My 7 year old has a lump in his tummy. the walk in clinic doctor said he thinks it is lymphoma and needs to do a untrasound. what is that?

High frequency sound: Ultrasound is a painless way of looking under the skin without cutting. Using high-frequency sound waves, the tissue under the skin can be seen as liquid (fluid), solid, or gas (air) based on how sound is reflected and transmitted through them. It's an easy 1st step to distinguish a cyst (benign, liquid) from a tumor (solid, could be serious, could be fatty / benign). Good luck!