Video endoscopy systems allow the viewing of live, color images of the interior of the body during diagnostic and therapeutic endoscopic procedures. They also enable these images to be stored, retrieved, and otherwise electronically manipulated. The endoscopes are inserted through natural openings in the body or through small punctures; therefore, MIS procedures are much less traumatic than open surgical procedures and result in less discomfort and usually in shorter recovery periods. Consequently, some procedures can be performed on an outpatient basis. Laparoscopy allows minimally invasive examination and treatment of organs and tissue within the peritoneum during procedures such as cholecystectomy and appendectomy that previously required open abdominal surgery. Arthroscopy, an alternative to open arthrotomy, enables the diagnosis and treatment of many joint diseases and injuries. In gastrointestinal endoscopy, a flexible endoscope is inserted into the rectum or esophagus, allowing the examination and removal of foreign bodies and polyps and the diagnosis of ulcers and cancer. Bronchoscopy evaluates the interior of the respiratory tract, particularly the trachea and the bronchi of the lungs.
Principles of Operation
Video endoscopy systems comprise modular image detection/processing systems, monitors, and recording devices, as well as other accessories such as insufflators, irrigation and suction pumps, and carts.
The main components of the video image detection system are the endoscope, display, camera head adapter (if required), processor, and fiberoptic light source. The image detection system typically uses a photosensitive silicon sensor, called a charge-coupled device (CCD) or chip, which is composed of millions of photoelectric picture elements (pixels) arranged in a rectangular grid. Using a fiberoptic light source for illumination, the lens system focuses the light reflected from the field of view (FOV) onto the CCD’s pixels, which electronically capture the image.
Standard two-dimensional (2-D) video endoscopy systems use either one or three monochrome CCDs. Newer three-dimensional (3-D) systems utilize two separate cameras for image capturing; other systems may use a complementary metal oxide semiconductor (CMOS) chip instead.
Video Camera
In the most commonly used single-chip system, a mosaic color filter overlies the CCD to obtain color images. The filter consists of different color strips that cover specific pixels. The white light reflected from the FOV is filtered into specific colors (e.g., blue, green, red), and each pixel then responds electronically to a specific color. The mosaic data from the pixels is sent to the video processor, where all the colored image signals are combined and converted to a balanced color image that is compatible with standard color video displays. The other single-chip system (known as RGB [red, green, blue] sequencing) uses a rotating color-filter wheel inserted in the path of a flashing light source. This causes short, rapid, sequential bursts of red, green, or blue light to be emitted from the tip of the endoscope, tinting the FOV. The red, green, and blue images are detected by the CCD and transmitted to the processor, where they are combined.
Three-chip systems have a prism that separates the incoming white light into red, green, and blue beams, which are sent to one of three dedicated CCDs. These systems are designed to provide better color reproduction than single-chip systems.
With traditional nonvideo fiberscopes and rigid endoscopes, an endoscopic camera (also called a camera head) containing the CCD is attached to the proximal end of the endoscope. The camera’s lens directs the light to the CCD and determines the focal length. Endoscopic cameras are available with different focal lengths; some also have digital or optical zoom capability. On video endoscopes, the CCD is an integral component of the distal tip of dedicated rigid and flexible endoscopes; thus, a camera head is not required. The electronic image is then transmitted from the CCD to the video processor through the camera head or video endoscope cable.
Video Processor
Video processors (sometimes called camera control units [CCUs]) have inputs for either one or two camera-head or video-endoscope cables. The front panel also usually has controls that can adjust the brightness and color of the image, capture and label videos and images, and in some cases select and adjust water, air, and suction. In addition to the electronics for image processing, processors used in gastrointestinal endoscopy sometimes also house integral fiberoptic light sources and air, water, and suction pumps. Air insufflation is typically used to expand the intestines to insert and maneuver the scope and increase the FOV. Suction helps remove debris from the distal tip of the endoscope and accumulated fluids, such as sterile water or saline used to wash the surgical site. Insufflation and irrigation during surgery (e.g., laparoscopy, arthroscopy, hysterectomy, ureterorenoscopy, neuroendoscopy) are accomplished with separate devices.
The processor sorts the electric signal from the camera head according to pixel location and intensity, converting the image to a usable electronic format. It compiles the color elements into a full-color electronic image that is filtered and displayed on one or more monitors, output to a recording or storage device, or routed to remote sites such as a doctor’s office. Discrete pictures are displayed at a rate fast enough to appear continuous to the human eye.
Light Source
Successful illumination of the FOV is required to produce a useful video image. Light sources produce a high level of light, which is directed through a fiberoptic light guide cable and the endoscope to illuminate the surgical field. In addition to manual controls for adjusting the light level, many systems have automatic brightness modes that automatically detect and adjust the light level to optimize the image. Some systems also have a white-balancing feature to adjust the basic components of the color system according to the lighting conditions.
The light source usually contains a xenon, LED, or metal-halide arc bulb (e.g., 300 watts) to produce the light required for video images; some light sources have backup bulbs and bulb-life meters.
Peripherals
Since the final image quality is limited by the weakest link in the video chain, display quality is important. When using systems marketed as “HD” or “high-definition,” it is necessary to use a display with a resolution matching or exceeding that of the output signal resolution produced by the video processor. Otherwise, the monitor may be used to “scale” the signal for display, which may diminish image quality. Widescreen LCD or LED monitors, which can display a variety of formats, including HDTV, have become the norm.
In some systems, the image occupies only a certain portion of the screen, allowing room for patient data. Many suppliers offer data-entry keyboards or touchscreens so that endoscopy staff can enter data into the video image frame. Several processing systems can display the image in various formats, including picture-in-picture and four images on one display, and many suppliers also offer remote controls for operating the processor and video systems.
The processed images can be documented and archived using various recording devices. These components can be connected to the processor and display by standard video signal cables. Hard-drive, CD, DVD burners and USBs can be used to save data directly to a computer or network. VCRs offer various playback modes; special-effects playback includes freeze frame, frame-by-frame advance, onscreen picture search at high speed (shuttle search), and slow motion.
Purchase Considerations
ECRI Institute Recommendations
The most important selection factor for surgical video systems is image quality. Although the image quality of 3-CCD systems generally surpasses that of 1-CCD systems, this specification is highly subjective. Hospitals should use each system on a trial basis before making a purchasing selection to allow surgeons to offer input.
A video system should be compatible with many flexible and rigid endoscopes with appropriate adapters. Ease of use is also an important consideration. Since some surgeons prefer to have direct control over surgical video system functions, systems that allow control of multiple functions from the camera head, as well as from other components such as the front panel and keyboard, may be attractive. Recommended video processor features include auto-illumination, auto-white balance, and zoom control.
Video endoscopy systems should allow the user to output a wide range of video signal formats. Y/C connection should be standard on any system. 3-CCD systems should include RGB format to take advantage of their higher picture resolutions. It is recommended that systems marketed as “HD” or “high-definition” have at least one digital output. Some hospitals may also wish to purchase systems with digital output (e.g., DVI, SDI, HD-SDI, 3G SDI) for recording images or video onto recording media or an information system or to display digital images on a surgical display. The video processor should have digital outputs that match the inputs of existing image capture devices or operating room integration systems.
The camera should be compatible with the hospital’s preferred method of reprocessing. Systems that are compatible with multiple methods, including autoclaving, should be given strong consideration.
The light source should not cause excessive heating at manufacturer-recommended illumination levels. For safety, light sources should be equipped with a standby feature to suspend light output, which is active at start-up. Output at startup differs: <10%, setting from last use, or standby. Light sources with LED lamps last 5,000 to 30,000 hours versus 500 hours for xenon lamps and therefore do not require lamp replacement like xenon lamps.
This article is adapted from ECRI Institute’s Healthcare Product Comparison System (HPCS), a searchable database of technology overviews and product specifications for capital medical equipment. The source article is available online to members of ECRI Institute’s HPCS; learn more at www.ecri.org/components/HPCS.
