Читать книгу Small Animal Laparoscopy and Thoracoscopy - Группа авторов - Страница 78

The video camera system consists of the camera head, CCU, and monitor. Heads include adapters with different focal lengths that determine the displayed image size. However, image size and magnification can be adjusted more conveniently with an integrated optical zoom knob located on the camera head. Optical zoom produces a true magnified image without compromising the resolution, unlike digital zoom, which merely increases pixel size [1–5, 8, 13].

An important consideration may be the flexibility of the chosen camera for different procedures and different endoscopes. It may be prudent to consider both a variable focal distance head as well as a CCU that is compatible with all the types of scopes that might be used in practice (fiberscopes, videoendoscopes, and rigid telescopes). Multidisciplinary and versatile systems may support a broad endoscopy service for a reasonable investment. Larger practices may, however, consider having separate systems for different services [1–5].

Medical cameras contain a computer “chip,” which transforms the optical image into an electronic signal transmitted to the CCU. Recent improvements in miniaturization of complementary metal‐oxide‐semiconductor (CMOS) “chips” have led to standardization of CMOS cameras as high‐end quality devices whose performance and image quality are equivalent or superior to earlier CCD (charge‐coupled device) cameras [1–5].

Although endoscopic camera quality has previously been defined by single‐chip or three‐chip technology, it is currently more relevant to embrace HD image technology. An HD image can be produced with either a single CMOS chip or three‐chip camera, which provides a wide screen display (Figure 3.8a). The HD aspect ratio of 16 : 9 more closely approximates the human visual field than the historical 4 : 3 standard and allows the surgeon to observe instruments entering the surgical field sooner than with a traditional monitor [1–5].

However, HD cameras differ in resolution and light sensitivity, performance characteristics that affect detail recognition, color, features, and price. Some newer cameras, for example, have integrated image capturing capabilities or image processing options that enhance contrast or brighten dark areas (see Enhanced Contact Endoscopy section below). Full HD cameras deliver superior picture resolution (1920 × 1080 pixels) and progressive scanning, as opposed to interlaced scanning. The progressive scanning method simultaneously displays all 1080 lines for every frame, thus producing the smoothest, clearest image, especially when the video content is motion intensive.

New generation full HD camera heads have titanium bodies, making them light, robust, and autoclavable, in contrast to older models only sterilizable by gas or soaking [1–5, 8, 9]. Newer camera heads provide intraoperative access to customizable functions with the push of a button on the head, such as white balance, image capture, video recording, image enhancement, zoom, and many others.

For standard veterinary abdominal and thoracic MIS procedures, a CMOS single‐chip FULL HD camera head and CCU are considered the standard of care, bringing to practice the best and most affordable medical technology. Nevertheless, for specific or more advanced applications, dedicated technologies are also available.

Figure 3.8 (A) FULL HD CMOS single chip lightweight camera, 1920 × 1080 pixels. Zoom can be activated by programmed touch button in camera head. (B). 4K camera with NIR/ICG, IMAGE 1 S^TM 4U RUBINA.

Source: © KARL STORZ SE & Co. KG, Germany.

It is critical to remember that for endoscopic images to be displayed in HD, each component of the imaging chain must be HD compatible, from the camera head to the transmission media and systems (CCU and cables) to the monitor [1–5, 13, 17].

A major milestone toward the goal of higher image definition, using image enhancement technology, was attained with the marketing of HD television (HDTV) camera systems. The ongoing process in this huge consumer technology sector has led to a variety of 3D endoscope systems culminating in the introduction of Ultra HD systems providing the 4K standard (Figure 3.8b) with a horizontal screen display resolution of approximately 4000 pixels as opposed to 1080 with full HD.

Over the last decade, various methods and technologies to enhance contrast, and early detection of mucosal and submucosal lesions, were described and used in clinical practice. These include autofluorescence (AF), conventional chromoendoscopy (CC), and recently enhanced contact endoscopy (ECE). These technologies were developed because white light endoscopic routine evaluation might fail to identify early‐stage lesions in epithelial or subepithelial layers, or to detect accurate margins in macroscopic lesions.

ECE is based on the dynamic fusion of the conventional IEE (image‐enhanced endoscopy) with CE (contact endoscopy) – but without the need for vital staining – and thus combines the advantages of both modalities.

Currently, imaging technologies that provide detailed contrast enhancement of the mucosa and blood vessels are widely used in many human medical specialties. The major focus of current research and development in the field of endoscopic imaging technologies is on the advancement of image‐enhanced endoscopy (IEE) systems (i‐SCAN, NBI, and IMAGE1 S^TM). The IMAGE 1 S^TM (KARL STORZ Tuttlingen, Germany) is a versatile digital full HD video system, providing specific color rendering of the acquired broad visible spectrum within the HD‐camera system. Since spectral separation is obtained within the camera system and amplified by adapted color processing algorithms, the IMAGE 1 S^TM does not require a dedicated narrow band light source and operates with a standard light source using the whole spectrum of light information. Therefore, this system enhances the appearance of the mucosal surface structures and subepithelial vasculature by selected wavelengths of light providing five different predefined spectral ranges in addition to the standard mode with white light: CLARA, CLARA + CHROMA, CHROMA, SPECTRA A, SPECTRA B. The KARL STORZ IMAGE 1 S system was awarded the Innovation of the Year by EAES – European Association for Endoscopic Surgery, in 2014 when the product was introduced, becoming a standard since then, for modern laparoscopic and thoracoscopic surgery.

ECE is currently used in small animal endoscopy (i.e. gastrointestinal, respiratory, and urinary systems) and MIS (laparoscopy and thoracoscopy). Enhancement of different vascular patterns, surface contrast, and elimination of edge shadowing allow surgical procedures to be performed with higher levels of accuracy compared to previous standard video imaging systems [18, 19].

Fluorescence is the property in which certain molecules (fluorochromes) emit fluorescent radiation when excited by a laser beam or exposed to near‐infrared light (NIR) at specific wavelengths. Once the light energy is absorbed by the fluorochrome's organic molecules, an excitation of delocalized electrons from ground state to a higher energy level occurs. Upon return from the excited singlet state to the ground state, energy is emitted in the form of photons, reaching the observer's eye as fluorescence of a specific wavelength.

Fluorescence image‐guided surgery (FIGS) is a medical imaging technique that uses fluorescence to detect properly labeled structures during surgery. Its purpose is to guide the surgical procedure and provide the surgeon a real‐time view of the operating field. When compared to other medical imaging modalities, FIGS is cheaper and superior in terms of resolution and number of molecules detectable. As a drawback, penetration depth is usually very poor (100 microns) in the visible wavelengths, but it can reach up to 1–2 cm when excitation wavelengths in the near infrared are used. FIGS is performed using imaging devices with the purpose of providing real‐time simultaneous information from color reflectance images (bright field) and fluorescence emission. One or more light sources are used to excite and illuminate the sample. Light is collected using optical filters that match the emission spectrum of the fluorophore. Imaging lenses and digital cameras are used to produce the final image [20–22].

Indocyanine green dye (ICG) was developed for near‐infrared (NIR) photography by Kodak Research Laboratories in 1955 and introduced for clinical use in 1956. Several clinical applications comprised the use of ICG, such as cirrhotic liver resection.

New successful applications of ICG were very recently published. For example, the use of this dye for assistance during a hepatic metastasectomy allows to identify superficially located colorectal liver metastases and in some patients it was possible to localize small lesions otherwise undetectable by typical procedures.

ICG is recognized to be relatively free of adverse effects when injected into the bloodstream and has been used in veterinary medicine extensively. Once excited with a specific wavelength of light, ICG becomes fluorescent, and this phenomenon can be detected using specific filter scopes and cameras, and then displayed on a screen. Some specific areas with ICG accumulating abilities can be seen, which would not occur with a normal white light endoscopic imaging system. ICG rapidly binds to plasma proteins after its intravascular injection, resulting in minimal leakage to the interstitial compartment.

The major limitation in FIGS is the availability of clinically approved fluorescent dyes. Indocyanine Green has been widely used as a nonspecific agent to detect sentinel lymph nodes (SLN) during surgery.

ICG‐NIR is classified as a nontargeted dye. This means that following administration, the pharmacokinetics of the molecule are known in detail, and this defines whether a probe is a good imaging agent for the observation of a given target according to its biodistribution, excretion pathways, accumulation patterns, etc. In general, nontargeted probes show poor differentiation between malignant and healthy tissue boundaries. A major area of research in fluorescence imaging is the identification and approval of new targeted dyes, which will offer better tissue differentiation at a reasonable cost.

Future trends in fluorescence imaging will depend on the research and development of antibody binding and specific tissue‐binding dye abilities. This step will expand the opportunities for targeted oncologic surgery and specific planning for complete tissue resection. Most of these specific fluorophore molecules rely on NIR fluorescence properties, and their ability to bind to receptors on specific cell membranes or extracellular matrix enzymes. They can efficiently recognize the intended molecular target and selectively accumulate on the malignancy sites, thereby rendering dramatic improvements in signal‐to‐background ratio over nontargeted probes.

The complete system can be switched from standard white light mode to NIR/ICG mode, and vice versa, simply by foot‐pedal control, or with camera head buttons on the new generation 4K NIR/ICG cameras (RUBINA^® – KARL STORZ). When used in NIR/ICG fluorescence mode, the technology can either offer images in blue or green, which enhances the image in highly perfused and fluorescent areas (blue mode), to more intense fluorescence and detailed delineation against surrounding tissue (green mode) [20–22]. RUBINA cameras (KARL STORZ) present also other NIR/ICG advantages such as Monochromatic Fluorescence which enables black and white imaging mode for better operating contrast, sharper edges, and brightness (Figure 3.9a).

Videoendoscopic oncologic surgery can benefit from NIR technology, since ICG is used to map neoplastic tissues and their lymphatic drainage. Consequently, mapped lymph nodes are surgically removed, allowing for subsequent histopathological analysis. Sentinel lymph node mapping is now enhanced with the use of the Fluorescence Intensity Map, since it achieves an improved distinction between lymph nodes and surrounding lymphatic pathways.

The recent introduction of Intensity Map enables the surgeon to interpret the grade of fluorescence displayed on the screen and correlate that with an intensity fluorescence scale, throughout the procedure, thus resulting in improved perception of tissue marking over surgical time. Overlaid images of white light and NIR/ICG are combined and processed with intelligent analysis software. With a specialized CCU, miniscule fluorescence tonal differences not visible to the human eye are detected and highlighted by a color scale mapping system.

Ranging from blue tones (the weakest fluorescence signal) to yellow/orange (the strongest fluorescence signal), color mapping maximizes early detection of lymphatic circulation, and SLN. The color grading system also positively influences the distinction of SLN from subsequent lymph nodes, which can be very helpful in surgical decision making.

The standard endoscopic imaging systems provide the surgeon with indirect monocular views of the operative field, denying the operator the binocular depth cues that provide a sense of stereopsis. The loss of binocular vision in a two‐dimensional (2D) display causes visual misperceptions – mainly loss of depth perception, adding to the surgeon's fatigue.

One of the biggest challenges for laparoscopic surgeons is hand–eye coordination within a 3D scene observed on a 2D display. Experienced surgeons learn to use monocular depth cues such as light and shade, relative size of objects, object interposition, texture gradient, aerial perspective, and motion parallax instead of stereovision. Using these cues, all laparoscopic operations can be accomplished; however, time and accuracy may be lost as these techniques do not completely compensate for loss of stereoscopic depth perception [23–32].

The 3D HD view with enhanced haptic feedback makes laparoscopic surgery safer and more intuitive. It improves hand–eye coordination and surgical precision, with the use of all conventional instruments. The 3D view provides increased depth perception and more accurate measurement of the dimensions of the anatomical spaces, enhancing the skills of the laparoscopic surgeon to manipulate tissues, dissect, design surgical strategies, and place intracorporeal sutures. Studies have reported less strain on the surgeon when using 3D rather than 2D vision [33–38].

Recent technological advances have led to sophisticated high‐resolution systems and light polarizing glasses that are lighter and more comfortable. A dual‐optical scope is connected to a two‐chip imaging system that transmits two pictures to a stereoscopic screen. When the surgeon wears polarized 3D glasses, the two images are merged by the brain into one single image that gives the perception of depth.

Stereoscopic vision improves accuracy in laparoscopic skills for novices. Several studies demonstrated a marked reduction in the number of repetitions and errors.

Few 3D systems are used yet in veterinary practice, but in the near future as popularity increases and prices are reduced, availability will increase, likely resulting in improved performance of laparoscopic surgical procedures. Nevertheless, when choosing between 3D and ECE (enhanced contact endoscopy) or NIR/ICG, the latter two currently stand as a more rational, cost‐effective options for small animal endoscopy and MIS [39–43].