There are a number of causes for an inflamed colon, or colitis.
Ulcerative Colitis and Crohn's disease are both forms of Inflammatory Bowel Disease. Ulcerative colitis causes inflammation of the interior lining, and Crohn's causes inflammation throughout.
There is also infectious colitis, antibiotic associated colitis, irritable bowel disease, and more.
I don't know what your symptoms were that first brought you to have a CT scan, but I have had to have all of the tests you're describing. Unpleasant though they may be, they aren't as bad as they were 10 years ago, when you usually didn't get anesthetic, especially for the colonoscopy.
Good luck and i hope it all goes well for you.
at 2:15 PM on Nov. 3, 2008