Physics Hemodynamic and doppler terminology

Aliasing

a “wrap around” on spectral doppler. it occurs when blood velocity exceeds the Nyquist limit (PRF/2)

aliasing is

a signal on the opposite side of the baseline and never occurs with CW

what increases the chance for aliasing?

deeper samples, and higher frequency (doppler shift increases with high freq.)

how is aliasing fixed?

increase PRF (scale) (#2), lower frequency, decrease depth (#3), drop baseline (affects only appearance), use CW (#1)

Amplitude

Brightness ~ Intensity and Power

Bernoulli effect

decreased pressure in regions of increased flow speed ~ the stenosis

as flow energy increases, pressure energy decreases

venous flow is affected by

gravity and respiration.

what happens with inspiration?

decreases intrathoracic pressure, increases abdominal pressure.

Bidirectional:

the instrument can distinguish between positive and negative shifts.

Nondirectional:

instrument just detects the movement of blood aka non coherent

Clutter:

low frequency doppler shifts (and high intensity) in spectral display. (wall filters are used to eliminate.)

Tissue motion from pulsating vessels can cause clutter.

what kind of artifact is clutter?

noise artifact from moving tissue

what will happen to the spectral tracing if the wall filter is too high?

some/ most of the low tracings will disappear. cannot see the end diastolic.

compliance:

the ability of a vessel to expand and contract with volume of blood.

veins more than arteries.

continuity rule:

volumetric flow rate must remain constant proximal, at, and distal to the stenosis.

blood speeds up in the narrowed area (stenosis)

continuous wave doppler:

uses two crystals; one sends, one receives.

does not alias, but has no depth or range resolution.

uses an oscillator to determine frequency.

disturbed flow:

altered from streamline flow. (goes around a bend)

occurs at bifurcations and proximal to stenosis.

type of laminar flow

doppler angle:

angle of doppler sample.

0 degrees is best

90 degrees , no shift.

inverse to cosine.

doppler effect:

the effect.

change in frequency (or wavelength) due to motion of sound source, reciever, or reflector.

doppler equation:

doppler shift (FD)= 2 X velocity X transducer frequency X cosine / propagation speed.

FD= 2 x F x V x Cos / C

doppler shift increases if:

frequency and cosine increase

Cos is (inversely/ directly) related to angle

inversely

increase in frequency

increase in doppler shift (FD)

doppler shift equation:

DS = Fr - Ft

RBCs moving towards is a

positive doppler shift

RBCs moving away is a

negative doppler shift

duplex instrument

spectral doppler and grayscale (triplex includes color)

Eddies:

“cross currents”, whirlpools, indicates turbulence. Vortex’s

Frictional loss:

energy loss ~ heat.

“blood sliding on a vessel”

blood slows down at vessel wall

Fast Fourier transform (FFT):

the mathematical technique used to detect/ analyze spectral doppler shift.

it is a digital technique.

Used for spectral and CWD.

accurate, displays individual velocities.

Filter:

removes unwanted high amplitude, low frequency shifts (clutter)

Flow:

to move in a stream and continuously change positions, sometimes directions.

Fluid:

ability to flow and conform to the shape of their containers

Gate:

sample volume

region where the doppler is sampled.

wider gate samples more RBCs

Gradient slope:

different energies at different locations.

Helical flow:

twisting / corkscrew type of flow

indicates turbulent flow

Hemodynamics:

force and motion

blood and power

study of blood moving through the circulatory system.

Hydrostatic pressure:

gravitational pull.

effect of gravity and blood pressure

Laminar flow:

streamlines are aligned and parallel.

different speeds.

Normal.

Magnitude:

height of doppler shift

vertical axis displays velocity

Nyquist limit:

the “speed limit” for blood flow.

aliasing will occur if blood flow exceeds this limit.

nyquist limit =

PRF / 2

Parabolic Flow:

bullet shaped flow.

velocity is highest at the center, and lowest at the walls.

Phasic flow:

affected by respirations

change of speeds.

venous flow

Phase Quadrature (Detector):

detector in the instrument that determines direction and separates the doppler shift voltages into forward and reverse channels.

pertains to CWD.

sends to separate speakers so positive and negative shifts can be heard separately

Plug flow:

all layers of blood travel at the same velocity.

blood flowing constant across the tube

Poise:

unit for resistance/ viscosity

Poiseulle’s equation

VFR = change in P x D / length X viscosity

Pressure:

driving force behind fluid.

in the body it is the heart pump.

pressure differences are needed for flow to occur.

PRF:

increasing this reduces aliasing, but increases frame rate.

use lower PRF for slower flow and higher PRF for higher velocities

Pulsatile Flow:

arterial; non steady flow

affected by cardiac contractions

acceleration and deceleration

Pulsatility index:

measures resistance

velocity max - velocity min / mean velocity

Pulsed Doppler:

uses the pulse technique.

advantage: has range resolution

Range gate:

depth of sample

shorter gate lengths are used for spectral analysis.

shorter gate lengths improve quality of the spectral display. shorter is best!

SV width =

beam width

Range ambiguity:

CWD does not use pulses

a disadvantage of CW

an advantage is that it does not alias.

does not know where the sample comes from.

Resistance (flow):

opposition to flow.

sometimes shows flow reversal if resistance is high.

Reynolds number:

predicts the onset of turbulence

Critical Reynolds number:

> 2000

If velocity ______, Re number _____

increases

if viscosity ____, Re number _____

increases, decreases

Sample volume

region from which the doppler echoes return

width of SV =

beam width

Spectral broadening:

widening of the doppler shift spectrum

increased range of speeds/ frequency

can be due to disturbed or turbulent flow

spectral broadening is often found

distal to a stenosis or from turbulent flow

Some smaller vessels will have ____

Spectral broadening

Steady flow:

does not accelerate and decelerate

this is found in Veins

Stenosis:

narrowing of a vessel.

streamlines:

layers of blood sliding on each other

Turbulence:

chaotic flow, eddies, cross current

happens after a stenosis

Velocity:

speed and direction

Cm/s

distance/ time

Viscosity:

resistance to change shape or flow.

units: poise

Thickness

high viscous, high resistance

Volumetric flow rate (VFR):

volume of blood passing through an area per unit of time ~ diameter and length of tube ~ avg flow speed X cross sectional area of vessel (tube)

if pressure difference ____, VFR _____

increase (s)

If resistance _____, VFR _____

increases, decreases

if tube length increases, resistance ____, and VFR ____

increases, decreases

if diameter ____, resistance ____ and VFR increases

increases, decreases

if viscosity _____, resistance _____ and VFR _____

increases, increases, decreases

Wall filter:

decreases clutter.

rejects unwanted low frequency (high amplitude doppler shifts)

“reject button”

Window:

reduction of spectral broadening

the opening in the spectral tracing

~ larger vessels

Windkessel effect;

compliant vessel producing extended forward flow or flow reversal in diastole

Zero Crossing detector:

analog device that provides an instantaneous avg doppler shift that varies over the cardiac cycle

it counts how often the doppler shift voltage changes from a negative to positive (vice versa)

the higher the count the higher the frequency

the avg doppler shift yielded by the zero crossing technique favors ________

lower frequencies

_____ presents mean doppler shift on a strip chart recorder

zero crossing detector

simpler instruments ~ mean velocities only

VFR (volumetric flow rate) formula

VFR= change P x D / length x velocity