Ultrasound Physics and Wave Parameters

Vocabulary flashcards covering the basics of ultrasound physics, sound wave characteristics, pulsed waves, intensities, interactions of sound with media, and the range equation.

Mega-

Million

Micro-

Millionth

X-axis

Runs side to side / horizontal

Y-axis

Runs up & down / vertical

Unrelated

Not associated with each other

Related / Proportional

Are associated with each other

Directly Related / Proportional

Associated that when one increases, the other increases

Inversely Related / Proportional

Associated that when one increases, the other decreases

Reciprocal Relationship

Multiplied together it equals one

Length Units

$\text{cm}$ and $\text{ft}$

Area Units

$\text{cm}^2$ and $\text{ft}^2$

Volume Units

$\text{cm}^3$ and $\text{ft}^3$

Media

Substance or material through which a wave, like a sound wave, travels + transfers energy

Mechanical Wave

Particles in medium move

Compression

Pushed together

Rarefaction

Stretched apart

Acoustic Propagation Properties

Effect of medium upon the sound wave

Biologic Effects

Effects sound waves have on tissue

Acoustic Variable

Pressure, density, distance

Pressure

Force in an area / $\text{Pa}$

Density (Chapter 2)

Mass in volume / $\text{kg/cm}^3$

Particle Motion

Something other than pressure, density, or distance

Acoustic Parameters

Period, frequency, amplitude, power, intensity, wavelength, propagation speed

Transverse Waves

Particles move perpendicular to direction of wave

Longitudinal Waves

Particles move in same direction that the wave goes

In-phase waves

Peaks occur at same time

Out-of-phase waves

Peaks occur at different times

Interference

Combine to create single wave

Constructive Interference

Resultant wave is larger

Destructive Interference

Resultant wave is smaller

Parameters

Describe features of a sound wave

Sound Source

Ultrasound system & transducer

Medium

The tissue

Period

Time it takes a wave to vibrate a single cycle

Frequency

of events that occur in a specific duration of time

Infrasound

Sound wave less than $20\,\text{Hz}$ / so low humans can't hear

Audible Sound

Frequencies between $20\,\text{Hz} - 20,000\,\text{Hz}$ / can hear

Ultrasound

Frequency higher than $20,000\,\text{Hz}$ ($20\,\text{kHz}$) / too high we can't hear

Hertz

Events per second

Cycle

Our event

Magnitude

Strength of magnitude

Amplitude

The bigness of a wave

Peak to Peak Amplitude

Difference between max & min values

Power

Rate of energy transfer

$$\propto$$

Proportional to

Intensity (Chapter 3)

Concentration of energy in a sound beam

Wavelength

Length of 1 complete cycle

Propagation Speed

Rate a sound wave travels through a medium

Soft Tissue

Typical biological medium

Stiffness

Describes the ability an object has to resist compression

Density (Chapter 3)

Describes weight of a material

Bulk Modulus

Describes the ability an object has to resist compression

Elasticity

Describes the ability an object has to compress

Compressibility

Describes the ability an object has to compress

Continuous Sound (Wave)

Acoustic energy produced by a transducer that continuously transmits a sound wave without any breaks or pauses in time

Pulsed Sound (Wave)

A short burst of acoustic cycles that travels together as a single unit, followed by a period of silence where the transducer listens for echoes

Pulse

Collection of cycles that travel together

Transmit Time

Talking, or "on" time

Receive Time

Listening, or "off" time

Pulse Duration

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

Spatial Pulse Length

Distance that a pulse occupies in space from the start to end of a pulse

Pulse Repetition Period

The time from start of 1 pulse to the start of the next pulse

Depth of View

The max distance into the body under ultrasound

Pulse Repetition Frequency

of pulses that an ultrasound system transmits into the body each second

Duty Factor

The % or fraction of time that the system transmits a pulse

Intensity (Chapter 5)

Beam's power divided by its area

Spatial

Distance or space

Temporal

All time, transmit, + receive

Peak

Max value

Average

Mathematical value

Pulsed (Intensity)

Transmit time

Spatial Peak Intensity

Beam's intensity at location where it is maximum

Spatial Average Intensity

Average intensity across the beam's entire cross-sectional area

Temporal Peak Intensity

Beam at the instant in time of its max value

Pulse Average Intensity

During pulse duration - the transmit time

Temporal Average Intensity

Entire pulse repetition period

SPTA

Spatial Peak, Temporal Average

Beam Uniformity Coefficient

Describes the spread of a beam in space

Propagate

To travel or move through a medium

Boundary

The interface or border separating 2 different media

Attenuate

The decrease or loss in wave intensity + amplitude as sound travels through a medium

Amplify

To increase the strength, amplitude, or intensity of a signal

Logarithms

A mathematical scale based on powers of 10 used to measure relative signal strength

Decibels

The logarithmic unit used to measure relative changes in sound intensity or signal strength

Relative Change

The ratio or comparison of a final value to an initial value rather than an absolute measurement

Positive Decibel

An increase in signal strength or intensity

Negative Decibel

A decrease in signal strength or intensity

Attenuation

The total reduction in intensity, power, + amplitude of a sound wave travels through a medium

Path Length

The total distance the sound wave travels through a medium

Reflection

The redirection of a portion of the sound beam back toward the transducer at a media boundary

Specular Reflector

Reflection from a large, smooth boundary where sound is redirected in one organized direction

Diffuse Reflector

Reflection from an irregular or rough surface that scatters sound in multiple directions

Scattering

The random redirection of sound in many directions when striking small or rough interfaces

Rayleigh Scattering

Occurs when reflector dimensions are much smaller than wavelength, redirecting sound equally in all directions (special scattering)

Absorption

The conversion of sound energy into heat within a medium

Attenuation Coefficient

The amount of attenuation that occurs per cm of sound travel

Total Attenuation

The total loss of sound intensity over a given distance

Half-Value Layer Thickness

The distance sound travels in a tissue that reduces its intensity to 1/2

Transmission

The portion of the sound beam that continues forward into the next medium

Acoustic Impedance

The resistance to sound travel in a medium, calculated as tissue density multiplied by propagation speed