This PDF file contains the front matter associated with SPIE Proceedings volume 7554, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

We report on the design of a frequency domain optical coherence tomography (FD-OCT) system, fiber optic imaging catheter, and image processing algorithms for in vivo clinical use in the human coronary arteries. This technology represents the third generation of commercially-available OCT system developed at LightLab Imaging Inc. over the last ten years, enabling three-dimensional (3D) intravascular imaging at unprecedented speeds and resolutions for a commercial system. The FD-OCT engine is designed around an exclusively licensed micro-cavity swept laser that was co-developed with AXSUN Technologies Ltd. The laser's unique combination of high sweep rates, broad tuning ranges, and narrow linewidth enable imaging at 50,000 axial lines/s with an axial resolution of < 16 μm in tissue. The disposable 2.7 French (0.9 mm) imaging catheter provides a spot size of < 30 μm at a working distance of 2 mm. The catheter is rotated at 100 Hz and pulled back 50 mm at 20 mm/s to conduct a high-density spiral scan in 2.5 s. Image processing algorithms have been developed to provide clinically important measurements of vessel lumen dimensions, stent malapposition, and neointimal thickness. This system has been used in over 2000 procedures since August 2007 at over 40 clinical sites, providing cardiologists with an advanced tool for 3D assessment of the coronary arteries.

The inhomogeneous backscattering distribution of low-coherent light in blood vessels, which appears as waisted double fan-shaped intensity pattern, is investigated in an in vivo mouse model and flow phantom measurements using high resolution spectral domain optical coherence tomography in the 1.3 μm wavelength region. Based on a predicted orientation of the red blood cells towards laminar flow, an angular modulation of the corresponding backscattering crosssection inside the vessels is assumed. In combination with the signal attenuation in depth by absorption and scattering, a simple model of the intravascular intensity modulation is derived. The suitability of the model is demonstrated exemplarily at the saphenous artery of the mouse during different states of the heart cycle as well as at phantom measurements with well known flow characteristics. The obtained data and the predicted model show good correspondence to each other which leads to the conclusion that the red blood cell orientation seems to be the reason for the observed intensity distribution inside the blood vessels. Therefore, the analysis of the intravascular intensity pattern might be useful for the evaluation of flow characteristics. Additional investigations of the precise angular backscattering of the complex shaped red blood cells are necessary for further model refinement.

We report on the feasibility of rapid, high resolution, 3-dimensional swept source optical coherence tomography (3D SSOCT) to detect early airway injury changes following smoke inhalation exposure in a rabbit model. The SSOCT system obtains 3-D helical scanning using a microelectromechanical system (MEMS) motor based endoscope. Real-time 2-D data processing and image display at the speed of 20 frames per second are achieved by adopting the technique of shared-memory parallel computing. Longitudinal images are reconstructed via an image processing algorithm to remove motion artifacts caused by ventilation and pulse. We demonstrate the ability of the SSOCT system to detect increases in tracheal and bronchial airway thickness that occurs shortly after smoke exposure.

We evaluate the feasibility of optical coherence tomography (OCT) and optical coherence microscopy (OCM) for imaging of benign and malignant thyroid lesions ex vivo using intrinsic optical contrast. Thirty four thyroid gland specimens were imaged from 17 patients, covering a spectrum of pathology, ranging from normal thyroid to neoplasia and benign disease. The integrated OCT and OCM imaging system allows seamlessly switching between low and high magnifications, in a way similar to traditional microscopy. Good correspondence was observed between optical images and histological sections. The results provide a basis for interpretation of future OCT and OCM images of the thyroid tissues and suggest the possibility of future in vivo evaluation of thyroid pathology.

Adaptive optics spectral domain optical coherence tomography (AO SD-OCT) has provided three-dimensional high isotropic resolution retinal images in vivo. In order to enhance the image quality of deep region of the eye, the alternative wavelength of 1-μm has been used for ophthalmic OCT. This study aims to develop AO SD-OCT with one-micrometer probe and demonstrated high penetration and high resolution retinal imaging. A broadband 1-μm SLD light source (Suplerlum) have the center wavelength of 1.03 μm and the spectral bandwidth of 106 nm. Axial scans were obtained by an InGaAs line scan camera with the speed of 47,000 Hz. The aberrations of the system and the eye were measured by Shack-Hartmann wavefront sensor (HASO32, Imagine Eyes, France) and corrected by a single deformable mirror (Mirao52, Imagine Eyes). The AO closed loop was working with the iteration frequency of 7 Hz. The residual root mean square (RMS) wavefront error was typically reduced to 0.1 μm. Seven eyes of 7 normal subjects were examined. The signal gain was found for all subjects with AO. The waving interface of nerve fiber layer and ganglion cell layer, the interface between ganglion cell layer and inner plexiform layer and choroid-sclera interface were observed. AO SD-OCT with one-micrometer probe may be useful not only for the investigation of photoreceptors but also nerve fiber abnormalities.

Vitreoretinal surgery visualization is inherently limited by the ability to distinguish between tissues with subtle contrast, and to judge the location of an object relative to other retinal substructures. Inherent issues in visualizing thin translucent tissues, in contrast to underlying semitransparent ones, require the use of stains such as indocyanine green, which is toxic to retinal tissue. Spectral domain optical coherence tomography (SDOCT) has demonstrated strong clinical success in retinal imaging, enabling high-resolution, motion-artifact-free cross-sectional imaging and rapid accumulation of volumetric macular datasets. Current generation SDOCT systems achieve <5 μm axial resolutions in tissue, and have been used to obtain high resolution datasets from patients with various retinopathies. While OCT imaging has been considered for various non-ophthalmic intrasurgical applications, it is uniquely suited for vitreoretinal surgery where multiple layers of the retinal structure are readily accessible, and where high resolution cross-sectional viewing can have an impact on surgery as it is performed today. Real-time cross-sectional OCT imaging would also provide critical information relevant to the location and deformation of structures that may shift during surgery. Here, we demonstrate an opto-mechanical design for an intraoperative microscope-mounted OCT system (MMOCT) and preliminary in vivo human retinal imaging using this system in a test subject. By adapting an Oculus Binocular Indirect Ophthalmo-Microscope (BIOM3) suspended from a Leica microscope with SDOCT scanning and relay optics, we have demonstrated real-time cross-sectional imaging of multiple layers of the retinal structure, allowing for SDOCT augmented intrasurgical microscopy for intraocular visualization.

Weakly scattering tree shrew retina has been imaged in vitro with full field swept source optical coherence tomography, visualising multiple intraretinal layers. The system utilises a 50nm bandwidth Superlum SLD, to acheive ~8μm of axial resolution and 4μm of transversal resolution. Volumetric images of retinal tissue with dimensions of 1248x936x678μm (horizontal by vertical by axial) were recorded in two second (equivalent of 153,600 A-scans per second) with a measured signal to noise ratio of 75dB. From the 5mW of SLD optical power available, 720μW illuminates the sample, giving a power per pixel of 4.6nW, ten times less power per pixel then standard FDOCT systems. After upgrading the camera and redesigning the optical beam path, 82dB of SNR was realised.

We reported recently an active tracking device based on white light coherence ranging using a spectrally interrogated Michelson interferometer, which was used to monitor and correct for the axial displacement of the eye and head of the imaged subject in a confocal scanning ophthalmoscope/ en face OCT system (SLO/OCT) by tracking the axial position of the eye fundus. Both the tracking and imaging interferometers share the eye interface optics and the patient eye and also an optical path difference (OPD) changing device in the reference (fast voice coil mounted retroreflector), that keeps them locked at constant OPD values. As a consequence, the sensitivity of the tracking interferometer is not affected by the spectrometer sensitivity roll-off with increased OPD and mirror term ambiguity tracking errors close to OPD = 0 are eliminated. Moreover, the axial tracking range is only limited by the voice coil stage travel range and the tracking system has an update time better than 5 ms. We investigate the potential of the new configuration for acquiring volumetric data free of axial eye motion artifacts for two different lateral field sizes. Sets of SLO and en face OCT images at progressively deeper locations in the retina are simultaneously acquired for two lateral sizes, 15°x15° and 3.5°x3.5°. The large lateral field size provides a means of navigating the retina, while the high magnification small lateral size imaging reveals interesting microscopic details of the retinal morphology.

We demonstrate an ultra-high speed full rang spectral domain optical coherence tomography system based on CMOS camera at 140,000 A-scans per second. By implementing beam-offset method, a constant modulation frequency is introduced into each B-scan that enables the reconstruction of the full range complex SDOCT images from in vivo biological specimens. To make use of the full acquisition capacity of detection camera used in the system, we developed system control software that streams the raw spectral fringe data directly into the computer memory. The feasibly of our high speed full range SDOCT system is demonstrated for imaging the dynamics of anterior segment of human eye in vivo.

Conventionally, cell chemotaxis is studied on two-dimensional (2D) transparent surfaces due to limitations in optical and image data-collection techniques. However, substrates which more closely mimic the natural environment of cells are often opaque or three-dimensional (3D). The non-invasive label-free imaging technique of frequency domain optical coherence tomography (OCT) has high axial and transverse resolution of >4μm, comparatively high penetration depth and the ability to acquire volumes in a few seconds, therefore offering the potential to visualize moving cells in 3D (2D+time) and 4D (3D+time). Cell migration is demonstrated in 3D on opaque surfaces, and in 4D within an agarose gel. The speed and directionality of wild type (Ax2) cell movement is seen to be comparable on agar and nitrocellulose filter substrates. Differences can be clearly seen in the character of cell movement between Ax2, myosin knockout (mhcA-) and PLC null ~10μm Dictyostelium discoideum cells in 4D using ultrahigh resolution OCT. OCT is therefore shown to be a useful technique for the study of cell migration.

This paper describes a temporal carrier based Heterodyne Interferometer and associated phase demodulation techniques which are suitable for phase imaging of live cells. A Mach-Zehnder Interferometer is integrated to the microscope and two acousto-optic modulators are employed, to generate a temporal carrier that allows heterodyne approach to phase demodulation. Two demodulation schemes are presented: (a) Digital heterodyne phase extraction technique to extract the static phase information of the carrier signal, and (b) dynamic phase extraction technique for extracting phase variation in the carrier signal. The Heterodyne interferometer enables fast phase imaging and coupled with digital heterodyne phase extraction process, the system provides excellent temporal phase stability (standard deviation < 2 nm for 16 second measurement). This technique is employed for quantitative phase imaging of 3T3 fibroblast cells immersed in cell media. When there is phase variation, the temporal carrier signal is modulated and its instantaneous frequency is directly related to the variation. The dynamic phase extraction technique first determines the instantaneous frequency, which is then integrated with respect to time to obtain timevarying phase. The algorithm is able to extract a time varying phase, caused by a stimulated vibration at 30 Hz and 40 nm amplitude.

Biocompatibility studies of percutanous implants in animal models usually involve numerous lethal biopsies for subsequent morphometric analysis of the implant-tissue interface. A common drawback of the study protocol is the restriction of the analysis to one final time point. In this study optical coherence tomography (OCT) was used to visualize and enable quantification of the local skin anatomy in the vicinity of a percutaneous implant in an animal model using hairless mice. Non invasive in vivo optical biopsies were taken on predetermined time points after implantation and ex vivo in situ at the day of noticeable inflammation. The custom made Fourier-domain OCT system was programmed for imaging with different scanning schemes. A spoke-pattern of 72 cross-sectional scans which was centred at the midpoint of the circular shaped implants was acquired and worked best for the in-vivo situation. Motion-artefact-free three-dimensional tomograms were obtained from the implant site before excision and preparation for histology. Morphometric parameters such as epithelial downgrowth, distance to normal growth and tissue thickness were extracted from the images with a simple segmentation algorithm. Qualitatively, the OCT B-Scans are in good agreement with histological sections. Therefore, OCT can provide additional valuable information about the implant-tissue interface at freely selectable time points before the lethal biopsy. Locally confined quantitative assessments of tissue-implant interaction for in vivo postoperative monitoring can be carried out.

Optical coherence tomography (OCT) has shown promise at non-destructively characterizing engineered tissues such as collagen gels. However, as the collagen gels develop, the OCT images lose contrast of structures as the gels develop, making visual assessment difficult. Our group proposed quantitatively characterizing these gels by fitting the optical properties from the OCT signals. In this paper, we imaged collagen gels seeded with smooth muscle cells (SMCs) over a 5-day period and used the data to measure their optical properties. Our results showed that over time, the reflectivity of the samples increased 10-fold, corresponding to a decrease in anisotropy factor g, without much change in the scattering coefficient μs. Overall, the optical properties appeared to be dominated by scattering from the collagen matrix, not the cells. However, SMCs remodeled the collagen matrix, and this collagen remodeling by the cells is what causes the observed changes in optical properties. Moreover, the data showed that the optical properties were sensitive to the activity of matrix metalloproteinases (MMPs), enzymes that break down local collagen fibrils into smaller fragments. Blocking MMPs in the SMC gels greatly impeded both the remodeling process and change in optical properties at day 5. Treating day 1 acellular gels with MMP-8 for 3 hr managed to partially reproduce the remodeling observed in SMC gels at day 5. Altogether, we conclude that matrix remodeling in general, and MMPs specifically, greatly affect the local optical properties of the sample, and OCT is a unique tool that can assess MMP activity in collagen gels both non-destructively and label free.

High speed, three-dimensional optical coherence tomography (3D OCT) at 800nm, 1060nm and 1300nm with approximately 4μm, 7μm and 6μm axial and less than 15μm transverse resolution is demonstrated to investigate the optimum wavelength region for in vivo human skin imaging in terms of contrast, dynamic range and penetration depth. 3D OCT at 1300nm provides deeper penetration, while images obtained at 800nm were better in terms of contrast and speckle noise. 1060nm region was a compromise between 800nm and 1300nm in terms of penetration depth and image contrast. Optimizing sensitivity, penetration and contrast enabled unprecedented visualization of micro-structural morphology underneath the glabrous skin, hairy skin and in scar tissue. Higher contrast obtained at 800 nm appears to be critical in the in vitro tumor study. A multimodal approach combining OCT and PA helped to obtain morphological as well as vascular information from deeper regions of skin.

Diseased states of tissue are accompanied by changes in both the microanatomy and biochemistry. Optical Coherence Tomography (OCT) is a high resolution imaging technique that allows micron scale high contrast volumetric imaging of tissue microanatomy to a depth of up to 2 mm. Fluorescence Lifetime Imaging Microscopy (FLIM) provides 2-D maps of the concentration of fluorescent biomolecules identified with their corresponding lifetime map. The combination of OCT and FLIM into one imaging system holds promise for identifying diseased states of tissue with improved sensitivity and specificity. We have developed a combined OCT/FLIM system that capable of simultaneous high-speed coregistered micro-anatomical and biochemical real-time imaging of tissues. The OCT/FLIM system is capable of a maximum A-line rate of 59 kHz for OCT and a maximum pixel rate of 30 kHz for FLIM. A 40 nm bandwidth 830 nm SLED provides 7.6 μm axial resolution for OCT. The OCT sample light and FLIM excitation co-propagate through an ultra-wide bandwidth achromatic objective lens to provide co-registered images with 15 μm and 100 μm resolution for OCT and FLIM, respectively. The FLIM subsystem was validated using dyes with well characterized spectral properties. The combined system has been tested and optimized on human postmortem coronary arteries and in vivo hamster cheek pouch. Once optimized, real-time data acquisition and processing would be possible with the system. Future applications of this technology include early detection and diagnosis of oral cancer and the characterization of arterial plaques.

A key issue in laser surgery is the inability for the human operator to stop the laser irradiation in time while cutting/ablating delicate tissue layers. In the present work, we forward-image through the laser machining front in complex biological tissue (dense bovine bone) to monitor the incision's approach to subsurface interfaces in real-time (47-312 kHz line rate). Feedback from imaging is used to stop the drilling process within 150 micron of a targeted interface. This is accomplished by combining the high temporal and spatial resolution of infrared optical coherence tomography (OCT) with a robust, turn-key, high brightness fiber laser. The high sensitivity of the imaging system (~100 dB) permit imaging through the rapidly changing beam path even with the additional scattering caused by the thermal cutting process. In spectral-domain OCT, the imaging acquisition period is easily locked to the machining laser exposure. Though motion-induced artifacts reduce interface contrast, they do not introduce incorrect depth measurements as found in other OCT variants. Standard tomography imaging of the tissue (B-scans) is also recorded in situ before and after laser processing to highlight morphology changes.

In this paper we report that optical inhomogeneity of flowing fluid has influence on Doppler OCT measurement. Additional Doppler signal from scattering steady medium below blood vessels is visible. To investigate this phenomenon, the experiments with different scattering mediums and different well controlled experimental configurations were carried out. Imaging was performed using SOCT instrument with CCD camera, and joint Spectral and Time domain OCT method was used during data analysis.

Monitoring retinal vessel flow properties may aid the screening and the treatment of eye pathologies. We propose to extend the full range ability of the BM-mode scanning technique to high flow structures. The major difference of the proposed method resides in the utilization of a parabolic phase modulation in the reference arm along the B-scan direction. This enables to suppress artifacts generated by the mirror image removal of large velocity structures. We imaged the retina using 1ìm spectral-domain optical coherence tomography and show that this technique enables to have phase-resolved Doppler image where artifacts provoked by high flow vessels are removed. This improvement may help retinal blood flow imaging.

We present a simple and efficient numerical technique for segmentation retinal and choroidal blood vasculature with bulk motion correction in functional Doppler Spectral Optical Coherence Tomography (Doppler SOCT). The technique uses local variance of velocity tomogram which is higher in the areas of the tomogram with internal flow. The resulting variance map reveals the position of vessels. This can be used either for vessel segmentation purposes or for masking the vessels on velocity tomograms. The remaining velocity information is connected only with static structure velocity offset. As only Fourier transformations are used in calculations the algorithm removes the bulk motion from velocity tomograms and provides images of segmented vessels with speed of 80 000 lines/s. The algorithm is shown to work with velocity tomograms obtained by joint Spectral and Time domain OCT (STdOCT).

To preserve the speed advantage of Fourier Domain detection in Optical Coherence Microscopy (OCM), extended depth of field (DOF) is needed. To assess and improve the DOF and the lateral resolution, we analyzed the coherent transfer function (CTF) of OCM. In the spectral domain detection, each wavelength has its own specific CTF, sampling a different part of the object's spatial frequency spectrum. For classical optics and increasing numerical apertures these regions start to overlap and bend, which limits the depth of field. Bessel-like beams produced by axicon lenses circumvent these detrimental effects, but introduce side lobes. Decoupling the detection and the illumination apertures gives more flexibility in engineering a CTF and optimizes the lateral resolution and the DOF at the same time all while reducing these side lobes. We evaluated different combinations of Gaussian and Bessel-like illumination and detection optics. Using Bessel-like beams as well in the illumination as in the detection paths, but with different side-lobe radii, we obtained a lateral resolution of 2μm invariant over an extended depth of field of more than 300μm, at a signal penalty of only 12dB compared to classical Gaussian optics.

Multichannel optical coherence tomography (MOCT) imaging is demonstrated using a high-power wavelength-swept laser source. The main benefit of MOCT is faster image acquisition rates without a corresponding increase in the laser tuning speed. The wavelength-swept laser was constructed using a compact telescope-less polygon-based filter in Littman arrangement. High output power, necessary for MOCT, was achieved by incorporating two serial semiconductor optical amplifiers in a ring laser cavity in Fourier domain mode-locked configuration. The laser has a measured wavelength tuning range of 111 nm centered at 1329 nm, coherence length of 5.5 mm, and total average output power of 131 mW at 43 kHz sweeping rate. Using this laser, a six-channel imaging system was constructed. The imaging arm consisted of a multi-fiber push-on connector mounted on a galvanometer-based scanner. All channels, spaced 250 μm apart, were focused at the same depth. Six-channel OCT imaging to achieve 258 kHz scan rate is demonstrated. The increase in effective frame rate using multichannel acquisition may be beneficial for 3-dimensional in-vivo imaging where bulk tissue motion can adversely affect the image quality.

Optical coherence tomography (OCT) is a medical imaging technology capable of producing high-resolution, crosssectional images through inhomogeneous samples, such as biological tissue. It has been widely adopted in clinical ophthalmology and a number of other clinical applications are in active research. Other applications of OCT include material characterization and non-destructive testing. In addition to current uses, OCT has a potential for a much wider range of applications and further commercialization. One of the reasons for slow penetration of OCT in clinical and industrial use is probably the cost and the size of the current systems. Current commercial and research OCT systems are fiber/free space optics based. Although fiber and micro-optical components have made these systems portable, further significant miniaturization and cost reduction could be achieved through the use of integrated photonic components. We demonstrate a Michelson interferometer using integrated photonic waveguides on nanophotonic silicon on insulator platform. The size of the interferometer is 1500 μm x 50 μm. The structure has been tested using a mirror as a reflector. We can achieve 40 μm axial resolution and 25 dB sensitivity which can be substantially improved.

We demonstrate a frequency comb (FC) swept laser and a frequency comb Fourier domain mode locked (FC-FDML) laser for applications in optical coherence tomography (OCT). The fiber-based FC swept lasers operate at a sweep rate of 1kHz and 120kHz, respectively over a 135nm tuning range centered at 1310nm with average output powers of 50mW. A 25GHz free spectral range frequency comb filter in the cavity of swept lasers causes the lasers to generate a series of well defined frequency steps. The narrow bandwidth (0.015nm) of the frequency comb filter enables a ~-1.2dB sensitivity roll off over ~3mm range, compared to conventional swept source and FDML lasers which have -10dB and - 5dB roll offs, respectively. Measurements at very long ranges are possible with minimal sensitivity loss, however reflections from outside the principal measurement range of 0-3mm appear aliased back into the principal range. In addition, the frequency comb output from the lasers are equally spaced in frequency (linear in k-space). The filtered laser output can be used to self-clock the OCT interference signal sampling, enabling direct fast Fourier transformation of the fringe signals, without the need for fringe recalibration procedures. The design and operation principles of FC swept lasers are discussed and interferometric measurement applications are proposed.

We demonstrate a novel reflective Fabry-Perot tunable laser (RFPTL) for high speed swept-source optical coherence tomography (OCT) imaging applications. This external cavity semiconductor laser uses a silicon MEMS tunable Fabry- Perot filter in a novel reflective mode of operation. The laser is packaged in a compact 25x15 mm fiber-pigtailed butterfly package. Lasers at 1060 and 1300 nm wavelengths have been demonstrated with tuning ranges up to 140 nm, fast scan rates of 100 kHz, and coherence lengths greater than 13 mm. We also describe OCT imaging with these lasers. RFPTL lasers with 1-2 μm wavelengths and tuning ranges of 250 nm have also been demonstrated for a wide range of applications.

We present a novel frequency-swept light source working at 1060nm that utilizes a tapered amplifier as gain medium. These devices feature significantly higher saturation power than conventional semiconductor optical amplifiers and can thus improve the limited output power of swept sources in this wavelength range. We demonstrate that a tapered amplifier can be integrated into a fiber-based swept source and allows for high-speed FDML operation. The developed light source operates at a sweep rate of 116kHz with an effective average output power in excess of 30mW. With a total sweep range of 70 nm an axial resolution of 15 μm in air (~11μm in tissue) for OCT applications can be achieved.

A high-speed, ultra-broad band wavelength swept source based on Fourier domain mode-locking (FDML) technique was demonstrated. Two semiconductor optical amplifiers were used as the gain media. The laser is capable of FWHM tuning range of more than 180 nm and the edge-to-edge scanning range of more than 220 nm at 100 kHz sweeping rate. With the built swept source, an ultra high resolution high speed FDOCT system was developed which can achieve axial resolution of 3 μm in tissue. Imaging of rabbit trachea was demonstrated with the FDOCT system.

A multiband frequency-swept laser source is proposed using wavelength division multiplexing based on the periodic transfer function of a scanning Fabry-Perot interferometer. The optical spectra from different wavelength bands can be combined to create an ultra wideband light source which may significantly improve the spatial resolution of optical coherent tomography (OCT). Parallel processing for data measured in different wavelength bands was used to speed up signal analysis. A proof-of-concept experiment was conducted to demonstrate the feasibility of the proposed technique.

Polarization sensitive optical coherence tomography (PS-OCT) was used to investigate the polarization properties of melanin. Measurements in samples with varying melanin concentrations revealed polarization scrambling, i.e. depolarization. The results indicate that the depolarizing appearance of pigmented structures like, for instance, the retinal pigment epithelium (RPE) is likely to be caused by the melanin granules contained in these cells.

We demonstrate full range imaging of polarization-sensitive swept-source optical coherence tomography (PS-SS-OCT) at 1 μm wavelength. Continuous source polarization modulation and BM-mode scan are applied simultaneously. The complex conjugate ambiguity is removed for both of the intensity and phase retardation images. Our method can extend the measurable depth range and improve the image quality of polarization-sensitive imaging of retina.

We present a polarization sensitive spectral domain optical coherence tomography system that is capable to retrieve with a single camera both retardation and optical axis orientation. The method is based on a differentiation between orthogonal polarization channels through spatial modulation introduced by an electro-optic modulator. Proof-of principle using a chromatic quarter wave plate designed for 1300nm as a sample and acquisitions of a piece of borealis, a highly birefringend plastic is provided. Results of the method for in-vivo imaging of a fingertip are presented.

We demonstrated high-speed spectral domain polarization-sensitive optical coherence tomography (SD-PSOCT) using a single InGaAs line-scan camera and an optical switch at 1.3-μm region. The polarization-sensitive low coherence interferometer in the system was based on the original free-space PS-OCT system published by Hee et al. The horizontal and vertical polarization light rays split by polarization beam splitter were delivered and detected via an optical switch to a single spectrometer by turns instead of dual spectrometers. The SD-PSOCT system had an axial resolution of 8.2 μm, a sensitivity of 101.5 dB, and an acquisition speed of 23,496 Alines/s. We obtained the intensity, phase retardation, and fast axis orientation images of a biological tissue. In addition, we calculated the averaged axial profiles of the phase retardation in human skin.

We developed a fiber based ultra high resolution polarization sensitive spectral domain optical coherence tomography system. The system is based on polarization maintaining fibers and retrieves the backscattered intensity, birefringence and optic axis orientation with only one A-scan per measurement location. In addition a light source with a bandwidth of 100nm was implemented. The setup was used to image the polarization properties of the human retina.

We present theoretical and experimental studies on the sensitivity variation versus optical path difference (OPD) in Fourier domain spectral interferometry using configurations which produce Talbot bands. Such configurations require that the two interfering beams use different parts of the diffraction grating in the interrogating spectrometer. We show that by manipulating the power distribution within the two interfering beams, the OPD value where maximum sensitivity is achieved can be conveniently tuned, as well as the sensitivity variation with OPD. Furthermore, creating a gap between the two beams leads to adjustment of the minimum detectable OPD value, while the widths of the beams determine the maximum detectable OPD value. These features cannot be explained by theoretical models involving spectrometer resolution elements only. Improvement in the sensitivity variation with depth is demonstrated experimentally.

A novel processing technique called Non-Harmonic Analysis (NHA) is proposed for high-resolution OCT imaging. Conventional Fourier-Domain OCT relies on the FFT calculation which depends on the window function and length. NHA can resolve high frequency without being influenced by window function or frame length of sampled data. The results show that NHA process realizes practical image resolution equivalent to 100nm swept range by using significantly reduced wavelength range, and also implies the potential of high resolution imaging capability without the need of a broadband source.

A novel technique for axial resolution improvement of Optical Coherence Tomography (OCT) systems is presented. The technique is based on step-frequency encoding of the OCT signal, using frequency shifting. A resolution improvement by a factor of ~ 7 is achieved without the need for a broader bandwidth light source. This method exploits a combination of two basic principles: the appearance of beating, when adding two signals of slightly different carrier frequencies, and the resolution improvement of OCT images by deconvolution of the interferogram with the encoded source autocorrelation function. In OCT, step-frequency encoding can be implemented by performing two A-scans, with different carrier frequencies and subsequently adding them to create the encoded signal. Deconvolution of the resulting interferogram, using appropriate kernels, results in a narrower resolution width when the frequency steps are appropriately selected.

In this contribution a proof of concept for the alternate way of twofold increasing the axial resolution of Optical Coherence Tomography systems is shown. On the contrary to expanding the bandwidth of the light source, the number of passes of light between sample and the Michelson interferometer is increased. In two simplified novel configurations of Spectral OCT devices designed for this research, the interferometer is equipped with polarization controlling elements in order to force light to pass the distance from the beam splitter to the sample four times: during the first pass the initial linear polarization of the probing beam is converted to the perpendicular one and on return to the interferometer deflected by the polarization sensitive beam splitter towards the additional mirror reflecting it back to the sample. After the second pass the state of polarization is changed again and restored to the initial one in order to interfere with the reference beam. As a result in both set-ups optical paths difference between both arms of the Michelson interferometer is twofold longer comparing to the standard system. This results in two times smaller axial calibration coefficient and finally twofold increase of an effective axial resolution for the same coherence length of the light source. In the paper the experimental evidences are given and limitations of the method discussed.

High-resolution optical molecular imaging has become a vital tool for understanding and measuring physiologically important biometrics on the cellular and subcellular level. In spite of significant recent advances in microscopy, molecular imaging of most endogenous biomolecular species remains elusive. Directly imaging endogenous biomolecules without the aid of exogenous tags is highly desirable. We developed pump-probe optical coherence microscopy (PPOCM) based on our previous success in integrating pump-probe absorption spectroscopy with optical coherence tomography. A fixed human skin tissue with melanoma was imaged by the PPOCM system. The preliminary results show that PPOCM can provide better can clear contrast between normal tissue and melanoma than OCM. This system also can be used to image other chromophores.

Cystic fibrosis (CF) is a genetic defect in the cystic fibrosis transmembrane conductance regulator protein and is the most common life-limiting genetic condition affecting the Caucasian population. It is an autosomal recessive, monogenic inherited disorder characterized by failure of airway host defense against bacterial infection, which results in bronchiectasis, the breakdown of airway wall extracellular matrix (ECM). In this study, we show that the in vitro models consisting of human tracheo-bronchial-epithelial (hBE) cells grown on porous supports with embedded magnetic nanoparticles (MNPs) at an air-liquid interface are suitable for long term, non-invasive assessment of ECM remodeling using magnetomotive optical coherence elastography (MMOCE). The morphology of ex vivo CF and normal lung tissues using OCT and correlative study with histology is also examined. We also demonstrate a quantitative measure of normal and CF airway elasticity using MMOCE. The improved understanding of pathologic changes in CF lung structure and function and the novel method of longitudinal in vitro ECM assessment demonstrated in this study may lead to new in vivo imaging and elastography methods to monitor disease progression and treatment in cystic fibrosis.

Optical coherence tomography (OCT) is a non-invasive and promising imaging modality with high resolution that is an order of magnitude higher than current diagnostic techniques. However, its use in detecting early-stage cancer is limited due to insufficient contrast level in biological tissue, which can be enhanced by harnessing contrast agents [e.g., gold nanoparticles (Au NPs)]. Enhanced penetration by creating micropassages and distribution by ultrasonic force (multimodal topical delivery) was proven to overcome two major barriers (stratum corneum and epithelial barriers) in topically administering Au NPs using an in vivo oral dysplasia hamster model (overall 150% enhanced OCT contrast). Expanded progress on a highly efficient and versatile Au NP-releasing polymer microneedle platform showed a promising next generation multi-modal delivery of Au NPs.

A new method for monitoring ultra-small changes in blood hematocrit (~0.2%) based on measurement of refractive index changes in vitro using Phase Sensitive Spectral Domain Optical Coherence Tomography modality (PhS-SDOCT) is introduced. The developed system has an axial resolution of ~8 μm, phase sensitivity of ±0.01 radians, imaging depth of 3.4 ± 0.01 mm in air, and image acquisition speed of 29 kHz. The experimental accuracy for monitoring refractive index changes as a function of hematocrit level in blood is found to be ±1.5x10^-4 (±0.2%). Obtained results indicate that the PhS-SDOCT can be used to monitor ultra-small changes in the hematocrit and in vitro and, potentially, in tissue blood vessels in vivo.

Many solutions have been proposed to produce phase quantitative images of biological cell samples. Among these, Spectral Domain Phase Microscopy combines the fast imaging speed and high sensitivity of Optical Coherence Microscopy (OCM) in the Fourier domain with the high phase stability of common-path interferometry. We report on a new illumination scheme for OCM that enhances the sensitivity for backscattered light and detects the weak sample signal, otherwise buried by the signal from specular reflection. With the use of a Bessel-like beam, a dark-field configuration was realized. Sensitivity measurements for three different illumination configurations were performed to compare our method to standard OCM and extended focus OCM. Using a well-defined scattering and reflecting object, we demonstrated an attenuation of -40 dB of the DC-component and a relative gain of 30 dB for scattered light, compared to standard OCM. In a second step, we applied this technique, referred to as dark-field Optical Coherence Microscopy (dfOCM), to living cells. Chinese hamster ovarian cells were applied in a drop of medium on a coverslide. The cells of ~15 μm in diameter and even internal cell structures were visualized in the acquired tomograms.

The recent advent of ultra high frame rate cameras gives rise to the possibility of constructing swept source full-field OCT systems with achievable volume rates approaching 10Hz and net A-scan rates approaching 10MHz. Unfortunately, when illuminated with partially coherent light, full-field OCT in turbid media suffers resolution and SNR degradation from coherent multiple scattering, a phenomenon commonly referred to as crosstalk. As a result, most FFOCT systems employ thermal sources, which provide spatially incoherent illumination to achieve crosstalk rejection. However, these thermal sources preclude the use of swept source lasers. In this work, we demonstrate the use of a carefully configured FFOCT system employing multimode fiber in the illumination arm to reduce the spatial coherence of a partially coherent source. By reducing the coherence area below the system resolution, the illumination becomes effectively spatially incoherent and crosstalk is largely rejected. We compare FFOCT images of a USAF test chart positioned beneath both transparent and turbid phantoms using both illumination schemes.

We demonstrate an alternative yet effective approach for spatial gating without mechanical pinhole scanning. We take advantage of the intrinsic property of the robust self-interference effect of low-coherence enhanced backscattering under low spatial coherence illumination. The unique combination of low spatial coherence illumination and differential angle imaging permits the implementation of multiple independent virtual pinholes into a large area imaging platform. Thus, our imaging approach substantially minimizes cross-talk among adjacent pixels, rejects the background light caused by out-of-plane scattered light, and thereby enhances image contrast and resolution.

We have recently shown that for any oblique sample movement containing a transverse velocity component, the prevalent classic Doppler model assuming that the phase shift is proportional to the axial velocity component is erroneous for spectrometer-based FD OCT. While the previous derivation assumed a continuous integration of the photocurrent, we extend the new Doppler model for detectors with a shutter control by taking the detector dead time into account. Because an analytical solution for the new relation between phase shift and oblique sample displacement can not be given, numerically calculated universal contour plots, which are valid for any center wavelength and beam size, are presented for detector dead times ranging from 5 % to 90 %. Compared to systems with a duty cycle of 100 %, the average phase shift does not approach a constant value for large transverse displacements and high sample velocities. In contrast, at large detector dead times and with this small integration times, the numerically simulated phase shift corresponds almost to the assumed one according to the classic Doppler model for the investigated velocity range. The theoretical results were verified by using a flow phantom model.

Optical Coherence Microscopy (OCM) utilizes a high NA microscope objective in the sample arm to achieve an axially and laterally high resolution OCT image. An increase in NA, however, leads to a dramatically decreased depth of focus (DOF), and hence shortens the imaging depth range so that high lateral resolution is maintained only within a small depth region around the focal plane. One solution to increase the depth of imaging while keeping a high lateral resolution is dynamic-focusing. Utilizing the voltage controlled refocus capability of a liquid lens, we have recently presented a solution for invariant high resolution imaging using the liquid lens embedded within a fixed optics hand-held custom microscope designed specifically for optical imaging systems using a broadband light source at 800 nm center wavelength. Subsequently, we have developed a Gabor-Domain Optical Coherence Microscopy (GD-OCM) that utilizes the high speed imaging of spectral domain OCT, the high lateral resolution of OCM, and the ability of real time refocusing of our custom design variable focus objective. In this paper we demonstrate in detail how portions of the infocus cross-sectional images can be extracted and fused to form an invariant lateral resolution image with multiple crosssectional images acquired corresponding to a discrete refocusing step along depth enabled by the varifocal probe. We demonstrate sub-cellular resolution imaging of an African frog tadpole (Xenopus Laevis) taken from a 500 μm x 500 μm cross-section.

In vivo determination of three-dimensional and dynamic geometries of alveolar structures with adequate resolution is essential to develop numerical models of the lung. To gain insight into the dynamics of alveoli a thorax window was prepared in anesthetized rabbits by removal of muscle tissue between 3^rd and 4^th rib without harming the parietal pleura. The transparent parietal pleura allows contact-free imaging by intra-vital microscopy (IVM) and 3D optical coherence tomography (3D-OCT). We have demonstrated that it is possible to acquire the identical region in the inspiratory and expiratory phase, and that OCT in this animal model is suitable for generating 3D geometry of in vivo lung parenchyma. The 3D data sets of the fine structure of the lung beneath the pleura could provide a basis for the development of threedimensional numerical models of the lung.

We present a combined optical Doppler tomography/spectral Doppler imaging modality to quantitatively evaluate the dynamic blood circulation and the artery blockage before and after a localized ischemic stroke in a mouse model. Optical Doppler Tomography (ODT) combines the Doppler principle with optical coherence tomography for noninvasive localization and measurement of particle flow velocity in highly scattering media with micrometer scale spatial resolution. Spectral Doppler imaging (SDI) provides complementary temporal flow information to the spatially distributed flow information of Doppler imaging. Fast, repeated, ODT scans across an entire vessel were performed to record flow dynamic information with high temporal resolution of cardiac cycles. Spectral Doppler analysis of continuous Doppler images demonstrates how the velocity components and longitudinally projected flow-volume-rate change over time for scatters within the imaging volume using spectral Doppler waveforms. Furthermore, vascular conditions can be quantified with various Doppler-angle-independent flow indices. Non-invasive in-vivo mice experiments were performed to evaluate microvascular blood circulation of a localized ischemic stroke mouse model.

The material behaviour of sutured tendons is important in healing models as mechanical trauma to the tendon during surgery can compromise the healing process. This work demonstrates the use of spectral domain optical coherence tomography (SD-OCT) for the monitoring of normal and injured, and subsequently repaired flexor tendons and their behaviour under load. Vertical crimp patterns in normal tendons were observed to be replaced by uniform scattering as the load increases, but the crimp periods in sutured tendons were constrained at the suture site, with gap separation at the suture joint tapering off at high loads. This information could be useful for surgeons who need to balance gap separation in healing tendons and sustainable load.

Aim and objectives. The morphology and position of the temporo-mandibular disc are key issues in the diagnosis and treatment of arthrogenous temporo-mandibular disorders. Magnetic resonance imaging and arthroscopy are used today to identify: flattening of the pars posterior of the disc, perforation and/or adhesions in the pars intermedia of the disc and disc displacements. The present study proposes the investigation of the temporo-mandibular joint disc by optical coherence tomography (OCT). Material and methods. 8 human temporo-mandibular joint discs were harvested from dead subjects, under 40 year of age, and conserved in formalin. They had a normal morphology, with a thicker pars posterior (2,6 mm on the average) and a thinner pars intermedia (1mm on the average). We investigated the disc samples using two different OCT systems: an en-face OCT (time domain (TD)-OCT) system, working at 1300 nm (C-scan and B-scan mode) and a spectral OCT system (a Fourier domain (FD)-OCT) system , working at 840 nm (B-scan mode). Results. The OCT investigation of the temporo-mandibular joint discs revealed a homogeneous microstructure. The longer wavelength of the TD-OCT offers a higher penetration depth (2,5 mm in air), which is important for the analysis of the pars posterior, while the FD-OCT is much faster. Conclusions: OCT is a promising imaging method for the microstructural characterization of the temporo-mandibular disc.

In this paper, we have demonstrated a polarization sensitive subcutaneous and muscle imaging based on common path optical coherence tomography (CP-OCT) using near infrared source. The axial and lateral resolutions of our PS-OCT system are 9μm and 6μm, respectively. The internal structural information has been extracted by the real-time signal analysis (Fourier Transform) from the modulated spectral intensity depending on the beam and tissue birefringence. Preliminary results using fresh beef and in vivo rat show that we can visualize the birefringence effect of the tissue collagen fibers in the samples for better image contrast and sensitivity for detection of hidden dermal structures. Compared to conventional CP-OCT, our proposed PS-OCT could provide depth-resolved images, which reflect tissue birefringence.

The first clinical trial of optical coherence tomography (OCT) combined with multiphoton tomography (MPT) and dermoscopy is reported. State-of-the-art (i) OCT systems for dermatology (e.g. multibeam swept source OCT), (ii) the femtosecond laser multiphoton tomograph DermaInspectTM, and (iii) digital dermoscopes were applied to 47 patients with a diversity of skin diseases and disorders such as skin cancer, psoriasis, hemangioma, connective tissue diseases, pigmented lesions, and autoimmune bullous skin diseases. Dermoscopy, also called 'epiluminescent microscopy', provides two-dimensional color images of the skin surface. OCT imaging is based on the detection of optical reflections within the tissue measured interferometrically whereas nonlinear excitation of endogenous fluorophores and the second harmonic generation are the bases of MPT images. OCT cross sectional "wide field" image provides a typical field of view of 5 x 2 mm² and offers fast information on the depth and the volume of the investigated lesion. In comparison, multiphoton tomography presents 0.36 x 0.36 mm² horizontal or diagonal sections of the region of interest within seconds with submicron resolution and down to a tissue depth of 200 μm. The combination of OCT and MPT provides a synergistic optical imaging modality for early detection of skin cancer and other skin diseases.

Optical Coherence Tomography is a powerful tool for diagnostic imaging of the ocular posterior chamber. Recent advances in OCT technology have facilitated acquisition of high resolution volumetric images of the retina and optic nerve head. In this report, we investigate optic nerve head imaging in humans using a home-built laboratory grade OCT system in the 800nm wavelength region. We also introduce the development of a computational model of the optic nerve head morphology in order to study physiological changes which may be associated with elevated intra-ocular pressure.

In the dynamic OCT of mental sweating, we have found internal mental sweating without ejection of excess sweat from the spiral lumen to the skin surface. Internal sweating occurs more often in the case where mental stress is applied to a volunteer, and it is more useful for evaluation of activity of the sympathetic nerve. Furthermore, the MIP imaging has been proposed for quick 3-D imaging of the spiral lumen of sweat glands. Using time-sequential MIP images with the frame spacing as short as 1.4 sec, several sweat glands can be tracked simultaneously to quantify sweating stimulated by a mental stress.

Reason for using optical coherence tomography (OCT) to locate the germinal disc is the questionable and ethically alarming killing of male layer chickens because for the layer line only the females are necessary. To avoid this and to protect the animal rights, the sex of the fertilized chicken egg has to be determined as early as possible in the unincubated state. Because the information whether the chick becomes male or female can be found in the germinal disc an accurate localization for sexing is essential. The germinal disc is located somewhere on top of the yolk and has a diameter of approximately 4 - 5 mm. Different imaging methods like ultrasonography, 3D-X-ray micro computed tomography and magnetic resonance imaging were used for localization until now, but found to be impractical. The goal of this study is to prove if OCT can be a moderate approach for the precise in ovo localization. Because the eggshell is an impenetrable barrier for OCT and to minimize the penetration of germs a very small hole is placed in the eggshell and a fan-shaped optical scanning pattern is used.

Wavelength tunable sampled grating distributed Bragg reflector (SG-DBR) lasers used for telecommunications applications have previously demonstrated the ability for linear frequency ramps covering the entire tuning range of the laser at 100 kHz repetition rates¹. An individual SG-DBR laser has a typical tuning range of 50 nm. The InGaAs/InP material system often used with SG-DBR lasers allows for design variations that cover the 1250 to 1650 nm wavelength range. This paper addresses the possibility of concatenating the outputs of tunable SGDBR lasers covering adjacent wavelength ranges for enhancing the resolution of OCT measurements. This laser concatenation method is demonstrated by combining the 1525 nm to 1575 nm wavelength range of a "C Band" SG-DBR laser with the 1570nm to 1620 nm wavelength coverage of an "L-Band" SG-DBR laser. Measurements show that SGDBR lasers can be concatenated with a transition switching time of less than 50 ns with undesired leakage signals attenuated by 50 dB.

The method of spectral selection, based on small optical connection between tilted short Fabry-Perot interferometer and semiconductor optical amplifier has been proposed. It was shown, that short Fabry-Perot interferometer under certain inclination reflects back in narrowband lines, typical for transmitted spectrum. This effect has been used for creation swept semiconductor laser with wavelength tuning range 25 nm at central wavelength 1290 nm and coherence length 8 mm.

We developed a swept source laser using a micro electro mechanical systems(MEMS) scanner mirror, and demonstrated optical coherence tomography. To enable both the wide tuning wavelength range and high scanning frequency, we introduced 2-degree-of-freedom(2-DOF) MEMS scanner mirror. A tunable optical filter is composed of a MEMS scanner mirror and a diffraction grating which is arranged in Littrow configuration. We built a swept source laser which has a wavelength range of 143 nm, center wavelength of 1304 nm, and a peak power of 16 mW. OCT measurements are performed at a rate of 17.9 kHz and doubled 35.9 kHz at unidirectional and bidirectional sweeps, respectively. The system sensitivity is 101.5 dB.

We demonstrated a real-time display of processed OCT images using a linear-in-wavenumber (linear-k) spectrometer and a graphics processing unit (GPU). We used the linear-k spectrometer with optimal combination of a diffractive grating with 1200 lines/mm and a F2 equilateral prism in the 840 nm spectral region, to avoid calculating the re-sampling process. The calculations of the FFT (fast Fourier transform) were accelerated by the low cost GPU with many stream processors, which realized highly parallel processing. A display rate of 27.9 frames per second for processed images (2048 FFT size × 1000 lateral A-scans) was achieved in our OCT system using a line scan CCD camera operated at 27.9 kHz.

We present a method to obtain additional depth resolved spectroscopic information from standard frequency domain optical coherence tomography (FDOCT) images. This method utilizes Fourier transforms of signal peaks within the complex FDOCT depth profiles to extract depth resolved spectroscopic information. For verification of the depth resolved spectroscopic image analysis method, theoretical simulations as well as experimental studies are demonstrated. Both show accurate depth resolved spectroscopic reconstruction enabling a depth allocation of material specific transmission spectra due to absorption. This analysis tool improves significantly the image contrast and allows image mapping of material specific spectral characteristics.

Empirical mode decomposition (EMD) is a new adaptive data analysis method in which the analyzed data is decomposed into a limited number of intrinsic mode functions (IMFs) through a sifting process. One problem with EMD is mode mixing, which has been solved by Wu et al using ensemble EMD (EEMD). In this paper, we applied the EEMD method to data acquired from optical coherence tomography (OCT) to improve the image quality. First, the original OCT fringe data is converted from linear wavelength to linear frequency through a calibration process. Second, the calibrated data is decomposed into different IMFs by EEMD. Third, the physical meaning of different IMFs was analyzed. Fourth, IMFs that represented noise were removed from the calibrated fringe data. The noise removed fringe data was then Fourier transformed to get depth information. EEMD was found to be able to separate different frequency noise into different IMFs. The signal to noise ratio of OCT image was improved by removing the IMFs that represent noise from the acquired fringe data.

A complication of Fourier domain optical coherence tomography (OCT) methods, such as spectral domain and swept source OCT, is the complex conjugate ambiguity due to inverse Fourier transform of real-valued data. As a result, the image is symmetric to the zero plane, and only half of the theoretical imaging depth range is used to avoid overlapping "mirror images" that confuse the image. We have previously demonstrated harmonic detection in a video-rate spectral domain OCT system using a high speed line scan camera. Harmonic detection removes the complex conjugate ambiguity by providing the real and imaginary components of the spectral interferogram. In this work, we show that harmonic detection is easily applied to swept source OCT to remove the complex conjugate ambiguity while maintaining the imaging performance of the original swept source instrument. Harmonic detection swept source OCT allows simultaneous experimental determination of the real and imaginary components of each spectral interferogram without the need to measure consecutive A-scans at differing phase. This harmonic detection swept source optical coherence tomography system exhibits 110 dB sensitivity, up to 55 dB dynamic range, ≥ 50 dB complex conjugate rejection, and operates at the full 16 kHz sweep rate of the swept source laser for real-time video rate imaging.

Different algorithms for performing Fourier transforms with unequally sampled data in wavenumber space for Fourier-domain optical coherence tomography are considered. The efficiency of these algorithms is evaluated from point-spread functions obtained with a swept-source optical coherence tomography system and from computational time. Images of a 4-layer phantom processed with these different algorithms are compared. We show that convolving the data with an optimized Kaiser-Bessel window allowing a small oversampling factor before computing the fast Fourier transform provides the optimal trade-off between image quality and computational time.

We evaluated several, previously published, complex conjugate artifact removal methods and algorithms that have been proposed for Fourier domain optical coherence tomography (Fd-OCT). To ensure comparable conditions, only one OCT system was used, but with modified data acquisition schemes, depending on the requirements of each method/algorithm. This limited our evaluation to single spectrometer based Fd-OCT approaches. The suppression ratio of complex conjugate artifact images using a paperboard is assessed for all tested methods. Several other metrics are also used for comparison, including a list of additional hardware requirements (beyond standard Fd-OCT components) and data acquisition schemes. Finally, in vivo human finger pad and nail images are presented for comparison to the standard Fd- OCT images and full-range images.

Optical coherence tomography is an emerging non-invasive technology that provides high resolution, cross-sectional tomographic images of internal structures of specimens. It holds great potentials for a wide variety of applications, especially in the field of biomedical imaging. OCT images, however, are usually degraded by significant speckle noise. Here we report a 3D approach to attenuating speckle noise in OCT images. This approach is based on the 3D curvelet transform, and is conveniently controlled by a single parameter that determines the threshold in the curvelet domain. Unlike 2D approaches which only consider information in individual images, 3D processing, by analyzing all images in a volume simultaneously, has the advantage of also taking the information between images into account. This, coupled with the curvelet transform's nearly optimal sparse representation of curved edges that are common in OCT images, provides a simple yet powerful platform for speckle attenuation. We show the approach suppresses a significant amount of speckle noise, and in the mean time preserves and thus reveals many subtle features that could get attenuated in other approaches.

Optical coherence tomography (OCT) allows non-invasive imaging of sub-surface structures in vivo, ideally without a need for target preparation. In conventional OCT, the contrast for blood vessels depends on a variety of factors and can be challenging. Speckle variance has been recognized as a method to enhance contrast for blood flow without the application of contrast agents in OCT images. Here, we demonstrate the possibility of extracting blood flow information from a volumetric OCT datasets that was obtained routinely from a human participant. We used a commercially available OCT system with a clinical CE-mark. The light source has a central wavelength of 1310 nm. Using Multi-Beam technology, the system achieves an isometric resolution of better than 7.5 μm in tissue over the entire imaging depth of around 1 mm. At 1 mm image width, 21 frames (B-scans) per second can be imaged. We used the speckle variance in order to enhance the contrast for blood vessels in vivo. This method allowed us determining the presence and depth of blood flow within the 1 mm penetration depth, without dependence on direction or orientation of the blood flow with respect to the scanning beam.

Tissues such as skin, fat or cuticle are non-transparent because inhomogeneities in the tissue scatter light. We demonstrate experimentally that light can be focused through turbid layers of living tissue, in spite of scattering. Our method is based on the fact that coherent light forms an interference pattern, even after hundreds of scattering events. By spatially shaping the wavefront of the incident laser beam, this interference pattern was modified to make the scattered light converge to a focus. In contrast to earlier experiments, where light was focused through solid objects, we focused light through living pupae of Drosophila melanogaster. We discuss a dynamic wavefront shaping algorithm that follows changes due to microscopic movements of scattering particles in real time. We relate the performance of the algorithm to the measured timescale of the changes in the speckle pattern and analyze our experiment in the light of Laser Doppler flowmetry. Applications in particle tracking, imaging, and optical manipulation are discussed.

An efficient technique of the coherent noise separation of and compensation for in spectral-domain optical coherence tomography (SD-OCT) is proposed and validated. The coherent noise is separated during one exposure by modulating the relative delay of the signal and reference waves by a certain waveform. It is shown that the influence of internal motions in an object on the coherent noise separation quality can be reduced by increasing of modulation frequency. The technique has been numerically and experimentally validated.

We found that the bandwidth in the formula calculating the depth resolution of OCT is usually not the same as the bandwidth of the light source; the effective spectral profile for the interfering signal is determined by the dot product of the electric vectors of the light field in the two interfering arms. We thus introduced a new concept: the effective bandwidth in spectraldomain OCT (SD-OCT). Through theoretical and experimental analyses we found that the effective bandwidth is a function of both the polarization matching conditions (PMC) and the path length difference (PLD) between the sample and reference arms.

This paper reports a combined speckle and polarization-difference approach for imaging absorbing inhomogeneities embedded in optical scattering medium. Mathematical morphological operation has been used to suppress the speckle coarse grains and reconstruct the position of the absorbing inhomogeneities embedded in turbid medium. Moreover, we quantify the scattering coefficient of the background medium using the average granulometric size. Then the local speckle contrast ratio is applied to enhance the edges of absorbing objects.