PhD on Optical Coherence Tomography in Visible

I am proposing to use the PhD position to research and develop solutions to overcome some of the challenges faced by Optical Coherence Tomography (OCT) instruments when driven by optical sources emitting in the visible (VIS) spectral range, for imaging the human eye (more specifically the retina), in-vivo. The main advantage of developing VIS-OCT instruments is due to their diagnostic potential allowed by their improved lateral and axial resolution when imaging the eye compared to the technology currently used with near-infrared light sources.

One of the challenges to be faced with using a visible range light source is the attenuation of light when the OCT imaging technique is applied in vivo and in particular, the eye. The biological tissue light must travel across the eye to reach the retina, is characterised by a quite large optical attenuation coefficient, and therefore the number of photons reaching the retina is low, and subsequently the images obtained are much poorer than those obtained using near-infrared light sources. Image quality is also affected by low levels of back-scattering of visible light on tissue, and the fact that a lower limit of optical power from the light source entering the eye is imposed in comparison to a near-infrared source which contributes to a large noise level in the OCT images obtained.

Another aspect of the imaging technique which would be addressed is the way the image quality is determined by the use of camera-based OCT systems. Swept source OCT gives a better range of axial imaging in comparison to camera-based due to their narrow instantaneous coherence length. However swept sources are not available for the visible range and therefore this is an area where improvements need to be made to help the potential for visible light OCT to be used in new diagnostic technology.

Addressing these issues to improve visible light OCT for biomedical imaging would enable us to produce high resolution images of the human retina (of the static tissue) and OCT angiography images of the micro-vasculature of the back of the eye. Researching the imaging technique would also allow development of an imaging instrument which is easier to build than those which do not use a visible light source, as well as the imaging method to provide potential for new spectroscopic techniques as a result.