29th January 2014
The easiest way to improve your veterinary ultrasound image is to ensure that you are using the correct pre-sets, if your machine has them. The advantage of using a pre-set is that it puts you in the best starting place for that particular examination and reduces the amount of alterations you need to make to all the background settings. A cardiac ultrasound pre-set for example, will commonly feature a lower grey scale which in turn will increase the frame rate. This is useful because in a cardiac examination, you are less interested in subtle differences in tissue density and more concerned with fast moving anatomy.
The selection of veterinary pre-sets varies from machine to machine. There is often a pre-set button which makes things easy, or sometimes you can change pre-sets on a probe key located on the scanner. Some scanners allow you to create your own pre-sets which can be useful in practices with multiple users with differing preferences.
Most digital veterinary ultrasound probes are now multi-frequency and it is important to scan on an appropriate wavelength. The higher the frequency, the greater the resolution of the image. The lower the frequency, the greater the penetration. There is always a trade-off between resolution and penetration, so you need to select the highest frequency that will give you sufficient penetration. It isn’t as simple as selecting a high frequency for a small animal and a low frequency for a larger one. It’s more about the depth of the organ that you need to visualise. For example, a kidney that is close to the surface in a large dog should be viewed on a higher frequency than a deeper structure in a fat cat! Ultrasound finds it hard to penetrate fat, so obese animals are notoriously difficult to image. Dropping the frequency for these animals is often helpful.
Gain effectively controls the brightness of the ultrasound image, but it’s easy to make the mistake of having the gain set too high in the belief that it will make things easier to see. Increasing the gain will increase the brightness of both true signal and noise which always confuses the issue. It is better to have the gain set lower and make sure that you are scanning in a darkened room.
If your system has time gain compensation (TGC) then you have the ability to alter the gain in steps down the screen. Ultrasound beams are attenuated as they travel through tissue, so the deeper they go, the weaker the signal returning. This results in the image becoming darker further down the screen. The standard position to have your TGC set at is on a diagonal slant from left to right to compensate for this, although each machine is different. The best way to determine the correct settings for your TGC in a small animal abdominal exam for example is to start your scanning at the xiphysternum and optimise the image of the liver at this point. If you alter the controls so that the liver appears a uniform brightness throughout, you can probably leave the TGC controls alone for the rest of the exam.
Ultrasound depth is an often forgotten control that makes a huge difference. The organ that you are visualising should fill around three quarters of the screen. You will not get a very clear image of a chihuahua’s kidney if you are scanning at 15cm depth! Remember that you will probably have to adjust the gain and the frequency after changing depth to optimise your image.
Some veterinary ultrasound machines allow you to alter the number and position of focal points on the screen. Increasing focus points makes the machine work harder and will reduce frame rate. So to visualise movement you need to ensure that you only have a single focus point. Multiple focus points are useful for larger organs in the abdomen.
The ultrasound beams will be concentrated at the level of the focus points, which will improve resolution in these areas, so make sure that they are level with the organ that you are wishing to examine.
Your local BCF Account Manager would be delighted to help you with any aspect of your veterinary ultrasound machine controls, especially if you have queries about presets or would like help in creating your own.