Chapter 19

Question 1

Creation of everyday doppler shift

Answer 1

The change in frequency as a result of relative motion between the sound source and the receiver

Question 2

Doppler shifts

Answer 2

are created when transmitted sound waves strike moving red blood cells

Question 3

Positive Doppler Shift

Answer 3

When red blood cells move toward the transducer
The reflected ƒ is higher than the transmitted ƒ

Question 4

Negative Doppler Shift

Answer 4

When red blood cells move away from the transducer
The reflected ƒ is lower than the transmitted ƒ

Question 5

The 2 represents the fact that there are two Doppler shifts during an ultrasound exam

Answer 5

First Shift: Receiver (RBC) moves towards or away from the sound source (probe).
Second Doppler Shift: The RBC is hit with the beam and reflects it back towards the probe, thus becoming the sound source while the probe is now the receiver

Question 6

Nondirectional Doppler systems

Answer 6

simply measure the presence of moving blood cells by detecting a Doppler shift

Question 7

Bidirectional Doppler

Answer 7

Bidirectional distinguishes the direction of flow

Question 8

Doppler spectrum

Answer 8

Flow towards is displayed above the baseline
Flow away is displayed below the baseline

Question 9

Phase quadrature (quadrature detection)

Answer 9

is the commonly used signal processing technique used to identify direction in bidirectional Doppler systems

Question 10

Continuous Wave Doppler

Answer 10

Requires two crystals:
One constantly transmits while the other continuously receives the reflected signals from RBC
Advantage: because it is constantly sampling the motion of the red blood cells, CW can accurately measure very high velocities
Disadvantage: Doppler shifts and velocities are arising from the entire length of the beam; therefore, uncertain from where the highest velocity came
A second disadvantage is reflections from deeper RBCs will have lower amplitude

Question 11

range ambiguity

Answer 11

Doppler shifts and velocities are arising from the entire length of the beam

Question 12

Duplex imaging

Answer 12

When there is a 2D reference image and PW or CW Doppler graph/display on the screen

Question 13

interval display

Answer 13

Older systems periodically briefly interrupt the Doppler display (thick black line seen) to update the 2D reference image

Question 14

simultaneously (display)

Answer 14

both the 2D and the Doppler display are live (the reference image is not frozen and no black update lines interrupt the Doppler display)

Question 15

dedicated CW or “Pedoff” probe

Answer 15

Cross shaped wand with a spherical footprint
2 crystals in the shape of a semicircle

Question 16

Pulsed Wave Doppler

Answer 16

One crystal alternates between sending and receiving ultrasound pulses
Advantage: Selecting the exact location of Doppler interrogation called range resolution, range specificity or freedom from range ambiguity artifact
Disadvantage: inaccurate measurement of high velocity signals

Question 17

Continuous Wave Transducers

Answer 17

While performing CW Doppler with a conventional imaging array probe, a select pair of crystals (and associated electronics) are used for the Doppler

Question 18

Pulsed Wave Doppler Transducers

Answer 18

is accomplished by a single crystal in the imaging probe

Question 19

Aliasing

Answer 19

presents as high velocities being cut off and wrapped around our Doppler baseline and displayed as if they are moving in the opposite direction
With audio, aliasing presents as sound arising from the incorrect speaker

Question 20

the Nyquist Limit

Answer 20

when aliasing will occur in PW Doppler

Question 21

these things will reduce aliasing

Answer 21

Imaging shallower (increase PRF)
Lower velocities (decrease DS)
Using a lower frequency probe (decrease DS)

Question 22

Five techniques may be used to avoid aliasing artifact

Answer 22

1: Increase the scale to its maximum

#2: Select a new view with a shallower sample volume
#3: Select a lower frequency probe
#4: Shift the baseline so that the entire velocity scale is devoted to one direction
#5: Switch to continuous wave Doppler

Question 23

Color Flow Doppler

Answer 23

reports average or mean velocities

Question 24

Color Maps

Answer 24

Color Doppler uses a “legend” or “key” to assign the mean velocities at each location a color

Question 25

Color Map: No flow

Answer 25

black line and the color black represent no Doppler shift

Question 26

Velocity Mode Color Maps

Answer 26

inspect any horizontal line on a velocity map there is no change in color from side to side

Question 27

Variance Mode Color Maps

Answer 27

inspect any horizontal line on a variance map there is a change in color from side to side colors to the left represent laminar flow, colors to the right turbulent flow

Question 28

Color flow does not angle correct

Answer 28

only the mean velocity of parallel flow is close to the velocity indicated on the color map

Question 29

Aliasing occurs in color flow imaging

Answer 29

When color flow aliases it does so in a wrap around fashion relative to the color bar

Question 30

help to remove aliasing from a color Doppler display

Answer 30

-Adjust the color scale (PRF) to its maximum (low velocities will no longer get assigned a color) -Select a lower frequency transducer -Try to obtain a shallower color sector -Baseline shift may suffice to unwrap the signal on the display

Question 31

Transverse Flow

Answer 31

(cross sectional flow) requires that we look at the direction of flow relative to scan plane

Question 32

“BART”

Answer 32

the standard map where Blue = Away and Red = toward

Question 33

Flow Reversal

Answer 33

flow cuts across the color map baseline

Question 34

Doppler Packets or ensemble

Answer 34

The number of pulses sent down each scan line in your color sector

Question 35

Larger packets (larger ensemble) have advantages

Answer 35

Main: color fill in More accurate velocity information More sensitive to low flow

Question 36

The disadvantage to larger packet sizes (sending down more pulses)

Answer 36

is decreased frame rate and temporal resolution

Question 37

Color Line Density

Answer 37

Choosing a high line density when in color modality, increases the number of lines in the color region of interest

Question 38

Power Doppler

Answer 38

A color is assigned based on the amplitude (signal strength) of the returning Doppler Shift AKA: Color Angio, Energy Mode

Question 39

Advantages to Power Doppler

Answer 39

-Increased sensitivity to low or slow flow such as venous or small vessel flow -Unaffected by Doppler angles unless the angle is exactly 90 degrees -No aliasing since the velocity information is ignored

Question 40

Disadvantages to Power Doppler

Answer 40

-No velocity or direction information -Low PRF are used to detect slow flow therefore frame rates are lower than conventional color flow, and the lowest of all modalities -Susceptible to motion of the probe, patient, soft tissue which may result in a burst of color = flash artifact or ghosting

Question 41

Temporal resolution lowest to highest:

Answer 41

Power Doppler Color Doppler 2D single line frames CW/PW Doppler and M-Mode

Question 42

Crosstalk

Answer 42

Appears as identical Doppler spectrum above and below the baseline A type of mirror artifact

Question 43

clutter

Answer 43

small Doppler shifts may be produced by moving anatomy, these low velocity signals appear on the Doppler spectral tracing

Question 44

ghosting artifact

Answer 44

small Doppler shifts may be produced by moving anatomy, When these low velocity signals are assigned a color

Question 45

Wall filters

Answer 45

-eliminate small Doppler shifts or slow flow around the baseline on the Doppler spectrum -eliminate color arising from slow velocity reflectors such as tissue

Question 46

Tissue Doppler

Answer 46

At times we do determine the Doppler shifts and velocities coming off the walls of the left ventricle

Question 47

Spectral Analysis

Answer 47

Reflections arising from a mass of moving blood cells will have many Doppler shifted identifies the individual Doppler shifts

Question 48

Two methods of digital spectral analysis are currently used

Answer 48

1. Fast Fourier Transform (FFT) 2. Autocorrelation

Question 49

Fast Fourier Transform

Answer 49

-is a digital computer-based technique used to process both PW and CW Doppler signals -exceedingly accurate -It displays all individual components (shifts) that make up the complex reflected signal (every shift/velocity gets a brightness dot)

Question 50

Several situations will increase spectral broadening:

Answer 50

1. Turbulent flow 2. Continuous wave Doppler 3. Pulsed Doppler with a large sample gate

Question 51

The Doppler shift

Answer 51

The difference in frequency between what is transmitted and received