Endoscopic fluorescence visualization of 5-ALA photosensitized central nervous system tumors in the neural tissue transparency spectral range

Abstract Background: Fluorescence endoscopy systems for photosensitizer visualization have proved to be powerful tools for highlighting malignant tumor boundaries as well as detecting small, visually non-detectable, residual parts during photodynamic therapy. Most of these devices use excitation wavelengths in the blue visual spectrum range (405 nm) which limits the penetration depth in the tissue. Objective: In the study being presented in this article an apparatus and a method were developed for performing endoscopic fluorescence diagnostics of photosensitizer accumulation using excitation light in the red part of visual spectrum, i.e., 635 nm, which allows not only a deeper penetration of light into the tissue but also better scanning abilities and a higher diagnostic quality. Additionally, 635-nm radiation can penetrate thin layers of blood which appear during surgery. Material and methods: In order to use 635-nm excitation, a specially designed video endoscopy system was developed. The key feature of the video system is a dual camera video receiver where one sensitive B/W camera receives the fluorescence signal and a color camera receives the real-time image in natural colors during navigation. The software developed for the apparatus allows overlaying of the video output of fluorescence image on top of the conventional color image in real-time. The experimental setup and method were tested on Intralipid-based phantoms with protoporphyrin IX (PpIX) concentrations of 0.5–5 mg/kg, and then on two patients during surgery. The patients were administered 20 mg/kg 5-ALA photosensitizer 3 h before surgery according to standard practice of 5-ALA in neurosurgery. Results: The experiments demonstrate that the designed setup is sensitive enough for clear visualization of biological concentrations of PpIX in both phantoms with 0.5 mg/kg PpIX and previously photosensitized tissues of patients. Conclusion: Further prospective validation is needed to translate the results to clinical practice.