Had routine ct's with contrast and without, for kidney stones. Now they want to send me for a CT urogram. What is the difference?

Contrast. A plain ct looks for stones. A ct urogram uses IV contrast (dye) to better evaluate the renal pelvis and ureter (the "tube" connecting your kidneys to your bladder). These structures are not well seen without contrast. A greater amount of contrast is used in a urogram than normal contrast ct to better fill these structures.