Guidance
3 The diagnostic tests
The assessment compared 3 intervention tests with 1 comparator.
The interventions
3.1 A conventional endoscopy system includes an endoscope, a light source, a video processor and a monitor. The light source produces light which is sent to the end of the endoscope. The video processor converts electrical signals into video signals and shows them on the monitor.
3.2 There are 2 types of virtual chromoendoscopy: optical chromoendoscopy and digital chromoendoscopy. Optical chromoendoscopy technologies have optical lenses, built into the endoscope's light source, which selectively filter white light to give narrow-band light. Digital chromoendoscopy technologies include digital processing of endoscopic images, which are produced in real-time by a video processor. Both methods can be switched on directly from an endoscope and are intended to allow high-contrast imaging of the mucosal surface without the need for dyes and additional equipment.
Narrow Band Imaging
3.3 Narrow Band Imaging (NBI; Olympus) is a feature of recent Olympus 200 series video endoscopy systems. The company states that NBI should only be used in models with high-definition or high-resolution imaging. NBI is produced by the light source and displayed through the video processor and monitor. Optical filters are used on white light, resulting in narrow-band light, which consists of 2 wavelengths: 415 nm blue light and 540 nm green light. Narrow-band light is absorbed by vessels but reflected by mucosa, which increases the contrast between the vessels and the surrounding mucosa compared with using standard white light. The endoscopist can turn the NBI filter on or off as needed, to switch between standard white light and narrow-band imaging.
Flexible spectral imaging colour enhancement
3.4 Flexible spectral imaging colour enhancement (FICE; manufactured by FujiFilm and distributed by Aquilant Endoscopy) is a software-based feature of Fuji endoscopy systems. Standard white light is directed at the tissue and the reflected light is captured and processed. Software turns conventional images into reconstructed spectral images by limiting the wavelengths of the light; the images are then shown in real-time. The image can be viewed in 10 different colour combinations. The pre-set wavelength patterns can also be changed manually. The endoscopist can move between the conventional image and the FICE image using a switch on the endoscope.
i‑scan
3.5 i‑scan (Pentax Medical) is a software-based image enhancement technology for use with Pentax endoscopy systems. Images from standard white light endoscopy can be processed using 3 algorithms:
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surface enhancement, which improves the contrast between light and dark regions
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contrast enhancement, which adds blue colour to relatively dark areas to show mucosal surface detail
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tone enhancement, which changes the colour contrast to improve visibility of mucosal structure and blood vessels.
3.6 The 3 algorithms are used in different combinations to give 3 modes for detecting, characterising and demarcating lesions. The endoscopist can move between the conventional image and the different i‑scan image modes by pushing a button on the endoscope.
The comparator
Histopathology
3.7 The comparator for this assessment is histopathology. It is assumed that in current practice all detected polyps are removed and sent to the laboratory for histopathology assessment. Polyps are examined to determine whether they are adenomatous, and therefore at high risk of cancer, or hyperplastic, and so at low risk.