chp 19 part 1

Question 1

The process of extracting the low doppler frequency from the tranducer’s carrier frequency is called _________?

Answer 1

Demodulation

Question 2

When blood cells move toward the transducer the Doppler shift is _______? (positive, negative)

Answer 2

positive

Question 3

When the reflected frequency is higher than the transmitted frequency the Doppler shift is _________? (positive, negative)

Answer 3

positive

Question 4

When blood cells move away from the transducer the Doppler shift is __________? (positive, negative)

Answer 4

negative

Question 5

When the reflected frequency is lower than the transmitted frequency the Doppler shift is __________? (positive, negative)

Answer 5

negative

Question 6

Doppler shifts are created when transmitted sound waves strike moving ________?

Answer 6

RBC’s

Question 7

Blood cells moving away from the transducer reflect sound with a __________?

Answer 7

lower frequency

Question 8

Blood cells moving toward the transducer reflect sound with a __________?

Answer 8

higher frequency

Question 9

_______, which is purely a _____________, indicates the distance that a red blood cell moves in 1 sec.

Answer 9

Speed, magnitude

Question 10

What is defined by magnitude and direction?

Answer 10

Velocity

Question 11

Doppler shift is _____________ related to the velocity of the blood cells.

Answer 11

Directly (The faster the velocity, the greater the doppler frequency)

Question 12

If Doppler shift is 8kHz when the bloods velocity is 2m/s, what will happen if the velocity slows to 1m/s?

Answer 12

Doppler shift will be halved to 4kHz

Question 13

Doppler shift is __________ related to transducer frequency.

Answer 13

directly

Question 14

A Doppler study is performed with a 2MHz transducer and the Doppler shift is 3kHz. If a 4MHz transducer is used what will the Doppler shift be?

Answer 14

6kHz

Question 15

The Doppler shift represents 100% of the true velocity when blood flow is ________________ to the sound beam? (direction)

Answer 15

Parallel

Question 16

When blood cells are moving either directly toward or directly away from the transducer, the velocity measurement is ________% accurate.

Answer 16

100

Question 17

When an __________ exists between the direction of flow and the sound beam, the measured velocity is less than the true velocity.

Answer 17

angle

Question 18

If the sound beam and flow direction are not parallel, what determines how much of the velocity is measured?

Answer 18

The % of the true velocity that is measured depends on the

Cosine of the Angle

Question 19

What is the relationship between the cosine 0 and the Doppler shift?

Answer 19

directly related ( If cosine 0 is reduced by half, the measured Doppler shift will be halved )

Question 20

When the angle between the direction of motion and sound is __º (degrees) or ___º (degrees), flow is parallel to the sound beam.

Answer 20

0º, 180º ( the measured and true velocities are equal )

Question 21

Cos 0º is 1, indicating flow in which direction

Answer 21

toward the transducer

Question 22

Cos 180º is -1, indicating flow in which direction

Answer 22

away from the transducer

Question 23

When the direction of flow is perpendicular (90º) to the sound beam, what is the measured velocity?

Answer 23

0, because the Cos of 90º is zero (Thus doppler shifts and velocities cannot be measured with perpendicular incidences)

Question 24

What is the cosine of 60º

Answer 24

0.5 ( so measured velocity at 60º is one-half the actual velocity)

Question 25

When blood travels at 2 m/s at a 60º angle to the sound beam, Doppler reports the velocity as what?

Answer 25

1 m/s

Question 26

The most common clinical Doppler devices are __________, which distinguish the direction of flow toward or away from the transducer.

Answer 26

bidirectional

Question 27

Doppler spectrum can be displayed graphically, showing flow toward the transducer is displayed ________ the baseline, and flow away from the transducer is displayed __________ the baseline.

Answer 27

above, below

Question 28

Commonly used signal processing technique for bidirectional Doppler?

Answer 28

Phase quadrature, or quadrature detection

Question 29

What is higher arterial velocities or venous velocities?

Answer 29

arterial

Question 30

How many crystals are required for Contiuous Wave Doppler?

Answer 30

2 ( one transmits and one receives )

Question 31

The greatest advantage of continuous wave doppler is its ability to accurately measure very high velocities. T or F

Answer 31

True

Question 32

What is the limitation ,with Continuous wave Doppler, when signals arise form all blood cells in the region of overlap between the transmit and receive beams?

Answer 32

Range Ambiguity

Question 33

Does a dedicated continuous wave transducer create anatomical images?

Answer 33

no (they have increased sensitivity and detect low amplitude reflections and small Doppler shifts)

Question 34

What is simultaneous anatomic imaging and Doppler called?

Answer 34

duplex imaging

Question 35

Dedicated continuous wave transducers do not use backing material. T or F

Answer 35

True

Question 36

What four things result due to the continuous wave transducer not having a backing material?

Answer 36

1. undampened transmitted signal 2. narrow bandwidth 3. high quality factor 4. higher sensitivity

Question 37

How many crystals are required for pulsed wave doppler?

Answer 37

1 PZT

Question 38

The greatest advantage of pulsed Doppler is being able to select the exact location where velocities are measured, called ____________?

Answer 38

range resolution, range specificity, or freedom from range ambiguity artifact

Question 39

The small marker used in pulsed Doppler that the sonographer positions on a two dimensional image?

Answer 39

Gate or sample volume

Question 40

When high velocity flow in one direction is incorrectly displayed as traveling in the opposite direction it is called ________?

Answer 40

aliasing

Question 41

Studies that simultaneously perform imaging and pulsed Doppler are also called what?

Answer 41

duplex

Question 42

Pulsed Doppler transducers are imaging transducers and contain backing material. T or F

Answer 42

True

Question 43

What characteristics of imaging transducers does pulsed doppler transducer have?

Answer 43

low quality factor lower sensitivity wide bandwidth pulses

Question 44

What is the most common error associated with Doppler ultrasound?

Answer 44

Aliasing (false identity)

Question 45

The very top of the spectral display is called the _________ and the part of the spectrum appearing at the bottom is called _________ when flow is toward the transducer.

Answer 45

Nyquist limit, aliasing

Question 46

Aliasing only occurs with pulsed Doppler. T or F

Answer 46

true

Question 47

Nyquist limit is _______ of the pulse repetition frequency (PRF)

Answer 47

one-half Nyquist (hz) = PRF/2

Question 48

The highest Doppler frequency or velocity that can be measured without the appearance of aliasing

Answer 48

Nyquist limit

Question 49

Two ways to avoid aliasing

Answer 49

* raise the Nyquist limit | * reduce the Doppler shift

Question 50

When the sample volume is ________, the PRF is low and the Nyquist limit is low.

Answer 50

Deep

Question 51

When the sample volume is _________, the PRF is high and velocity is sampled many times each second, and the Nyquist limit is high.

Answer 51

shallow

Question 52

____________ (higher, lower) frequency transducers create more aliasing.

Answer 52

Higher

Question 53

Less Aliasing

Answer 53

* slower blood velocity * lower frequency transducer * shallow gate (high PRF)

Question 54

More Aliasing

Answer 54

* faster blood velocity * higher frequency transducer * deep gate (low PRF)