English ▼
Français
Español
Portuguese
日本
繁體中文
Video camera
Authors
Abstract
The description of the video camera covers all aspects of this piece of equipment. The technical key steps of the chapter are presented in a step by step way: structure/function, laparoscopic requirements, choices of camera system, advantages/disadvantages, practical issues, usage problems.
Consequently, this operating technique is well standardized for the management of this condition.
Consequently, this operating technique is well standardized for the management of this condition.
|
Media type
 Publication
2003-11
|
Popular
Favorites
 Audio
   |
E-publication
WeBSurg.com, Nov 2003;3(11).
URL: http://www.websurg.com/doi-ot02en304a.htm
URL: http://www.websurg.com/doi-ot02en304a.htm
Video camera
1. Introduction
The development and miniaturization of video transmission systems used in videoscopic surgery has made it possible to perform complex endoscopic surgical procedures. The whole surgical team is now able to follow the procedure and participate actively. The images can be recorded on a variety of storage media or teletransmitted to surgeons at a distance. Technological advances mean that it is now possible to obtain excellent image quality, even when operative conditions are difficult (bleeding, emergencies, etc.). The use of high performance cameras should therefore be considered an essential safety requirement, as well as a means of providing optimal visual comfort for the surgeon.2. Structure/function
• General description
The camera system is composed of a camera head with its attached cable and a camera control unit.The camera head attaches to the endoscope and is responsible for capturing the image transmitted along the endoscope and converting it to an electrical signal. The camera control unit receives the signal from the camera head and processes the image in preparation to be sent as a video signal to a monitor. Modern camera heads are about the size of the surgeon’s hand and lightweight to allow for easy manipulation.
The camera head:
The camera head construction includes the following important components:
- the photo CCD;
- lens and focusing ring ( + / - mechanical zoom);
- coupling mechanism for attaching to endoscope;
- water-resistant casing and integrated cable.
The photo CCD:
Central to the capture and transmission of the image is the CCD sensor (Charge-Coupled-Device). This is an integrated circuit coated with transparent quartz and comprised of photo sensitive elements (photosites) that transform the captured light image comprised of photons (light energy) into negatively charged electrons (electrical energy). These electrons flow along the camera cable to the camera control box to be processed. When light hits the photosite, an electrical current is generated that is proportional to the intensity of light received. The CCD uses semi-conductor technology and incorporates a grid pattern on which individual photosites, or microscopic photo-sensors, are laid out horizontally and vertically. Each of these photosites generates the signal for a single pixel. (The pixel is the smallest unit on the image). Together the signals from all the photosites create the pattern of pixels that generate the overall image on the screen.
• CCD: basic principles
• Resolution 1
The higher the number of pixels contained in an image, the better the quality will be and thus, greater detail will be contained in the image.• Image sensors
Image sensors have evolved rapidly as progress has been made in electronics.At the same time as their capacity to analyze light has increased so they have decreased in size. The size of the CCD is traditionally measured in inches and the ratio of its width to its height is 4:3, corresponding to the shape of video monitors. Initially, image sensors were 2/3 of an inch (8.8 x 6.6 mm), then decreased to 1/2 of an inch (6.4 x 4.8 mm) and more recently to 1/3 of an inch (4.8 x 3.6 mm) or 1/4 of an inch (3.2 x 2.4 mm).
Currently, CCD image sensors offer a resolution ranging from 480 x 320 pixels (153,600 pixels) to several million pixels for the most powerful models. These CCDs are not all adapted for surgical video cameras. The usual resolution of the best surgical cameras is around 450,000 pixels.
• Number of CCDs used
The first video cameras used only one CCD sensor (mono-CCD-analogue) combined with a mosaic filter for the three primary colors (red-green-blue). Such systems required 4 photosites to generate the signal for one pixel (1 red, 2 green and 1 blue).• Tri-CCD
All new video cameras use a tri-CCD, or 3-chip system (analogue or digital). This incorporates a beam splitter, which divides the light in the image into the three primary colors and directs each to a separate CCD sensor, each sensor being dedicated to one of the primary colors.• Other principles
Video signal coding:The information relating to each pixel is converted into binary code (0 or 1) by the analogue-digital converter. There is usually an eight digit binary code (8 bits) per pixel, allowing for 256 different values (2 to the power of eight). As each pixel of color is reproduced on the screen by composition of the three primary colors (red, green and blue), it is possible to create up to 16,777,216 different colors (256 x 256 x 256).
Sensitivity to light:
This parameter, specified in Lux, defines the minimum amount of light needed by the camera to produce a clear image. The lower the number, the less light the camera will need. Ideally, it should be less than 1.5 Lux. The best video cameras can see at less than 1 Lux/Signal-to-Noise (S/N) ratio:
This measurement, defined in decibels (dB), is directly related to the amplification and the treatment of the video signal by the camera. The higher the ratio, the less risk there will be of interference “noise”, and therefore the purer the signal will be, allowing for a stable and coherent final image. This ratio should not be lower than 50 dB. It is particularly important to compare the S/N ratio for low levels of illumination. Certain cameras, in order to improve their sensitivity to light, have an “image gain” function. This artificial amplification of the video signal causes an increase in interference, which results in a grainier image. It is therefore advisable to compare the sensitivity (Lux) for different cameras that offer an equivalent S/N ratio. Interference is easier to identify in the darker parts of the image. For example, if the signal is ten times higher than the noise, the noise gets lost in the signal and is not noticeable. On the other hand, if the signal is only two times higher, the noise becomes perceptible. This applies to sound in the same way: we notice noise more when we are surrounded by silence!
• CCD: structure and function
• 1
There are only a few CCD manufacturers in the world. All manufacturers use the same CCDs, but develop their own signal processing electronics, which represents the main added value of video cameras.• 2
The original CCD used a mechanical shutter to separate the light images reaching the photosites and this technology is now obsolete. Current CCDs are able to continuously receive light without disturbance of image transfer. There are various systems in use today but the most commonly used for videoscopic surgery is called Interline Transfer CCD technology. In this system the photosites are organized into columns and rows on the CCD grid. The first element of the photosite responds to the photons from the image that strikes it by accumulating charge (photoelectric effect). This packet of electrical charge is proportional to the quantity of photons received during a given time (integration time). This packet of charge is transferred into a storage and transfer channel called the vertical shift register. The packets of charge are then transferred to a single horizontal shift register, which lies beneath the vertical register. All the packets from the horizontal register are then sent to a memory buffer before they are amplified and sent to an analogue-digital converter. This sequence occurs every 1/50th of a second with a PAL system (1/60th of a second with NTSC), alternating the odd and even lines, in order to be compatible with the various available video display systems (two interlaced fields – see chapter on video monitors).• CCD sensor with micro-lenses
In order to recuperate the “lost” photons between each photosite on the CCD sensor, micro-lenses are etched on each of these photosites to direct and concentrate all of the photons onto the photosensitive cells. This improves the camera’s sensitivity to light, without digital signal treatment.• Lens and focus ring
Before the image from the endoscope reaches the photo CCD, it is focused by a lens placed in front of the CCD. A focus ring allows the surgeon to make adjustments to the distance between the lens and the CCD so that the focus of the observed object in the image can be kept sharp. The newest systems have an autofocus mechanism that controls the lens in response to changes in the observed image. If the camera is fitted with a mechanical zoom the focal length of the camera can be adjusted. By moving the CCD and focusing lens away from the eyepiece lens of the endoscope the image can be magnified, however, the field of view reduced. The majority of camera systems utilize a digital zoom, 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 zoom is used.The coupling mechanism:
The camera head needs to be securely coupled to the endoscope to ensure accurate transmission of the image. The eyepiece of most endoscopes is fairly standard but the coupling devices for each manufacturer tend to be different. The coupling device holds the camera lens at a fixed distance from the eyepiece lens of the endoscope. Manufacturers design their cameras to match exactly with their endoscopes; for this reason mixing different systems can sometimes lead to loss of image quality.
Camera casing and cable:
The camera casing is designed to protect the encased electronics and lens system. It needs to be able to withstand cleaning procedures and a degree of mechanical stress. Special alloys and plastics are used to construct the tough, resistant casing. Frequent usage inevitably leads to deterioration in the surface of the casing. However, significant damage to the casing should be repaired to avoid possible damage to the delicate electronics contained within.
• Camera control unit
• Control unit
Once the CCD has generated the image signal it is relayed to the camera control unit where the signal can be amplified and processed before being sent out to the video monitor. The output signal needs to relay information about image brightness and the balance of red, green and blue. The industry standard default white screen has a brightness of 6500°K. The reference value given to Y for this default screen is 1 (Yref). The brightness (Y) at any time can be calculated from the signal intensities of the three primary colors:Y = 0.3R + 0.59G + 0.11B
When the image is at the default brightness of 6500°K then
0.3R + 0.59G + 0.11B = 1 = Yref
The majority of camera control units have a number of functions including most importantly white balance and shutter control. With the development of digital image processing difficult problems of diffraction and overexposure due to reflection from structures close to the camera can be compensated for while maintaining good overall brightness and increasing the contrast in shadowed areas.
Camera input:
The camera is connected to the camera control unit via a shielded cable. Each manufacturer has a unique multipin socket, usually placed on the front of the camera control unit to which this cable connects. The camera plug is supplied with a watertight cap to prevent water getting into the electrical connections during the cleaning process.
Video signal outputs:
Located, usually, on the back of the camera control unit are the connections for the video monitor. Because there are a variety of industry standards for video signal transfer, the manufacturers have provided a selection of possible connections on the back of the camera control unit.
• Connections 1
RGB (red-green-blue): The video signal for each color is carried by a separate shielded cable and synchronized with a fourth cable (RGB-S). Brightness (Y) is calculated by adding the three colors according to the formula shown above. Four separate BNC (Bayonet Neill Concelman) connections are used.• Connections 2
Y/C or S-video = S-VHS:This carries two separate signals, one for light intensity and synchronization (Y), and one for chrominance (C). Using the formula above there is sufficient information in this single signal to calculate levels of each of the primary colors. The cable is usually shielded and carries four wires ( + and - for each signal). A four pin connection is used (some manufacturers use a 6 pin socket and carry additional control signals on the additional cables).
Composite video:
This carries a single analogue signal along a shielded cable. The signal for light intensity and color (chrominance) are combined into a single signal. A BNC connection is used.
Digital:
Digital output connection (e.g. DVI): this type of connection is not widely used, because it must be connected to a LCD or computer monitor. Presently the display quality is inferior to a classic cathode ray tube monitor. This connection permits recording on a digital medium without deterioration of the signal.
The quality of the transmitted image is dependant on the type of connection used. From an electronic point of view, the more information sent from the camera control unit to the monitor per unit time the better the potential quality of the image. Thus in theory, in an otherwise calibrated and optimized system the lowest quality is obtained by the single cable composite BNC connection and the optimal quality is obtained by the RGB connection. However, since the resolution is generally limited by the monitor, there is no notable improvement with a RGB connection as compared to a Y/C connection. It should be noted that with a RGB connection, the colors cannot be modified by the controls on the monitor.
• Image processing
Although older systems provided only limited image control such as white balance and shutter control, the latest generation of camera systems offers a much larger variety of image processing functions:White balance: sets the video output signal to white (Y = 1) when pushed. For a correct signal for white to be set, the camera must be pointed at a white object illuminated with the operating light source. Once this is set, correct color balance for the associated light conditions is achieved. It should be adjusted when the light source has reached its operating temperature, about 5 minutes after it has been turned on.
Gain: use of the gain switch permits artificial amplification of the video signal, giving it more power. There are often several levels of amplification, ranging from 5 to 15 dB, for example. This can be useful if the image is underexposed. However, the gain boost has a major disadvantage: it produces an increase in the noise level that is equivalent to the increase in the signal level, generating a grainy pattern, which is especially visible in dark areas of the image.
Shutter: activation of the shutter electronically decreases the amount of time the CCD is allowed to build a charge and therefore decreases the brightness when the light is too strong. It is usually also possible to reduce the intensity of the light source (see chapter “Cold light source”). However, in automatic systems only one of these two adjustments should be activated, and it is usually better to set the camera shutter to automatic as it offers more precise adjustment.
Autofocus: automatically focuses the camera according to the distance between the camera and the object situated in the center of the image. In practice, it can be more of a hindrance than a help, since anything entering the field of view, for example an instrument or trocar will cause an unwanted change of focus.
Specialty: selects different factory preset digital image processing parameters. These are designed to optimize visual conditions for different types of surgery, by taking into account the types of color encountered in the operative field and to the type of endoscope used.
Enhancement: digital image processing permits an increase in the contrast and a digital enhancement of the outlines of the image, in order to distinguish the planes better and artificially create a sense of depth without a loss in quality. However, excessive image processing makes the outlines look hard and artificial.
Zoom: newer systems often have a zoom function that can be used directly from the camera head. This zoom is generally not a true optical zoom (movement of the camera lenses) but a digital zoom. The zoom is achieved by a magnification of the pixels combined with cropping of the image. As a result, the resolution and the sharpness of the image deteriorate rapidly, which accounts for the fact that the enlargement factor is usually limited to 1.5x.
Image capture: this function can also be controlled from the camera head and allows the surgeon to signal to the camera control unit to capture a single frame (usually as a jpeg file) onto a storage device (usually a removable card) or to send the image directly to a printing device.
3. Laparoscopic requirements
In order to maintain optimal visual conditions the video camera should be changed every 3 to 4 years. Beyond this time period normal wear alters the image provided by the camera. In addition technological advances are occurring so rapidly that cameras much older than this have been superseded by superior systems. In the future, particularly with fully digital cameras, technological progress will probably be slower.4. Choices of camera system
The camera system is essentially designed to serve one purpose, that is, to convert the image from the endoscope into the highest possible quality video signal. Structural differences between available systems tend to be small (e.g. additional image control buttons). All new camera systems are of the three-chip design so single chip systems will only be found amongst existing operating sets. Camera heads can be found with right-angled coupling mechanisms incorporating a prism to bend the image through 90. These are often used in urology so that the camera head does not obstruct the surgeon’s view. Newer camera systems provide digital video outputs. When these systems are connected to monitors and recording devices that can accept a digital signal then there exists the advantage of loss free transfer of the video signal. At present most monitor systems still use video technology that requires an analogue signal. With improving technology in computer monitors such as LCDs, which use digital signals, in the future, pure digital systems may come to replace the traditional digital-analogue systems. When choosing a camera system the surgeon must consider the whole image chain he/she will be using. The camera system should be tested with his/her endoscope, light system and monitor. The quality should then be assessed under the kind of conditions that the surgeon usually works.5. Advantages/disadvantages
Single chip vs. 3-chip:For a given size of CCD and photosite density, the 3-chip system can generate four times greater resolution than the single chip system. Because manufacturers have tried to make their cameras as small as possible the current 3-chip video cameras produce better resolution of the final image with better color accuracy.
Digital vs. analogue ouputs:
Digital transfer of the video signal provides loss free transmission. However at present the quality of monitors able to directly display digital images is not as good as standard analogue video monitors. However, high quality digital recording devices do exist allowing the image to be subsequently viewed/edited on digital computer systems.
Manual focus vs. autofocus:
Most camera systems in use today provide just manual focus. This requires the camera operator to stop what he/she is doing during an operation and adjust the camera. Newer systems are offering the option of autofocus so that the camera operator does not have to worry about focus. However, the autofocus can respond in an unwanted fashion to instruments and trocars, which enter the field of view.
6. Practical issues
• Practical issues
Set-up:Endoscopic cameras are relatively easy to use, as all of the connections are standardized. The only adjustment that needs to be made on most cameras is the white balance. These cameras can be used with light sources whose color temperatures can vary between 2500 and 6000 degrees Kelvin. Before starting a surgical procedure, it is essential to adjust the default white setting of the camera to the actual white provided by the light source. If the white balance is not correctly adjusted, or if it is adjusted before the operating temperature of the light source has been reached, the image will appear with chromatic errors (e.g. too green, or too red).
Maintenance:
In order to maintain optimal visual conditions the video camera should be changed every 3 to 4 years. Beyond this time period normal wear alters the image provided by the camera. In addition technological advances are occurring so rapidly that cameras much older than this have been superseded by superior systems. However, in the future, particularly with fully digital cameras, technological progress will probably be slower.
Sterilization:
It is mandatory for cameras to be sterile when in contact with the operative field. Most cameras can be sterilized by immersion in glutaraldehyde at 2.5%. This sterilization method alters the appearance of the camera, but as long as the camera remains waterproof it will not be damaged. The electrical connection must be sealed prior to cleaning. If fluid gets into the camera the electronic components will be damaged. In this case, the camera should be returned to the manufacturer for repairs.
Advantage: decoupling the scope from the camera is straightforward;
Disadvantage: premature alteration and aging of the camera and greater risk of damage.
Use of protective sheaths:
Most surgical teams use a protective sheath to protect their cameras. Various models are available on the market, and most of these offer satisfactory protection.
Advantages:
- the camera is always available;
- no need to sterilize;
- less deterioration and risk of damage.
Disadvantage:
- impossible to rapidly change endoscopes during the surgical procedure unless a ring adapter is used (see below).
The occasional problem of fog between the camera and the endoscope is more difficult to rectify.
• Use of ring adapters
Certain manufacturers propose a sterile ring adapter that can be placed between the camera and the endoscope. Theoretically, these ring adapters are very practical, because they enable the surgeon to change endoscopes when they are connected to the camera. In reality, they move the head of the camera 2 cm away from the endoscope leading to a reduced field of view, a decrease in brightness and a loss in the quality of the image.7. Usage problems
The main problems that can occur when using a camera are usually related to connection problems. A surgical procedure should not begin until a perfect image quality has been obtained. The main errors and malfunctions of the camera are as follows:No image:
Camera not plugged in or switched on, connections loose, defective cables, light source not connected to the endoscope, monitor not connected.
Major colorimetric problem (image saturated in blue, green or red tints):
This type of chromatic error occurs most often with RGB cameras, and either results from an improper white balance, or from faulty connections: rupture in the cable conveying the red, green or blue. Solution: readjust the white balance, change the cable.
Image too dark:
An image that is too dark can be related to a defect in the endoscope or light source, a defect in a cable, or partial failure of transmission of the luminance signal through a Y/C cable. Blood very effectively absorbs light so a blood-filled operative field will always appear dark – always maintain excellent hemostasis!
Black and white image:
This problem may result from a bad color adjustment on the monitor or from a defect in the cable conveying the chrominance when there is a Y/C connection.
Noticeable noise, graininess:
This problem can appear if the gain or enhancement controls are increased to their maximum. Intermittent interference may originate from other electrical devices in the OP room (e.g., activation of the diathermy machine). Such interference should not occur if the video cables are well shielded.
Blurry image, low clarity:
Check that the camera has been focused correctly and make sure that the lenses are not dirty.
Image not centered:
Make sure that the endoscope is correctly coupled to the camera.
More often than not a poor image is due to a simple problem that can be corrected by the OP 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 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.
8. Conclusions
Miniature video cameras provide the surgeon with an optimal view of the operative field. Analogue cameras are being superseded by digital processing cameras and fully digital cameras. Digital systems offer multiple image processing features that improve the quality of the image by a better color rendition and enhancement of image outlines. In addition, they make it possible to process and store the visual information without any deterioration, thus allowing noise-free transmission of the video signal. Thanks to digital technology, new video cameras are able to generate high quality realistic images that can be adapted to a variety of surgical conditions. Image processing has allowed the production of images with good overall brightness, contrast and accurate color representation despite differing light conditions.
This enhancement of the surgeon’s visual perception of the operative field improves the precision and safety of surgical performance.