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Echo Physics > Chap. 7 Level 1 > Flashcards

Chap. 7 Level 1 Flashcards

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1
Q

What is the Doppler effect

A

An apparent change in frequency caused by relative motion (Police sirens driving away) that results from a change in wavelength

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2
Q

Equation for determining Doppler shift change in frequency

A

Fdop = F detected - F transmitted = change in frequency

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3
Q

What is formula for Doppler shift

A

Fdop = 2(Fo)V/C

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4
Q

What is the Doppler effect

A

An apparent change in frequency which results in a change of wavelength

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5
Q

Doppler shift equation solving for velocity

A

V = C x Fdop/2(Fo) x cos

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6
Q

What angle is the flow when coming towards the transducer and away from the transducer

A
  • 0 degrees
  • 180 degrees
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7
Q

Formula for Fdop with angle

A

Fdop = 2(Fo)(V)(cos)/c

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8
Q

Increasing “ “ increases reflectivity and attenuation

A

Frequency

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9
Q

What is the optimal frequency for Doppler

A

Less than 2Mhz, you can see a depth > 5cm

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10
Q

What is RBC aggregation

A

RBC cannot be measured individually. RBC combine as a group creating constructive interference and create increased signal strength

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11
Q

Define the Doppler insonification angle

A

The angle that is formed between the transducer and direction of the target

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12
Q

What Doppler angles represent a positive and negative shift

A
  • Doppler angle < 90 = pos shift & pos velocity
  • Doppler angle > 90 = negative shift & neg velocity
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13
Q

What is wall filtering

A

Attenuates the lower frequency velocity signals

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14
Q

What is the human visible dynamic range

A

Less than 36 decibels (fewer than 64 shades of gray)

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15
Q

Equation for dynamic range of Doppler

A

20 x Log (A biggest/A smallest)

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16
Q

Wall filter range for adult echo

A

200hz - 600 hz

17
Q

What happens if wall filters are set to low

A

Doppler circuit saturates creating large white spikes on Doppler

18
Q

What happens if wall filters are set too high?

A

Doppler signal may be completely eliminated

19
Q

What is fast Fourier transform

A

A technique for separating a spectrum into its individual frequency components called bins

20
Q

What are the bins in FFT

A
  • Each bin corresponds to a narrow range of frequency shifts that can be converted to velocity using the Doppler equation
  • lowest frequency = lowest velocity
21
Q

What post processing element is used to make Doppler signals have a greater dynamic range

A

Compression

22
Q

What quantities does Doppler show on 2D display

A

Velocity, amplitude, time

23
Q

Which modality does aliasing occur?

A

Pw because of the listening period

24
Q

How to determine max detectable frequency shift in pw

A

Nyquist variation: Fdop = PRF/2

25
Q

What parameters effect aliasing on Doppler shift

A
  • higher velocity of blood
  • insonification angle close to 0 or 180
  • high transmit frequency
26
Q

What is aliasing

A

The Doppler signal peaks peaking into the bottom of the scale

27
Q

What is happening when adjusting scales

A
  • PRF changes; low PRF = big scale
  • As you decrease scales, you decrease dead time of pw
28
Q

Alternative options if aliasing continues

A
  • lower freq transducer
  • different view that represents same flow
  • use cw
  • use hprf doppler
29
Q

What is the spectral window

A

The open area between the baseline and the spectrum

30
Q

What is modal flow

A
  • Refers to a visual spectral envelope
  • the mode of all velocity measured
31
Q

How to determine if range ambiguity is present

A
  • if changing Doppler scale, the envelope shouldn’t change
32
Q

What is HPRF Doppler

A
  • a hybrid of both CW and PW
  • uses timing of shallower gate depth w/ focusing on deeper depth
  • allows for higher detectable velocity that pw can’t pick up
33
Q

What degree does inson angle need to be to receive 100% Doppler shift

A

0 degrees or 180 degrees

34
Q

If Doppler shift angle is other than 0 or 180, what can occur

A

The calculated velocity would be less than the actual velocity

35
Q

What is color Doppler

A

A color image that is generated by repeatedly generating lines of data from the same direction to create a color packet

36
Q

Why does color Doppler typically have Lower resolution

A

Larger packet sizes improve color sensitivity but require more time, lowering the resolution of the image

Echo Physics (5 decks)

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