Colitis cannot be definitively diagnosed with an ultrasound, as ultrasound is primarily used for diagnosing solid organs such as the liver, gallbladder, spleen, kidneys, and pancreas. For hollow organs, the diagnosis is obscured by gas and food inside the intestines, making ultrasound less effective. For patients suspected of having colitis, the best examination is a colonoscopy. A colonoscopy can clearly show the extent and severity of the inflammation. CT scans also hold diagnostic value as they can reveal thickening and edema of the colonic wall. CT scans are less painful compared to colonoscopies, which can be somewhat painful.