Development of a real-time spectral imaging system using in-site micro-LED-based illumination and high-speed micro-camera for endoscopic applications

Abstract

We designed a compact, real-time LED-based endoscopic imaging system for the detection of various diseases including cancer. In gastrointestinal applications, conventional endoscopy cannot reliably differentiate tumor from normal tissue. Current hyperspectral imaging systems are too slow to be used for real-time endoscopic applications. We are investigating real-time spectral imaging for different tissue types. Our objective is to develop a catheter for real-time hyperspectral gastrointestinal endoscopy. The endoscope uses multiple wavelengths within UV, visible, and IR light spectra generated by a micro-LED array. We capture images with a monochrome micro camera, which is cost-effective and smaller than the current hyperspectral imagers. A wireless transceiver sends the captured images to a workstation for further processing, such as tumor detection. The spatial resolution of the system is defined by camera resolution and the distance to the object, while the number of LEDs in the multi-wavelength light source determines the spectral resolution. To investigate the properties and the limitations of our high-speed spectral imaging approach, we designed a prototype system. We conducted two experiments to measure the optimal forward voltages and lighting duration of the LEDs. These factors affect the maximum feasible imaging rate and resolution. The lighting duration of each LED can be shorter than 10 ms while producing an image with a high signal-to-noise ratio and no illumination interference. These results support the idea of using a high-speed camera and an LED-array for real-time hyperspectral endoscopic imaging.

Keywords: FPGA; Hyperspectral imaging (HSI); LED array; Multispectral imaging (MSI); cancer; gastrointestinal endoscope; monochrome camera; wireless transceiver.

Figure 1.

The schematic block diagram of the hyperspectral endoscopic system.

Fig. 2

The schematic diagram of the proposed hyperspectral endoscope catheter.

Figure 3.

The designed hyperspectral evaluation template (A) and the printed template (B).

Figure 4.

(A) Experimental setup for the feasibility study. (B) LED array, camera, and spectral template inside the dark box.

Figure 5.

Forward bias pulse of LEDs.

Figure 6.

Captured images for different pulse widths (top: LED of 505 nm, bottom: LED of 660 nm).

Figure 7.

SNR_dB versus the pulse width applied to the LED forward voltage.

Figure 8.

(A) SNR_dB versus LED forward voltage. (B) Light reflection versus forward voltage for four sample LEDs

Figure 9.

Seven-channel data cube. The yellow arrows show the corresponding ROIs for the channels.