I don't know if a sonogram or xray can detect oral cancers. My understanding is that in order for a scan (CT, MRI or PET, not xray or sonogram) to detect this cancer, it has be a contrasted scan. Which means they inject you with a contrasting agent and take the scan. Because cancer cells have a higher metabolic rate than normal cells, the contrasting agent tends to collect in those cells and "light up" in the scan. That being said, they should be able to stick a needle in the suspected mass and extract some cells from it for pathological review. This is known as a Fine Needle Aspiration (FNA). The FNA method was how my cancer was initially diagnosed. I hope this helps and best of luck.
-Brett