We therefore believe that FLIM has a potential future clinical role in imaging BCCs for rapid and noninvasive tumour delineation and as an aid to determine adequate excision margins with best preservation of normal tissue.

The autofluorescence of biological tissue can be exploited for the detection and diagnosis of disease but, to date, its complex nature and relatively weak signal levels have impeded its widespread application in biology and medicine. We present here a portable instrument designed for the in situ simultaneous measurement of autofluorescence emission spectra and temporal decay profiles, permitting the analysis of complex fluorescence signals. This hyperspectral fluorescence lifetime probe utilizes two ultrafast lasers operating at 355 and 440 nm that can excite autofluorescence from many different biomolecules present in skin tissue including keratin, collagen, nicotinamide adenine dinucleotide (phosphate), and flavins. The instrument incorporates an optical fiber probe to provide sample illumination and fluorescence collection over a millimeter-sized area. We present a description of the system, including spectral and temporal characterizations, and report the preliminary application of this instrument to a study of recently resected (<2 h) ex vivo skin lesions, illustrating its potential for skin cancer detection and diagnosis.

Abstract. High-speed ͑video-rate͒ fluorescence lifetime imaging ͑FLIM͒ through a flexible endoscope is reported based on gated optical image intensifier technology. The optimization and potential application of FLIM to tissue autofluorescence for clinical applications are discussed.

Fluorescence imaging is used widely in microscopy and macroscopic imaging applications for fields ranging from biomedicine to materials science. A critical component for any fluorescence imaging system is the excitation source. Traditionally, wide-field systems use filtered thermal or arc-generated white light sources, while point scanning confocal microscope systems require spatially coherent (point-like) laser sources. Unfortunately, the limited range of visible wavelengths available from conventional laser sources constrains the design and usefulness of fluorescent probes in confocal microscopy. A ‘hands-off’ laser-like source, electronically tunable across the visible spectrum, would be invaluable for fluorescence imaging and provide new opportunities, e.g. automated excitation fingerprinting and in situ measurement of excitation cross-sections. Yet more information can be obtained using fluorescence lifetime imaging (FLIM), which requires that the light source be pulsed or rapidly modulated. We show how a white light continuum, generated by injecting femtosecond optical radiation into a micro-structured optical fibre, coupled with a simple prism-based tunable filter arrangement, can fulfil all these roles as a continuously electronically tunable (435–1150 nm) visible ultrafast light source in confocal, wide-field and FLIM systems.

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Optical imaging of tissue autofluorescence has the potential to provide rapid label-free screening and detection of surface tumors for clinical applications, including when combined with endoscopy. Quantitative imaging of intensity-based contrast is notoriously difficult and spectrally resolved imaging does not always provide sufficient contrast. We demonstrate that fluorescence lifetime imaging (FLIM) applied to intrinsic tissue autofluorescence can directly contrast a range of surface tissue tumors, including in gastrointestinal tissues, using compact, clinically deployable instrumentation achieving wide-field fluorescence lifetime images of unprecedented clarity. Statistically significant contrast is observed between cancerous and healthy colon tissue for FLIM with excitation at 355 nm. To illustrate the clinical potential, wide-field fluorescence lifetime images of unstained ex vivo tissue have been acquired at near video rate, which is an important step towards real-time FLIM for diagnostic and interoperative imaging, including for screening and image-guided biopsy applications.

Target cells are thought to regulate the survival of afferent neurons during development by supplying limiting amounts of neurotrophic factors, but the degree to which afferent neurons remain dependent on target-derived support in the adult is uncertain. In this study, uninjured basal forebrain cholinergic neurons did not die after excitotoxic ablation of their target neurons in young adult rats, indicating that they are either not dependent on neurotrophic factors for survival or can obtain trophic support from other sources after target neurons are lost. This finding suggests that cholinergic cell death in neurodegenerative conditions such as Alzheimer's disease is not due solely to a loss of target neurons or factors provided by them.

We report the development of a high-speed wide-field fluorescence-lifetime imaging (FLIM) system that provides fluorescence-lifetime images at rates of as many as 29 frames/s. A FLIM multiwell plate reader and a potentially portable FLIM endoscopic system operating at 355-nm excitation have been demonstrated.