What is the average velocity of ultrasound in soft tissue at 5 MHz
1540 Meters per second
Red Blood cells are an example of
Non-specular reflector
Which has a higher acoustic impedance coefficient
Solid
A hyperechoic Region
Echogenic
The angle of refraction is described by
Snells Law
What is reflection in multiple directions from a reflector that is small relative to the wavelength?
Rayleigh Scatttering
Receiver demodulation can not be controlled by the sonographer?
True
Reflection at a tissue interface depends primarily on
Impedance
Azimuthal resolution is also known as
Lateral Resolution
What is the Doppler shift frequency in soft tissue if the transmitted frequency is 3 MHz and the velocity of a reflector is 20 cm/s
780 Hz
True or False...Intensity of the ultrasound beam is proportional to the square root of the acoustic pressure
False
True or false...Aliasing is not a problem with color flow imaging?
False
True or false...Density is an acoustic variable
True
If th PRF increases, duty factor ____
Increases
True or false...A-mode is mainly used to measure distance?
True
Period is
The time it takes to complete a single cycle
Spatial pulse length is determined by the
Oscillator
Transmission angle is less than the incident angle if the propagation speed of
Medium 2 is less than that of medium 1
Diffraction is the
Spreading out of an ultrasound beam
Annular array transducers steer the beam
Mechanically
____ is a Rayleigh Scatter
Red cell
True or false...A bit is the smallest part of digital "word"
True
Velocity times density equals
Impedance
What is the pulse duration for five cycles of 5 MHz ultrasound?
1.0 microsecond
Aliasing artifacts are unique to
Pulsed Doppler
True or false...Intensity reflection coefficient depends on acoustic impedance mismatch
True
True or False...Velocity of sound in a medium is constant regardless of frequency?
TRUE
Density is not an acoustic variable
False
If the PRP increases, duty factor
Decreases
True or False...A high PRF is needed to image deep structures
False
Longitudinal waves are
Parrallel to the axis of the wave propagation
Wavelength has the greatest effect on
Axial Resolution
What is necessary to calculate distance to a reflector?
Propagation speed and round trip time
Scattering is
Redirection of the sound beam in many directions
The percentage of ultrasound reflected at an air/liquid interface is
High
A specular reflector has surface texture___ the wavelength of the incident wave
Irrelevant to
In a cathode ray tube displays device the electron beam is steered by
Deflection plates
If it takes 50 microseconds for a pulse to return as an echo, how deep is the reflector?
3 cm
Q value is determined by
Frequency and bandwidth
Shadowing artifacts are
Caused by differences in attenuation
True or False...A-mode scanning represents the depth of the signal in the horizontal dimension
True
Poiseuille's equation states that the volume rate of flow through a vessel is inversely proportional to
Blood viscosity
True or False...Temperature is an acoustic variable
True
Spatial pulse lengh ___ if the frequency is increased
Decreases
The Reynolds number predicts aliasing
False
Transverse waves are
Perpendicular to the axis of the wave propagation
Beam diameter determines
Lateral Resolution
Mirror image artifact is sometimes seen near the
Diaphragm
The Binary number 1011000 equals the decimal number
88
Low Frequency transducers have
Longer wave lengths and greater penetration
ALARA PRINCIPLE
Use minimum output power and highest receiver gain required to produce optimal images
AIUM Suggest
-Do not perform studies without reason
-Do not prolong studies without reason
-Minimize exposure time
Transverse Wave
Particles move in a perpendicular direction or to the direction of the wave
Longitudinal wave
Particles move in the same direction as the wave
Compressions are regions of
higher density and pressure
Rarefaction are regions of
lower density and pressure
Acoustic Variables inform us of which waves are
sound waves
Acoustic Parameters describe the features of
a particular sound wave
Period is
The time required to complete a single cycle
Frequency is $
Number of certain events that occur in a particular time duration
Ultrasound is $
A wave with a frequency exceeding 20,000 Hz (20 KHz)
Audible Sound is $
Heard by man, frequencies between 20Hz and 20,000Hz
Infrasound is $
Sound with frequencies less than 20 Hz
As frequency increases period,
decreases
As frequency decreases period
increases
Amplitude is
The difference between the average value and the maximum value of an acoustic variable. The variation of an acoustic variable.
Units of Amplitude, Those of acoustic variables
Pressure
Density
Particle motion
Relationship between Power and Amplitude
Power is proportional to the waves amplitude squared
If the Amplitude is doubled, the power is increased by a factor of four (quadrupled)
2x2=4
Wavelength is
The length or distance of a single cycle.
Determined by source and medium
Which intensity has the lowest power?
SATA
Propagation Speed is
The rate that sound travels through a medium. Also called velocity or speed
Speed and wavelength are directly related
remember
Stiffness and speed
same direction
Density and speed
opposite directions
Bulk modulus is the same as
stiffness
Interference is
when two waves overlap at the same location and at the same instant in time, they combine into one new wave
Constructive interference $
Occurs when the amplitude of the new, combined wave is greater than the original two waves. In phase waves interfere constrctively
Destructive interference $
The amplitude of the new wave is less than one of the original waves. Out of phase waves interfere destructively.
The effects of ultrasound upon tissues are called
bioeffects
Pulsed sound $
in diagnostic imaging, short burts or pulses, of acoustic energy are used to create anatomic image.
A pulse is a collection of cycles that travel together.
Pulse Duration $
The time from the start of a pulse to the end of that pulse, the actual time. that the pulse is on
In clinical imaging, a pulse is comprised of $
2-4 cycles
Pulse repetition period
is the time from the start of one pulse, to the start of the next pulse. It includes one pulse duration and one "listening time"
As imaging depth increases $
Pulse Repetition period increases
Pulse repetition Frequency
Is the number of pulses that occur in one second
Typical values for PRF $
1,000 to 10,000 Hz (1-10 kHz)
Shallow image
Higher Pulse Repetition Frequency
Deep image
Lower image, lower PRF
As imaging depth increases, PRF
decreases (inverse relationship)
Duty factor
The percentage or fraction of time that the system transmits sound. Important when discussing intensities.
Typical values for duty factor $
from 0.1% to 1% or 0.001 to 0.01
CW sound cannot be used to make $
anatomical images
Important concept
Terms that have the same meaning
shallow imaging Deep Imaging
high pulse repetition Frequency Low pulse repetition frequency
short pulse repetition period long pulse repetition frequency
high duty factor low duty factor
Spatial Pulse Length
The length or distance that a pulse occupies in space. The distance from the start to the end of one pulse.
By adjusting the imaging depth, the operator changes the
pulse repetition period, pulse repetition frequency, and duty factor
Intensity is
the concentration of the power in a beam
Units for intensity
Watts/square cm, w/cm2
SPTP
Spatial Peak
SATP
Spatial average, temporal peak
SPTA $
Spatial peak, temporal average
most important for thermal bioeffects
Three commandments on Intensity
1. Intensities may be reported in various ways with respect to time and space
2. Intensity is the key parameter with regard to bioeffects
3. The different intensities are important in the study of bioeffects. SPTA intensity is the most relevant intensity with respect to tissue heating.
Decibels
A logarithmic scale
A relative scale- ratio of the final to the initial strengths
A comparision, therefore, two intensities are needed to calculate decibels
What are the units of relative amplitude?
dB
Positive decibels means getting bigger. The intensity is
increasing
Negative decibels
means getting smaller. The intensity is increasing
Attenuation is
The decrease in intensity, power and amplitude of a sound wave as it travels. This unrelated to speed! The further US travels, the more attenuation occurs.
Attenuation units
dB, decibels (must be negative)
Three components of Attenuation
Absorption (sound energy converted into heat energy)
Scattering
Reflection
Attenuation in different media AIR
much, much more attenution than in soft tissue. GEL is used to remove air from the path of ultrasound.
Attenuation in different media LUNG AND BONE
More than soft tissue, bone absorbs and reflects. Lung scatters.
Attenuation in Different Media
WATER
Water much, much less than soft tissue
Attenuation in blood is equal to that in
Soft tissue
Attenuation is unrelated to propagation speed. Attenuation increases with
Higher frequency or
Longer path length
A 3 MHZ sound beam travels through two media. It attenuates 5 dB in medium A and 6 dB in medium B. what is the total attenuation that the sound beam undergoes as it travels through both media?
11 dB
A 10 MHZ sound beam travels through two media. It Attenuates 5 dB in medium A and 1 dB in medium B. What is the total attenation that the sound beam undergoes through both media?
6 dB
A 3 Mhz sound beam travels 10cm, 6 cm in medium A and 4 cm in medium B. The total attenuation is 14 dB. If the sound beam attenuated 4 dB in medium A, then how much attenuation occured in medium B.
10dB
A 3 MHz sound beam travels 7cm in a medium. The total attenuation is 5 dB. How much attenuation will a 6 Mhz sound beam undergo when traveling 3.5cm in the same medium
5 dB
Reflection $
Occurs when propagating sound energy strikes a boundary between two media and some returns to the transducer.
Specular Reflection
Reflections from a smooth reflector (mirror) are specular and return in one direction.
Specular reflection also occur when the wavelength is much smaller than the irreugularities in the boundary.
Rayleigh Scattering $
If a reflector is much smaller than the wavelength of sound, sound is uniformly distributed in all directions (omnidirectional) Higher frequency sound undergoes more Rayleigh scattering. A red blood cell is a Rayleigh scattering.
Rayleigh scattering is related to $
Frequency
Attenuation Coefficient
the amount of atttenuation per centimeter. A way to report attenuation without dealing with distance.
Units for Attenuation Coefficient
dB/cm
Impedance is calculated not $
measured
Reflection of an ultrasound wave depends upon different acoustic impedances of the media on $
either side of the boundary
Two media a & b, have the same propagation speed. Medium a's density is 10% higher than medium B's.
Therefore medium A's impednace is 10% higher than medium B's
In soft tissue, attenuation coefficient is directly related to
Frequency
if frequency doubles, atten. coeff. will double
Rayleigh scattering is related to
Frequency 4
Normal incidence
Perpendicular, Orthognonal, Right angle, ninety deggres
Remember PORNN
Oblique incidence
Anthing other than 90 degrees, not at right angles.
Acute angle
less than 90 degrees and are oblique
Obtuse Angle
are greater than 90 degrees and are oblique
A sound wave with an intensity of 50 w/cm 2, strikes a boundary and is totally reflected. What is the intensity reflection coefficient
100%
A sound wave, with an intensity of 50w/cm2, strikes a boundary and is totally reflected. What is the reflected intensity?
50w/cm2
The intensity reflection coefficient of sound beam is 99.9% . what percent of sound is transmitted into the body?
0.1%
Reflection occurs only
if two media at the boundary have different acoustic impedances
Transmission and reflection may or may not occur with oblique incidence, but there are no simple
rules to predict if so.
Refraction is
transmission with a bend. Refraction is a change in direction as sound transmits from one medium to another.
Refraction requires
occurs when two conditions are met.
1. Oblique incidence and
2. different propagation speeds
Snells Law
The physics of refraction are described by Snells law
Sound wave strikes a boundary at normal incidence. The impedances of the two media are indentical. What percentage of the sound wave is refracted?
0%
Range equation
since the average speed of US in soft tissue (1.54 km/s) is known the time of flight and distance that US travels in the body are directly related.
Time of flight is the time needed for a pulse to travel to and from the transducer and the reflector is called
go return time or time of flight or round trip time
When one reflector is twice as deep as another reflector, the pulses time of flight is doubled for the deeper reflector. In other words
The time of flight will be increased by a factor of two
In soft tissue, every 13 micro seconds of go return time means the reflector is
1cm deeper in the body
Transducer is
any device that converts one form of energy to another.
Piezoleletric Effect is
A property of certain materials to create a voltage when pressure is applied or when they are mechanically deformed.
Piezoelectric materials
also called ferroelectric material
Man made-lead zirconate titanate
PZT is also called
ceramic, active element, or crystal
Curie temperature or curie point
if PZT is heated above this temperature, it loses its piefzoelectricity. the PZT is depolarized
Sterilization
The complete destruction of all living microorganisms by means of exposure to heat, chemical agents or radiation.
Disinfection
Refers to the application of a chemical agent to reduce or eliminate infectious organisms on an object, such as a transducer.
The piezoeletric crystal. Also called the ceramic, PZT or crystal. It is 1/2
wavelength thick
DO not use a transducer with a
cracked housing or with a frayed wire
Short pulses create
better images
Bandwidth is
it is uncommon for a transducer to emit a sound beam with only a single pure frequency. Rather the pulse is more like a sound, "click" and contains a range of frequencies below and above the main frequency.
The bandwidth is the range of frequencies between the highest and lowest frequency emitted from the transducer.
Compared to therapeutic transducers, imaging transducers are
wide bandwidth or broadband
The main frequency emitted by the transducer is called the
center, resonant, primary or natural frequency
quality factor is
a unitless number
Continuous wave transducer
sound waves frequency equals the frequency of the voltage applied to the PZT by the machines electronics.
Pulsed transducer
the main or center frequency of the US for a pulsed txr is determined by 2 characteristics of the crystal
Thickness and
propagation speed
When a PZT crystal is half as thick, the sounds frequency is
twice as high
Pulsed transducer, the thinner the active element the higher
the transducers resonant or natural frequency
(think of an hour glass)
THe thickness of the PZT crystal equals
1/2 of the wavelength of sound in the crystal.
The thickness of the matching layer is
1/4 of the wavelength of sound in the matching layer.
When a transducer is covered with a sterile cover with gel on the inside, what can the transducer not come into contact with in order to create an image?
talcum powder
Beam width
Narrow beams create
better images
Beam Width
As sound travels, the width of the beam changes
starts out at exactly the same size as the transducer diameter
gets progressively narrower until it reaches its smallest diameter then it
diverges
Focal Depth is
the distance from the transducer face to the focus. also called the focal length or near zone length
Near zone
Fresnal zone
The region or zone in between the transducer and the focus. sound beams converge in the near zone
Far zone
Fraunhofer zone
The region or zone deeper than the focus, beyond the near field. Sound beams diverge in the far zone.
All numerical values have $
Corresponding units
How many hertz is 3MHz?
3,000,000
How much bigger is a billion than a million
1,000 times
How many milliliters are contained in a jar filled with 5 liters of fluid?
5,000
How many liters are in 80ml of fluid?
0.080
Acoustic Propagation Properties
the effects of the medium upon the sound wave
Biologic effects is $
the effects of the sound wave upon the biologic tissue
Sound is $
Comprised of compressions (increase in pressure or density) and rarefractions (decrease in pressure or density)
*Sound must travel through a medium, cannot travel through a vacuum.
*Sound is a mechanical, longitudinal wave
*Sound travels in a straight line
Acoustic Variables IDENTIFY $
certain waves as sound waves.
Three acoustic variables $
Pressure-concentration of force within an area force/area units Pascals
Density
Distance
Transverse wave $
Particles move in a perpendicular direction or to the direction of the wave
Longitudinal wave $
Particles move in the same direction as the wave
Compressions are $
Regions of higher density & pressure
Rarefractions are $
regions of lower density & pressure
Period is
the time required to complete a single cycle
Frequency is
the number of certain events that occur in a particular time duration
Ultrasound is $
a wave with a frequency exceeding 20,000 Hz (20KHz). This frequency is so high that it is not audible.
Audible Sound $
Heard by man, frequencies between 20Hz and 20,000Hz
Infrasound $
Sound with frequencies less than 20Hz
Amplitude
The difference between the average value and the maximum value of an acoustic variable. The variation of an acoustic variable.
Units of Acoustic variables $
Pressure-Pascals
Density-Grams/cubic cm
Particles motion-cm, inches, units of distance
Amplitude may be expressed in $
Decibels dB
Power
The rate that work is performed, or the rate of energy transfer
Relationship between power and amplitude $
Power is proportional to the waves amplitude squared
If the amplitude is doubled, the power is increased by a factor of $
quadrupled
2x2=4
Intensity is
The concentration of energy in a sound beam
Intensity is proportional to the amplitude of the wave $
squared
Wavelength $
the length of distance of a single cycle
In Soft tissue, sound with a frequency of 1MHz has a wavelength of $
1.54mm
In sound tissue, sound with a frequency of 2MHz has a wavelength of $
0.77mm
In soft tissue, divide 1.54mm by $
frequency in MHz
Propagation speed
the rate that sound travels through a medium. Also called velocity or speed.
Remember $ 1.54kms=1,540m/s=1.54mm/micros
,
Remember $
Lung (air)<<fat<soft tissue<<bone
Tendon $
about 1,850 speed
Stiffness and Speed $
Same direction
Density and Speed $
Opposite directions
Bulk modulus is the same as $
stiffness
Interference
when two waves overlap at the same location and the same instant in time, they combine into one new wave.
Constructive interference $
In-phase waves interfere constructively
Destructive Interference $
Out of phase waves interfere destructively
Pulsed sound: In diagnostic ultrasound imaging, short burts, or pulses of acoustic energy are used to create $
anatomic images
Pulse duration $
the time from the start of a pulse to the end of that pulse, the actual time, that pulse is on
Remember: A pulse is a pulse, the talking time
does not change
as imaging depth increases $
PR period increases
as imaging decreases $
PR period decreases
Pulse Repetition Frequency
is the number of pulses that occur in one second
as imaging depth increases Pulse repetition Frequency
Pulse repetition Frequency decreases
Duty Factor is UNITLESS
.
Spatial Pulse Length is
The length or distance that pulse occupies in space. the distance from the start to the end of one pulse.
Intensity is
the concentration of the power in a beam.
units for intensity$
watts/square cm, w/cm2
Which intensity has the lowest point $$
SATA
Spatial average, temporal average
which intensity is most important for thermal bioeffects$
SPTA
Spatial peak, temporal average
Three commandments of Intensity$
Intensities may be reported in various ways with respect to time and space
Intensity is the key parameter with regard to bioefftects
The different intensities are important in the study of bioefftects. SPTA intensity is the most relevant intensity with respect to tissue heating.
Logarithms is
a novel way of rating numbers
Decibels
a logarithmic scale
a relative scale- RATIO$
What are the units of relative amplitude$
dB
Positive decibels means getting bigger. the intensity is
increasing
10db means ten times bigger.
The final intensity is 10 times bigger than the original intensity
Negative decibels means getting smaller. The intensity is $
decreasing.
Attenuation is
The decrease in intensity, power and amplitude of a sound wave as it travels. This is unrelated to speed.
Attenuation in blood is equal to tha in$
soft tissue
Reflection is $
occurs when propagating sound energy strikes a boundary between two media and some returns to the transducer.
Specular Reflection$
Reflection from a smooth reflector (mirror) are specular and return in one direction
Specular reflectors also occur when the wavelength is$
much smaller than the irregularities in the boundary.
A red blood cell is $
a Rayleigh scatterer
Rayleigh Scattering is related to $
frequency
Impedance is calculated not $
measured
Range equation $ since the average speed of US in soft tissue (1.54km/sec) is known, the time of flight and distance that US travels in the body are
directly related
The time needed for a pulse to travel to and from the transducer and the reflector is called$
go return time or time of flight or round trip time
In soft tissue, every 13microsecond of go-return time means the reflector is $
1cm deeper in the body.
Transducers is$
any device that converts one form of energy to another
Piezoelectric effect $
A property of certain materials to create a voltage when pressure is applied or when they are mechanically deformed
Piezoelectric materials also called ferroelectric material $
Natural-quartz, Rochelle salts, tourmaline
man-made-barium titanate, lead metaniobate, lead titanate, lead zirconate tianate (PZT)
PZT is also called$
ceramic, active element, or crystal
Sterilization$
the complete destruction of all living microorganisms by means of exposure to heat, chemical agents, or radiation.
Disinfection$
refers to the application of chemical agent to reduce or eliminate infectious organisms on an object, such as a transducer
Do not use a transducer with a $
cracked housing or frayed wire
Bandwidth is$
the range of frequencies between the highest and the lowest frequency emitted from the transducer
Continuous wave transducers <3
sound waves frequency equals the frequency of the voltage applied to the pzt by the machine electronics.
Pulsed transducers $
The main or center frequency of the US for a pulsed txr is determined by 2 characteristics
Thickness and Propagation speed
when a transducer is covered with a sterile cover with gel on the inside, what can the transducer not come into contact with? $
talcum powder
Beam width RULE
Narrow beams create better images
Focus or Focal point is
the location where the beam reaches its minimum diameter
Focal depth $
the distance from the transducer face to the focus. Also called focal length or near zone length
Near zone (fresnal zone) is $
the region or zone in between the transducer and the focus. Sound beams converge in the near zone.
Far zone (Fraunhofer Zone)$
the region or zone deeper than the focus, beyond the near field. Sound beams diverage in the far zone.
Focal Zone $
the region surrounding the focus where the beam is "sort of narrow" and the picture is relatively good.
At the end of the near zone, the beam diameter is $
1/2 the transducer diameter.
At two near zone lengths, the beam diameter is $
equal to the transducer diameter.
Focal depth
distance from the transducer to the focal point.
Focal depth is determined by$
transducer diameter and frequency
Sound beam divergence
describes the spread of the sound beam in the deep far zone.
Sound beam divergence is determined by $
transducer diameter and the frequency
Diffraction$
V-shaped wave also called a Huygens wavelet.
Huygens Principle $
This principle explains the hourglass shape of an imaging transducer sound beam
Resolution
the ability to image accurately
Axial resolution
the ability to distinguish two structures that are close to each other front to back, parallel to, or along the beams main axis
Lateral Resolution $
the minimum distance that two structures are separated by side to side or perpendicular to the sound beam that produces two distinct echoes.
Lateral resolution is approximately equal to $
beam diameter
Focusing alters beam 3 ways
narrower waist in the US beam
shallower focus
smaller focal zone
A-mode X-Axis-reflector depth $
measured by
pulses time of flight
A-mode Y-axis-amplitude echo
measured by
echo strength
B-mode z-axis $
brightness of dot
Mechanical scanning element shape$
the crystal is circular and disc shaped like a coin
Mechanical scanning Defective crystal $
destroys entire image
Phased Arrays$
adjustable focus or muti-focus; achieved electronically
Mechanical scanning image shape $
fan or sector shaped, scan lines diverge or separate with depth.
Transducer arrays$
collection of active elements in a single transducer.
Transducer array element $
a single slab of PZT cut into separate pieces called elements.
Transducer array-channel$
combination of electronic circuitry, the wire and the element.
Linear swtiched or sequntial arrays-Crystals $
large transducers with multiple, approximately 200 elements arranged in a line.
Linear switched-element shaped$
each element in a linear switched array is rectangular
Linear switched-steering$
no steering, pulses sent down parallel lines. the scan lines are parallel and are equally shaped.
Linear switched-image shaped $
rectuangular image shape, no wider than the transducer.
Phased arrays-meaning$
adjustable focus or multi-focus; achieved electronically.
Phased array$-Crystal, steering and focusing
a collection of electric pulses is delivered to all of the transducers elements in various patterns.
The patterns focus and steer the US beam during transmission, Thus, focus and steering are electroinic.
Phased array-$ approximately 100-500 crstyals are in
the transducer
Annular phased arrays crystals$
concentric rings The array looks like a bulls eye target.
Annular phased array STEERING $
Steering is performed mechanically. HINT this is unlike other phased array transducers
Dynamic Aperture$
a form of electronic receive, electronic focusing.
Two dimensional arrays creates$
3d ultrasounds images. 3-D imaging measures volumes (such as a cyst)
Real time imaging is $
The production of a motion picture
Temporal Resolution $
The ability to accurately locate moving structures at any particular instant in time
ex. How good is my movie?
Temporal Resolution is determined by:$
Temporal resolution depends only upon frame rate. More images per second improves temporal resolution
what does not decrease temporal resolution $
narrower sector
a sonographer, using a phased array ultrasound system, turns off the multi-focus feature. What is the most likely consequence of this action?$
the temporal resolution improves
pulser $
creates the firing pattern for phased array systems. This is called the beam former
THE AIUM SUGGESTS $
Do not perform studies without reason
Do not prolong studies without reason
Minimize exposure time
Use minimum output power and highest receiver gain required to produce optimal image. ALARA principle
Mechanical Index is higher (more likely to produce cavitation) with
higher pressure -beams and
lower frequency -sound
A structure that produces more echoes than surrounding soft tissue is said to be
Hyperechoic
The piezoelectric effect was discovered by
Pierre and jacques curie
a statement that describes an ultrasound
Display of physical interaction of sound energy and matter
Unit measure of frequency is
Hertz
Red blood cells are an example of
non-specular reflector
The angle of refraction is described by
Snells Law
What is reflection in multiple directions from a reflector that is small relative to the wavelength.
Rayleigh scattering
Receiver demodulation can not be controlled by the sonographer
TRUE
Reflection at at tissue interface depends primarily on
impedance
Azimuthal resolution is also known as
lateral resolution
Intensity of the ultrasound beam is proportional to the square root of the acoustic pressure
FALSE
Aliasing is not a problem in color flow imaging
false
Density is an acoustic variable
true
Period is
the time it takes to complete a single cycle
Diffraction is the
spreading of an ultrasound beam
Annular array transducers steer the beam
Mechanically
a bit is the smallest part of a "digital word"
TRUE
Velocity times density equals
impedance
Aliasing artifacts are unique to
Pulsed doppler
Compensation is $
used to create image of uniform brightness from top to bottom
Compression $
reducing the total range, the smallest to largest signal
purpse of compression is$
to allow us to see all gray shades
Demodulation$
changes the signals form to one more suitable for TV display
we use REJECT to$
eliminate low level noise in our images
Output Power$
when the image is too bright due to high output power, the lateral and longitudinal resolution degrade
Harmonics$
are multiples of the transducer frequency
Harmonics are created in the TISSUES, not
in the transducer or receiver
Sound travels slightly faster in regions of$
COMPRESSION
Sound travels slightly slower in regions of
rarefraction (lower pressure)
Bistable
only 2 choices:white or black, on or off, high contrast narrow dynamic range, poor contrast resolution
Gray scale-
many levels of brightness (white, light gray, medium gray, dark gray, black etc.
Controls-BRIGHTNESS
determines the brillance of the signals displayed
Controls-Contrast
determines the range of brilliances that are displayed. Bistable images are high contrast
Pixel$
The smallest element of a digital picture
Pixel density$
The more pixels per inch, the greater the detail in the image. The detail is called spatial or detail resolution
The best spatial resolution is obtained with more elements or pixels in the matrix.
d
Spatial resolution on a digital display is determined by
the pixels density (the number of pixels per inch)
Postprocessing$
is performed on frozen images
Read Magnification$
Occurs after the image is in the scan converter. POST PROCESSING.
Write magnification$
occurs upon azquisition of the ultrasound reflections. Preprocessing
Longitudinal waves are
parallel to the axis of the wave propagation
Wavelength has the greates effect on
axial resolution
What is necessary to calculate distance to a reflector?
propagation speed and round trip time
In a cathode ray tube display device the electron beam is steered by
deflection plates
shadowing artifacts are caused
by differences in attenuation
Mirror images are seen near the
diaphragm
Edge enchancement$
Most useful to emphasize the boundary between different tissues
Dynamic range$
the ratio of the largest to the smallest signal strength that each component processes
PACS$
Picture Archiving and communications System
Laminar flow may have
parabolic or plug patterns
small regions of laminar flow will have$
similar velocities and narrow doppler spectra
Turbulent flow
small regions of turbulent flow have vastly different velocities (doppler spectral broadening)
Energy
blood flows when the total fluid energy at one location differs from the total fluid energy at another location. this is called an energy gradient.
Velocity changes
at a stenosis
Anemia reduces $
viscosity because the blood is thinner
Stenosis cause$
changes in flow direction
increased velocity in the stenosis, highest velocity at the point of maximum narrowing
turbulence at exit
pressure gradient across the stenosis
arterial flow loses its pulsatile nature and becomes more continous
Doppler shift$ or doppler frequency
the change in variation, in the frequency of sound as a result of motion between the sound source and the receiver. Greater velocities create greater doppler shifts.
Doppler measures
frequency shift, not amplitude
Typical values for doppler shift
20HZ-20 kHz
flow towards transducers increased
frequency
flow away from transducers
decreased frequency
Doppler measures$
Velocity not speed
Non-coherent processing used with
uni-directional doppler
Phase quadrate processing used in
bidirectional doppler
Continuous wave doppler
Number of crystals
Two crystals in the transducer
Advantage of Continuous wave doppler
able to measure very high velocities accurately
Pulsed wave doppler $
Number of crystals
one, crystal, alternates between sending and receiving
Pulsed wave doppler$ Advantage
Echoes arise only from the area of interrogation, the sample volume or gate. we adjust the receive gate
Eliminating aliasing "improves $
the ability to measure the maximum veloctiy with doppler
The horizontal axis or X-axis of a doppler spectrum is
time
The vertical or Y-axis of a doppler spectrum is
Doppler shift or Velocity
Gray shades on a doppler spectrum are related to
1. Amplitude of the reflected signal or
2. number of red blood cells creating the reflection
Color flow doppler is$
pulsed ultrasound technique and is subject to
range resolution or specificity
aliasing
Color doppler reports
average velicities also called mean velocities
color jet size is most affected by
color dopper gain setting
Color Power doppler Advantages
Increased sensitivity to the low flows, e.g. venous flow, flow in small vessels
Hyperechoic$
portions of an image that are brighter than surrounding tissues, or tissues that appear brighter than normal.
Shadowing
There are occasions when the US beam is unable to pass through a structure because the structure has a higher than usual attenutaion. When this occurs, any structures that lie deeper than the initial structure are not imaged or displayed. This is a shadow-aechoic or hypoechoic
Edge shadowing or shadowing by refraction
refraction at the edge of a circular structure can also create an artifact. This is called shadowing by refraction or edge shadow
Enhancement
Hyperechoic occurs when
the medium through which the sound travels has a lower attenutation rate than soft tissue
Mirror image $
sound may bounce off of a strong reflector, called a mirror, in its path and be directed.
Ultrasound$ systems assume that sound travels directly to a reflector and back to the transducer$
Speed errors appear as a $
step off, split or cut
Grating lobe artifact can be reduced or cured by dividing each element into even smaller, miniature pieces. This is called
Subdicing
Lobe artifacts degrade
Lateral resolution
Speckle
grainy appearance not directly from reflections from tissues.
Created by interfence effects of scattered sound, both constructive and destructive, from the many tissue reflectors
