Fluorescence imaging spectroscopy utilising acousto-optic tuneable filters

A novel prototype instrument for mutli-spectral imaging applications is described. The device is based on an acoustooptic tuneable filter (AOTF) that can be easily attached to many standard imaging systems (e.g. endoscope or fluorescence microscope). The instrument developed offers significant advantages over typical fixed-filter based systems in terms of flexibility, performance and diagnostic potential. The selected AOTF was designed to have a large acceptance aperture suitable for imaging applications. Any filtering centre-wavelength in the visible range (450 to 700nm) can be rapidly selected by either random access or by continuous tuning thus providing a versatile performance. The prototype instrument has been demonstrated for in-vivo applications where it was attached to the eyepiece of a commercial endoscope allowing simultaneous white light and fluorescence endoscopy. Autofluorescence of endogenous protoporphyrin IX (PpIK), a biomarker of diseased tissues undergoing an inflammatory response, was mapped in vivo on a rat model. The AOTF device was also coupled to the viewing port of a commercial fluorescence microscope thus realising a powerful fluorescence imaging spectrometer capable of detecting and mapping fluorescent biomolecules in vitro.