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Advances in video and imaging in ureteroscopy
Urol Clin N Am 31 (2004) 33–42
Advances in video and imaging in ureteroscopy Yeh Hong Tan, MDa,b, Glenn M. Preminger, MDa,* a
Division of Urology, Department of Surgery, Duke University Medical Center, Box 3167, Room 1572D, White Zone, Durham, NC 27710, USA b Department of Urology, Singapore General Hospital, Outram Road, Singapore 169608
Over the last decade, significant improvements have been made in endoscopic equipment, especially in video and imaging technologies. Coupled with better-designed rigid, semirigid, and flexible endoscopes, enhanced digital imaging systems allow complex endourologic procedures to be accomplished with greater ease and superior accuracy. This article highlights advances in endoscopic video systems, along with image management technology that can be used during ureteroscopic procedures. Illumination Illumination of the operative field is an integral part of endoscopic surgery. Currently, highintensity light sources, usually halogen and xenon, are favored; however, halogen sources produce a slightly yellow light requiring compensation during white balancing of the endoscopic camera system. Xenon sources provide a more natural and whiter color. The fiberoptic bundles that run through the endoscopes permit rapid transmission of light and digital information in a small space. The light is conducted to the operative field by fiberoptic bundles that contain glass fiber or special fluid. Because the glass fiber bundles are more flexible, they are more widely used, even though they are less efficient in light transmission owing to a fiber mismatch at the junctions of the light cable and endoscope [1]. Contemporary light sources often have an automatic light-sensing feature, which quickly
* Corresponding author. E-mail address: [email protected] (G.M. Preminger).
adjusts the light output as required by the camera. This automatic light adjustment feature is particularly helpful during endoscopic procedures as the endoscope is rapidly moved throughout the urinary tract, causing different levels of illumination. Light intensity is automatically adjusted to maintain a preset level. Similarly, some digital camera systems are equipped with an ‘‘automatic iris’’ system, which electronically increases or decreases the aperture of the camera shutter. If the camera system is equipped with a light-sensing feature, there is no need for an automatic intensity-adjusting light source [2]. Newer charged coupled device (CCD) or image sensor based endoscopic cameras feature electronic exposure (Fig. 1). This system varies the effective exposure period (ie, lightgathering time) of the CCD as the live image is captured. Typical CCD exposure periods range from approximately 1/60 of a second to 1/10000 of a second under very bright conditions. This electronic process can be used to maintain the brightness in the image. When the image brightness must be reduced to improve picture clarity, the image signal exposure period can be reduced electronically instead of adjusting the iris of the light source. Shadows have an important role in depth perception and spatial orientation. Studies have demonstrated that endoscopic task performance significantly improves with video systems that provide proper illumination and appropriate shadows in the operative field [3]. Many of the currently used endoscopes employ a simple frontal illumination technique that produces an optically flat and shadowless image with resultant poor contrast. Newer illumination and imaging technologies provide shadow-inducing systems using a single-point or multipoint illumination system. One of these techniques employs the use of two
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and optical fibers is necessary for the production of a bright image during endoscopic use. Different sized endoscopes require the appropriate lens diameter to ensure an optimal lens-to-fiber ratio. Endoscopes with larger diameter lenses but fewer illumination fibers may give bright images when used to look at external objects in a room, but they fail during endoscopic applications, producing an image that is noticeably less bright [9].
Digital imaging Fig. 1. CCD cameras (Courtesy of Olympus America, Melville, New York; with permission.)
independent illumination fiber bundles, with one fiber bundle ending at the front lens, as designed in conventional endoscopes, and the other fiber bundle ending behind the tip of endoscope. This configuration results in an improved image with better contrast owing to shadow formation. Spatial orientation and perception between anatomic structures are considerably enhanced [4]. Endoscopes Most rigid endoscopes use a rod lens system. Alternatively, flexible and semirigid endoscopes use fiberoptic bundles for light transmission and image relay. The optical fibers provide the advantage of light transmission over a long distance with minimal loss of signal. Moreover, the fiberoptic bundles can be flexed or bent without disrupting alignment, as might occur with rigid rod lens systems. With further miniaturization, more compact fiberoptic cables can be produced, allowing for the development of smaller and more flexible endoscopes. Significant changes have taken place in the design of flexible ureteroscopes since their introduction. Besides the decrease in size and diameter of the instrument, the incorporation of a working channel and the improved maneuverability with active tip deflection and secondary deflection have extended the use of the flexible ureteroscope in diagnosis and therapy [5–8]. Recent developments have focused on improved image quality. In rod lens rigid endoscopes, the use of a multilayer antireflection coating helps to reduce light loss and improves image quality. The application of aspherical and doublet lenses results in decreased image distortion and chromatic aberrations. The right balance of lenses
Conventionally, endoscopic still images and videos of surgical procedures have been captured and stored in an analog format. Reproduction and storage of analog images are time and image consuming. Analog images tend to degrade in quality over time and during image processing. During endoscopic procedures, analog images transmitted through fiberoptic bundles are converted into continuous voltage waveforms before being displayed on an analog video monitor. Because analog signals are susceptible to degradation during the translation process, these images often lack the detail necessary to identify subtle pathologic processes. Current digital technology has revolutionized endourology with the introduction of digital still and video camera systems. Image capture: endoscopic camera systems and the charged coupled device The current generation of endoscopic cameras is based on the CCD chip. The digital image is captured on a CCD using a digital still or digital video camera. Photoreceptors within the CCD rapidly assess the different light intensities that make up the endoscopic image. The CCD generates pixels by converting unique light intensities within an image into corresponding electronic signals, which are then transmitted to a storage element on the chip [10]. Digital cameras are classified according to the amount of resolution determined by the number of pixels and the number of CCD chips. The average CCD resolution of single-chip camera ranges between 400,000 and 440,000 pixels, whereas threechip cameras exceed 450,000 pixels. The display resolution of the cameras ranges between 350 to 450 and 700 horizontal lines for single-chip and three-chip cameras, respectively [4]. A significant improvement in CCD camera technology has been the development of the threechip camera that contains three individual CCD
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chips for the primary colors—red, green, and blue (RGB). In addition to composite super video home system (SVHS) and component signals, the threechip cameras also provide an ‘‘uncoded’’ RGB signal. Color separation is achieved using a prism system overlying the chips [9]. This three-chip camera design provides improved color fidelity and enhanced image resolution. Moreover, three-chip cameras produce less ‘‘noise’’ owing to the pure RGB signals [11,12]. A digital converter captures each voltage signal as an image and translates the voltage values into discrete numbers, either 0 or 1. The encoded numbers for each image element, or pixel, include information on color, light intensity, and contrast. These variables can then be modified using image processing software within the camera [12]. In theory, three-chip cameras produce better quality images than single-chip cameras. Despite the apparent advantages of three-chip cameras, some clinical comparisons have favored one-chip systems. Using normal video monitors, previous studies have implied that the resolution between the two cameras does not alter the visual perception of an image. Studies have found that digital contrast enhancement is a more important feature for endoscopic imaging than the number of camera chips. Three-chip cameras seem to have no advantage over well-designed, single-chip systems [9,13]. This apparent limitation may change with the introduction of high-resolution digital monitors and high-definition television (HDTV), because the amount of image information and the degree of perception are increased with these digital imaging modalities [14].
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by the CCD chip, digitalized, and converted into electrical signals for transmission. This endoscope design has fewer interfaces, allowing the digital information to be transmitted directly to an image display unit with minimal image loss, interference, and distortion [1,15]. The creation of true video endoscopes will especially benefit flexible ureteroscopes. Because internal optics will not be required in the long flexible shafts of these ureteroscopes, more durable deflection cables or larger working channels can be used to improve the durability of these fragile devices [7,8,10]. With no need to attach a camera head to the eyepiece of the scope, the videoscope cable can be secured to the light cord for attachment to the video system, providing a more lightweight and convenient setup. Currently, this technology has only been incorporated into larger rigid endoscopes (laparoscopes) and some flexible endoscopes (colonoscopes, bronchoscopes, and cystoscopes) (Fig. 3) [16–18]. Recent technologic advances have allowed the miniaturization of CCD chips. One can expect to see an integrated digital video ureteroscope to replace standard flexible ureteroscopes in the near future. Another development in digital camera technology includes the use of a single monochrome CCD chip with alternating RGB illumination to form a color image rather than using three chips with three separate color filters. This design reduces the space requirements and takes advantage of established high-resolution monochrome CCD chip technology [15]. This design is currently used in a digital video cystoscope (Olympus America, Mellville, New York).
Video endoscopy (‘‘chip on a stick’’) A major advance in endoscopy systems has been the development of digital video endoscopes. Miniaturization of chip technology now allows a CCD chip to be incorporated at the distal end of the endoscope (chip on a stick) (Fig. 2). Instead of relaying optical images from the objective lens at the distal end of the scope to a camera attached to the eyepiece, the image is immediately captured
Fig. 2. Chip on a stick technology (Courtesy of Olympus America, Melville, New York; with permission.)
Fig. 3. Flexible video cystoscope (Courtesy of Olympus America, Melville, New York; with permission.)
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Future development in endoscopic imaging Although reflected white light is used to produce an endoscopic image, this light can be absorbed, scattered, or cause ‘‘autofluorescence.’’ These additional light–tissue interactions are being explored for advanced imaging technologies. Improvement in endoscopic imaging can be achieved by incorporating an optical magnification lens system at the tip of the endoscope (magnification) or by using other light–tissue interactions (spectroscopy). Magnifying or zoom endoscopes have a lens system built into the tip of instrument, which can be used to magnify small areas up to 100-fold. During optical spectroscopy, different spectra can be identified depending on the wavelength of the light used, as well as various tissue properties. Some of these spectra can be highly tissue specific and can be used to identify areas of ischemia, inflammation, and nonapparent malignancy. With this technique, multiple ‘‘optical biopsies’’ can be taken from suspicious areas, instead of conventional histologic biopsies [19]. Although these techniques are still investigational, they remain an attractive option for future ureteroscopic evaluation of the upper urinary tract.
Digital enhancement and digital filter technologies A recent advance in digital imaging has been the development of enhancement and filtering modalities that can be used to improve endoscopic images. Digital contrast enhancement improves the image quality by accentuating the existing transitions in endoscopic images. Enhancement is accomplished using clusters of pixels known as kernels. When the digital contrast enhancement feature is activated, the center pixel in each kernel determines the state of its surrounding pixels. If variations are present in the levels of contrast or brightness between the center pixel and the average of its surrounding eight pixels, those differences are enhanced without compromising other aspects of the image quality, resulting in increased definition. When variations are not present, no changes occur. This process allows finer details to become discernible to the naked eye. During flexible endoscopy, a characteristic honeycomb pattern is formed because of the spaces between individual fiberoptic fibers. When used with flexible endoscopes, digital filters smooth out the image by expanding the image of each individual fiber to ‘‘fill in the gaps.’’ By distributing the illumination evenly among fibers, a nearly
seamless image is produced without the honeycomb appearance and with consistent lighting. These beneficial effects of digital enhancement and fiberoptic filtering have been studied in detail. During rigid and semirigid ureteroscopy, digital enhancement improves structure identification and image detail and minimizes background noise. Moreover, the digital fiberscope filter significantly improves images during flexible ureteroscopic procedures [14].
Digital imaging, video documentation, and editing Over the last few years, digital imaging has slowly revolutionized the field of videoendoscopy. Although images can be captured initially in the analog format, they can be converted digitally later using a digital camera or scanner. The introduction of digital still cameras has taken image documentation and editing to a new dimension. Currently, newer surgical video systems have an integrated digital image capture system, allowing immediate capture of still images from endoscopic procedures (Figs. 4, 5A, 5B) [10]. Alternatively, a less expensive digital still image capture adapter can be connected to endoscopic camera systems [12]. Digital still images can usually be recorded in Joint Photographic Experts Group (JPEG), tagged image file (TIFF), or bitmap (BMP) formats. These digital images can be edited and optimized on the computer using various graphic software packages. Incorporating medical images into the patient’s record and creating an image library can enhance urologic practice [20,21]. The quality of the digital
Fig. 4. Example of integrated video- and image-capturing screen (Courtesy of Olympus America, Melville, New York; with permission.)
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Fig. 6. (A, B) Digital image capture system using CD or DVD (Courtesy of Stryker Endoscopy, San Jose, California; with permission.) Fig. 5. (A, B) Digital image capture system using Smart Media (Courtesy of Olympus America, Melville, New York; with permission.)
image required depends on its purpose. Lowresolution images ranging from 1 to 2 megapixels can be used for E-mail attachment or Power Point presentations. A higher-quality image between 3 and 4 megapixels is more useful if a printed image is required. When storage is not an issue, the image should be obtained at its highest resolution, allowing for future image manipulation. Currently, most video recordings during endoscopic procedures are performed in conventional analog VHS or SVHS formats, which can be digitally converted. The introduction of digital video recording devices has allowed video footage to be recorded directly into a digital format (ie, Digital Video [DV], Moving Picture Experts Group [MPEG] 1 and MPEG 2) (Figs. 6A, 6B). These video-capturing systems can be part of an expensive commercial integrated video system, DV camera, DVD recorder, or a low cost personal computer with a DV capture card [22]. Digital video editing can be performed on a personal computer using various editing programs (ie, Adobe Premiere Adobe Systems Inc., San Jose, CA). Smaller still digital images can be stored on different digital storage media (SmartMedia, Com-
pact Flash, Secure Digital, Multi Media card, and Memory Stick) up to 1 gigabyte (GB), depending on the media used. For larger files, especially video clips, a Zip Disk (up to 750 megabytes [MB]), CDROM (up to 700 MB), and, lately, DVD (up to 17 GB) can be used. Nevertheless, image storage continues to be a problem, especially with large numbers of digital files. Picture archiving and communication systems (PACS) are being developed and will ultimately have an important role in filmless medical imaging in the near future [23–25]. Image display systems and high-definition video systems The development of high-quality image display systems has become essential during endoscopic surgery. Previous studies have demonstrated that the inherent optical quality of most endoscopes and CCD cameras exceeds the display resolution of standard television [26]. With the limited resolution of current analog National Television Standards Committee (NTSC), Phase-Alternation-by-Line (PAL), and Sequential Color and Memory (SECAM) monitors, there is a demand for higherresolution image display systems. One such digital display system is HDTV. The most common HDTV formats used in the United States are
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720p and 1080i, where p represents progressive scanning (ie, each scan includes every line for a complete picture) and i signifies interlaced scanning (ie, each scan includes alternate lines for half a picture). These scan rates translate into a frame rate of up to 60 frames per second, twice that of conventional television monitors. HDTV offers greatly enhanced picture quality with improved image resolution. HDTV pixel numbers range from 1 to 2 million, compared with the range of 300,000 to 1 million for NTSC, PAL, or SECAM. The other significant feature of the HDTV format is its wider aspect ratio (the width to height ratio of the screen) of 16:9 compared with the ratio of 4:3 for NTSC, PAL, and SECAM screens. Studies have suggested that the wider aspect ratio provides more information for the viewer, enhancing diagnostic and therapeutic interventions [12,27]. The future application of high-definition imaging (HDI) technology will improve endoscopic image resolution based on CCD chips. The European standard HDI chip resolution is 2,340,250 pixels, resulting in 1250 horizontal lines. HDI has the advantage of resolution enhancement for image brilliance and the augmentation of secondary depth clues such as shadows. Other techniques under development for image resolution enhancement include the use of complementary metal oxide semiconductor (CMOS) technology to replace the CCD sensors [4]. CMOS and CCD imagers are manufactured in a silicon foundry, and the equipment used is similar; however, alternative manufacturing processes and device architectures make the imagers different in their capability and performance. It is technically feasible, but not economical, to use a CCD processor to integrate other camera functions, such as the clock driver and signal processing. These functions are normally implemented into secondary chips; therefore, most CCD cameras are composed of several chips. One of the major benefits of CMOS cameras over the CCD design lies in the high level of product integration that can be achieved through virtually all of the electronic camera functions onto the same chips. Typically, CMOS processors allow lower power use and lower system cost. The improved resolution and color separation of HDI provide better diagnosis and enhance the effect of secondary spatial cues, leading to easier orientation, particularly if the images are combined with improved illumination. Despite their current high cost, the price of HDTV cameras and monitors will continue to decline as newer prod-
ucts come onto the consumer market. With further optimization of size and weight of the camera system, HDTV can become a standard feature for endoscopic imaging and display during ureteroscopic procedures. Three-dimensional video endoscopic systems Stereoscopic vision is essential for precise surgical performance and operative safety during endoscopic surgery; however, most current video endoscopic systems provide a two-dimensional, flat image. Recent advances in imaging technology allow three-dimensional video techniques to be used during endoscopic surgery. Most of the current three-dimensional video systems have four basic principles of stereoendoscopic image processing in common: image capture, conversion of 60 to 120 Hz images, presentation of left and right images on a single monitor, and separation of the left and right eye images [28,29]. A threedimensional video endoscopic system captures two slightly different images of the operative field, which are then transmitted to the monitor so that the images of the right and left cameras are alternatively displayed (sequential display procedure) with a frequency of 100/120 Hz. Several image-capturing methods have been employed, including the dual lens system, single lens systems, electronic video endoscopic system, and a system of single rod lenses with two beam paths. The three-dimensional imaging display may be achieved by two methods—with active liquid crystal display glasses or with polarizing glasses. In both instances, the brain fuses the right- and left-sided images on the appropriate imaging site. This technology is based on the physiology of retinal image persistence and is different from normal stereoscopic imaging [9]. Comparisons of two- and three-dimensional video systems offer conflicting results in experimental and clinical practice. Although the benefits of enhanced depth perception provided by threedimensional systems have been demonstrated in various studies, three-dimensional endoscopic technology has not been widely used owing to its high cost and relative lack of availability. Moreover, some studies have demonstrated no evidence of improved performance when using threedimensional systems during endoscopic procedures [30,31], suggesting that a higher-resolution video system might be more advantageous than threedimensional endoscopic imaging [27]. Currently, three-dimensional imaging systems are used for the
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most part during laparoscopic and robotic surgical procedures for true stereoscopic imaging. Threedimensional imaging will most likely not have a significant role in ureteroscopic procedures. Virtual reality endoscopic simulation Endourologic procedures require specific training to achieve competency. Opportunities for clinical experience can be reduced by limited operative time (limited operative time refers to limited hours in the resident’s work week, ie, 80 hour work week), available cases, and the increasing expectations of patients. Ethical and cost issues may further limit the use of animal or cadaver models for training purposes [32–34]. Although hands-on training using bench models can successfully teach the novice endourologic skills, these methods lack the variety encountered in true clinical conditions [35,36]. Moreover, inanimate simulators lack the realistic feel of living tissue. Advances in virtual reality simulation offer a practical tool for urologists to practice various endourologic procedures ranging from basic to complex in an inanimate but dynamic lifelike environment without risk to patients or ethical issues. Accurate reproduction of anatomic structures provides a realistic virtual reality surgical simulation. Models should also provide appropriate tactile feedback and spatial cues [32]. Because endourologic procedures require little in the way of complex anatomic and tactile feedback, one of the earliest simulators in urology was a virtual reality ureteroscopy simulator (Immersion Medical, Gaithersburg, Maryland) [33]. This simulator allowed urologists to explore the ureter and kidney for pathologic processes, specifically, stones and tumors. Limitations included a lack of true anatomic representation and inadequacy in computer graphics. Recent advances in computing power, virtual reality graphics, and physical modeling techniques have resulted in a new endoscopic simulator (URO Mentor system, Symbionix, Tel Aviv, Israel). This commercially available, virtual reality modular endoscopic simulator provides virtual cystoscopy and ureteroscopy procedures using either rigid or flexible endoscopes. Real-time fluoroscopy with simulation of C-arm control and viewing of fluoroscopic images of injected contrast can also be combined with endoscopic procedures. Various endourologic procedures can be simulated realistically, including cystoscopy, retrograde pyelography, insertion of a guidewire, ureteral stenting, ureteroscopy, stone
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fragmentation, and fragment removal using various tools. In addition, simulated tumor resection and treatment of stricture and obstruction can be reproduced [37]. Recent studies demonstrated that use of this virtual reality simulator resulted in rapid acquisition of ureteroscopic skills by urologic trainees [38,39]. These studies demonstrated a significant reduction in procedure time, task performance, and overall performance in those subjects who had practiced on the simulator. Endourologic skills also can be validated using virtual reality simulation [34,40]. Further advances in computer and software technology will allow virtual reality simulation to become more realistic in the near future. Similar to its use in the aviation industry, virtual reality simulation will most likely be incorporated into the training, testing, and credentialing of endourologists over the next 5 to 10 years.
Internet and telemedicine In recent years, telemedicine, defined as the use of electronic information and communication technologies to provide and support health care from a distance, has become an important aspect in patient care. Advances in digital imaging, highspeed computer connections, and the widespread availability of the Internet have allowed a steady growth of telemedicine within urology [41]. Digital images obtained from various sources such as a digital still or video camera, scanner, CT, and MR imaging can be exchanged over the Internet at high speeds using current transmission modalities such as an Integrated Services Digital Network (ISDN) (128 kbps), T1 lines (1.54 megabits per second [Mbps]), coaxial cable (up to 6 Mbps), and Asymmetric Digital Subscriber Line (ADSL) (1–3 Mbps) [12,21,42]. Currently, there are two types of telemedicine systems. The first system is synchronous and realtime video conferencing. In general, real-time motion requires that images are generated at a speed of 30 frames per second [43]. The advantage of live video teleconferencing is that it allows real-time interaction between physicians and patients with full-motion audiovisual images, developing a true physician–patient relationship. In addition, various medical centers can be linked with the teleconferencing facility to promote tele-education and teleconsultation. With the proper equipment, digital images, including endoscopic pictures, pathologic slides, and radiologic images, can be
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transmitted in real time. Currently, the high cost of real-time telemedicine systems and communication networks prevents the widespread use of this technology. A teleconferencing system can cost more than $80,000, not including the connection fee, which can be as high as $800 per month [44]. Recent studies have demonstrated that high-quality HDTV image-orientated telemedicine could be provided via ISDN lines or communication satellites; however, the minimum setup cost is prohibitive at greater than $1,000,000 [45]. Alternatively, telemedicine can be accomplished using an asynchronous or ‘‘store and forward’’ system, whereby the information is transmitted via E-mail or the Internet. The recipients can review and respond to the information transmitted at their convenience, because the data are stored in a locally accessible, computerized data storage and retrieval system [46,47]. More surgical disciplines, including urology, are using this technology. Current store and forward technology is improving with better software development and secure transmission of encrypted data over the Internet [21]. Despite the lack of real-time interaction, these systems remain effective and useful tools for medical care and endourologic training [42]. In addition, teleradiology as part of telemedicine systems is being evaluated as a mechanism to provide rapid, accurate, and cost-effective diagnostic radiographs. Studies have shown that a highquality affordable teleradiology system is effective and accurate when compared with plain films for assessing the presence of urinary calculi [48]. In an evaluation of urolithiasis, the decisions made in 38% of initial telephone consultations involving stone management were changed when images were transmitted and reviewed by consulting urologists. This telemedicine application enhanced the clinical decision-making process by allowing for improved quality of care through immediate access and effective transfer of information among the referring urologist, patient, and stone center specialist [49]. Standardization of input devices for image data exchange is essential for telemedicine. The Digital Imaging and Communications in Medicine (DICOM) standard exists for radiologic images, but there is no standard for other digital images such as endoscopic still pictures or video clips. There is an urgent need for standardization and integration of telemedicine hardware [45]. Upcoming challenges in telemedicine will include decisions on physician licensing requirements, the regulation of telemedicine, reimbursement for
consultations, and protection of patient confidentiality [42]. Summary Advances in image processing and display technologies, such as digital imaging, HDTV, and virtual reality, will ultimately allow integration of endoscopic imaging with diagnosis and therapy during ureteroscopic procedures. Further improvements in simulation technology and telemedicine should improve surgical training and greatly benefit patient care.
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Advances in video and imaging in ureteroscopy Yeh Hong Tan, MDa,b, Glenn M. Preminger, MDa,* a
Division of Urology, Department of Surgery, Duke University Medical Center, Box 3167, Room 1572D, White Zone, Durham, NC 27710, USA b Department of Urology, Singapore General Hospital, Outram Road, Singapore 169608
Over the last decade, significant improvements have been made in endoscopic equipment, especially in video and imaging technologies. Coupled with better-designed rigid, semirigid, and flexible endoscopes, enhanced digital imaging systems allow complex endourologic procedures to be accomplished with greater ease and superior accuracy. This article highlights advances in endoscopic video systems, along with image management technology that can be used during ureteroscopic procedures. Illumination Illumination of the operative field is an integral part of endoscopic surgery. Currently, highintensity light sources, usually halogen and xenon, are favored; however, halogen sources produce a slightly yellow light requiring compensation during white balancing of the endoscopic camera system. Xenon sources provide a more natural and whiter color. The fiberoptic bundles that run through the endoscopes permit rapid transmission of light and digital information in a small space. The light is conducted to the operative field by fiberoptic bundles that contain glass fiber or special fluid. Because the glass fiber bundles are more flexible, they are more widely used, even though they are less efficient in light transmission owing to a fiber mismatch at the junctions of the light cable and endoscope [1]. Contemporary light sources often have an automatic light-sensing feature, which quickly
* Corresponding author. E-mail address: [email protected] (G.M. Preminger).
adjusts the light output as required by the camera. This automatic light adjustment feature is particularly helpful during endoscopic procedures as the endoscope is rapidly moved throughout the urinary tract, causing different levels of illumination. Light intensity is automatically adjusted to maintain a preset level. Similarly, some digital camera systems are equipped with an ‘‘automatic iris’’ system, which electronically increases or decreases the aperture of the camera shutter. If the camera system is equipped with a light-sensing feature, there is no need for an automatic intensity-adjusting light source [2]. Newer charged coupled device (CCD) or image sensor based endoscopic cameras feature electronic exposure (Fig. 1). This system varies the effective exposure period (ie, lightgathering time) of the CCD as the live image is captured. Typical CCD exposure periods range from approximately 1/60 of a second to 1/10000 of a second under very bright conditions. This electronic process can be used to maintain the brightness in the image. When the image brightness must be reduced to improve picture clarity, the image signal exposure period can be reduced electronically instead of adjusting the iris of the light source. Shadows have an important role in depth perception and spatial orientation. Studies have demonstrated that endoscopic task performance significantly improves with video systems that provide proper illumination and appropriate shadows in the operative field [3]. Many of the currently used endoscopes employ a simple frontal illumination technique that produces an optically flat and shadowless image with resultant poor contrast. Newer illumination and imaging technologies provide shadow-inducing systems using a single-point or multipoint illumination system. One of these techniques employs the use of two
0094-0143/04/$ - see front matter Ó 2004 Elsevier Inc. All rights reserved. doi:10.1016/S0094-0143(03)00103-4
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and optical fibers is necessary for the production of a bright image during endoscopic use. Different sized endoscopes require the appropriate lens diameter to ensure an optimal lens-to-fiber ratio. Endoscopes with larger diameter lenses but fewer illumination fibers may give bright images when used to look at external objects in a room, but they fail during endoscopic applications, producing an image that is noticeably less bright [9].
Digital imaging Fig. 1. CCD cameras (Courtesy of Olympus America, Melville, New York; with permission.)
independent illumination fiber bundles, with one fiber bundle ending at the front lens, as designed in conventional endoscopes, and the other fiber bundle ending behind the tip of endoscope. This configuration results in an improved image with better contrast owing to shadow formation. Spatial orientation and perception between anatomic structures are considerably enhanced [4]. Endoscopes Most rigid endoscopes use a rod lens system. Alternatively, flexible and semirigid endoscopes use fiberoptic bundles for light transmission and image relay. The optical fibers provide the advantage of light transmission over a long distance with minimal loss of signal. Moreover, the fiberoptic bundles can be flexed or bent without disrupting alignment, as might occur with rigid rod lens systems. With further miniaturization, more compact fiberoptic cables can be produced, allowing for the development of smaller and more flexible endoscopes. Significant changes have taken place in the design of flexible ureteroscopes since their introduction. Besides the decrease in size and diameter of the instrument, the incorporation of a working channel and the improved maneuverability with active tip deflection and secondary deflection have extended the use of the flexible ureteroscope in diagnosis and therapy [5–8]. Recent developments have focused on improved image quality. In rod lens rigid endoscopes, the use of a multilayer antireflection coating helps to reduce light loss and improves image quality. The application of aspherical and doublet lenses results in decreased image distortion and chromatic aberrations. The right balance of lenses
Conventionally, endoscopic still images and videos of surgical procedures have been captured and stored in an analog format. Reproduction and storage of analog images are time and image consuming. Analog images tend to degrade in quality over time and during image processing. During endoscopic procedures, analog images transmitted through fiberoptic bundles are converted into continuous voltage waveforms before being displayed on an analog video monitor. Because analog signals are susceptible to degradation during the translation process, these images often lack the detail necessary to identify subtle pathologic processes. Current digital technology has revolutionized endourology with the introduction of digital still and video camera systems. Image capture: endoscopic camera systems and the charged coupled device The current generation of endoscopic cameras is based on the CCD chip. The digital image is captured on a CCD using a digital still or digital video camera. Photoreceptors within the CCD rapidly assess the different light intensities that make up the endoscopic image. The CCD generates pixels by converting unique light intensities within an image into corresponding electronic signals, which are then transmitted to a storage element on the chip [10]. Digital cameras are classified according to the amount of resolution determined by the number of pixels and the number of CCD chips. The average CCD resolution of single-chip camera ranges between 400,000 and 440,000 pixels, whereas threechip cameras exceed 450,000 pixels. The display resolution of the cameras ranges between 350 to 450 and 700 horizontal lines for single-chip and three-chip cameras, respectively [4]. A significant improvement in CCD camera technology has been the development of the threechip camera that contains three individual CCD
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chips for the primary colors—red, green, and blue (RGB). In addition to composite super video home system (SVHS) and component signals, the threechip cameras also provide an ‘‘uncoded’’ RGB signal. Color separation is achieved using a prism system overlying the chips [9]. This three-chip camera design provides improved color fidelity and enhanced image resolution. Moreover, three-chip cameras produce less ‘‘noise’’ owing to the pure RGB signals [11,12]. A digital converter captures each voltage signal as an image and translates the voltage values into discrete numbers, either 0 or 1. The encoded numbers for each image element, or pixel, include information on color, light intensity, and contrast. These variables can then be modified using image processing software within the camera [12]. In theory, three-chip cameras produce better quality images than single-chip cameras. Despite the apparent advantages of three-chip cameras, some clinical comparisons have favored one-chip systems. Using normal video monitors, previous studies have implied that the resolution between the two cameras does not alter the visual perception of an image. Studies have found that digital contrast enhancement is a more important feature for endoscopic imaging than the number of camera chips. Three-chip cameras seem to have no advantage over well-designed, single-chip systems [9,13]. This apparent limitation may change with the introduction of high-resolution digital monitors and high-definition television (HDTV), because the amount of image information and the degree of perception are increased with these digital imaging modalities [14].
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by the CCD chip, digitalized, and converted into electrical signals for transmission. This endoscope design has fewer interfaces, allowing the digital information to be transmitted directly to an image display unit with minimal image loss, interference, and distortion [1,15]. The creation of true video endoscopes will especially benefit flexible ureteroscopes. Because internal optics will not be required in the long flexible shafts of these ureteroscopes, more durable deflection cables or larger working channels can be used to improve the durability of these fragile devices [7,8,10]. With no need to attach a camera head to the eyepiece of the scope, the videoscope cable can be secured to the light cord for attachment to the video system, providing a more lightweight and convenient setup. Currently, this technology has only been incorporated into larger rigid endoscopes (laparoscopes) and some flexible endoscopes (colonoscopes, bronchoscopes, and cystoscopes) (Fig. 3) [16–18]. Recent technologic advances have allowed the miniaturization of CCD chips. One can expect to see an integrated digital video ureteroscope to replace standard flexible ureteroscopes in the near future. Another development in digital camera technology includes the use of a single monochrome CCD chip with alternating RGB illumination to form a color image rather than using three chips with three separate color filters. This design reduces the space requirements and takes advantage of established high-resolution monochrome CCD chip technology [15]. This design is currently used in a digital video cystoscope (Olympus America, Mellville, New York).
Video endoscopy (‘‘chip on a stick’’) A major advance in endoscopy systems has been the development of digital video endoscopes. Miniaturization of chip technology now allows a CCD chip to be incorporated at the distal end of the endoscope (chip on a stick) (Fig. 2). Instead of relaying optical images from the objective lens at the distal end of the scope to a camera attached to the eyepiece, the image is immediately captured
Fig. 2. Chip on a stick technology (Courtesy of Olympus America, Melville, New York; with permission.)
Fig. 3. Flexible video cystoscope (Courtesy of Olympus America, Melville, New York; with permission.)
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Future development in endoscopic imaging Although reflected white light is used to produce an endoscopic image, this light can be absorbed, scattered, or cause ‘‘autofluorescence.’’ These additional light–tissue interactions are being explored for advanced imaging technologies. Improvement in endoscopic imaging can be achieved by incorporating an optical magnification lens system at the tip of the endoscope (magnification) or by using other light–tissue interactions (spectroscopy). Magnifying or zoom endoscopes have a lens system built into the tip of instrument, which can be used to magnify small areas up to 100-fold. During optical spectroscopy, different spectra can be identified depending on the wavelength of the light used, as well as various tissue properties. Some of these spectra can be highly tissue specific and can be used to identify areas of ischemia, inflammation, and nonapparent malignancy. With this technique, multiple ‘‘optical biopsies’’ can be taken from suspicious areas, instead of conventional histologic biopsies [19]. Although these techniques are still investigational, they remain an attractive option for future ureteroscopic evaluation of the upper urinary tract.
Digital enhancement and digital filter technologies A recent advance in digital imaging has been the development of enhancement and filtering modalities that can be used to improve endoscopic images. Digital contrast enhancement improves the image quality by accentuating the existing transitions in endoscopic images. Enhancement is accomplished using clusters of pixels known as kernels. When the digital contrast enhancement feature is activated, the center pixel in each kernel determines the state of its surrounding pixels. If variations are present in the levels of contrast or brightness between the center pixel and the average of its surrounding eight pixels, those differences are enhanced without compromising other aspects of the image quality, resulting in increased definition. When variations are not present, no changes occur. This process allows finer details to become discernible to the naked eye. During flexible endoscopy, a characteristic honeycomb pattern is formed because of the spaces between individual fiberoptic fibers. When used with flexible endoscopes, digital filters smooth out the image by expanding the image of each individual fiber to ‘‘fill in the gaps.’’ By distributing the illumination evenly among fibers, a nearly
seamless image is produced without the honeycomb appearance and with consistent lighting. These beneficial effects of digital enhancement and fiberoptic filtering have been studied in detail. During rigid and semirigid ureteroscopy, digital enhancement improves structure identification and image detail and minimizes background noise. Moreover, the digital fiberscope filter significantly improves images during flexible ureteroscopic procedures [14].
Digital imaging, video documentation, and editing Over the last few years, digital imaging has slowly revolutionized the field of videoendoscopy. Although images can be captured initially in the analog format, they can be converted digitally later using a digital camera or scanner. The introduction of digital still cameras has taken image documentation and editing to a new dimension. Currently, newer surgical video systems have an integrated digital image capture system, allowing immediate capture of still images from endoscopic procedures (Figs. 4, 5A, 5B) [10]. Alternatively, a less expensive digital still image capture adapter can be connected to endoscopic camera systems [12]. Digital still images can usually be recorded in Joint Photographic Experts Group (JPEG), tagged image file (TIFF), or bitmap (BMP) formats. These digital images can be edited and optimized on the computer using various graphic software packages. Incorporating medical images into the patient’s record and creating an image library can enhance urologic practice [20,21]. The quality of the digital
Fig. 4. Example of integrated video- and image-capturing screen (Courtesy of Olympus America, Melville, New York; with permission.)
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Fig. 6. (A, B) Digital image capture system using CD or DVD (Courtesy of Stryker Endoscopy, San Jose, California; with permission.) Fig. 5. (A, B) Digital image capture system using Smart Media (Courtesy of Olympus America, Melville, New York; with permission.)
image required depends on its purpose. Lowresolution images ranging from 1 to 2 megapixels can be used for E-mail attachment or Power Point presentations. A higher-quality image between 3 and 4 megapixels is more useful if a printed image is required. When storage is not an issue, the image should be obtained at its highest resolution, allowing for future image manipulation. Currently, most video recordings during endoscopic procedures are performed in conventional analog VHS or SVHS formats, which can be digitally converted. The introduction of digital video recording devices has allowed video footage to be recorded directly into a digital format (ie, Digital Video [DV], Moving Picture Experts Group [MPEG] 1 and MPEG 2) (Figs. 6A, 6B). These video-capturing systems can be part of an expensive commercial integrated video system, DV camera, DVD recorder, or a low cost personal computer with a DV capture card [22]. Digital video editing can be performed on a personal computer using various editing programs (ie, Adobe Premiere Adobe Systems Inc., San Jose, CA). Smaller still digital images can be stored on different digital storage media (SmartMedia, Com-
pact Flash, Secure Digital, Multi Media card, and Memory Stick) up to 1 gigabyte (GB), depending on the media used. For larger files, especially video clips, a Zip Disk (up to 750 megabytes [MB]), CDROM (up to 700 MB), and, lately, DVD (up to 17 GB) can be used. Nevertheless, image storage continues to be a problem, especially with large numbers of digital files. Picture archiving and communication systems (PACS) are being developed and will ultimately have an important role in filmless medical imaging in the near future [23–25]. Image display systems and high-definition video systems The development of high-quality image display systems has become essential during endoscopic surgery. Previous studies have demonstrated that the inherent optical quality of most endoscopes and CCD cameras exceeds the display resolution of standard television [26]. With the limited resolution of current analog National Television Standards Committee (NTSC), Phase-Alternation-by-Line (PAL), and Sequential Color and Memory (SECAM) monitors, there is a demand for higherresolution image display systems. One such digital display system is HDTV. The most common HDTV formats used in the United States are
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720p and 1080i, where p represents progressive scanning (ie, each scan includes every line for a complete picture) and i signifies interlaced scanning (ie, each scan includes alternate lines for half a picture). These scan rates translate into a frame rate of up to 60 frames per second, twice that of conventional television monitors. HDTV offers greatly enhanced picture quality with improved image resolution. HDTV pixel numbers range from 1 to 2 million, compared with the range of 300,000 to 1 million for NTSC, PAL, or SECAM. The other significant feature of the HDTV format is its wider aspect ratio (the width to height ratio of the screen) of 16:9 compared with the ratio of 4:3 for NTSC, PAL, and SECAM screens. Studies have suggested that the wider aspect ratio provides more information for the viewer, enhancing diagnostic and therapeutic interventions [12,27]. The future application of high-definition imaging (HDI) technology will improve endoscopic image resolution based on CCD chips. The European standard HDI chip resolution is 2,340,250 pixels, resulting in 1250 horizontal lines. HDI has the advantage of resolution enhancement for image brilliance and the augmentation of secondary depth clues such as shadows. Other techniques under development for image resolution enhancement include the use of complementary metal oxide semiconductor (CMOS) technology to replace the CCD sensors [4]. CMOS and CCD imagers are manufactured in a silicon foundry, and the equipment used is similar; however, alternative manufacturing processes and device architectures make the imagers different in their capability and performance. It is technically feasible, but not economical, to use a CCD processor to integrate other camera functions, such as the clock driver and signal processing. These functions are normally implemented into secondary chips; therefore, most CCD cameras are composed of several chips. One of the major benefits of CMOS cameras over the CCD design lies in the high level of product integration that can be achieved through virtually all of the electronic camera functions onto the same chips. Typically, CMOS processors allow lower power use and lower system cost. The improved resolution and color separation of HDI provide better diagnosis and enhance the effect of secondary spatial cues, leading to easier orientation, particularly if the images are combined with improved illumination. Despite their current high cost, the price of HDTV cameras and monitors will continue to decline as newer prod-
ucts come onto the consumer market. With further optimization of size and weight of the camera system, HDTV can become a standard feature for endoscopic imaging and display during ureteroscopic procedures. Three-dimensional video endoscopic systems Stereoscopic vision is essential for precise surgical performance and operative safety during endoscopic surgery; however, most current video endoscopic systems provide a two-dimensional, flat image. Recent advances in imaging technology allow three-dimensional video techniques to be used during endoscopic surgery. Most of the current three-dimensional video systems have four basic principles of stereoendoscopic image processing in common: image capture, conversion of 60 to 120 Hz images, presentation of left and right images on a single monitor, and separation of the left and right eye images [28,29]. A threedimensional video endoscopic system captures two slightly different images of the operative field, which are then transmitted to the monitor so that the images of the right and left cameras are alternatively displayed (sequential display procedure) with a frequency of 100/120 Hz. Several image-capturing methods have been employed, including the dual lens system, single lens systems, electronic video endoscopic system, and a system of single rod lenses with two beam paths. The three-dimensional imaging display may be achieved by two methods—with active liquid crystal display glasses or with polarizing glasses. In both instances, the brain fuses the right- and left-sided images on the appropriate imaging site. This technology is based on the physiology of retinal image persistence and is different from normal stereoscopic imaging [9]. Comparisons of two- and three-dimensional video systems offer conflicting results in experimental and clinical practice. Although the benefits of enhanced depth perception provided by threedimensional systems have been demonstrated in various studies, three-dimensional endoscopic technology has not been widely used owing to its high cost and relative lack of availability. Moreover, some studies have demonstrated no evidence of improved performance when using threedimensional systems during endoscopic procedures [30,31], suggesting that a higher-resolution video system might be more advantageous than threedimensional endoscopic imaging [27]. Currently, three-dimensional imaging systems are used for the
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most part during laparoscopic and robotic surgical procedures for true stereoscopic imaging. Threedimensional imaging will most likely not have a significant role in ureteroscopic procedures. Virtual reality endoscopic simulation Endourologic procedures require specific training to achieve competency. Opportunities for clinical experience can be reduced by limited operative time (limited operative time refers to limited hours in the resident’s work week, ie, 80 hour work week), available cases, and the increasing expectations of patients. Ethical and cost issues may further limit the use of animal or cadaver models for training purposes [32–34]. Although hands-on training using bench models can successfully teach the novice endourologic skills, these methods lack the variety encountered in true clinical conditions [35,36]. Moreover, inanimate simulators lack the realistic feel of living tissue. Advances in virtual reality simulation offer a practical tool for urologists to practice various endourologic procedures ranging from basic to complex in an inanimate but dynamic lifelike environment without risk to patients or ethical issues. Accurate reproduction of anatomic structures provides a realistic virtual reality surgical simulation. Models should also provide appropriate tactile feedback and spatial cues [32]. Because endourologic procedures require little in the way of complex anatomic and tactile feedback, one of the earliest simulators in urology was a virtual reality ureteroscopy simulator (Immersion Medical, Gaithersburg, Maryland) [33]. This simulator allowed urologists to explore the ureter and kidney for pathologic processes, specifically, stones and tumors. Limitations included a lack of true anatomic representation and inadequacy in computer graphics. Recent advances in computing power, virtual reality graphics, and physical modeling techniques have resulted in a new endoscopic simulator (URO Mentor system, Symbionix, Tel Aviv, Israel). This commercially available, virtual reality modular endoscopic simulator provides virtual cystoscopy and ureteroscopy procedures using either rigid or flexible endoscopes. Real-time fluoroscopy with simulation of C-arm control and viewing of fluoroscopic images of injected contrast can also be combined with endoscopic procedures. Various endourologic procedures can be simulated realistically, including cystoscopy, retrograde pyelography, insertion of a guidewire, ureteral stenting, ureteroscopy, stone
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fragmentation, and fragment removal using various tools. In addition, simulated tumor resection and treatment of stricture and obstruction can be reproduced [37]. Recent studies demonstrated that use of this virtual reality simulator resulted in rapid acquisition of ureteroscopic skills by urologic trainees [38,39]. These studies demonstrated a significant reduction in procedure time, task performance, and overall performance in those subjects who had practiced on the simulator. Endourologic skills also can be validated using virtual reality simulation [34,40]. Further advances in computer and software technology will allow virtual reality simulation to become more realistic in the near future. Similar to its use in the aviation industry, virtual reality simulation will most likely be incorporated into the training, testing, and credentialing of endourologists over the next 5 to 10 years.
Internet and telemedicine In recent years, telemedicine, defined as the use of electronic information and communication technologies to provide and support health care from a distance, has become an important aspect in patient care. Advances in digital imaging, highspeed computer connections, and the widespread availability of the Internet have allowed a steady growth of telemedicine within urology [41]. Digital images obtained from various sources such as a digital still or video camera, scanner, CT, and MR imaging can be exchanged over the Internet at high speeds using current transmission modalities such as an Integrated Services Digital Network (ISDN) (128 kbps), T1 lines (1.54 megabits per second [Mbps]), coaxial cable (up to 6 Mbps), and Asymmetric Digital Subscriber Line (ADSL) (1–3 Mbps) [12,21,42]. Currently, there are two types of telemedicine systems. The first system is synchronous and realtime video conferencing. In general, real-time motion requires that images are generated at a speed of 30 frames per second [43]. The advantage of live video teleconferencing is that it allows real-time interaction between physicians and patients with full-motion audiovisual images, developing a true physician–patient relationship. In addition, various medical centers can be linked with the teleconferencing facility to promote tele-education and teleconsultation. With the proper equipment, digital images, including endoscopic pictures, pathologic slides, and radiologic images, can be
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transmitted in real time. Currently, the high cost of real-time telemedicine systems and communication networks prevents the widespread use of this technology. A teleconferencing system can cost more than $80,000, not including the connection fee, which can be as high as $800 per month [44]. Recent studies have demonstrated that high-quality HDTV image-orientated telemedicine could be provided via ISDN lines or communication satellites; however, the minimum setup cost is prohibitive at greater than $1,000,000 [45]. Alternatively, telemedicine can be accomplished using an asynchronous or ‘‘store and forward’’ system, whereby the information is transmitted via E-mail or the Internet. The recipients can review and respond to the information transmitted at their convenience, because the data are stored in a locally accessible, computerized data storage and retrieval system [46,47]. More surgical disciplines, including urology, are using this technology. Current store and forward technology is improving with better software development and secure transmission of encrypted data over the Internet [21]. Despite the lack of real-time interaction, these systems remain effective and useful tools for medical care and endourologic training [42]. In addition, teleradiology as part of telemedicine systems is being evaluated as a mechanism to provide rapid, accurate, and cost-effective diagnostic radiographs. Studies have shown that a highquality affordable teleradiology system is effective and accurate when compared with plain films for assessing the presence of urinary calculi [48]. In an evaluation of urolithiasis, the decisions made in 38% of initial telephone consultations involving stone management were changed when images were transmitted and reviewed by consulting urologists. This telemedicine application enhanced the clinical decision-making process by allowing for improved quality of care through immediate access and effective transfer of information among the referring urologist, patient, and stone center specialist [49]. Standardization of input devices for image data exchange is essential for telemedicine. The Digital Imaging and Communications in Medicine (DICOM) standard exists for radiologic images, but there is no standard for other digital images such as endoscopic still pictures or video clips. There is an urgent need for standardization and integration of telemedicine hardware [45]. Upcoming challenges in telemedicine will include decisions on physician licensing requirements, the regulation of telemedicine, reimbursement for
consultations, and protection of patient confidentiality [42]. Summary Advances in image processing and display technologies, such as digital imaging, HDTV, and virtual reality, will ultimately allow integration of endoscopic imaging with diagnosis and therapy during ureteroscopic procedures. Further improvements in simulation technology and telemedicine should improve surgical training and greatly benefit patient care.
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