Final Flashcards
Absorption
occurs when ultrasonic energy is converted into another energy form, such as heat.
Directly related to frequency (scattering)
higher frequency waves attenuate more absorption
As a pulse passes through soft tissue, a certain amount of acoustic energy remains in the tissue as heat. What is this constituent of attenuation called?
absorption
Rectification and smoothing are components of which of the following?
Demodulation: changes the electric signals to make them suitable for display on a monitor
Not adjustable
no effect on image
Rectification vs Smoothing
Rect.: converts all negative voltages into positive voltages.
Smoothing: places a smooth line around the “bumps” and evens them out.
The process of reducing the difference between the smallest and largest voltages
Compression
performed twice
once: keeps electrical signal levels within the accuracy range of the system’s electronics
second: keeps an image’s gray scale content within the range of detection by the human eye
Energy per unit area of a sound beam is called
Intensity
Determined by sound source
Adjustable
Intensity = Power (W) / Area (cm^2)
units: Watts/cm^2
the concentration of energy in a sound beam
A mirror image artifact can appear along side of the true anatomy
False
The artifact is located deeper than the real structure
If density is increased, with everything else remaining the same, propagation velocity will:
decrease
The acoustic impedance mismatch between air and soft tissue will be:
High !
The Fresnel is the _____
Near zone
is the region from the transducer to the focus (blue arrow). The beam gradually narrows, or converges, within the near zone to 1/2 the width of the active element
What event does Snell’s law govern?
quantifies the physics of refraction
Sin (transmission angle) / sin (incident angle) = Speed of Medium 2 / Speed of Medium 1
The color flow image provides information on (1) the existence of flow, (2) the location of flow in the image, (3) flow direction relative to the transducer, (4) the maximum flow velocity.
existence of flow, location of flow, direction of flow, (mean velocity)
A sonographer is performing a study on a patient and desires superior depth resolution. Which of the following changes would create such a system? (5)
depth resolution also called axial resolution
1) Shorter spatial pulse length
2) Shorter pulse duration
3) Higher frequencies (shorter wavelength)
4) Fewer cycles per pulse (less ringing)
5) Lower numerical values
All of the above
Axial resolution describes the accuracy related to visualizing two structures that are ____ to a sound beam’s main axis.
parallel
How long does it take for sound to make a round trip to and from the skin’s surface o a reflector 5 cm deep in soft tissue?
65 us
Which of the following correctly lists substances in an increasing order of ultrasound velocity?
a) Air, water, liver, bone
b) Bone, water, liver, air
c) Air, bone, water, liver
d) Bone, air, liver, water
Bone (3,500 m/s)
Soft tissue (1,540 m/s)
Water (1,480 m/s)
Air (330 m/s)
A)
As the impedances of two media become vastly different, the ________
Reflection increases
-when a sound beam strikes a tissue boundary at a 90 degree angle (normal incidence), reflection occurs only if the media on either side of the boundary have different impedances.
Refraction only occurs if there is:
-Oblique incidence and different propagation speeds
Refraction: is a change in direction of wave propagation when traveling from one medium to another.
Occurs only with oblique incidence (not normal) and different propagation speeds of the two media.
The ability of a system to detect weak reflectors is:
sensitivity
The technique used to create the color-flow display is:
Autocorrelation
is the digital technique used to analyze color
Pulser
Sends electric pulses to the transducer
creates and controls the electrical signals sent to the transducer that generate sound pulses.
Determines the amplitude, pulse repetition period, and pulse repetition frequency.
Transducer
Produces ultrasound pulses
transmitting signal is changed electrical energy into acoustic energy
Receiving signal is changed from acoustic energy into electrical energy.
Signal processor
Processes voltages received from the beam former
Image processor
Converts image information from the electrical to visual form
Display
Visual information
-presented processed data.
Maybe a flat screen monitor, a transparency, a spectral plot or a variety of other formats.
The Nyquist limit is equal to:
1/2 PRF
-The Nyquist frequency (or Nyquist limit) is the highest Doppler frequency or velocity that can be measured without the appearance of aliasing.
-The Nyquist limit is one half of the pulse repetition frequency
-Aliasing appears when the doppler shift exceeds this speed limit.
What information does Doppler shift provide?
Velocity
-The frequency of sound changes when the sound source and the receiver move closer together or farther apart.
-This principle is used to measure the velocity of blood in the circulation.
What component of the Ultrasound units contains the memory?
Scan converter
-Gray scale imaging was initially made possible with the use of scan converters, which first store information and later display it.
The peak pressure of height of a wave is known as:
amplitude
The letters “SPTA” are a means of expressing:
Intensity measurement method
Spatial Peak Temporal Average
-is the most relevant intensity with respect to tissue heating
SPTP -> Im -> SPPA -> SPTA -> SATA
Shadowing may result from high amounts of reflection of ultrasound energy.
False
high attenuation
With the velocity being constant, if the frequency is doubled, wavelength is:
Decreased by a factor of 2
Frequency and wavelength are inversely related.
Ex: if a wave’s frequency is twice that of another, the wavelength will be half as much.
v = wf
If there is an increase in transducer frequency the PRF:
Stays the same
PRF is unrelated to frequency
related to depth of view
Pulse Repetition Frequency: is the number of pulses that an ultrasound system transmits into the body each second.
_________ is a redirection of ultrasound in many directions as a result of a rough boundary between two media.
Scattering
If the amount of damping decreases the period:
increase!
________ resolution is determined by the spatial pulse length.
Axial
Axial resolution is related to the spatial pulse length.
Not adjustable
Shorter pulses improve axial resolution
Spatial pulse length is determined by both the sound source and the medium.
Lateral resolution is also called:
Angular
Transverse
Azimuthal Resolution
A transducer with more than one active element is called:
Array
as many as 100 to 300 elements
A sound wave is a pressure wave made of compressions and rarefactions.
True
With a 2 MHz transducer, in soft tissue, the wavelength is approximately:
Speed (m/s) = frequency (Hz) x wavelength (m)
Soft tissue: 1,540 m/s or 1.54 mm/us
1.54 (mm/us) / 2 MHz = 0.77 mm
What of the following frequencies are NOT in the ultrasound range?
a) 10,000 Hz
b) 1 MHz
c)100,000 Hz
d) 0.1 MHz
Ultrasound
Greater than 20 kHz
(20,000 Hz, 0.02 MHz)
(A)
If medium 2 impedance is equal to medium 1 impedance:
100% of the intensity will be transmitted
acoustic impedance: is the acoustic resistance of sound traveling in a medium
-If both mediums are IDENTICAL and the incidence was normal then only transmission occurs because the impedances of the media are the same.
-If both mediums are DIFFERENT with a normal incidence and different impedance, both reflection and transmission occur.
Increasing the power, in effect, causes an increase in the system sensitivity:
!
Which of the following is NOT a general ultrasound instrumentation component?
interpolation
If the ultrasound beam is OFF the duty factor is:
0
Duty factor: is the percentage or fraction of time that the system transmits a pulse
Determined by sound source only
The minimum value of duty factor is 0%, which exists only when the transducer is silent.
Duty factor is inversely related to imaging depth.
Filtering widens bandwidth:
!
Preprocessing involves the manipulation of data before it is stored.
true
A highly damped transducer has:
Poor axial resolution
Reduced spatial pulse length
Decrease bandwidth
Increased quality factor
-Reduced spatial pulse length
Enhanced axial resolution
Wide bandwidth
Low quality factor
decreased sensitivity
If there is an increase in transducer frequency, the period:
decreases
Period and frequency are inversely related to each other
As frequency increases, period decreases
As frequency decreases, period increases
Acoustic impedance is defined as the product of:
Speed of sound in tissue and density of tissue
-is calculated by multiplying the density of a medium by the speed at which sound travels in the medium.
Impedance (rayls) = density (kg/m^3) x prop. Speed (m/s)
Amplification
increases all amplitudes
Compensation
Corrects for the attenuation.
-Makes the picture bright from the top to the bottom
Filtering
reduces noise
Detection
Converts pulses from radio frequency to video form
Compression
Decreases the dynamic range of the received echo
-performed twice
-keeps the electrical signal levels within the accuracy range of the system’s electronics.
An electric phased array transducer always produces a sector image:
True
The image created by a phased array transducer is fan or sector-shaped.
Multipath artifacts result from
-Echoes that take an indirect path back to the transducer
is created when sound pulses glance off a second structure on the way to or from the primary reflector.
A-mode
A graphic presentation with vertical spikes arising from a horizontal baseline; the height of the vertical spikes represent the amplitude of the deflected echo.
Strong echoes create tall spikes
Weak echoes create short spikes
x-axis: depth
y-axis: amplitude
B-mode
A two-dimensional image of internal body structures displayed as dots; the brightness of the dots is proportional to the amplitude of the echo; the image is applicable to both real-time and static scanners.
Weaker dots are darker gray
Stronger dots are brighter
x-axis: depth
y-axis: none
z-axis: amplitude
M-mode
A graphic presentation of moving structures in a waveform; the display is presented as a group of lines representing the motion of moving interfaces versus time.
x-axis: time
y-axis: depth
Density
Mass divided by volume
Concentration of mass in a volume (kg/cm^3)
Propagation
progression or travel
Frequency
number of cycles per unit time
Power
rate at which work is done
Duty Factor
The product of pulse duration and pulse repetition rate
-is the percentage or fraction of time that the system transmits a pulse
Duty factor % = pulse duration / pulse rep. Period x 100
Bandwidth
Range of frequencies contained in the ultrasound pulse
-It is the difference between the highest and lowest frequencies.
Acoustic Impedance
Density multiplied by sound propagation speed
Is the acoustic resistance to sound traveling in a medium
Absorption
Conversion of sound to heat
Quality Factor
Operating frequency divided by bandwidth
-Is a unitless number that is inversely related to bandwidth.
Quality factor = main frequency / bandwidth
Intensity
Power divided by area
Is the concentration of energy in a sound beam.
Divide the beam’s power by the beam’s cross-sectional area.
attenuation
Progressive weakening of the sound beam as it travels through a medium
Bit
binary digit
smallest amount of computer memory
Cavitation
Is the interaction of sound waves with microscopic, stabilized, gas bubbles in the tissues (gaseous nuclei)
Coupling medium
A liquid placed between the transducer and the skin
Damping
A method of reducing pulse duration by electrical or mechanical means
The backing material restricts the extent of PZT deformation. Causes short duration and length
Gray scale
The number of intensity levels between black and white
Matching layer
Plastic material placed in front of the transducer face to reduce the reflection at the transducer surface
Pixel
picture element
Static imaging
single frame imaging
images displayed one frame at a time
Which of the following is true?
SPTA is always equal or greater than SPTP
SPTP is always equal or greater than SPTA
SATA is always equal or greater than SATP
SPTA is always equal or greater than SATP
b) SPTP is always equal or greater than SPTA
SPTP → Im → SPPA → SPTA → SATA
Spatial peak intensity is ALWAYS higher than the Spatial average intensity.
The frame rate of a real-time scanner will not depend on
Frequency
Three factors determine the number of pulses to create an image:
1) sound’s speed in the medium
2) the depth of view in image
3) Liner per angle of sector (line density)
Harmonic imaging relative to conventional pulse-echo imaging has:
Better lateral resolution /
Grating lobes in electronic array systems:
Increase with increased steering angle
Decrease with increased steering angle
Are eliminated at high frame rates
Are not likely to produce artifacts
Increase with increased steering angle
Which of the following parameters cannot be evaluated by the AIUM test object?
Gray scale
Dynamic range
Azimuthal resolution
Depth resolution
Gray scale and Dynamic range !
When using the AIUM test object, which of the following should be kept constant for comparisons? (6)
Output power
TGC
Reject
Transducer, MHz, and focus
(All the above) /
An increase in amplitude from structures that lie behind a weak attenuator is:
Reflection
Enhancement
Artifact
All of the above
Enhancement
Shadowing:
Can be caused by strong reflectors
Can cause missing display information
Is the result of attenuation
Is an absence of transmission
All the above
when too much attenuation occurs, prevents the display of deep reflecting surfaces of structures
Dead-zone artifacts are seen in the posterior portion of the image.
False
The dead zone is the region close to the transducer where images are inaccurate.
It extends from the transducer to the shallowest depth
Ring-down artifact is thought to be caused by resonance
True
The comet- tail artifact resembles reverberation
True
From a single crystal, the beam profile not being entirely uniform produces the artifact called a (an):
Side lobe
Lobes created by a single crystal transducer, such as a mechanical probe, is called side lobe
Acoustic speckle is a resolution artifact
True
A method of identifying a mirror-image artifact is to change the scanning angle
True
Registration is the ability to properly reproduce a structure from any angle
True
