Chapters 1-24 Flashcards
reciprocal relationship
when two numbers with a reciprocal relationship are multiplied together, the result is one. EX: 2 x 1/2 = 1
increase by a factor means
multiply by that number
decrease by a factor means
divide by that number
10^9 means…..
giga, G, billion
10^6 means…..
mega, M, million
10^-3 means….
milli, m, thousandth
10^-6 means…
micro, u, millionth
10^-9 means….
nano, n, billionth
10^3 means….
kilo, k, thousand
sound is …..
- a mechanical wave
- travels in a straight line
- sound waves are longitudinal
acoustic propagation properties are…
the effects of the medium upon the sound wave
Biologic effects are….
the effects of the sound wave upon the biologic tissue through which it passes
acoustic variables
the way sound waves are identified
- pressure - pascals (Pa)
- density - kg/cm^3
- distance - cm, mm
acoustic parameters
a waves features or characteristics
Decibels are what?
-a relative measurement, a comparisson, a ratio, logarithmic
Negative decibels describe what?
Signals that are decreasing in strenght or are getting smaller
Attenuation is determined by what two factors?
Path length and frequency of sound
How are frequency and attenuation related?
Directly
What 3 processes contribute to attenuation?
Reflection, scattering & absorption
Specular reflection is?
When the beam reflected hits a smooth boundary
Diffuse reflection (rough boundary) is aka?
Backscatter
intensity =
power (w) / area (cm^2)
Power is related to?
amplitude squared
Intensity is related to?
amplitude squared
Power is related to?
intensity
Wavelength (mm) =
1.54 mm/us /frequency (MHz)
speed (m/s) =
frequency (Hz) x wavelenght (m)
as stiffness increases…..
speed increases
as denstiy increases….
speed decreases
bulk modulus is the same as?
stiffness
which 5 parameters describe pulsed sound?
- pulse duration
- pulse repetition period
- pulse repetition frequency
- duty factor
- spatial pulse length
what is duty factor?
the percentage of time that the system transmits a pulse
With shallow imaging we have….
- less listening
- shorter PRP
- higher RRF
- higher duty factor
With deep imaging we have….
-more listening
-longer PRP
-lower PRF
lower duty factor
what is the duty factor for continuous wave sound?
1.0 (100%)
what is the typical value for duty factor for pulsed wave sound?
0.2 -0 .5%
what are the intensity measurement methods?
- SPTP
- SATP
- SPTA (tissue heating & bioeffects)
- SATA
- SPPA
- SAPA
all intensities have units of ?
W/cm^2
What are the temporal intensities from largest to smallest?
Itp, Imax, Ipa, Ita
What is the rank of intensities from largest to smallest?
SPTP, Im, SPPA, SPTA, SATA
What happened to sound as he travels in the body?
It attenuates
What are the units of attenuation?
dB
Decibels require what?
2 intensities
Positive decibels report signals that or what?
Increasing and strength or getting larger
Decibel notation is?
A relative measurement, a comparison, a ratio,logarithmic
Negative decibels describe signals that are what?
Decreasing and strength are getting smaller
Attenuation is determined by what two factors?
Path length and frequency of sound
More attenuation happens with?
Longer distances and higher frequencies
Less attenuation happens with?
Shorter distances and lower frequencies
What the processes contribute to attenuation?
Reflection, scattering, and absorption
What are the two forms of reflection?
Specular and diffuse
Diffuse reflection a.k.a.?
Backscatter
What is scattering?
Random redirection of sound in many directions
What is the relation between frequency and Rayleigh scattering?
Proportional to frequency to the fourth power
What is the attenuation Coefficient?
Is the number of decibels of attenuation that occurs when sound travels 1 cm
What are the units of attenuation coefficient?
dB/cm
What is the half-value layer thickness?
Is the distance sound travels in a tissue that reduces intensity of sound to one half its original value
What are the bases for ultrasonic imaging?
Reflection and transmission
What are the units of impedance?
Rayls
What is normal incidence also called?
Perpendicular, Orthogonal, right angle, 90°
What is incident intensity?
Is the sound wave’s intensity immediately before it strikes a boundary
What percentage of a sound waves intensity is reflected at a boundary between two Soft tissues?
Very little 1% or less
What percentage of a sound wave’s intensity is transmitted at a boundary between two soft tissues?
Most 99% or more
When we have normal incidence reflection occurs only if?
The media on either side of the boundary have different impedances
What to physical principles always apply to reflection with oblique incidence?
Conservation of energy and reflection equals incident angle
Refraction occurs only you?
Oblique incidence and different propagation speeds of the two media
What is Snell’s law?
It’s quantifies the physics of refraction
If speed 1 equals speed 2….
No refraction, transmission angle equals incident angle
Speed 2 greater than speed 1…..
Transmission angle greater the incident angle
Speed 2 less than speed 1…
Transmission angle less than incident angle
What is the go return time?
The elapsed time from pulse creation to pulse reception
What is the 13 µs rule?
For every 13 µs of go return time the object creating the reflection is 1 cm deeper in the body
What does the backing material enhance?
Axial resolution
In decreasing order of impedance….
PZT>Matching layer>gel>skin
What are 3 consequences of backing material?
Decrease sensitivity, wide bandwidth,and low-quality factor
What are the characteristics of damping material?
High degree of sound absorption and acoustic impedance similar to PZT
What is bandwidth?
The range frequency found in a pulse
With continuous wave transducers, electrical frequency equals……
Acoustic frequency
What 2 characteristics of the active element combine to determine the frequency of sound?
Speed of sound in the PZT and thickness of the PZT
What are the characteristics of high frequency waves imaging transducers?
Thinner PZT crystals & PZT with higher speeds
What are the characteristics of low. Frequency pulsed wave imaging transducers?
Thicker PZT crystals and PZT with lower speeds
What gives us a shallow focus?
Small diameter PZT & lower frequency
What gives us a deep focus?
Large diameter PZT and higher frequency
What gives us less divergence?
A larger diameter and higher frequency
What gives us more divergence?
Smaller diameter and lower frequency
What are HUYGEn’s wavelets aka?
Spherical waves, or diffraction patterns (v shaped waves)
What is axial
resolution?
It deals with structures that are parallel to the sound beam
LARRD stands for?
Longitudinal, axial, range, radial and depth
What is better axial resolution associated with?
Shorter spatial pulse lenght, shorter pulse duration, higher frequencies (shorter wavelength), fewer cycles per pulse (less ringing) and lower numerical values
What is lateral resolution?
It relates to structures that are positioned perpendicular to the sound beam
What does LATA stand for?
Lateral, angular, transverse, and azimuthal
Where is lateral resolution Best at?
At the focus
What does focusing do?
It concentrates the sound energy into a narrower beam and thus improve lateral resolution
Fixed focusing is aka?
Conventional or mechanical focusing
What are the effects of focusing?
Beam diameter in near field and focal zone is reduced, focal depth is shallower, beam diameter in the far zone increases and focal zone is smaller.
What are the three basic modes oh viewing ultrasound information?
Amplitude mode, brightness mode, and motion mode
With M-mode….
X-axis displays time
Y-axis displays depth
With B-mode….
X-axis displays depth
Z-axis displays amplitude
With A-mode….
X-axis displays depth
Y-axis displays amplitude
What are the US system’s main components?
Transducer, pulser and beam former, receiver, display, storage, and master synchronizer
What is the pulser’s function?
It creates electrical signals that excite the transducers PZT crystals and create sound beams
what are array transducers?
they contain multiple active elements; an array comprises a single slab of PZT cut into a collection of separate pieces called elements
3 types of array transducers are:
linear, annular and convex
phased array always means what?
adjustable or multi-focus
What creates electronic steering?
slope
slice thickness or elevational resolution is what?
it deals with shallow to deep
side to side and above to below the imaging plane
side and grating lobes degrade what?
lateral resolution
side lobes are created by what?
mechanical transducers
grating lobes are created by what?
array transducers
What is apodization?
when stronger electrical signals are used to excite the inner crystals and progressively weaker electrical spikes excite the outer crystals. Lobes are diminished
What is subdizing?
when a crystal is divided into a group of smaller crystals called sub-elements. These sub-elements are electrically joined and act as if they are a single crystal, which reduces grating lobes
what is dynamic aperture aka variable aperture?
it can be used to make a sound beam narrow over a greater range of depths and thus optimize lateral resolution
frame rate is determined by what 2 factors?
- sound’s speed in the medium
- the depth of imaging
Tframe and frame rate are?
inversely related
what system settings affect frame rate?
imaging depth (deeper, lower FR) and number of pulses per frame (less pulses, higher FR)
what factors determine the number of pulses per frame?
- number of focal points
- sector size
- line density
multifocusing does what to FR?
it decreases FR and disminishes temporal resolution
multifocus improves what?
lateral resolution
Sector size aka FOV, does what to FR?
if narrow this means less pulses, so it increases FR
What does line density do to FR?
If we increase line density, we decrease FR
What does high line density do?
it increases spatial resolution, but decreases temporal resolution
what type of resolution does multi-focusing improve?
lateral resolution
To have higher FR, we need to have?
- shallower imaging
- single focus
- narrow sector
- low line density
To have lower FR, we need to have?
- deeper imaging
- multiple focal points
- wide sector
- high line density
What is the transducer output aka?
Output gain, acoustic power, pulser power, energy output, transmitter output power or gain.
what are the six components of an US system?
- Transducer
- Pulser and beam former
- receiver
- display
- storage
- master sychronizer
what is the function of the pulser?
it determines amplitude, PRP, and PRF
what is the function of the beam former?
determines the firing delay patterns for phased array systems
output power increases what?
signal to noise ratio
what are the receiver operations?
- amplification (remember alphabetical order)
- compensation
- compression
- demodulation
- rejects
what happens with amplification (dB)?
all electrical signals in the receiver are affected identically by amplification
what is compression?
it alters the gray scale mapping of an us image; aka log compression or dynamic range
what does demodulation do?
a 2 part process that changes the electrical signal into a form more suitable for display; rectification and smoothing (or enveloping)
what does reject affect?
only weak signals affected; strong signals remain unchanged
what is contrast?
a control that determines the range of brilliances within the displayed image. Bistable images are high contrast
what are some limitations of analog scan converters?
image fade, image flicker, instability, deterioration
what are some advantages of digital scan converters?
uniformity, stability, durability speed, and accuracy
what is pixel density?
the number of picture elements per inch
what’s a bit?
the smallest amount of computer memory
what is a byte?
a group of 8 bits such as 10011111
what do get with fewer bits per pixel?
fewers shades of gray and degraded contrast resolution
what do we get with more bits per pixel?
more shades of gray and improved contrast resolution
EX: how many possible shades of gray are displayed with 5 bits of memory?
multiplying 2 by itself 5 times yields = 32
coded excitation provides what?
- higher signal to noise ratio
- improved axial resolution
- improved spatial resolution
- improved contrast resolution
- deeper penetration
what is coded excitation?
creates very long sound pulses containing a wide range of frequencies; it occurs in the pulser
what does PACS stand for?
picture archiving and communications system
what does DICOM stand for?
digital imaging and computers in medicine
what is dynamic range?
a method of reporting the extent to which a signal can vary and still be accurately measured; units dB
what are the mathematics of compression?
add or subtract
with fewer shades of gray we have….
- few choces
- black and white (bistable)
- narrow dynamic range
- high contrast
with more shades of gray we have….
- many choices
- gray scale
- wide dynamic range
- low contrast
tissue harmonics are
- created in tissues
- created during transmission
- created by non-linear behavior
- primarily created along the beams main axis
what is pulse inversion harmonics?
it’s designed to utilize harmonic reflections, which are distortion free, while eliminating distorted fundamental reflections; a positive and then a negative pulse is transmitted down each scan line.
modulation harmonics is what?
another imaging technique specifically disigned to augment harmonic reflections, while eliminating distorted fundamental reflections.
contrast agents must must meet what requirements?
- safe
- metabolically inert
- long lasting
- strong reflector of ultrasound
- small enough to pass through capillaries
What is contrast harmonics?
they are created because microbubbles act in a non-linear manner when struck by sound waves; they are created during reflection
what are contrast agents (aka microbubbles)?
they are gas bubbles encapsulated in a shell; they are designed to create strong reflections that actually “light up” blood chambers, vessels or other anatomic regions
Contrast bubbles…..
expand to a greater extent than they shrink
what is the Mechanical Index?
the amount of contrast harmonics produce may be estimated by this number
higher MI increases with?
large pressure variation and lower frequency
lower MI increases with?
small pressure variation and higher frequency
With the highest MI, greater than 1, we get?
- strongest harmonics
- bubble disruption
- extreme nonlinear behavior
- lowest frequency sound
- highest beam strength
- bubbles expands greatly
flow aka volume flow rate indicates what?
the volume of blood moving during a particular time; units are volume divided by time, ex: 5L/min
what is velocity?
speed that indicates direction
what is pulsatile flow?
when blood moves in variable velocity, blood accelerates and decelerates as a result of cardiac contraction; associated with arterial circulation
what is phasic flow?
when blood moves in variable velocity, blood accelerates and decelerates as a result of respiration; associated with venous circulation
what is steady flow
when fluid moves at a constant speed or veloctiy
what is laminar flow
when the flow streamlines are aligned and parallel; associated with normal physiologic states
what are the 2 types of laminar flow?
plug and parabolic (bullet shaped)
what is the Reynold’s number?
it predicts whether flow is laminar or turbulent
what is turbulence?
chaotic flow patterns in different directions and speeds; (eddie current or a vortex); associated with pathology
what is a murmur or a bruit?
sound associated with turbulence
what is a thrill?
tissue vibration associated with turbulence
what is the Reynold’s number for turbulence flow?
greater than 2000
what are the 3 forms of energy?
- kinetic (moving object)
- pressure(stored or potential energy)
- gravitational(stored or potential energy associated with elevated objects)
what are the 3 energy losses in the circulation?
- viscous loss (units of Poise)
- frictional loss
- inertial loss
what are the effects of a stenosis?
- change in flow direction
- increased velocity as vessel narrows
- turbulence downstream from the stenosis
- pressure gradient across the stenosis
- loss of pulsatility
Where is pressure lowest at a stenosis?
at the vessel’s narrowest point (stenosis)
where is velocity of blood the highest?
at the stenosis
what is Bernoulli’s principle?
describes the relationship between velocity and pressure in moving fluid
pressure gradient increases when either what?
- flow increases
- resistance increases
flow increases when either what?
- pressure gradient increases, or
- resistance decreases
in the circulatory system, what are the resistance vessels called?
arterioles
electrical resistance is reported in units of?
ohms
what is the shape of a vein as pressure increases?
hourglass shape(lower pressure), oval shape (intermediate pressure) and round shape(higher pressure)
what is hydrostatic pressure?`
it’s related to the weight of blood pressing on a vessel measured at the height above or below heart level
in a supine individual, what is the hydrostatic pressure ?
in this case, all parts of the body are at the same level of the heart, hydrostatic pressure is zero everywhere
in a standing individua, what is the hydrostatic pressure? depends upon whether the measurement is made above or below heart level
depends upon whether the measurement is made above or below heart level;-50 ( finger when the patient fully extends an arm toward the sky) -30 (top of head), 0 (at the level of the heart), 50 (at the level of the hips) 75 (at the level of the knees and 100 at the level of the ankle)
what happens with inspiration?
- diaphragm moves downward the abd
- thoracic pressure decreases
- abd pressure increases
- venous return to the heart increases
- venous flow in legs decreases
what happens with expiration?
- diaphragm moves upward into the thorax
- thoracic pressure increases
- abdominal pressure decreases
- venous return to the heart decreases
- venous flow in leg increases
Doppler shift, aka doppler frequency is what?
a change in frequency, the frequency of sound changes when the sound source and the receiver move closer together or farther apart
what is a positive doppler shift?
when blood cells move toward the transducer, they reflect sound with a higher frequency
what is negative doppler shift?
when blood cells move away from the transducer, they reflect sound with a lower frequency
Doppler shift?
2 x velocity of blood x transducer frequency x cos / propagation speed
Doppler shift is directly related to what?
velocity
when does the first shift occur?
when the sound wave from the transducer strikes moving blood cells
when does the second doppler shift occur?
it results from the transducer’s reception of the sound wave from moving red blood cells
what do the x and y axis of a doppler spectrum represent?
- x-axis = time
- y-axis = doppler shift or velocity
Doppler shift is directly related to what?
frequency of the transmitted sound
when does the doppler shift represent 100% of the true velocity?
when blood flow is is parallel to the sound beam
what happens when an angle exists between the direction of flow and the sound beam?
the measured velocity is less than the true velocity
what determines how much of the velocity is measured, when the sound beam and flow direction are not parallel?
it depends on the cosine of the angle between the sound beam and the direction of motion
How is doppler shift related to cosine?
directly related, when the cosine doubles, the doppler frequency doubles; the cosine increases as angles approach zero degrees
doppler shift and velocites cannot be measured when?
with a perpendicular incidence, 90 degrees
when is flow parallel to the sound beam?
when the angle between the direction of motion and sound is 0 or 180 degrees
cosine 0 degrees is 1, this indicates?
flow toward the the transducer
cosine 180 degrees is -1 indicates?
flow away from the transducer
Since the cosine of 60 degrees is 0.5, the measure velocity at 60 degrees is what
one half the actual velocity
what is bidirectional doppler?
spectral doppler tracing flow toward and away from the tranducer (above and below the baseline)
what is phase quadrature aka quadrature detection?
a commonly used signal processing technique for bidirectional doppler
a pulsed doppler transducer is characterized by?
- at least one crystal
- damped PZT
- low Q-factor
- wide bandwidth
- lower sensitivity
a CW doppler transducer is characterized by?
- at least 2 crystals
- undamped PZT
- high Q-factor
- narrow bandwidth
- higher sensitivity
pulsed doppler gives us?
- range resolution
- sample volume
- limited maximum velocity- Nyquist limit
- aliasing
CW doppler gives us?
- range ambiguity
- region of overlap
- unlimited maximum velocity
- no asiasing
with imaging we have?
- normal incidence- 90 degrees
- higher frequency, improves resolution
- pulsed wave only
- minimum of 1 crystal
with doppler we have?
- 0 or 180 degrees
- lower frequency-avoids aliasing
- pulsed or CW
- min. of 1 (pulsed ) or 2 (CW) crystals
what is aliasing?
the most common error associated with doppler ultrasound; it happens when very high velocities in one direction are incorrectly displayed as going in the opposite diretion
what is the Nyquist limit aka Nyquist frequency?
is the highest Doppler frequency or velocity that can be measured without the appearance of aliasing
we get less aliasing with?
- slower blood velocity
- lower frequency transducer
- shallow gate (high PRF)
we get more aliasing with?
- faster blood velocity
- higher frequency transducer
- dep gate (low PRF)
what two methods to eliminate aliasing, increase PRF?
increasing the scale and moving to a new view with a shallower sample volume (increase the Nyquist limit
what do the following techniques to eliminate aliasing do?
- lower transducer frequency
- zero baseline shift
- CW doppler
- decreases Doppler shift
- aliasing remains but display more appealing
- never aliases, but range ambiguity
what does eliminating aliasing improve?
the ability to measure the maximum velocity with Doppler
what does color doppler measure?
mean or average velocity
what does spectral doppler measure (pulsed and CW) measure?
peak velocity
what are the two mot commonly used doppler color maps used?
velocity mode and variance mode
with a variance mode, what do colors on the Lt represent?
laminar flow
with variance mode, what do colors on the Rt represent?
turbulent flow
with any color flow image that is sector-shaped, the horizontal vessel will display what?
both the toward and away colors, the center of the lument will be black
with any color flow image that has a rectangular shape, the horizontal vessel will display what?
1 color, and one can determine the direction of flow by placing an imaginary line in the upper corner and placing one’s finger her and slide it away from the imaginary line
what are doppler packets aka ensemble?
multiple ultrasound pulses used to accurately determine blood velocities
packets composed of a larger number of pulses have what 2 advantages?
- more accurate velocity measurements
- increased sensitivity to low flow
what disadvantages are there with packets with more pulses?
- more time needed to acquire data
- reduced frame rate
- decreased temporal resolution
what is power doppler aka energy mode or color angio?
it identifies the presence of a doppler shift, but does not evaluate speed or direction
what are 3 advantages of power mode?
- increased sensitivity to low flow or velocity
- unaffected by doppler angles, unless the angle is exactly 90 degrees
- no aliasing, since the velocity information is ignored
what are 3 disadvantages of power mode?
- no measurement of velocity or direction
- lower frame rates
- suscepitble to motion of the transducer, pt, or soft tissues
what does a wall filter aka high pass filter do?
eliminates low frequency doppler signals near the baseline (ghosting and clutter)
what is crosstalk?
a mirror image artifact
what is spectral analysis?
a tool that breaks the complex signal into its basic “building blocks” and identifies the individual velocities that make up the reflected doppler signal
what does Fast Fourier Transform used for?
to process both pulsed and continous wave doppler signals
what are the advantages of FFT?
exceedingly accurate and displays all individual velocity components that make up the complex reflected signal
what is autocorrelation aka correlation function used for?
to analyze color flow doppler
for color to appear in a vessel, what must be created?
an angle other than 90 degrees must be created between the direction of flow and the direction of the sound beam
when will color NEVER appear in a vessel?
when the directions of flow and sound are perpendicular
what happens when we have a color flow images and our color gain level is too high?
color appears throughout the box, color confetti
what happens when our color gain is too low?
all color disappears from the image
what happens when we have a spectral display, and our pulsed doppler gain is too high?
gray scale noise appears throughout the spectrum
what happens when we have a spectral display, and our pulsed doppler gain is too low?
all gray scale will disppear
when should aliasing be considered?
when we have peculiar color variation
how can we distinguish bidirectional flow from aliasing with color flow doppler?
flow reversal is present in a vessel when the colors red, black and blue are next to each other; if the colors that touch each other go around the outside of the map, aliasing is present
how can we eliminate or reduce aliasing from a color doppler image?
the most effective way is to increase the velocity scale
what other effect does increasing the scale have on a color doppler image?
it decreases the sensitivity to slow flows
what happens when we increase the walter filter in a color flow image?
ghosting artifact disappears and removal of color from the slow flow states; increasing the wall filter leaves the high velocity flows inchanged
in a doppler spectrum, what happens when we increase the wall filter?
the wall filter, selectively eliminates low frequency doppler shifts near the baseline; this does not affect the appearance of higher velocity flows
if we have a color flow image and increase the wall filter, what happens?
it eliminates low frequency doppler shifts; is does not get rid of aliasing
what happens when we increase the scale in a color flow image?
aliasing disappears and so does the low frequency flows
what are the 6 assumptions of imaging systems?
- sound travels in a straight line
- sound travels directly to a reflector and back
- sound travels in soft tissue @ exactly 1,540 m/s
- reflections arise only from structures positioned in the beam’s main axis
- the imaging plane is very thin
- the strength of a reflection is related to the characteristic of the tissue creating the reflection
when are reverberations created?
when a sound wave bounces back and forth between two strong reflectors; the first two reflections are real, the others are artifacts; assum #2
when does comet tail aka ring down artifact appear?
when a sound wave bounces back and forth between two very closely spaced objects; assum #2
when does shadowing artifact happen?
when sound hits a highly attenuating object such as bone; assum #6
when are edge shadows created?
as sound beams refract and diverge along the edge of a curved structure; assump #6
what is enhancement artifact?
a hyperechoic region that extends beneath structures with abnormally low attenuation; assum # 6
what is focal enhancement aka focal banding?
is a hyperechoic horizontal region at the depth of the focus; assum #6
when does mirror image artifact appear?
when sound reflects off a strong reflector (mirror), and is redirected toward a second structure; assum # 1 and 2
what is crosstalk?
it’s an artifact that appears on a spectral doppler display
what happens with speed error artifact?
it’s created when a sound wave propagates through a medium at a speed other than that of soft tissue, the correct number of reflectors are displayed, but appear at incorrect depths; assump # 3
what do lobe artifacts degrade?
lateral resolution
how can side lobes artifacts be reduced?
subdizing and apodization
what do we get with refraction artifact?
a second copy of a true reflector incorrectly appears on the image; the artifact is at the same depth as the true reflector; assum #1
what is slice thickness artifact aka section thickness artifact or partial volume artifact?
the thickness of an imaging plane varies, the portions of the slice have inferior elevational resolution when compared to thinner portions; assump #5
what is lateral resolution artifact, aka point spread artifact?
it may create one reflection on the image from two reflectors, it may also create a horizontal reflection from a smaller reflector
what is axial resolution artifact?
it may create one reflection from multiple small reflectors
