Doppler

Question 1

Relative motion between the sound source and the receiver. The change in frequency is due to

Answer 1

Doppler shift / doppler frequency

Question 2

Doppler frequency is used to measure the

Answer 2

velocity

Question 3

Process the extracts the low doppler frequency from the transducers carrier frequency

Answer 3

demodulation

Question 4

Doppler shift formula

Answer 4

Doppler shift (hz) = reflected frequency - transmitted frequency

Question 5

When blood cells move toward the transducer it creates a ____ and the reflective frequency is ___ than transmitted

Answer 5

positive doppler shift / higher

Question 6

Doppler shifts are created when ___ sound waves strike moving red blood cells

Answer 6

transmitted

Question 7

Doppler shifts range from ___ to ___ whereas transducer frequencies range from ____ to _____

Answer 7

20 to 20,000 hz / 2 mhz to 10 mhz

Question 8

Velocity is defined by

Answer 8

magnitude and direction

Question 9

doppler shift equation

Answer 9

Doppler shift = 2 x velocity x transducer frequency x cos / prop speed

Question 10

Relationship between velocity and doppler shift

Answer 10

directly / the faster the velocity, the greater the doppler frequency

Question 11

the x axis of a doppler spectrum represents ___ and the y axis represents ___

Answer 11

time / doppler shift (velocity)

Question 12

requires 2 crystals in the transducer

Answer 12

CW doppler

Question 13

The greatest advantage of CW doppler is

Answer 13

ability to accurately measure very high velocities

Question 14

Disadvantages of CW doppler

Answer 14

range ambiguity and lack of TGCs

Question 15

Transducer that does not create anatomic images and contains only 2 elements

Answer 15

CW transducer

Question 16

Since CW transducers do not have damping material, what are the characteristics

Answer 16

narrow bandwidth, high Q factor, and high sensitivity

Question 17

The crystal alternates between sending and receiving sound pulses so only 1 put crystal is needed.

Answer 17

PW doppler

Question 18

The greatest advantage of PW doppler is

Answer 18

being bale to select the exact location where velocities are measured (range resolution)

Question 19

In PW doppler, the velocities are measured from the

Answer 19

sample volume (gate)

Question 20

The most common error associated with PW doppler is

Answer 20

aliasing

Question 21

High velocity flow in one direction is incorrectly displayed as traveling in the opposite direction

Answer 21

Aliasing

Question 22

Since PW transducer have backing material, what are the characteristics

Answer 22

wide bandwidth, low sensitivity, low Q factor

Question 23

The very top of the baseline is called the

Answer 23

Nyquist limit

Question 24

Aliasing occurs when the doppler sampling rate is ___ in comparison to the measured blood velocities

Answer 24

too low

Question 25

The highest doppler frequency/velocity that can be measured without the appearance of aliasing

Answer 25

Nyquist frequency (limit)

Question 26

Nyquist limit formula

Answer 26

Nyquist limit (hz) = PFR/ 2

Question 27

2 ways to avoid aliasing are

Answer 27

raise the nyquist limit and reduce the doppler shift

Question 28

___ frequency transducers create more aliasing

Answer 28

higher

Question 29

5 techniques to avoid aliasing

Answer 29

Increase PRF Select a shallower sample volume lower frequency transducer use baseline shift use CW doppler

Question 30

Range resolution, sample volume, nyquist limit, and aliasing (what doppler)

Answer 30

PW doppler

Question 31

Range ambiguity, region of overlap, unlimited max velocity, no aliasing

Answer 31

CW doppler

Question 32

PW transducer characteristics (5)

Answer 32

1 crystal dampened pzt low Q factor Wide bandwidth low sensitivity

Question 33

CW transducer characteristic (5)

Answer 33

2 crystals undampened pzt high Q factor narrow bandwidth high sensitivity

Question 34

Higher frequency, pw only, 1 crystal, and normal incidence

Answer 34

Imaging

Question 35

0 or 180 agrees, low frequency, pulsed or cw, 1 or 2 crystals

Answer 35

Doppler

Question 36

Color doppler measures

Answer 36

mean velocity

Question 37

Spectral doppler measures

Answer 37

peak velocity

Question 38

Provides information regarding direction of flow. It is a pulsed ultrasound technique.

Answer 38

Color flow doppler

Question 39

Color flow doppler has range ___

Answer 39

resolution (range specificity)

Question 40

The 2 most commonly use dictionaries for color maps are

Answer 40

Velocity and variance mode

Question 41

The black region in the middle of the color map represents

Answer 41

No doppler shift

Question 42

This mode provides information on flow direction and velocity

Answer 42

Velocity mode

Question 43

With velocity mode maps, the color change is always

Answer 43

up and down

Question 44

This mode distinguishes laminar flow from turbulent flow

Answer 44

Variance mode

Question 45

Colors on the left side of the map represent

Answer 45

laminar flow

Question 46

With variance mode, the color change

Answer 46

side to side and up - down

Question 47

Non directional color doppler and only identifies the presence of a doppler shift

Answer 47

Power doppler

Question 48

Power doppler is also called

Answer 48

energy mode or color angio

Question 49

Used to eliminate low frequency doppler shifts from moving anatomy. Serve as a reject

Answer 49

Wall filter

Question 50

Wall filters are also called

Answer 50

high pass filters

Question 51

Special form of mirror image artifact arising only from spectral doppler.

Answer 51

Cross talk

Question 52

Crosstalk results from

Answer 52

doppler gain is too high The incident angle is near 90 degrees between the flow direction and the sound beam

Question 53

Tool that breaks the complex signal into its basic building blocks and identifies the individual velocities that make up the reflected doppler signal

Answer 53

Spectral analysis

Question 54

A digital technique used to process both pulsed and cw doppler signals. that distinguishes laminar flow from turbulent flow

Answer 54

Fast Fourier transform (FFT)

Question 55

Used to analyze color flow doppler. Less accurate but faster than fast Fourier transforms

Answer 55

Autocorrelation