billionth
List all these metric terms in increasing order:
A. mega
B. micro
C. milli
D. hecto
E. deca
F. deci
micro, milli, deci, deca, hecto, mega
List all these metric terms in decreasing order:
A. nano
B. canti
C. giga
D. kilo
E. hecto
F. micro
giga, kilo,hecto, centi, micro, nano
Sound pulses travel through biologic tissue, or __.
Media
All waves carry _ from one location to another.
Energy
Sound is a __ wave in which particles in the medium move.
Mechanical
Sound cannot travel through a ; it must travel through a .
Vacuum, medium
What does compressed mean?
Squeezed together
What does rarefied mean?
Stretched apart
Sound travels in a __ line.
Straight
Sound waves are __ waves.
Longitudinal
What is the propagation speed dependent on?
The medium
Are there any biologic effects on tissue?
No
Sound waves are identified by
Oscillations in acoustic variables
What are the three acoustic variables? (With their units)
pressure – pascals (Pa), density – kg/cm^3, distance – cm, mm
If something other than pressure, density, or distance (particle motion) rhythmically oscillates in a wave, then the wave…
Is not a sound wave
Sound waves are also known as
Acoustic waves
What are the seven Acoustic Parameters?
Period, frequency, amplitude, power, intensity, wavelength, propagation speed
Particles move in a direction that is perpendicular to the direction that the wave propagates in what wave?
Transverse wave
Particles move in the same direction that the wave propagates in a __ wave.
Longitudinal
When are a pair of waves considered in-phase?
When their peaks and troughs occur at the same time and at the same location
Considered “in step”
What happens when two waves are out-of-phase?
Their peaks occur at different times, and so do their troughs
“out of step”
What is interference?
When more than one beam travels in a medium and arrive at the same location at exactly the same time
These waves lose their individual characteristics and combine to form a single wave
The interference of in-phase waves results in a single wave of amplitude. This is called __.
Greater, constructive interference
(Larger Wave)
The interference of a pair of out-of-phase waves results in the formation of a single wave of _ amplitude. This combination is called _____________.
Lesser, destructive interference
(Smaller Wave)
When frequencies of waves differ, what kind of wave occurs?
Both constructive and destructive interference
What do waves transfer from one location to another?
Energy
Two waves are traveling in a medium and arrive at a location at the same time. What event takes place?
Interference
Which types of waves will exhibit both constructive and destructive interference?
Waves of different frequency
What units are used to report the pressure of a sound beam?
Pascals, Pa
What describes features of a sound wave?
Parameters
What is the source of a sound wave?
The ultrasound system and the transducer
Some parameters are determined by the tissue through which the sound is traveling, also called a __.
Medium
What is period? And what is it determined by?
The time it takes a wave to vibrate a single cycle, or the time from start of a cycle to the start of the next cycle
It is determined by the source
What is frequency? And what is it determined by?
The number of cycles that occurs in one second
Determined by the sound source only
1 cycle/second =
1 Hertz
If the frequency of a sound wave is less than , it is below the threshold of human hearing and cannot be heard. These are defined as _____.
20 Hz, infrasonic
Audible sound waves that humans can hear are frequencies between ___________.
20 Hz and 20,000 Hz
What is ultrasound’s frequency?
Greater than 20,000 Hz or 20 kHz
Why is frequency important in diagnostic sonography?
It affects penetration and image quality
Period and frequency are __ related to each other.
Inversely
When two reciprocal parameters are multiplied together, the result is:
1
What three parameters describe the size, or magnitude, or strength of a sound wave?
Amplitude, power, intensity
What is Amplitude?
The “bigness” of a wave. It is the difference between the maximum value and the average or undisturbed value of an acoustic variable
Also the difference between the minimum value and the average value of the acoustic variable
What is Amplitude determined by? And is it adjustable?
Initially, amplitude is determined only by the sound source, however amplitude decreases as sound propagates through the body (attenuation)
Yes, a control on ultrasound systems allows the sonographer to alter initial amplitude
What is the difference between amplitude and peak-to-peak amplitude?
Amplitude is measured from the middle value to the maximum value. Peak-to-peak amplitude is the difference between maximum and minimum values of an acoustic variable
Peak-to-peak is twice the value of the amplitude
What is power?
The rate of energy transfer or the rate at which work is performed. Power, like amplitude, describes the “bigness” of the wave
What is power determined by? And can it be changed?
Determined by the sound source only
It CAN be changed
How are amplitude and power related?
Both describe the size, or magnitude of a wave. When power increases, so does amplitude
Power is proportional to…
amplitude^2
What is intensity?
The concentration of energy in a sound beam Intensity = Power/area
What is intensity determined by? And is it adjustable?
Sound Source
Yes, it is adjustable
How is intensity related to power and amplitude?
Intensity is proportional to power
Intensity is proportional to amplitude^2
What is the distance or length of one complete cycle called?
Wavelength
What is wavelength determined by? And is it adjustable?
Both the medium and source
No, it is not adjustable
What is the relationship between wavelength and frequency?
As long as a wave remains in one medium, wavelength and frequency are inversely related
As frequency increases, wavelength decreases. The lower the frequency, the longer the wavelength
What is the wavelength of 1 MHz sound in soft tissue?
1.54 mm
What is the wavelength of other frequency sound waves in soft tissue?
Sound with a frequency of 2 MHz has a wavelength of 0.77 mm in soft tissue. 1.54mm/2 = 0.77 mm
What is the wavelength equation?
wavelength = (1.54mm/μsec)/(frequency)
Why is wavelength important in diagnostic ultrasound?
Wavelength plays an important role in image quality
Shorter wavelength sound usually produces higher quality images with greater detail (higher frequency)
What is the distance that a sound wave travels through a medium in 1 second called?
Propagation Speed
What does the speed of sound range from?
500m/s to 4000m/s
What is Propagation Speed determined by? And is it adjustable?
The Medium
No, it is not adjustable
What is the speed of sound in soft tissue?
1,540 m/s
1.54 mm/μsec
1.54 km/s
1 mile per second
What has the slowest propagation speed? And the longest?
Slowest: Lung (Air, Gas)
Longest: Bone
What is the speed of sound in Blood?
1,560 m/s
What is the order for speed of sound from lowest to highest in Water, Metals, and Air?
Air, Water, Metals
What determines the speed of sound in that medium?
Stiffness, density
What describes the ability of an object to resist compression?
Stiffness; A stiff material will retain its shape if it is squeezed; whereas a non-stiff material will change its shape
How does stiffness affect speed?
Stiffness and Speed are directly related
As materials become stiffer, the speed of sound in the material increased
Non-stiff media are described as…
Elastic or compressible
What describes the relative weight of a material?
Density
How does density affect speed?
Density and speed are inversely related. As materials become more dense (heavier), the speed of sound in the material decreases
When Stiffness increases, Speed __
Increases
When Density Increases, Speed __
Increases
What two parameters are reciprocals?
Period and Frequency
What is the only parameter that is determined by the medium?
Speed
What is wavelength decided by?
Both the Sound Source and the Medium
What are the units of:
wavelength –
frequency –
intensity –
propagation speed –
period –
power –
wavelength – millimeters
frequency – hertz
intensity – watts/cm^2
propagation speed – meters/second
period – second
power – watts
Dos the medium or the sound source determine these parameters?
wavelength –
frequency –
intensity (initial) –
propagation speed –
period –
power (initial) –
amplitude (initial) –
wavelength – both
frequency – source
intensity – source
propagation speed – medium
period – source
power – source
amplitude – source
Which of the following cannot be changed by the operator?
wavelength
frequency
intensity
propagation speed
period
power
amplitude (initial)
Wavelength, frequency, propagation speed, period
True or False. A wave with a frequency of 15,000 MHz is ultrasonic.
True (any wave >20,000 hertz)
True or False. If the amplitude of a wave is increased to 3 times its original value, the intensity in increased by 6 times.
False (if we triple amplitude, we increase intensity by a factor of nine)
True or False. If the power of a wave is halved ,the intensity is reduced to one-fourth its original value.
False (intensity is the power/area, if we halve the power we will halve the intensity)
True or False. Propagation Speed increases as Frequency increases.
False (frequency is unrelated to speed)
Medium 1 has a density of 9 and a stiffness of 6. Medium 2 has a density of 8 and a stiffness of 6. In which medium will sound travel slower?
Medium 1: Since both media have the same stiffness, the medium with the greater density has the lower propagation speed
If the power in a beam is 1 watt and the area is 5cm^2, what is the beams intensity?
0.2 W/cm^2
If intensity remains the same while the power had doubled, what has happened to the beam area?
Doubled (if intensity stays the same, whatever happens to power also has to happen to area)
A sound beam travels a total of 10 cm in 2 seconds. What is the speed of the sound?
5 cm/sec
True or False. Propagation speed increases as frequency increases.
False
True or False. Propagation speed increases as frequency decreases.
False
True or False. Propagation speed does not change as frequency increases.
True (propagation speed and frequency are unrelated)
What is the wavelength of a 3 MHz sound in soft tissue?
0.51 mm (wavelength = 1.54mm/frequency in MHz)
The effects of sound waves on tissue in the body are called __.
Bioeffects
Which of the following are considered acoustic variables?
Frequency, density, particle motion, temperature, period, and pressure
Density, particle motion, and pressure
Which of the following are considered acoustic parameters?
frequency, density, distance, pressure, and period
Frequency and period
The effects of tissue on sound waves are called __.
Acoustic Propagation Properties
The effects of a medium on an ultrasound wave are called ___ _.
Acoustic Propagation Properties
How are frequency and period related?
Inversely
How are amplitude and power related?
Directly
How are amplitude and intensity related?
Directly
How are power and intensity related?
Directly
How are wavelength and intensity related?
Unrelated
How are wavelength and frequency related?
Inversely
How are acoustic velocity and density related?
Inversely
How are elasticity and speed of sound related?
Inversely
How are acoustic velocity and compressibility related?
Inversely
How are stiffness and sound speed related?
Directly
How are frequency and sound speed related?
Unrelated
How are frequency and intensity related?
Unrelated
How are power and frequency related?
Unrelated
What are the five parameters to describe pulsed sound?
Pulse duration, pulse repetition period, pulse repetition frequency, duty factor, and spatial pulse length
What is pulsed ultrasound?
A pulse of an ultrasound is a collection of cycles that travel together. The entire pulse moves as a single item
What are the two components of pulsed ultrasound?
Transmit, talking, or “on” time
Receive, listening, or “off” time
What is the actual time from the start of pulse to the end of that pulse called?
Pulse duration (a single “on” time)
What is pulse duration determined by? And can it be adjusted?
Sound source, NO
Pulse duration (μsec) =
cycles x period (μsec)
or
cycles/frequency (MHz)
Pulse duration is directly proportional to _.
cycles in a pulse and to period
Pulse duration is __ proportional to frequency.
Inversely
What creates pulses of long duration?
Many cycles in the pulse, and individual cycles with long periods
What creates pulses of short duration?
Few cycles in the pulse, and individual cycles with short periods
Which type of pulse duration is more desirable in diagnostic imaging?
Shorter duration pulses are desirable for imaging because they create images of greater accuracy
What is Spatial Pulse Length?
The distance that a pulse occupies in space from the start to the end of a pulse.
What determines Spatial Pulse Length? And is it adjustable?
Both the source and the medium. No it is not adjustable.
Spatial Pulse Length (mm) =
cycles x wavelength (mm)
Spatial Pulse Length is _ proportional to frequency.
Inversely
What is the difference between pulse duration and pulse length?
Pulse duration is the TIME that a pulse in “on”
pulse length is the DISTANCE of the pulse end to end
Two characteristics that create long pulses are:
Many cycles in the pulse
Cycles with longer wavelengths
Two characteristics that create short pulses are:
Fewer cycles in the pulse
Cycles with shorter wavelengths
Which types of pulse length is more desirable in diagnostic imaging?
Shorter pulses are desirable because they create more accurate images
What is the time from start of one pulse to the start of the next pulse called?
Pulse Repetition Period
Pulse Repetition Period is determined by the __ that the sonographer selects.
Imaging depth
What is PRP determined by? And is it adjustable?
Sound Source
Yes, it is adjustable
When the system is imaging at shallow depths, the time from one pulse to the next is __.
Short
What is depth of view?
The maximum distance into the body that an ultrasound system is imaging
How are PRP and depth of view related?
Directly related
What are the two components of pulse repetition period?
Transmit time (pulse duration) and the receive time
Which component of PRP can the sonographer change?
Receive time or “listening time” (alter the depth of the image)
What is pulse repetition frequency?
The number of pulses that an ultrasound system transmits into the body each second
What is the PRF determined by? And is it adjustable?
Sound Source, Yes
When the system is imaging shallow, the pulse repetition frequency is _.
Higher
PRF is not related to frequency. It is related only to _ _ _.
Depth of view
How are PRF and depth of view related?
Inversely related (as depth of view increases, PRF decreases)
An ultrasound machine is imaging to a depth of 2 cm. Would the pulse repetition frequency be described as high or low?
High
Relationship between Pulse Repetition Period and Pulse Repetition Frequency
PRP and PRF are inversely related. (when PRF increases, the repetition period decreases)
PRF (Hz) =
1/PRP
77,000 cm/s/imaging depth (cm)
PRP =
1/PRF
imaging depth (cm) x 13 μsec/cm
PRF x PRP =
1
True or False. Two waves can have identical pulse repetition frequencies, even if their pulse repetition periods are different.
False (two waves can never have identical PRF’s if their pulse repetition periods are different)
True or False. Two waves can have identical PRF’s, even if their periods are different.
True (period and pulse repetition frequency are unrelated)
True or False. Two waves can have identical PRF’s, even if their frequencies are different.
True (frequency and pulse repetition frequency are unrelated)
True or False. PRF and pulse repetition period are determined only by the imaging depth.
True
What is duty factor?
The percentage or faction of time that the system is transmitting a pulse
What is duty factor determined by? And is it adjustable?
Sound Source
Yes, it is adjustable
Duty factor (%) =
(pulse duration/pulse rep. period) x 100
What are the maximum and minimum values for duty factor?
Maximum = 1 or 100%
Minimum = 0%
Pulse wave ultrasound the duty factor is only _%.
1 (listening 99% of the time)
How does the sonographer change duty factor?
When imaging depth is altered.
If all the other factors remain unchanged, what happens to the duty factor when the pulse repetition frequency increases?
Increases
If all other factors remain unchanged, what happens to the duty factor when the pulse repetition frequency increases?
Decreases
If all other factors remain unchanged, what happens to the duty factor when the pulse repetition period increases?
Decreases
If all other factors remain unchanged, what happens to the duty factor when the sonographer uses a new transducer with a longer pulse duration?
Increases
What is the duty factor if the pulse duration is 1 μsec and the pulse repetition period is 1 ms?
0.001
By adjusting the imaging depth, the operator changes the ______, ___, and __.
Pulse repetition period, pulse repetition frequency, and duty factor
__ is the time from the start of a pulse to the end of that pulse.
Pulse duration
__ is the time from the start of a pulse to the start of the next pulse.
Pulse Repetition Period
Pulse repetition frequency is the reciprocal of _.
Pulse repetition period
By changing the image depth, what does the operator also change?
PRF, Duty Factor, and PRP
What is the duty factor if the pulse duration is 1 microsecond, and the pulse repetition period is 1 second?
The duty factor is 0.001 or 10^-3
(10^-6 divided by 10^-3 = 10^-3 or 0.001)
What is the duty factor if the pulse duration is 1 millisecond, and the pulse repetition period is 1 second?
The duty factor is 0.001 or 0.1%
(0.001 divided by 1.0 = 0.001)
What is Intensity?
A beam’s power divided by its area
What is temporal intensity?
Refers to all time, transmit (pulse duration) and receive
What is pulsed intensity?
The average intensity for the pulse duration only
What does spatial refer to?
Location or space.
What is the beam’s intensity at the location where it is maximum called?
Spatial peak intensity
The average intensity across the beam’s entire cross-sectional area is called __.
Spatial average intensity
Spatial peak intensity is always _ than the spatial average.
Higher
The term temporal refers to __.
Time
Measuring the intensity of the beam at the instant in time of its maximal value is called the _____.
Temporal peak intensity
What is SPTP?
Measured at the location where intensity is maximum (highest value intensity)
What is SPPA?
Measured at the location where intensity is maximum, averaged over the transmit time (pulse duration)
What is SPTA?
Measured at the location where intensity is maximum and averaged over all time, both the transmit and receive times (Used to test for bioeffects)
What is SATA?
Measured over the entire cross-sectional area of the sound beam, and over all time (lowest value intensity)
All intensities have units of __.
W/cm^2
What is the number that describes the spread of a beam in space called?
The Beam Uniformity Coefficient (SP/SA factor)
Unitless with a value of 1 or greater
What describes the relationship of beam intensities with time?
Duty factor
For continuous wave ultrasound, the beam is always “on” and the pulse average and temporal average intensities are __.
The same
SPTA = SPPA and SATA = SAPA
When pulsed and continuous wave sound beams have the same SPTP intensities, the __ wave beam has the higher SPTA intensity.
Continuous
When pulsed and continuous wave sound beams have the same SATP intensities, the __ wave beam has the higher SATA intensity.
Continuous
__ average intensity is averaged only during the pulse duration (“on” time).
Pulse
__ average intensity is averaged during the PRP (both the “on” and “off” times)
Temporal
The rank of intensities from largest to smallest is:
SPTP -> SPPA -> SPTA -> SATA
As sound travels in the body, it weakens, or __.
Attenuates
After a sound wave is received by the transducer, converted into electricity and returned to the ultrasound system, it is strengthened or __.
Amplifide
When a waves intensity doubles, the relative change is…
+3 dB
When the intensity increases 10-fold, the relative change is…
+10 dB.
When the intensity is reduced to 1/2 its original value, the relative change is…
-3 dB.
When the intensity is reduced to 1/10 its original value, the relative change is…
-10 dB.
A reduction in the intensity of a sound beam to one-half of its original value is _ dB.
-3 dB
A reduction in the intensity of a sound beam to one-quarter of its original value is _ dB.
-6 dB
-10 dB means that the intensity is reduced to __ of its original value.
One-tenth
dB is a mathematical representation with a and ____ scale.
Logarithmic and relative
True or False. We need one intensity to calculate decibels.
False
A waves intensity is 2 mW/cm^2. There is a change of +9 dB. What is the final intensity?
16 Mw/cm^2
Every dB change means that the intensity will __.
Double
Every 10 dB change means that the intensity will _.
Increase ten times
If the final intensity of a sound beam is more than the initial intensity, then the gain in dB is __ .
Positive
If the initial intensity of a sound beam is less than the final intensity, then the gain in dB is _.
Positive
What is attenuation determined by?
Path length, and frequency of sound
Distance and Attenuation are _ related.
Directly
Frequency and Attenuation are _ related.
Directly
As sound strikes a boundary, a portion of the wave’s energy may be redirected, or _, back to the sound source.
Reflected
Reflection is likely to occur when…
The boundary is large
What is specular reflection?
When the boundary is smooth, the sound is reflected in only one direction in an organized manner
What is diffuse reflection?
When a wave reflects off an irregular surface, it radiates in more than one direction (also called backscatter)
What are the advantages and disadvantages of diffuse reflection?
Advantage: interfaces as suboptimal angles to the sound beam can still produce reflections that the transducer will receive
Disadvantage: the backscattered reflections will have a lower strength than specular reflections
What is scattering?
The random redirection of sound in many directions
Why does scattering happen?
When the tissue interface is small; that is, equal to or less than the wavelength of the incident sound beam
Scattering is directly related to frequency. Therefore, higher frequency sound beams scatter much __ than lower frequency beams.
More
What is a special form of scattering that occurs when the structure’s dimensions are much smaller than the beam’s wavelength?
Rayleigh scattering
Rayleigh scattering =
Frequency^4
When there is a higher frequency, there is pulses, _ penetration, attenuation, and __ resolution.
Shorter pulses, less penetration, more attenuation, and better resolution
When does absorption occur?
When ultrasonic energy is converted into another energy form, such as heat
Absorption is __ related to frequency.
Directly
What is attenuation coefficient?
The number of decibels of attenuation that occurs when sound travels one centimeter
total attenuation (dB) =
Attenuation coefficient (dB/cm) x distance (cm)
The attenuation coefficient is __ of the frequency in soft tissue.
One-half
In soft tissue: attenuation coefficient (dB/cm) =
Frequency (MHz)/2
atten. coef. = 0.5 dB/cm/MHz
Air (lung) and Bone have extremely __ attenuation compared to sift tissue.
High
Biologic fluids (blood, urine, amniotic fluid) have _ attenuation.
Low
What has the lowest attenuation?
Water
What is the half-value layer thickness?
The distance that sound travels in a tissue that reduces the intensity of sound to one-half its original value
What are synonyms of half-value layer?
Penetration depth, depth of penetration, half-boundary layer
What does the half-value layer thickness depend on?
The medium and the frequency of sound
If there is a thin half-value, there is a _ frequency sound and a media with _ attenuation rate.
High, high
If there is a thick half-value, there is a _ frequency sound and a media with _ attenuation rate.
Low, low
What is impedance?
The acoustic resistance to sound traveling in a medium
impedance (rayls) =
Density (kg/m^3) x prop. speed (m/s)
What is impedance determined by?
The medium
What is a synonym to impedance?
Characteristic impedance
Name three components of attenuation.
Absorption, reflection, and scattering
As the path length increases, the attenuation of ultrasound in soft tissue __.
Increases
Attenuation in lung tissue is __ than attenuation in soft tissue.
Greater
Attenuation in bone is __ than attenuation in soft tissue.
Greater
Attenuation in air is __ than attenuation in soft tissue.
Greater
What are the units of attenuation?
decibels (dB)
T or F. In a given medium, attenuation is unrelated to speed of sound.
True (attenuation and propagation speed are unrelated)
What is the relationship between ultrasound frequency and the attenuation coefficient in soft tissue?
In soft tissue, the attenuation coefficient in dB per centimeter is approximately one half of ultrasonic frequency in MHz
What are the units of the half-value layer thickness?
Distance; centimeters
As frequency decreases, depth of penetration _.
Increases
As path length increases, the half boundary layer __.
Remains the same
Impedance is a characteristic of _.
Only the medium
As the path length increases, the attenuation coefficient of ultrasound in soft tissue __.
Remains the same
Acoustic impedance = x ___.
Impedance = density (kg/m^3) x propagation speed (m/s)
Two media A and B have the same densities. The speed of sound in medium A is 10% higher than in medium B. Which medium has the higher acoustic impedance?
Medium A
Impedance is important in _ at boundaries.
Reflections
Which is better to use while examining a carotid artery., a 7.5 or 3.0 MHz transducer?
7.5 MHz transducer (superficial)
What are the three types of angles?
Acute – <90 degrees Right – exactly 90 degrees Obtuse – >90 degrees
All angles that do not equal 90 degrees are called _ angles.
Oblique
What does normal incidence mean?
The incident sound beam strikes the boundary at exactly 90 degrees.
(also called: perpendicular, orthogonal, right angle)
What is an oblique incidence?
When the incident sound beam strikes the boundary at any angle other than 90 degrees
What is the sound wave’s intensity immediately before it strikes a boundary called?
Incident intensity
What is reflected intensity?
The intensity of the portion of the incident sound beam that, after striking a boundary, continues forward in the same general direction it was traveling
incident (starting) intensity =
Reflected intensity + transmitted intensity
What is the intensity reflection coefficient (IRC)?
The percentage of the intensity that bounces back when a sound beam strikes the boundary between two media
What is the intensity transmission coefficient (ITC)?
The percentage of ultrasound intensity that passes in the forward direction when the beam strikes an interface between two media
IRC (%) + ITC (%) =
100%
A sound wave with intensity of 50 W/cm^2 strikes a boundary and is totally reflected. What is the intensity reflection coefficient?
100%
A sound wave with intensity of 50 W/cm^2 strikes a boundary and is totally reflected. What is the reflected intensity?
50 W/cm^2
IRC (%) =
(Z2-Z1/Z2+Z1)^2 x 100
If the two media have identical impedances, there will be…
No reflection
If two media have slightly different impedances, there will be…
A small reflection
If two media have substantially different impedances, there will be…
A large reflection
A pulse of ultrasound is propagating in soft tissue, such as liver. The pulse strikes a boundary with a different soft tissue at normal incidence. What portion of the intensity is reflected back toward the transducer? Why?
A very small percentage of sound, typically less than 1%, is reflected at a boundary between two soft tissues
Very little reflection occurs when the impedances have similar, but not identical, values
Sound is traveling in a medium and strikes a boundary with normal incidence. If 63% of the wave’s intensity is reflected back toward the transducer what percentage is transmitted?
37%
ITC (%) =
(transmitted intensity/ incident intensity) x 100
or
1 – intensity reflection coefficient
Sound is traveling from bone to soft tissue. The impedances of the media differ significantly, and 90% of the beam’s intensity is reflected. What percentage of the intensity is transmitted?
100% of the energy must be accounted for
If 90 % is reflected 10% must be transmitted
In _ incidence, it is complicated to tell whether the sound ill reflect or transmit after striking a boundary.
Oblique
What two principles always apply to reflection with oblique incidence?
Conservation or energy
reflection angle = incident angle
incident intensity (W/cm^2) =
reflected intensity + transmitted intensity
angle of incidence =
angle of reflection
If the sound beam bends or changes direction after is strikes an interface at an oblique angle, this is called…
refraction
What is refraction?
a change in direction of wave propagation when traveling from one medium to another.
Refraction only occurs if two conditions are satisfied:
oblique incidence (not normal)
and
propagation speeds of the two media are different
What is snell’s law?
sin(transmission angle)/sin (incident angle) = speed of Medium 2/speed of Medium 1
Under what conditions will the transmission angle equal the incident angle?
if the two media are the same
Under what conditions will the transmission angle be greater than the incident angle?
when medium 2 is greater than medium 1
Under what conditions will the transmission angle be less than the incident angle?
when medium 2 is less than medium 1
A pulse of ultrasound propagates in soft tissue, such as liver. The pulse strikes a soft tissue – soft tissue interface with oblique incidence. Some of the sound energy is transmitted. To what extent is the transmitted beam refracted?
The transmitted beam undergoes little to no refraction. A transmitted beam is refracted when the incidence is oblique and the propagation speeds are different.
A sound wave strikes a boundary at normal incidence. The impedances of the two media are identical. What percentage of the sound wave is refracted?
0%, refraction cannot occur with normal incidence
What property has units of rayls? How is it determined?
Impedance
Impedance = density x speed
What is the elapsed time from pulse creation to pulse reception called?
go-return time or time-of-flight
The time-of-flight is __ related to the depth that a sound pulse travels.
directly
depth (mm) =
1.54 mm/μsec x go-return time (μsec)/2
For every _ μsec of go-return time, the object creating the reflection is 1 centimeter deeper in soft tissue.
13
Since a pulse travels to the reflector and back to the transducer, the total distance that a pulse travels is…
twice the reflector depth
A sound wave is created by a transducer, reflects off an object, and returns to that transducer. The depth of the reflector is 10 cm in soft tissue. What is the go-return time?
130 μsec
A sound wave is created by a transducer, reflects off an object, and returns to the transducer. The go-return time is 26 μsec. What is the depth of the reflector?
2 cm
A sound wave is created by a transducer, reflects off an object, and returns to the transducer. The go-return time is 26 μsec. What is the total distance that the pulse traveled?
4 cm
The maximum imaging depth (depth of view) during an ultrasound exam is 10cm. The sonographer adjusts the imaging depth to 20 cm. What happens to pulse repetition period?
it is doubled
The maximum imaging depth during an ultrasound exam is 10 cm. The sonographer adjusts the imaging depth to 20 cm. What happens to pulse repetition frequency?
it is halved
The imaging depth during an ultrasound exam is 10 cm. The sonographer adjusts the imaging depth to 5 cm. What happens to pulse repetition period?
it is halved
A sound wave is created by a transducer, reflects off an object, and returns to the transducer. The imaging depth is 10 cm in soft tissue. What is the maximum pulse repetition frequency?
7.7 kHz
A sound wave is created by a transducer, reflects off an object, and returns to the transducer. The maximum imaging depth is 7.7 cm. What is the PRF?
77,000/7.7 = 10,000 Hz
A sound wave is created by a transducer, reflects off an object, and returns to the transducer. The go-return time is 130 μsec. What is the maximum PRF?
7,700 Hz.
What is axial resolution?
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.
What is axial resolution determined by? And is it adjustable?
SPL (shorter pulses improve axial resolution)
It is not adjustable because the SPL is fixed.
What are the synonyms to axial resolution?
longitudinal, range, radial, or depth resolution
LARRD
What is the relationship between the numerical value of the axial resolution and the image quality?
Lower numerical values of axial resolution indicate a shorter pulse. Shorter pulses create more accurate images; therefore, the image quality is better with lower numbers.
axial resolution (mm) =
spatial pulse length/2
or
(wavelength (mm) x # cycles in pulse)/2
What allows some transducers to have better axial resolution than others?
axial resolution is r=determined by the pulse length, with shorter pulses yielding improved axial resolution.
How is a shorter pulse created?
less ringing and higher frequency
What is less ringing?
Dampening the crystal to create fewer cycles in the pulse
What is the ability to accurately distinguish two structures lying closely together called?
resolution
The ability to distinguish two structures lying closely together front-to-back or parallel to the sound beam is called __.
longitudinal, axial, range, radial, depth resolution
Axial resolution is measured with units of _.
distance, such as mm.
The more cycles in a pulse, the _ the numerical value of the range resolution is.
greater
If a new pulsed transducer has many more cycles in its pulse, the image accuracy __.
degrades
_ frequency transducers generally have the best range resolution.
high
In soft tissue, a 3 cycle, 1 MHz pulse has a length of a pulse is 4.5 mm. What is the axial resolution?
2.25 mm.
Two different transducers create sound pulses. One transducer is labeled 5 MHz and the other, 3 MHz. Which transducer is more likely to create a more accurate image with relation to axial resolution? Which transducer probably has a lower numerical measure of axial resolution?
The 5 MHz transducer. The higher frequency transducer creates a shorter pulse and thus has a lower numerical measure of axial resolution. Lower numbers mean improved image quality.
Wha happens during transmission?
electrical energy from the system is converted into sound
What happens during reception?
the reflected sound pulse is converted into electricity
What is the piezoelectric effect?
the property of certain materials to create a voltage when they are mechanically deformed
What is the reverse piezoelectric effect?
when a voltage is applied to piezoelectric materials, they change shape
What are the materials that change sound into electricity (and vice versa)?
piezoelectric or ferroelectric
What materials are commonly used in clinical transducers?
lead zirconate titanate (PZT)
also known as ceramic, active element, or crystal
What are the 7 components of a basic transducer?
case, electrical shield, acoustic insulator, PZT or active element, wire, matching layer, and backing material (also called the damping element)
What is the case?
the cylindrical tube, constructed of metal or plastic, that protects the internal components of the transducer from damage.
What is the electrical shield?
Thin metallic barrier lining the inside of the case.
What is acoustic insulator?
A thin barrier of cork or rubber that isolates or “uncouples” the internal components of the transducer from the case. Prevents vibrations in the case from inducing an electrical voltage in the PZT of the transducer.
What is the wire?
Provides an electrical connection between PZT and the ultrasound system.
What is the matching layer?
increases the efficiency of sound energy transfer between the active element and the body, and protects the active element
What is the backing material (or damping element)?
bonded to the back of the active element, it reduces the “ringing” of the pulse.
The matching layer and gel _ the efficiency of sound transfer between the transducer’s PZT and the skin.
increase
How thick are the matching layer and the active element of a basic ultrasound transducer?
The thickness of the matching layer is one quarter of the wavelength of sound in the matching layer.
The thickness of the active element is one-half of the wavelength of sound in the active element.
What are the characteristics of damping material?
high degree of sound absorption, and acoustic impedance similar to PZT.
What are additional consequences related to the use of a backing material?
decreased sensitivity
wide bandwidth
low quality factor
What does decreased sensitivity mean?
the transducers with damping material are less able to convert low-level sound reflections into meaningful electrical signals during reception.
What is bandwidth?
the range, or difference, between the highest and lowest frequencies in the pulse. Thus, imaging probes are identified as short pulse, wide bandwidth.
Long duration events are bandwidth, whereas short duration events are bandwidth.
narrow, wide
quality factor =
main frequency/bandwidth
A shorter pulse has a _ Q-factor.
lower
A longer pulse has a __ Q-factor.
higher
How is PZT created?
created by exposing the material to a strong electrical field while being heated to a substantial temperature. (polarization)
What is the Curie temperature, and what is its importance?
the temperature that the PZT is polarized is called the Curie temperature or Curie point.
If the polarized PZT is heated above the Curie temperature, the crystal’s piezoelectric properties are destroyed. (depolarized)
What is the difference between sterilization and disinfection? Which method is used on transducers?
Sterilization is the destruction of all microorganisms by exposure to extreme heat, chemical agents, or radiation.
Disinfection is the application of a chemical agent to reduce or eliminate infectious organisms on an object.
Ultrasound transducers only require disinfection.
Pulse length is __ related to pulse duration.
directly
Q-factor is _ related to bandwidth.
inversely
Pulse duration is __ related to bandwidth.
inversely
T or F. Shorter duration events (such as dampened pulses) are more likely to be wide bandwidth.
True.
What occurs when a PZT crystal’s temperature is elevated above the Curie point?
the PZT is depolarized
In a continuous wave transducer, electrical frequency =
acoustic frequency
The frequency of sound emitted by a continuous wave transducer is determined by what?
the frequency of the electrical signal created by the ultrasound system
What characteristics of the active element determine the frequency of sound created by a pulsed wave transducer?
speed of sound in the PZT and the thickness of the PZT
How does the speed of sound in PZT affect frequency?
in a pulsed wave transducer, the speed of sound in PZT and the frequency of sound are directly related. When the speed of sound in PZT is faster, the frequency of sound created by a pulsed wave transducer is higher.
How does the thickness or the PZT crystal affect frequency?
For pulsed wave transducers, thinner active elements create higher frequency sound pulses. PZT thickness and frequency are inversely related.
The thickness of the PZT crystal in a pulsed wave transducer is equal to _ of the wavelength of sound in the PZT.
one-half
frequency (MHz) =
sounds speed in PZT (mm/μsec)/2 x thickness (mm)
True or False. The acoustic impedance of the matching layer is approximately the same as the acoustic impedance of skin.
False.
True or False. Imaging transducers are usually of high rather than low bandwidth.
True.
True or False. A very high Q factor transducer is used more often in diagnostic imaging transducers than a low Q factor.
False.
True or False. A pulse with a long pulse duration is likely to have a narrow bandwidth.
True.
True or False. The damping material in a transducer increases the sensitivity.
False.
True or False. The damping material in a transducer increases pulse length.
False.
True or False. The damping material in a transducer decreases the pulse duration.
True.
True or False. The damping material in a transducer improves the system’s lateral resolution.
False.
True or False. The damping material in a transducer improves the system’s longitudinal resolution.
True.
True or False. The damping material in a transducer decreases the bandwidth.
False.
True or False. The damping material in a transducer decreases the quality factor.
True.
True or False. If the frequency of the electrical excitation voltage of a pulsed wave transducer is 6 MHz, then the operating frequency of the transducer is 6 MHz.
False. (with pulsed wave transducers, the frequency of sound is not determined by the electrical signal)
True or False. If the pulse repetition frequency of a transducer is increased, then the frequency of sound produced by the transducer remains the same.
True. (frequency and pulse repetition frequency are not related)
True or False. The diameter of the active element of a transducer helps to determine the frequency of the sound produced by the transducer.
False. (the diameter of the active element does not determine the frequency of sound created by the transducer)
True or False. If the frequency of the electrical excitation voltage of a continuous wave transducer is 6 MHz, then the operating frequency of the transducer is 6 MHz.
True. (the frequency of the electrical voltage and the frequency of the sound beam are identical with continuous wave transducers)
True or False. Two piezoelectric crystals are made from the same material. The thicker crystal will make a pulsed transducer with a higher frequency.
False. (thicker active elements create sound with lower frequency, not higher)
True or False. Two piezoelectric crystals are made from the same material. The thicker crystal will make a pulsed transducer with a lower frequency.
False. (with a continuous wave transducer, active element thickness does not determine the sound beam’s frequency)
True or False. The normal propagation speed in piezoelectric material is about 3 to 5 times greater than that in soft tissue.
True. (sound travels much faster in PZT than in soft tissue)
Which type of transducer has a greater Q-factor: therapeutic or imaging?
imaging transducers use more backing material than therapeutic transducers.
In an imaging transducer, what is the purpose of attaching the backing material to the PZT?
improve image quality
A pulsed-wave transducer has a resonant frequency of 5 MHz. The lowest frequency in the pulse is 2 MHz and the highest is 8 MHz. What is the bandwidth?
8 MHz – 2 MHz = 6 MHz
The resonant frequency = the _
main or center frequency
What is the Q-factor?
resonant frequency/ bandwidth
At the starting point, the beam width is…
exactly the same as the transducer diameter.
What are the five terms that describe the shape and regions of a sound beam?
focus, near zone, focal length, far zone, focal zone
Where is the beam narrowest?
focal point (one-half the width of the beam as it leaves the transducer)
What is the near field? Another name for it?
the region from the transducer to the focus, fresnel zone
What is the focal length or NZL?
the distance from the transducer to the focus
What is the far zone? Another name for it?
the region starting at the focus and extending deeper, fraunhofer zone
At depths more than two bear zone lengths, the beam is _ than the active element.
wider
What is the focal zone?
a region around the focus where the beam is relatively narrow and image detail is superior (half located in near and other half located in far)
The focus marks the end of the _.
near zone
At the depth of the focus, the sound beam starts to _ or widen, which marks the beginning of the ___ zone.
diverge, far (Fraunhofer)
At depths more than twice the focal length, the beam’s width __ that of the transducer.
exceeds
Adjustable focus systems are called __.
Phased array
What characteristics of a fixed-focus transducer determine the focal depth?
transducer diameter and frequency of the sound
How does transducer diameter affect the focal depth?
increasing diameter results in a deeper focus; therefore, transducer diameter and focal depth are directly related.
(beams from larger diameter active elements will have deeper focus)
How does frequency affect focal depth?
Higher frequency sound results in a deeper focus; therefore, frequency and focal depth are directly related
Even with high frequency sound, an extremely small diameter locates the focus _.
shallower
focal depth (cm) =
diameter (mm)^2 x frequency (MHz)/61.6
or
diameter (mm)^2/40 x wavelength (mm)
A pair of 6 MHz probes are identical except for active element diameter. The active element diameters are 6mm and 10mm, respectively. The sound beam of which probe will have a shallower focus?
6mm active element. Smaller diameter crystals produce beams with shallower foci.
A pair of 9 mm diameter probes are identical except for frequency, which is 3 MHz and 6 MHz, respectively. Which beam will have a shallower focus?
3 MHz beam. (focal depth increases with increasing frequency)
True or False. Transducer frequency and near zone length are inversely related.
False. (directly related)
True or False. Wavelength and near zone length are inversely related.
True
True or False. Active element diameter and near zone length are directly related.
True
Beam divergence describes…
the gradual spread of the ultrasound beam in the far field.
How does transducer diameter affect beam divergence in the far field?
Smaller diameter crystals produce beams that spread out, or diverge, more in the far zone. (crystal diameter and beam divergence are inversely related) Larger diameter crystals produce beams that diverge less in the far field
Larger diameter crystals and higher frequency sound improve __ in the far field.
lateral resolution
How does frequency alter beam divergence in the far field?
Lower frequency sound beams spread out or diverge more in the deep far zone. (frequency and beam divergence are inversely related)
A pair of 6 MHz probes are identical except for active element diameter, which is 6 mm and 10 mm, respectively. Which beam will be more compact in the far field?
10mm active element has a less divergent beam. (larger diameter crystals produce beams that diverge less in the far field)
A pair of 9 mm diameter probes are identical except for frequency, which are 3 MHz and 6 MHz. Which sound beam will spread out more in the far field?
3 MHz beam is more divergent. (beams are more compact as frequency increases)
True or False. Transducer frequency and beam divergence are inversely related.
True.
True or False. Active element diameter and beam divergence are inversely related.
True.
What are sound waves are produced by? What shape do they diverge in?
tiny pieces of PZT, V-shape
When is the V-shaped wave created? And what are they called?
when the source is about the size of the sound’s wavelength. Called spherical waves, diffraction patterns, or HUYGEN’S wavelets
Huygen’s principle states…
that a large active element may be thought of as millions of tiny, distinct sound sources.
Where does destructive interference occur?
in the areas where the sound beam is absent
What does resolution refer to?
accuracy in imaging
Lateral resolution distinctly identifies two structures that are very close together when they are _ to the sound beam.
perpendicular
What is lateral resolution determined by?
the width of the sound beam (narrower beams have better resolution)
Synonyms to lateral resolution are:
angular, transverse, azimuthal resolution (LATA)
Where is lateral resolution best?
at the focus where the beam is narrowest.
lateral resolution (mm) =
beam diameter (mm)
Which type of resolution is superior in clinical imaging systems: lateral resolution or axial resolution?
Axial resolution because ultrasound pulses are shorter than they are wide.
Higher frequencies improve both axial and lateral resolutions because…
axial: the shorter pulses associated with high frequency sound
lateral: in the far field, high frequency pulses diverge less than low frequency ones. (high frequency sound beams are narrower than low frequency beams)
How does focusing improve lateral resolution?
by concentrating the sound energy into a narrower beam
What are the three methods of focusing?
external focusing – with a lens
internal focusing – with a curved active element
phased array focusing – with the electronics of the ultrasound system
Internal and External focusing may be used with…
single element transducers
Both external and internal focusing are considered _.
fixed (conventional or mechanical)
focal depth and the extent of focusing cannot be changed
What does external focusing use?
a lens
What does internal focusing use?
a curved piezoelectric crystal that concentrates the sound energy into a narrower beam
What type of fixed focusing is the most common?
Internal Focusing
Phased array means…
adjustable or multiple focusing
What happens to a beam when it is focused?
beam diameter in the near field and focal zone narrows
focus is moved closer to transducer
beam diameter beyond focal zone widens (improves lateral resolution in near zone)
focal zone size is reduced
The ability to distinguish two structure lying close together is called __.
resolution
The ability to distinguish two structures lying close together front-to-back is called _.
longitudinal, axial, range, radial, depth resolution
The ability to distinguish two structures lying close together side by side is called _.
lateral, angular, transverse, azimuthal resolution
Axial resolution and lateral resolution are both measured with units of _.
distance, such as mm
When the number of cycles in a pulse increases while the frequency remains the same, the numerical value of the range resolution _.
increases (with more cycles in a pulse, the pulse becomes longer)
When the number of cycles in a pulse increases (more ringing) while the frequency remains the same, the image quality __.
degrades. (when the number of cycles increases, the SPL increases, and the image quality decreases)
__ frequency transducers have the best range resolution.
high frequency
Name the 4 synonyms for axial resolution.
longitudinal, range, radial, depth resolution
Name the 3 synonyms for lateral resolution.
angular, azimuthal resolution, and transverse
The length of a pulse is 8 mm. What is the minimum distance between two reflectors, positioned one in front of the other, that still produces two echoes on our image?
4 mm (one half the pulse length!)
The frequency of a transducer does not change. If the diameter of the new piezoelectric crystal increases, what happens to the near zone length?
increases
The frequency of a transducer does not change. If the diameter of the new piezoelectric crystal increases, what happens tot he beam diameter in the far zone?
decreases
The frequency of a transducer does not change. If the diameter of the new piezoelectric crystal increases, what happens to the wavelength?
no change
The frequency of a transducer does not change. If the diameter of the new piezoelectric crystal increases, what happens to the beam diameter in the near zone?
increases
Narrow beams improve…
lateral resolution
What is A-mode?
Amplitude, series of upward spikes. (the higher the returning spike, the higher the amplitude) X-axis of a-mode is depth
A-modes are accurate in determining ___.
the depth of reflectors
What is B-mode?
Brightness, the brightness of the once invisible dot indicates the strength of the reflection. (weak reflections appear as darker gray dots, strong reflections are white dots) X-axis is depth
What was the form form of grayscale imaging?
B-Mode
What is M-mode?
Motion, horizontal wavy lines represent the changing depth of the reflecting surfaces are produced on the paper. X-axis = time, Y-axis = depth
What is M-mode primarily used for?
assess the motion of cardiac walls and structures
What is the only display mode that provides information regarding reflector motion with respect to time?
M-mode
With A-mode, what does the X-axis display?
depth of the reflector
With M-mode, what does the Y-axis display?
depth of the reflector
Which mode provides the foundation for real-time, grayscale anatomic imaging?
B-mode, or brightness mode
With A-mode, what does the Y-axis display?
amplitude of the reflected signal
In M-mode, what does the X-axis display?
time
With B-mode Which axis is related to the strength of the reflection?
the z-axis
How does an ultrasound system create high quality, two-dimensional images?
Two characteristics of sound that make it difficult to create two-dimensional images are: sound travels only in a straight line, and sound beams must be narrow to optimize lateral resolution.
The use of multiple pulses to create a two-dimensional image overcomes both of these difficulties.
In a mechanical transducer, the PZT crystal is ___ to create the image.
physically moved
Mechanical transducer image shape:
fan or sector-shaped
Mechanical transducers have a _ focal depth.
fixed
When there is any damage done to the crystal in a mechanical transducer,
the entire image is lost
Array transducers are comprised of…
a single slab of PZT cut into a collection of separate pieces called elements. Each active element is connected by a wire to its own electronic circuitry int he ultrasound system.
The linear phased array has _ moving parts. And the beam is steered and focused using an electrical techniques called _.
no, phasing
What is the image shape created by a phased array?
fan or sector-shaped
Elements of a phased array are what shape?
rectangular and narrow
Sound beams are focused _ with linear phased array transducers.
electronically
Advantage of phased array systems is:
the availability of electronically controlled, adjustable focusing, which allows the sonographer to match the beam’s characteristics to the clinical circumstances.
Damage to one of the elements of a phased array transducer results in…
inconsistent or erratic beam steering and focusing.
How many elements in a phased array probe are excited to create a single sound pulse?
All the active elements in a linear phased array probe are fired to create each sound beam.
What is the beam former?
the electronics within the ultrasound system that create the voltages to the transducer element
When the spike line is straight, an __ is created.
unfocused sound beam
How does the pattern of electrical spikes from the beam former focus the sound beam during transmission?
When the outer crystals are excited earlier than the inner crystals, the curved pattern creates a focused sound beam. This means the beam will be directed straight ahead.
Brightness of the display is affected by?
Receiver amplification (gain)
Acoustic speckle is an artifact produced by what?
interference of tiny acoustic wavelets
Side lobe artifact is a result of what condition?
Acoustic energy radiating in a direction different than the main axis of the beam
A sound wave is
mechanical, longitudinal
A compression area of a sound wave is
high pressure, high density
A rarefaction area of a sound wave is
low pressure, low density
Which is considered an acoustic variable
pressure
Which is a unit for pressure
N/m2
Which is a unit for density
lbs/cm3
Which wave propagates in a medium
sound
The range for ultrasound is
greater than 20KHz
__ is the number of wave cycles per second
frequency
One kilohertz is equal to
1,000 cycles per second
One megahertz is equal to
1,000,000 cycles per second
The useful frequency range for clinical imaging ultrasound is
2 MHz to 10 MHz
Frequency is determined by the
source
Frequency affects all of the following, except: wavelength, resolution, penetration, impedance
impedance
The times per cycle is
period
The period for a 5 MHz probe is
0.2usec
If frequency increases, period will
decreases
Period is determined by the
source
Period multiplied by the number of cycles in a pulse equals
pulse duration
The distance between cyclical peaks is
wavelength
The symbol for wavelength is
lambda
The wavelength of a 5 MHz probe in soft tissue is
0.3 mm
As frequency increases, wavelength (assume same medium)
decreases
Wavelength is determined by the
source and medium
As wavelength decreases
resolution improves
The rate at which a sound vibration propagates through a medium is called all of the following, except: sound speed, prop speed, speed of sound, velocity
velocity
The units for propagation speed include all the following, except: km/sec, mph, msec, mm/sec
msec
The average speed of sound in soft tissue is
1540 m/sec
Arrange the following in increasing order of sound speed in soft tissue
air, fat, muscle, soft tissue, muscle, bone
The prop speed of sound of the ceramic lead zirconate titanate (PZT) is approx
4000 m/sec
speed of sound is determined by
medium
The peak variation minus the mean variation is
amplitude
All of the following are possible units for amplitude, except: degrees, decibels, Pascal, watts
degrees
The maximum variation of an acoustic variable is 60. The mean value is 45. The maximum value is 30. The amplitude is
15
Amplitude is determined by
source
Which ultrasound machine control will affect amplitude
output power
As sound propagates through a medium, amplitude
decreases
The total energy transferred is
power
Power is determined by
source
The amplitude of a wave is 4, power is
8
Power may be affected by which gain control
transmit
The rate of energy transferred into a particular area is
intensity
The units for intensity are
mmHg
The highest measured intensity is
spatial peak, temporal peak
The lowest measured intensity is
spatial average, temporal average
According to the AIUM, there have been no proven biological effects for unfocused ultrasound below
100 mW/cm2 SPTA
According to the AIUM, there have been no proven biological effects for focused ultrasound below
1 W/cm2 SATP
Intensity is determined by
source
Which gain controls affect intensity
transmit
Assuming the same area, what effect will an increase in power have on intensity
increase
What effect will an increase in area have on intensity if power remains unchanged
decrease
For continuous wave ultrasound, which intensities are equal
SPTP, SPTA
The factor that describes the spatial intensity distribution across a sound beam is the
SP/SA factor
The minimum value for the beam uniformity ratio is
1
Ultrasound transducer A has an SP/SA factor of 40. Ultrasound transducer B has a SP/SA factor of 20. Which transducer has the brightest center
transducer A
An increase in intensity is determined to be 30 decibels. The intensity is increased by
10 x 10 x 10 or 1,000
For soft tissue, a 75% loss in intensity can be expressed in decibels as
-6dB
The number 1540 may be expressed in scientific notation as
1.540 x 10(-1 power)
The number 0.1492 may be written in scientific notation as
1.492 x 10(-1 power)
Arrange the following in the proper increasing order: giga, mega, kilo, hecto, deca
deca, hecto, kilo, mega, giga
Arrange the following in the proper increasing order: milli, centi, deci, micro, nano
deci, centi, milli, micro, nano
Arrange the following units of length in increasing order: kilometer, meter, centimeter, micrometer, nanometer
micrometer, millimeter, centimeter, meter, kilometer
Which unit would be best to use to express aortic valve area
centimeters squared
Express the average prop speed of sound in soft tissue
1.54 mm/usec, 1540 m/sec, 1.54 km/sec
The acoustic characteristic of a medium is
impedance
A reflection will occur at the boundary of two media if the media impedance are
dissimilar
The percentage of sound energy reflected at a fat/muscle interface is approx
1%
The percentage of sound energy reflected at a soft tissue/air interface is approx
50%
A reflector that is smooth surfaced and large is called
specular
examples of specular reflectors
mitral valve, interventricular septum, carotid artery
Specular reflectors are highly dependent on
incident angle
Reflectors that are rough surfaced and small are known as
scatter
Scatter reflectors are highly dependent on
transmit frequecy
The strength of backscatter is dependent upon
density, size, impedance
Reflectors that reflect ultrasound energy equally in all directions are called
Rayleigh
The best example of a scatter reflector is (the)
organ parenchyma
The best example of of a Rayleigh scatter is the
red blood cell
The ultrasound beam strikes an interface at 90 degrees. The incidence is considered
perpendicular
The optimal angle to strike specular reflectors are
direct
The reflected intensity coefficient may be calculated by the formula
[Z2-Z1/Z2+Z1]2
The ultrasound beam strikes an interface at 74 degrees. This incidence is considered
oblique
The incidence angle is 36 degrees. The reflected angle is
36 degrees
The change in sound travel direction as sound crosses a boundary is known as
refraction
The incident angle is 53 degrees. The prop speed in medium 1 is 1540m/sec. The prop speed in medium 2 is 1580m/sec. The reflection angle is
53 degrees
The incident angle is 46 degrees. The prop speed in medium 1 is 1540m/sec. The prop speed in medium 2 is 1540m/sec. The reflected angle is 46 degrees. The transmitted angle is
46 degrees
The incident angle is 72 degrees. The prop speed in a medium 1 is 1580m/sec. The prop speed in medium 2 is 1680m/sec. The reflection angle is 72 degrees. The transmitted angle is
greater than 72 degrees
In soft tissue, if the frequency of a wave is increased the Propagation Speed (PS) will…
Remain the Same because stiffness and density affect Propagation Speed.
What is the audible range?
20-20,000Hz
20,000Hz=Ultrasound
Frequency is measured in
Hertz (Hz)
is
Cycles per Second
Not affected by sonographer
Increase Frequency; Decrease Depth
A period is the length of time it takes for
one complete wavelength to pass a fixed point
PRP is determined by
Transmit time and receive time.
Period is measured in
Time (μs)
When the sonographer changes the imaging depth what parameters are changed?
PRP, PRF, Duty Factor
What is duty factor?
The percentage or fraction of time that the system is transmitting a pulse (Time Sound is ON or ON-Time).
Propagation Speed in SOFT TISSUE
1.54 mm/μs
(1540 m/sec)
Unit of measurement for Pulse Duration, Duty Factor, PRP, and Period
Time, (μs)
Pulse duration is determined by
Sound Source Only
Pulse Duration is controlled by
the ultrasound system and transducer
Pulse Duration Formula
pulse duration (μs) = # cycles in pulse/frequency(MHz)
PD= Number of cycles in Pulse/ Frequency(Hz)
Spatial Pulse Length (SPL) (measurement)
The distance that a pulse occupies in space from the start to the end of a pulse.
(mm)
Typical values for spatial pulse length in soft tissue.
0.1 to 1.0 mm
Spatial pulse length is determined by
sound source and medium
Spatial Pulse Length is directly proportional to
the Number of Cycles in the Pulse
and
the Wavelength
(Directly Proportional means that increased SPL will increase both the number of cycles in the pulse and the wavelength if increased).
Spatial pulse length is inversely proportional to
Frequency (MHz)
(Inversely Proportional means that increased SPL will lower frequency. This is because axial resolution is better with lower frequency)
Pulse Duration (PD)
The actual time from the start of a pulse to the end of that pulse; a single transmit, talking, or “on” time.
Time the pulse is on typically measured in (ms).
Pulse Length
The distance of the pulse start to end or the
duration or length of a single pulse
Pulse Length is typically measured in (mm).
the ability of an object to resist compression and relates to the hardness of a medium?
Stiffness.
Think:
↑ Stiffness ↑ Speed
↓ Density ↑ Speed
An increase in pulse repetition frequency would lead to:
Increasing pulse repetition frequency, increases duty factor.
↑ PRF ↑ Duty Factor
Which of the following would have the highest propagation speed?
Bone has the highest propagation speed, at 2000-4000 m/s.
What has the lowest propagation speed?
air technically has the lowest propagation speed at 300 m/s
Which has the Slowest Propagation Speed?
Water
Soft Tissue
Bone
Lung tissue
Lung Tissue
As imaging depth increases, the pulse repetition frequency (PRF) must:
Decrease
As imaging depth increase, pulse repeition freqency (PRF) decreases.
↑ Imaging Depth ↓ PRF
What describes the amount of refraction that occurs at an interface?
Snell’s law
Refraction: the redirection of the transmitted sound beam
Snell’s law describes the angle of transmission at an interface based on the angle of incidence and the propagation speeds of the two media.
Pressure is typically expressed in:
Pascals (Pa)
The typical range of frequency for diagnostic ultrasound imaging is
1-20 Mhz is the typical range of frequency for diagnostic ultrasound imaging.
The attentuation coefficient in soft tissue is equal to:
Attentuation Coeffcient = 1/2 (one half of the frequency in soft tissue)
The attentuation coeffcient (in dB/cm) is the rate at which sound is attentuated per unit depth.
Micro is denoted as:
Micro is denoted as millionth (µ)
What is described as the distance over which one cycle occurs?
Wavelength is distance over which one cycle occurs, or the distance from the beginning of one cycle to the end of the same cycle.
Remember, it asks for distance over which one cycle occurs.
Stiffness and propagation speed are
Directly Related
Also remember:
↑ Stiffness ↑ Speed
↓ Density ↑ Speed
Areas of high pressure and density are referred to as:
Compressions
What type of wave is sound?
Mechanical and Longitudinal Wave
The frequency ranges for ultrasound are:
Ultrasound frequency is 20 to 20,000 Hz
The speed of sound in soft tissue is
Speed of sound in soft tissue is 1540 m/s
Which transducer fires the elements in groups?
Linear sequenced array fires the elements in groups
The units for wavelength is
Wavelength units are (Millimeters)
Enhancement is caused by
Weakly attenuating structures
The wavelength in a material having a propagation speed of 1.5 mm/µs employing a transudcer frequency of 5.0 MHz is:
0.3 mm
wavelength = c/f
1.5 mm/µs / 5 MHz = 0.3 mm
An ultrasound transducer converts
Electrical energy into Mechanical energy and vice versa
Lowest attenuation to highest
bone, muscle, fat, air
If frequency doubles, what happens to the wavelength?
Wavelength is decreased by 1/2
Frequency and Wavelength are:
Inversely related
What happens to intensity if the amplitude of a signal is halved?
Amplitude halved will result in intensity quartered
amplitude = intensity2
Ultrasound pulses contain a range of frequencies called
bandwidth
How is time related to frequency
inversely
What describes the percentage of time that sound is on?
Duty factor is the percentage of time the sound is being transmitted
A 3 dB gain would indicate an increase in intensity by:
Two Times
3 dB results in doubling of intensity (or power)
The intensity of the ultraosund beam is usually greater at the focal zone because of
the smaller beam diameter
Attenuation denotes
Progressive weakening of the sound beam as it travels
Which of the following has the lowest intensity
SATA is the lowest of the intensities
What is the definition of the beam uniformity ratio?
Beam Uniformity Ratio =
Spatial peak / Spatial average
Continuous wave Doppler has a duty factor of
100%
CW Doppler is always transmitting sound making it’s duty factor 100%
The spatial pulse length is defined as:
the product of the wavelength and the number of cycles in a pulse?
SPL = wavelength x cycles
What term and philosophy relates the amount of exposure time for the sonographer and patient during a diagnostic ultrasound examination?
ALARA – As Low As Reasonably Achievable
What term is defined as the body’s pathologic response to illness, trauma or severe physiologic or emotional stress?
Shock
The inertia of the medium describes its:
Density.
Inertia is described by Newton’s principle – an object at rest will stay at rest. An object in motion stays in motion, unless acted on by an outside force.
Greatest attenuation would occur at:
long distance with high frequency
A 3MHz sound beam travels through two media. It attenuates 5 dB in medium A and 6 dB in medium B.
Total attentuation is 11 dB
Attenuation simply adds up as sound travels.
What would you do to create a wave with the highest possible intensity?
Highest intensity would occur with a short distance and low frequency.
Lowest Attenuation is found at
lowest frequency, with the shortest path length.
What results in the most attenuation?
most attenuation occurs at the high frequency and long distance.
Which media has the greatest attenuation and the slowest speed?
Air
Air > Bone & Lung > Soft Tissue > Water
What type of wave is sound?
Mechanical and Longitudinal wave
The speed of sound in soft tissue:
1540 m/s
The unit for wavelength:
Distance (mm)
Enhancement is caused by:
weakly attenuating structures
Lowest attenuating to highest attenuation
Fat-Muscle-Bone-Air
List propagation speed from lowest to highest
Air-Fat-Muscle-Bone
Which of these media has the lowest attenuation and the greatest speed?
bone
tendon
lung
fat
air
Bone
Air > Bone & Lung > Soft Tissue > Water
Bone is more stiff than air
(remember ↑ stiffness, ↑ speed)
What describes the physics of refraction mathematically?
Snell’s Law
What is a reflection arising from a rough boundary?
Non-specular
Specular reflection is from a smooth reflector (like mirrors). They return in one direction.
Whereas, non-specular is diffuse or scatter, reflection from a rough boundary.
When time-of-flight is measured, we can determine the __?
Reflector Depth
A sound pulse travels from the transducer to location A, reflects off of it, and returns to the transducer in 130 μs.
How deep is location A?
Location A is 10 cm from the transducer
Total travel distance would be 20 cm
Which of the following would be considered the narrowest part of a sound beam?
The focus is the narrowest part of the beam
Which of the following is the part of the transducer that stops the ringing of the element?
The damping material helps stop the ringing of the transducer
Along with image depth, which of the following also determines the frame rate?
Image depth and the number of lines per frame determines the frame rate.
Which type of resolution is an accurate representation of moving structures?
Temporal resolution, also known as frame rate, is the ability to display moving structures in real time.
What type of transducer that utilizes elements arranged in a concentric pattern?
The annular array transducer ultilizes elements arranged in concentric rings
What transducer would be considered an advantage of linear array over a phased array transducer?
The linear array has a wider near field of view compared to a phased array transducer
Mechanical Transducers:
Have moving parts
Uses a motor to steer the beam
Most transducers are no longer mechanical May be focused with a lens or phased focuses
Along with crystal diameter, the divergence in the far field is also determined by…
Frequency
and crystal diameter determines the divergence in the far field
What would cause an increase in frame rate?
Decreasing the imaging depthwould increase the frame rate
When you decrease the imaging depth it can work faster (increase frame rate) because it doesn’t have to go as deep.
The diameter of the beam in the Fresnel zone/near zone does what?
Decreases
Which resolution is best in the clinical imaging?
Axial resolution is best in imaging
will increase the near zone length?
A large crystal diameter with high frequency would increase the near zone length
What will decrease beam divergence in the far field?
A large crystal diameter and high frequency would decrease the beam divergence in the far field
Imaging transducers have
Imaging transducers have low quality factors and wide bandwidiths.
What is the speed of a wave with a wavelength of 3 m and a frequency of .1 Hz?
0.3 m/s
wave speed= frequency x wavelength
Wavelength and Frequency are
inversely proportional to each other
How do you calculate the speed of a wave given the wavelength and frequency?
Frequency (Hz) x wavelength (distance)= Wave Speed
What is the speed of a wave with a frequency of 2 Hz and a wavelength of 87 m?
174 m/s
2Hz x 87m= 174m/s
speed of a wave: frequency x wavelength
The __ of a wave is the number of wavelengths that pass a fixed point in a second.
frequency
Frequency is the number of wavelengths that pass a fixed point in a second
A sound wave is traveling in the body and propagates from muscle to air. What percentage of the sound wave is most likely reflected at the muscle-air boundary?
75%
Which of the following lists is in decreasing order?
Mega, kilo, deca, milli, nano
The conversion of sound energy to heat
Absorption
Acoustic Speckle
the interference pattern caused by scatterers that produces the granular appearance of tissue on a sonographic image
Acoustic Variables
changes that occur within a medium as a result of sound traveling through that medium
Amplitude
The maximum or minimum deviation of an acoustic variable from the average value of that variable; the strength of the reflector
Attenuation
A decrease in the amplitude and intensity of the sound beam as sound travels through tissue.
Attenuation Coefficient
The rate at which sound is attenuated per unit depth
Axial Resolution
The ability to accurately identify reflectors that are arranged parallel to the ultrasound beam
Backscatter
Scattered sound waves that make their way back to the transducer and produce an image on the display
Beam Uniformity Ratio
The ratio of the center intensity to the average spatial intensity; also referred to as the SP/SA factor or beam uniformity coefficient
Capacitive Micromachined Ultrasound Transducers
Technology used to create comparable transducer technology to piezoelectric materials
Compression
An area in the sound wave of high pressure and density
Continuous Wave
Sound that is continuously transmitted
Damping
The process of reducing the number of cycles of each pulse in order to improve axial resolution
Decibels
A unit that establishes a relationship or comparison between two values of power, intensity, or amplitude
Density
Mass per unit volume
Directly Related
Relationship that implies that if one variable decreases, the other also decreases or if one variable increases, the other also increases;
also referred to as Directly Proportional
Distance
How far apart objects are
AKA vibration or displacement
Duty Factor
The percentage of time that sound is actually being produced
Elasticity
The ability of a material to bounce back after being disturbed
Frequency (Hz)
The number of cycles per second
Half-Intensity Depth
the depth at which sound has lost half of its intensity
Half Intensity Depth is also called
Half-Value Layer Thickness
Hertz (Hz)
A unit of frequency
Hydrophone
a device used to measure the output intensity of the transducer
Impedence
the resistance to the propagation of sound through a medium.
Inertia
Newton’s principle that states that an object at rest stays at rest and an object in motion stays in motion, unless acted on by an outside force.
Intensity
the power of a wave divided by the area over which it is spread; the energy per unit area
Intensity Reflection Coefficient (IRC)
The percentage of sound reflected at an interface.
The percentage of the sounds intensity that is reflected when sound hits a boundary or tissue
Interface is the dividing line between 2 different media.
Intensity Transmission Coefficient (ITC)
The percentage of sound transmitted at an interface
-or-
The percentage of intensity that continues forward after beam strikes an interface
Interface
The dividing line between two different media
Inversely Related
Relationship that implies that if one variable decreases, the other increases or if one variable increases, the other decreases; also referred to as inversely proportional
Longitudinal Wave
Waves in which the molecules of the medium vibrate back and forth in the same direction that the waves are traveling.
Medium
Any form of matter; Solid, Liquid, or Gas
Non-specular Reflectors
Reflectors that are smaller than the wavelength of the incident beam
Which gain will increase the risk of bioeffects?
Transmit
What is considered the memory of an ultrasound instrument?
Digital Scan Converter
Spectral Broadening Suggests
Turbulent Flow
What happens to axial resolution with Pulse Wave Doppler
Axial Resolution Degrades when using Pulse Wave Doppler
What color is usually used in Color Flow Doppler variance map to indicate turbulent flow?
Green
A Doppler (high pass filter) eliminates?
high amplitude signals, low velocity flow
The Doppler wall filter is considered a:
High Pass Filter
The Nyquist Limit is equal to:
PRF/2
Pulse Repetition Frequency divided by two
Multiple echoes, equally spaced originating from a gas bubble is called
Ring Down
An increase in red blood cell velocity will____________Doppler Shift:
Increase
increase in rbc velocity increases Doppler shift
The primary advantage of CW Doppler is:
Absence of Sampling Rate
The range for ultrasound begins:
at 20,000Hz or 20KHz
(Useful Frequency Range for Clinical Imaging is 2MHz-10MHz)
Which instrument control affects the amplitude (db) of the outgoing signal?
Transmit Gain;
Amplitude can be affected by the sonographer
What is used to convert Doppler shift information into color?
Autocorrelation
What is used to process conventional Doppler shift information but is too slow of a method for Color Doppler?
Fast Fourier transform
Pulse Repetition Frequency
The number of pulses that an ultrasound system transmits into the body each second.
Unit: Hz. Typically 4-15 KHz.
PRF and Depth of View are inversely related.
When the system is imaging deeper, the pulse repetition frequency is lower, as well as, the number of pulses created each second.
What is the best way to increase the near field length of an ultrasound beam?
Increase Transducer Diameter
What is the range of frequencies produced by a dampened PZT element?
bandwidth
What is bandwidth?
range of frequencies in a pulse
The percentage of time that the ultrasound instrument is emitting ultrasound is called?
Duty Factor
The maximum value is 1, the minimum is 0
What is the unit of Duty Factor?
Duty Factor is Unit-less
If the ultrasound is produced as a continuous wave (CW), the duty factor will have a value of 1. With Pulsed Wave the whole value of On-Time is fractioned.
What is Q-factor or Quality Factor?
The “Q factor” describes the bandwidth of the sound emanating from a transducer
Transducer Q Factor (Q = Quality) is associated with two characteristics of the crystal
- purity of their sound and
- length of time the sound persists
(Unitless measurement)
Fundamental Frequency(Hz)/Bandwidth(range of frequency in the pulse)
The unit of duty factor is:
Unitless
Clinical imaging transducers are:
Wide bandwidth; Low Q factor
Wide range of frequencies in the pulse and short period of time that the sound is emitted (pulsed wave)
Power/Area=
Intensity
Increasing wavelength will_______frequency?
Decrease
Beam Properties
The ultrasound beam propagates as a longitudinal wave from the transducer surface into the propagation medium, and exhibits two distinct beam patterns: – a slightly converging beam out to a distance specified by the geometry and frequency of the transducer (the near field), and – a diverging beam beyond that point (the far field).
Does Beam Width directly affect frame rate?
No:
The following directly affect frame rate:
Depth of Penetration
Field of View
Number of Focuses
and Line Density
What affects frame rate?
Depth of Penetration, Field of View, Number of Focuses, and Line Density.
Frame Rate= Number of Frames/Second
When will a reflection occur at the boundary of two media?
If the acoustic impedances of the tow media are different.
Snell’s Law
Describes the relationship between the angles and the velocities of the waves.
When an ultrasonic wave passes through an interface between two materials at an oblique angle, and the materials have different indices of refraction, both reflected and refracted waves are produced
In ultrasound, Snell’s Law
is a formula used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves passing through a boundary between two different isotropic media.
The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant, for a given frequency.
The Angle of Incidence
Refers to the angle of deviation from a perpendicular line to the surface of the tissue
Therefore, the desired orthogonal(perpendicular) incident wave in ultrasound should be considered to have an angle of incidence of zero.
When the angle of incidence is greater, fewer sound waves are reflected back to the transducer resulting in a more hypoechoic (darker) image with less clarity.
The optimal reflection with the most sound waves occurs when the angle of incidence approaches zero and is virtually perpendicular (orthogonal) to the tissue of interest.
Law of Reflection
the angle of incidence is equal to the angle of reflection
Mechanical Transducers utilize what kind of focusing?
Fixed Focusing:
Sonographers cannot determine the location of # of foci.
Mechanical Transducers use Cross-Sectional imaging, rotating wheel, wobbler, and oscillating mirror.
The transducer frequency is primarily determined by the transducer element’s what?
Thickness
For pulsed transducers..the main or center frequency of the transducer is determined by the thickness and the propagation speed of the piezoelectric material.
PZT is also called
Ceramic, Active Element, or Crystal
A strongly focused transducer implies a:
Short focal length and Increased Beam Divergence
B-mode displays reflector:
Amplitude and Distance
An increase in the number of pixels on the display will improve:
Detail Resolution
Propagation speed is determined by
Medium only – density and stiffness of media
Bulk Modulus describes the change in the material’s volume under external stress.
Increasing transmit gain increases everything except:
Frequency
Gain is a receiving function
•Does not impact how much energy is transmitted to patient (i.e. power)
The correct depth placement of reflectors depends primarily upon:
Propagation Speed
What will increase the color flow jet area displayed?
Increasing Color Gain
Increasing Propagation Speed
air: 330 m/sec
fat: 1450 m/sec
water: 1480 m/sec
soft tissue: 1540 m/sec
liver: 1550 m/sec
kidney: 1560 m/sec
blood: 1570 m/sec
muscle: 1580 m/sec
bone: 4080 m/sec
The most common type of transducer used in echo is:
Sector Phased Array
What are the four acoustic variables?
- Temperature
- Density
- Particle Motion
- Pressure
The Doppler effect is presented as a _______ when the source and the receiver are in motion relative to each other.
Frequency Shift
- or – Doppler Shift
receiver toward the transducer= + shift
receiver away from transducer = – shift - toward (above baseline)
- away (below baseline)