pressure, density, and particle vibration; sound wave quantities that vary in space and time
acoustic variables
region of low density and pressure in a compressional wave
rarefaction
reduction in differences between small and large amplitudes. region of high density and pressure in a wave
compression
wave in which the particle motion is parallel to the direction of wave travel (compressional wave)
longitudinal wave
number of cycles per second
frequency
unit of frequency, one cycle per second; unit of pulse repetition frequency, one pulse per second.
hertz
T/F
A wave is a traveling variation of some quantity or quantities.
True
T/F
Sound is a traveling variation of acoustic variables.
True
T/F
Acoustic variables include pressure, density, and particle motion.
True
T/F
A cycle is one complete variation in pressure or other acoustic variable.
True
T/F
Frequency is the number of cycles in a wave that occur in 1 second.
True
One hertz is one cycle per second. The abbreviation for hertz is Hz.
True
T/F
One kilohertz is 1000 cycles per second. The abbreviation for kilohertz is kHz.
True
T/F
One megahertz is one million cycles per second. The abbreviation for megahertz is MHz.
True
sound of frequency too low for human hearing (<20 hertz)
Infrasound
sound of frequency too high for human hearing (>20,000 hertz)
Ultrasound
imaging depth
penetration
time per cycle
period
the common unit for period in ultrasound
microsecond (μs)
Period = 1/Frequency
T (μs) = 1 / f (MHz)
If frequency increases, period _______.
decreases
length of space over which a cycle occurs
wavelength
T/F
Wavelength is commonly expressed in millimeters.
True
the speed with which a wave moves through a medium
propagation speed
Wavelength is = propagation speed (c) divided by frequency
λ (mm) = c (mm/μs) / f (MHz)
If frequency increases, wavelength ______.
decreases
the resistance of a material to compression
stiffness
Propagation speeds are highest in ______ and lowest in ______.
solids (highest)
gases (lowest)
Propagation speed values in soft tissue range from _____ to _____.
1.44 to 1.64 mm/μs
The average propagation speed of sound in tissue is _____.
1.54 mm/μs
progression of travel
propagation
sound propagation in which the propagation speed depends on pressure causing the wave to shape to change and harmonics to be generated
nonlinear propagation
the primary frequency in a collection of frequencies that can include odd and even harmonics and subharmonics
fundamental frequency
frequencies that are even and odd multiples of another, commonly called fundamental or operating frequency
harmonics
a wave in which cycles repeat indefinitely; not pulsed.
continuous wave
ultrasound produced in pulsed form by applying electric pulses or voltages of one or a few cycles to the transducer
pulsed ultrasound
a brief excursion of a quantity from its normal value; a few cycles
pulse
T/F
With continuous wave ultrasound, cycles repeat indefinitely. Pulsed ultrasound consists of pulses separated by gaps in time. A pulse is a few cycles of ultrasound.
True
number of pulses per second
pulse repetition frequency or pulse repetition rate
interval of time from the beginning of one pulse to the beginning of the next
pulse repetition period
PRF is commonly expressed in
kilohertz
PRP is commonly expressed in
milliseconds
PRP (ms) = 1 / PRF (kHz)
If pulse repetition frequency increases, pulse repetition period ______.
decreases
Interval of time from beginning to end of a pulse
pulse duration
T/F
Shorter pulses, compared with longer ones, improve the quality of sonographic images.
True
T/F
Sonographic pulses are typically 2 or 3 cycles long. Doppler pulses are typically 5 to 30 cycles long.
True
Pulse duration = period (time for one cycle) X number of cycles in the pulse (n)
PD (μs) = n X T (μs)
T/F
Pulse duration is the time for a pulse to occur.
True
T/F
If frequency is increased, period is decreased, reducing pulse duration. If the number of cycles in a pulse is reduced, pulse duration is decreased.
True
fraction of time that pulsed ultrasound is on
duty factor
T/F
Longer pulses increase the duty factor because the sound is on more of the time.
range of frequencies contained in an ultrasound pulse; range of frequencies within which a material, device, or system can operate.
bandwidth
bandwidth divided by operating frequency
fractional bandwidth
nonspecific term referring to amplitude or intensity
strength
maximum variation of an acoustic variable or voltage
amplitude
power divided by area
intensity
rate at which work is done; rate at which energy is transferred
power
T/F
If beam power increases, intensity increases. If beam area decreases (focusing), intensity increases.
True
force multiplied by displacement
work
conversion of sound to heat
absorption
decrease in amplitude and intensity with distance as a wave travels through a medium
attenuation
portion of sound returned from a media boundary; echo
reflection
diffusion or redirection of sound in several directions upon encountering a particle suspension or a rough surface
scattering
reflection
echoes
unit of power or intensity ratio; the number of decibels is 10 times the logarithm (to the base 10) of the power or intensity ratio.
decibel
attenuation per centimeter of wave travel
attenuation coefficient
time it takes a wave to vibrate a single cycle
period
Period is determined by the ________ _______.
sound source
the number of particular events that occur in a specific duration of time. in ultrasound, the number of cycles that occur in one second
frequency
Diagnostic range of frequency in ultrasound
2 MHz - 10 MHz
Frequency is determined by the ______ _______.
sound source
Frequency and period have what type of relationship
inversely proportional and a reciprocal relationship
distance or length of one complete cycle
wavelength
wavelength is determined by the ______ ______ and the _____.
sound source and medium
shorter wavelengths produce ______ quality images
higher
frequency and wavelength have a _______ relationship as long as they are in the same medium
inverse
the distance that a sound wave travels through a medium in 1 second
propagation speed
propagation speed is determined by the
medium
order the medium that sound travels the fastest in (normal states of matter)
solids
liquids
gases
2 medium characteristics that affect propagation speed
stiffness
density
propagation speed and stiffness are ______ related
directly
other name for stiffness
bulk modulus
propagation speed and density are ______ related
inversely
the difference in the maximum value and the average or undisturbed value of an acoustic variable may also be the difference between the minimum and the average
amplitude
amplitude is _______ by the sonographer
adjustable
the difference between the maximum and minimum values of an acoustic variable
peak-to-peak amplitude
rate of energy transfer
power
power is measured in
watts
power is _____ by the sonographer
adjustable
power is ______ to the amplitude ______
proportional
squared
concentration of energy in a sound beam
intensity
intensity = power/cross sectional area
Intensity is measured in
watts/cm ^2
intensity is _______ by the sonographer
adjustable
intensity and power are ________
proportional
intensity is proportional to the amplitude _______
squared
What parameters describe pulsed sound?
pulse duration
pulse repetition period
pulse repetition frequency
duty factor
spatial pulse length
the actual time from the start of a pulse to the end of that pulse
pulse duration
pulse = # cycles X period
pulse duration = # cycles / frequency
pulse duration is ______ to the number of cycles in the pulse
proportional
pulse duration is ______ proportional to the period
directly
Pulse duration is _______ proportional to the frequency
directly
long pulses have either
many cycles
individual cycles with long periods
short pulses have either
few cycles in the pulse
individual cycles with short periods
clinical imaging uses pulses that contain how many cycles
2-4
distance from the start of a pulse to the end of that pulse
spatial pulse length
SPL = # of cycles X λ
SPL is ______ proportional to the number of cycles
directly
SPL is ______ proportional to the wavelength
directly
SPL is _______ proportional to frequency
inversely
The major difference between SPL and PD
SPL refers to distance
PD refers time
time from the start of one pulse to the start of the next pulse . includes the pulse duration and the listening time
PRP
PRP is related to the ____ of view
depth
PRP and imaging depth are ______ related
directly
the number of pulses that are transmitted into the body each second
Pulse repetition frequency
depth of view and PRF are ______ related
inversely
PRP and PRF are _______ related and ______
inversely related and reciprocals
seconds (PRP) go with hertz (PRF)
milliseconds (PRP) go with ______ (PRF)
kilohertz
the percentage of time or fraction of time that the system is transmitting a pulse
duty factor
duty factor% = (pulse duration / PRP) X 100
a duty factor of 1 would refer to a ______ wave
continuous wave
a duty factor of 0 means the system is _____
off
duty factor is _____ related to imaging depth
inversely
What are the 7 parameters required to completely characterize a sound wave?
period
frequency
wavelength
speed
amplitude
power
intensity
tissue/material through which the sound waves travel
medium
3 parameters describe the size, magnitude, or strength of a sound wave
amplitude
power
intensity
10^9 giga G billion
10^6 mega M million
10^3 kilo k thousand
10^2 hecto h hundred
10^1 deca da ten
10^-1 deci d tenth
10^-2 centi c hundredth
10^-3 milli m thousandth
10^-6 micro µ millionth
10^-9 nano n billionth