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physics 3 > chp 19 part 1 > Flashcards

chp 19 part 1 Flashcards

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1
Q

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

A

Demodulation

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2
Q

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

A

positive

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3
Q

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

A

positive

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4
Q

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

A

negative

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5
Q

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

A

negative

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6
Q

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

A

RBC’s

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7
Q

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

A

lower frequency

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8
Q

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

A

higher frequency

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9
Q

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

A

Speed, magnitude

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10
Q

What is defined by magnitude and direction?

A

Velocity

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11
Q

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

A

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

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12
Q

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

A

Doppler shift will be halved to 4kHz

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13
Q

Doppler shift is __________ related to transducer frequency.

A

directly

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14
Q

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?

A

6kHz

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15
Q

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

A

Parallel

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16
Q

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

A

100

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17
Q

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

A

angle

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18
Q

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

A

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

Cosine of the Angle

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19
Q

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

A

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

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20
Q

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

A

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

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21
Q

Cos 0º is 1, indicating flow in which direction

A

toward the transducer

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22
Q

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

A

away from the transducer

23
Q

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

A

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

24
Q

What is the cosine of 60º

A

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

25
Q

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

A

1 m/s

26
Q

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

A

bidirectional

27
Q

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.

A

above, below

28
Q

Commonly used signal processing technique for bidirectional Doppler?

A

Phase quadrature, or quadrature detection

29
Q

What is higher arterial velocities or venous velocities?

A

arterial

30
Q

How many crystals are required for Contiuous Wave Doppler?

A

2 ( one transmits and one receives )

31
Q

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

A

True

32
Q

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?

A

Range Ambiguity

33
Q

Does a dedicated continuous wave transducer create anatomical images?

A

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

34
Q

What is simultaneous anatomic imaging and Doppler called?

A

duplex imaging

35
Q

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

A

True

36
Q

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

A
  1. undampened transmitted signal
  2. narrow bandwidth
  3. high quality factor
  4. higher sensitivity
37
Q

How many crystals are required for pulsed wave doppler?

A

1 PZT

38
Q

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

A

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

39
Q

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

A

Gate or sample volume

40
Q

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

A

aliasing

41
Q

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

A

duplex

42
Q

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

A

True

43
Q

What characteristics of imaging transducers does pulsed doppler transducer have?

A

low quality factor
lower sensitivity
wide bandwidth pulses

44
Q

What is the most common error associated with Doppler ultrasound?

A

Aliasing (false identity)

45
Q

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.

A

Nyquist limit, aliasing

46
Q

Aliasing only occurs with pulsed Doppler. T or F

A

true

47
Q

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

A

one-half

Nyquist (hz) = PRF/2

48
Q

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

A

Nyquist limit

49
Q

Two ways to avoid aliasing

A
  • raise the Nyquist limit

* reduce the Doppler shift

50
Q

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

A

Deep

51
Q

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

A

shallow

52
Q

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

A

Higher

53
Q

Less Aliasing

A
  • slower blood velocity
  • lower frequency transducer
  • shallow gate (high PRF)
54
Q

More Aliasing

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

physics 3 (2 decks)

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