Laparoscopes

The majority of currently available rigid laparoscopes are derived from the Hopkins-type rod-shaped lens system developed in 1952.4 This lens system, which is contained in the core of the laparoscope, focuses and transmits the light from the abdomen to the camera. Modern versions consist of rod-shaped lenses, air-filled spaces between the lenses, and additional lenses that compensate for peripheral distortion. Optical fibers at the periphery of the scope transmit light from the light source into the abdomen. Alternatively, the rod lens relay system can be eliminated by incorporating miniaturized charge-coupled devices mounted distally on the top of the scope.

Currently, various kinds of laparoscopes are available with different diameters and viewing angles (Figure 2.1). We generally recommend using a standard 10-mm laparoscope for routine colorectal procedures,

Laparoscope

Figure 2.1. Visual field of the laparoscope depending on the viewing angle: A 0°, B 30°, C laparoscope with a flexible tip.

Figure 2.1. Visual field of the laparoscope depending on the viewing angle: A 0°, B 30°, C laparoscope with a flexible tip.

because its wide overview images are optimal for multiquadrant colorectal procedures. Miniature laparoscopes (less than 5 mm in diameter), if combined with a powerful light source and high-quality video camera, may have a certain role in selected procedures, such as biopsy, lysis of adhesion, and stoma creation. As for viewing angles, a straight-viewing (0°) laparoscope allows more intuitive perspective than an oblique-viewing laparoscope.5 We believe, however, that colorectal laparoscopic surgeons should familiarize themselves with the oblique-viewing (i.e., 30°) laparoscope, because of its greater flexibility in viewing fixed and deeper structures that may be blind to 0° laparoscopes (e.g., the splenic flexure or deep pelvic structures).

Some surgeons have advocated theoretical advantages of the three-dimensional (3-D) viewing system in laparoscopic surgery.6 Currently, various types of 3-D laparoscopy have become available. In general, 3-D laparoscopes provide a separate image to each eye through a variety of display mechanisms, thereby creating the perception of a stereoscopic image with true depth cues. These images may be viewed on a video monitor with specially shuttered glasses, or through a head-mounted display. The binocular information provided by such 3-D viewing systems could potentially increase the precision of laparoscopic task performance while decreasing performance time. Previous studies have shown that a 3-D system can enhance performance of surgeons in laboratory settings; however, its role in laparoscopic surgery has yet to be demonstrated. Future improvements in resolution, illumination, and ease of use, is required to widely spread this technology, and there will be an expanding role for 3-D imaging in the future.

Cameras

With the most widely used laparoscopic video systems, a video camera (so-called "camera head") is connected to the eyepiece of a traditional rod-lens laparoscope (Figure 2.2). The basis of the video camera is the 1/3-1/2 or 2/3-inch solid-state charge-coupled device (CCD), in which the imaging chip is composed of a thin, flat silicon wafer.7 The CCD matrix comprises a rectangular grid of horizontal and vertical rows of minute image sensors called "pixels." The resolution of the CCD is determined by the number of pixels its surface can accommodate. "Single-chip" cameras use a color mosaic on a single CCD chip with 400,000 to 440,000 pixels, to detail the red, green, and blue (RGB) component of the image. However, "three-chip (3-CCD)" cameras use prisms that split the image into three paths that then pass through RGB filters into three separate CCD chips, providing a red, green, or blue signal, respectively. The resolving power of 3-CCD cameras becomes greater compared with single-chip cameras, because one CCD chip is used for each primary color, whereas only one CCD chip is used for all colors in single-chip cameras.

The information sent from CCD chips is then processed by a camera control unit (CCU) for transmission to the monitor (Figure 2.3). The majority of current CCUs have several different types of analog outputs: composite, Y/C (or S), and RGB signals. RGB signals provide the best image available with today's technology.2 Latest model of CCU has a digital output and can be connected to a digital flat-screen display without any degradation of image quality during data transmission (as described later in this chapter).

One of the emerging technologies is the "chip-on-a-stick" videolapa-roscope.7 This system has a single 3 x 4 mm CCD chip mounted at the distal end of the laparoscope directly behind the objective lens system (Figure 2.4). With this technology (so called "direct" videoendoscopy), the conventional rod-lens system is no longer necessary, and the image-quality degradation caused by the traditional optical relay system is virtually eliminated. Although it is still technically challenging to

Laparoscopic Rod Lens System
Figure 2.2. Camera head connected to conventional rod-lens laparoscope.
Rod Lens Scanners
Figure 2.3. CCD, video processor, and monitor.

mount 3 CCD chips or a high-performance single CCD chip in the restricted space of the distal tip, the image quality is at least as good as "indirect" videoendoscopy. With this "chip-on-a-stick" technology, it has become possible to make the distal portion of the laparoscope either rigid or flexible. Several products have been put on the market, and our current preference is a videolaparoscope with this technology (EndoEye®; Olympus, Tokyo, Japan). One major need is to produce a laparoscope that eliminates manual lens cleaning.

Light Sources

Currently, the high-intensity xenon light source (300 W) is most widely used for advanced laparoscopic procedures, because it provides supe-

Olympus Endoalpha
Figure 2.4. A chip-on-a-stick videolaparoscope (Endoalpha™, Olympus, Tokyo, Japan).

rior illumination compared with older halogen light sources.8 Its performance, however, is not fully appreciated if the bulb and/or light guide (light transmission cable) has been deteriorated. The light bulb should be inspected and changed at regular intervals. The surgical team should recognize that the light guide contains bundles of fragile fiberglass cables. If damaged, it may seriously limit the quantity of light transmitted.

Monitors

The resolution of the monitor screen on which the image is displayed is determined by the number of lines exhibited.9 With regular singlechip cameras, the resolution of a standard analog cathode ray tube (CRT) video screen ranges between 450 and 600 horizontal lines. Three-chip cameras provide an enhanced video image with 700 horizontal lines of resolution. However, the measured resolution in the monitor screen may be only marginally improved over that of a single-chip camera.7 To fully appreciate the high-quality images of three-chip cameras, a monitor with higher resolution is required.

The digital flat-screen display (liquid crystal display: LCD) is still in a relatively early stage of development. The flat LCD screens are lighter in weight than CRT screens, therefore can be placed more easily in an optimal position for the operating surgeon to manipulate and observe in one axis. The resolution varies according to the pixel number and the size of the screen. The signal input is digital, therefore images can be displayed on the screen without any degradation in quality. Although this technology seems promising, the actual image on the digital screen has not surpassed the "analog" image generated by good laparoscope with three-chip video camera and recent CRT monitor in an RGB formation.2 With future technological improvements, we believe the use of digital LCD screens will become mainstream in surgical laparoscopy.

Another promising technology is a head-mounted display. Early head-mounted displays suffered from low resolution and were bulky and uncomfortable to wear. However, more recent designs offer higher resolution, lighter weight, and a cordless design. The surgeon can stand in a comfortable operating position with an unobstructed view of both the operative field and the video image.10 If head-mounted displays are used exclusively, the need for monitor booms can be eliminated, and the operating environment can be further simplified.

Recording Devices

Photodocumentation is becoming an important byproduct of laparo-scopic surgery. With recent digital technological evolution, it has become easy and practical to capture still images digitally from any laparoscopic procedures. Images can be printed out in theater, but can be also transferred by a variety of storage systems to a computer and recorded in various digital formats (Figure 2.5). Those images, once stored electrically, can be easily transferred to an electric patient record (database) and utilized for various purposes.

Laparoscopes
Figure 2.5. Images stored in various digital formats.

Video footage of a laparoscopic procedure is currently recorded more often in either VHS or s-VHS formats and digitized later; however, it can be also recorded directly in a digital format. Current versions of videoendoscopes used for laparoscopic procedures have an analog capture chip, and the analog signal is immediately digitized for viewing on a monitor or for recording. This will change, and chips will record the data as digital data from the start in the near future.3

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