Vascular Lab Flashcards
What is the Doppler Effect?
A change in frequency caused by moving objects.
What are the two components of Sonography?
1) Sending pulsees of ultrasound into the body.
2) Using echoes recived from the anatomy to produce an image.
What are ultraound gray-scale scans?
pulse-echo images of tisssue cross-sections
Brightness of an echo represents what?
stength of the echo
A linear scan is composed of what?
many parralel scans
A sector scan is composed of many scan lines with what in common?
their origin
What shape is a linear scan?
rectangular
A sector scan has what shape?
a slice of pie
What shapes can the top of a sector scan have?
pointed or curved
Sonography is accomplished by what technique?
Pulse-echo
Transducers send what and receive what?
U/S pulses and echoes
What re the three displays of Doppler information?
Strip-chart recording, spectral display, color display
Sounds is a traveling variation of what?
Acoustic variables
What are acoustic variables (3)?
Pressure, density, and particle motion
What terms are used to describe all waves? (6)
frequency period wavelenght propagation speed amplitude intensity
What is frequency?
the number of cycles in a wave that occur in 1 second (Hz)
As sound travels, what are regions of low pressure and high pressure called?
rarefaction, compression
What frequency does ultrasound have?
> 20, 000Hz
what is a hertz?
One cycle per second
What is a period?
the time it takes fro one cylce to occur
How does period relate to frequency (equation)?
P=1/F
what is Wavelength?
length of space over which a cycle occurs
What is propagation speed?
What is the order of propagation speed (gas, solid, liquid)?
speed with which a wave moves through a medium
gas, liquid, solid(highest)
how are wavelength, propagation speed, and frequency related (equation)?
Wavelength = propagation speed/frequency
Propagation speed are determined by what characteristics of the medium?
Density which is the concentration of matter
Hardness which is the resistance of the material to compression
What medium has higher propagation speeds, solid or gas?
solid
What is non-linear propagation of a sound wave?
when higher pressure portions of the wave travel faster and lower pressure travel slower. This gives the wave a saw-tooth shape.
How many frequencies does a sinusoidal waveform have? a sawtoothed waveform?
one, multiple
What is the first frequency and subsequentfrequencies of a saw-toothed waveform called?
Fundamental, harmonics
What is the difference is CW US and Pulsed US
CW, US cycles repeat indefinitely
PW, pulses seperated by gaps in time. one pulse is a few cycles of US
When is Pulsed US used?
Sonography and most of Doppler US
What additional terms describe pulsed U/S over CW?
pulse-repitition frequency, pulse-repitition period pulse duration duty factor spatial pulse length
what is pulse repetition frequency (PRF)?
Number of pulses occurring in 1 second
what is pulse repetition period (PRP)?
time to the beginning of the next
When PRF increases what does PRP do?
Decreases
What is pulse duration?
the time that it takes for one pulse to occur
How many pulses for sonographic vs Doppler pulses
2-3, 5-20
How is pulse duration related to the period?
PD= period x # of cycles in the pulse (microsecs)
If frequency is increased what happens to the period?
decreases
If # of cycles in a pulse is reduced what happens to pulse duration?
it decreases
What give better sonographic images shorter or longer pulses?
Shorter pulses
What is Duty Factor?
the fraction of time that pulsed U/S is on (ie it is not on all the time so it is not 100%)
How is duty factor related to the pulse duration and pulse repetition period?
DF= PD/PRP
Duty factors for sonographics U/S vs Doppler?
0.1-1%, 0.5-5%
What is spatial pulse length?
the distance from the begining to the end of a pulse
What is amplitude?
the maximum variation that occurs in an acoustic variable
What is intensity?
The rate at which energy passes through a unit of area
What is the equation for intensity?
I=power/area (cm2)
What is power?
the rate at which energy is trasnferred
Is intensity constant across a sound beam?
no it highest in the center and falls of in the periphery
What happens to intensity in pulsed U/S
some value during the pulse and zero in between
Is intensity constant within pulses?
starts out high then decreases towards the end of the pulse
What is attenuation
The weakening of sound as it propogates
What are the consequences of attenuation? (2)
limits imaging depth, and we must compensate for attenuation with our imaging instrument
What causes attenuation?
As the sound beam travels amplitude and intensity will decrease. Sound is absorbed as it travels and sound scatters and is reflected off of tissue interfaces and heterogeneous tissue.
What units quantify attenuation?
decibels
What is the attenuation coefficient?
Attenuation that occurs with each centimeter the sound wave travles
As frequency increases what does attenuation do?
increases
as frequency increases what does penetration do?
decreases
In practice what kind of frequency is used for deeper penetration?
lower frequencies
What is the reflection and scattering of sounds waves at organ and tissue interface called?
Echoes
What is perpendicular incidence?
incident sound either reflect back the direction it came from or continues in the same direction (often both occur). the wave that continues is perpendicular incidence
What value is impedance measured in?
rayls
What is impedance?
relationship between acoustic pressure and the speed of particle vibrations in a sound wave.
What is the equation for impedance?
imp = density x propagation speed
What is intensity reflection coefficient? intensity transmission coefficient?
divide the echo intensity by the incident intensity and you get the intensity that is reflected (IRC)
divide the transmitted intensity by the incident intensity and you get the intensity that is transmitted to the second medium (ITC)
What is the incidence angle?
it is the angle measured from a line perpendicular to the surface used when the U/S is at an oblique incidence
For oblique incidence what happens to the reflected sound waves (reflection angle)?
they are reflected away from the transducer
What is refraction?
the change of direction of sound when crossing a boudary
what is transmission angle?
the angle away from a line perpendicular to the surface that the sound wave is travelling through the tissue
if propagation speeds are equal, what happens to the incidence angle and the transmission angle?
If propagation speed is greater in the second medium?
if the propagation speed is less in the second medium?
in which scenarios is there refraction?
the angle are equal
the transmission angle is greater
the transmission angle is less
the last two, if speed are equal there is no refraction
What is scattering?
redirection of sound in many directions by a heterogeneous object
Why is the U/S display a dot pattern?
it is displaying the interference pattern of the scatter distribution scanned
why do solids have higher propagation speed then liquids?
they have greater stiffness
What are odd harmonics of 2MHz?
EVEN?
6, 10, 14
4, 8, 12
If wavelength is 0.154 mm (over 1micros/sec) what is the propagation speed?
WL= propagation speed/time
1.54mm/microsec
The number of pulses occurring in one second is called what?
pulsed repetition frequency
What is the fraction of time the pulsed US is actually on for called?
Duty Factor
pulse duration = number of cycles in the pulse x what?
the period
the duty factor of CW doppler is what?
1 (100%)
What can be calculated if you have propagation speed and frequency?
wavelength
Which has higher propagation speed, higher or lower stiffness?
Higher
What is the first harmonic of 3 MHz?
6
If wavelength is 2 and the frequency is doubled, what does the wavelength become?
1
If propagation speed is doubled and frequency held constant, what happens to the wavelength?
It is doubled
What does non-linear propagation mean? (2)
depends on the pressure
waveform chages shape as it travels (saw-tooth)
If density is 100okg/m and propagation speed is 1540 m/s what is the impedence?
1540000 rayls
How many cycles are there in 1 second of CW 5 MHz US?
5000000
What is the unit for intensity?
W/cm2
Intensity is proportional to what value squared?
amplitude
If area is doubled and the power remains unchanged, what happens to intensity?
halved
If power is doubled and area remains unchanged what happens to intensity?
Double
If both power and area are doubled, what happens to intensity?
unchanged
If amplitude is doubled what happens to intensity?
quadrupled
If power is 10mW and bean area is 2 cm2, what is the spatial average intensity?
5mW/cm2
Multiplying pulse average intensity by duty factor yields what kind of intensity?
temporal average intensity
Which of the following are equal for CW
spatial peak, spatial average, temporal peak, temporal average
temporal peak and average
If duty factor 0.5 and pulse average intensity is 4 mW/cm2 what is the temporal average intensity?
2
attenuation is the reduction of what 2 factors?
intensity and amplitude
for soft tissue the attenuation per cm for each MHz of requency is what?
0.5
For soft tissue the attenuation coefficient at 3MHz is approximately what?
1.5 dB/cm
What does attenuation do in soft tissue when frequency increases?
increases
Absorption converts sound to what?
heat
Can absorption be greater then attenuation?
no attenuation includes asorption
Is attenuation higher in bone or soft tissue?
bone
What is the attenuation coefficient for soft tissue at 10MHz?
5 dB/cm
What is the attenuation coefficient for soft tissue at 10MHz?
2.5 db/cm
What does image depth (penetration) do when frequency increases?
decreases
If the intensity of a 4 MHz U/S entering soft tissue is 2 W/cm2, what is the intensity at 4cm?
0.32 W/cm2 (attenuation is 8dB and intensity ratio is 0.16)
