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Depiction of the high concentration of molecules in radiographic contrast media solutions. The two boxes represent a 1.2-nm-deep 12 x 12-nm section of the solution; that is, the small squares are 1.2 x 1.2 nm, and each solid circle represents a single contrast agent molecule of iohexol with dimensions of 1.0 x 1.2 x 1.2 nm. Upper box represents 150 mg of iodine per milliliter of iohexol, which is equivalent to approximately 0.4 mol/L solution. Lower box represents 75 mg of iodine per milliliter of iohexol, which is equivalent to approximately 0.2 mol/L solution; in this box, the size of one globular enzyme molecule (cross-hatched circle) of size similar to that of albumin is also shown.