ABSTRACT
This chapter describess the basic chemistry and biology of the contrast agents (CAs) used as imaging pharmaceuticals in the X-ray, MRI, and ultrasound imaging modalities. In X-ray imaging, a high-energy beam of X-rays is absorbed to varying degrees by tissues depending on their average density and atomic number. The discovery of X-rays by Wilhelm Roentgen in 1895 led almost immediately to X-ray images of human body parts, famously his wife’s hand, and from there by 1896 to injection of heavy metals such as Pb into cadaver veins. Iodinated X-Ray Contrast Agents (XRCAs) absorb X-rays, creating a shadow image. In vivo, XRCA should be noninteractive, demonstrating no physiological effects other than distribution and excretion. The large systemic effects and pain that resulted from the hyperosmolality of ionic XRCA agents were not manifest in the much smaller volumes of gadopentetate delivered. While XRCAs operate by a simple absorbance principle, the MRCAs’ operative mechanism is far more complex.
