Ultrasound Physics
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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


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


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.
True

DF = PD (μs) / PRP (μs)
DF =( PD (μs) X PRF (kHz) ) / 1000 (kHz / MHz)

T/F
If pulse duration increases, duty factor ______.
increases

if PRF increases, pulse repetition period _____ and duty factor ________.

length of space over which a pulse occurs
spatial pulse length

Spatial pulse length = length of each cycle X the number of cycles in the pulse
SPL (mm) = n X λ (mm)

T/F
Spatial pulse length is the length of space that a pulse takes up.
True

T/F
If the number of cycles in a pulse increases, spatial pulse length increases. If frequency increases wavelength and spatial pulse length decrease.
True

T/F
Shorter pulses improve sonographic image resolution.
True

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


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)

2 medium characteristics that affect propagation speed

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
peaktopeak amplitude

rate of energy transfer
power

power is measured in
watts

power is _____ by the sonographer
adjustable

power is ______ to the amplitude ______

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
24

distance from the start of a pulse to the end of that pulse
spatial pulse length


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

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