Illumination

Illumination of the operative field is an integral part of laparoscopic surgery. High-intensity light sources, usually halogen and xenon, are currently employed the most. However, halogen sources produce a slightly yellow light requiring compensation with white balancing of the endoscopic camera system. Xenon sources provide a more natural white light. Fiberoptic bundles contain either glass fiber or special fluid run through the endoscope and permit rapid transmission of light to the operative field and digital information in a small space. Although less efficient in light transmission due to a fiber mismatch at the junctions of the light cable and endoscope, the glass fiber bundles are more flexible, and therefore more widely used (12).

Modern light sources often have an automatic light-sensing feature, which quickly adjusts the light output as required by the camera. This automatic light adjust-

Shadows play an important role in depth perception and spatial orientation. Endoscopic task performance significantly improves with video systems providing proper illumination and appropriate shadows in the operative field.

ment feature is particularly helpful during endoscopic procedures, as the endoscope may be rapidly moved throughout different parts of the urinary tract with variable levels of illumination. Light intensity is automatically adjusted to maintain a preset level. Similarly, some digital camera systems are equipped with an "automatic iris" system, which electronically increases or decreases the "aperture" of the camera shutter. Automatic intensity-adjusting light source is not required if the camera system is equipped with such a light-sensing feature (2). Newer charge couple device or image sensor-based endoscopic cameras feature electronic exposure. This system varies the effective exposure period (i.e., light gathering time) of the charge couple device as the live image is captured. Typical charge couple device exposure periods range from approximately 1/60 of a second to 1/10,000 of a second under very bright conditions. This electronic process can be used to maintain the brightness of the image. When the image brightness must be reduced to improve picture clarity, the image signal exposure period can be reduced electronically instead of adjusting the iris of the light source.

Shadows play an important role in depth perception and spatial orientation. Endoscopic task performance significantly improves with video systems providing proper illumination and appropriate shadows in the operative field (25).

Many of the current endoscopes employ a simple frontal illumination technique that produces an optically flat and shadowless image with resultant poor contrast. Using a single-point or multipoint illumination system, newer illumination and imaging technologies provide shadow-inducing systems. One of these techniques employs the use of two independent illumination fiber bundles, with one fiber bundle ending at the front lens, as designed in conventional endoscopes, and the other fiber bundle ending behind the tip of endoscope. This configuration results in an improved image with better contrast due to shadow formation. Spatial orientation and perception between anatomical structures are considerably enhanced (4).

The development of high-quality image display systems has become essential during endoscopic surgery.

Current applications of high-definition television in medicine include diagnostic and therapeutic maneuvers during endo-scopic surgery. The increased resolution and clarity have been shown to greatly facilitate surgical performance.

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