SPI Flashcards
billion
10^9
giga
G
million
10^6
mega
M
thousand
10^3
kilo
k
hundred
10^2
hecto
h
ten
10^1
deca
da
tenth
10^-1
deci
d
hundreth
10^-2
centi
c
thousandth
10^-3
milli
m
millionth
10^-6
micro
billionth
10^-9
nano
n
Sound is a ______, ________ wave.
mechanical, longitudinal
Sound carries _____ from place to place.
Energy.
What are the acoustic variables?
Pressure, Density, Distance.
Define Pressure.
Concentration of force within an area.
(force/area)
units:Pascals (Pa)
Define Density.
Concentration of mass within a volume.
units: kg/cm^3
Define Distance.
Measure of particle motion
units: cm, ft, miles
With a transverse wave, particles travel in which direction?
Travel in a perpendicular direction, perpendicular to the wave.
With a longitudinal wave, particles travel in which direction?
Particles move in the same direction as the wave.
Acoustic Variables vs. Acoustic Parameters
Acoustic Variables inform us of which waves are sound waves while Acoustic Parameters describe the features of a particular sound wave.
7 parameters of continuous waves.
Period Frequency Amplitude Power Intensity Wavelength Propagation Speed
Period
Time required to complete a single cycle.
Determined by: source
units: microseconds
nonadjustable
Frequency
Number of certain events that occur in a particular time duration.
Determined by: source
units:hz
nonadjustable
Amplitude
Difference between the average value and the maximum value of an acoustic variable.
Determined by: source (initially)
units:pascals, cm
adjustable
Power
The rate that work is performed or rate of energy transfer. Determined by: source (initially) units:Watts adjustable Power=Amplitude^2
Intensity
Concentration on energy in a sound beam.
Determined by: source (initially)
units:watts/cm^2
adjustable
Wavelength
The length or distance of a single cycle.
Determined by: Both
units: meters, mm
nonadjustable
Propagation Speed
Rate that sound travels through a medium.
Determined by: Medium
units:m/s
nonadjustable
Equation for wavelength
wavelength = propagation speed (mm/microsec) / frequency (MHz)
Intensity is _________ related to power.
directly
Equation for intensity.
intensity = power(watts) / beam area(cm^2)
How to determine the wavelength in soft tissue.
divide 1.54 (mm/us) by the frequency (Mhz)
Density vs. Stiffness
increase in stiffness=increase in speed.
increase in density=decrease in speed.
Parameters of pulsed sound
Pulse Duration Pulse Repetition Frequency Pulse Repetition Period Duty Factor Spatial Pulse Length
Pulse Duration
The time from the start of a pulse to the end of that pulse. Determined by: source units: microsec Nonadjustable PD= # of cycles in pulse x period
Spatial Pulse Length
The length or distance that an entire pulse occupies in space. Determined by: Both units:mm Nonadjustable SPL=# of cycles x wavelength (mm)
Pulse Repetition Period
the time from the start of one pulse to the start of the next pulse; 1 pulse duration + 1 listening time.
Determined by: source
units:msec
Adjustable
Pulse Repetition Frequency
number of pulses created by the system in one second.
determined by: source
units:Hz
Adjustable
Duty Factor
% or fraction of time that the system transmits sound.
Determined by: source
unitless
adjustable
Duty factor is _____ related to depth.
Inversely; with shallower depth there is a higher duty factor, with more depth there is lower duty factor.
PRF is ____ related to depth.
Inversely; shallower image = higher PRF
deeper image = lower PRF
PRP is ____ related to depth.
Directly.
How are PRP and PRF related?
They are reciprocals.
Factors involved with deep imaging…
low PRF
low duty factor
long PRP
Factors involved with shallow imaging….
high PRF
high duty factor
short PRP
Definition of Intensity
The concentration of power in the beam
5 Key Words of Intensity
Peak- max value Average- mean value Spatial- refers to distance or space Temporal- refers to all time Pulsed- refers to transmit time only
The greatest intensity…
SPTP
The lowest intensity…
SATA
The intensity related to tissue heating…
SPTA
What is attenuation?
The decrease in intensity, power and amplitude of a sound wave as it travels.
units: dB
What are the three components of attenuation?
Absorption
Scattering
Reflection
With lower frequency and shorter path length there is ….
less attenuation
With higher frequency and longer path length there is….
more attenuation
Reflection occurs when…
propagating sound energy strikes a boundary between two media and some returns to the transducer
Specular reflection arises from a…
smooth reflector (they return in one direction)
Diffuse reflection or backscatter arises from…
rough boundary (sound is redirected in many directions)
When are specular reflections best seen?
When sound strikes the boundary at 90 degrees.
When does Rayleigh scattering occur?
When the reflector is much smaller than the wavelength of sound; sound is then uniformly distributed in all directions
Rayleigh scattering is related to…
Frequency^4
Higher frequency sound undergoes more…
Rayleigh scattering
What is the attenuation coefficient?
The amount of attenuation per centimeter.
units:dB
In soft tissue the attenuation coefficient is approx…
1/2 the frequency
Total attenuation equals…
path length(cm) x attenuation coefficient (dB/cm)
A mathematical expression that means ‘half the transducer frequency’ is…
0.5 dB/cm/MHz
Reflection of an ultrasound waves depends upon different
impedances
What is the equation for impedance?
impedance (rayls)= density (kg/m^3) x prop speed (m/s)
PORNN (normal incidence)
perpendicular
orthogonal
right angle
ninety degrees
Oblique incidence means…
not at right angles, anything other than 90 degrees.
What are the other names for Round Trip?
Time of flight
Go return time
What is the definition for time of flight?
The time needed for a pulse to travel to and from the transducer and the reflector
What is the average speed in soft tissue?
1.54 km/sec
In the 13 sec rule, what would the reflector depth and total distance traveled at 26 sec?
Reflector: 2cm
Total: 4cm
What is the relationship between time of flight and distance?
Directly related
What does speed equal?
Speed= distance/time
What is the definition of a transducers?
Any device that converts one form of energy into another
What is the Piezoelectric Effect?
Property of certain materials to create a voltage when pressure is applied or when material is mechanically deformed.
What are all of the Piezoelectric materials?
PZT
Ceramic
Active element
Crystal
What happens to the crystal when is exceeds the Curie Point?
Depolarizes
What is Sterilization?
Complete destructs of all living microorganisms by means of exposure to heat, chemical agents, or radiation
What is disinfection?
Application of chemical agent to reduce or eliminate infectious organisms on an object
What requires Sterilization?
Items that Penetrate skin or mucous membranes
What requires disinfection?
Things that come in contact with mucous membranes
What are transducers disinfected with?
Cider
Gluteradehyde
On the transducer, what does the case do?
Protects the internal components from damage and insulates the patient from electrical shock
Why don’t we use transducers with a cracked case or frayed wire?
Potential electric shock to patient
The matching layer is ___________ wavelength thick.
1/4
What are the impedances of the matching layer?
PZT>matching layer> gel> skin
What reduced the transducers ringing?
Damping element or Backing material
What is the “rule” for the backing material?
Short pulses create better images
What is the backing material made out of?
Epoxy resin impregnated with tungsten
With the damping material, what are the imaging transducer characteristics?
Damping is effective Short pulse and duration Low sensitivity* Wide bandwidth* Low Q Decreased output power
How come Therapeutic and Continuous wave transducers don’t use damping element?
They don’t create images
What does bandwidth mean?
Range of frequencies between the highest and the lowest frequency emitted from the transducer
What is another name for wide bandwidth?
Broadband
What are all the names of the main frequency emitted by the transducer?
Center
Resonant
Primary
Natural frequency
What is Quality factor?
Unitless number representing the extent of damping
What are the two characteristics that determine frequency in a pulsed transducer?
- Thickness
2. Propagation Speed
In pulsed transducers, what will have a high frequency?
Thin crystal and fast PZT
In pulsed transducers, what would have a low frequency?
Thick crystal
Slow PZT
When a PZT crystal is _____ as thick, the sounds frequency is ______ as high.
Half
Twice
Chart in book….
Component Thickness
- PZT crystal= 1/2 wavelength thick
- Matching layer= 1/4 wavelength thick
Pg. 57 cheater book
What creates better images?
Narrow beams
What is the focal point (focus)?
Location where the beam reaches its minimum diameter
What is the focal depth?
Distance from the transducer face to the focus.
What are the other names for focal depth?
Focal length
Near zone length
What is the near zone length?
Region or zone in between the transducer and the focus
Sound beams converge
What is another name for near zone?
Fresnel zone
What is the far zone?
Region or zone deeper than the focus, beyond the near field
Sound beams diverge
What is the focal zone?
Region surrounding the focus where the bean is “sort of narrow” and the image is good
What is focal depth determined by?
Transducer diameter (aperture)
Frequency
What is sound beam divergence determined by?
Transducer diameter
Frequency
What kind of sound wave does a large diameter crystal with a high frequency produce?
Less divergence in far field
What kind of divergence would a smaller diameter crystals with a lower frequency produce?
Large divergence in far zone
What is a continuous wave frequency determined by?
Electronic frequency
What is a pulsed frequency determined by?
Thickness of ceramic
Speed of sound
What is focal length determined by?
Diameter of ceramic
Frequency
What is divergence determined by?
Diameter of ceramic
Frequency
What is another name for V shaped wave?
Huygens wavelet
What produces the Huygens wavelet?
When produced by a tiny source, with a size near the wavelength of the sound waves will diverge in this shape as they propagate
What is the Huygens Principle?
Hourglass shape of an imaging transducers sound beam
The overall hourglass shape of a sound beam is the result of the ____________________ of many sound wavelets emitted from these numerous sound sources.
Constructive and destructive interference
What is Resolution?
Ability to image accurately
What is Axial Resolution?
Ability to distinguish two structures that are close to each other front to back, parallel to, or along beams axis
What is the synonym for Axial Resolution?
LARRD
What does LARRD stand for?
LARRD: Longitudinal Axial Range Radial Depth
What is the equation for Axial Resolution?
LARRD Resolution= Spatial Pulse Length/2
What does LARRD resolution improve with?
Less ringing
Higher frequency
When is Axial Resolution at its best?
Using transducers with the highest frequency and the fewest number per cycle
What is Lateral Resolution?
Minimum distance that two structures are separated by side-to-side or perpendicular to the sound beam that produces two distinct echoes
What is the synonym for Lateral Resolution?
LATA
What is the incident intensity?
intensity of the sound wave prior to striking a boundary.
What is the reflected intensity?
Portion of the incident intensity that, after striking a boundary, changes direction and returns back from where it came.
What is the transmitted intensity?
Portion of the incident intensity that, after striking a boundary, continues on in the same general direction that is was originally traveling.
What is the equation of incident intensity?
incident intensity = reflected intensity + transmitted intensity
What is the Intensity Reflection Coefficient?
The percentage of the US intensity that bounces back when the sound strikes a boundary.
What is the Intensity Transmission Coefficient?
The percentage of the incident intensity that after striking a boundary continues on in the same general direction that it was originally traveling.
Where does conservation of energy exists?
at a boundary.
IRC + ITC = ?
100%
When the reflected and transmitted intensities are added, what is the result?
The incident intensity
With greater impedance differences between the two media, the IRC ______, and the amount of reflection ____.
increases, increases
Whatever is not transmitted, must be ____.
reflected
What do we know about oblique incidence?
Nothing!
What is refraction?
Transmission with a bend.
Refraction requires what?
- ) oblique incidence
2. ) different speeds
Refraction cannot occur with…
Normal incidence and the same speeds.
Snell’s Law describes..
The physics of refraction
How are period and frequency related?
They’re reciprocals.
Narrower sound beams create better____________
Images
What is another name for transducer diameter?
Aperture
What is the focus (focal point)?
Location where the beam reaches its minimum diameter
What is focal depth?
Distance from the transducer face to the focus.
What is another name for focal depth?
Focal length
Near zone length
What is the near zone?
Region or zone in between the transducer and the focus. Sound beams converge!
What is another name for the near zone?
Fresnel zone
What is the far zone?
Region or zone deeper than the focus, beyond the near field. Sound beams diverge
What is another name for the far zone?
Fraunhofer zone
What is the focal zone?
Region surrounding the focus where the beam is “sort of narrow” and picture is relatively good
What is focal depth determined by?
Transducer diameter (aperture)
Frequency
Hint….
Compared to beams with a shallow focus, beams with a deep focus have a lower intensity at the focus
What will cause a shallow focus?
Small diameter
Low frequency
What will cause a deep focus?
Large diameter
High frequency
Define sound beam divergence.
Spread of the sound beam in the deep far zone
What factors affect sound beam divergence?
Transducer diameter (aperture)
Frequency
What kind of transducer would produce the best lateral resolution?
Beam narrower in far field
Large diameter
High frequency
Transducer that would produce the worst lateral resolution?
Far field diameter is wide.
Small diameter with low frequency
What is continuous wave frequency determined by?
Electronic frequency
What is Pulsed wave frequency determined by?
Thickness of ceramic
Speed of sound
What is focal length determined by?
Aperture of ceramic
Frequency
What is divergence determined by?
Aperture of ceramic
Frequency
What is another name for diffraction pattern?
Huygens wavelet
What is the shape of the waves produced by diffraction pattern?
V shaped wave
What is the Huygens Principle?
Hourglass shape of an imaging transducers sound beam
The overall hourglass shape of a sound beam is the result of the ______________________ interference of the many sound wavelets emitted from these numerous sound sources.
Constructive and destructive interference
What is resolution?
Ability to image accurately
What is Axial resolution?
Ability to distinguish two structures that are close to each other
Front to back
Parallel to
Along the beams main axis.
What is the synonym for Axial resolution?
LARRD:
Longitudinal Axial Range Radial Depth
What creates better axial resolution?
Shorter pulses
- short pulse means short spatial length or short pulse duration
What are the units for Axial resolution?
Mm, cm - units of distance
Equation:
LARRD= Spatial Pulse Length/2
What does LARRD improve with?
Less ringing
Higher frequency
Note….
As frequency increases, the numerical value of LARRD resolution decreases. This means high frequency transducers have improved LARRD resolution and create more accurate images.
What is Axial Resolution best with?
Highest frequency
fewest number of cycles per pulse
Define Lateral Resolution
Minimum distance that two structures are separated by
Side by side
Or perpendicular to sound beam that produces two distinct echoes
What is the synonym for Lateral resolution?
LATA:
Lateral
Angular
Transverse
Azimuthal
Note….
Lateral resolution = beam diameter
What is point spread artifact?
When two side by side structures are closer together than the beam width, only one wide reflection is seen on image
What are the three ways focusing alters the sound beam?
- Narrower “waist” in US beam
- Shallower focus
- Smaller focus zone
What are the general types of focusing?
- Fixed (conventional)(mechanical)
2. Adjustable (phased array)
What are the three methods of focusing?
- Lens- external focusing
- Curved Pizeoelectric Crystal- internal focusing
- Electronic focusing- adjustable
Note…
Single crystal transducers are always fixed focus
What are 2D images referred to as?
B-scans or “B-mode”
What is mechanical scanning?
Contains one disc, element
What is the steering for mechanical scanning?
Mechanical
What is the focusing for mechanical scanning?
Conventional or fixed
What is the image shape for mechanical scanning?
Sector
If the crystal is destroyed in mechanical scanning, what does the image look like?
No image.
Switched arrays are also known as what?
Sequential
What is the steering for linear switched?
No steering. Scan lines are parallel and remain equally spaced at depths
What is the focusing for a linear switched?
Fixed focusing or curved crystal
What is image shape for linear switched?
Rectangular
There is a defective Crystal in a linear switched, what will image look like?
Dropout from superficial to deep
Top to bottom
What does a phased array mean?
Adjustable focus or multi-focus
What is the steering and focusing for a phased array?
Electronic
What is the image shape for a phased array?
Sector shaped
What is the time delay for a phased array?
10ns
What is a beam former?
Created electronic patterns. Delays are 10ns
Multidimensional arrays
2D create 3D or 4D images.
What resolution does a 1 1/2 dimensional array improve?
Elevational
Vector array, what is the image shape?
Trapezoidal imaging
What is contrast resolution?
visualizing a variety of gray shades in an image.
What is spatial resolution?
visualizing detail in an image.
What is real-time imaging
“motion picture” A series of frames displayed in a rapid fashion to give the impression of constant motion.
What is temporal resolution?
the ability to accurately locate moving structures at anyh particular instant in time.
What is temporal resolution determined by?
Frame rate only
What are the units of temporal resolution?
Hertz (20Hz-100Hz)
What is frame rate determined by?
1) Imaging depth
2) # of pulses per image
What is frame rate limited by?
1) speed of sound in the medium
2) imaging depth
What is the fundamental limitation of temporal resolution?
Speed
What 3 things change the number of pulses in an image?
That are under sonographer control
1) # of pulses per scan line (multi-foucus)
2) sector size
3) line density
The 4th setting that the sonographer controls for temporal resolution, but dose not effect the number of pulses in an image?
maximum imaging depth
Temporal resolution improves with…
- shallower depth and fewer pulses
- less time to create am image (higher frame rate)
- more frames created each second
Temporal resolution degrades with…
- deeper and more pulses
- more time to create an image (lower frame rate)
- less frames created each second
If the imaging depth is doubled the frame rate will be..
halved
Improving image quality often degrades….
temporal resolution
Multi focus improves ….
Lateral resolution
Multi focus degrades..
temporal resolution
A narrow sector is better for..
temporal resolution
Line Density
the number of scan lines per degree of sector
Low line density degrades..
spatial resolution
With regard to line density, what will create a frame with fewer pulses?
Low Line density
The time required to make a frame is called?
Tf
Tf X FR=
1
When one frame is created in 1/10th of a second then the frame rate will be….
10/second or 10 Hz
What is an Ultrasound System?
a device that produces sound beams, retrieves the echoes and produces visual images and audio signals.
What are the 6 components of an Ultrasound system?
Master Synchronizer Transducer Pulser Receiver Display Storage
What communicates with all of the individual components, and organizes and times their functions so as to operate as
a single integrated system?
Master Synchronizer
What converts electrical into acoustic energy during transmission and converts acoustic in to electrical energy during reception?
Transducer
What controls the electrical signals sent to the active elements for sound pulse generation?
Pulser
What determines the pulse repetition period and pulse amplitude?
Pulser
What creates a firing pattern for phased array systems (beam former)?
Pulser
What processes the electronic signal produced by the transducer during reception and producing a picture on a display device?
Receiver
What is associated with the presentation of processed data for interpretation, monitor, speakers, paper record?
Display
A device or media that are used to permanently archive the data…
Storage
This increases the sound intensity created by the transducer and sent into the patient….
When the sonographer increases the output power.
For a phased array system the pulser is also called the…
beam former
Other words for Transducer Output
output gain acoustic power pulser power energy output transmitter output
What is determined by the excitation voltage from the pulser?
Transducer output
The crystal vibrates with a magnitude related to the….
Transducer output
What results from a transducer output change?
All reflections change..the brightness of the entire image changes.
Signal
meaningful portion of the data
noise
inaccurate part of the data. Degrades the quality of information.
High signal to noise ratio
the meaningful part of data is stronger=high quality image
Low signal to noise ratio
the inaccurate part of the data is stronger=poor quality image
Receiver functions
Amplification Compensation Compression Demodulation Rejection
What increases the strength of all electrical signals in the receiver prior to further processing?
Amplification
Amplification is also called…
receiver gain
Amplification changes the brightness of…
the entire image..”uniform amplification”
Preamplifier
alters the signal before it is amplified
Compensation
makes all echoes from similar reflectors appear identical regardless of depth. “uniform brightness from top to bottom”
What is used to create uniform brightness from top to bottom?
Compensation
TGC is
compesation
The more attenuation…
the more TGC must be used
TCG curve
near gain delay slope knee far gain
What will you adjust if you cannot see reflectors in the near field?
TGC
Compression
reduces the total range of signals, from smallest to the largest
What keeps signals within the operating systems electronics and the gray scale within the range of what the human eye can see?
compression
What decreases the dynamic range of the signals?
compression
What allows us to see all gray shades?
compression
What changes the gray scale mapping?
compression
What changes the signals form to one more suitable for display?
Demodulation
What part of demodulation changes all of the negative voltages in to positive ones?
rectification
What part of demodulation puts and envelope around the “bumps” to even them out?
Enveloping or Smoothing
What eliminates low-level noise in our images?
Rejection
Does rejection effect bright echoes?
NO
Output Power vs Receiver gain
When the term suggests outgoing function it is output power.
When the word indicates reception or incoming, the function is receiver gain
Harmonics
creates scans from sound reflections at 2x the transmitted frequency.
Where are harmonics created?
In the tissues
A transducer creates a sound pulse with a fundamental frequency of 2MHz. In the harmonic mode, an image is created from ?MHz sound reflections is displayed?
4
Non-linear behavior creates
harmonics
Sound moves slightly faster in regions of…
compression
Sound moves slightly slower in regions of
rarefaction (lower pressure)
Pulse inversion Harmonic Imaging
positive and negative pulses are transmitted down each scan line.
What is a disadvantage of pulse inversion imaging?
degrades temporal resolution, because the frame rate is half that of the fundamental imaging
Brightness
related to the brilliance of the image
contrast
determines the range of brilliancies that are displayed.
bistable
high contrast
Analog
real world
a variable attains a continuum of values
digital
computer world
a variable attains only discrete values
Scan converter
changes the data format.
Gray scale not possible with out it
Digital scan converter
converts the image into numbers . the numbers can be processed and translated for display as an image
The smallest element of a digital picture
pixel
pixel density
pixels per sq inch
low pixel density= poor spatial resolution
high pixel density= good spatial resoluion
spatial resolution on a digital display is determined by…
pixel density
spatial resolution is related to
the number of lines per frame
the smallest number of digital storage is
Binary Digit
a bit is
bistable, either 0 or 1
a group of bits is assigned to
each pixel
the more bits per pixel the
more shades of gray and the better the contrast resolution
Byte
8 bits
2 bytes
16 bits is a Word
If you have 10 bits per pixel how many shades of gray can be represented per pixel?
2 to the 10th power = 1024 shades of gray
How many bits are needed to represent 10 shades of gray?
4 . 4 bits can display up to 16 shades of gray.
2x2x2x2=16
Preprocessing
manipulating the data before the storage. Can not be reversed.
Post processing
manipulating the data after it has been stored. Performed on frozen images.
Electrical signals created by the PZT are
analog
Analog-Digital Conversion
Analog signal from transducer A to D converter Digital scan converter D to A converter Analog Signal dislpay
Read Magnification
number of pixels is unchanged and pixel size increases
Write Magnification
the size of the pixels stays the same and the number of pixels increases
Fill-In Interpolation
improves images by filling in the gaps between lines. Preprocessing.
Improves image detail (spatial resolution)
What artifact causes a granular appearance in tissues that are really homogenous? Created by interference effects.
Speckle
When are scan lines steered by the transducer in different directions or views, so structures are interrogated by multiple pulses from several different angles?
Spatial Compounding
What type of transducers can use Spatial Compounding?
Phased array
What provides a history of past frames that are overlaid or added on top of the current frame?
Temporal Compounding or Persistence
What divides the reflection into sub-bands of smaller frequency ranges and creates images from each of theses sub-bands?
Frequency Compounding
Dynamic Aperture
a from of electronic receive focusing
Uses a varying number of elements to receive a reflected signal.
Edge enhancement
increases the contrast at a boundary
What uses long sound pulses that contain a complex pattern of frequencies and cycles, called a code?
coded excitation
coded excitation takes place in the …
pulser
coded excitation improves…
signal to noise ratio penetration axial resolution spatial resolution contrast resolution
What technique produces images based on a change in shape when a force is applied to a tissue?
elsastography
What is rendering?
creates images with shadow, color, texture and optical effects.
dynamic range
the ratio of the largest to the smallest signal strength.
PACS
Picture Archiving and Communications System
DICOM
Digital Imaging and Communications in Medicine
NAS
network storage device used in PACS
What is flow?
the movement of a fluid from one location to another
Steady flow
fluid movement at a constant speed or velocity.
Pulsatile flow
arterial
cardiac contraction
high pressure
Phasic flow
venous
respiration
low pressure
What is Laminar flow?
streamlines are layered, may be “plug” or “parabloic”
Parallel and aligned
What is Turbulent Flow?
chaotic flow in many directions and speeds.
What is a swirling pattern of rotational flow?
vortex
What are small regions of turbulent flow that have vastly different velocities?
Doppler spectral broadening
When flow energy is lost, what does it convert to?
sound (murmurs, bruits)
vibration (thrill)
What is Energy Gradient?
When the total fluid energy at one location differs from the total fluid energy at another location.
What is another name for “motion energy”?
Kinetic Energy
What is a form of potential or stored energy that has the ability to perform work?
Pressure energy
What is the conversion of other forms of energy into heat?
Friciton
Viscosity
describes the thickness of a fluid (poise)
What increases the viscosity of blood?
Increased hematocrit or hemoglobin
What is a narrowing or irregularity in a lumen?
Stenosis
Units of resistance?
Ohms
What are the resistance vessels in circulation?
Arterioles
What is Bernoulli’s Principle?
In a stenosis, the highest velocity, lowest pressure and kinetic energy is highest at the maximum narrowing.
During Inspiration
Diaphragm desends pressure in the abd increases venous flow to legs decreases pressure in the thorax decreases venous return to heart increases
During Exhalation
Diaphragm ascends pressure in the abd decreases venous flow to legs increases pressure in the thorax increases venous return to heart decreases
What is the valsalva maneuver?
a bearing down or forceful attempt at expiration, when nose and mouth are closed. It increases pressure in the thorax and reduces all venous flow.
What is a doppler shift?
a change or variation in the frequency of the sound as a result of motion between the sound source and the receiver. or difference between received and transmitted frequencies.
positive doppler shift
when source and receiver are approaching each other, so the reflected frequency is higher than the transmitted.
negative doppler shift
when the source and receiver are moving apart, so the reflected frequency is lower than the transmitted.
Does doppler measure frequency or amplitude?
frequency
if emitted frequency is FE and reflected frequency is FR then…
FD (doppler frequency)=FR-FE
doppler shift is directly related to…
blood cell speed
frequency of the transducer
cosine of the angle
doppler shift is inversely related to…
speed of sound in the medium
doppler shift =
2x reflector speed x incident frequency x cos (angle) / propagation speed
What requires magnitude and direction?
velocity
How many crystals are in a continuous wave doppler?
2
1 always transmitting
1 always receiving
What is the advantage to continuous wave doppler?
high velocities are accurately measured
What are the disadvantages to continuous wave doppler?
range ambiguity
How many crystals are in a pulsed wave doppler?
1
What is the advantage to pulsed wave doppler?
since we have a gate we know where the flow is being measured, this is called range resolution or specificity
Aliasing is an disadvantage of what?
pulsed wave doppler
What is it called when you are imaging and using doppler at the same time?
duplex
What does x axis represent for doppler?
time
What does y axis represent for doppler?
velocity
What is it called when high velocities appear negative on doppler?
aliasing
Nyquist limit=
PRF/2
What king of doppler does not create aliasing?
continuous wave
Ways to reduce aliasing are…
use continuous wave use a lower frequency select a new view with a shallower sample volume increase the scale baseline shift
Do smaller or larger sample volumes (gates) produce a doppler spectra with a cleaner window?
smaller
What are gray shade on a doppler spectrum related to?
amplitude of the reflected signal
number of red blood cells creating the reflection
What doses color doppler report?
average velocities
When using color doppler in velocity mode what does the color on the top represent?
blood cells flowing towards the transducer
therefore bottom color represents flow away from transducer
When using color doppler in variance mode, what does the appearance of colors on the right side of the color bar mean?
turbulent flow
therefore left side represents laminar flow
What are multiple ultrasound pulses needed to accurately determine red blood cell velocities by Doppler called?
doppler packets
can be large or small
what are the advantages to large doppler packets?
greater accuracy
sensitivity to low flow
What are the disadvantages to large doppler packets?
more time required
frame rate and temporal resolution are reduced
What are the limitations of color power doppler?
no measurement of velocity or direction
lower frame rates
flash artifact
What are the advantages of color power doppler?
increase sensitivity to low flows
not affected by angle , except 90 degrees
no aliasing
When is spectral analysis used?
to identify the individual frequencies making up the complex signal
What are the current methods of spectral analysis?
fast fourier transform (FFT)
autocorrelation (less accurate but faster)
