Doctors use contrast agents, which enter the body intravenously, orally or rectally, to increase the clarity of images of the inner areas of the body during X-ray, ultrasound, magnetic resonance or computed tomography tests, explains the Radiological Society of North America. Contrast agents help radiologists identify normal and abnormal conditions, and they change the color of internal organs only for a short period.
Contrast agents alter the interaction of imaging equipment with the body by improving the appearance of tissues, blood vessels and organs on images taken during a diagnostic test, states the Radiological Society of North America. Doctors see what they would otherwise not notice when conducting an imaging test without using a contrast material.
Intravenous administration of a contrast agent involves injecting the material into a blood vessel, according to the Radiological Society of North America. Doctors sometimes administer a contrast agent by performing an enema or allowing a patient to swallow the material. They use barium sulfate and iodine-based compounds, which are commonly injected into a vein, when performing X-ray or computed tomography tests.
After an imaging test that uses a contrast agent, a patient normally eliminates the material through urine or stools, notes the Radiological Society of North America. Patients who receive iodine-based contrast agents should drink lots of water after imaging tests to flush out the contrast materials quickly.