Assessment of 5-aminolevulinic acid-induced fluorescence using novel exoscopes and their feasibility in glioma surgery: technical note.

Objective: Filter specifications for visualizing 5-aminolevulinic acid (5-ALA) tumor fluorescence are incorporated in neurosurgical wide-field microscopes. Novel exoscopes offer modified visualization technologies that should be comparable to older systems to prevent over- or underresection. In this technical note, the authors compare the fluorescence visualization technologies of three exoscopes.

Methods: Images of 73 tissue samples with heterogeneous fluorescence signals were acquired using the Aeos, ORBEYE, and Kinevo exoscope. Fluorescent areas as determined by six raters were calculated and compared with the gold standard, i.e., BLUE 400. Intraclass correlation coefficients (ICCs) were calculated to assess the reliability of the results. Protoporphyrin IX (PpIX) decay under continuous blue-light illumination was determined to assess photobleaching.

Results: The extent of fluorescence was significantly larger under the Aeos. There was no significant difference using the ORBEYE and the Kinevo exoscope. ICCs showed excellent (Kinevo exoscope and Aeos) and good (ORBEYE) reliabilities. The Aeos had the fastest PpIX decay rate.

Conclusions: The ORBEYE and the Kinevo exoscope are safe alternatives to the gold standard. The Aeos seems to be more sensitive regarding fluorescence visualization; however, it remains unclear whether this is at the expense of specificity. The photobleaching effect is stronger in novel exoscopes.