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