To Gain or Not to Gain

Hands up anyone that understands the gain controls on their ultrasound scanner and uses them correctly? Do you just ‘fiddle’ with them randomly as you’ve seen others doing it? Have you just left the gain controls as they were because someone has said ‘that’s how they should be set’? Using gain controls correctly is one of the four main settings in driving your scanner and they should be used throughout the scan to optimise the different zones of the image. From near field to far field (top to bottom), gain controls should be set dependent on the density of the tissue the ultrasound beam is being transmitted through. Your aim is to create a uniform image when scanning through a uniform density tissue without excessive bright or dark stripes throughout the image.

In a uniform density tissue you would normally turn down the near field gains, just to take the excess brightness away from a strong echo from the superficial area of the scan. Conversely, you will typically increase the gain for the signal returning from further away in the far field. These are weaker when they return to the probe, so need a little amplification to brighten them up. The gains in the middle are normally between near and far field settings, so you often end up with the ‘inverse S curve’ on the gain control sliders. Then there is overall gain control. This is used to increase or decrease all of the gains at one time. If you find your image is getting dark overall and you keep turning up the overall gain to compensate, it probably indicates poor contact between the probe and the patient and more gel should be applied. Just remember to turn your overall gain back down a bit once you have applied the gel.

Please remember as you scan through different areas of the body, different densities of tissue and, of course fluids, you should be adjusting the gain sliders accordingly. Don’t assume that because you set them for the tissue at the start they will remain correct for the remainder of the scan, they will need adjusting as you scan through various structures within the body. But don’t be scared to adjust them, the gain controls are quite prominent as they are designed to be used!