Omnipaque (iohexol) is a contrast agent used for x-rays. It is used for a range of intravascular diagnostic procedures, such as spinal cord imaging, coronary angiography, and body-cavity procedures. It comes in an injectable or oral form. Omnipaque is a low osmolar, nonionic, iodinated contrast agent that was first used in the United States in 1985. It has been used in more than 350 million people around the world.