We report a Talbot bands-based optical coherence tomography (OCT) system capable of producing longitudinal B-scan OCT images and en-face scanning laser ophthalmoscopy (SLO) images of the human retina in-vivo, with various degrees of simultaneity

Marques

Podoleanu

Potsaid

Wojtkowski

English

Marques, M.J.

Bradu, A.

Podoleanu, A.G.

Kent Academic Repository

Optical Coherence Tomography and ScanningLaser Ophthalmoscopy: approaches todual-channel retinal tissue imagingManuel J. Marques*, Adrian Bradu, and Adrian Gh. PodoleanuApplied Optics Group, School of Physical Sciences, University of KentCanterbury CT2 7NH, United Kingdom*mjmm2@kent.ac.ukAbstract: We report a Talbot bands-based optical coherence tomography (OCT) systemcapable of producing longitudinal B-scan OCT images and en-face scanning laser ophthal-moscopy (SLO) images of the human retina in-vivo, with various degrees of simultaneity.© 2014 Optical Society of AmericaOCIS codes: (110.4190) Imaging systems: Multiple imaging; (110.4500) Imaging systems: Optical coherence to-mography; (170.4460) Medical optics and biotechnology: Ophthalmic optics and devices;Due to a higher sensitivity and speed than their time domain (TD) counterpart, spectral domain (SD) methodsdominate the OCT technology of eye imaging [1]. The SD-OCT methods produce fast A-scans, which are used tocreate real time cross-section (B-scan) images.(a) (b)Fig. 1: (a) Schematic representation of the set-up devised, and (b) some of the results obtained with it: images of theretina of a volunteer taken from the two channels, yielding an en-face SLO image (top) and a B-scan OCT image(bottom), with a correspondence of features between the two being emphasized.For several reasons, an en-face image is also required when imaging the retina in the human eye. These reasons mayinclude the guidance of the OCT examination, or even the correction of motion artifacts created by imaging in-vivotissues with a low degree of fixation. SD-OCT methods allow the creation of such images, however when scanning overthe two orthogonal directions it is inevitable to obtain a full volumetric image, which will have to be post-processed,the image being then displayed static to the user.Several other techniques are available to generate an en-face image without resorting to a SD-OCT based method,which show the interest for presenting such images alongside the SD-OCT investigation delivering B-scans, with agood pixel-to-pixel correspondence between the two frames.Our method [2] involves a SD-OCT system (schematically described in Fig. 1a) whose spectrometer system has beenmodified to take advantage of Talbot bands [3]: the degree of overlapping between the two beams returning from theinterferometer on their way to the diffractive medium can be controlled and employed to shift the SD-OCT sensitivityprofile maximum away from the interferometer’s alignment point. This implementation involves a beam-splitter BSto couple the two beams, and by placing a specially-devised filter over the beam path that would not otherwise beused, one is capable of spatially separate the two components, therefore isolating the optical power returning from thesample and directing it to a highly-sensitive detector, forming a confocal image which is acquired in tandem and withthe same interface optics as the OCT image. Given that the system in question is used to image human retinal tissue,the confocal channel will yield images similar to the ones produced by a scanning laser ophthalmoscope (SLO). Thetwo frames are then acquired: an en-face SLO image and a depth profile (B-scan OCT), whose lateral position can becontrolled by means of a cursor overlaid on the SLO frame.With adequate acquisition and control systems in place, it is then possible to acquire these two frames with varyingdegrees of simultaneity and pixel-to-pixel correspondence. The constraints present are purely related to the speeds ofacquisition and scanning provided by current technology: the fastest CMOS camera in near-IR available is capable ofperforming up to 312,500 spectral reads per second [4] and current galvo-scanner technology (preferred over fasterscanning techniques, such as resonant scanners, to implement some of the operating modes described in [2]) cannotexceed a scanning rate of 1 kHz . One is capable of true simultaneity in terms of image acquisition and refresh if thetransversal range is sacrificed; conversely, if larger transversal ranges are desired the two channels will have to be readsequentially.Figure 1b features some of the results obtained with the system described. In all pairs of frames the retina fromthe same volunteer is being imaged in different regions, with varying lateral sizes (from 2.6 to 5 mm). The Talbotbands allow for an improvement of the OCT channel sensitivity at larger depths (measured up to 6 dB), thus reducingthe occurrence of mirror terms by reducing the need to place the sample very close to the alignment point of theinterferometer.With this method it is then possible to achieve simultaneous imaging of the two channels within the hardware-relatedconstraints. This will allow the clinician to have more information when performing an investigative analysis, as onecan guide the OCT-based depth profiling using a “bird’s eye” view provided by the SLO imagery.AcknowledgementsM. J. Marques acknowledges the support of the University of Kent through his University Scholarship. A. Braduand A. Gh. Podoleanu acknowledge the support of the European Research Council (ERC) (http://erc.europa.eu) CO-GATIMABIO 249889. A. Podoleanu is also supported by the NIHR Biomedical Research Centre at Moorfields EyeHospital NHS Foundation Trust and UCL Institute of Ophthalmology.References1. M. Wojtkowski, R. Leitgeb, A. Kowalczyk, T. Bajraszewski, and A. F. Fercher, “In vivo human retinal imagingby Fourier domain optical coherence tomography.” J. Biomed. Opt. 7, 457–63 (2002).2. M. J. Marques, A. Bradu, and A. G. Podoleanu, “Towards simultaneous Talbot bands based optical coherencetomography and scanning laser ophthalmoscopy imaging,” Biomed. Opt. Express 5, 1428–1444 (2014).3. A. Gh. Podoleanu, “Unique interpretation of Talbot Bands and Fourier domain white light interferometry,” Opt.Express 15, 9867–9876 (2007).4. B. Potsaid, I. Gorczynska, V. J. Srinivasan, Y. Chen, J. Jiang, A. Cable, and J. G. Fujimoto, “Ultrahigh speedspectral/Fourier domain OCT ophthalmic imaging at 70,000 to 312,500 axial scans per second,” Opt. Express16, 15149–15169 (2008).

In vivo human retinal imaging by Fourier domain optical coherence tomography.”

Marques acknowledges the support of the University of Kent through his

Podoleanu, “Unique interpretation of Talbot Bands and Fourier domain white light interferometry,”

Towards simultaneous Talbot bands based optical coherence tomography and scanning laser ophthalmoscopy imaging,”

Ultrahigh speed spectral/Fourier domain OCT ophthalmic imaging at 70,000 to 312,500 axial scans per second,” Opt.

Optical coherence tomography and scanning laser ophthalmoscopy: Approaches to dual-channel retinal tissue imaging

Manuel J. Marques

Adrian Bradu

Adrian Gh. Podoleanu

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Optical Coherence Tomography and Scanning Laser Ophthalmoscopy: approaches to dual-channel retinal tissue imaging

http://kar.kent.ac.uk/49279/1/summary_submitted.pdf

Optical coherence tomography and scanning laser ophthalmoscopy: Approaches to dual-channel retinal tissue imaging

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