How It Works: The Image System
How it Works
All endoscopes use fiberoptic bundles to transmit light from the light source connector to the distal tip of the insertion tube. A light guide bundle contains thousands of individual fibers, each fiber being much smaller than a human hair. An optical fiber is composed of two layers of glass of different reflective values which trap the light inside the length of the fiber. The flexibility of the fibers makes it possible for the light to bend around corners and curves. FiberTech can replace damaged light guide bundles.
Fiberoptic scopes also use a fiber bundle to transmit the image from the objective lens at the distal tip of the scope through the eyepiece to the user’s eye. Image guide bundles are a coherent structure which means that each fiber is in the same place at both ends of the bundle. This allows a clear image made up of many small pieces of the whole image. The glass fibers can break if the scope sustains trauma such as crushing of the insertion tube, severe impact, or excessive bending of the insertion tube. Moisture around the fibers can cause them to become brittle which also can result in fiber breakage. In a fiberoptic scope you can clearly see broken fibers in the image bundle. Each broken fiber appears as a black or gray dot in the image because that portion of the image is not being transmitted. A few broken fibers will not interfere with the image: more than about fifty broken fibers will be noticeable, especially if clustered in one area. Fiberoptic image bundles that meet manufacturer’s specifications are not readily available: scopes needing new image bundles will usually require overhauls by the manufacturer.
In a video endoscope, the image bundle is replaced with a video camera unit consisting of a lens assembly and an electronic chip (the charge-coupled device or CCD) attached to about 16 very small wires. The CCD chip is 2-3m in diameter, and is made up of thousands of microscopic elements. The image is produced by many individual sensors (pixels) that make up an image by detecting light level and colors. An external video processor then assembles the image. The image is transmitted along the wires to a video monitor and various peripheral devices to produce live motion images, hard copies, or computerized records.
All endoscopes have lenses in both the lighting and image systems. A fiberscope has a lens system in the eyepiece that provides magnification and focuses on the end of the fiber bundle. This allows the image viewed to appear much larger than the bundle itself. All flexible endoscopes use an objective lens system at the distal tip. This lens system reduces and focuses the image onto the surface of the image guide fiber bundle or the CCD chip. Objective lens system can be rebuilt, but if they are scratched or damaged by impact they will have to be replaced by the manufacturer. Therefore, it is very important to protect this lens from trauma. Another lens system focuses the light onto the area being examined to provide evenly distributed lighting. The light guide lenses in this system can be replaced when damaged.
Moisture is the image system’s worst enemy, especially chemicals used for reprocessing. In fact, fluids entering the scope cause approximately 80% of all image problems. The most important preventive measure you can take to avoid image problems is to prevent getting moisture into the scope in the first place. It is absolutely essential that the scope be leak tested after every procedure.
If the image of a fiber or video scope becomes cloudy, it may be due to debris on the image lens or to moisture inside the scope. Moisture can also create changes in the color or resolution of the image. If you notice the image is clear when the scope is outside the patient, it is probably due to moisture inside the scope. As the scope warms to the patient’s body temperature, the moisture condensed inside the objective lens. The scope can be tested for moisture by submerging the distal tip in warm water while observing the image for clouding.
With video scopes, you may see a rainbow effect, colored spots of abnormal color. This is caused by moisture interfering with the electrical signals from the CCD camera unit. All internal wiring in the scope is especially susceptible to damage from chemical solutions. The video chip itself is usually unharmed by the moisture. Once the scope is dried out and residue from the moisture is removed, the chip will return to normal working condition.
If a video scope is accidentally submerged without the waterproof cap or water is allowed to enter the electrical connector, serious damage can occur. Do not insert anything into the connector to remove the water because it may damage the pins or CCD camera by discharging static into the wiring. If the electrical connector is submerged, immediately send the scope to the repair facility to be evaluated. Never plug a scope into the processor if you suspect fluid has entered the scope. Moisture inside the scope can cause an electrical “short circuit” which can permanently damage the video camera.