Imaging of oily formulations in the gastrointestinal tract

The use of an imaging technique such as gamma scintigraphy to follow the behaviour of a formulation in the gastrointestinal tract is widely employed in the development of new therapeutic concepts. Such studies are facilitated by the availability of suitable radiolabels, incorporated into the formulation during manufacture. The range of labels for lipophilic excipients is very limited, although new brain-imaging agents may offer interesting possibilities. The use of alternative imaging modalities such as magnetic resonance imaging should also be considered. The difference in the T 1- or T 2-weighted signal from the oil against the aqueous contents provides a method of visualising an oil-based formulation in vivo without any modification to the formulation. This article reviews approaches in the search for suitable techniques for in vivo imaging of oral formulations containing a high proportion of oil.