Skin deep

A technique developed to detect faults in fibre-optic networks has been transformed into a system that can see through skin and produce moving images of organ surfaces. Developers of the technique at Manchester University and Manchester Children’s University Hospitals say it could remove the need for biopsies for some forms of cancer.

The technique, optical coherence tomography (OCT), relies on the translucency of skin and organ membranes and the quirks of wave physics, said research leader Mark Dickinson, a photon physics specialist at Manchester University. OCT developed in Manchester differs from other OCT systems in that it is faster, produces images with a higher resolution and is smaller than other OCT packages.

‘We use a broad-bandwidth light source which shines on the object you want to investigate, but before it reaches the object, it is split, and half of it goes down a reference path,’ said Dickinson. ‘You combine the light that is reflected back from each path to set up an interferometer. But because it’s a broad bandwidth, the only position in which you get a signal is when the length of the two beams is exactly the same.’

Controlling the length of the reference beam therefore controls the depth from which the object beam sends back images. ‘Vary that path length, and you dictate which plane within the object that you’re looking at,’ said Dickinson.

The depth to which the beam can penetrate flesh depends on the tissues it is being used to study: some tend to scatter light, and are therefore relatively impenetrable, whereas others absorb light, and are therefore easier to see into.

‘Typically, you can look down to 2-4mm, which doesn’t sound much but gives valuable information,’ said Dickinson. Better signal-processing techniques have improved the resolution possible through OCT, he added, which has led to its adoption by medics: resolutions of about 10 microns are possible.

Because the technique produces an image of a plane within the body, it is most useful for a method of study called optical sectioning, said Dickinson. ‘If you wanted to look at a depth within the skin or other tissues, you’d normally do a biopsy, then section the biopsy sample by slicing it thinly, and look at the slices under a microscope. This technique gives the same information without the need for a biopsy.’

Although the device, which is pistol-shaped and sized, can be used through the skin, it is more likely to be used inside the body to image organs. For this, Dickinson said, it would be used in conjuction with a fibre-optic probe that would be inserted into the body in a minor surgical procedure.

‘This would allow you to image membranes deep inside the body, and it will also mean you can see through membranes that you really don’t want to puncture,’ he said.

Another big advantage of OCT is that it can provide high-resolution moving images of near-video quality in real time, said Dickinson. ‘You can look at how drugs are affecting a membrane or organ being treated, as it happens, actually seeing the effect the drug is having.’

Paul Brenchley, director of the renal research labs at Manchester Children’s University Hospital, is working on this aspect of the project, and the teams are working on protocols for a clinical trial to begin this summer.

Although OCT is a versatile technique, Dickinson’s device can’t be used for all possible applications, he stressed. ‘It’s not like an X-ray machine; the light source, detector, fibres and so on are very specific to the particular application. So we’re targeting a number of applications and developing the technology accordingly.’