Air is the enemy of ultrasound! Air will cause dispersion of all waves even before entering the body. Gel acts as an acoustic interface between skin and the probe. The idea of a gel couplant is to remove the layer of air – whenever you are struggling to get a good image the first thing you should do is to try more gel.
A gel with enough adherence is ideal. In an extreme emergency, any gel will suffice
Try and warm it if you can.