When you get the ultrasound out in your busy veterinary practice, you often don’t have the time to stop and think about optimising your image. Most of the time you switch on and go, ruling various differentials in or out quickly (e.g. looking at a mass or performing an AFAST exam). But what happens if you are doing a detailed abdominal ultrasound in an animal with vague clinical signs and your image is just not that great?
Here are 4 basic steps to help get you started on the right track:
Getting your exam depth correct is vital. It’s fine to start at a greater depth to do a quick “screen” but when looking at organs in a detailed manner you need to not have too much “dead space” on your screen. It is advised that the area of interest should take up about 75% of the screen.
Once you are happy with your depth, the next step is to ask yourself: Are the ultrasound waves getting to the bottom of the image? If not, then you need to reduce your frequency to improve the penetration of the ultrasound waves.
If you are happy with the penetration of the ultrasound waves, then. you need to ask “is the detail good enough?” If it’s not, then you should increase your frequency to improve the resolution of the image.
Some machines display frequency as a number or in the following terms:
3. Focal Zone
Next set your focal zone(s) to increase resolution at a specified depth. Some systems adjust focal zones automatically according to depth and exam type, so you will not have the ability to adjust them manually.
4. Gain & Time-Gain Compensation
In most cases, “gain” is the control that people reach to first, but we advise that you leave it to last. Gain increases the overall amplification of returning ultrasound signals. If it is set too high, it will result in increased “noise”, obscuring detail.Too low a gain will result in a loss of diagnostic information, so a fine balance is required.Time-gain compensation allows you to selectively increase the amount of amplification at different depths (time intervals) to obtain a consistent gain throughout the image.