RGB-color forward-viewing spectrally encoded endoscope using three orders of diffraction

Abstract

Spectrally encoded endoscopy (SEE) is an ultra-miniature endoscopy technology that encodes each spatial location on the sample with a different wavelength. One challenge in SEE is achieving color imaging with a small probe. We present a novel SEE probe that is capable of conducting real-time RGB imaging using three diffraction orders (6th order diffraction of the blue spectrum, 5th of green, and 4th of red). The probe was comprised of rotating 0.5 mm-diameter illumination optics inside a static, 1.2 mm-diameter flexible sheath with a rigid distal length of 5 mm containing detection fibers. A color chart, resolution target, and swine tissue were imaged. The device achieved 44k/59k/23k effective pixels per R/G/B channels over a 58° angular field and differentiated a wide gamut of colors.

Fig. 1.

Schematic of the color SEE device.

Fig. 2.

The color SEE probe (inside of a straight rigid guide) and the motor with cables. The probe was disconnected mechanically and optically from the fibers at the motor side.

Fig. 3.

Schematic of the probe distal end.

Fig. 4.

(A) Ray tracing of SEE probe illumination optics in Zemax; (B) microscopic image at side view of the probe illumination optics; (C) optical microscopic image of the resin grating on the spacer’s surface from the direction of the yellow arrow in (B); (D) enlarged image in the yellow box in (C); (E) cross-sectional SEM image of the resin grating.

Fig. 5.

(A) Schematic of the custom grating’s diffraction orders and (B) Calculated diffraction efficiencies of the custom grating. The color bands of blue, green, and red in (B) correspond to the wavelength bands used in color SEE imaging for blue, green and red channels, respectively.

Fig. 6.

(A) Flexible probe detection sheath including multi-mode fiber bundle. The drive cable of the illumination optics was inserted into the inner sheath. (B) Rigid bent guide (304 Stainless steel tubing, McMaster-Carr, 14.5 Gauge) containing the SEE probe inside. The guide was bent near the distal end (probe bending radius = 5.4 mm and bending angle = 110°).

Fig. 7.

(A)-(C): Color chart images obtained using the color SEE device; Screenshots of the video taken at 30 Hz. The arrows denote false image artifact due to lower order illumination. (D): An image of the same color chart obtained using a digital still camera. The dashed circles correspond to the (A) (B) and (C) fields of view.

Fig. 8.

Magnified view of NBS 1963A resolution target imaging obtained using the SEE device (A, 11.0 lp/mm) and a commercial chip-on-the-tip endoscope (B, 7.1 lp/mm). Both of the working distances were 10 mm.

Fig. 9.

Ex vivo imaging of swine intertarsal joint, using (A-B) color SEE device, (C-D) chip-on-tip endoscope, and (E) digital still camera. Arrows in the image (E) indicate where the images (A)-(D) were obtained.