Focussing your image

You do it without thinking when you take a photo, yet very few people adjust the focus on their ultrasound scanner when scanning a case. Adjusting the focus on an your scanner is normally really easy to do and will help with the quality of your image, so make it one of your four major adjustments in every scan. There are two adjustments that can be made with the focus control:

• Adjustment of the focal zone size – your scanner will have the ability to either add additional focal zones and then space them out to give a larger focal zone, or to use a rotary control to increase the size of the single focal zone. The number of focal zones or size of zone is usually indicated by markers on the side of the image. One compromise of using a larger focal zone will be a reduced frame rate, which may make the image look blurry or laggy, particularly if the patient is moving or wriggling. If this is the case, reduce the size of the focal zone. There are other adjustments such as persistence (frame averaging), line density or even scan width that can help reduce the ‘blurriness’ of the image.
• Adjustment of the focus position – a control on the scanner will allow the position of the focal zone to be moved up and down the image. It’s important to position this at the level, or even just a bit below the structure of most interest in the image. If the main interest is closer to the skin move the focus up and if it’s deeper move the focus down. You will notice the image quality of the structure of interest improving when the focal zone is aligned with it.

Be prepared to alter the size and position of the focal zone during the scan as you move the probe over the patient. By using the four main controls (Depth, Focus, Frequency and Gain) during the scan, you will learn how to quickly and efficiently optimise the image quality to get better diagnostic scans. There are a huge number of other adjustments that can be made, but if your presets are set correctly, these four controls will have the most obvious effects on image quality.

For more information on the courses and other resources offered by the team at CPD Circle, please visit their website cpdcircle.co.uk.