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Sam's Physics II > Chapter 19 > Flashcards

Chapter 19 Flashcards

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1
Q

Doppler shift is also called…

A

Doppler frequency

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2
Q

The Doppler principle is used to measure?

A

blood cell velocities in circulation

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3
Q

The frequency of sound changes when

A

the sound source and the receiver move closer together or farther apart

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4
Q

The frequency does NOT change when

A

the distance between the sound source and the receiver remains constant

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5
Q

The process of extracting the low Doppler frequency from the transducer’s carrier frequency is

A

demodulation

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6
Q

Doppler shifts are created when

A

transmitted sound waves strike moving red blood cells

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7
Q

When blood cells move toward the transducer, the Doppler shift is

A

positive

the reflected frequency is higher than the transmitted frequency

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8
Q

When blood cells move away from the transducer, the Doppler shift is

A

negative

the reflected frequency is lower than the transmitted frequency

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9
Q

Doppler frequencies indicate what?

A

velocity NOT speed

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10
Q

Speed is

A

magnitude indicates the distance that a red blood cell moves in 1 second
units: cm/second or any distance/time

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11
Q

Velocity is

A

magnitude and direction

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12
Q

Example of speed and velocity

A

A car travels from New York to Florida at 50mph

speed: 50 mph (speed is magnitude)
velocity: 50 mph to the south (magnitude and direction)

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13
Q

The Doppler equation

A

Doppler shift = 2 X velocity of blood X transducer frequency X cos/ propagation speed

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14
Q

What is the relationship between the velocity of blood and Doppler shift?

A

Directly related

the faster the velocity, the greater the Doppler frequency

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15
Q

Why is there a 2 in the Doppler equation?

A

the 2 represents the fact that there are actually two Doppler shifts during a clinical ultrasound exam

1st: occurs when the sound wave from the transducer strikes moving blood cells
2nd: reflections return to the transducer

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16
Q

If the Doppler shift is measured with units of frequency, how do ultrasound systems report blood velocity?

A

modern ultrasound actually measure the frequency difference (in Hz) between the received and transmitted sound waves

17
Q

The X-axis of a Doppler spectrum represents what?

A

time

18
Q

The Y-axis of a Doppler spectrum represents what?

A

velocity

19
Q

What is the relationship between the transmitted frequency and the Doppler shift?

A

directly related

if the transducer’s frequency is doubled, the measured Doppler shift will also be doubled

20
Q

A Doppler study is done with a 2 MHz transducer, and the Doppler shift is 3 kHz. If the identical study is done with a 4 MHz transducer, the Doppler shift will be?

A

6 kHz

21
Q

Doppler shift measured in Hz

A

directly related to velocity

directly related to transducer frequency

22
Q

In order to measure the entire velocity the blood cells must be

A

parallel to the sound beam

23
Q

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

A

depends on the cosine of the angle between the sound beam and the direction of motion

24
Q

The most common clinical Doppler devices are

A

bidirectional

which distinguish the direction of flow toward or away from the transducer

25
Q

Flow toward the transducer is

A

displayed above the baseline

26
Q

Flow away from the transducer is

A

displayed below the baseline

27
Q

Phase quadrature or quadrature detection

A

is commonly used signal processing technique for bidirectional Doppler

28
Q

Continuous wave Doppler has how many crystals in the transducer?

A

2

one crystal transmits the sound wave and the other receives the signal

29
Q

Advantage of continuous wave Doppler

A

ability to accurately measure very high velocities

30
Q

Disadvantage of continuous wave Doppler

A

exact location of moving blood cells can’t be determined
signals from all blood cells in the region of overlap between the transmit and receive beams
lack of TGC

31
Q

The limitation of the continuous wave Doppler is called

A

range ambiguity

32
Q

Duplex imaging is

A

when simultaneous anatomic imaging and Doppler is used at the same time

33
Q

Dedicated continuous wave transducer do not use what?

A

backing material

34
Q

Not using backing material in a dedicated continuous wave transducer results in

A

undampened transmitted signal
narrow bandwidth
high quality factor (Q factor)
higher sensitivity

35
Q

Dedicated continuous wave transducers have

A

increased sensitivity

the detect low amplitude reflections and small Doppler shifts

Sam's Physics II (7 decks)

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