To provide illumination during VFI, a 455-nm laser diode (Nichia Corporation, Tokyo, Japan) was installed in the Pentax EPK-i; light from the blue laser diode was coupled to the bifurcating light guide used during white light imaging, and a mechanical control on the processor was used to switch between the two illumination modes. A driver (Wavelength Electronics, Bozeman, Montana) controls the input current to the laser diode and thus allows variation of the illumination intensity. The module holds a custom-designed long-pass filter () passing wavelengths of more than 500 nm in front of the CCD for the collection of proflavine fluorescence. The filters were cut from a custom-coated colored glass filter (Schott North America, Inc., Duryea, Pennsylvania); the thickness of the filter is 0.8 mm, and the optical density (OD) at the illumination wavelength is 3.8. The filter was designed to have out-of-band rejection of at least OD 3 for light ranging from normal incidence up to 70 deg incidence, accommodating the angular FOV of the endoscope. The edges of the filter were coated black to minimize the effect of stray light on the image. The filters were installed using a medical-grade, optically clear epoxy (#301-2FL, Epo-tek, Billerica, Massachusetts). With the module and the blue laser diode in place, the surface irradiance at the center of the FOV is approximately at 5 mm and approximately at 10 mm; both are typical working distances for imaging.