FEATURE ENDOSCOPY
Eyes inside the body
Matthew Dale looks at how photonics technology is aiding the development of smaller endoscopes with better functionality
L
enses using graphene-based technology may hold the key to transforming medical endoscopy, research results announced last year in Australia suggest. These lenses could scale down the optical components of endoscopes and reduce their overall size, ultimately broadening the usefulness of endoscopy in clinical applications. In addition, aspherical lenses are enabling the
production of disposable endoscopes that will dramatically reduce the chances of acquiring an infection during an endoscopic procedure. Meanwhile, in the Netherlands, researchers are applying sophisticated optical and laser technology to endoscopy, potentially helping cancer surgeons identify the borders between malignant and healthy tissue more precisely. Endoscopes allow doctors to explore inside the body and search for any abnormalities. They are designed to provide the best view while minimising discomfort felt by the patient. The majority of endoscopes take the form of a long flexible tube with a light source and miniaturised camera at one end. Bundles of fibre within the tube carry as much light towards the tip as possible. With the scene illuminated, the camera captures a stream of high resolution images that are sent as a signal back along the optical fibres to be processed by imaging software.
Endoscopes have a wide range of applications in medicine. They are used in investigative procedures to diagnose patients; for delicate keyhole surgeries to guide surgeons; and in certain cases they are fitted with surgical tools to perform operations. The functionality of an endoscope is therefore dependent on the
14 ELECTRO OPTICS l JUNE 2016
Images of structurally normal human brain tissue taken using (A) Vrije Universiteit’s table-top system via second and third harmonic generation, and (B) myelin-stained histology, along with different brain tissue samples (C-J)
technology that can be contained within its tip. Consequently, manufacturers are reducing the size of their optical systems to make room for integrating other components into the tip of the endoscope. However, compromises need to be made in
order to do this. Dr Stefan Beyer, manager of product development for medical applications at Berliner Glas, explained that a reduction in image quality is one of these compromises. ‘Image quality is a direct function of the numerical aperture,’ he said. ‘Therefore, the smaller the lenses used in an optical system, the less the quality. In order to compensate for this, very complex aspherical designs or software “tricks” are needed.’
In aspherical lenses, the radius of curvature varies according to the distance from the optical
axis. They are preferable to spherical lenses, in many cases, as they do not suffer from ‘spherical aberration’, an effect that prevents a lens from focusing all the incoming light to a single point. Ingo Gretschel, vice president of micro optics at Qioptiq, now part of Excelitas, highlighted the challenges in producing micro optics, even with modern production techniques. ‘There’s no new development in manufacturing that enables these smaller lenses to be made,’ explained Gretschel. ‘In order to maintain lens quality while producing extremely small lenses, we must first use larger lenses than are normally needed. These larger lenses are then centred down to the final size.’ Manufacturers are therefore limited by the production techniques currently available. However, like Beyer, Gretschel sees aspherical lenses as the route to smaller optical systems: ‘A
@electrooptics |
www.electrooptics.com
OSA publishing/ Marlos Groot/ VU University Amsterdam
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