Optimizing Ultrasound Image Quality - Brian Gill

Optimizing Ultrasound Image Quality, a Guide for Physicians, Part 1 MAY 5, 2013 BY BRIAN GILL

http://www.providianmedical.com/blog/improving-ultrasound-image-quality-a-guide-for-physicians-part-1/


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Before you start, adjust the brightness and/or contrast on your monitor

Most manufacturers suggest you start with 90-100% contrast, then adjust the brightness. The greyscale bar (shown in image on right) shows the ultrasounds current greyscale from white to black. Start by setting the lighting in the room as it will be when you’re scanning. Next, turn the brightness to its highest point, then concentrate on the very bottom of the greyscale bar. It will be the darkest point. Slowly turn the brightness down until the darkest level is black and no longer visible. The top should be white, but not oversaturated. If you have a contrast adjustment (many portables do not), you can set this to your liking… however note that adjusting the contrast will have an impact on your brightness setting.

Setting the brightness is the only adjustment you’ll make that does not change with each new exam. All of the settings below are not saved on the ultrasound machine unless you go through specific steps to save a custom preset. In other words, feel free to play around, you can always start over by reselecting the preset.

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Don’t fear the gain control

The gain knob will likely be your most-used imaging control. This adjusts the overall brightness of the ultrasound image. You’ll find yourself going to this control on nearly every scan.

TGC: Those ultrasound slider things

TGC Slidepots

With the exception of SonoSite, each machine has 5-10 slide controls grouped together. These are TGC or Time Gain Compensation controls. They adjust gain in specific areas of the image (near-, mid-, and far-field). The best way to see what they do: slide one of them all the way to the right, then all the way to the left while looking at a live image. You’ll see that a certain section of the image turns very bright, then very dark.

When you receive the ultrasound, these TGC controls appear as they do in the image on the left… in a straight line down the middle. Most techs adjust these to left-of-center for the nearfield (top), and slowly move to right-of-center as image quality decreases deeper in the image. The idea is to have lower gain in the nearfield, and higher gain deeper in the image where image quality is weaker.

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Ultrasound Focus position, focal zones

These are two oft-overlooked image optimization features. The focal position tells the ultrasound the depth at which you’d like the highest resolution. As you move the focal position up and down, you’ll see a triangle or dot move up or down the left or right side of the image. You’ll see the image resolution improve in the area of the selected focal position.

Focal zones allow you to have multiple focus points. As you increase the number of focal zones, your frame rate will decrease and the image will refresh slowly.

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Dynamic Range (Compression)

Dynamic Range (aka Compression) allows you to tell the ultrasound machine how you want the echo intensity displayed as shades of gray. A broad/wide range will display more shades of gray and an overall smoother image. A smaller/narrow range will display fewer shades of gray and appear as a higher contrast with a more black-and-white image.

To make things confusing, some manufacturers (Ahem… GE) call it Dynamic Range on a live image, then change it to Compression when the image is frozen. Yeah, that’s not confusing at all!

Frame Average/Persistence

Frame averaging, or persistence, are similar functions in which multiple image frames are combined, or “averaged” into a single image. Its apparent affect is similar to that of Speckle Reduction, in which the image appears smoother and noise is reduced in the image.

Reject

Reject or rejection filter tells the machine the minimum level of echo displayed. For example, if you have a lot of noise in the image, you can increase the Reject level to eliminate the weaker signals, thereby cleaning up the image and suppressing the weakest signals.

Enhance/Edge Enhance

With Edge Enhancement, the ultrasound attempts to make a sharper image by combining adjacent signals. This will have an effect of showing higher contrast and brighter edges of structures.

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