Physics Ch. 19 & 20 Flashcards by Hope Spriggs

A change in frequency that comes from motion between sound source and the receiver as they move closer and farther apart

Doppler shift

How well did you know this?

Not at all

Perfectly

Another name for doppler shift

doppler frequency

How well did you know this?

Not at all

Perfectly

What is doppler used to measure

velocity of blood in the circulation

How well did you know this?

Not at all

Perfectly

Process of extracting the low doppler frequency change from the transducers transmitted frequency

demodulation

How well did you know this?

Not at all

Perfectly

Doppler shift (HZ)=

reflected frequency - transmitted frequency

How well did you know this?

Not at all

Perfectly

Doppler shifts are in the _____ range of frequencies (_______)

audible, 20Hz-20kHz

How well did you know this?

Not at all

Perfectly

Doppler shifts are created when transmitted sound wave strikes

moving red blood cells

How well did you know this?

Not at all

Perfectly

Blod flow moving toward the transducer is

positive doppler shift

How well did you know this?

Not at all

Perfectly

Positive doppler shift: the _____ frequency is HIGHER than the _____ frequency

reflected, transmitted

How well did you know this?

Not at all

Perfectly

Blood flow is moving away from the transducer

negative doppler shift

How well did you know this?

Not at all

Perfectly

Negative doppler shift: the reflected frequency is _____ than the transmitted frequency

lower

How well did you know this?

Not at all

Perfectly

Speed is _____ only

magnitude

How well did you know this?

Not at all

Perfectly

Velocity is ______ and ______

magnitude, direction

How well did you know this?

Not at all

Perfectly

Doppler shift is directly related to

velocity, frequency, cosine

How well did you know this?

Not at all

Perfectly

Doppler shift is inversely related to

speed of sound in soft tissue

How well did you know this?

Not at all

Perfectly

The faster the velocity, the _____ the doppler shift

greater

How well did you know this?

Not at all

Perfectly

What is the doppler equation

2 x vel of blood x transducer frequency x cosine / prop speed

How well did you know this?

Not at all

Perfectly

Why is there a 2 in the doppler equation

First when sound from transducer hits the moving blood cells / Second when the transducer receives the returning sound wave

How well did you know this?

Not at all

Perfectly

Doppler shift is measured in units of

frequency

How well did you know this?

Not at all

Perfectly

Velocity is measured in units of

cm/sec

How well did you know this?

Not at all

Perfectly

If the transducers frequency is doubled, the measured ______ will also be doubled

doppler shift

How well did you know this?

Not at all

Perfectly

What about velocity changes with transducer frequency

the calculated velocities will be the same regardless of the frequency of the transducer

How well did you know this?

Not at all

Perfectly

The measurement of the doppler depends on the relationship between the

direction of blood flow and direction in which the sound wave propagates

How well did you know this?

Not at all

Perfectly

When the blood cells are moving parallel to the sound beam (__ to __) the

0 degrees- 180 degrees, entire velocity is measured and 100% accurate

How well did you know this?

Not at all

Perfectly

When blood cells are moving perpendicular (____) to the sound beam, there is

no doppler shift and no velocity measurement is attainable

If the sound beam and flow direction are not parallel, only a percentage of the true velocity is measured and that depends on the

cosine of the angle between the sound beam and the direction of flow

Measured velocity=

true velocity x cosine

Positive and negative doppler shift. Flow toward and away from the transducer

bidirectional doppler

Signal processing technique for bidirectional doppler

phase quadrature/quadrature detection

Doppler that requires TWO crystals

continuous wave doppler

What do the two CW doppler crystals do

one constantly transmits and the other constantly receives

What is the advantage of CW

ability to accurately measure very high velocities

Disadvantages of CW and what is the name for it

cannot determine exact location of the highest velocity, range ambiguity

Reflections created during CW from blood cells located deeper will have

lower amplitude (weaker signal) than reflections from shallower depths

What are CW transducers also called

dedicated CW transducer, blind transducer, pedoff transducer

CW transducers do not have

backing material

What are the 4 qualities of a dedicated CW transducer

undampened transmitted signal, narrow bandwidth, high Q factor, higher sensitivity

Simultaneous anatomic imaging and doppler is called

duplex imaging

Only one crystal is necessary, alternates between sending and receiving

Pulsed wave doppler

2 advantages of PW

select exact location for velocity measurement / use of sample volume or gate

When choosing the exact location for PW, what is this called

range resolution, range specificity, range specific

What does the sample volume/gate use

time of flight calculation

What is the disadvantage of PW

inaccurate measurement of high velocity signals (aliasing)

PW doppler transducers have backing material so they have

low Q factor, low sensitivity, wide bandwidth

Doppler gain settings alter the gray scale content of the spectral display

spectral doppler gain

Spectral doppler wall filters selectively eliminates ____ frequency doppler shifts near the ____ of the spectral display

low, baseline

The wall filter does not affect the appearance of

higher velocity flows

Most common error associated with doppler ultrasound

aliasing

An alias is a ______ which is very _____ velocities in one direction are ____ displayed as going in the ______ direction

false identity, high, incorrectly, opposite

The very top of the display is called

nyquist limit

The part of the spectrum appearing at the bottom is called

aliasing

Aliasing occurs when the

doppler PRF is too low in comparison to the measured blood velocities (nyquist limit surpassed)

Nyquist limit=

PRF/2

highest doppler shift or velocity that can be measured without the appearance of aliasing

nyquist limit

Two ways to avoid aliasing

raise the nyquist limit (PRF), reduce the doppler shift

The sampling rate of PW doppler is the

PRF

When the sample volume is deep, the PRF is

low

Deeper sample volume shave a lower _____ and create _____

PRF, aliasing

When the sampler volume is shallow, the PRF is _____, Nyquist limit is _____

high, high

Five techniques to avoid/correct aliasing

1. adjust scale (PRF) to max 2. Use a different u/s window and shallower sam volume 3. lower frequency trans 4. adjust baseline 5. use cw doppler

Gray shades of spectral display are related to

amplitude of reflected signal, number of blood cells creating the reflection

Velocity info is coded into colors and superimposed on a 2D gray scale anatomic image

color flow doppler

Color doppler provided info regarding ______ and is considered _____

direction of flow, semi-quantitative

Color doppler reports/measures ____ or ____ velocities

average, mean

Two most commonly used maps/dictionaries are called

velocity mode, variance mode

The colors provide info on flow direction and mean velocity and is shown on the color map in which direction

velocity mode, top to bottom

Provides more info, can distinguish between laminar and turbulent flow. What direction is the color map read

Cariance mode, side to side

The multiple ultrasound pulses for blood velocities is called

packet/ensemble

To correct aliasing on color doppler you

increase scale/PRF/Nyquist limit

What does the color look like with aliasing

color wrap around reds to blues

What does color look like with flow reversal

red to black to blue

The wall filter selectively eliminateds _______ doppler shifts. The wall filter leaves the _________ unchanged.

low frequency, high velocity flows

Identifies only the presence of a doppler shift

power doppler

Does power doppler evaluate velocity or direction

Power doppler is also called

energy mode or angio

In power mode, the amplitude of the reflection is directly related to the

number of moving blood cells

Advantages of power mode

increased sensitivity to low flow, unaffected dopp angles, no aliasing

Disadvantage to power mode

no velocity or flow direction

On spectral analysis, the artifacts are called

clutter

With color doppler, the artifacts are called

ghosting

How do we eliminate ghosting or clutter artifacts

wall filter

Used to eliminate low frequency doppler shifts from moving anatomy rather than from moving blood cells ("reject")

wall filter

Special form of mirror image artifact that only arises with spectral doppler

crosstalk

Appears as an identical doppler spectrum both above and below the baseline

crosstalk

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

spectral analysis

What are the two methods of spectral analysis

fast fourier transform (FFT), autocorrelation

A digital technique used to process both pulsed and continuous wave doppler signals

fast fourier transform

Spectral display of an FFT distinguishes

laminar flow from turbulent flow

Digital technique used to analyze color doppler, less accurate but faster

autocorrelation