Wondershare PDFelement Laparoscopic Imaging Systems Prof. Dr. R. K. Mishra INTRODUCTION It is well-known that laparoscopy is the consequence of advances made in the field of medical engineering. Each surgical specialty has different requirement of instruments. Laparoscopy was initially criticized owing to the cost of specialized instruments and possible complications due to these sharp long instruments. Also, it necessitated difficult hand-eye coordination. Gradually, the technique gained recognition and respect from the medical fraternity since it drastically reduced many of the complications of the open procedure. Minimal access surgery (MAS) has developed rapidly only after grand success of laparoscopic cholecystectomy. Computer-aided designing of laparoscopic instruments is an important branch of medical engineering. It is now possible to control the access through microprocessor controlled laparoscopic instruments. New procedures and instruments are innovated regularly which make it important for the surgeon to be familiar with the developments. Laparoscopy is a technologically-dependent surgery and it is expected that every surgeon should have reasonably good knowledge of these instruments. LAPAROSCOPIC TROLLEY The mobile laparoscopic video cart is equipped with locking brakes and has four antistatic rollers. The trolley has a drawer and three shelves (Fig. 1). The upper shelves have a tilt adjustment and used for supporting the video monitor unit. Included on the trolley is an electrical supply terminal strip, mounted on the rear of the second shelf (from the top). Recently, ceiling mounted trolleys are launched by many companies which are ergonomically better and consume less space in operation theater. IMAGING SYSTEMS ■ Light source ■ Light cable ■ Telescope ■ Laparoscopic camera ■ Laparoscopic video monitor The imaging system is a chain of equipment that is link together in place perfectly and functioning well to produce Fig. 1: Laparoscopic trolley. an excellent laparoscopic image. The break in this sequential pass of links of the chain will be rendered our imaging system impotent. The classic imaging chain starts with a light source and ends in the monitor, requiring seven pieces of equipment, known as the magnificent seven—light source, fiberoptic light cable, laparoscope, camera head, video signal processor, video cable, and monitor (Fig. 2). This imaging chain is often supported by a cast of VCRs, photo printers, or digital capture devices. The surgeon and the operating room team must work together to ensure optimal equipment function through careful handling of the equipment in the operating room and during the sterilization process. Yet, when the image is poor, many operating teams become paralyzed, unable to function without the aid of a medical engineer—“understanding can overcome any situation, however, mysterious or insurmountable, it may appear to be” Accordingly, understanding the (imaging) . video system will allow the operating surgeon to do the basic troubleshooting for his or her system and not be totally dependent on nursing or technical staff, especially at night when experienced personnel may not be available. The advent of integrated operating suites has not changed the principles of this basic idea.
10 Wondershare PDFelement SECTION 1: Essentials of Laparoscopy Fig. 2: The magnificent seven of the basic imaging chain. Light Source It is clear and easy to say that life, recently, is impossible without light and simply no light, no laparoscopy. The light source is the often-overlooked soldier of the video laparoscopic system. High-intensity light is created with bulbs of halogen gas, xenon gas, or mercury vapor. The bulbs are available in different wattages “150 W and 300 W” and should be chosen based on the type of procedure being performed. Because light is absorbed by blood, any procedure in which bleeding is encountered may require more light. We use the stronger light sources for all advanced laparoscopy. Availability of light is a challenge in many bariatric procedures where the abdominal cavity is large. A good laparoscopic light source should emit light as much as possible near the natural sunlight. Three types of light source are in use today: 1. Halogen light source 2. Xenon light source 3. Metal halide light source. The output from the light sources is conducted to the telescope by light cables that contain either glass fiber bundles or special fluid. The halogen light source is used in the medical field since last 20 years, but the spectral temperature of these lights is 3,200 K which makes it too different and too low from natural sunlight. The midday sunlight has approximately 5,600 K color temperature. In practice, the yellow light of the halogen bulb is compensated in the video camera system by white balancing. A more suitable light source for laparoscopic cameras involves the creation of an electrical arc in a metal halide system or in xenon. This electrical arc is produced in same way as in flash of photographic camera. Xenon has a more natural color spectrum and a smaller spot size than halogen. The xenon light source emits a spectral temperature of color of approximately 6,000 K on average for a power of 300 W (Fig. 3). Fig. 3: Spectrum of light. Arc generated lamps have a spectral temperature that gradually decreases with use and white balance is required before each use. The bulb needs replacing after 250–500 hours of usage, depending on the type of lamp. One of the main advantages of the laparoscopy is that of obtaining a virtually microsurgical view compared to that obtained by laparotomy. Quality of the image obtained very much depends on the quantity of light available at each step of optical and electronic system. The interface of the laparoscopic team works with a standard light source. It is essential for the laparoscopic team, particularly the surgeons, to know about all the switch and function of the light source. All essential details of the equipment and all the action required on the part can be found on the operating manual of the product. Many light sources record and display the hours of service and alert the biomedical or medical engineer (or the well-informed surgeon) when it is time to make a change. When the lifetime rating of the bulb has been exceeded, the subsequent performance of the light source becomes unpredictable, often slowly dwindling until the surgeon just cannot produce a well-lit scene, despite the fact that a bright light seems to emanate from the laparoscope (Fig. 4). A typical light source consists of: ■ A lamp (bulb) ■ A heat filter ■ A condensing lens ■ Manual or automatic intensity control circuit (shutter).
Wondershare PDFelement CHAPTER 2: Laparoscopic Imaging Systems Fig. 4: Xenon light source: Bulb-life display is shown. Lamp (Bulb) Lamp or bulb is the most important part of the light source. When the bulb fails, the entire system is out of commission until either the bulb is replaced or a new light is brought to bear. The quality of light depends on the lamp used. Several modern types of light sources are currently available (Fig. 5). These light sources mainly differ on the type of bulb used. Three types of lamp are used more recently: 1. Quartz halogen incandescent lamp 2. Xenon lamp 3. Metal halide vapor arc lamp Halogen bulbs (150 W) or tungsten-halogen bulb: It is an incandescent lamp with a transparent quartz bulb and a compressed gas filling that includes a halogen. Quartz is used instead of glass to permit higher temperatures, higher currents, and therefore greater light output. The lamp gives brilliant light. The halogen combines with the tungsten evaporated from the hot filament to form a compound that is attracted back to the filament, thus extending the filament’s life. The halogen gas also prevents the evaporated tungsten from condensing on the bulb and darkening it, an effect that reduces the light output of ordinary incandescent lamps. First used in the late 1960s in motion-picture production, halogen lamps are now also used in automobile headlights, underwater photography, and residential lighting. Incandescent (to begin to glow): It is so hot to the point of glowing or emitting intense light rays, as an incandescent light bulb. Quartz, one of the most common of all rock-forming minerals and one of the most important constituents of the earth’s crust. Chemically, it is silicon dioxide (SiO2). It occurs in crystals of the hexagonal system, commonly having the Fig. 5: New generation light source bulb. form of a six-sided prism terminating in a six-sided pyramid; the crystals are often distorted and twins are common. Quartz may be transparent, translucent, or opaque; it may be colorless or colored. The halogen lamp takes its name from the halogens included in the gas within its tungsten-filament bulb, added to prolong filament life and increase brightness. Halogen: Any of the elements of the halogen family, consisting of fluorine, chlorine, bromine, iodine, and astatine. They are all monovalent and readily form negative ions. Halogen bulbs provide highly efficient crisp white light source with excellent color rendering. Electrodes in halogen lamps are made of tungsten filament. This is the only metal with a sufficiently high melting temperature and sufficient vapor pressure at elevated temperatures. They use a halogen gas that allows bulbs to burn (light) more intensely. Halogen bulbs use low voltages and have an average life of 2,000 hours. The color temperature of halogen lamp is around 5,000–5,600 K. These lamps are economical and can be used for laparoscopic surgery if low budget setup is required. Xenon lamps (300 W): Xenon (symbol Xe): A colorless, odorless, and highly unreactive gaseous nonmetallic element found in minute quantities in the atmosphere and extracted commercially from liquefied air. Atomic number is 54. The radioactive isotope 133Xe, having a half-life of 5.3 days, is used for diagnostic imaging in assessment of pulmonary function, lung imaging, and cerebral blood flow studies. Xenon lamps consist of a spherical or ellipsoidal envelope made of quartz glass, which can withstand high thermal loads and high internal pressure. For ultimate image quality, only the highest-grade clear fused silica quartz is used. It is typically doped, although not visible to the human eye, to absorb harmful ultraviolet (UV) radiation generated during operation. The color temperature of xenon lamp is 11
12 Wondershare PDFelement SECTION 1: Essentials of Laparoscopy about 6,000–6,400 K. The operating pressures are tens of atmospheres at times, with surface temperatures exceeding 600°C. The smaller, pointed electrode is called the cathode, which supplies the current to the lamp and facilitates the emission of electrons. To supply a sufficient amount of electrons, the cathode material is doped with thorium. The optimum operating temperature of the cathode tip is approximately 2,000°C. To obtain this precise operating temperature, the cathode tip is pointed and in many cases, it has a groove on the pointed tip to act as a heat choke. This heat choke causes the tip to run at a higher temperature. This configuration of the cathode tip allows for a very high concentration of light from the cathode tip and a very stable arc. The anode, the larger electrode, receives electrons emitted by the cathode. Once the electrons penetrate the anode face, the resulting energy is converted to heat, most of which radiates away. The large, cylindrical shape of the anode helps to keep the temperature low by radiating the heat from the anode surface. The advantage of xenon bulb is that it used two electrodes (cathode and anode) and there is no filament as in halogen bulb, so it has somewhat a fixed lifetime with an average of 1,500 hours. The two most frequently used types of lamps are halogen and xenon. The main difference between them is in the colors obtained. The xenon lamp has a slightly bluish tint. The light emitted by xenon lamp is more natural as compared to halogen lamp. However, most of the cameras at present analyze and compensate these variations by means of automatic “equalization of whites” (2,100– 10,000 K), which allows the same image to be obtained with both light sources. A proper white balancing before start of the operation is essential for obtaining a natural color. The white light is composed of equal proportion of red, blue, and green color. At the time of white balancing, the camera sets its digital coding for these primary colors to equal proportion, assuming that the target is white. If at the time of white balancing, the telescope is not seeing a perfectly white object, the setup of the camera will be incorrect, and the color perception will be poor. The newer light source of xenon is defined as a cool light, but practically it is not completely heat free and it should be cared for ignition hazard. Metal halide vapor arc lamp (250 W): Halide: A halide is a binary compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative (or more electropositive) than the halogen, to make a fluoride, chloride, bromide, iodide, or astatide compound. Many salts are halides. All group 1 metals form halide compounds which are white solids at room temperature. A halide ion is a halogen atom bearing a negative charge. The halide ions are fluoride (F–), chloride (Cl–), bromide (Br–), iodide (I–), and astatide (At–). Such ions are present in all ionic halide salts. Metal halides are used in high-intensity discharge lamps called metal halide lamps such as those used in modern street lights. These are more energy efficient than mercuryvapor lamps and have much better color rendition than orange high-pressure sodium lamps. Metal halide lamps are also commonly used in green houses or in rainy climates to supplement natural sunlight. Examples of halide compounds are: sodium chloride (NaCl), potassium chloride (KCl), potassium iodide (KI), lithium chloride (LiCl), copper (II) chloride (CuCl2), silver chloride (AgCl), and chlorine fluoride (ClF). Metal halide lamps, a member of the high-intensity discharge (HID) family of lamps, produce high light output for their size, making them a compact, powerful, and efficient light source. By adding rare earth metal salts to the mercuryvapor lamp, it improved luminous efficacy and light color is obtained. Originally created in the late 1960s for industrial use, metal halide lamps are now available in numerous sizes and configurations for commercial and residential applications (Figs. 6 to 8). Like most HID lamps, metal halide lamps operate under high pressure and temperature and require special fixtures to operate safely. In metal halide lamp, a mixture of compounds (comprising mostly salts of rare earths and halides as well as the mercury which provides the conduction path) is carefully chosen to produce an output which approximates to “white” light as perceived by the human eye (Fig. 9). There are two types of metal halide lamp generally used. They are iron iodide lamp and gallium iodide lamp. Iron iodide is a broad emitter and enhances the spectral output of the lamp in the 380 nm. Gallium iodide has the effect of introducing spectral lines at 403 nm and 417 nm of the electromagnetic spectrum (Fig. 10). The intensity of the light delivered by any lamp also depends on the power supply of the source. However, increasing the power poses a real problem as it generates more heat. At present, the improvements made to the cameras means that it is possible to return to reasonable power levels of 250 W. However, 400 W units are preferable in order to obtain sufficient illumination of the abdomen even when bleeding causes strong light absorption. It is important to remember that a three-chip camera requires more light than single-chip camera, so a 400 W light source is recommended for three-chip camera. Light-emitting diode light source: Light-emitting diode (LED) technology is rapidly becoming the modern-day benchmark for illumination. New range of LED light source units is available offering high performance, quality, durability, and
Wondershare PDFelement CHAPTER 2: Laparoscopic Imaging Systems Fig. 6: A metal halide gas discharge lighting system provides illumination for a college baseball game. Note the various colors of the lights as they warm up. Fig. 7: A low-bay light fixture using a high wattage metal halide lamp of the type used in factories and warehouses. Fig. 8: A linear/tubular metal halide lamp lit up at half power. Fig. 9: Metal halide bulb. Fig. 10: Internal structure of metal halide tube. (1) ARC tube; (2) Tungsten electrodes; (3) Stem; (4) Ceramic heat shield; (5) Stainless steel frame; (6) Spring supports; (7) Button getter and strip getters; (8) Ceramic spacer; (9) Nickel-plated brass base; (10) EN weld; (11) Ceramic insulator; (12) Deep eyelet; (13) Resistor; (14) Bimetal switch; (15) Starter assembly; (16) HPS ARC tube; (17) End coat. 13
14 Wondershare PDFelement SECTION 1: Essentials of Laparoscopy Fig. 11: Light-emitting diode (LED) light source. economy. The economy is due to the longevity of the lamp units. For example, at an average of 30,000 hours operating life, the LED units offer years of trouble-free performance as well as the inherent cost saving of replacement bulbs. At an average of 30,000 hours, the operating life of LED light sources exceeds the standard life of high-performance light sources. 250 workdays per year at 10 hours each equals an operating life of approximately 10–12 years (Fig. 11). Most incandescent and halogen bulbs are in the Kelvin range (2,700–3,000 K). Fluorescent, metal halide, and LED bulbs can be purchased with color temperature options from 2,700 to 6,500 K. Why LED Light Source? Light-emitting diodes offer definite advantages over conventional lamps: ■ Purchase costs are quickly justified due to the long life (30,000 hours) and minimal power consumption ■ Extremely economical ■ Ultra-low maintenance ■ Clear return on investment ■ High energy efficiency with 90% reduced power consumption over conventional bulb types ■ Ready to go, instantly (full light intensity available as soon as the unit is powered on) ■ Environmentally friendly. Heat Filter For 100% of energy consumed, a normal light source (a light bulb) converts approximately 2% to light and 98% as heat. This heat is mainly due to the infrared spectrum of light and due to obstruction in the pathway of light. If infrared travels through the light cable, the cable will become hot. A heat filter is introduced to filter this infrared in fiberoptic cable. A cool light source lowers this ratio by creating more light, but does not reduce the heat produced to zero. This implies a significant dissipation of heat, which increases as the power rating increases. A cold light is light emitted at low temperatures from a source that is not incandescent such as fluorescence or phosphorescence. Incandescence is the emission of light (visible electromagnetic radiation) from a hot body as a result of its temperature. The sources are protected against transmitting too much heat at present. The heat is essentially dissipated in transport, along the cable, in the connection with the endoscope and along the endoscope. While it is remarkable how little heat is delivered to the tip of the laparoscope, the effects are cumulative. A lighted laparoscope or fiberoptic bundle in direct contact with paper drapes or the patient’s skin will cause a burn after 20 or 30 seconds and must be avoided. Some accidents have been reported due to burning caused by the heat of the optics system. It is therefore important to test the equipment, particularly if assemblies of different brands are used. Condensing Lens The purpose of condensing lens is to converge the light emitted by lamp to the area of light cable input. In most of the light source, it is used for increasing the light intensity per square cm of area. Manual or Automatic Intensity Control Circuit (Shutter) Manual adjustment allows the light source to be adjusted to a power level defined by the surgeon. In video cameras, close-up viewing is hampered in too much light whereas more distant view is too dark. To address this, the luminosity of most of the current light sources is adjustable. The advanced light source system is based on the automatic intensity adjustment technology. The video camera transforms the signal into an electronic signal. This electronic signal is coded in order to be transported. The coding dissociates the luminance and chrominance of the image. The luminance is the quantity of light of the signal (black and white) that dictates the quality of the final image. When there is too much light for the image (when the endoscope is near to the tissue), the luminance signal of the oscilloscope increases. On the other hand, when the luminosity is low (distant view or red surroundings), the luminance is low and the electronic signal is much weaker. A good quality luminance signal is calibrated to 1 mV. Overexposed images make the electronic signal pass above 1 mV whereas underexposed images make the signal drop below 1 mV. Light sources equipped with adjustment analyze the luminance. If the signal is significantly higher than 1 mV, they lower the power and bring the signal back within the standards. Conversely, if the signal is too weak, they increase their intensity.
Wondershare PDFelement CHAPTER 2: Laparoscopic Imaging Systems These systems are extremely valuable, permitting work to be performed at different distances from the target in good viewing conditions. However, the cameras currently available are often equipped with a regulation system, which is capable of automatic gain control in poor light condition and the purchase of a light source with adjustment associated with a camera equipped with an adjustment system is a double purchase that is unnecessary. Troubleshooting of laparoscopic light source: Troubleshooting for inadequate lighting is shown in Table 1. A laparoscopic surgeon should be technically wellacknowledged of the principle of the instrument they are using. The purchase of a costly instrument is not an answer for achieving a good task, ability to handle them is equally important. Infrared light source: The new infrared LED light source provides real-time endoscopic visibility and near-infrared fluorescence imaging. This enables surgeon to perform minimally invasive surgery (MIS) using standard endoscopic visible light as well as visual assessment of vessels, blood flow, related tissue perfusion, and biliary anatomy nearinfrared imaging. In addition, this infrared visualization technology is very useful to transilluminate the ureters with fiberoptic ureteric kit (IRIS U-kits) available (Fig. 12). TABLE 1: Troubleshooting of light source. Probable cause Remedy • Loose connection at source or scope • Light is on “manual-minimum” • Bulb is burned out • Fiberoptics are damaged • Automatic iris adjusting to bright • Reflection from instrument • • • • • • Adjust connector Go to “automatic” Replace bulb Replace light cable Dim room lights Reposition instruments or switch to “manual” Fig. 12: Light-emitting diode (LED) light source with infrared emission capability. Light Cable Minimal access surgery depends on the artificial light available in closed body cavity and before the discovery of light source and light cable; mirrors were used to reflect the light on to the subject where direct light access was not possible. In 1954, a major breakthrough in technology occurred in the development of fiberoptic cables (Fig. 13). The principle of fiberoptic cable was based on the total internal reflection of light. Light can be conducted along a curved glass rod due to multiple total internal reflections. Light would enter at one end of the fiber and emerge at the other end after numerous internal reflections with virtually all of its intensity. Total Internal Reflection An effect that combines both refraction and reflection is total internal reflection (Fig. 14). Consider light coming from a dense medium like water into a less dense medium like air. When the light coming from the water strikes the surface, part will be reflected and part will be refracted. Measured with respect to the normal line perpendicular to the surface, the reflected light comes off at an angle equal to that at which it is entered while that for the refracted light is larger than the incident angle. In fact, the greater the incident angle, the more the refracted light bends away from the normal. Thus, increasing the angle of incidence from path “1” to “2” will eventually reach a point where the refracted angle is 90o, at which point the light appears to emerge along the surface between the water and air. If the angle of incidence is increased further, the refracted light cannot leave the water. It gets completely reflected. The interesting thing about total internal reflection is that it is really total. That is 100% of the light gets reflected back into the more dense medium, as long as the angle at which it is incident to the surface is large enough. Fig. 13: Fiberoptic light cable. 15
16 Wondershare PDFelement SECTION 1: Essentials of Laparoscopy Fig. 14: Refraction of light from water into air. Fig. 15: Fiberoptic cable, total internal reflection. Fiberoptics uses this property of light to keep light beams focused without significant loss (Fig. 15). The light enters the glass cable and as long as the bending is not too sudden, it will be totally internally reflected when it hits the sides and thus is guided along the cable. This is used in telephone and TV cables to carry the signals. Light as an information carrier is much faster and more efficient than electrons in an electric current. Also, since light rays do not interact with each other (whereas electrons interact via their electric charge), it is possible to pack a large number of different light signals into the same fiberoptics cable without distortion. You are probably most familiar with fiberoptics cables in novelty items consisting of thin, multicolored strands of glass which carry light beams. Nowadays, there are two types of light cable available: 1. Fiberoptic cable 2. Liquid crystal gel cable fibers, the curvature radius of light cable should be respected and in any circumstances it should not be <15 cm in radius. If the heat filter or cooling system of light source does not work properly, the fibers of these light cables are burnt (melt) and it will decrease the intensity of light dramatically (Fig. 19). If poor quality fibers are used, it might burn just within a few months of use. Fiberoptic Cable Fiberoptic is the science or technology of light transmission through (a bundle of optical fibers) a very fine, flexible glass or plastic fibers. Fiberoptic cables are made up of a bundle of optical fiber glass threads waged at both ends. The fiber size used is usually 20–150 µ in diameter. A good fiberoptic cable will transmit all the spectrum of light without loss (Fig. 16). They have a very high quality of optical transmission, but are fragile. The light inside these fibers travels on the principle of total internal reflection without losing much of its intensity. The multimode fiber maintains the intensity of light and the light can be passed in a curved path of light cable (Fig. 17). As the light cables are used progressively, some optical fibers break (Fig. 18). The loss of optical fibers may be seen when one end of the cable is viewed in daylight. The broken fibers are seen as black spots. To avoid the breakage of these Liquid Crystal Gel Cable These cables are made up of a sheath that is filled with a clear optical gel (liquid crystal). Crystal (a clear, transparent mineral or glass resembling ice) is a piece of solid substance, such as quartz, with a regular shape in which plane faces intersect at definite angles, due to the regular internal structure of its atoms, ions, or molecules. Within a crystal, many identical paralleled-piped unit cells, each containing a group of atoms, are packed together to fill all space (see illustration). In scientific nomenclature, the term crystal is usually short for single crystal, a single periodic arrangement of atoms. Most gems are single crystals. However, many materials are polycrystalline, consisting of many small grains, each of which is a single crystal. For example, most metals are polycrystalline (Fig. 20). Liquid crystal: Substance that flows like a liquid, but maintains some of the ordered structure characteristic of a crystal. Some organic substances do not melt directly when heated, but instead turn from a crystalline solid to a liquid crystalline state. When heated further, a true liquid is formed. Liquid crystals have unique properties. The structures are easily affected by changes in mechanical stress, electromagnetic fields, temperature, and chemical environment. Liquid crystal gel cables are capable of transmitting up to 30% more light than optic fibers. Due to lighter and better color temperature transmission, this cable is recommended in those circumstances, where documentation (movie, photography, or TV) is performed.
18 Wondershare PDFelement SECTION 1: Essentials of Laparoscopy optical fiber cables, which are as fragile as the gel cables but their flexibility makes them much easier to maintain. Attachment of the Light Cable to the Light Source Conventional attachment has a right angle connection for light source and camera. Recently, new attachment for light cable is available known as display control interface (DCI) (Fig. 21). The benefit of this is that it maintains upright orientation regardless of angle of viewing, using autorotation system. It also provides single-handed control of the entire endoscope camera system. Maintenance of Light Cable Fig. 18: Broken fibers showing significant loss of light. The following points should be followed for the maintenance of light cable: ■ Handle them carefully ■ Avoid twisting them Fig. 19: Burnt fiber causes significant reduction in intensity of light. Fig. 20: Structure of a simple crystal.
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