The Osmolality is the osmotic concentration, an indicator of fluid balance in the body's tissues.
Osmolal describes an ion concentration of a solution in moles per kilogram of solvent (mol/kg), while osmolar describes an ion concentration in moles per liter (mol/L).

The various gas microbubble contrast media are generally safe with low toxicity in humans. The tolerance of these agents is much higher than that of most x-ray agents, a reflection perhaps of the higher expectation of safety and convenience for ultrasound.
Extensive preclinical and clinical trials have demonstrated an excellent ultrasound contrast agent safety profile, the main side effect being a mild and transient local discomfort at the injection site which results from the high osmolality of these agents. Each contrast agent has its own profile of adverse effects, but all have been trivial thus far.

See also Ultrasonic Contrast Agents.