Doppler Artifacts Ch19,20, 21

Artifacts include reflections that are described as:

* Not real * Not seen on the image * incorrect shape or size * incorrect position * incorrect brightness

4 Characteristics of reverberation:

* appear in multiples * appear equally spaced * are located parallel to the sound beam's main axis. * are located at ever-increasing depths

Cosine of a 90 degree angle = Cosine of 0 degree angle = Cosine of 180 degree angle =

0 1 -1

P. 347, Fig 20.8 A, B. 1. What artifact appears in image A? 2. ___________ within a vessel are an indication of aliasing. 3. Image B: color closest to vessel walls is red (bottom of color scale) so which direction is this blood flow traveling? Blue is in center of vessel (top of color scale), which direction is it traveling?

1. Aliasing occurs in Color Doppler image 2. color changes 3. Red: away from transducer or from Lt to Rt Blue: towards the transducer or from Rt to Lt.

1. How can we distinguish bidirectional flow from aliasing with color flow Doppler? 2. Do they appear the same? 3. What holds the key to distinguishing one from the other?

1. Determine which colors on image are next to each other and compare to color scale. 2. They appear differently 3. the color scale

What causes Crosstalk Doppler artifact?

1. Doppler Gain set too high 2. Incident angle is near 90° when flow is at beams focus.

What 2 advantages does FFT have?

1. Exceedingly Accurate 2. Displays all individual velocity components that make up the complex reflected signal.

Six basic assumptions of imaging systems

1. Sound travels in a straight line 2. Sound travels directly to a reflector and back 3. Sound travels in soft tissue at exactly 1,540m/s 4. reflections arise from structures positioned along the beam's main axis. 5. The imaging plane is very thin. 6. Strength (intensity) of the reflection is related to the scattering characteristics of the tissue creating the reflection.

P. 342: Fig 20.3 A, B, and C. 1. In image A there is no color flow shown, why? 2. What will make color appear in the vessel? 3. Is there an alternative method to make color appear in vessel other than changing the angle?

1. The US beam is at a 90 degree angle to (perpendicular to) the flow in the vessel. Cosine of 90 is Zero, no doppler shift is created or measured, no color appears. 2. Change the angle b/t the direction of the sound beam and the direction of the blood flow. 3. NO

Causes of artifacts:

1. violation of assumptions 2. equipment malfunction or poor design 3. the physics of ultrasound 4. operator error

How do you eliminate Ghosting artifact on color Doppler displays? How does it work?

A wall filter. Wall filter eliminates color that can arise "bleeding" from slow Velocity reflectors such as nearby tissue.

If the colors that touch each other in an image go around the outside of the color map ________ is present.

Aliasing

P. 344, Fig 20.5A, B, C; Carotid artery: Image A: is high quality and of diagnostic value. Image B: What single control on an US system can make color appear all throughout the color box as in this image? How does this occur? A term that describes this appearance is what? Image C: What single control on an US system can make color disappear as shown in this image? How can the sonographer correct this?

Image B: Color Gain setting; When the color gain setting is set to an inappropriately HIGH level. Color Confetti Image C: Color Gain setting; When the color gain setting is set inappropriately too LOW all the color disappears. The sonographer can INCREASE THE COLOR GAIN.

P. 346, Fig 20.7 A, B,C. Spectral Doppler Gain Image A: high quality, diagnostic value Image B: What alteration is responsible for the change in appearance from Image A to Image B? What controls this occurrence and how did it change this? Image C: What is responsible for the change b/t image A and C and how so? What has occurred due to this?

Image B: Gray scale noise appears all throughout the spectrum. Pulsed Doppler gain setting. Pulsed Doppler gain setting is set too HIGH causing gray scale noise. Image C: Pulsed Doppler gain setting is now set too LOW. All gray scale noise has disappeared but so has the meaningful Doppler spectrum.

How do you eliminate Clutter on spectral displays?

Increase the Wall filter

How does reverberation effect assumption #2 in imaging systems?

It is invalid in reverberation

Autocorrelation is (more/less) accurate than FFT? Autocorrelation is (faster/slower) than FFT?

Less; Faster

Color "bleeds" into moving anatomy with a ______ wall filter. With _______ wall filters, low velocity reflectors such as tissue are without color.

Low; higher

Can wall filters work on high freq Doppler shifts? What happens to a high velocity flow in an artery if the wall filter is increased?

No, only on Low freq shifts. Nothing, wall filter has no effect on high velocity Doppler shifts.

Six assumptions are incorporated into imaging system designs. Artifacts occur when when these assumptions are _____________.

Not true.

Earlier methods of Doppler analysis are _______ nowadays. They include: (name 3).

Obsolete. Zero Cross'g Detectors; Chirp-Z transform, & time interval histograms.

Review image characteristics: Hyperechoic, Hypoechoic, Anechoic, Isoechoic, Homogenous, Heterogenous.

P. 356

FFT, Fast Fourier Transform is _________ technique that is used in spectral analysis to process what type(s) of Doppler signals?

Pulsed and continuous wave

A wall filter serves as a _______ for Doppler

Reject

Def- appear on the display as multiple, equally spaced echoes caused by the bouncing of the sound wave b/t two strong reflectors positioned parallel to the US beam.

Reverberation

In laminar flow, most blood cells travel at _____________. The spectral trace is described how?

Similar velocities. Narrow, well-defined line.

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

Spectral analysis

A wall filter eliminates low freq Doppler signals near the ________.

Spectral baseline

With turbulent flow, the pulsed Doppler spectral window is filled in and termed what?

Spectral broadening

Low freq Doppler shifts are called Clutter on what?

Spectral displays

The region between the baseline and spectrum is called what?

Spectral window

What is the significance of FFT displaying all individual vel components?

The FFT can then distinguish laminar flow from turbulent flow. P 336

Crosswalks true pattern is ____________. But it appears as ________.

Unidirectional, bidirectional

Slow moving anatomy like heart muscle or pulsing vessel may create what?

Very low freq Doppler shifts

How does increasing the wall filter effect spectral Doppler?

Wall filter selectively eliminates low freq Doppler shifts near the baseline. No longer visible near baseline. See fig 20.14, p. 352.

The _________ selectively eliminates low freq Doppler shifts. P. 351, fig 20.13A,B: Color image A shows Vein color (blue) and Artery color (red) with some Ghosting artifact extends outside the artery lumen ("bleeding"). What adjustment can the sonographer do to correct this? What effect will this have on the image that results in image B?

Wall filter. Sonographer can increase the wall filter. ghosting is corrected, color flow is seen only within the artery lumen and the color in the slowly moving blood cells in the vein and tissue is gone.

Does increasing the velocity scale have any other effect on a color Doppler image? If so, what is it?

Yes. Increasing the velocity scale DECREASES THE SENSITIVITY to slow flows.

Doppler shifts arise from _________.

moving blood.

PW Doppler accurately identifies what? Range ambiguity or range resolution? how sensitive compared to CW doppler? How good is temporal resolution? Aliasing or no aliasing? Records peak or mean velocity measurements?

the exact location of flow; Range resolution; moderately sensitive; very good temporal resolution; subject to aliasing; Peak velocity measurements.

Reverberation artifact places _________________ on the image.

too many reflections

Pg 343, Fig 20.4 A, B, C. 1. Why is there no color in image A? Steering box is angled ________. The vessel is horizontal or slanted? 2. What will make color appear in the vessel? 3. Any other way other than angle change to make color appear?

1. vessel does not have to be horizontal, in this image A it is slanted, steering box is angled to the left, however, this is still creating a 90 deg angle b/t the blood flow and US beam. No Doppler shift, no color appears. 2. Again, change the angle of the sound beam to that of the blood flow. Angle the steering box either to the right or horizontal since the vessel is slanted. 3. NO

_____________ should be considered a possible source of peculiar color variation, changing from red to blue & vice versa. (appearance that flow is going both directions in single vessel).

Aliasing

An error in imaging is termed what?

Artifact

Correlation Function aka for

Autocorrelation

Slow flows are assigned to what area of the color map?

Black, in center of map.

Summary of Doppler modality roles: Includes summary of the following

CW doppler, PW doppler, Color Flow, Power mode

With turbulent flow, blood flow is described as what? Meaning, within the sample volume, it is moving at _____________ & _________.

Chaotic; different speeds and different directions.

What is the first thing to do anytime a vessel is colorless.

Check the angle between flow and sound.

In laminar flow, the spectral window is __________? In turbulent flow the pulsed Doppler spectral window is _________?

Clear; filled in

Low freq Doppler shifts are called Ghosting artifact on what?

Color Doppler

___________ _________ has evolved into a primary diagnostic tool. Unfortunately, _________ or _________ images can be created with color doppler. Doppler images demand _________ ______ and __________.

Color Doppler; suboptimal or non-diagnostic; careful analysis and interpretation.

Wall filters are used in both _________ and __________.

Color flow and spectral Doppler.

All blood cells within a sample volume (do or do not) travel at the same direction and speed?

Do Not

FFT stands for

Fast Fourier Transform

2 methods of spectral analysis

Fast Fourier Transform (FFT) and Autocorrelation

What is another name for wall filter?

High Pass Filters

Crosstalk appears as an _________ Doppler spectrum. Meaning, both _____ & ______ the baseline.

Identical; Above & below

If aliasing appears in an artery on a color flow image what is the most effective way the sonographer can do to correct this, increase the velocity scale or wall filter? How do we know that aliasing is for sure occurring to make this adjustment? The vein near this same artery is showing blue color. After increasing the scale, the blue color disappears. Why? Why did the sonographer not increase the wall filter?

Increase the velocity scale. Check the color map and compare to colors in image, the appearance of adj. colors shows aliasing occurs. Increasing the scale eliminates the blue color b/c sensitivity to slow flow is reduced. Changing wall filter would eliminate the blue color in vein but arterial flow would not be changed. A wall filter will alter low velocity flows, while leaving high velocity flow unchanged. See fig 20.16, p.354

What is the most effective way to reduced or eliminated aliasing on a color Doppler image? *remember the 5 tech's, are all applicable to color Doppler images? Can you switch to CW Doppler on a color Doppler image?

Increase the velocity scale. No, not all listed on p. 319 are applicable. No, CW doppler is not applicable.

Pg 345, Fig 20.6 - Normal Kidney images A, B, C. Image A: high quality and diagnostic value Image B: What single control on an US system can create what is in image B? Image C: What single control on an US system can make this image? Can angle b/t sound beam and blood flow play a role in this image?

The color gain setting is set too high. The color appears throughout the entire color box. Color Confetti appearance. Color gain setting is now set too low, making all the color disappear. Since this is sector-shaped image, angle does not play a role.

P. 352, Fig 20.14 A,B: in image A, Doppler shifts close to the baseline are displayed. In image B, Doppler shifts no longer appear. What adjustment did the sonographer make?

The sonographer increased the wall filter.

Why are earlier methods of Doppler analysis now obsolete? Name 2 reasons

They were Analog; only the mean velocity was reported

Many Doppler-shifted freq arise from __________.

a mass of moving blood cells.

Example of low velocity scale on an artery (high velocity vessel) creates _______ with that vessel. Correction is to do what? Example of high velocity scale on a vein (low velocity vessel) causes what with an increased velocity scale?

aliasing. Increase the velocity scale making it high velocity. No color flow seen in vein, scale to high for low velocity vessel.

CW Doppler identifies highest velocity jets where? Range ambiguity or range resolution? how sensitive is it compared to PW doppler, Pwr mode or color flow? How good is it's temporal resolution? Aliasing or no aliasing? Records peak or mean velocity measurements?

anywhere along the length of US beam; Range ambiguity; the most sensitive; very good temporal resolution; No aliasing; Peak velocity measurements

Why is autocorrelation used with color Doppler?

because of the enormous amount of the data that is processed.

A special form of mirror image artifact that arises only with spectral doppler

crosstalk

Autocorrelation is defined as....

digital technique used to analyze color flow doppler

Color flow provides 2D flow information on the _______. Range resolution or range ambiguity? Sensitivity? Size of color jet is most affected by what? How good is temporal resolution? Aliasing or no aliasing? Records mean or peak velocity measurements?

direction of flow directly on the anatomic image; Range resolution; Moderately sensitive; color Doppler gain settings; Reduced temp resolution due to multiple packets; Subject to aliasing based on pulsed US; Mean velocity measurements

If the colors that touch each other in the image go through the map's middle, _________ is present.

flow reversal

It is important to establish whether the absence of color is due to one of two factors?

from low color gain or b/c of perpendicular incidence

The wall filter does not effect the appearance of ________ ______ flows. ________________________ are created by slowly moving structures like venous blood flow.

higher velocity; small Doppler shifts

Power Mode is used with _______ velocity or _____ ______ blood flow. Range resolution or range ambiguity? Sensitivity? How good is temp resolution? Aliasing or no aliasing? Records mean or peak velocity measurements?

low, small volume; Range Resolution; greater sensitivity than color flow; Lowest temp resolution of all; No aliasing, subject to Flash artifact; No velocity measurements.

Def-(short version) Reverberations appear as what? Reverberations resemble what?

multiple, equally spaced echoes; a ladder or Venetian blind.

When using a color map, flow reversal is present in a vessel when colors red, black and blue are________________.

next to each other.

The first two reflections in reverberation closest to the transducer are considered _________. The remaining deeper echoes do not correctly correspond to ____________________.

real; true anatomic structures

Def- a wider range of velocities and Doppler shifts within a sample volume. p 336, fig 19.43

spectral broadening

The amount of color present on a color flow Doppler image can be controlled with what?

the color Doppler gain setting