An international team of researchers has made an advancement to the technique of optical coherence tomography (OCT) that holds implications for ophthalmology, dermatology, cardiology, and the early detection of cancer. The work was conducted by University of Adelaide, Technical University of Denmark (DTU), Aerospace Corp., and University of St. Andrews. One of the current challenges in OCT is the scattering of light in tissue that obscures information at depth. OCT relies on light being backscattered within the sample. This occurs when light passes between different layers of cells, for example. Getting a discernible signal from depths beyond 1 mm is enormously challenging due to several factors, including signal from intervening tissue. Spatially offset OCT demonstrates reduced attenuation with increasing offset in layered phantoms. The research enabled the scientists to redefine their view on OCT signal formation and, in theory, to use the adapted technique for improved diagnostics. Courtesy of University of St. Andrews. The current work challenges the conventional wisdom that says an OCT signal is dominated by light and has undergone a single backscattering event, whereas light scattered many times is detrimental to image formation. The researchers found an alternative viewpoint — that selective collection of multiple scattered light can lead to improved image contrast at depth, particularly in highly scattering samples. They showed how this could be implemented with minimal additional optics by displacing the light delivery and collection paths. The researchers introduced an original geometry that decouples the incident and collection fields by introducing a spatial offset between them, leading to preferential collection of multiple scattered light. A wave optics-based theoretical framework supports the experimentally demonstrated improvement in contrast, and the effective signal attenuation can be reduced by more than 24 dB. Notably, a ninefold enhancement in image contrast at depth is observed in scattering biological samples. The team dubbed the method spatially offset OCT (SO-OCT) and demonstrated it in two experimental setups. The first is a homebuilt system and requires the translation of a single optical component to achieve enhancement on both image quality and depth penetration. The second setup is an adaptation of a commercially available frequency domain OCT system with a custom-built add-on enabling spatially offset detection, which can be readily incorporated into many existing OCT systems. According to Peter Andersen, co-corresponding author from DTU, the research and demonstrations revealed insights that will enable practitioners of the method to extract more information and to improve diagnosis of disease. The research was supported by funding from the U.K., the EU, and the Australian Research Council. The research was published in Science Advances (www.doi.org/10.1126/sciadv.adh5435).
