Abstract: The invention relates to a formulation comprising a dry material (e.g. lyophilised or spray dried) comprising at least one film forming surfactant and a gas or a gas mixture usable in diagnostic imaging, to a process for the preparation thereof and to a suspension obtainable by reconstituting said formulation with an aqueous carrier for use in contrast imaging. The invention also relates to a container comprising the dry material in contact with a gas. The gas associated with the dry material is at a pressure lower than the atmospheric pressure.