Highlighting the Undetectable - Fluorescence Molecular Imaging in Gastrointestinal Endoscopy

Abstract

Flexible high-definition white-light endoscopy is the current gold standard in screening for cancer and its precursor lesions in the gastrointestinal tract. However, miss rates are high, especially in populations at high risk for developing gastrointestinal cancer (e.g., inflammatory bowel disease, Lynch syndrome, or Barrett's esophagus) where lesions tend to be flat and subtle. Fluorescence molecular endoscopy (FME) enables intraluminal visualization of (pre)malignant lesions based on specific biomolecular features rather than morphology by using fluorescently labeled molecular probes that bind to specific molecular targets. This strategy has the potential to serve as a valuable tool for the clinician to improve endoscopic lesion detection and real-time clinical decision-making. This narrative review presents an overview of recent advances in FME, focusing on probe development, techniques, and clinical evidence. Future perspectives will also be addressed, such as the use of FME in patient stratification for targeted therapies and potential alliances with artificial intelligence. KEY MESSAGES: • Fluorescence molecular endoscopy is a relatively new technology that enables safe and real-time endoscopic lesion visualization based on specific molecular features rather than on morphology, thereby adding a layer of information to endoscopy, like in PET-CT imaging. • Recently the transition from preclinical to clinical studies has been made, with promising results regarding enhancing detection of flat and subtle lesions in the colon and esophagus. However, clinical evidence needs to be strengthened by larger patient studies with stratified study designs. • In the future fluorescence molecular endoscopy could serve as a valuable tool in clinical workflows to improve detection in high-risk populations like patients with Barrett's esophagus, Lynch syndrome, and inflammatory bowel syndrome, where flat and subtle lesions tend to be malignant up to five times more often. • Fluorescence molecular endoscopy has the potential to assess therapy responsiveness in vivo for targeted therapies, thereby playing a role in personalizing medicine. • To further reduce high miss rates due to human and technical factors, joint application of artificial intelligence and fluorescence molecular endoscopy are likely to generate added value.

Keywords: Artificial intelligence; Cancer; Early detection; Fluorescence; Fluorescence molecular endoscopy; Gastrointestinal endoscopy; Inflammation; Molecular imaging; Near-infrared fluorescence; Optical imaging; Personalized medicine; Targeted biopsy.

Fig. 1

Light spectra and wavelengths. (a) The NIR spectrum lies between 780 and 2500 nm. Currently, almost all fluorescently labeled probes for FME are designed to emit in the NIR-I spectrum (780–900 nm). This design choice addresses three fundamental challenges: photon scattering by tissues, tissue autofluorescence, and tissue damage. First, the long wavelengths associated with both excitation and emission allow for deep-tissue imaging due to reduced scattering and increased penetration. Second: probes emitting in this spectral region benefit from high signal-to-background ratio, due to avoiding spectral regions associated with tissue autofluorescence. Third: the lower photon energies result in reduced tissue damage. (b) Example of excitation and emission spectra of the fluorescent dye IRDye 800CW. Due to vibrational relaxation in the excited or ground state orbitals, emitted photons must be equal to or lower in energy than the excitation photons. The emission spectrum is therefore red-shifted to longer wavelengths

Fig. 2

Schematic overview of a NIR-FME system. This figure illustrates the integration of a fiber bundle and an external NIR-fluorescence camera with a clinical endoscope. The NIR-system fiber bundle is inserted through the working channel of a standard clinical HD video endoscope (HDE). 750 nm laser light and short-pass filtered (SPF) white light from a LED are delivered through the illumination fibers of the fiber bundle to the distal end of the endoscope. Fluorophore-emitted and reflected white light return through the imaging fibers of the fiber bundle and are subsequently split by a dichroic mirror. Visible light is then detected by a color camera, and emitted fluorescent light is passed through a band-pass filter before being detected by an NIR-fluorescence camera. Previously published in Gut [13]

Fig. 3

Overview of real-time VEGFA-targeted FME in Barrett’s esophagus. (a) Schematic overview and timeline of two NIR-FME approaches, i.e., intravenous administration and topical application. (b) Examples of results after intravenous administration of bevacizumab-800CW, and (c) results after topical application. The first row in Fig. 3c displays a lesion that was not visible during white light endoscopy but turned out to be adenocarcinoma. Previously published in Gut [13]