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April 20th 2019

Due to the ever-advancing possibilities of medical interventions the need for improved diagnostics is increasing as well. Many techniques are available to examine the body without actually having to penetrate it. Each of these methods has its own penetration depth and image resolution as well as a mechanism that ensures a contrast on the images. X-ray imaging, imaging with magnetic resonance (MRI), and ultrasonography look very deep into a body, but have a limited resolution. Optical coherence tomography (OCT) makes high-resolution images, down to a single cell, but has a penetration depth of just 1.5 to 2 mm. By inserting an OCT catheter into the body the method can still be used to image the epithelial layers of the lungs, oesophagus and intestines. The majority of cancers develop in these layers.

Interference technique
OCT makes use of the interference of broadband light in a Michelson-interferometer. Using this approach, the researchers can investigate the light that reflects to the detector via the tissue. In recent years this technique has been fundamentally improved, as a result of which the signal for a given quantity of light has increased by at least a factor of one hundred. By spectrally separating the light detected, the shot noise (a minimum quantity of noise that is always present) can be reduced by more than two orders of magnitude. A single photon reflected by the tissue can therefore be detected.

To make optimal use of this development, with which more than one hundred images per second can be made, the researchers from this programme have developed a catheter in which a mirror makes more than six thousand revolutions per minute to scan the tissue. The catheter contains a micro motor with a diameter of 1 mm.

In this film the use of the catheter in the lungs of a living goat can be seen.

Tumours break down biological tissues, especially collagen, an important component of connective tissue. Collagen changes the polarisation of light. The OCT method also registers such changes in light polarisation and can therefore image the breakdown of collagen. In the past year the researchers have made images of muscle tissue and ligaments using this system.