Narrow Band Imaging in Flexible Endoscopic Evaluation of Swallowing—How Does It Work?

Purpose: The purposes of this study were to compare the visibility of various color groups in different dilutions using narrow band imaging (NBI) and white light (WL) and to determine an optimal color combination using NBI and WL for multicolor flexible endoscopic evaluation of swallowing (FEES), for example, to test different consistencies. Method: Preliminary examinations were performed in the oral cavity of two healthy volunteers. Various dyes were tested using NBI and WL to evaluate their visibilities. In the case of a clearly discernible color change, the visibility differ-ences in the dilution series under WL and NBI were recorded and compared. Subsequently, an abbreviated dilution series with NBI and WL was performed in a volunteer as part of a swallow endoscopy to determine whether the results from the oral cavity could be transferred to the hypopharynx. Results: The enhancement of visibility using NBI compared with WL can be proven. When NBI was used, yellow and red food dyes and their mixtures showed distinct color changes. The reacting dyes were still visible under NBI, even at a 10-times-higher dilution, requiring a lower dye concentration for FEES. For increased visibility, the dyes used for FEES with NBI must contain colors from a small range in the yellow and red spectra, which are close to the filter maxima of NBI. Both colors are well visible under WL when combining red and green (secondary color of yellow). Conclusions: Certain food colorings are visible 10 times more diluted under NBI than under WL. In a multicolored approach, optimal visibility under NBI and WL can be achieved by combining green and red. This new high-sensitivity FEES should be highlighted to allow an instant distinction from WL-FEES; we suggest "FEES+."