Polarization-sensitive Fourier domain optical coherence tomography

Polarization sensitive Fourier domain optical coherence tomography (PS-FD-OCT) using fiber components with continuous polarization modulation is demonstrated. The incident polarized light is modulated by electro-optic modulator (EO modulator) synchronized with lateral B-scanning. By the incident polarization modulation and the polarization sensitive spectrometer, the depth-resolved Jones matrix image of biological sample can be measured. This method uses both polarization modulation method and Fourier transform method. In this paper, the algorithm is described and the phase retardation image of chicken breast muscle is measured.

To describe key developments of optical biometry and optical coherence tomography (OCT) for ophthalmic applications made by one of the pioneering research groups. Partial coherence interferometry (PCI) as the basic ranging technology for modern optical biometry and for OCT was introduced for biomedical applications in the 1980s. Later, Fourier domain (FD) OCT was introduced and demonstrated to provide superior sensitivity as compared to time domain OCT. Further developments comprised ultrahigh-resolution OCT and deep-penetration OCT at wavelengths of approximately 1050 nm. Important functional extensions comprise Doppler OCT/OCT angiography, polarization-sensitive OCT, and adaptive optics OCT. High-precision PCI biometry has found extensive applications in cataract surgery and in research on intraocular lens design. Optical coherence tomography, especially in the second-generation variant of FD OCT, is now indispensable for ocular diagnostics in general and for retinal diagnostics in particular; 1050 nm OCT shows improved penetration into deeper layers like the choroid. The contributions of the Vienna research group helped to establish PCI biometry and FD OCT as the gold standards in their respective fields.

Osteoarthritis is a prevalent medical condition that presents a diagnostic and therapeutic challenge to physicians today because of the inability to assess the integrity of the articular cartilage early in the disease. Polarization sensitive optical coherence tomography (PS-OCT) is a high resolution, non-contact imaging modality that provides cross-sectional images with additional information regarding the integrity of the collagen matrix. Using PS-OCT to image provides information regarding thickness of the articular cartilage and gives an index of biochemical changes based on alterations in optical properties (i.e. birefringence) of the tissue. We demonstrate initial experiments performed on specimens collected following total knee replacement surgery. Articular cartilage was imaged using a 1310 nm PS-OCT system where both intensity and phase images were acquired. PS-OCT images were compared with histology, and the changes in tissue optical properties were characterized. Analysis of the intensity images demonstrates differences between healthy and diseased cartilage surface and thickness. Phase maps of the tissue demonstrated distinct differences between healthy and diseased tissue. PS-OCT was able to image a gradual loss of birefringence as the tissue became more diseased. In this way, determining the rate of change of the phase provides a quantitative measure of pathology. Thus, imaging and evaluation of osteoarthritis using PS-OCT can be a useful means of quantitative assessment of the disease.

This Letter presents a spectral-domain, polarization-sensitive optical coherence tomography (PS-OCT) system, where the light collection from the two arms of the interferometer is performed exclusively using single-mode fibers and couplers, and the two orthogonal polarization components are sequentially detected by a single line camera. Retardance measurements can be affected by polarimetric effects because of fiber birefringence and diattenuation in fiber couplers. This configuration bypasses such issues by performing polarization selection before the collection fiber through the combination of a polarization rotator and a linear polarizer. Retardance calibration is achieved with a Berek compensator. Similar net retardance maps of a birefringent phantom are obtained for two different settings of induced fiber birefringence, effectively demonstrating the tolerance of the configuration to fiber-based disturbances.

Numerical analysis of one-shot full-range FD-OCT system based on orthogonally polarized light

Visual acuity is dependent on corneal shape and size. A minor variation in surface geometry can cause a deformation of corneal geometry, which affects its optical performance. In this work we demonstrate an algorithm for the simultaneous measurement of corneal tomography and topography with a traditional point-scanning Fourier domain optical coherence tomography (FD-OCT) system. A modified wavelength scanning interferometry (mWSI) algorithm enabled topographical evaluation of the surface with nanometer-scale resolution, which is superior to the micrometer-scale resolution of traditional OCT structural imaging. We validated the technique with an optically flat mirror, standard roughness gauges, and atomic force microscopy (AFM). The mirror results show nanometer-scale sensitivity (~3.5 nm), and the mWSI measurements were in good agreement (error ~5%) with the specifications of the roughness comparator and AFM, demonstrating the accuracy of the technique. Following validation, the measurements were made on pig corneas in situ at various artificially controlled intraocular pressures (IOP) and before and after cross-linking (CXL). The results show that the mean surface roughness increased by ~65% after removal of the epithelium in preparation for CXL but did not change as a function of IOP. The demonstrated method could be used for simultaneous measurement of tissue tomography with micrometer-precision and topography with nanometer-precision.

The conventional Fourier domain optical coherence tomography system requires single scanner for two dimensional cross-sectional image and two scanners for volumetric image. Parallel spectral domain optical coherence tomography has advantage of single scanner for volumetric image, while two dimensional cross-sectional images are obtained by parallel acquisition of illuminated line on sample using area camera. In this study, the industrial inspection of optical thin film on touch screen panels was demonstrated using parallel spectral domain optical coherence tomography. The cross-sectional and volumetric images were acquired to detect the internal sub layer defects in optical thin film which are difficult to observe using visual or machine vision based inspection methods. The results indicate the possible application of the proposed system in touch screen panels inspection for quality assurance of product at consumer end.

In this study, we have developed a phase-sensitive Fourier-domain optical coherence tomography system to simultaneously measure the in vivo inner ear vibrations in the hook area and second turn of the mouse cochlea. This technical development will enable measurement of intra-cochlear distortion products at ideal locations such as the distortion product generation site and reflection site. This information is necessary to un-mix the complex mixture of intra-cochlear waves comprising the DPOAE and thus leads to the non-invasive identification of the local region of cochlear damage.

This study was designed to investigate the effect of a single-drop instillation of different lacrimal substitutes on tear film thickness (TFT) assessed with optical coherence tomography in patients with mild to moderate dry eye disease. The study was performed in a randomized, double-masked, controlled parallel group design. Patients received a single dose of either unpreserved trehalose 30 mg/mL and sodium hyaluronate 1.5 mg/mL (TH-SH, Thealoz Duo), unpreserved sodium hyaluronate, 0.15% (HA, Hyabak) or sodium chloride, 0.9% (NaCl, Hydrabak) eye drops. Sixty patients finished the study according to the protocol. TFT was measured with a custom-built ultrahigh-resolution Fourier domain optical coherence tomography system providing a resolution of 1.2 μm. The mean TFT before treatment was 2.5 ± 0.4 μm. Ten minutes after instillation, TFT significantly increased in the TH-SH group from 2.4 ± 0.4 to 3.1 ± 0.9 μm (P < 0.01) and in the HA group from 2.4 ± 0.3 to 2.9 ± 0.5 μm (P < 0.01), whereas no significant change was observed in the NaCl group (from 2.6 ± 0.4 to 2.7 ± 0.4 μm, P = 0.76). The increase in TFT remained statistically significant up to 240 minutes after administration of TH-SH. In contrast, the increase in TFT after administration of HA was only statistically significant at 10, 20, and 40 minutes after drop instillation. The findings of this study indicate that single instillation of TH-SH and HA eye drops increases TFT in patients with dry eye disease. The data also indicate longer corneal residence of the TH-containing eye drops. The effect of multiple instillation and long-term use of artificial tears on TFT warrants further investigation.

We present a three-dimensional (3-D) endoscopic optical coherence tomography (OCT) system based on a dual axis microelectromechanical system (MEMS) mirror. The diameter of MEMS mirror was 1.2 mm and both axes were capable of scanning up to 20° (optical) at greater than 1 kHz with excellent linearity. The MEMS mirror was packaged in a machined acrylic endoscopic housing which provided mechanical protection and electrical interconnects as well as optical alignment of the MEMS device to a focusing GRIN lens. The endoscopic MEMS probe was integrated and tested with both a fiber-based time domain (TD) OCT system and Fourier domain (FD) OCT system. Combining the 2-axis lateral scanning of the MEMS device with an axial scan allowed 3-D volume images to be obtained at a rate of 3 frames/s for the TD system and 7 frames/s for the FD system. In the initial investigations, in vivo 3-D OCT images of a human finger as well as images of animal tissue such as healthy rabbit trachea, normal and cancerous regions of hamster cheek pouch tissue were obtained. These images allowed real-time diagnosis of diseased tissue and also clearly delineated important features and tissue structures.

In swept source polarization depth encoding polarization sensitive optical coherence tomography (PS-OCT), the laser jitter induces additional noise to the polarization sensitive measurement. In this Letter, we developed a numerical algorithm to correct the jitter phases based on the image data using the Mueller matrix calculus. The algorithm was demonstrated on in vivo retina imaging of a guinea pig with a custom-built PS-OCT system. The performance of the proposed algorithm was almost comparable to the conventional method of using a physical calibration signal. By not requiring a hardware generated calibration signal and k-clock, the proposed algorithm is useful to reduce the complexity and the cost of a polarization depth encoding PS-OCT system.

Radiofrequency ablation (RFA) is an important standard therapy for cardiac arrhythmias, but direct monitoring of tissue treatment is currently lacking. We demonstrate an RFA catheter integrated with polarization sensitive optical coherence tomography (PSOCT) for directly monitoring the RFA process in real time. The integrated RFA/OCT catheter was modified from a standard clinical RFA catheter and includes a miniature forward-viewing cone-scanning OCT probe. The PSOCT system was validated with a quarter-wave plate while the RFA function of the integrated catheter was validated by comparing lesion sizes with those made with an unmodified RFA catheter. Additionally, the integrated catheter guided catheter-tissue apposition and monitored RFA lesion formation in cardiac tissue in real time. The results show that catheter-tissue contact can be characterized by observing the features of the blood and tissue in the acquired OCT images and that RFA lesion formation can be confirmed by monitoring the change in phase retardance in the acquired PSOCT images. This system demonstrates the feasibility of an integrated RFA/OCT catheter to deliver RF energy and image the cardiac wall simultaneously and justifies further research into use of this technology to aid RFA therapy for cardiac arrhythmias.

The lateral resolution of Fourier domain optical coherence tomography (FD-OCT) systems is limited by the depth of focus that can be achieved over the desired imaging depth at the chosen wavelength. I present a solution in which multiple beams focused at different depths are scanned together, so that a mosaic image can be produced, with at least double the resolution possible from a single beam system. Side-benefits also arise from the ability to combine data from each beam to improve signal-to-noise. The theory of this approach is discussed, advantages, and also the practical realisation in a variety of ex-vivo and in-vivo OCT imaging probes, together with results from a number of applications.

Optical coherence tomography (OCT) is a non-invasive interferometric imaging technique offering millimeter penetration depths of a sample with outstanding axial resolution. In this work a parallel Fourier domain optical coherence tomography (FD OCT) system is presented which records full tomograms of the sample structure in parallel. A fully parallel FD OCT system allows fast real time imaging of biological tissues.

Blood flow measurement with spectrometer-based Fourier domain optical coherence tomography (FD-OCT) is limited by the motion-induced signal fading and the resulting reduction of flow sensitivity. Therefore, we have numerically simulated the signal power decrease of an obliquely moved scattering layer as a function of the absolute sample velocity composed of an axial and transverse component. In contrast to the prevalent expectance, the resulting signal damping is not only the sum of axial and transverse effect. In this study, we take advantage of the signal decay and present the feasibility to quantify high flow velocities at which the standard Doppler OCT does not work any longer. For the validation of our approach, a flow phantom model consisting of a 1%-Intralipid solution and a 320 &mu;m glass capillary was used. With this phantom study, depth-resolved flow was visualized and the quantitative velocities were extracted from the OCT images without phase information.