| Summary: | 博士 === 國立陽明大學 === 生醫光電研究所 === 104 === A bright and uniform white light illumination is a critical factor for endoscopy. white Light-emitting diode (LED), which possesses many advantages like long life time, higher efficacy and lower power consumption, has gradually become a standard light source for endoscopic diagnose and surgery. During treatment, the light emitted from white LED to illuminate the target is delivered by a bundle of fibers placed in the endoscope tube. However, the lighting cone resulted from the traditional endoscopic lighting system is restricted by the small numerical aperture (NA) of fiber, which causes the illuminated area failing to cover the field of view (FOV) of the CMOS camera of the endoscope and having a dark peripheral in the displayed images. Therefore, an auxiliary light source is needed to improve the background illumination.
Another problem exists in current endoscopy is the total diameter of the endoscope. The advent of miniature CMOS sensor with outer diameter is as small as 1.4mm means the light delivery system of endoscope also needs downsizing so that the incision can be smaller in video assisted thoracic surgery (VATS) and the invasiveness can be reduced when a narrower cavity has to be passed for access. Although tip-mounted white LED chips with small footprint packaged with CMOS image sensor can reduce the outer diameter of endoscope, the generated heat at the distal end is another problem to be solved.
In this paper, two models of light sources are presented for remedying the two problems. For the non-uniform illumination caused by the endoscopic lighting system, a compact foldable LED lighting ring is designed and implemented as an auxiliary light source directly placed at the operation field to improve the image quality. The LED lighting ring is composed of thirty white LED chips which are equally arranged on two semi-circle arcs. The ends of the two arcs are connected with silicone gel so that the LED lighting ring can be folded and placed on the bottom ring of the wound retractor. When the LED lighting ring is released, it will recover to the original ring shape for illumination. The other ends of the two arcs are connected to the control unit which provides electric power to the LED chips and monitor the temperature accumulated on the ring, once the temperature exceeds the setting value, the total system will power off. The illumination performance of the LED lighting ring is compared with a standard white LED light source. The lighting angle of LED lighting ring in vertical and horizontal direction is 120°, which is larger than the FOV of the CMOS image sensor (62°) and the standard LED light source (45°). The in vivo images are also acquired with the porcine model to that a more balanced lighting in the living hog's chest cavity was achieved when the LED lighting ring was activated.
As for the downsizing of the outer diameter of the endoscope, our purpose is to couple laser light into one multimode fiber. White light for endoscopic illumination is generated by supercontinuum, and RGB laser system. A scattering cap is attached to the tip of the fiber to broaden the emitted radiation so that the illuminated area with uniform lighting is larger than the FOV of the CMOS image sensor. Some filters are used to reduce the power contributed in the red spectrum of supercontinuum and adjust the correlated color temperature (CCT) to improve the image contrast. The illumination performance and acquired in vivo images of supercontinuum is compared with a standard medical white LED module.
Although we have shown the feasibility of supercontinuum being a light source for endoscopy, the high price, and complex filtration prohibit supercontinuum from being used for clinical treatment. On the other side, too many light sources used during MIS will make surgeons confuse because different CRI and CCT generate different image qualities. Since minimize the outer diameter of endoscope for single access surgery is unavoidable, finding a substitute for LED to create a new type of lighting ring is necessary. Besides, unifying light source is also important for MIS. Therefore, RGB laser, which is more compact and cost effective, is very suitable to be a unique illuminant during single access surgery. With the brand new glass based side illumination fiber for making a lighting ring to illuminate the operative field, we can create an all fiber illumination system. For RGB laser system, the quantitative (including CRI and illuminance) and in vivo experiments of narrow band imaging (NBI) are conducted. The output power and power density at the fiber tip is also measured to prove that the diffused laser light is safer. The illuminated area and illuminance of fiber lighting ring composed of side illumination fiber and RGB laser are also measured, and compared with the former LED lighting ring.
With the improved beam angles and the uniformity of the illumination intensity brought by the diffuse element, the laser based light sources present as a versatile compact light source ideally suited to the miniaturized CMOS image sensor to form an ultra-slim endoscopic system for diagnosis and minimally invasive surgery. The unique capacity is expected to enable a wide variety of procedures and promise unprecedented
opportunities in medical applications.
|
|---|
