High resolution spectral-domain optical coherence tomography using a thermal light source

A high resolution spectral-domain optical coherence tomography (SD-OCT) system based on a thermal light source was presented. A novel normalized method was introduced to remove the background noise and the DC noise of the interference spectrum. A Gaussian spectral calibration procedure was performed to improve axial resolution and image quality before reconstructing OCT image. With the proposed method, the quality of the obtained images was greatly improved. Two-dimensional (2D) cross-sectional images with axial resolution of 1.2?μm were obtained. Furthermore, the film thickness of single-layer film sample was obtained. The experimental result demonstrates the SD-OCT system has potential for film thickness measurement and surface topography.     

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.     

Ultra-high resolution spectral domain optical coherence tomography using supercontinuum light source

An ultra-high resolution spectral domain optical coherence tomography (SD-OCT) was developed using a cost-effective supercontinuum laser. A spectral filter consists of a dispersive prism, a cylindrical lens and a right-angle prism was built to transmit the wavelengths in range 680–940 nm to the OCT system. The SD-OCT has achieved 1.9 μm axial resolution and the sensitivity was estimated to be 91.5 dB. A zero-crossing fringes matching method which maps the wavelengths to the pixel indices of the spectrometer was proposed for the OCT spectral calibration. A double sided foam tape as a static sample and the tip of a middle finger as a biological sample were measured by the OCT. The adhesive and the internal structure of the foam of the tape were successfully visualized in three dimensions. Sweat ducts was clearly observed in the OCT images at very high resolution. To the best of our knowledge, this is the first demonstration of ultra-high resolution visualization of sweat duct by OCT.     

Investigation on spectral-domain optical coherence tomography using a tungsten halogen lamp as light source

The objective of this research was to investigate a new detection method using a thermal light source in a spectral domain optical coherence tomography (SDOCT) operation to improve both image acquisition rate and axial resolution economically. A tungsten halogen lamp was chosen as the illumination source and a Michelson fiber interferometer was employed to generate the interference pattern of an object collected by a spectrometer; the inner structure of the object was obtained from the interference pattern by a Fourier transform. An experiment was performed by measuring a thin film coated on a glass base with the system, and the experimental results indicated that the structure of the thin film could be clearly observed as expected. It was theoretically stated and experimentally verified that the technique was feasible and enables imaging to realize the reconstructions of internal structure of engineering and biological object.     

Simultaneous swept source optical coherence tomography of the anterior segment and retina using coherence revival

We report on an implementation of coherence revival-based heterodyne swept source optical coherence tomography that is capable of simultaneously imaging the anterior and posterior eye. A polarization-encoded sample arm was used to efficiently focus orthogonal polarizations on the anterior segment and retina. Depth encoding was achieved using coherence revival, which allows for multiple depths within a sample to be simultaneously imaged and frequency encoded by carefully controlling the optical pathlength of each sample path. This design is a significant step toward whole-eye optical coherence tomography (OCT), which would enable customized ray-traced modeling of patient eyes to improve refractive surgical interventions and eliminate optical artifacts in retinal OCT diagnostics. We demonstrated the feasibility of this system for in vivo imaging by simultaneously acquiring images of the anterior segments and retinas in healthy human volunteers.     

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

Optical Coherence Tomography (OCT) is a new technology for performing high-resolution cross sectional imaging. OCT is analogous to ultrasound imaging, except that it uses light instead of sound. OCT can provide cross sectional images of tissue structure on the micron scale in situ and in real time. OCT functions as a type of optical biopsy and is a powerful imaging technology for medical diagnostics because unlike conventional histopathology which requires removal of a tissue specimen and processing for microscopic examination, OCT can provide images of tissue in situ and in real time. OCT can be used where standard excisional biopsy is hazardous or impossible, to reduce sampling errors associated with excisional biopsy, and to guide interventional procedures.     

Ultrahigh-resolution optical coherence tomography with a fiber laser source at 1 microm

We report a compact, high-power, fiber-based source for ultrahigh-resolution optical coherence tomography (OCT) near 1 microm. The practical source is based on a short-pulse, ytterbium-doped fiber laser and on generation of a continuum spectrum in a photonic crystal fiber. The broadband emission has an average power of 140 mW and offers an axial resolution of 2.1 microm in air (<1.6 microm in biological tissue). The generation of a broad bandwidth is robust and efficient. We demonstrate ultrahigh-resolution, time-domain OCT imaging of in vitro and in vivo biological tissues.     

Quantification of glucose levels in flowing blood using M-mode swept source optical coherence tomography

The increase of glucose levels in blood changes the viscosity of flowing fluids and shape of the erythrocytes. Both of these can affect the details of light scattering as can be quantified via decorrelation times measured by optical coherence tomography (OCT). The relative contributions of these competing effects have been studied by examining the motion dynamics of deformable asymmetrical (red blood cells, RBCs with ∼7 μm diameter and ∼2 μm thickness) and non deformable symmetrical (polystyrene microspheres, PSM with 1.4 μm diameter) flowing scattering particles. The fluid flow under the action of gravity was modulated by changing the glucose concentrations. Quantitative analysis of the OCT’s M-mode autocorrelation functions enabled the derivations of the translational diffusion coefficients. These systematic studies are aimed at eventual tissue imaging scenarios with speckle-variance OCT to obtain local glucose concentrations maps.     

Spectral shaping for non-Gaussian source spectra in optical coherence tomography

We present a digital spectral shaping technique to reduce the sidelobes (ringing) of the axial point-spread function in optical coherence tomography for non-Gaussian-shaped source spectra. The spectra of two superluminescent diodes were combined to generate a spectrum with significant modulation. Images of onion cells demonstrate the improved image quality in a turbid biological sample. A quantitative analysis of the accompanying penalty in signal-to-noise ratio is given.     

一种新型的专用于光学相干层析系统的宽带光纤光源

报道了一种新型的专用于光学相干层析系统的输出光谱为准高斯型的宽带超荧光光纤光源.该光源采用掺饵光纤作为增益介质.其关键技术是在抽运源的输出端增加了光耦合器，并在光源输出端插入多级长周期光纤光栅对铒离子的自发光谱进行调制和整形；同时采用光控器和温控器来控制抽运源的输出以提高光源输出功率的稳定性.该光源的中心波长为1.57μm，输出光谱的3dB带宽大于75nm，输出功率为27mW.实验结果表明，该光源输出光谱的自相关函数的旁瓣峰被大大削弱，可以满足光学相干层析系统的应用. 关键词： 光学相干层析术 超荧光光纤光源 长周期光纤光栅 光耦合器     

Parallel frequency-domain optical coherence tomography scatter-mode imaging of the hamster cheek pouch using a thermal light source

We use a parallel frequency-domain optical coherence tomography (FDOCT) system to generate a scatter-mode image of the hamster cheek pouch epithelium. To our knowledge, this is the first optical coherence tomography (OCT) image of a biological sample obtained using a thermal light source in the frequency domain. The system employs an imaging spectrometer to acquire depth-resolved profiles from adjacent spatial points without the need for any scanning. To enable this imaging modality, we have considered that signals originating from multiple depths combine in a different manner in FDOCT compared to time-domain optical coherence tomography (TDOCT). Because a multicomponent FDOCT signal is a coherent sum, it is necessary to limit the number of modes that contribute to the detected signal. Conversely, multicomponent TDOCT signals can be represented as incoherent sums, where increasing the number of modes improves the signal.     

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.     

Multi-channel spectral-domain optical coherence tomography using single spectrometer

Multi-channel detection is an effective way to improve data throughput of spectral-domain optical coherence tomography(SDOCT).However,current multi-channel OCT requires multiple detectors,which increases the complexity and cost of the system.We propose a novel multi-channel detection design based on a single spectrometer.Each camera pixel receives interferometric spectral signals from all the channels but with a spectral shift between two channels.This design effectively broadens the spectral ba...     

Phase calculation with a swept source in optical coherence tomography: Jitter influence

An analysis of phase modifications introduced by laser jitter in frequency-domain optical coherence tomography (OCT) is described. It is shown that a 1D spurious phase function is introduced as a consequence of this phenomenon. This phase function is added to any other introduced by the object under analysis causing a superposition of both. The result may impose some limitations for unambiguous determination of phase changes of objects. Experimental and theoretical results are presented.     

Second-harmonic optical coherence tomography

Second-harmonic optical coherence tomography, which uses coherence gating of second-order nonlinear optical responses of biological tissues for imaging, is described and demonstrated. Femtosecond laser pulses were used to excite second-harmonic waves from collagen harvested from rat tail tendon and a reference non-linear crystal. Second-harmonic interference fringe signals were detected and used for image construction. Because of the strong dependence of second-harmonic generation on molecular and tissue structures, this technique imparts contrast and resolution enhancement to conventional optical coherence tomography.     

Fiber-optic-bundle-based optical coherence tomography

A fiber-optic-bundle-based optical coherence tomography (OCT) probe method is presented. The experimental results demonstrate this multimode optical fiber-bundle-based OCT system can achieve a lateral resolution of 12 microm and an axial resolution of 10 microm with a superluminescent diode source. This novel OCT imaging approach eliminates any moving parts in the probe and has a primary advantage for use in extremely compact and safe OCT endoscopes for imaging internal organs and great potential to be combined with confocal endoscopic microscopy.     

Spectroscopic optical coherence tomography

Spectroscopic optical coherence tomography (OCT), an extension of conventional OCT, is demonstrated for performing cross-sectional tomographic and spectroscopic imaging. Information on the spectral content of backscattered light is obtained by detection and processing of the interferometric OCT signal. This method allows the spectrum of backscattered light to be measured over the entire available optical bandwidth simultaneously in a single measurement. Specific spectral features can be extracted by use of digital signal processing without changing the measurement apparatus. An ultrabroadband femtosecond Ti:Al(2)O(3) laser was used to achieve spectroscopic imaging over the wavelength range from 650 to 1000 nm in a simple model as well as in vivo in the Xenopus laevis (African frog) tadpole. Multidimensional spectroscopic data are displayed by use of a novel hue-saturation false-color mapping.     

Two-wavelength optical coherence tomography

We present the results of studies of the basic principles and describe the design of a low-coherence two-wavelength interferometer based on polarization-maintaining fiber. The interferometer was developed for optical coherence tomography (OCT) imaging of the internal structure of living biological tissue simultaneously at two wavelengths, 830 and 1300 nm. Images of several sites of living biological tissue are presented and analyzed.     

Tracking optical coherence tomography

An experimental tracking optical coherence tomography (OCT) system has been clinically tested. The prototype instrument uses a secondary sensing beam and steering mirrors to compensate for eye motion with a closed-loop bandwidth of 1 kHz and tracking accuracy, to within less than the OCT beam diameter. The retinal tracker improved image registration accuracy to <1 transverse pixel (<60 microm). Composite OCT images averaged over multiple scans and visits show a sharp fine structure limited only by transverse pixel size. As the resolution of clinical OCT systems improves, the capability to reproducibly map complex structures in the living eye at high resolution will lead to improved understanding of disease processes and improved sensitivity and specificity of diagnostic procedures.