Kremkau Chapter 2 - Key Terms Flashcards
Absorption
Conversion of sound to heat.
Acoustic
Having to do with sound.
Acoustic variables
Pressure, density, and particle vibration; sound wave quantities that vary in space and time.
Amplitude
Maximum variation of an acoustic variable or voltage.
Attenuation
Decrease in amplitude and intensity with distance as a wave travels through a medium.
Attenuation coefficient
Attenuation per centimeter of wave travel.
Backscatter
Sound scattered back in the direction from witch it originally came.
Bandwitdth
Range of frequencies contained in an ultrasound pulse; range of frequencies within which a material, device, or system can operate.
Compression
Reduction in differences between small and large amplitudes. Region of high density and pressure in a compressional wave.
Constructive interference
Combination of positive or negative pressures.
Continuous wave
A wave in which cycles repeat indefinitely; not pulsed. (CW)
Contrast agent
A suspension of bubbles or particles introduced into circulation to enhance the contrast between anatomic structures, thereby improving their imaging.
Coupling medium
A gel used to provide a good sound path between a transducer and the skin by eliminating the air between the two.
Cycle
One complete variation of an acoustic variable.
Decibel
Unit of power or intensity ratio; the number of decibels is 10 ties the logarithm (to the base 10) of the power or intensity ratio. (dB)
Density
Mass divided by volume.
Destructive intereference
Combination of positive and negative pressures.
Duty factor
Fraction of time that pulsed ultrasound is on.
Echo
Reflection.
Energy
Capability of doing work.
Fractional bandwidth
Bandwidth divided by operating frequency.
Frequency
Number of cycles per second.
Fundamental frequency
The primary frequency in a collection of frequencies that can include odd and even harmonics and subharmonics.
Harmonics
Frequencies that are even and odd multiples of another, commonly called fundamental or operating frequencies.
Hertz
Unit of frequency, one cycle per second; unit of pulse repetition frequency, one pulse per second. (Hz)
Impedance
Destiny multiplied by the sound propagation speed.
Incidence angle
Angle between incident sound direction and a line perpendicular to the boundary of a medium.
Intensity
Power divided by area.
Intensity reflection coefficient
Reflected intensity divided by incident intensity; the fraction of incident intensity reflected.
Intensity transmission coefficient
Transmitted intensity divided by incident intensity; the fraction of incident intensity transmitted into the second medium.
Interference
Combinations of positive and/or negative pressures
Kilohertz
One thousand hertz. (kHz)
Longitudinal wave
Wave in which the particle motion is parallel to the direction of wave travel (compressional wave).
Medium
Material through which a wave travels.
Megahertz
One million hertz. (MHz)
Nonlinear propagation
Sound propagation speed depends on pressure causing the wave shape to change and harmonics to be generated.
Oblique insidence
Sound direction that is not perpendicular to media boundaries.
Penetration
Imaging depth.
Period
Time per cycle.
Perpendicular
Geometrically related by 90 degrees.
Perpendicular incidence
Sound direction that is perpendicular to the boundary between media.
Power
Rate at which work is done; rate at which energy is transferred.
Pressure
Force divided by the area in a fluid.
Propagation
Progression or travel.
Propagation speed
Speed at which a wave moves through a medium.
Pulse
A brief excursion of a quantity from its normal value; a few cycles.
Pulse duration
Interval of time of beginning to end of a pulse.
Pulse-repetition frequency
Number of pulses per second; sometimes called pulse repetition rate. PRF
Pulsed ultrasound
Ultrasound produced in pulsed form by applying electric pulses or voltages of one or a few cycles to the transducer.
Range equation
Relationship between round-trip pulse travel time, propagation speed, and distance to a reflector.
Rarefaction
Region of low density and pressure in a compressional wave.
Rayl
Unit of impedance.
Reflection
Change of sound direction on passing from one medium to another.
Reflection angle
Angle between the reflected sound direction and a line perpendicular to the media boundary.
Reflector
Media boundary that produces a reflection; reflecting surface.
Refraction
Change of sound direction on passing from one medium to another.
Scatter
An object that scatters sound in many directions because of its small size or its surface roughness.
Scattering
Diffusion or redirection of sound in several directions upon encountering a particle suspension or a rough surface.
Sound
Traveling wave of acoustic variables.
Spatial pulse length
Length of space over which a pulse occurs.
Speckle
The granular appearance of images and spectral displays that is caused by the interference of echoes from the distribution of scatters in tissue.
Specular reflection
Reflection from a large (relative to wavelength), flat, smooth boundary.
Stiffness
Property of a medium; applied pressure divided by the fractional volume change produced by the pressure.
Strength
Nonspecific term referring to amplitude or intensity.
Transmission angle
Angle between the transmitted sound direction and a line perpendicular to the media boundary.
Transverse wave
A sound wave in which the transmitted sound direction and a line perpendicular to the media boundary.
Ultrasound
Sound having frequency greater than what humans can hear (greater than 20 kHz).
Wave
Traveling variation of one or more quantities
Wavelength
Length of space of which a cycle occurs.
Pulse-repetition frequency
PRF. Number of pulses per second; sometimes called pulse repetition rate.
