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Endoscopic Photography

endoscopes image fiber optical

ANDREW PAUL GARDNER, BSc ABIPP MIMI ARPS RMIP
UCL Ear Institute Photographic Unit

Endoscopic photography includes the acquisition of an image from inside any inaccessible space using some form of optical transmission lens system. Images are viewed using a mirror or conveyed through a series of lenses and prisms in a rigid tube, through flexible fiber-optic devices or captured by miniature sensors at the end of a suitable probe. Endoscopy, which means to look inside, is derived from the Greek endon “within” and skopein “look at.”

Endoscopy is a routine procedure in medicine and veterinary science used to explore body cavities and internal structures either through natural orifices or through small incisions during “keyhole surgery.” A range of surgical procedures may be performed using miniature instruments passed through channels alongside the optical components of the endoscope.

Endoscopes are also used to inspect cavities and other inaccessible parts of buildings, machinery, and any other physical structures. They allow covert observation and photography of activity within enclosed spaces such as animal or bird nests or during security and surveillance operations. Specially reinforced endoscopes are used to inspect extreme and hostile environments such as within combustion chambers or nuclear facilities. Endoscopes can provide realistic views and “walkthroughs” of architectural models by providing a ground level viewpoint of a scaled street scene.

Endoscopes date from antiquity and were either bladed devices to enlarge an existing opening or simple open tubes, often tapered to permit easy insertion and to allow light to enter the cavity. Archaeologists have discovered Roman instruments designed to examine the human ear, nose, throat, vagina, and rectum. Early endoscopists used either sunlight or candlelight for illumination. Although endoscopes had greatly improved by the early nineteenth century, lack of adequate illumination prevented the pioneers of medical photography from obtaining endoscopic photographs. John Avery, MD, a surgeon at the Charing Cross Hospital, London, may have experimented with endoscopic photography in the 1840s. Using a mirror held at the back of the throat, Johann Nepomuk Czermak obtained the first endoscopic photograph, a view of the larynx, in 1860. In 1878, Theodor Stein made a camera, the “Heliopiktor,” which could be used with different optical devices including endoscopes. By the late 1880s, doctors began to obtain useful endoscopic images, taking advantage of improvements in photographic emulsions and aided by miniature electric lamps built into the endoscope tip.

Modern rigid endoscopes have a complex optical design developed by Professor Harold Hopkins in the UK. “Hopkin’s Rod” endoscopes deliver bright and high quality circular images that may be focused through a lens onto a film or image sensor. Some have a straight optical axis, but others include a prism at the tip to provide an angled view.

In 1957, Basil Hirschowitz introduced fiber-optic endoscopes, which allowed an image to be carried along a long, flexible, instrument that could be guided through the digestive tract. These use a “coherent” fiber-optic bundle in which the relative position of each fiber is the same at the entrance and exit face to ensure the correct transmission of an image. This is made up of a regular dot pattern, corresponding to the pattern of fibers at the exit face, and limits the resolution available.

As smaller image sensors were developed, endoscope manufacturers designed equipment in which the image was captured directly at the endoscope tip rather than carried optically to a camera attached to the eyepiece. This “chip on a stick” technology can be implemented in the larger diameter endoscopes, either rigid or flexible, to produce very high-quality digital still images or video. A far higher resolution is possible than with fiber-optic endoscopes.

Endoscopic illumination is now typically provided by non-coherent fiber-optic guides that run alongside the image path. In many biomedical applications, where heat can damage delicate tissues, a cold light source is used in which heat is filtered from the light. Portable, battery-powered, light sources are available for industrial and other off-site applications.

The most recent development is capsule endoscopy, where a small capsule containing a miniature video device with its own light source can be swallowed, which transmits images to a recorder worn in a belt. This permits recording throughout the digestive system, including those areas beyond the reach of other endoscopes.

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