For the purpose of medical imaging, a certain substance is introduced into the human body to change the image contrast of the body's local tissues. This substance is called "Contrast Media". Iodinated contrast agent is the most commonly used X-ray contrast agent, and it is also the basic diagnostic drug for cardiovascular imaging under X-ray.
Since its development, the iodinated radiocontrast dye has undergone a development process from ionic to non-ionic, from hypertonic to hypotonic and to isotonic:
(1) Hypertonic contrast agent is an ionic monomer, and its osmotic pressure is as high as 5-7 times of plasma osmotic pressure; due to relatively more adverse reactions, it has been rarely used at present.
(2) The hypotonic contrast agent is named according to that its osmotic pressure is significantly lower than that of the ionic hypertonic contrast agent (such as diatrizoate meglumine), which includes two types of contrast agents: non-ionic monomer and ionic dimer. Its osmotic pressure is about twice that of plasma.
(3) The isotonic contrast agent was developed to further reduce the osmotic pressure after the hypotonic contrast agent. The isotonic contrast agent is a non-ionic dimer whose osmotic pressure is equal to the plasma osmotic pressure.
According to the iohexol package insert, the basic structure of the current clinically used iodine-containing iohexol contrast is 3-acetyl-2,4,6-tribenzoic acid, which is a benzene ring containing 3 iodine. According to different properties, contrast agents can be divided into monomer and dimer contrast agents, ionic and nonionic iodinated contrast, hypertonic, sub-hypertonic and isotonic contrast agents (Table 1).
Table 1 Classification and physical and chemical properties of commonly used iodine contrast agents
Structure and classification
( mg /ml)
The first generation of hypertonic ionic monomer
The second generation of sub-hypertonic nonionic monomer
Hypotonic ionic dimer
The third generation of isotonic nonionic dimer