It won't show IBS, because IBS is based on a specific cluster of symptoms minus red flags.
But it can help to show its not something else like IBD conditions and Diverticuloses or even other problems.
In a way its used to rule out other conditions, which are not IBS and too get a good look at the colon.
Spasman it is a diagnotic tool to physically look at the colon for abnormalities, such as IBD, polyps, diver, cancer and other conditions that effect the colon.
In IBS the colon would look normal with a colonoscopy.