GE Vivid Color Doppler Adjustment Guide
©Walter Rasmussen, R.D.C.S.
Today’s ultrasound machines have far superior imaging capabilities than previous generations however, unless the sonographer is willing to experiment and make adjustments based upon an understanding of ultrasound physics, the resulting images will be of considerably less diagnostic value than they could have been.
As it is stated on other pages of this website, using color Doppler is not as simple as pushing of a single button.(http://echocardiographyskills.com/color-doppler-imaging-adjustment) The sonographer needs to be concerned with gain, beam penetration, scale, frame rate and image processing because they all greatly affect color Doppler resolution.
Because of GE’s unique labeling system and some hidden menus, the imaging and color Doppler adjustments for the GE Vivid series of ultrasound machines can be difficult to understand. The following controls are explained:
Color Doppler Gain
Color Doppler Gain should be coordinated with all of the adjustments listed below. As mentioned in the section dedicated to color Doppler, Gain is adjusted by increasing it until random colored pixels (representing noise) are observed and then slightly backing-off until the point that they disappear.
Color Doppler Scale
The conventional setting for color Doppler Scale is 50 to 60 cm/sec. For adult echocardiography, better results are obtained at or slightly above 60 cm/sec. Keeping the color Doppler scale consistent in a lab is very important for the interpretation of serial echocardiograms.
Increasing Beam Penetration with Color Doppler Frequency Adjustment
As in 2-D imaging, the color Doppler frequency greatly affects how far from the transducer, images can be obtained. Too many sonographers adjust the machine to the lowest frequency and leave it at that for everyone, but this is a shortcut that results in a poor quality image when it need not be. At lower frequencies, the jet area is blurred and exaggerated like a camera that is slightly out of focus because of the longer wavelength.
For a good starting point on all adult echo exams, set the frequency at 2.2 MHz. For more difficult to image areas, lower the frequency to 2.1 or 2.0 MHz. Patients with exceptionally clear images can be adjusted above 2.2 MHz (but keep your eye on the color Doppler scale because it might change).
It is important that frequency should be adjusted to clean up the image only when there is little or no resultant loss of jet visualization. So, if when raising the frequency, the regurgitation image becomes fainter and starts to diminish in size, increase the gain until speckled noise appears. If increasing the gain does not help maintain the image, then the frequency should be lowered despite background clutter and a slight loss of resolution.
Beam penetration is not just a matter of changing the adjustments on the machine. Just as or more important is the effort level and skills that a sonographer has that give the ultrasound beam a chance to reach the tissue.
If regurgitation is present, the sonographer should make sure that the best possible image is being obtained by angling and repositioning (sliding) the transducer (sometimes by just a few millimeters) in order to allow that narrow ultrasound beam to slip between obstacles in the line of sight. A really good example of this can sometimes be seen while imaging a prosthetic mitral valve from the apical position. Often times, if the transducer is slid just a few millimeters in every direction while observing the valve, a narrow regurgitant jet right at the valve’s point of coaptation is seen that is otherwise blocked by the artificial composition of the valve.
In all other cases, realize that the ultrasound beam encounters tissue in line of sight to area of interest, some of which impedes the energy resulting in a fainter image. If the sonongrapher changes the position of the transducer to search for a clearer line of sight (that transfers more energy), the area of interest is illuminated better.
Color Doppler Image Processing
While on page 2 of the color Doppler adjustment menu, a brief summary of the other adjustments available on this page is warranted:
For best performance set all of the above adjustments at zero.
Above are the optional image processing adjustments that can greatly affect the quality of color Doppler. Remember that this ultrasound machine is designed to be used in all types of medical ultrasound imaging however, there are many adjustments that should not be applied to echocardiography.
DDP (Data Dependent Processing) affects temporal resolution (persistence). Lateral averaging will reduce lateral resolution. Radial averaging will reduce axial resolution. Notice that all are set on zero. If you experiment with these settings, you can obtain a softer color Doppler map however, the softer the image, the lower the resolution. A softer/smoother color Doppler image is generally less desirable due to the degradation of the resolution that results.
Above: Image without excessive processing.
Above: Over-processed image.
As can be seen on the above images, excessive image processing can blur and de-focus an image, resulting in lower resolution. Color Smoothing should be avoided because it destroys the color mosaic that is so important to finding turbulent areas and velocity borders. DDP increases image persistence, which averages frames and blurs the data. Lateral averaging and radial averaging blur the image in their respective planes.
This adjustment changes not only the frame rate, but temporal resolution and map sensitivity. Frame rates should be kept as high as possible (to keep it above 16 frames/sec) however not through the use of the frame rate knob.
The Frame Rate knob (above), is available while in Color Doppler Mode.
For a good starting point, set the Frame Rate adjustment to the middle of the range. This will work well in adult echocardiography for average imaging conditions when there is a fair to good quality two dimensional image.
Turning the Frame Rate adjustment to the right will increase resolution for when the patient yields super clear two-dimensional images (excellent penetration). Turning the Frame Rate adjustment to the left lowers frame rate and can be helpful for low blood flow areas such as the IVC or pulmonary veins.
The frame rate target is above 16 frames/sec and is even better when in the 20’s. In actual practice, leave the frame rate knob adjustment in the middle of the range. The best way to increase frame rates (when it falls below 17 frames/sec) is to narrow the background 2-D image and keep the color box only as wide as necessary for the area of interest. This is preferential because only using the Frame Rate dial will sacrifice some other resolution parameter such as line density.
Once Color Doppler is activated, use the trackball to position the color box over the area of interest. The kidney buttons, surrounding the trackball control the size of the color box
The color box should be placed and sized for the specific area of interest in order to help keep the frame rates high. For example, for the mitral valve from the apical window, adjust the width to include the whole mitral annulus and the length sufficient to include the complete length of the regurgitation jet. It is detrimental to the diagnostic quality of a color Doppler exam to use an unnecessarily large color box and a full-width 2-D image because lower frame rates, and lower resolution will result.
Apical 4 chamber view of mitral regurgitation. Color box width is adjusted just to cover the mitral annulus and deep enough to include the complete length of the MR jet.
Apical 4 chamber view. The background sector image and color box are set too wide, resulting in low frame rates and decreased resolution.
Tilting the image while using color Doppler with a narrow sector image is one of the most labor-intensive (annoying) aspects of using the GE Vivid product. Why they do not allow the sector image to be scrolled with the track ball like every other ultrasound brand is perplexing, but that is the way it is.
Above: The image is tilted slightly toward the right ventricle in order to maintain a narrowed sector image while in color Doppler.
The tilt control is an important adjustment when a narrowed 2-D background image is used. Narrowing the 2-D image increases frame rates, thus increasing temporal resolution, allowing more detailed analysis of fast flood flow however, on GE Vivid machines, when the 2-D image is narrowed, there is no other way to tilt the image toward the area of interest.
A lower resolution alternative to the tilt function can be achieved by using the zoom feature. Turn the Zoom knob one click and Tilt the narrowed image as necessary, in order to move the sector into place over the area of interest. The amount of tilt is limited to the size of the background 2-D sector image. Since the background image width is not decreased by much using this method, lower frame rates and decreased temporal resolution result, thus defeating the purpose of narrowing the sector image.
Sample Volume Size:
Sample Volume size affects the general resolution of the color Doppler map. For echocardiography, the SV size should be small because of the many small jets encountered. A sample volume size of 0.7 mm is recommended for the GE color Doppler system.
Color Doppler Priority versus Tissue Priority
A very important adjustment on ultrasound machines is called Tissue Priority. The sonographer needs to be very careful with this adjustment because if it is set to much toward tissue priority, the color Doppler map itself can be erased, thus affecting the diagnostic capabilities of the system. The default setting for Tissue Priority is 7 however the adjustment should be moved to favor Color Doppler, at level 2 to 5.
GE’s version of color Doppler tends to be cluttered with unwanted low velocities and noise, especially when the blood flow is horizontal to the the transducer, as in the parasternal long axis view. Unfortunately, using the filter, labeled “Low Velocity Reject”, often does not provide sufficient blocking of unwanted low velocities. In this case, Tissue Priority can be increased however it must be decreased again when not needed. In actual practice, Tissue Priority is rarely used and is kept at level 2 to 5. The sonographer should be aware of its position at all times so that important diagnostic information is not erased.