How are endoscopes being used at present?

Kazunari Nakamura, General Manager, Imaging Products Department, Olympus Medical Systems, Japan:

In medicine, endoscopes are inserted into the body as part of minimally invasive diagnostic procedures for visually inspecting the surfaces of the digestive system, respiratory tracts and even the inside of joints. This simple-looking flexible tube is invaluable for not only imaging, but is also used for biopsies and surgery. In Japan endoscopes are widely used for diagnosis of stomach cancer and in Europe and the USA they are used more for inspecting the colon. In spite of other medical diagnosis technologies, such as magnetic resonance imaging, endoscopy is still widely regarded as the most effective means of diagnosing early stages of cancer. Also, from the patient's perspective, endoscopy enables treatment without major surgery and reduces the time spent in hospital, improving their quality of life. In terms of sales, Olympus has a 70% share of the world market. The largest global markets are the Japanese and US, which are about the same size, and the European Union is the next biggest. We have now set up a subsidiary in China because we expect it to be an important market in the future.

Tell me about the 'capsule endoscope' that Olympus has developed.

The 26-mm-long Olympus Endocapsule is swallowed by patients and enables real-time imaging in the digestive tract. Credit: OLYMPUS

It consists of a capsule just 26-mm long and 11 mm in diameter that features a CCD sensor, six white LEDs as an illumination source and a wireless antenna. The biggest advantage is that it is painless. Patients swallow the capsule with water and there is no need for an anaesthetic. The capsule moves through the digestive system by peristaltic motion and takes real-time images, two frames every second. The images are transmitted to an antenna and hard-disk recorder worn on the body and then transferred to a workstation for analysis. It is possible to take continuous images for 8 hours, totalling 60,000 images. The capsules are routinely used in Europe and we hope to be able to use them in Japan soon. However, in spite of these features, at present, the capsule is only effective in imaging the small intestine because this is the only place where the capsule can be controlled properly. Development of capsules for imaging the stomach and colon will take more time.

How is endoscope technology being improved?

We have developed some endoscopes capable of producing very-high-resolution images, but image quality is not the only issue. We are developing observation technology using specific light to enable enhanced imaging of light reflected and absorbed, and in certain cases fluorescence emitted, from blood vessels in the mucosa [a moist tissue lining that generates mucus]. This technology provides information about the interior of mucosa, such as signs of the early stages of cancer. Our EVIS LUCERA SPECTRUM endoscopic video imaging system was launched in June 2006. This system uses two-wavelength imaging to identify hard-to-detect lesions. A dedicated built-in optical filter generates blue (415 nm) and green (540 nm) bands of light, which illuminate mucosa and the haemoglobin in blood to produce extremely high-contrast images of blood vessels. Such images cannot be obtained using white light. The narrow-band light is the key. The blue light provides information about the surface and the green delves much deeper into the tissue. Furthermore, when combined with the extremely sensitive CCD incorporated videoscope, this system enables autofluorescence imaging of mucosa irradiated with blue light. In fact this is the world's first gastrointenstinal endoscope for fluorescence observation.

What role will photonics play in developing new endoscopes?

I think that imaging single molecules using endoscopes will become a standard part of diagnosis in the future. Endoscopes will be used for imaging molecules labelled with fluorescent markers and for monitoring drug delivery to specific cells. The use of infrared light will increase as this wavelength range enables extraction of information from the mucosa. We are working closely with doctors to develop such technology.

High-quality light sources enabling the selection of a wide range of wavelengths are still required. One of the main issues is that the light sources must act as point sources for efficient coupling when attached to an optical fibre. At the moment we use xenon sources. Unfortunately, white LEDs are not bright enough yet. We are also developing an ultrasmall spectrometer device that we attach directly to the tip of the endoscope (inside the body) and use for imaging optically labelled molecules in vivo. The spectrometer provides wavelength selectivity at the tip and thereby increased sensitivity compared with a spectrometer located at the entrance to the optical fibre. This is the endoscope equivalent of a fluorescence microscope. I think that molecular imaging using endoscopes will become an increasingly important means of diagnosis. I expect that the photonics community will make significant contributions to the development of this technology.

Adarsh Sandhu is a professor at Tokyo Institute of Technology.