Iodinated contrast agents (typically iodine-substituted benzene derivatives) are bound either in nonionic or ionic compounds. Ionic contrast agents consist of the negatively charged anion and the positively charged cation. Used components of the anion are for example diatrizoate, iodamide, iothalamate or metrizoate and of the cation the sodium or meglumine ion. The osmotic pressure depends on the number of particles in solution. Ionic contrast agents have a greater osmolarity; double that of nonionic contrast agents due to delivering more iodine atoms per molecule.
Ionic contrast agents were developed first and are still in use depending on the examination. Iodine based contrast media are water soluble and as harmless as possible to the body. However, ionic agents have more side effects compared to nonionic contrast agents due to their high osmolarity.

See also Ionic Dimer.

Mesons are elementary particle which are strongly interacting bosons belonging to the hadron family. More than 140 different kinds of mesons are discovered by now. Mesons can be negatively or positively charged or neutral.

The nucleus is the positively charged center of an atom and contains most of the mass. Except for 1H, the atom core consists of a combination of the subatomic particles protons and neutrons.