Detection, characterization, and staging constitute
the fundamental elements in the endoscopic
diagnosis of gastrointestinal diseases, but histology
still remains the diagnostic gold standard.
New developments in endoscopic techniques may
challenge histopathology in the near future. An
ideal endoscopic technique should combine a
wide-field, “red flag” screening technique with
an optical contrast or microscopy method for
characterization and staging, all simultaneously
available during the procedure. In theory, biophotonic
advances have the potential to unite these
elements to allow in vivo “optical biopsy.”
These techniques may ultimately offer the potential
to increase the rates of detection of high risk
lesions and the ability to target biopsies and resections,
and so reduce the need for biopsy, costs,
and uncertainty for patients. However, their utility
and sensitivity in clinical practice must be evaluated
against those of conventional histopathology.
This review describes some of the most recent applications
of biophotonics in endoscopic optical
imaging and metrology, along with their fundamental
principles and the clinical experience
that has been acquired in their deployment as
tools for the endoscopist. Particular emphasis
has been placed on translational label-free optical
techniques, such as fluorescence spectroscopy,
fluorescence lifetime imaging microscopy (FLIM),
two-photon and multi-photon microscopy, second
harmonic generation (SHG) and third harmonic
generation (THG) imaging, optical coherence
tomography (OCT), diffuse reflectance, Raman
spectroscopy, and molecular imaging