Can ibs, ibd or ulcerative colitis be diagnosed by contrast iv, oral contrast and rectal contrast ct scan?

Not definitively: ulcerative colitis is type of IBD (inflammatory bowel disease), while IBS is irritable bowel syndrome, which has no overt inflammation. Neither can be reliably diagnosed on radiographic studies, although bowel wall thickening or even stranding pattern can suggest an inflammatory condition (not IBS). If recent bowel habit changes, fever, blood, nausea, diarrhea, would suggest seeking MD evaluation

IBS vs IBD: IBS does not really have any diagnostic test, it is diagnosed clinically after ruling out the other causes. IBD like Crohn's and Ulcerative colitis may show some findings in the GI tract on imaging studies.