Doppler Instruments and Analysis

Vocabulary terms and definitions covering Doppler instrumentation, color flow characteristics, spectral analysis techniques, and flow resistance based on the lecture notes.

Doppler Instruments

Instruments that respond to moving reflectors (RBCs) by detecting the Doppler shift, which is then converted to audible sound, visual displays, or spectral analysis.

Color Doppler

A pulsed ultrasound technique where Doppler shift information from a sample region is assigned colored echoes based on the direction of flow and superimposed on a 2D image.

Power Doppler

A technique used to measure energy differences and the strength of Doppler shifts based on the concentration of RBCs rather than velocity.

Spectral Analysis

A method of plotting or graphing Doppler frequencies or velocities versus time in order to evaluate reflector motion.

Color Flow Map

A color directory where the top color indicates flow toward the transducer ($+$ Doppler shift), the bottom color indicates flow away ($-$ Doppler shift), and black represents neutral flow.

Hue

The specific color perceived, such as red, blue, green, or yellow.

Luminance

The brightness of a color.

Saturation

The amount of hue mixed with white; less white results in greater saturation.

Variance Color Map

A map used to display disturbed and or turbulent flow (variations of flow velocities), typically using colors like yellow, cyan, and green.

Packet Size

Also known as ensemble length, it is the number of pulses or gates in a specific region; more pulses result in more accurate velocity measurements but lower frame rates.

Autocorrelation

The rapid technique used for obtaining mean Doppler shift information specifically for color Doppler.

Fast Fourier Transform (FFT)

The current mathematical technique used to obtain a spectrum from returning frequencies for both CW and PW Doppler; it is more accurate than autocorrelation but slower.

Phase Quadrature Detector

A technique that mixes and separates returning signals into direct and quadrature channels to distinguish between $+$ and $-$ Doppler shifts.

Continuous Wave (CW) Doppler

A system using separate source and receiving elements that detects motion at the intersection of the beams, capable of measuring very high velocities.

Range Ambiguity

An artifact in CW Doppler where motion is detected along the entire beam intersection, making it difficult to distinguish between different vessels.

Pulsed Wave (PW) Doppler

A system using a single transducer element for sending and receiving that allows for range resolution at a selected depth.

Range Resolution

Also called range gating, the ability of PW Doppler to select and control reflections at a specific depth or distance using a receiver gate.

Nyquist Limit

The upper limit to Doppler shift information detected by PW Doppler, defined as $Nyquist Limit = \frac{1}{2} PRF$. Surpassing this limit causes aliasing.

Aliasing

An artifact where peak color changes to the opposite peak color with no neutral color in between; it occurs when velocity surpasses the Nyquist limit.

Spectral Broadening

The fill-in of the acoustic window and increase in the range of frequencies present, often indicating turbulent flow, high Doppler gain, or improper gate placement.

Resistive Index (RI)

Also known as the Pourcelot Index, a ratio used to predict the resistive nature of flow, calculated as $RI = \frac{\text{Peak Systole} - \text{End Diastole}}{\text{Peak Systole}}$.

Zero-crossing detection

An early, outdated method of spectral analysis that counted the number of times a signal crossed zero in a specific time period.