SPI Unit 5

Types of information provided by Doppler ultrasound

Presence of flow

Direction of flow

Speed of flow

Character of flow

Doppler effect

The change in frequency (and wavelength) caused by motion of a sound source, receiver of reflector

Doppler shift (fD)

The difference between the frequency of the received sound and the frequency of the emitted sound

Doppler shift (fD) =

fR - fT

Doppler shift can determine

Direction and velocity

Doppler shift units

kHz

Doppler equation

fD = 2/c x v x fT x cos(angle)

Doppler modes

Color, power, tissue

Doppler modes cw or pw?

Pulsed wave so location Information can be displayed

Provides qualitative info

Spectral Doppler modes

Pulsed wave, pulsed wave tissue Doppler, continuous wave

Quantitative information

“Spenctral” refers to

Graphical representation of velocity (y axis) over time (x axis)

Doppler angle

Angle between the direction of sound propagation and the direction of flow

Should always be less than 60°

What happens when flow is perpendicular to the sound beam (90°)

No shift would be detected so no flow would be displayed

How to avoid perpendicular incidence

Steer the beam using sequencing or phasing

True or false:steering the color box changes the Doppler angle

True

Sample volume/gate

Region selected where Doppler information will be displayed

CW sample gate

Region of overlap between emitting and receiving beams

Color sample gate

Region of color box

PW spectral Doppler sample gate

Position and size of sample gate

Wall filter/reject

Filter out unwanted motion from the vessel walls

Wall thump/clutter

Movement of vessel walls

Tend to be low velocity, but create very high amplitude reflections

True or false: wall filter is only applicable for color Doppler

False

It is applicable to all Doppler modes

Spectral Doppler flow direction

Above baseline- toward transducer

Below baseline- away from transducer

Invert

Flips color map and spectrum

Autocorrelation

A mathematical process that rapidly determines shift information for each sample time (location) along the scan line

Autocorrelation is associated with what Doppler

Color Doppler

Mean

Average

Variance

The spread around the mean

How many Doppler samples (locations) are used per scan line

100-400

Hue

Color

Saturation

Intensity of color

Expressed as it differs from white

luminance

Brightness

Color map

Gives information about sign, magnitude and variance of the shifts

Color map hue

Determines sign of the shift (direction)

Color map saturation or luminance

shows shift magnitudes (velocity)

Variance map

Represents a change in hue from left to right across the map

Ensemble length/ packet size

Number of pulses used for each color scan line

Common ensemble length

10-20

Higher ensemble length provides

More accurate estimates of mean shift

Improved detecting of slow flow

More complete display of flow information

Relationship between ensemble length and FR

Inverse

Color Doppler persistence

Frame averaging technique that reduces noise similarly to gray scale

Relationship between color box width and FR

Inverse

Do we want to use a bigger or smaller color box

Smallest color box possible

Color priority

Priority selects the gray scale echo strength below which color (instead of gray) will be displayed at each pixel location

Low color priority

Weak

Little color displayed

High color priority

More color displayed

PRF/scale sets the limit at the ______

Color bar extremes

For color Doppler, is PRF controlled by operator/sonographer

Yes, sonographer can adjust PRF scale

Lower PRF scale color Doppler

Allows for display of slow flow

Higher PRF scale color Doppler

Shows high velocity without aliasing

Nyquist limit =

PRF / 2

Color baseline

Black area on color map where no shifts detected

Change in direction

Can color a baseline be adjusted

Yes, can be shifted up or down

Color inversion

Switched color assignment to other side of baseline on color map

Color Doppler gain

Amplification of Doppler echoes

Color Doppler limitations

Angle dependent

Low FR

Cannot use multiple foci

Displays mean shifts, not peak

Gives qualitative information, cannot give quantitative measurements

Color interpretation

Allows us to determine flow abnormalities

(Stenosis, blood clot, plaque)

Power Doppler

Color encodes the strength (power intensity) of the shifts

What is the power of the shifts determined by

The concentration of moving scatterers (blood cells)

What is power Doppler helpful for

Showing presence of flow

Power Doppler advantages

Angle independence

No aliasing

Improved sensitivity

Power Doppler disadvantages

No directional information

No flow speed information

No flow character information

Tissue Doppler imaging (TDI)

Color encodes movement of tissue

Angle dependent

Can you use pulsed wave spectral Doppler to measure velocities of tissue motion?

Yes you can

Is continuous wave damped

No, air is the backing material

Does pulsed wave detect complete Doppler shift

No, obtains samples of it

Continuous wave advantages

No aliasing- shows high velocity

Can use high frequencies

Sensitive to low velocities

continuous wave disadvantages

No depth selectivity

Potential overlap of Doppler signals

Pulsed wave advantages

Depth selectivity

Adjustable sample volume size

Pulsed wave disadvantages

Aliasing limits max velocity

Doppler shift detector aka

Quadrate phase detector

Doppler shift detector

Identifies forward and reverse components of the Doppler signal

Determines direction of motion

Fast Fourier Transform (FFT)

Mathematical process to present Doppler shifts in frequency order in a Doppler frequency spectrum

Breaks down the Doppler signals into individual frequencies

Displays frequencies as vertical lines

Spectral display brightness

Intensity if the echo

Spectral Doppler scale -PRF

Adjusts the velocity displayed in the y axis

When do you increase spectral Doppler scale

For higher velocity or to eliminate aliasing

When do you decrease spectral Doppler scale

For low velocity flow

What does adjusting spectral Doppler baseline correct?

Corrects for aliasing

Spectral Doppler gain

A,polities the Doppler shifts and makes the waveform appear brighter

When to increase spectral Doppler gain

to show low amplitude velocities

When to decrease spectral Doppler gain

To eliminate noise

Evaluation of spectral Doppler waveforms include

Direction of flow

Velocity of flow

Type and character of flow

Various measurements (RI, AT, PI)

Spectral window

Black area under a waveform

Narrow range of velocities

Spectral broadening

Widening of the Doppler shift spectrum

Filling in of the spectral window

Broad range of velocities

causes of spectral broadening

Disturbed or turbulent flow

Large sample volume

Type of flow

Laminar

Type of flow

Disturbed

Type of flow

Turbulent

Type of flow

Laminar

Type of flow

Disturbed

type of flow

Turbulent

Peak systolic velocity (PSV)

Highest peak of a waveform corresponding to cardiac systole

End diastolic velocity (EDV)

Velocity at the end of diastole, just before systole

Acceleration time (AT)

Time between beginning of systolic flow and its peak velocity, useful for predicting significant stenosis

Doppler indices

Provides info about vascular resistance and compliance

Resistive index (RI) =

PSV - EDV / PSV

Pulsatility index (PI) =

PSV - EDV / mean velocity

Antegrade

Forward flow

Flows in normal direction for the artery being evaluated

Retrograde

Reverse flow

Flow opposite to the normal direction for the artery being evaluated

Bidirectional

“To-fro”

Blood flow enters and

Eaves a contained space via the same orifice