Pulse Wave Doppler

Question 1

What is the Doppler effect?

Answer 1

the change in frequency or wavelength of echo signals that occurs when there is a relative motion between the sound source (probe) and reflecting surfaces (rbcs)

Question 2

What does Doppler effect determine?

Answer 2

the velocity of the moving reflectors and the direction of flow

Question 3

the Doppler effect/shift is the difference between what?

Answer 3

the received frequency and the transmitted frequency

Question 4

what is the audible range

Answer 4

20Hz - 20,000Hz

Question 5

Doppler shift formula

Answer 5

∆F(Doppler shift) = 2Fov*cosθ / c

Question 6

What units are used for:

• frequency shifts
• velocities

Answer 6

• kilohertz kHz

- meters/sec

Question 6

What units are used for:

• frequency shifts
• velocities

Answer 6

• kilohertz kHz

- meters/sec

Question 7

what is the cosine when the angle is

• 0
• 60
• 90

Answer 7

1
.5
0

Question 8

As the angle between the transducer and flow decreases - what happens to the Doppler shift?

Answer 8

it increases as we get closer to 0 angle / cosine of 1

Question 9

what does it mean by a wide bandwidth

Answer 9

a large range of frequencies

Question 10

relationship between the flow velocity and Doppler shift

Answer 10

faster velocity = higher Doppler shift

Question 11

CW Doppler

Answer 11

2 crystals - the beam is directional with a region of beam overlap

Question 12

what determines the CW frequency?

Answer 12

the applied voltage

Question 13

main disadvantage to CW Doppler - and why

Answer 13

range ambiguity - inability to tell where the Doppler signal is coming from

because of the long pulse length - no backing material in CW Doppler, resulting in poor axial resolution

Question 14

advantages of CW Doppler

Answer 14

measures high velocities, no aliasing, small probe sizes, use of high frequencies

Question 15

main advantage of PW Doppler

Answer 15

range resolution - allows tech to place and know where the Doppler information is derived from

Question 16

definition of Nyquist limit

Answer 16

the level at which aliasing will begin to occur

1/2Doppler PRF

Question 17

how does aliasing occur?

Answer 17

if the velocity of the reflector, RBCs, are moving too fast for the sampling rate (PRF) - aliasing will occur

Question 18

when aliasing does occur… what can be done to correct it?

Answer 18

• adjust the spectral baseline and or scale
• find different window with shallower depth
• lower the frequency

Question 19

disadvantage of PW Doppler

Answer 19

can’t accurately measure high velocities due to aliasing

Question 20

on spectral analysis - what does the vertical axis represent? the horizontal?

Answer 20

• vertical: frequency shift or velocity

- horizontal: time

Question 21

flow direction is determined within where?

Answer 21

the demodulator of the Doppler receiver

Question 22

what causes spectral broadening?

Answer 22

turbulent flow
tortuous vessels
sample gate too close to vessel wall
just distal to stenosis

Question 23

waveform magnitude or waveform brightness

Answer 23

known as the amplitude of the signal

shown by how “bright” the spectral disaplay is

Question 24

what does Fast Fourier Transformer do? how?

Answer 24

it performs signal processing or spectral analysis
-does so by using a mathematical technique to make a conversion from the Doppler shift information into the visual spectral analysis

Question 25

what does peak flow speeds and spectral broadening mean?

Answer 25

a vertical thickening of the spectral trace

Question 26

pulsatility index formula

Answer 26

PI = max velocity - min velocity / mean velocity

Question 27

Resistivity index formula

Answer 27

RI = max velocity - min velocity / max velocity

Question 28

systolic/Diastolic ratio formula

Answer 28

ratio = peak systolic velocity / end diastolic velocity

Question 29

what is a packet?

Answer 29

the color information is obtained by positioning many pulsed Doppler lines and gates over the area of interest

Question 30

packets are composed of how many pulses per line of color?

Answer 30

3 and 30 - the more pulses, the slower the frame rate