Chapter 2 Kremkau Flashcards
conversion of sound to heat
absorption
derived from the Greek word for hearing
Acoustic
pressure, density, and particle vibrations
acoustic variables
indicators of the strength of sound, related to how loud the sound would be if it could be heard
amplitude
the weakening of sound while it propagates
attenuation
the attenuation that occurs with each centimeter the sound wave travels. Its units are decibels per centimeter. The farther the sound travels the greater the attenuation
attenuation co-efficient
decibels per centimeter
attenuation
sound scattered back in the direction from which it originally came
backscatter
range of frequencies
bandwith
the shorter the pulse, the _____ the bandwidth
broader
regions of high pressure and density
compression
echoes that arrive at transducer in such a way that they reinforce each other
constructive interference
ultrasound in which cycles repeat indefinitely
continuous wave
liquid suspensions that are injected into the circulation intravenously are used to increase echogenicity
contrast agents
a gel that is used to provide a good sound path from the transducer
coupling medium
pressure and density increase and decrease, and particles of the medium oscillate in motion
cycle
units used to quantify attenuation
decibel
the concentration of matter
(mass per unit volume)
density
echoes that may arrive at the transducer in such a way that they partially or totally cancel each other out
destructive interference
the fraction of time that pulsed ultrasound is on. Indicates how much of the time the ultrasound is on
duty factor
the reflected and scattered sound waves
echo
the ability to accomplish work
energy
bandwidth divided by operating frequency. Unitless. Describes how large the bandwidth is compared with operating frequency
fractional bandwidth
expresses the number of cycles in a wave that occur in 1 second
frequency
original frequency
fundamental frequency
any other wave shape containing additional frequencies that are even and odd multiples of the original frequency
harmonics
one cycle per second
hertz
determines how much of an incident sound wave is reflected back into the first medium and how much is transmitted into the second medium. Equal to the density of a medium multiplied by the propagation speed in it. Increases if density increases or if propagation speed increases
impedance
unit for impedance
Rayl
the direction of travel with respect to the boundary given
incidence angle
the rate at which energy passes through a unit area
intensity
dividing the reflected (echo) intensity by the incident intensity that is reflected
intensity reflection coefficient
dividing the transmitted intensity by the incident yields the fraction of the incident intensity that is transmitted into the second medium
intensity transmission coefficient
scatterers moving in and out of beam, interference alternates between being constructive and being destructive, resulting in a displayed dot pattern - a grainy appearance - that does not directly represent scatterers but, rather, represents the interference pattern of the scatterer distribution scanned
interference
1,000 Hz
Kilohertz
sound is a mechanical, compressional wave in which back and forth particle motion is parallel to direction of wave travel. Also know as compressional wave.
Longitudinal wave
a thing that sound propagates through
medium
1,000,000 Hz
Megahertz
propagation in which speed depends on pressure and the shape of the wave changes
nonlinear propagation
when the incident sound beam encounters the boundary between two mediums at an angle
oblique incidence
half-value depth for the specific ultrasound frequency
penetration
the time is takes for one cycle to occur
period
denotes a direction of travel of the ultrasound wave perpendicular to the boundary between the two media
perpendicular incidence
the rate at which energy is transferred from one part of a system to another or from one location to another. Energy transferred divided by the time required to transfer, that is, the transfer rate.
Power
Units of Power
Watts and MilliWatts
sound is a traveling variation in _______.
pressure
the speed at which a particular value of an acoustic variable moves, at which a cycle moves, and at which the entire wave moves
propagation
the speed with which a wave moves through a medium
propagation speed
ultrasound pulse is a few cycles of ultrasound. They are separated in time with gaps of no ultrasound
pulse
the time it takes for one pulse to occur. Equal to period times the number of cycles in the pulse. Expressed in microseconds
pulse duration
the number of pulses that occur in 1 second
pulse-repetition frequency
refers to the time from the beginning of one pulse to the beginning of the next. Its common units are milliseconds.
Pulse-repetition period
not on continuously. a few cycles of ultrasound
pulsed ultrasound
the distance to a reflector calculated from the propagation speed and pulse-round trip travel time
range equation
regions of low pressure and density
rarefaction
return of the sound wave back to the transducer
reflection
a change in acoustic impedance across a boundary between tissues
refraction
cellular tissues or particle suspensions such a blood
scatterer
the redirection of sound in many directions by rough surfaces (sometimes called diffuse scattering) or by heterogeneous media
scattering
transverse wave
shear wave
the length of a pulse from front to back. Equal to the length of each cycle times the number of cycles in the pulse
Spatial pulse length
a form of acoustic noise in sonographic imaging
speckle
a type of surface reflectance often described as a mirrorlike reflection of light from the surface
specular reflection
the resistance of a material to compression
stiffness
related to how loud the sound would be if it could be heard. Amplitude and intensity are indicators
strength
depends on propagation speeds in the media
transmission angle
shear wave
transverse wave
frequency higher than the range of human hearing
ultrasound
a traveling variation in one or more quantities called wave variables
wave
the length of space that one cycle takes up
wavelength
sound of a frequency too low for human hearing
infrasound
if frequency increases, period _______.
decreases
if frequency increases, wavelength _______.
decreases
Highest propagation speeds
solids
lowest propagation speeds
gases
average propagation speed in soft tissues
1.54 mm/us
If PRF increases, PRP ________.
decreases
Sonographic pulses are typically __-__ cycles long
2-3
Doppler pulses are typically __-__ cycles long
5-30
If frequency increases, pulse duration _______.
decreases
If the number of cycles in a pulse is decreased, pulse duration is _______.
decreases
If the pulse duration increases, the duty factor ______.
increases
If PRF increases, duty factor _______.
increases
if the number of cycles in a pulse increases, SPL ______.
increases
_______ pulses improve sonographic image detail resolution
shorter
if beam power increases, intensity ________.
increases
if attenuation coefficient increases, attenuation _______.
increases
if path length increases, attenuation _______.
increases
if frequency increases, attenuation ________.
increases
if frequency increases, penetration ________.
decreases
impedance increases if density of propagation speed ______.
increase
if the difference between the impedances increases, the ITC _______.
increases
if IRC increases, ITC _______.
decreases
while round trip time increases, calculated reflector distance _______.
increases
frequency
period
wavelength
propagation speed
amplitude
intensity
terms used to describe sound
when pressure is higher, the medium is ______.
denser
when pressure is lower, the medium is ________.
less dense
human hearing range
20-20,000 Hz
Infrasound range
less than 20 Hz
Ultrasound range
20,000 Hz or more
T = 1 / f
Period
also known as cycle length
wavelength
propagation speed units
m/s mm/us
wavelength depends on ______ and ____.
frequency
propagation speed
^ = c / f
wavelength
Shear wave propagation speeds in soft tissues
.5 - 10 m/s
rate of change of a position of an object
speed
speed with direction of motion specified
velocity
propagation speed depends on ______ and ______.
density
stiffness
c (m/s) = elasticity / density
propagation speed
increase in stiffness, _______ propagation speed
increases
increase in density ______ propagation speed
decreases
In nonlinear propagation, propagation speed depends on ______.
pressure
PRF units
kHz
PRP units
milliseconds
PRP decreases, PRF _______
increases
PD = n x T
pulse duration
PD decreases if number of cycles in pulse _______.
decreases
PD decreases if frequency _______.
increases
Duty factor continuous wave
100%
_______ pulses increases duty factor
longer
Higher PRFs _________ DF
increases DF
units of DF
no units
DF = PD (us) / PRP (us) = PD (us) x PRF (kHz) / 1000 kHz/MHz)
Duty Factor
Typical DFs for sonography
.1-1.0%
Typical DFs for Doppler ultrasound
.5-5%
SPL = ^ x n
Spatial pulse length
SPL increases with _______ and ________.
wavelenth
SPL increases with _______ and ________.
wavelength
number of cycles in the pulse
SPL decreases with ________ frequency.
increasing
units for spatial pulse length
mm
shorter pulse lengths ______ resolution
improve
the higher number of frequencies, the _______ the bandwidth
broader
determines the number of scan lines produced per second
frequency
operating frequency / bandwidth
quality factor
shorter pulses have broader bandwidth and ______ QFs.
lower
indicators of the strength of sound
amplitude and intensity
energy transferred divided by time required to transfer energy (transfer rate)
power
units for power
watts and milliwatts
beam area units
cm squared
intensity units
w/cm2 mw/cm2
power divided by amplitude
Intensity
increase in power ______ intensity
increases
increase in area _______ intensity
decreases
proportional to amplitude squared
intensity
if amplitude is doubled, intensity is ________.
quadrupled
if amplitude is halved, intensity is _______.
quartered
the greatest intensity found across the beam
spatial peak
the average for all values found near the center and the small values near the periphery
spatial average
the greatest intensity found in the pulses as it passes by
temporal peak
the average for all values found in a pulse include the large values found at its beginning and the smaller values found near the end
pulse average
includes the “dead” time between pulses where there is zero intensity
temporal average
TA = PA x DF
temporal average
reduction in amplitude and intensity as sound travels through
attenuation
dominant factor of attenuation
absorption
attenuation coefficient units
db/cm
corresponds to an intensity ratio of one-half, that is, an intensity reduction of 50%
3dB
corresponds to an intensity ratio of one-tenth, that is, an intensity reduction of 90%
10 db
a (dB) = ac (db/cm) x L (cm)
attenuation
attenuation coefficient increases, attenuation _______.
increases
attenuation increases with _______ frequency.
increasing
in soft tissues, there is approximately _____dB of attenuation per centimeter for each megahertz of frequency for a longitudinal wave
.5
a = 1/2 f (MHz) x L (cm)
attenuation
equal to the fraction of the intensity (at the beginning of the path) that remains at the end of the path
intensity ratio
Penetration decreases while frequency ______.
increases
Intensities of the echo and transmitted sound depend on:
incident intensity at boundary
impedances of the media on either side of the boundary
Impedance increases if density or propagation speed ______.
increases
z = pc
impedance
average soft tissue impedance
1,630,000 rayls
IRC depends on _____
impedances
IRC = R / I = z2 - z1 / z2 + z1 ^2
intensity reflection coefficient
the greater the differences in impedances the _____ the echo
stronger
ITC = T/I = 1 - IRC
intensity transmission coefficient
if ITC increases, IRC
decreases
if impedances are equal than _____
no echo
Reflection angle always equals the _______.
incidence angle
No refraction occurs if propagation speeds are ______.
equal
2 requirements for refraction to occur
oblique incidence
different propagation speeds
Most contrast agents contain
microbubbles of gas
In soft tissue, the round trip time is ___ us for each centimeter of depth.
13
D (mm) = 1/2 [c x pulse round trip time]
range equation
a wave is a traveling variation in quantities called wave _____.
variables
sound is a traveling variation in quantities called _____ variables.
acoustic
acoustic variables include ______, _______, and particle motion.
pressure, density
The wavelength of a 7-MHz ultrasound in soft tissues is ____.
.22
It takes __ us for ultrasound to travel 1.54 cm in soft tissue.
10
If propagation speed is doubled and frequency is held constant, the wavelength is ______.
doubled
if frequency in soft tissue is doubled, propagation speed is ______.
unchanged
if wavelength is 2mm and frequency is doubled, the wavelenth becomes ____.
1
The second harmonic of 3 MHz is ____ MHz.
6 MHz
Odd harmonics of 2 MHz are ______ MHz.
6, 10, 14
Even harmonics of 2 MHZ are _____ MHz.
4, 8, 12
If the density of a medium is 1000 kg/cm3 and the propagation speed is 1540 m/s, the impedance is ____ rayls.
1,540,000
If the wavelength is 2mm, the SPL for a three-cycle pulse is ____ mm.
6
the SPL in soft tissue for a two-cycle pulse of frequency 5 MHz is ____ mm.
.6
The PD in soft tissue for a two-cycle pulse of frequency 5 MHz is ____us.
.4
For a 1-kHz PRF, the PRP is _____ ms.
1
How many cycles are there in 1 second of continuous wave 5 MHz ultrasound?
5.000,000
how many cycles are there in 1-seecond of pulsed 5 MHz ultrasound with a DF of .01 (1%)?
none of the above
