Endoscopes

The description of the Endoscopes covers all aspects of the surgical procedure used for the management of (description de la pathologie en cause). Operating room set up, position of patient and equipment, instruments used are thoroughly described. The technical key steps of the surgical procedure are presented in a step by step way: Introduction, Structure/function, Choice of endoscopes, Advantages/disadvantages, Practical issues, Usage problems, Conclusions. Consequently, this operating technique is well standardized for the management of this condition.

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Endoscopes

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Abstract
The description of the Endoscopes covers all aspects of the surgical procedure used for the management of (description de la pathologie en cause).
Operating room set up, position of patient and equipment, instruments used are thoroughly described. The technical key steps of the surgical procedure are presented in a step by step way: Introduction, Structure/function, Choice of endoscopes, Advantages/disadvantages, Practical issues, Usage problems, Conclusions.
Consequently, this operating technique is well standardized for the management of this condition.
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2005-09
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E-publication
WeBSurg.com, Sept 2005;5(09).
URL: http://www.websurg.com/doi-ot02en308a.htm

Endoscopes

1. Introduction
Surgical endoscopes utilize high performance optical technology. The choice of endoscope requires a good deal of consideration since it is one of the most expensive pieces of surgical equipment both in terms of capital cost and maintenance. A good endoscope needs three qualities. It must be able to transmit a good level of brightness, both in bringing light into the operative field and carrying the image to the camera. It must have large depth of field and minimal distortion of image viewed. Finally the endoscope should also be able to withstand the mechanical and thermal constraints of the sterilization processes.
2. Structure/function
• Structure
The rigid endoscope is comprised of a metal tube that contains two channels. One carries light to illuminate the operative field and the other carries the image of the operative field to the camera. The image channel is made up of a series that are successively placed one after the other and separated by spacers. As the image passes through each lens it is inverted and the number of lenses depends on the length of the endoscope. This system is known as the Inverting Real Image Lens System (IRILS) and permits refraction of the light while maintaining overall luminosity of the endoscope. The “eyepiece” lens at the end of the series acts to magnify the image before it reaches the camera.

The endoscope can be divided into five distinct parts:
Objective lens system:
The lens located at the distal end of the endoscope captures the image and directs it back through the endoscope. Its focal length is generally fixed. It determines the magnification of the object and the field of view of the endoscope. By changing the angle between the long axis of the lens and the axis of the endoscope the direction or “angle of view” can be changed.
Rod-lens assembly:
A series of spaced glass rod lenses continually refocus the image up through the scope. Metal spacers separate each rod lens to maintain the appropriate focal distance between lenses. The number of lenses depends on the length of the endoscope. A longer scope requires more lenses but this reduces overall luminosity and increases the fragility of the system. In order to minimize the reduction in luminosity due to reflective loss all of the endoscope’s lenses are treated with an anti-glare system. This consists in coating each lens surface with a thin layer of magnesium fluoride, using a vacuum pack process. Thus, it is important to avoid damaging the optical surface of the endoscope.
Ocular lens:
The last lens in the series, at the proximal end of the camera, magnifies and focuses the image for transmits to the camera. This part of the endoscope is designed to allow coupling to the camera lens.
Light post:
Set at an angle to the main axis of the scope is a connection point for the cold light source cable. This connection must be of high optical and mechanical quality in order to avoid loss of light and overheating.
Light channel:
This runs along the length of the endoscope carrying light from the light post to the tip of the scope. The light is carried in a bundle of glass fibers. At each end of the channel the fibers are cut, polished and capped to produce a light-transmitting surface.









• Function
• Focal length/brightness
The optical quality of the endoscope is determined by the same optical laws that govern optical quality in photography.

Focal length:
The focal length of the endoscope is determined by the aperture of lens at the tip of the laparoscope (objective lenses). An object at the focal distance appears its natural size within the image. However, when the object is brought closer to the lens, then it appears magnified whereas if it is moved further away then it appears smaller between the system and the object. If the endoscope is coupled to a camera fitted with a mechanical zoom the focal length of the camera can be adjusted. By moving the CCD (Charge-Coupled-Device) sensor away from the eyepiece lens the image is magnified but the field of view reduced. However, most camera zooms are digital, which means that the image processor in the camera control unit simply magnifies each pixel. Thus although the image may appear magnified the resolution is diminished, leading to a decrease in the quality of the image, which becomes more apparent the more the digital zoom is used.
Brightness:
The brightness of the image diminishes the further the light has to travel and the narrower the channel along which it has to pass. Thus a long, small caliber endoscope will transmit an image of much reduced brightness compared to a short, wide caliber scope.
• Depth of field
The depth of field is the distance between near and far objects in the field, which appear focused. For a particular laparoscope this is fixed being determined by the configuration of the lenses and the caliber of the scope with a narrower scope having a deeper depth of field.
• Peripheral light loss
Peripheral light loss (vignetting):
There are two reasons why the periphery of the field of view can appear dark. The first is simply that the shape of the image transmitted to the camera by the endoscope is not exactly the same shape as the CCD. This problem can be corrected by image processing that can crop the image. The second cause is due to reduced light transmission through the periphery of the lens. The poorer the quality of the lens the more exaggerated this effect becomes.
• Width of field
The angle of view is the angle subtended by two points diametrically opposite each other at the extremity of the field of view and the tip of the endoscope. By changing the curvature of the objective lens the angle of view can be changed. However, increasing the curvature of the lens produces more distortion in the peripheral part of the field of view (barreling or fish-eye effect).
Again the higher the quality of the lens, the less the distortion.
The desirable features of brightness and depth of field, and angle of view and minimal distortion, require opposite characteristics from the endoscope. This makes it difficult and costly to construct endoscopes with a large depth and width of field, high brightness and minimal distortion.
3. Choice of endoscopes
• Monocular endoscopes
• Angle and width of view
Most endoscopes used in laparoscopic and endoscopic surgery are monocular endoscopes. A wide choice is available on the market.
Direction (angle) of view:
Endoscopes with varying tip angulations ranging from 0 degrees (standard forward looking scope) to 120 degrees are available.

When laparoscopy was first introduced for digestive procedures, endoscopes with angulated tips of 25, 30 or 40 degrees were widely used. Currently, their use is in decline as the brightness and field of view offered by angled endoscopes is generally inferior to those offered by 0 degree endoscopes. However, recent angled endoscopes with much improved optical properties are just being introduced. It should be noted that the view provided by an angled endoscope can impair surgical performance particularly in surgeons with limited experience.
Width of view
The width of view of the endoscope usually varies from 20 to 60 degrees although scopes with widths of views of 80° now exist.
• Caliber of endoscope
Endoscopes are available with diameters from 3 to 12 millimeters. In general, the narrower the scope the less bright the image and the narrower the width of field. Certain manufacturers have developed endoscopes that are less than 3 millimeters in diameter. The principles of function of these endoscopes differ from conventional endoscopes. The image is transmitted via optical fibers, as the rod-lens system is not adapted for such small diameters. The depth of field, optical quality and light transmitted by these endoscopes are considerably inferior to the standard 10 mm endoscopes. However, the optical quality of these micro-endoscopes is improving, although they remain difficult to use because they are so fragile.
• Stereoscopic endoscopes
Several manufacturers have developed endoscopes that provide a stereoscopic view of the operating field. Stereoscopic endoscopes transmit two images to a pair of video cameras. The image has to be viewed on a special projection system and a number of different systems exist. The use of stereoscopic systems is currently limited. The only regular use of the stereoscopic vision is for Trans-anal Endoscopic Microsurgery (TEM). They have also been incorporated into robotic laparoscopic systems.
Principles of function:
Stereoscopic endoscopes have two image channels with 6.3 millimeter lenses set either for straight vision (0 degrees) or for oblique vision (50 degrees - used in TEM). They have a 75 degree width of view. One of the disadvantages of these systems is the low brightness transmitted by these endoscopes compared to standard 10 mm endoscopes. This is due to the small diameter of the lenses. This is not problematic in transanal surgery because of the proximity of the operating field to the endoscope. However, in conventional surgery, the distance between the endoscope and the operating field means that the reduced luminosity is more apparent. In fact, the most limiting factor with these systems is the projection technology, which currently is inferior to standard surgical monitors.
• Other endoscopes
Flexible and semi-flexible endoscopes:
Certain manufacturers have developed systems for surgical endoscopes that are comparable to flexible endoscopes. Two different types of systems exist:
The first has a standard rigid section and a flexible tip. This articulated part consists of a fiber optic bundle just like those found in flexible gastrointestinal endoscopes. The image is otherwise transmitted from the tip to the eyepiece of the endoscope as a light image.
A more innovative system uses a CCD sensor placed at the distal end of the endoscope. Thus, the shaft of the endoscope transmits an electrical signal rather than a light image.
Neither of these two systems is widely used.

The data provided by manufacturers rarely specifies the qualities of endoscopes in terms of brightness, depth and width of field or distortion.
However, It is possible to check the quality of an endoscope:
“Fish-eye” distortion can be checked by viewing a written text on a piece of paper through the endoscope. If the text looks flat, then the distortion is limited. However, if it looks spherical, the distortion is important.
The depth of field can be assessed by viewing a line of text and analyzing the total near-far distance over which the text appears in focus. This should be over 10 cm. In endoscopes providing a smaller depth of field the surgeon will have to repeatedly readjust the scope’s position.
The brightness of an endoscope is dependent not only upon its light channel and lens system but also upon the light cable and light source. Before assessing the endoscope for light transmission it must be attached to an optimized light source.
4. Advantages/disadvantages
Angle of view:
Most laparoscopic surgical procedures can be performed with straight (0 degree) endoscopes. Some surgeons, however, prefer to use endoscopes with an angled line of sight, usually 30 degrees, in order to explore areas that are difficult to visualize (gastroesophageal reflux disease surgery, urological surgery, gynecological surgery).

Advantages of forward looking endoscope (0 degree):
- most common type of scope => wide choice;
- effective for most procedures;
- higher brightness;
- larger field of view;
- larger depth of field.
- but unable to visualize some operative areas.

Advantages of 30 degree, 50 degree, 70 degree endoscopes:
- possibility to explore areas of the operative field that are difficult to access with a 0° endoscope.
But =>
- lower brightness;
- more difficult to control field of view;
- light post must be kept vertical to avoid rotating field of view.

Gauge of endoscope:
The wider the endoscope the more light transmitted and thus the better the final clarity of the viewed image. Narrower endoscopes have the advantage of passing down smaller trocars but generally have a narrower field of view. Thus a narrow scope may be perfectly adequate for a diagnostic or simple procedure and results in a smaller scar. However, for more complex procedures a broader scope gives a brighter and larger field of view.

Conclusion:
An ideal endoscopic surgery kit would include a complete range of endoscopes (0 to 25, 30, 40, 50 and 70 degrees) and a variety of gauges (12, 10, 5 and even 3 mm). At the present time, since cameras are not sterilized, it is difficult to change endoscopes during the operation while maintaining proper sterilization. Before starting the operation, the surgeon usually has to choose the endoscope that will be used throughout the procedure.
5. Practical issues
Set-up:
Most endoscopes have no particular adjustment possibilities. Endoscopes should be used at body temperature or room temperature to prevent too much fog from forming on the end of the endoscope. Warming the scope in a flask of hot saline can be particularly effective. A variety of liquid preparations is available and can be applied to the tip to help reduce fogging.

Maintenance:
Endoscopes are designed to be tough in order to protect the fragile systems of lenses that are glued within the scope. If there is an extreme temperature increase or an impact, the orientation of the lenses can be disturbed and the quality of the vision altered irreparably. This explains the often short life-span of endoscopes in the operating room.
Before the operation it is important to check the overall condition of the endoscope, search for signs of impact that could have dislodged a lens and caused a distortion of the image or a decrease in the light transmitted.
The light fiber bundle can also be damaged resulting in a decrease in the amount of light transmitted to the operating field.
It is recommended to carefully clean the endoscopes with a plastic brush and soap, especially the end inserted in the abdomen. Indeed, the accumulation of blood and protein at the end of the endoscope, combined with the heat from the light, cause a coagulation of the proteins and a progressive alteration of the quality of the light and image transmitted. For this reason, the tips of endoscopes must be frequently cleaned.

Sterilization:
Every country has its own legislation. Whereas many countries authorize sterilization by simple immersion in glutaraldehyde, other countries, such as France and Germany, require autoclave sterilization. This means that the endoscopes must be able to withstand high temperatures (134°C for sterilization for CJD (Creutzfeld-Jakob Disease) prion, at a pressure of 2 bars for a period varying from 5 to 18 minutes, depending on country legislations. For older generation endoscopes that cannot withstand autoclaving, it is mandatory to perform a high level disinfection by immersion in glutaraldehyde for one hour, in order to sterilize against prion.
http://www.fda.gov/
6. Usage problems
Most problems with endoscopes can be easily corrected by the surgeon. However, if an endoscope is found to be damaged causing deterioration in picture quality, it should be returned to the manufacturer for repair.

Continual fogging/loss of image:
Check that the endoscope is not too cold.
Check that blood and fat are not dripping onto the tip of the endoscope from the trocar. Cold CO2 gas running in the optical trocar can also make fogging worse – change CO2 to other trocar, do not use optical trocar to vent pneumoperitoneum.

Blurry image, low clarity, focusing problems:
Inspect the lenses at both ends of the endoscope for dirt and damage.
Look through the eyepiece at a well illuminated object held at about 10 cm from the tip of the endoscope. The image should be crisp.
Ensure the endoscope is properly coupled to the camera head.

Image not centered:
Make sure that the endoscope is correctly coupled to the camera.

Poor illumination:
Check that a working light source is properly attached to the light pillar of the scope.
Look at the shaft of the endoscope for evidence of damage to the light bundle. Check the tip and eyepiece for dirt and damage.

More often than not a poor image is due to a simple problem that can be corrected by the operating room team. A systematic review of the image chain is required. Start at the light source. Follow the light along the cable and through the endoscope to the operative field. Check the lens at each end of the endoscope. Check the lens at the end of the camera head and the coupling of the endoscope to the camera. Check the focus. Check the integrity of the camera cable and the camera connection for water and bent pins. Check that the camera control unit is powered up and that the white balance, shutter and gain are correctly set. Check the video connection to the camera control unit. Look for damage of the cable carrying the video signal to the monitor. Finally check the monitor, first which type of video input you have (RGB, Y-C, Composite) then which channel (A or B). Make sure the settings on the front match the connections on the back. Check the picture settings (color balance, brightness, contrast) unless you have an RGB connection. Demagnetize the screen (degauss).

It can be helpful to draw a simple diagram showing the connections of the various elements of your particular videoscopic system.
7. Conclusions
The endoscope is central to the performance of successful video-assisted surgery. The endoscope is a high precision instrument and the slightest disturbance can result in a major alteration of the transmitted image. This accounts for the high cost and fragility of these systems.