Chapter 2 Flashcards
Aborption
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 which it originally came
Bandwidth
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, abbreviate 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 times the logarithm (to the base 10) of the power or intensity ratio. Abbreviated dB
Density
mass divided by volume
destructive interference
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 harmonic and subharmonics
harmonics
frequencies that are even and odd multiples of another, commonly called fundamental or operating frequency
Hertz
unit of frequency, one cycle per second; unit of pulse repetition frequency; one pulse per second. abbreviated Hz
impedance
density 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. abbreviated kHz
longitudinal wave
wave in which the particles 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 in which the propagation speed depends on pressure causing the wave shape to change and harmonics to be generated
oblique incidence
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 from beginning to end of a pulse
pulse-repetition frequency
number of pulsed per second; sometimes called pulse repetition rate. abberviated PRF
pulse-repetition period
interval of time from the beginning of one pulse to the beginning of the next
pulsed ultrasound
ultrasound produced in pulsed form by applying electric pulses or voltages of one or few cycles to the transducer
range equation
relationship between round-trip pulse travel time, propagation speed, and distance to a reflector
rarefraction
region of low density and pressure in a compressional wave
Rayl
unit of impedance
reflection
portion of sound returned from a media boundary; echo
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 scatterers 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 particle motion is perpendicular to the direction of wave travel
ultrasound
soung having a frequency greater than what humans can hear, that is greater than 20 kHz
wave
traveling variation of one or more quantities
wavelength
length of space over which a cycle occurs
