One of the best methods to make a diagnosis of uroliths is radiography. Many stones are radiopaque, which means they show up vividly on an x-ray. Radiopaque stones include struvite and calcium oxalate. Some stones are radioulucent, and depending on size and number, do not show up on a regular x-ray. These stones are diagnosed by injecting air, dye, or a combination of both, into the bladder to outline any suspected stone. Radiolucent stones include ammonium urate.
This is the side view of a dog with a very large radiopaque stone in its urinary bladder.
This is a picture of the stone that was in the x-ray above.
Other stones aren't always this smooth. Even though this stone is small, the roughened edges were probably painful in this dogs bladder.