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Title: Point-spread function phantoms for optical coherence tomography.

Author: Tomlins, P H, Ferguson, R A, Hart, C, Woolliams, P D
(An asterisk (*) after an author's name indicates a non-NPL author)

Source: OP 2, August 2009
ISSN: 1754-2944

Abstract: Optical coherence tomography (OCT) is maturing as a powerful imaging modality in medical and non-medical fields. As the use of this technique increases, so too do the requirements for consistent and robust characterisation methods for fundamental system performance. An important baseline metric in this respect is the system 3D point-spread function (PSF) that ultimately limits the optical resolution of an instrument. In this article, we present a theoretical description of the OCT lateral and axial PSF and outline design considerations for constructing PSF measurement phantoms using clear resin, doped with a low density of micro-spheres. The theoretical treatment identifies a v2 enhancement of the lateral resolution due to re-combination of the reference and sample fields. Furthermore, we study the potential PSF degrading effects of optical dispersion and spherical aberration. It is shown that the dispersion coefficient of any material chosen for PSF phantoms must be carefully considered with respect to the OCT coherence length. Additionally, it is found that spherical aberation due to refraction at the surface of a phantom becomes important for numerical apertures of 0.4 or more at depths greater than 0.5 mm, which may be important in optical coherence microscopy. An important design consideration for PSF phantoms is the target `point' size, that is required to be less than 15% of the PSF full-width at half maximum. The phantoms consist of a clear epoxy resin, doped wih a low density of monodispersed silica micro-spheres. The preparation, measurement and analysis of such phantoms is discussed and we demonstrate how these phantoms can be used to characterise the PSF of an OCT instrument throughout the B-Scan image plane, yielding quantitative information about the spatial distribution of resolution.

Document Type: NPL Report

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