The present invention relates to novel compounds of formula (I), or a detectably labelled compound, stereoisomer, racemic mixture, pharmaceutically acceptable salt, hydrate, or solvate thereof, that can be employed in the imaging of alpha-synuclein aggregates and determining an amount thereof. Furthermore, the compounds can be used for diagnosing a disease, disorder or abnormality associated with an alpha-synuclein aggregates, including, but not limited to, Lewy bodies and/or Lewy neurites (such as Parkinson's disease), determining a predisposition to such a disease, disorder or abnormality, prognosing such a disease, disorder or abnormality, monitoring the evolution of the disease in a patient suffering from such a disease, disorder or abnormality, monitoring the progression of such a disease, disorder or abnormality and predicting responsiveness of a patient suffering from such a disease, disorder or abnormality to a treatment thereof.