Ultrasound Physics

pressure, density, and particle vibration; sound wave quantities that vary in space and time

region of low density and pressure in a compressional wave

reduction in differences between small and large amplitudes. region of high density and pressure in a wave

wave in which the particle motion is parallel to the direction of wave travel (compressional wave)

number of cycles per second

unit of frequency, one cycle per second; unit of pulse repetition frequency, one pulse per second.

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A wave is a traveling variation of some quantity or quantities.

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Sound is a traveling variation of acoustic variables.

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Acoustic variables include pressure, density, and particle motion.

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A cycle is one complete variation in pressure or other acoustic variable.

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Frequency is the number of cycles in a wave that occur in 1 second.

One hertz is one cycle per second. The abbreviation for hertz is Hz.

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One kilohertz is 1000 cycles per second. The abbreviation for kilohertz is kHz.

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One megahertz is one million cycles per second. The abbreviation for megahertz is MHz.

sound of frequency too low for human hearing (<20 hertz)

sound of frequency too high for human hearing (>20,000 hertz)

imaging depth

time per cycle

the common unit for period in ultrasound

Period = 1/Frequency

If frequency increases, period _______.

length of space over which a cycle occurs

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Wavelength is commonly expressed in millimeters.

the speed with which a wave moves through a medium

Wavelength is = propagation speed (c) divided by frequency

If frequency increases, wavelength ______.

the resistance of a material to compression

Propagation speeds are highest in ______ and lowest in ______.

Propagation speed values in soft tissue range from _____ to _____.

The average propagation speed of sound in tissue is _____.

progression of travel

sound propagation in which the propagation speed depends on pressure causing the wave to shape to change and harmonics to be generated

the primary frequency in a collection of frequencies that can include odd and even harmonics and subharmonics

frequencies that are even and odd multiples of another, commonly called fundamental or operating frequency

a wave in which cycles repeat indefinitely; not pulsed.

ultrasound produced in pulsed form by applying electric pulses or voltages of one or a few cycles to the transducer

a brief excursion of a quantity from its normal value; a few cycles

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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.

number of pulses per second

interval of time from the beginning of one pulse to the beginning of the next

PRF is commonly expressed in

PRP is commonly expressed in

PRP (ms) = 1 / PRF (kHz)

If pulse repetition frequency increases, pulse repetition period ______.

Interval of time from beginning to end of a pulse

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Shorter pulses, compared with longer ones, improve the quality of sonographic images.

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Sonographic pulses are typically 2 or 3 cycles long. Doppler pulses are typically 5 to 30 cycles long.

Pulse duration = period (time for one cycle) X number of cycles in the pulse (n)

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Pulse duration is the time for a pulse to occur.

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If frequency is increased, period is decreased, reducing pulse duration. If the number of cycles in a pulse is reduced, pulse duration is decreased.

fraction of time that pulsed ultrasound is on

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Longer pulses increase the duty factor because the sound is on more of the time.

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

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If pulse duration increases, duty factor ______.

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

length of space over which a pulse occurs

Spatial pulse length = length of each cycle X the number of cycles in the pulse

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Spatial pulse length is the length of space that a pulse takes up.

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

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Shorter pulses improve sonographic image resolution.

range of frequencies contained in an ultrasound pulse; range of frequencies within which a material, device, or system can operate.

bandwidth divided by operating frequency

nonspecific term referring to amplitude or intensity

maximum variation of an acoustic variable or voltage

power divided by area

rate at which work is done; rate at which energy is transferred

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If beam power increases, intensity increases. If beam area decreases (focusing), intensity increases.

force multiplied by displacement

conversion of sound to heat

decrease in amplitude and intensity with distance as a wave travels through a medium

portion of sound returned from a media boundary; echo

diffusion or redirection of sound in several directions upon encountering a particle suspension or a rough surface

reflection

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.

attenuation per centimeter of wave travel

time it takes a wave to vibrate a single cycle

Period is determined by the ________ _______.

the number of particular events that occur in a specific duration of time. in ultrasound, the number of cycles that occur in one second

Diagnostic range of frequency in ultrasound

Frequency is determined by the ______ _______.

Frequency and period have what type of relationship

distance or length of one complete cycle

wavelength is determined by the ______ ______ and the _____.

shorter wavelengths produce ______ quality images

frequency and wavelength have a _______ relationship as long as they are in the same medium

the distance that a sound wave travels through a medium in 1 second

propagation speed is determined by the

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

other name for stiffness

propagation speed and density are ______ related

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 is _______ by the sonographer

the difference between the maximum and minimum values of an acoustic variable

rate of energy transfer

power is measured in

power is _____ by the sonographer

power is ______ to the amplitude ______

concentration of energy in a sound beam

intensity = power/cross sectional area

Intensity is measured in

intensity is _______ by the sonographer

intensity and power are ________

intensity is proportional to the amplitude _______

What parameters describe pulsed sound?

the actual time from the start of a pulse to the end of that pulse

pulse = # cycles X period

pulse duration = # cycles / frequency

pulse duration is ______ to the number of cycles in the pulse

pulse duration is ______ proportional to the period

Pulse duration is _______ proportional to the frequency

long pulses have either

short pulses have either

clinical imaging uses pulses that contain how many cycles

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

SPL = # of cycles X λ

SPL is ______ proportional to the number of cycles

SPL is ______ proportional to the wavelength

SPL is _______ proportional to frequency

The major difference between SPL and PD

time from the start of one pulse to the start of the next pulse . includes the pulse duration and the listening time

PRP is related to the ____ of view

PRP and imaging depth are ______ related

the number of pulses that are transmitted into the body each second

depth of view and PRF are ______ related

PRP and PRF are _______ related and ______

seconds (PRP) go with hertz (PRF)
milliseconds (PRP) go with ______ (PRF)

the percentage of time or fraction of time that the system is transmitting a pulse

duty factor% = (pulse duration / PRP) X 100

a duty factor of 1 would refer to a ______ wave

a duty factor of 0 means the system is _____

duty factor is _____ related to imaging depth

What are the 7 parameters required to completely characterize a sound wave?

tissue/material through which the sound waves travel

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