Evaluation of effective noise bandwidth for broadband optical coherence tomography operation.

Key noise parameters in optical coherence tomography (OCT) systems employing splitters with a nonflat spectral response are evaluated using a supercontinuum fiber laser source with a spectrum of 450 nm-1700 nm and a time domain OCT architecture based on 1300 nm fiber splitters. The spectral behavior of the splitter leading to balanced detection is measured over a range of 300 nm. Because of spectrally different signals at the balanced detector input a residual excess photon noise term results. A rigorous treatment of this noise term [Appl. Opt.43, 4802 (2004)] introduced two new quantities that take into account the spectral properties of the coupler. In this report, we have evaluated these two noise bandwidth quantities and comparatively assessed the noise behavior predicted by the classical theory with the theory based on the two new noise bandwidths. We show that under certain operating parameters, the additional excess photon noise is twice that predicted for a coupler with a flat spectral response.

Multidimensional en-face OCT imaging of the retina.

Fast T-scanning (transverse scanning, en-face) was used to build B-scan or C-scan optical coherence tomography (OCT) images of the retina. Several unique signature patterns of en-face (coronal) are reviewed in conjunction with associated confocal images of the fundus and B-scan OCT images. Benefits in combining T-scan OCT with confocal imaging to generate pairs of OCT and confocal images similar to those generated by scanning laser ophthalmoscopy (SLO) are discussed in comparison with the spectral OCT systems. The multichannel potential of the OCT/SLO system is demonstrated with the addition of a third hardware channel which acquires and generates indocyanine green (ICG) fluorescence images. The OCT, confocal SLO and ICG fluorescence images are simultaneously presented in a two or a three screen format. A fourth channel which displays a live mix of frames of the ICG sequence superimposed on the corresponding coronal OCT slices for immediate multidimensional comparison, is also included. OSA ISP software is employed to illustrate the synergy between the simultaneously provided perspectives. This synergy promotes interpretation of information by enhancing diagnostic comparisons and facilitates internal correction of movement artifacts within C-scan and B-scan OCT images using information provided by the SLO channel.

Simultaneous OCT/SLO/ICG imaging.

PURPOSE: To evaluate how information from combined coronal optical coherence tomography (OCT) and confocal laser scanning ophthalmoscopy (SLO) with integrated simultaneous indocyanine green (ICG) dye angiography can be used in the diagnosis of a variety of macular diseases. METHODS: A compact chin-rest-based OCT/confocal imaging system was used to produce the OCT image and excite the fluorescence in the ICG dye. The same eye fundus area can be visualized with coronal (C-scans, en face) OCT and ICG angiography simultaneously. Fast T scanning (transverse scanning, en face) was used to build B- or C-scan OCT images along with confocal SLO views, with and without ICG filtration. The OCT, confocal SLO and ICG fluorescence images were simultaneously presented in a three-screen format. A live mixing channel overlaid the ICG sequence on the coronal OCT slices in a fourth panel for immediate comparison. RESULTS: Thirty eyes were imaged. The pathologic conditions studied included classic and occult neovascular membranes, vascularized RPE detachments, polypoidal choroidal vasculopathy, traumatic choroidal rupture, diabetic maculopathy, central serous retinopathy, and macular drusen. Images were evaluated with special attention toward identifying novel relationships between morphology and function revealed by the superimposition of the studies. CONCLUSIONS: Simultaneous visualization of an en face (coronal, C-scan) OCT image and of an ICG angiogram, displayed side by side and superimposed, permits more precise correlations between late fluorescence accumulation with structures deep to the retinal surface at the retina-choroid interface. The multiplanar scanning also permits immediate B-scan OCT cross-sectional views of regions of abnormal fluorescence. The paper demonstrates the synergy between the two types of studies, functional and anatomic, in providing a more complete view of the pathologic condition.

Investigations of the eye fundus using a simultaneous optical coherence tomography/indocyanine green fluorescence imaging system.

We develop a dual-channel optical coherence tomography/indocyanine green (OCT/ICG) fluorescence system based on our previously reported ophthalmic OCT/confocal imaging system. The confocal channel is tuned to the fluorescence wavelength range of the ICG dye and light from the same optical source is used to generate the OCT image and to excite the ICG fluorescence. The system enables the clinician to visualize simultaneously en face OCT slices and corresponding ICG angiograms of the ocular fundus, displayed side by side. C-scan (constant depth) and B-scan (cross section) images are collected by fast en face scanning (T-scan). The pixel-to-pixel correspondence between the OCT and angiography images enables the user to precisely capture OCT B-scans at selected points on the ICG confocal images.

Simultaneous optical coherence tomography--Indocyanine Green dye fluorescence imaging system for investigations of the eye's fundus.

We have developed a dual-channel optical coherence tomography-Indocyanine Green dye (OCT-ICG) fluorescence system based on a previously reported ophthalmic OCT confocal imaging system. The confocal channel is tuned to the fluorescence wavelength range of the ICG, and light from the same optical source is used to generate the OCT image and to excite the ICG fluorescence. The system enables the clinician to visualize simultaneously en face OCT slices and corresponding ICG angiograms of the ocular fundus, displayed side by side. C-scan (constant depth) and B-scan (cross section) images are collected by a fast en face scan (T scan). The pixel-to-pixel correspondence between the OCT and angiography images allows the user to capture OCT B scans precisely at selected points on the ICG confocal images.

Sequential optical coherence tomography and confocal imaging.

We report a system capable of sequentially acquiring two en-face images of different depth resolutions. The two images are generated by use of different principles, optical coherence tomography (OCT) and confocal microscopy, and have depth resolutions, at present, of better than 20 microm and over 0.12 mm, respectively. The lower-depth-resolution image is ideal for target positioning before collection of stacks of en-face OCT images. Switching between the two types of image by flipping an opaque screen in the reference arm, coupled with self-adjusting gain operation of avalanche photodiodes in the receiver. We illustrate the usefulness of the system by imaging a leaf and an optic nerve in vivo.

Combined multiplanar optical coherence tomography and confocal scanning ophthalmoscopy.

We demonstrate the clinical application of a multiplanar imaging system that simultaneously acquires en face (C-scan) optical coherence tomography (OCT) and the corresponding confocal ophthalmoscopic images, along with cross-sectional (B-scan) OCT at specifiable locations on the confocal image. The advantages of the simultaneous OCT and confocal acquisition as well as the challenges of interpreting the C-scan OCT images are discussed. Variations in tissue inclination with respect to the coherence wave surface alter the sampling of structures within the depth of the retina, producing novel slice orientations that are often challenging to interpret. We have evaluated for the first time the utility of C-scan OCT for a variety of pathologies, including melanocytoma, diabetic retinopathy, choroidal neovascular membrane, and macular pucker. Several remarkable new aspects of clinical anatomy were revealed using this new technique. The versatility of selective capture of C-scan OCT images and B-scan OCT images at precise points on the confocal image affords the clinician a more complete and interactive tool for 3-D imaging of retinal pathology.