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Tech advancements lead to improved OCT imaging apps

Posted: 28 Jun 2011     Print Version  Bookmark and Share

Keywords:optical coherence tomography  OCT  retinal pathology 

Over the last several years, the technology that enables optical coherence tomography (OCT) has significantly improved. When it first debuted, OCT was a natural fit for ophthalmologists to utilise the near-infrared light-based technology to create very high-resolution images of the far reaches of the eye. Since eye tissue is translucent, OCT can provide images revealing retinal pathology and can also be used to diagnose and monitor many retinal diseases like glaucoma and macular edema. Now, a raft of medical applications for OCT has emerged and several exciting new applications are in development.

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Figure 1: Example of OCT instrument utilised by an ophthalmologist.

What is OCT?
OCT imaging is analogous to ultrasound, employing reflected near-infrared light as the imaging medium to create its image instead of reflected sound. The near infrared source (typically 800 1300nm) is split into two paths. One path is applied to the sample tissue while the other to a reference mirror. Interferometry is used to coherently gate the back scattered reflections from the sample tissue with the light from the reference arm as the sample arm is scanned across the tissue. Digital signal processing algorithms are performed on the coherently gated light to achieve a depth-resolved axial scan. Stacking such scans results in 2D or 3D images of the tissue. OCT can typically resolve an image to a tissue depth of three to five millimeters (mm) at a very high resolution of less than 10 microns.

A key component in OCT systems, the reference mirror, was mechanical in first-generation time domain systems. As a result, the machines were slow and the resolution of the images was limited. Second-generation OCT systems replaced the mechanical reference mirror with a fixed mirror and employed a spectrometer and powerful digital signal processing techniques like Fast Fourier Transforms (FFT), magnitude computation, and log compression to resolve the embedded depth information and combine it with the lateral scan data in real time. This enabled dramatically reduced imaging times along with improved image resolution.

Biomedical apps of OCT
Today, the majority of OCT medical systems in place are used for ophthalmologic purposes, however, several new and promising applications have emerged over the last few years. For example, Ear/Nose/Throat (ENT) physicians and pediatricians may make up a new group of doctors who adopt OCT technology as a diagnostic tool. Typically, the otoscope is employed by physicians to examine the ear, ear canal and tympanic membrane for signs of redness which would indicate a bacterial infection. OCT could improve the certainty of diagnosis by imaging surface skin as well as subcutaneous membranes to determine if infection causing bacteria is present. Following several doses of an antibiotic, OCT systems could then be used to analyse whether the antibiotic has been effective. If the infecting bio-film has been removed, the patient could cease taking the antibiotic.

Other emerging OCT medical applications include dental diagnostic systems and inter-operative uses of the technology. Dentists could employ OCT imaging to identify early stage cavities and certain gum disorders, which might otherwise be missed by x-rays and visual inspection, resulting in more effective preventive procedures.

As an inter-operative technique, OCT could analyse the presence or absence of cancer during the surgical procedure to remove a tumor. Typically, surgeons remove tissue around a tumor with the hope that all cancer cells have been removed. The removed tumor along with its surrounding margin tissue is then analysed in a pathology lab typically requiring weeks to obtain a written report after the operation. Because OCT images are at the same resolution as histology/pathology, an OCT system in the operating room could enable the surgeon during the procedure to exactly know how much tissue to remove with exacting safe margin. This would eliminate costly and painful follow-up surgeries required to remove the missed cancer tissue. OCT technology enables physicians to see at histology resolution levels in real time so they can make better decisions during the first surgical procedure to remove a tumor.

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