Simplified method for polarization-sensitive optical coherence tomography

We report a method for extracting the birefringence properties of biological samples with micrometer-scale resolution in three dimensions, using a new form of polarization-sensitive optical coherence tomography. The method measures net retardance, net fast axis, and total reflectivity as a function of depth into the sample. Polarization sensing is accomplished by illumination of the sample with at least three separate polarization states during consecutive acquisitions of the same pixel, A scan, or B scan. The method can be implemented by use of non-polarization-maintaining fiber and a single detector. In a calibration test of the system, net retardance was measured with an average error of 7.5 degrees (standard deviation 2.2 degrees ) over the retardance range 0 degrees to 180 degrees , and a fast axis with average error of 4.8 degrees over the range 0 degrees to 180 degrees .     

Absolute fast axis determination using non-polarization-maintaining fiber-based polarization-sensitive optical coherence tomography

We report on a new calibration technique that permits the accurate extraction of sample Jones matrix and hence fast-axis orientation by using fiber-based polarization-sensitive optical coherence tomography (PS-OCT) that is completely based on non-polarization-maintaining fiber such as SMF-28. In this technique, two quarter-wave plates (QWPs) are used to completely specify the parameters of the system fibers in the sample arm so that the Jones matrix of the sample can be determined directly. The device was validated on measurements of a QWP and an equine tendon sample by a single-mode fiber-based swept-source PS-OCT system.     

Optic axis determination accuracy for fiber-based polarization-sensitive optical coherence tomography

We present a generalized analysis of fiber-based polarization-sensitive optical coherence tomography with an emphasis on determination of sample optic axis orientation. The polarization properties of a fiber-based system can cause an overall rotation in a Poincaré sphere representation such that the plane of possible measured sample optic axes for linear birefringence and diattenuation no longer lies in the QU-plane. The optic axis orientation can be recovered as an angle on this rotated plane, subject to an offset and overall indeterminacy in sign such that only the magnitude, but not the direction, of a change in orientation can be determined. We discuss the accuracy of optic axis determination due to a fundamental limit on the accuracy with which a polarization state can be determined as a function of signal-to-noise ratio.     

Two-dimensional depth-resolved Mueller matrix of biological tissue measured with double-beam polarization-sensitive optical coherence tomography

A double-beam polarization-sensitive system based on optical coherence tomography was built to measure the Mueller matrix of scattering biological tissue with high spatial resolution. The Jones matrix of a sample can be determined with a single scan and subsequently converted into an equivalent nondepolarizing Mueller matrix. As a result, the system can be used to measure the Mueller matrix of an unstable sample, such as soft tissue. The polarization parameters of a porcine tendon, including magnitude and orientation of birefringence and diattenuation, were extracted by decomposition of the measured Mueller matrix.     

Simulation of polarization-sensitive optical coherence tomography images by a Monte Carlo method

We introduce a new Monte Carlo (MC) method for simulating optical coherence tomography (OCT) images of complex multilayered turbid scattering media. We demonstrate, for the first time of our knowledge, the use of a MC technique to imitate two-dimensional polarization-sensitive OCT images with nonplanar boundaries of layers in the medium like a human skin. The simulation of polarized low-coherent optical radiation is based on the vector approach generalized from the iterative procedure of the solution of Bethe-Saltpeter equation. The performances of the developed method are demonstrated both for conventional and polarization-sensitive OCT modalities.     

Full range spectral domain optical coherence tomography using a fiber-optic probe as a self-phase shifter

We present a full range handheld probe type spectral domain optical coherence tomography (SD-OCT) method. Here, the sample arm is composed of a tilted fiber-optic cantilever scanner; thus, the phase shift concurrently occurs while sample scanning. With the phase shift, we could achieve a full range complex-conjugate-free OCT image with no additional phase shifters in the reference arm. To realize this technique, a magnetically actuated probe was adopted. Full range SD-OCT images of a pearl, human fingernail, and human tooth were subsequently obtained using this suggested probe. The scanning range and acquisition speed were 3?mm and 20 frames/s?, respectively.     

Two-dimensional birefringence imaging in biological tissue by polarization-sensitive optical coherence tomography

Using a low-coherence Michelson interferometer, we measure two-dimensional images of optical birefringence in bovine tendon as a function of depth. Polarization-sensitive detection of the signal formed by interference of backscattered light from the sample and a mirror in the reference arm give the optical phase delay between light that is propagating along the fast and slow axes of the birefringent tendon. Images showing the change in birefringence in response to laser irradiation are presented. The technique permits rapid noncontact investigation of tissue structural properties through two-dimensional imaging of birefringence.     

In vitro birefringence imaging with spectral domain polarization-sensitive optical coherence tomography

Spectral domain polarization-sensitive optical coherence tomography （SDPS-OCT） is a depth-resolved polarization-sensitive interferometry which integrates polarization optics into spectral domain optical co- herence tomography （SD-OCT）. This configuration can obtain birefringence information of samples and improve the imaging speed. In this paper, horizontally polarized light is used to replace natural light of the source. Then, right-rotated circularly polarized light is the incident sample light. To obtain two orthogonal components of the polarized interferogram, the reflected light of the reference arm is set to be 45° linearly polarized light. These two components are acquired by two spectrometers synchronously. The system was employed to achieve 12.8μm axial resolution and 4.36μm transverse resolution. We have imaged in vitro chicken tendon and muscle tissues with these svstem.     

Passive component based multifunctional Jones matrix swept source optical coherence tomography for Doppler and polarization imaging

We present a fiber based multifunctional Jones matrix swept source optical coherence tomography (SS-OCT) system for Doppler and polarization imaging. Jones matrix measurement without using active components such as electro-optic modulators is realized by incident polarization multiplexing based on independent delay of two orthogonal polarization states and polarization diversity detection. In addition to polarization sensitivity, this system measures Doppler flow without extra hardware for phase stabilized SS-OCT detection. An eighth-wave plate was measured to demonstrate the polarization detection accuracy. The optic nerve head of a retina was measured in vivo. Detailed vasculature and birefringent structures were investigated simultaneously.     

Power-efficient nonreciprocal interferometer and linear-scanning fiber-optic catheter for optical coherence tomography

A nonreciprocal fiber-optic interferometer is demonstrated in an optical coherence tomography (OCT) system. The increased power efficiency of this system provides a 4.1-dB advantage over standard Michelson implementations. In addition, a new linear-scanning fiber-optic catheter is demonstrated that avoids the rotary optical junction that is required in circumferential scanning systems. These advancements have permitted the clinical implementation of OCT imaging in the human gastrointestinal tract.     

High-speed fiber based polarization-sensitive optical coherence tomography of in vivo human skin

A high-speed single-mode fiber-based polarization-sensitive optical coherence tomography (PS OCT) system was developed. With a polarization modulator, Stokes parameters of reflected flight for four input polarization states are measured as a function of depth. A phase modulator in the reference arm of a Michelson interferometer permits independent control of the axial scan rate and carrier frequency. In vivo PS OCT images of human skin are presented, showing subsurface structures that are not discernible in conventional OCT images. A phase retardation image in tissue is calculated based on the reflected Stokes parameters of the four input polarization states.     

Depth-resolved birefringence and differential optical axis orientation measurements with fiber-based polarization-sensitive optical coherence tomography

Conventional polarization-sensitive optical coherence tomography (PS-OCT) can provide depth-resolved Stokes parameter measurements of light reflected from turbid media. A new algorithm that takes into account changes in the optical axis is introduced to provide depth-resolved birefringence and differential optical axis orientation images by use of fiber-based PS-OCT. Quaternion, a convenient mathematical tool, is used to represent an optical element and simplify the algorithm. Experimental results with beef tendon and rabbit tendon and muscle show that this technique has promising potential for imaging the birefringent structure of multiple-layer samples with varying optical axes.     

Dental fiber-reinforced composite analysis using optical coherence tomography

An optical coherence tomography (OCT) system with 6 μm spatial resolution was employed to image the sites of fracture initiation and slow crack propagation in a fiber reinforced composite. Bar specimens (2 mm × 3 mm × 25 mm) of fiber reinforced composite were mechanically and thermally cycled to emulate oral conditions. The interior of the samples were analyzed prior and after the emulations. We analyzed the specimens that were intact after the loading cycling. The results demonstrated the capacity of the OCT technique to generate images of the sites fracture initiation, crack propagation, and regions surrounding the fracture, and it can be used in the future for quantitative analysis thus complementing other existing methods, with the main advantage of being non-destructive and non-invasive.     

Birefringence imaging of human skin by polarization-sensitive spectral interferometric optical coherence tomography

We have developed a spectral interferometric optical coherence tomography (OCT) system with polarization sensitivity that is able to measure a two-dimensional tomographic image by means of one-dimensional mechanical scanning. Our system, which has an axial resolution of 32 mum , calculates the distribution of each element of the Müller matrix of a measured object from 16 OCT images. The OCT system successfully reveals the birefringent nature of human skin tissue.     

Intraluminal fiber-optic Doppler imaging catheter for structural and functional optical coherence tomography

We describe a miniature fiber-optic Doppler imaging catheter for integrated functional and structural optical coherence tomography (OCT) imaging. The Doppler catheter can map blood flow within a vessel as well as image vessel wall structures. A prototype Doppler catheter has been developed and demonstrated for measuring the intraluminal velocity profile in a vessel phantom (conduit). A simple mathematical model is demonstrated to estimate the total flow rate. This estimation technique also enables the spatial range of flow measurements to be extended by approximately two times the normal OCT image-penetration depth. The Doppler OCT catheter could be a powerful device for cardiovascular imaging.     

Parallel optical coherence tomography using a CCD camera

Parallel optical coherence tomography is demonstrated using a 12-bit scientific-grade charge-coupled device array.A superluminescent diode in combination with a free-space Michelson interferometer was employed to achieve 10-μm axial resolution and 1.1-μm transverse resolution on a 902×575 μm2 field of view.We imaged a test mirror and bovine retinal tissue using a four-step phase shift method.     

Optical coherence tomography using a frequency-tunable optical source

We have developed a simple, wide-optical-bandwidth, high-resolution system for performing rapid optical frequency domain reflectometry measurements and applied it to multidimensional tomographic imaging. The source is a grating-tuned external cavity semiconductor laser with a tuning capability of 25 nm in 100 ms. We discuss system performance and show a two-dimensional optical coherence tomography image of a thin glass sandwich structure as a preliminary demonstration of the systems depth and resolution capabilities.     

Dual-path handheld system for cornea and retina imaging using optical coherence tomography

Optical Review - A dual-path handheld system is proposed for cornea and retina imaging using spectral domain optical coherence tomography. The handheld sample arm is designed to acquire two images...     

Performance analysis of a swept-source optical coherence tomography system with a quadrature interferometer and optical amplification

A performance analysis of signal to noise ratio for an optical coherence tomography system with quadrature detection and a semiconductor optical amplifier in the sample arm is discussed. The results are compared and discussed in relation to a conventional OCT system (without optical amplification). An increase of the signal to noise ratio up to 14 dB at a depth of 0.5 mm is obtained compared to the system without the optical amplifier. Overall, an improvement was demonstrated for signal coming from deeper regions within the samples. Arterial plaque from a myocardial infarction-prone Watanabe heritable hyperlipidemic (WHHLMI) rabbit is visualized and characterized using this system. Improvement of signal to noise ratio increases the penetration depth possible for OCT images, from 1 mm to 2 mm within the vessel wall of an artery. Preliminary results show that vulnerable plaque with fibrous cap, macrophage accumulations and calcification in the arterial tissue are measurable with this OCT system.     

Optical probe using eccentric optics for optical coherence tomography

We propose and demonstrate an OCT optical probe using eccentric optics. This probe enabled both forward imaging and side imaging by dividing a circular scanning area into two semicircular scanning areas using an external motor to rotate the flexible tube. The outer diameter of the probe was 2.6 mm, and its rigid portion length was 10 mm. The lateral resolution was 23 μm, and the eccentric radius was 1.1 mm. The circumferential length in scanning was 6.9 mm, and the working distance was 5 mm. OCT images of 1.5 mm × 6.9 mm (in tissue, axial × circumference), including forward image and side image, were measured with the axial resolution of 19 μm in air and a frame rate of one frame per second. The epidermis, dermis, and sweat gland of in vivo human ventral finger tips were observed.