Vascular Study Guide Chapter 1: Doppler Principles

What is the doppler equation to calculate velocity

- C i. Avg speed of sound in tissue (1540 m/s). This is programmed into the US system - V i. Estimated velocity - COS Θ i. Cosine of theta. this is the cosine value of the doppler angle of incidence. - Ft i. Transmitted doppler frequency. this is programmed into US system - Δf i. Frequency shift

Describe what is occuring in this image below and why it's happening. How can you fix it

- Spectral aliasing It occurs when the doppler freq shift exceeds one half PRF. The PRF is too low here so the top of the peak starts at the bottom again and works it's way up. To fix this, you need to increase the scale so it fits. PRF has been increased here to eliminate aliasing. increasing scale makes things smaller, decreasing makes things bigger.

What is the artifact below and how can it be fixed?

- The blue color on the left is residual "lag time" from reverse flow of the popliteal artery. If the frame rate is correct, it should be red like the image on the right instead of this "mosiac" of color. - Narrow the width of the color box to increase frame rate speed and eliminate artifact

Is this following example good steering or bad? Why?

-- Bad steering. poor spectral wavelength bc there is innapropriate beam steering and 90 degree angle to flow so shows no flow. c. *remember you want to steer to the side that's deeper and the and angle to flow should be 60 degrees

Standard color orientation is Blue _____, Red _____

-a. BART. Blue away Red towards

What is analog doppler a

. Common form of CW doppler. Displays instantaneous avg freq shift. Not depth specific and no sample volume. *Dr A said this is so obsolete but they just want us to know history of ultrasound. This has the same issues with CW with depth ambiguity

The difference in the transmitted frequency and the reflected frequency

Doppler shift:

A zero degree angle (doppler beam parallel to flow) results in the _____ frequency shift, whereas a _____ degree angle results in the lowest freq shift

a. 0 degree = highest freq shift b. 90 degrees = lowest freq shift

Low end economical US systems can be steered to only _____. High freq transducers usually can only be steered to _____

a. 15 degrees; 20 degrees

Continuous wave doppler has ____ piezo crystals

a. 2. One transmitting one receiving

For diagnostic ultrasound, transmitted doppler frequency is between _____

a. 2.0 - 10 MHz

How many pulses per scanline are required for color autocorrelation? How many are commonly used?

a. 3 pulses required b. 8-20 commonly used

What is the maximum about of steering

a. 30 degrees

If the beam is phased (steered) to 30 degrees, the angle to flow will be ___ a. 60 degrees

a. 60 degrees b. **steering angles and angle to flow are complimentary angles and need to add up to 90 degrees. So if steering angle is 30, angle to flow will be 60. steering angle 0, angle to flow 90.

What is the worst doppler beam angle to use

a. 90 degrees

Why does aliasing occur here?

a. Aliasing at region A because the angle is smaller than at region B therefore a higher frequency than at B

If the PRF color scale is set too low, _____ will occur. If set too high, _____

a. Aliasing; low velocity as in diastolic flow may not be detected.

What are other names for the angle to flow?

a. Angle theta, the doppler angle

What is strobe light affect and what causes it? How can it be fixed?

a. Artifact that Occurs when frame rate is too slow. slow frame rate in the lower extremities can cause a storbe light effect and results in poor vessel filling b. Can be fixed by narrowing the width of the color box

Generally, negative shift (flow away) is displayed ____ (above, below) the spectral baseline, unless _____ is enabled.

a. Below; "spectral INVERT"

Amplitude or power is displayed

a. By the brightness of the pixels.

What happens when wall filters are set improperly ? What is wrong the images below?

a. Can adversely affect waveform morphology b. On the left: the wall filter is set too low so its not filtering out low freq noise c. On the right: the wall filter is set too high so it's eliminating portions of the waveforms

What is autocorrelation?

a. Color information. most color doppler systems use to generate color image. b. An initial pulse transmitted along scan line, received echo is stored. c. Subsequent pulse - echoes are stored and compared to intial reference echo

Rule of thumb: to obtain a doppler angle of 60 degrees of less, streer to the side that's ____

a. Deeper

Another way to reduce aliasing?

a. Drop the spectral display baseline

The principal we use to detect blood flow:

a. Echo doppler

The density or number of scan lines (scanline density) also affects color image and frame rate. Higher line density (high number of scan lines within the color box) means ____ color spatial resolution but ____ frame rate

a. Good; slow

The faster the velocity, the _____ the frequency shift

a. Greater

If a transducer only steers the doppler beam to 20 degrees, this will result in 70 degree angle to flow. In order to create a lower 60 degree angle to flow, what can be done?

a. Heal Toe the transducer to decrease doppler angle to flow

The higher the transmitted frequency, the ____ the frequency shift for any given velocity

a. Higher

Time is displayed on _____

a. Horizontal axis (x-axis)

Aliasing can be useful in ______

a. Identifying the jet. Highlighting focal regions of velocity increase. adjusted to bring out the aliasing near point of maximum stenosis; visual clue where to place doppler sample volume

If the sound beam moved rapidly toward the observer, audible frequency will ______. If sound source moves rapidly away, frequency will ______

a. Increase; decrease b. *slinky car example

The _____ the angle (numerically), the higher the frequency shift

a. Lower

Autocorrelation provides the following information

a. Mean frequency shift b. Flow direction (sign = negative or positive) c. Variance (spread of frequencies, turbulence. amount of colors) d. Power or amplitude (is it robust red or strong)

Color doppler uses _______ to create real-time image of frequency shifts related to movement and acquire color information

a. Multiple scan lines

Flow away from doppler beam is ____ shift. Flow towards doppler beam is ____ shift. This is termed _____

a. Negative; positive; bi-directional doppler b. *remember slinky example... that sound moving away from source is LOWER freq. so the returning echo will be a lower freq/number to plug into doppler shift equation so it will be a negative number

In continuous wave doppler, is there an aliasing artifact?

a. No

If the returning freq is the same as the transmit freq, there is _____ doppler shift

a. No doppler shift; no movement or flow

If the beam is ______, it appears straight down and perpendicular to face of transducer and there is ___ degrees of beam steering

a. Not phased (un-steered); zero degrees

Is Continuous wave doppler specific for depth?

a. Not specific for depth.

Pulses per scan line are also known as the following terms

a. Packet size b. Ensemble length c. Color sensitivity d. Color quality

Typical measurements of velocity include

a. Peak systolic velocity (PSV) and end-diastolic velocity (EDV)

Beam steering in linear array transducers is done by _____. This allows the doppler beam to be steered _________

a. Phasing; To the left or to the right

With the feature "Intelligent Doppler", the doppler angle adjustment curser has an arrow that is adjusted to _______. Normal or ______ flow will be displayed _____ baseline regardless of steering and abnormal, or _____ flow, will be _____ baseline.

a. Point in the direction that flow is supposed to be traveling b. Normal = antegrade flow. displayed above baseline c. Abnormal = retrograde flow. displayed below baseline

If the returning frequencies are higher than the transmitted frequencies, the doppler shift will be a ____ value. If returning frequencies are lower, the doppler shift will be a ____ value

a. Positive value or positive (+) shift b. Negative value or negative (-) shift

number of pulse-echo cycles occurring in one second

a. Pulse repetition freq. PRF

______ detection and processing allows "directionality" to be determined

a. Quadrature

Purpose of estimating flow velocity?

a. Quantitation of arterial stenosis b. Define pathologic conditions

Describe the difference between range specificity and range ambiguity

a. Range ambiguity is what continuous wave system have due to not being depth specific. Range specificity is the opposite and what pulsed waves have since you do know the depth or sample volume. Rage gate = range specificity

Other names for sample volume?

a. Range gate, sample gate

Increasing the size of the sample volume increases the ____ of the doppler elements

a. Ring time. Pulse length is the "ring time" or duration of transmission b. Large SV = long pulse length; small SV = short pulse length

High number of pulses per scan line will produce ______ color but _____ frame rate

a. Robust and full color; lower frame rate (slow)

An integral part of pulse doppler system is _____.

a. Sample volume. It allows a specific region of a vessel to be analyzed

PRF in most systems in adjusted with ____ control in spectral and color doppler

a. Scale

Pulsed wave dopplers may consist of _______ or _____

a. Single crystal or array of elements

Types of transducer designs for pulsed wave doppler

a. Single element transducers b. Multi-element linear array c. Phased array transducers

Manufacturers use _____ to improve frame rates

a. Spatial averaging b. This is just filling in the spaces between the scanlines

A large sample volume increases _____ as there are more "lanes of traffic" being sampled

a. Spectral broadening . b. Small SV samples a more discrete area of flow, and spectral waveform displays less spectral broadening

Many doppler systems have autoinvert which will automatically flip flop the directional sign (+ or -) on spectral display when the doppler beam is _____

a. Steered in the opposite direction b. *this does not change color coding, just the color bar is reversed. The waveform also remains on the same side of baseline, but negative and positive signs flip

What is a single element PW doppler used for?

a. TCD - transcranial doppler

What are wall filters? What are some other names for wall filters

a. They eliminate low frequencies along the spectral baseline or color baseline. b. Also called High pass filters or Thump filters

The frequency of the transmitted signal depends on the _____ of the elements. The _____ the element, the higher the frequency. The _____ the element, the lower the frequency

a. Thickness or size; smaller; thicker b. Thin = high freq; thick = low freq

Fast-fourier transform FFT processes _______

a. Thousands of doppler shifts each second and subdivides freq into bins

What is the purpose of doppler beam steering?

a. To achieve a 60 degree angle to flow or less

With color gain, if set too high, the color will ________. If set too low _____

a. Too high: "bloom" out of the vessel onto the surrounding tissue or it may obscure disease. b. Too low: inadequate color filling

. With PW doppler, the same piezo elements are used for ____ and _____

a. Transmission and reception

Sample volume length determines the ______

a. Transmit pulse length

In a curved array, the doppler beam is unsteered. True or False

a. True

Describe the piezoelectric effect

a. Voltage applied to crystal and the piezoelectric elements vibrate. This converts electric energy into mechanical. b. The returning sound waves vibrate the piezo elements. This is the conversion of mechanical energy into electric.

What is range ambiguity ?

a. We don't no what depth the beam is coming from in continuous wave doppler. the beam shoots through artery and vein and will plot them on top of each other or average the frequency information together so the waveforms will be distorted. This is a bad thing

Low number of pulses per scan line will produce ____ color but ____ frame rate

a. Weak or "holey" color; high frame rate (fast)

Is the example below good steering or bad? Why?

a. b. Bad steering and bad angle alignment. Even though the angle reads 60 degrees, it is NOT a 60 degree angle to flow bc the curser is misaligned.

Why are the velocities different in the 3 examples below?

a. b. They each have different doppler angle (cosine values). The first one is at 60 which is correct

Color frame rate variables:

a. pulses per scan line (packet size) b. Density of scan lines c. Color box width d. PRF

The frequency shift is related to what three things

a. transmitted doppler frequency b. Velocity of blood cells c. Angle of doppler beam to flow

Doppler shift freq is displayed on _____

a. vertical axis (y-axis)

Aliasing occurs when doppler shift frequencies exceed ____. This is known as the ____ limit

a. ½ of PRF b. Nyquist limit

Equation for doppler shift a.

Δf = fr - ft