Hi, Thanks for writing in to us. A CAT scan is almost confirmatory for the presence of stones in your kidneys and ureters. A stone of size 2 mm can easily be located and found on a CAT scan. If no stones are there then most likely you do not have one. Sometimes pain can be felt even after the stone has passed. This is because the stone might have sharp edges and while on its ways out it can cause abrasions to the ureter or urethra and this gives rise to pain in the groin region. White spots on CAT scan might represent many things like calcium in vessels, radio opaque contrast material in various organs, any bony fragments in their normal found locations.