Abstract
This paper describes a digital method that is capable of automatically focusing optical coherence tomography (OCT) en face images without prior knowledge of the point spread function of the imaging system. The method utilizes a scalar diffraction model to simulate wave propagation from out-of-focus scatter to the focal plane, from which the propagation distance between the out-of-focus plane and the focal plane is determined automatically via an image-definition-evaluation criterion based on information entropy theory. By use of the proposed approach, we demonstrate that the lateral resolution close to that at the focal plane can be recovered from the imaging planes outside the depth of field region with minimal loss of resolution. Fresh onion tissues and mouse fat tissues are used in the experiments to show the performance of the proposed method.
Highlights
Optical coherence tomography (OCT) [1,2] is a relatively novel imaging modality that allows for non-invasive, cross-sectional imaging of the turbid biological tissues with micrometer resolution and with an imaging depth of up to 2 mm below the surface
Because of the use of the optical lens to focus the probe beam, only the OCT image that falls within the depth of field (DOF) exhibits the desired lateral resolution, whereas the OCT image that falls outside the DOF region is blurred laterally
Complex signals of each x-y/en face frame is considered as the optical sources in our model; and they are digitally focused onto the focal plane using diffraction Eq (9), where the distance z between de-focal plane and focal plane is determined by searching the minimal information entropy of the recovered images
Summary
Optical coherence tomography (OCT) [1,2] is a relatively novel imaging modality that allows for non-invasive, cross-sectional imaging of the turbid biological tissues with micrometer resolution and with an imaging depth of up to 2 mm below the surface. The vectorfield model [18] and ISAM [19] and angular spectrum diffraction method [20] do not require a prior knowledge about the optical parameters; they do require knowing the position of the beam focus before image reconstruction. It is not ideal, the PSF function may be measured by the use of a specialized phantom in a well-controlled separate experiment. We demonstrate the effectiveness of the proposed method by the use of fresh onion samples and fat tissues excised from mice
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