In vivo rat brain imaging was demonstrated using the FF OCM (full field optical coherence microscopy) with SMMF (short multimode fiber) of a diameter of 125 μm and a length of 7.33 mm. The spatial resolution was measured to be 2.0 μm. The influences of motions for OCM images and methods to detect motions were investigated using image processing. Measurements were combinations of 3D OCM imaging (M1) with measurement time 10min and en face imaging (M2) at fixed depth with 17.9 fps and the interval time of 1 min during 30 min. For Rat 1 measured point was at the prim somatosens cortex, and the insertion length (IL) was 3.2 mm, the motions were not remarkable. En face OCM images with the region of X 56.3 μm, Y 56.3 μm, and Z 110 μm were measured. For Rat 2 measured point was at med parietal association cortex, and IL was 3.1 mm. Difference images and those intensity profiles showed the lateral motion of 5 µm between two sequent en face OCM images. For both cases, 3D images similarly showed the spatial arrangement of nerve fibers. The feasibility that the motions of tissues could be detected under the SMMF using sequential difference images was shown. This might be applicable to detect the motions in deep areas in measurements such as the optical intrinsic imaging
We investigated a rapid imaging method to monitor the spatial distribution of total hemoglobin concentration (CHbT), the tissue oxygen saturation (StO2), and the scattering power b in the expression of musp=a(lambda)^-b as the scattering parameters in cerebral cortex using a digital red-green-blue camera. In the method, Monte Carlo simulation (MCS) for light transport in brain tissue is used to specify a relation among the RGB-values and the concentration of oxygenated hemoglobin (CHbO), that of deoxygenated hemoglobin (CHbR), and the scattering power b. In the present study, we performed sequential recordings of RGB images of in vivo exposed brain of rats before, during, and after hindlimb electrical stimulation. The remarkable increases in CHbO, CHbT, and StO2 were induced by hindlimb electrical stimulation whereas significant decreases in the scattering power b and CHbR were observed after the onset of stimulation. It has been reported that cerebral blood flow (CBF) and blood oxygen level-dependent (BOLD) signal responses show better correlation with post-synaptic local field potentials than with spiking activity. Positive CBF and BOLD responses during stimulation are associated with an increase in neuronal activity and decrease in deoxyhemoglobin content. Therefore, the decrease in the scattering power b of somatosensory cortex after hindlimb electrical stimulation is indicative of slow post-synaptic potential change. The results in this study indicate potential of RGB camera-based imaging to evaluate both hemodynamics and synaptic activity in brain tissue.
We investigated a rapid imaging method to monitor the spatial distribution of total hemoglobin concentration (CHbT), the tissue oxygen saturation (StO2), and the scattering power b in the expression of musp=a(lambda)^-b as the scattering parameters in cerebral cortex using a digital red-green-blue camera. In the method, Monte Carlo simulation (MCS) for light transport in brain tissue is used to specify a relation among the RGB-values and the concentration of oxygenated hemoglobin (CHbO), that of deoxygenated hemoglobin (CHbR), and the scattering power b. The results in this study indicate potential of the method to evaluate the physiology and loss of tissue viability in biological tissues.
In achieving minimally invasive accessibility to deeply located regions the size of the imaging probes is important. We demonstrated full-field optical coherence tomography (FF-OCM) using an ultrathin forward-imaging short multimode fiber (SMMF) probe of 50 μm core diameter, 125 μm diameter, and 7.4 mm length for optical communications. The axial resolution was measured to be 2.14 μm and the lateral resolution was also evaluated to be below 4.38 μm using a test pattern (TP). The spatial mode and polarization characteristics of SMMF were evaluated. Inserting SMMF to in vivo rat brain, 3D images were measured and 2D information of nerve fibers was obtained. The feasibility of an SMMF as an ultrathin forward-imaging probe in FF-OCM has been demonstrated.
We investigated a rapid imaging method to monitor the spatial distribution of total hemoglobin concentration (CHbT), the tissue oxygen saturation (StO2), and the scattering power b in the expression of musp=a(lambda)^-b as the scattering parameters in cerebral cortex using a digital red-green-blue camera. In the method, Monte Carlo simulation (MCS) for light transport in brain tissue is used to specify a relation among the RGB-values and the concentration of oxygenated hemoglobin (CHbO), that of deoxygenated hemoglobin (CHbR), and the scattering power b. In the present study, we performed sequential recordings of RGB images of in vivo exposed brain of rats while changing the fraction of inspired oxygen (FiO2), using a surgical microscope camera system. The time courses of CHbO, CHbR, CHbT, and StO2 indicated the well-known physiological responses in cerebral cortex. On the other hand, a fast decrease in the scattering power b was observed immediately after the respiratory arrest, which is similar to the negative deflection of the extracellular DC potential so-called anoxic depolarization. It is said that the DC shift coincident with a rise in extracellular potassium and can evoke cell deformation generated by water movement between intracellular and extracellular compartments, and hence the light scattering by tissue. Therefore, the decrease in the scattering power b after the respiratory arrest is indicative of changes in light scattering by tissue. The results in this study indicate potential of the method to evaluate the pathophysiological conditions and loss of tissue viability in brain tissue.
KEYWORDS: Brain, Tissues, Cerebral cortex, Mode conditioning cables, Hemodynamics, Cameras, In vivo imaging, Digital cameras, RGB color model, Monte Carlo methods, Diffuse reflectance spectroscopy
Nervous system relies on a continuous and adequate supply of blood flow, bringing the nutrients that it needs and removing the waste products of metabolism. Failure of these mechanisms is found in a number of devastating cerebral diseases, including stroke, vascular dementia, brain injury and trauma. Vasomotion which is the spontaneous low-frequency oscillation derived by the contraction and relaxation of arterioles and appears to be an intrinsic property of the cerebral vasculature, is important for monitoring the cerebral flow, tissue metabolism and health status of brain tissue. In the present study, we investigated a method to visualize the spontaneous low-frequency oscillation of cerebral blood volume based on the sequential RGB images of exposed brain.
We demonstrated FF OCM(full field optical coherence microscopy) using an ultrathin forward-imaging SMMF (short
multimode fiber) probe of 50 μm core diameter, 125 μm diameter, and 7.4 mm length, which is a typical graded-index
multimode fiber for optical communications. The axial resolution was measured to be 2.20 μm, which is close to the
calculated axial resolution of 2.06 μm. The lateral resolution was evaluated to be 4.38 μm using a test pattern. Assuming
that the FWHM of the contrast is the DOF (depth of focus), the DOF of the signal is obtained at 36 μm and that of the OCM is 66 μm.
The contrast of the OCT images was 6.1 times higher than that of the signal images due to the coherence gate. After an
euthanasia the rat brain was resected and cut at 2.6mm tail from Bregma. Contacting SMMF to the primary somatosensory
cortex and the agranular insular cortex of ex vivo brain, OCM images of the brain were measured 100 times with 2μm step.
3D OCM images of the brain were measured, and internal structure information was obtained. The feasibility of an
SMMF as an ultrathin forward-imaging probe in full-field OCM has been demonstrated.
KEYWORDS: Scattering, Brain, Cameras, Tissues, Digital cameras, RGB color model, Oxygen, In vivo imaging, Neuroimaging, Monte Carlo methods, Light scattering, Hemodynamics
We propose a rapid imaging method to monitor the spatial distribution of total hemoglobin concentration (CHbT), the tissue oxygen saturation, and the scattering power b in the expression of μs’=aλ-b as the scattering parameters in cerebral cortex using a digital red-green-blue camera. In the method, the RGB-values are converted into the tristimulus values in CIEXYZ color space which is compatible with the common RGB working spaces. Monte Carlo simulation (MCS) for light transport in tissue is used to specify a relation among the tristimulus XYZ-values and the concentration of oxygenated hemoglobin, that of deoxygenated hemoglobin, and the scattering power b. In the present study, we performed sequential recordings of RGB images of in vivo exposed rat brain during the cortical spreading depolarization evoked by the topical application of KCl. Changes in the total hemoglobin concentration and the tissue oxygen saturation imply the temporary change in cerebral blood flow during CSD. Decrease in the scattering power b was observed before the profound increase in the total hemoglobin concentration, which is indicative of the reversible morphological changes in brain tissue during CSD. The results in this study indicate potential of the method to evaluate the pathophysiological conditions in brain tissue with a digital red-green-blue camera.
The brain relies on a continuous and adequate supply of blood flow, bringing the nutrients that it needs and removing the
waste products of metabolism. It is thus one of the most tightly regulated systems in the body, whereby a whole range of
mechanisms act to maintain this supply, despite changes in blood pressure etc. Failure of these mechanisms is found in a
number of devastating cerebral diseases, including stroke, vascular dementia and brain injury and trauma. Spontaneous
contraction and relaxation of arterioles (and in some instances venules) termed vasomotion has been observed in an
extensive variety of tissues and species. Vasomotion has a beneficial effect on tissue oxygenation and enhance blood
flow. Although vasomotion is strictly a local phenomenon, the regulation of contractile activity of vascular smooth
muscle cells is dependent on the complex interplay between vasodilator and vasoconstrictor stimuli from circulating
hormones, neurotransmitters, endothelial derived factors, and blood pressure. Therefore, evaluation of the spontaneous
oscillations in cerebral vasculatures might be a useful tool for assessing risk and investigating different treatment
strategies in neurological disorders, such as traumatic brain injury, seizure, ischemia, and stroke. In the present study, we
newly propose a method to visualize the spontaneous low-frequency oscillation of cerebral blood volume based on the
sequential RGB images of exposed brain.
KEYWORDS: Oxygen, Hemodynamics, Digital cameras, Cameras, Brain, In vivo imaging, Monte Carlo methods, RGB color model, Tissues, Diffuse reflectance spectroscopy, Neuroimaging, Cerebral cortex
The concentrations of oxygenated and deoxygenated hemoglobin and regional oxygen saturation in rat brains were
visualized based on the RGB images acquired while changing fraction of inspired oxygen.
We investigate a method to estimate the spectral images of reduced scattering coefficients and the absorption coefficients of in vivo exposed brain tissues in the range from visible to near-infrared wavelength (500-760 nm) based on diffuse reflectance spectroscopy using a digital RGB camera. In the proposed method, the multi-spectral reflectance images of in vivo exposed brain are reconstructed from the digital red, green, blue images using the Wiener estimation algorithm. The Monte Carlo simulation-based multiple regression analysis for the absorbance spectra is then used to specify the absorption and scattering parameters of brain tissue. In this analysis, the concentration of oxygenated hemoglobin and that of deoxygenated hemoglobin are estimated as the absorption parameters whereas the scattering amplitude a and the scattering power b in the expression of μs’=aλ-b as the scattering parameters, respectively. The spectra of absorption and reduced scattering coefficients are reconstructed from the absorption and scattering parameters, and finally, the spectral images of absorption and reduced scattering coefficients are estimated. We performed simultaneous recordings of spectral diffuse reflectance images and of the electrophysiological signals for in vivo exposed rat brain during the cortical spreading depression evoked by the topical application of KCl. Changes in the total hemoglobin concentration and the tissue oxygen saturation imply the temporary change in cerebral blood flow during CSD. Change in the reduced scattering coefficient was observed before the profound increase in the total hemoglobin concentration, and its occurrence was synchronized with the negative dc shift of the local field potential.
KEYWORDS: Absorption, Tissue optics, Scattering, Light scattering, Brain, In vivo imaging, Tissues, Monte Carlo methods, Reflectivity, Diffuse reflectance spectroscopy
Diffuse reflectance spectroscopy using fiber optic probe is one of most promising technique for evaluating optical properties of biological tissue. We present a method determining the reduced scattering coefficients μs’, the absorption coefficients μ a, and tissue oxygen saturation StO2 of in vivo brain tissue using single reflectance fiber probe with two source-collector geometries. In the present study, we performed in vivo recordings of diffuse reflectance spectra and the electrophysiological signals for exposed brain of rats during normoxia, hyperoxia, hypoxia, and anoxia. The time courses of μa in the range from 500 to 584 nm and StO2 indicated the hemodynamic change in cerebral cortex. Time courses of μs’ are well correlated with those of μa in the range from 530 to 570 nm, which also reflect the scattering by red blood cells. On the other hand, a fast decrease in μs’ at 800 nm were observed after the respiratory arrest and it synchronized with the negative deflection of the extracellular DC potential. It is said that the DC shift coincident with a rise in extracellular potassium and can evoke cell deformation generated by water movement between intracellular and extracellular compartments, and hence the light scattering by tissue. Therefore, the decrease in μs’ at 800 after the respiratory arrest is indicative of changes in light scattering by tissue. The results in this study indicate potential of the method to evaluate the pathophysiological and loss of tissue viability in brain tissue.
Diffuse reflectance spectroscopy using a fiber optic probe is a promising technique for evaluating the optical properties of biological tissue. We herein present a method for determining the reduced scattering coefficient, μs′, the absorption coefficient, μa, and the tissue oxygen saturation, StO2, of in vivo brain tissue using a single-reflectance fiber probe with two source-collector geometries. We performed in vivo recordings of diffuse reflectance spectra and of the electrophysiological signals for exposed rat brain during the cortical spreading depression evoked by the topical application of KCl. The time courses of μa at 500, 570, and 584 nm indicated the hemodynamic change in the cerebral cortex as well as StO2. At 570 nm, the time course of μs′ was well correlated with that of μa, which also reflects the scattering by RBCs. On the other hand, increases in μs′ at 500 and 584 nm and a decrease in μs′ at 800 nm were observed before the profound increase in μa, and these occurrences were synchronized with the negative dc shift of the local field potential. The resultant change in the slope of μs′(λ) is indicative of the morphological changes in the cellular and subcellular structures induced by the depolarization due to the temporal depression of the neuronal bioelectrical activity. The results of the present study indicate the potential application of the proposed method in evaluating the pathophysiological conditions of in vivo brain.
In order to estimate multispectral images of the absorption and scattering properties in the cerebral cortex of in vivo rat brain, we investigated spectral reflectance images estimated by the Wiener estimation method using a digital RGB camera. A Monte Carlo simulation-based multiple regression analysis for the corresponding spectral absorbance images at nine wavelengths (500, 520, 540, 560, 570, 580, 600, 730, and 760 nm) was then used to specify the absorption and scattering parameters of brain tissue. In this analysis, the concentrations of oxygenated hemoglobin and that of deoxygenated hemoglobin were estimated as the absorption parameters, whereas the coefficient a and the exponent b of the reduced scattering coefficient spectrum approximated by a power law function were estimated as the scattering parameters. The spectra of absorption and reduced scattering coefficients were reconstructed from the absorption and scattering parameters, and the spectral images of absorption and reduced scattering coefficients were then estimated. In order to confirm the feasibility of this method, we performed in vivo experiments on exposed rat brain. The estimated images of the absorption coefficients were dominated by the spectral characteristics of hemoglobin. The estimated spectral images of the reduced scattering coefficients had a broad scattering spectrum, exhibiting a larger magnitude at shorter wavelengths, corresponding to the typical spectrum of brain tissue published in the literature. The changes in the estimated absorption and scattering parameters during normoxia, hyperoxia, and anoxia indicate the potential applicability of the method by which to evaluate the pathophysiological conditions of in vivo brain due to the loss of tissue viability.
Clinically it is important to image structures of brain at deeper areas with low invasions, for example, the pathological
information is not obtained enough from the white matter. Preliminarily we have measured transmission images of rat
brain using the short graded-index multimode fiber (SMMF) with the diameter of 140μm and length of 5mm. SMMF
(core diameter, 100μm) was cut using a fiber cleaver and was fixed in a jig. Fiber lengths inside and outside jig were
3mm and 2mm, respectively. The jig was attached at the 20x objective lens. The conventional optical microscope was
used to measure images. In basic characteristics, it was confirmed that the imaging conditions almost corresponded to
calculations with the ray-transfer matrix and the spatial resolution was evaluated at about 4.4μm by measuring the test
pattern. After euthanasia the rat parietal brain was excised with thickness around 1.5mm and was set on the slide glass.
The tissue was illuminated through the slide glass by the bundle fiber with Halogen lamp. The tip of SMMF was
inserted into the tissue by lifting the sample stage. The transmission image at each depth from 0.1mm to 1.53mm was
measured. Around the depth of 1.45mm, granular structures with sizes of 4-5μm were recognized and corresponded to
images by HE stained tissue. Total measurement time was within 2 hours. The feasibilities to image the depth of 5
mm with SMMF have been shown.
We investigate a method to estimate the spectral images of reduced scattering coefficients and the absorption coefficients
of in vivo exposed brain tissues in the range from visible to near-infrared wavelength (500-760 nm) based on diffuse
reflectance spectroscopy using a digital RGB camera. In the proposed method, the multi-spectral reflectance images of
in vivo exposed brain are reconstructed from the digital red, green blue images using the Wiener estimation algorithm.
The Monte Carlo simulation-based multiple regression analysis for the absorbance spectra is then used to specify the
absorption and scattering parameters of brain tissue. In this analysis, the concentration of oxygenated hemoglobin and
that of deoxygenated hemoglobin are estimated as the absorption parameters whereas the scattering amplitude a and the
scattering power b in the expression of μs'=aλ-b as the scattering parameters, respectively. The spectra of absorption and
reduced scattering coefficients are reconstructed from the absorption and scattering parameters, and finally, the spectral
images of absorption and reduced scattering coefficients are estimated. The estimated images of absorption coefficients
were dominated by the spectral characteristics of hemoglobin. The estimated spectral images of reduced scattering
coefficients showed a broad scattering spectrum, exhibiting larger magnitude at shorter wavelengths, corresponding to
the typical spectrum of brain tissue published in the literature. In vivo experiments with exposed brain of rats during
CSD confirmed the possibility of the method to evaluate both hemodynamics and changes in tissue morphology due to
electrical depolarization.
The relations and correlation coefficients (CCs) between the OCT signal and the modified state entropy (MSE) of electroencephalogram (EEG) have been studied. Three dimensional (3D) OCT images of rat brains through the thinned skull and EEG have been measured simultaneously anesthetizing to reduce brain activity with the quadrature fringe widefield OCT. Measured 3D volumes are 4mm × 4mm × 2.8mm (Depth). MSE is the product of state entropy of EEG and its effective value. Depth profiles were obtained at the selected three points on the surface of thinned skull. For chosen each depth, the relative signal intensity (RSI) is defined as the ratios of signal intensity to first signal intensity. Deepening the anesthesia RSI increased and MSE decreased to show negative correlation and CCs from -0.31 to -0.56. These results indicate enhancements of the feasibility of OCT as a tool for monitoring/diagnosing the brain tissue viability.
To visualize hemodynamics in cerebral cortex of in vivo rat brain during cortical spreading depression, we investigate a spectral reflectance imaging technique based on the Wiener estimation for a digital RGB camera.
KEYWORDS: Absorption, Scattering, Tissue optics, Light scattering, In vivo imaging, Brain, Monte Carlo methods, Reflectivity, Tissues, Diffuse reflectance spectroscopy
Diffuse reflectance spectroscopy using fiber optic probe is one of most promising technique for evaluating optical properties of biological tissue. We present a method determining the reduced scattering coefficients μs’, the absorption coefficients μa, and tissue oxygen saturation StO2 of in vivo brain tissue using single reflectance fiber probe with two source-collector geometries. In this study, we performed in vivo recordings of diffuse reflectance spectra and the electrophysiological signals for exposed brain of rats during the cortical spreading depression (CSD) evoked by the topical application of KCl. The time courses of μa in the range from 500 to 584 nm and StO2 indicated the hemodynamic change in cerebral cortex. Time courses of μs’ are well correlated with those of μa in the range from 530 to 570 nm, which also reflect the scattering by red blood cells. On the other hand, increases in μs’ at 500 and 584 nm were observed before the profound increase in μa and they synchronized with the negative DC shift of the local field potential. It is said that the DC shift coincident with a rise in extracellular potassium and can evoke cell deformation generated by water movement between intracellular and extracellular compartments, and hence the light scattering by tissue. Therefore, the increase in μs’ at 500 and 584 nm before the profound increase in μa are indicative of changes in light scattering by tissue. The results in this study indicate potential of the method to evaluate the pathophysiological conditions of in vivo brain.
KEYWORDS: Absorption, Scattering, In vivo imaging, Brain, Monte Carlo methods, Cerebral cortex, Tissue optics, Light scattering, Reflectivity, Diffuse reflectance spectroscopy
We present a new method determining the absorption coefficients and the reduced scattering coefficients of in vivo rat
cerebral cortex using single reflectance fiber probe with two source-collector geometries. Experiments with optical
phantoms were conducted to evaluate the performance of the proposed fiber probe system. In order to confirm the
possibility of the method to evaluate changes in the optical properties of cerebral cortex, we performed in vivo
experiments for exposed rat brain during CSD evoked by the pinprick stimulation.
We describe a novel compact real-time single-shot full-field optical coherence tomography based on a dual-channel
phase-stepper optics, which employs a 2-D quaternionic analytic signal processing technique to reconstruct the en-face
OCT image. The experimental setup was based on a Linnik type polarization Michelson interferometer followed by a
dual-channel phase-stepper optics and a single CCD camera to capture two 180° phase stepped images simultaneously.
The interferometer is illuminated using a SLD source with central wavelength of 842 nm and spectral bandwidth of 16.2
nm, yielding an axial resolution of 19.8 μm. Using a 10 X (0.25-NA) microscope objective and a single CCD camera,
the system covers an area of 325μm x 300μm (325 × 300 pixels) with a transverse resolution of 4.4 μm. We demonstrate
the feasibility of this system for real-time imaging of scattering specimens such as a diaptomus.
We demonstrate a compact single-shot full-field optical coherence tomography (OCT) system for obtaining real-time
high-resolution depth resolved en-face OCT images from weakly scattering specimens. The experimental setup is based
on a Linnik type polarization Michelson interferometer and a four-channel compact polarization phase stepper optics.
The four-channel phase-stepper optics comprise of a dual channel beam splitter, a Wollaston prism and a pair of wave
plate for simultaneously capturing four quadratually phase-stepped images on a single CCD. The interferometer is
illuminated using a SLD source with a central wavelength of 842 nm and a bandwidth of 16.2 nm, yielding an axial
resolution of 19.8 μm. Using a 10 × (0.25-NA) microscope objective and a CCD camera with 400 × 400 pixels, the
system covers an area of 225 μm × 225 μm with a transverse resolution of 4.4 μm. The en-face OCT images of an onion
is measured with an exposure time of 7ms and a frame rate of 28 fps.
We demonstrate axial-lateral parallel time-domain optical coherence tomography using an optical zoom lens and highorder diffracted lights at 830 nm to adjust imaging range. Our 2-D CCD camera (640 x 480 pixels, 207fps) measured a depth-resolved interference image using diffracted light as the reference beam and a linear illumination beam without any scan. The lateral range can be varied continuously from 6.4 to 1.6 mm by increasing the magnification of optical zoom lens. The axial range can be adjusted discretely from 1st to 7th orders because we used a diffraction grating with 300 lines/mm in a 830 nm wavelength region.
We developed axial-lateral parallel time domain optical coherence tomography (OCT) with an ultrahigh-speed
complementary metal oxide semiconductor (CMOS) camera. A cylindrical lens is inserted in the signal arm to
illuminate the sample with a linear beam that can be moved horizontally by a galvano scanner. A reflective grating is
installed in the Littrow configuration so that first-order diffracted light propagates backward along the incoming path at
the reference beam to obtain a continuous delay. The backscattered light from the sample and the diffracted light from
the grating are imaged onto a CMOS camera (512 × 512 pixels, 17 × 17 &mgr;m pixels, 10 bit resolution, frame rate 3000
fps) using an achromatic imaging lens. The camera obtains a depth-resolved interference image using diffracted light
as the reference beam and a linear illumination beam without axial and vertical scans. We can obtain the OCT images
(512 × 512 pixels) at 1,500 fps by calculating two sequential images. To create a 3-D image, the linear probe beam
was scanned at 3 Hz to obtain volume data. 500 interference images per scan (corresponding to 250 OCT images
through calculations from two sequential images) created a 3-D dataset of 512 × 250 × 512 pixels. The experimental
sensitivity was approximately 76 dB after 2 × 2-pixel binning. The system was successfully used to image the human
finger in vivo.
We demonstrated that a synthesized light source (SLS) consisting of two low coherence light sources is capable of enhancing spatial resolution in optical coherence tomography (OCT). The axial resolution of OCT is given by the half of coherence length of the light source. We fabricated an SLS with a coherence length of 2.3 μm and the side lobe intensity of 29% under the intensity ratio of LED 1: LED 2 = 1: 0.4 by combining two light sources, LED 1 with a central wavelength of 700 nm and spectral bandwidth of 100 nm, and LED 2 of 898 nm and 85 nm. The coherence length of 2.3 μm is 56% of the shorter coherence length in two LED's, therefore the axial resolution is 1.2 μm.
Optical coherence tomography (OCT) is a powerful technique for imaging the random scattering medium. Resolution improvement is an important task in the OCT. A novel low coherence interferometer (LCI) in which three reference mirrors are used to generate reference lights is proposed for obtaining higher resolution. The output signal of this LCI is a superposition of interference of signal light with three reference lights. Through adjusting the relative intensities of reference lights, the width of the axial point spread function for the LCI can be reduced, then the resolution of the LCI will be improved. The influence of fluctuations of wavelength and mirror separation on the resolution improvement are investigated. It is expected that this new approach may provide an effective and useful technique for optical measurement.
The optical coherence tomography (OCT0 is a novel imaging technique for producing high-resolution cross-sectional images of the internal microstructure. Resolution improvement is an important task in the OCT. A new approach is proposed for achieving shorten coherence length by combining several low coherence sources to improve the resolution of the OCT. This optimization synthesis problem belongs to solving an inverse source problem. An optimization algorithm is used to select the parameters of sources for decreasing the effective coherence length and inhibiting side lobe simultaneously. Computer simulations are presented to approve our method. By combining three light sources, the coherence length can be reduced to 57% of the smallest one of a single source used and the side lobes are lower than 5% of the center packet.
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