Noncontrast CT is used To detect acute hemorrhage in the brain, urinary calculi, and lung nodules To characterize bone fractures and other skeletal abnormalities IV contrast is used To improve imaging of tumors, infection, inflammation, and trauma in soft tissues To assess the vascular system, as when pulmonary embolism, aortic aneurysm, or aortic dissection is suspected Oral or occasionally rectal contrast is used for abdominal imaging; sometimes gas is used to distend the lower gastrointestinal (GI) tract and make it visible.