Vocab Ch. 5 Flashcards
Flow
to move in a stream continually changing position and possibly direction.
Fluids
a material that flows and conforms to the shape of its container (gas or liquid).
Flow Resistance
pressure difference divided by volume flow rate for steady flow.
R(g/cm4-s)=8xL(cm)x viscosity(poise)/Pi x[r4(cm4)]
Volumetric Flow Rate
volume of fluid passing a point per unit of time (per second or minute).
Q(mL/s)=changeP(dyne/cm2)/R(poise)
Pressure Gradient (slope)
pressure difference divided by distance between the two pressure locations.
Viscosity
resistance of fluid to flow.
R(poise)=changeP(dyne/cm2)/Q(mL/s)
Plug flow
flow with all fluid portions traveling with the same flow speed and direction.
Laminar flow
flow in which fluid layers slide over each other in a smooth, orderly manner, with no mixing between layers.
Parabolic flow
laminar flow with a profile in the shape of a parabola.
Disturbed flow
flow that cannot be described by straight parallel streamlines.
Turbulent flow
random, chaotic, multidirectional flow of a fluid with mixing between layers; flow that is not laminar.
Pulsatile flow
flow that accelerates and decelerates with each cardiac cycle.
Continuity Rule
blood is neither created nor destroyed as it flows through a vessel.
Bernoulli Effect
pressure reduction in a region of high-flow speed. Pressure Drop (where V2=flow speed at stenosis): △P=4(V2)2
Doppler effect
a change in frequency caused by the motion of reflectors.
Doppler shift
reflected frequency minus incident frequency; a change in frequency that occurs as a result of motion.
fD(kHz)-fR-fT OR
DopplerShift = [2 x v of blood x freq of transducer x cosΘ] / propagation speed
Doppler angle
the angle between the sound beam and the flow direction.
Spectral analysis
separation of frequencies in a Doppler signal for display as a Doppler spectrum.
Aliasing
improper Doppler-shift information from a pulsed-wave Doppler or color Doppler instrument when the true Doppler shift exceeds one half the PRF.
Nyquist limit
the Doppler-shift frequency above which aliasing occurs. (PRF/2) MHz
Color Doppler display
the presentation of two-dimensional, real-time Doppler-shift information superimposed on a real-time, gray-scale, anatomical, cross-sectional image.
Autocorrelation
a rapid technique, used in most color Doppler instruments, for obtaining mean Doppler-shift frequency.
Wall filter
an electric filter that passes frequencies above a set level and eliminates strong, low-frequency Doppler shifts from pulsating heart or vessel walls.
Clutter
noise in the Doppler signal that generally is caused by high-amplitude, Doppler-shifted echoes from the heart and vessel walls.
Priority
the gray-scale strength below which color Doppler information is shown preferentially on a display.
Baseline shift
movement of the zero Doppler-shift frequency or zero flow speed line up or down on a spectral display.
Ensemble length
number of pulses used to generate one color Doppler image scan line.
Variance
a measure of spectral broadening.
Power Doppler Display
color Doppler display in which colors are assigned according to the strength (amplitude, power, intensity, energy) of the Doppler-shifted echoes.
Hue
the color perceived based on the frequency of light.
Saturation
the amount of hue present in a mix of white.
Luminance
brightness of a presented hue and saturation.
Continuous Wave
a wave in which cycles repeat indefinitely; not pulsed.
CW Doppler
a Doppler device or procedure that uses CW ultrasound.
Bidirectional Instrument
is an instrument that is capable of distinguishing between positive and negative Doppler shifts (forward and reversed flow).
Sample Volume
the anatomical region from which pulsed Doppler echoes are accepted.
Doppler Spectrum
the range of frequencies present in Doppler-shifted echoes.
Spectral Doppler Display
the presentation of Doppler information in a quantitative form. Visual display of a Doppler spectrum.
Range Gate
a device that allows only echoes from a selected depth (arrival time) to pass.
Duplex Instrument
an ultrasound instrument that combines gray-scale sonography with pulsed Doppler and possibly, CW Doppler.
Fast Fourier Transform (FTT)
a mathematical technique used to generate Doppler shift spectral displays.
Spectral Broadening
the widening of the Doppler-shift spectrum or the increase in the range of Doppler-shift frequencies present that occurs because of a broadened range of flow velocities encountered by the sound beam.
