The present application relates to a diagnostic composition comprising: a. a compound of Formula I, b. ethanol, c. water, and d. a hydroxycarboxylic acid, a salt of a hydroxycarboxylic acid or a mixture thereof. The diagnostic composition can be used in the selective detection of disorders and abnormalities associated with Tau aggregates such as Alzheimer's disease (AD) and other tauopathies, for example, using Positron Emission Tomography (PET). The present invention also relates to a method of preparing the claimed diagnostic composition.
