Chapter 19: Doppler Effect in Biology - Key Terms and Definitions

doppler principle

used to measure the velocity of blood in the circulation

doppler shift/doppler frequency

produced by relative motion of sound source and receiver.

doppler frequency

motion towards tor away from the transducer that causes a change in the main frequency shift

doppler shift

a low frequency that "rides" on top of the much higher frequency

demodualtion

the process of extracting the low doppler frequency from the transducers carrier frequency

postive doppler shift

blood cells move towards the transducer

the reflected frequency is higher than the transmitted frequency

negative doppler shift

blood cells move away from the transducer

the reflected frequency is lower than the transmitted frequency

speed

purely a magnitude, indicates the distance that a RBC moves in 1 sec

velocity

defined by magnitude and direction

doppler equation

doppler shift = 2 x velocity of blood x transducer frequency x cos0 / propagation speed

measured velocity

= true velocity x cosine

bidirectional doppler

direction of flow toward or away the transducer with spectral tracing/ or audio

below the baseline indicates a negative shift

above the baseline indicates a positive shift

phase quadrature/ quadrature direction

a commonly used signal processing technique for bidirectional flow

CW doppler

2 crystals in the transducer one sends one recievese

range ambiguity

depth of reflections cannot be determined because reflections are being measured from entire overlap area of transmit and receive beams

duplex imaging/scanning

simultaneous anatomic imaging and doppler

PW doppler

1 PZt alternates between transmit and receive, velocities are samples many times per second

range resolution

the greatest advantage of PW Doppler

ability to select the exact location where velocities are measured by placing a small marker called the gate or sample volume on a 2D image

aliasing

most common error associated with doppler ultrasound. high velocity flow in one direction is incorrectly displayed as traveling in the opposite direction

nyquist limit

highest doppler frequency or velocity that can be measured without the appearance of aliasing

gray shades of a spectrum

related to amplitude of the reflected signal

color flow doppler

a form of 2D doppler where velocity information is coded into colors and sperimposed on a 2D gray scale anatomic image

color map

a dictionary or lookup table

used to convert measure velocites into colors that appear on the image

velocity mode

provides information on flow direction and velocity colors above the black stipe indicate flow towards the transducer or positive doppler shifts colors below the black stripe indicate flow away from the transducer or negative doppler shift

variance mode

same information provided as velocity mode but also distinguishes laminar from turbulent flow

doppler packets

multiple u/s pulses per scan line are used to accurately determine blood velocities

larger packets are composed of larger number of pulses per scan line

power doppler

energy mode or color angio

no velocity or direction information only detects flow, the amplitude of the reflection is directly related to the number of moving blood cells

spectral analysis

a tool that breaks the complex signals into its basic building blocks and identifies velocities that make up the reflected doppler signal

FFT

autocorrelation

FFT

a digital technique used to process both CW and PWS doppler signals

spectral window

a region of a FFT spectral trace between the baseline and the spectrum when clear = laminar flow spectral broadening = turbulent flow

spectral broadening

turbulent flow the pulsed doppler spectral window is filled in a wider range of velocities and doppler shifts are within the sample volume

autocorrelation

correlation function

digital technique used to analyze color doppler because of the enormous amount of data that is processed