Section 1
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PRF and frequency are
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Last updated
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Date created
Mar 1, 2020
Cards (164)
Section 1
(50 cards)
PRF and frequency are
independently controlled by the sonographic instrument Not related
Frequency units
Hertz (Hz)
increasing density
decreases the speed of sound in tissues
Human hearing
20 Hz to 20,000 Hz
Continuous Wave vs Pulsed ultrasound
Ultrasound in which cycles repeat indefinitely Not used Pulses: Separated in time with gaps of no ultrasound
The stiffer the media , the ___ sound propagates
faster
Stiffness
resistance of a material to compression EX: Sponge=low stiffness/high compressibility/low sound speeds rock=high stiffness/low compressibility/high sound speeds
Pulse Duration
Time it takes for 1 pulse to occur PD(us)=NcxT(us)
Another word for sound traveling
Propagates
propagation speed is determined by
the medium primarily its stiffness (hardness)
When the pressure is higher, the medium is
more dense
fundamental frequency
original frequency
Density
mass/volume
Average propagation speed in soft tissues
1540 m/s or 1.5 mm/us
Acoustic Variables
1. Pressure 2. Density 3. Temperature 4. Particle Motion
Wavelength
-Length of space that one cycle takes up -Distance from the beginning to the end of one cycle -Cycle length -mm Y(mm)=c(mm/us)/f(Mhz) c=1.54 mm/us
Bone propagation speed is ___ than soft tissue because ____
speeds are higher because more solid
Nonlinear propagation
propagation in which speed depends on pressure and the shape of the wave changes
the higher the temp of a solid or liquid, the ___ the propagation of sound waves
faster
Pressure
Cyclic variations of mechanical force; sine wave
Why is propagation speed important?
sonographic instruments use it to accurately locate echoes on the display
Frequency
-measurement of how often something happens -count of how many complete cycles of pressure occurs in 1 sec f=#of cycles in 1 sec
PRP/PRF equation
PRP (ms) = 1/PRF(kHz)
PRF
# of pulses in 1 sec Units: Kilohertz (kHz)
Lung tissue propagation speed is ____ than soft tissue because ____
much lower speed because lung has air
Period
-the time that it takes a complete cycle or wave oscillation to occur -T(us)=1/f(Mhz)
Rarefraction
Regions of low pressure and density
Sound requires what to travel?
Medium cannot be vacuum
Transverse Wave
motion perpendicular to the direction of wave travel. EX: light, radio, and microwaves Electromagnetic waves are transverse waves of electric and magnetic fields that involve no particle motion
Why is the use of harmonics important?
Harmonic frequency echoes improves the quality of sonographic images
PRP related to PRF
Reciprocal PRP (ms) = 1/PRF(kHz) When more pulses occur in a sec, the time between them decreases
Period equation
T(us)=1/f(Mhz)
Longitudinal Wave
back and forth particle motion is parallel to the direction of wav travel Ex: Sound waves
PRP
time from the beginning of one pulse to the beginning of the next pulse Units: ms
PRF increases while PRP
decreases
Ultrasound
Sound waves with frequencies above 20,000 Hz.
high temp ____ the density of medium
lower
When the pressure is lower, the medium is
less dense
Propagation speeds are highest in ____ and lowest in _____
highest in solids lowest in gases
If frequency increases, the wavelength will
decrease
If frequency increases, period
decreases
Sound is described by
frequency period wavelength Propagation speed Amplitude Intensity
Harmonics
The even and odd multiples
Wave
Traveling variation in one or more quantities
A cycle is
one complete variation in pressure or other acoustic variable
Sound is a
-Mechanical compressional wave -Longitudinal wave -Traveling variation of acoustic variables
Infrasound
Sound waves with frequencies below 20 Hz.
Why is PRF important?
determines how quickly images are generated
Wavelength equation
λ(mm)=c(mm/us)/f(MHz)
Compression
Regions of high pressure and density
Section 2
(50 cards)
DF units
none Decimal or percentage
Why is Attenuation important?
1. Limits imaging depth 2.its weakening effects on the image must be compensated by the diagnostic instrument.
Longer the SPL, ______ the attenuation
the greater the attenuation
If attenuation coefficient increases, attenuation ________
increase
PD decreases if the number of cycles in a pulse is ___
decreased or frequency is increased
PRF determines
# of scan lines produced pr second and #of images produced pr second (FR)
SPL equation:
SPL(mm)=Nc x λ(mm)
Spatial Pulse Length
the length of a pulse
If the attenuation coefficient increases, attenuation
increases a=acxL
Impedance
determines how much of an incident sound wave is reflected back into the first medium and how much is transmitted into the second medium Units:Rayls z(rayls) = p(kg/m^3) x c(m/s)
Attenuation
weakening of sound while it propagates Units: Decibels a(dB)=1/2(dB/cm-MHz) x f(MHz) x L (cm) a(dB)=ac(dB/cm)xL(cm) attenuation=absorption + scattering
Energy
the ability to do work Ex:Heat, light, x-rays, microwaves, mechanical motion
Impendance increases if
density increases or Propagation increases z=p x c
If the path length increases ... attenuation ...
increases
PD equation
PD(us)=NcxT(us)
Sonographic pulses are typically ____ or ____ cycles long.
2 or 3 cycles
Amplitude
The measure of how far the particles in the medium move away from their normal rest position. Max-normal=Amplitude
If PRF increases, then DF
increases
Intensity and Amplitude
I=Amplitude^2
Absorption
conversion of sound to heat
If the frequency increases, Attenuation ____
Increases a=1/2 x f x L
What are strength indicators of sound
Intensity and amplitude
attenuation coefficient
Attenuation that occurs with each centimeter Units: dB/cm a=ac(dB/cm) x L(cm)
If amplitude is halved, intensity is
quartered
Higher/increasing PRF ____ the DF because
increases DF because there is less listening time between pulses
Perpendicular incidence
sound direction that is perpendicular to the boundary between media
Bandwith
The range of frequencies with a given band, in particular that is used for transmitting a signal.
intensity reflection coefficient (IRC)
IRC=Ir/Ii [(Z2-Z1)/(Z2+Z1)]^2 Reflected/Incident
Intensity transmitted coefficient (ITC)
ITC=It/Ii 1-IRC Transmitted/incident
The intensities of the reflected sound and the transmitted sound depend on the
incident intensity at the boundary and the impedances of the media on either side of the boundary
Longer pulses ___ the DF because ____
increase DF because the sound is on more of the time
Duty Factor
Fraction of time that pulsed ultrasound is on
What is the reciprocal of bandwidth called?
quality factor (Q)
Sum of the reflected and transmitted intensities must equal
1
Attenuation is higher in ___ than soft tissue
lung and bones
The shorter the pulse (few # of cycles) the ___ the number of frequencies it contains (___ bandwidth)
Shorter the pulse, higher number of frequencies, Broader bandwidth
DF equation
DF = PD(us)/PRP(us)
Shorter SPL's create images with... A) less detail B) does not change C) greater detail
greater detail improves resolution
Typical DF for sonography is
range of 0.1% and 1.0%
What is the dominant factor that contributes to attenuation of ultrasound in soft tissue?
Absorption
The farther the sound travels, the ________ the attenuation
greater
Power
-rate at which energy is transferred from one part of a system to another -energy transferred/the time rquired to transfer energy Units:Watts (W)
fractional bandwidth
bandwidth divided by operating frequency -Unitless
attenuation increases, frequency
increases a=1/2 x f x L
Sound is a form of what kind of energy?
mechanical energy
Shorter pulses ____ the quality of sonographic images
improve!
The greater the difference between the impedances...
the stronger the echo
Intensity
rate at which energy passes through a unit area I(mW/cm^2)=P(mW)/A(cm^2)
If the amplitude is doubled, the intensity is
quadrupled
The greater the similarity of the impedances...
the weaker the echo
Section 3
(50 cards)
Why is scattering beneficial in ultrasound?
Need to see the "fog" and not mirror the transducer
propagation speed of 2 mediums and transmitted and incident angle
If c1<c2 then 0i<0t c1>c2 then 0i>0t
Sound is a traveling variation in quantities called
acoustic variables
If IRC increases, the ITC
decreases
Speckle
form of acoustic noise in sono imaging
lower freq = ____ sensitivity
better sensitivity because more penetration
Nonlinear propagation means that __________.
propagation speed depends on pressure, the waveform changes shape as it travels and harmonics to be generated
Scattering
redirection of sound in many directions by rough surfaces or by heterogeneous media such as blood
Attenuation is the reduction in ___ and ___ as a wave travels through a medium
Amplitude and intensity
A wave is a traveling variation in quantities called
wave variables
the DF for a pulse ultrasound is
always less than 1
Refraction
Change in direction of sound when it crosses a boundary
With perpendicular incidence, two media ______ and the incident _______ must be known to calculate the reflected intensity.
impedances, intensity
range equation:
d(mm)= 1/2(c x t) c=1.54 t=13us or t(us)/13(us/cm)= d(cm)
Under what 2 conditions does refraction not occur?
1.perpendicular incidence 2. equal media propagation speeds
Specular reflection
Mirror-like reflection smooth and flat boundary
The greater the elasticity, the ___ the velocity
slower velocity= 1/elasticity
2 requirements for refraction to occur
oblique incidence different propagation speed on either side of the boundary
To position the echoes properly on the display , what 2 items of information are required
1. direction from which the echo came 2.the distance to the reflector or scatterer where the echo was produced
the DF of a continuous wave sound is
1 (100%)
If the direction of sound changes when it crosses a boundary...
the transmission angle is different from the incident angle (Refraction)
Sound Beam Sensitivity
The ability of the sound beam to reach and display the weakest echoes
Image depth also is referred to as
penetration
Perpendicular incidence
incidence angle is 0
Propagation speed equation
c=square root(B(Bulk modulus)/p(density)
The transmitted angle depends on
propagation speeds in the media
If you have a stronger echo ..
less remains to travel into the second medium
sound is a
A mechanical longitudinal wave
Greater amplitude, ___ PD
longer *No change in frequency
SPL is the
length of space that a pulse occupies while it travels
If the media impedances are the same
no echo because no sound is reflected at the boundary and all of it travels into the second medium as if there are no boundary
13us/cm rule
13 us time for very centi
Attenuation is the weakening of sound caused by
absorption , reflection, and scattering
imaging depth decreases
PRF increases
Bulk modulus
measure of stiffness of medium or resistance of medium to being compressed Equation: C=Square root of B/p(density)
How to calculate transmitted angle
Med 2/ Med 1 = ratio Ratio x angle of incidence or refraction = transmitted
Elasticity
demonstrate by a return to the original shape when the pressure is lowered to its initial value
Oblique incidence
direction of travel of the incident ultrasound that is not perpendicular to the boundary between 2 mediums
The incidence angle is always equals the
reflection angle 0i=0r
When ultrasound encounrers a boundary with perpendicular incidence, the ___ of tissues must be different to produce a reflection (echo)
impedance
Absorption can be greater than attenuation in a given medium at a given frequency(T/F)
False Atten=abs+scatt
If the propagation speed through the second medium is greater than through the first medium, the transmission angle is ________.
greater than the incident angle (refraction)
Incident angle is zero (Perpendicular) there is ____ refraction with 2 different propagation speeds of 2 media
no refraction even though there may be different propagation speeds in the media
Amplitude is the maximum _________ that occurs in an acoustic variable.
variation
Coupling medium
provide good sound path from the transducer to the skin eliminating the thin layer of air that would reflect sound
Incident angle
the angle between the incident ray and the normal
Elasticity depends on
strength of the force and elastic properties of the object
Backscatter
sound scattered back in the direction from which it originally came
What is a typical DF for sonography?
0.1
Oblique incidence reflected sound...
does not return to the transducer but travels off in some other direction
Section 4
(14 cards)