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OCT aids doctors in theatre

08 Aug 2007

Optical coherence tomography can aid surgeons who have to decide where the boundary between cancerous and non-cancerous tissue lies.

Clinicians could soon be using turnkey optical coherence tomography (OCT) systems to help establish the boundaries of cancerous tissue during an operation, thanks to work that is ongoing at UK-based start-up Michelson Diagnostics (MDL). After a successful pilot trial of its technology, MDL is now planning more extensive clinical studies.

"The aim of our initial study was to prove how useful OCT could be in vivo," Gordon McKenzie, MDL's Applications Director, told optics.org. "We now know that we can identify clinical features in real time using our OCT system and give information directly at the time of the operation. What you really want to look at is what you are leaving behind in the patient."

OCT is the direct optical analogue of ultrasound and builds up an image of optical reflections caused by a change in the refractive index. MDL's first product is a microscope-based system that has been designed for researchers who wish use OCT.

"Our initial study was done ex vivo on tissue that was removed in the normal course of procedures," said McKenzie. "It was used on the excised tissue before it was sent to pathology labs and has not yet been used been used directly on patients."

The pilot study was done at Gloucestershire Royal Hospital where the team believes OCT is particularly promising for work on lymph nodes and Barrett's oesophagus. Work is now ongoing to build up an understanding of exactly what can and cannot be seen with OCT and further double blind trials are in the pipeline.

At MDL, the focus is attracting further funding that will allow the company to develop an in vivo system. McKenzie is optimistic that an in vivo system will be available by the second quarter of 2008.

Where MDL believes it has the edge over its competition is an optical design that gives a resolution of less than 10 microns. A conventional OCT system uses a broadband source and a Michelson interferometer. The interferometer's reference mirror is coupled to a laterally scanning galvanometer, which builds up an image a small volume of tissue.

"We keep the mirror still and use a swept source that scans between 1260 and 1360 nm at a rate of 10 kHz," explained McKenzie. "We collect information in the frequency domain and Fourier Transform it to give a signal that is proportional to depth. Our setup means you collect information about the entire depth throughout the sweep of the laser giving better signal to noise and eliminating a moving part."

MDL has taken this idea a step further and its microscope system contains a single interferometer that has four parallel optical channels. "The channels can be focused to different depths," said McKenzie. "Each channel collects the whole image but is in tight focus at a particular depth. We knit the four channel images and end up with an image that has twice the lateral resolution compared with an image that was collected and focused over the whole depth. We have plans to scale this up further, with six channels or more giving a further resolution boost."

Jacqueline Hewett is editor of Optics & Laser Europe magazine.

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