The present invention relates to a compound of general formula (I) wherein R is hydrogen or tritium； F is fluoro or 18fluoro； or to a pharmaceutically acceptable acid addition salt. Compounds of formula I include 2-(6-fluoro-pyridin-3-yl)-9H-dipyrido[2,3-b；3',4'-d]pyrrole, 3H-2-(6-fluoro-pyridin-3-yl)-9H-dipyrido[2,3-b；3',4'-d]pyrrole and [18F]-2-(6-fluoro-pyridin-3-yl)-9H-dipyrido[2,3-b；3',4'-d]pyrrole. The compounds may be used for binding and imaging tau aggregates and related beta-sheet aggregates including besides others beta-amyloid aggregates or alpha-synuclein aggregates.
