The full-field optical coherence tomography (FFOCT) has been used to reconstruct the depth information and recover 3D object details at various depths. However, the current FFOCT system employs silicon-based detectors such as CMOS to capture optical signals, while the system sensitivity may degrade significantly when the wavelength of signals is longer than 1000 nm. Instead, the camera array based on Indium Gallium Arsenide (InGaAs) is capable to respond properly for signals with the wavelength ranging from 900 to 1700 nm. Therefore, in this paper, we first build an FFOCT hardware system based upon InGaAs camera. Furthermore, we study the unignorable noise and the low contrast in the detected image. Then, we design a post-processing algorithm to remove the noise and restore the objects in the image. Experimental results have shown that the whole system is capable of clearly showing the biomedical structure within cells.
Several studies have demonstrated the potential of short wavelength infrared (SWIR) reflectance, thermal imaging and optical coherence tomography for the nondestructive assessment of the activity of caries lesions. The purpose of this study was to test the hypothesis that the activity of arrested caries lesions on the coronal surfaces of extracted teeth would be changed by reducing the thickness of the highly mineralized transparent surface layer, which was measured using polarization sensitive optical coherence tomography (PS-OCT). The lesion activity was assessed using SWIR reflectance and thermal imaging during forced air drying of the lesion before and after mechanical removal of a surface layer ~ 50-μm thick covering the lesion. Both the intensity change in SWIR reflectance images at 1500- 1750-nm wavelengths after drying the lesions and the change in thermal emission measured with a thermal camera at 8-13-μm wavelengths increased significantly (P<0.05) after reducing the thickness of the mineralized surface layer in the lesions indicating the permeability of the lesion to fluids increased. These results provide further evidence that the presence of a highly mineralized outer surface layer is a key indicator of lesion arrest.
An algorithm is presented that can be used to obtain accurate optic axis orientation of birefringent tissue samples. A single-mode fiber (SMF)-based polarization-sensitive optical coherence tomography with a single linearly polarized incident light was used in the measurements in which the light reflected from the sample and detected by the spectrometer is linearly polarized light at 45 deg with respect to the experimental horizontal axis. By employing polarization controllers to completely specify the parameters of the fiber system, the absolute optic axis orientation could then be estimated accurately by analyzing the Mueller matrices of the fiber system and sample. The proposed algorithm has been validated in the quantification of the optic axis orientation of a quarter-wave plate. Finally, several birefringent tissue samples were imaged with this SMF-based system.
Motion artifacts and interference residuals limit the performance of conventional full-field optical coherence tomography (FF-OCT) for in vivo imaging. It is because piezoelectric translator-based phase-shifting method bring chromatic abberation with broadband light source and is wavelegnth-dependent. Many achromatic phase-shifters were designed and introduced additional mechanical vibrations into the imaging system. In this work, an achromatic phase-shifting mechanism was proposed with dual-channel FF-OCT. Based on a Linnik interferometer, a linear polarizer and a quarter-wave plate were employed in the reference arm to replace PZT and generate the circle polarized light beam. The light field reflected from the reference arm is supposed with the unpolarized light backscattered from the sample when the path difference is within the coherence length of the light source. With one phase difference of π/2 shifted by interference between the circle polarized light and unpolarized light. Two inteference beams were received by a pair of identical CCDs. With porposed numerical phase-shifting method based on Hilbert transform, the en face tomograms of sample will be reconstructed in a single-shot. The axial and lateral resolutions of the system are around 1.4µm and 0.8µm, respectively. Tomograms of Intel microchip were displayed with clear substructures. Three-dimensional miscrostructures of fresh and isolated mouse heart were obtained in video-rate. This article aims at producing fringe-free OCT images with imaging rate of 30fps.
In this paper, beam-shifting optical coherence tomography (BSOCT) is presented for speckle reduction and flow rate measurement. The sample beam is rotated about the optical axis of the objective lens to modulate the incident angle on sample; 17 and 3 incident angles are respectively performed for speckle reduction and flow rate measurement. The performance of the proposed technique is investigated on both phantom and in vivo experiments. By combining a 2D micro-electro-mechanical system (MEMS) and a zigzag scanning protocol, the frame rates of 45.2 Hz for speckle reduction and 25.6 Hz for flow rate measurement are achieved. With beam-shifting angle of 4.76º, the speckle noise reduction of 91% and the flow rate measurement precision of 0.0019 μl/s are achieved.
An image contrast correction method is proposed for en face images obtained with full-field optical coherence tomography (FFOCT). First, the mechanism of image contrast decrease in FFOCT is considered and the theoretical models of main parameters that degrade image contrast are analyzed. Second, changes of contrast with depth are calculated under various conditions, from which the main parameters that affect contrast in tissue are identified. Then based on the analysis, the methods are proposed for correcting image contrast. Finally, the en face tomographic images of human liver tissue at different depths with and without contrast correction are presented to demonstrate the capability of the method. The results are very helpful for correctly interpreting FFOCT images for applications in disease diagnosis.
The polarization-sensitive spectral domain optical coherence tomography (PSOCT) has the advantages of being able to
measure the polarization properties of samples, such as phase-retardation, diattenuation, depolarization, and optical axis
orientation, providing a contrast to identify the diseased area and normal area in tissues in PSOCT images.
Conventionally, the sample arm of PSOCT is fixed on the stage where biomedical tissues or models is placed, and the
OCT images is acquired by scanning with a galvanometer-based mirror. To be applied in the practical diagnosis, a
promising way is to design a hand-held device. To this end, it is required that probe is assembled with a small volume to
allow for comprehensively imaging large tissues areas at a microscopic scale, and is available to move on different
samples to be acquired quickly with negligible motion artifacts. Meanwhile, the probe should be manufactured wih well
stability to avoid system jitter error while it is used to detect the biological tissues in vivo. In this work, a design of a
hand-hold fiber-based PSOCT is described. The device is of the size of 10 cm (length) × 8 cm (width) × 6 cm (height).
Both the axial resolution and the imaging depth of the system are measured and were approximately 7 μm and 2.5 mm in
air, respectively, which are in good agreement with the theoretical predictions. The A-scan rate of the system is 70 kHz.
The structure is compact and all the components are fixed on the shell to reduce the motion artifact, resulting in a great
stability on measuring the tissues in vivo. The cross sectional images of ex vivo chicken breast, ex vivo pork cartilage
and in vivo forearm skin of human wolunteer are presented to demonstrate the capability of the system.
In this paper, a multi-beam optical coherence tomography (OCT) was used to reconstruct the microvascular image of human skin in vivo with phase resolved Doppler OCT (PRDOCT), phase resolved Doppler variance (PRDV) and speckle variance OCT (svOCT), in which the blood flow image was calculated by averaging the four blood flow images obtained by the four beams. In PRDOCT method, it is difficult to detect the blood flow perpendicular to optical axis of the probe beam for single beam OCT, but the multi-beam scanning method can solve this because the input angles of the four probe beams are slightly different from each other. The proposed method can further improve the signal-to-noise ratio (SNR) of the blood flow signals extracted by the three methods mentioned above.
The kidneys are essential regulatory organs whose main function is to regulate the balance of electrolytes in the blood, along with maintaining pH homeostasis. The study of the microscopic structure of the kidney will help identify kidney diseases associated with specific renal histology change. Spectrally encoded microscopy (SEM) is a new reflectance microscopic imaging technique in which a grating is used to illuminate different positions along a line on the sample with different wavelengths, reducing the size of system and imaging time. In this paper, a SEM device is described which is based on a super luminescent diode source and a home-built spectrometer. The lateral resolution was measured by imaging the USAF resolution target. The axial response curve was obtained as a reflect mirror was scanned through the focal plane axially. In order to test the feasibility of using SEM for depth-section imaging of an excised swine kidney tissue, the images of the samples were acquired by scanning the sample at 10 μm per step along the depth direction. Architectural features of the kidney tissue could be clearly visualized in the SEM images, including glomeruli and blood vessels. Results from this study suggest that SEM may be useful for locating regions with probabilities of kidney disease or cancer.
KEYWORDS: Photovoltaics, Wavefronts, Error analysis, Computer simulations, Optical components, Interferometers, Testing and analysis, Environmental sensing, Time metrology, High power lasers
The full-aperture and full-frequency absolute surfaces of optical flats are of great significant for industrial applications but hard to achieve. To measure them simultaneously, Kuechel proposed an absolute testing based on N-position rotations by adding a set of measurement data of N-position rotations, in comparison to the traditional four measurements. Algorithm simulation and absolute detection experiments have been conducted before, however, the influence of rotation angle error has not been analyzed, and the full-aperture contrast experiments have not been conducted. In this paper, the influence of rotation angle error was analyzed, and the measurement result is within acceptable range even when the angle error reaches 1°. Moreover, to verify the accuracy of this method, full-aperture contrast experiments were proposed innovatively besides the two linear profiles contrast experiments. The contrast experiments prove the accuracy of the full-aperture absolute measured results, other than the accuracy of the two linear profiles results.
With the unprecedented developments of the intense laser and aerospace projects', the interferometer is widely used in detecting middle frequency indicators of the optical elements, which put forward very high request towards the interferometer system transfer function (ITF). Conventionally, the ITF is measured by comparing the power spectra of known phase objects such as high-quality phase step. However, the fabrication of phase step is complex and high-cost, especially in the measurement of large-aperture interferometer. In this paper, a new fringe method is proposed to measure the ITF without additional objects. The frequency was changed by adjusting the number of fringes, and the normalized transfer function value was measured at different frequencies. The ITF value measured by fringe method was consistent with the traditional phase step method, which confirms the feasibility of proposed method. Moreover, the measurement error caused by defocus was analyzed. The proposed method does not require the preparation of a step artifact, which greatly reduces the test cost, and is of great significance to the ITF measurement of large aperture interferometer.
We present an imaginary part-based correlation mapping optical coherence tomography (IMcmOCT) technique for in vivo blood vessels imaging. In the conventional correlation mapping optical coherence tomography (cmOCT) method, two adjacent frames of intensity-based structural images are correlated to extract blood flow information and the size of correlation window has to be increased to improve the signal-to-noise ratio of microcirculation maps, which may cause image blur and miss the small blood vessels. In the IMcmOCT method, the imaginary part of a depth-resolved complex analytic signal in two adjacent B-scans is correlated to reconstruct microcirculation maps. Both phantom and in vivo experiments were implemented to demonstrate that the proposed method can provide improved sensitivity for extracting blood flow information in small vessels.
We report rapid and high-resolution tomographic en face imaging of human liver specimens by full-field optical coherence tomography (FF-OCT). First, the arrangement of the FF-OCT system was described and the performance of the system was measured. The measured axial and lateral resolutions of the system are 0.8 and 0.9 μm, respectively. The system has a sensitivity of ∼60 dB and can achieve an imaging rate of 7 fps and a penetration depth of ∼80 μm. The histological structures of normal liver can be seen clearly in the en face tomographic images, including central veins, cords of hepatocytes separated by sinusoidal spaces, and portal area (portal vein, the hepatic arteriole, and the bile duct). A wide variety of histological subtypes of hepatocellular carcinoma was observed in en face tomographic images, revealing notable cancerous features, including the nuclear atypia (enlarged convoluted nuclei), the polygonal tumor cells with obvious resemblance to hepatocytes with enlarged nuclei. In addition, thicker fibrous bands, which make the cytoplasmic plump vesicular nuclei indistinct, were also seen in the images. Finally, comparison between the portal vein in a normal specimen versus that seen in the rare type of cholangiocarcinoma was made. The results show that the cholangiocarcinoma presents with a blurred pattern of portal vein in the lateral direction and an aggregated distribution in the axial direction; the surrounding sinusoidal spaces and nuclei of cholangiocarcinoma are absent. The findings in this work may be used as additional signs of liver cancer or cholangiocarcinoma, demonstrating capacity of FF-OCT device for early cancer diagnosis and many other tumor-related studies in biopsy.
Spectrally encoded microscopy (SEM) is a new microscopic imaging technique in which a grating is used to illuminate different positions along a line on the sample with different wavelengths, reducing the size of system and imaging time. In this paper, a SEM device is described which is based on a swept source and a balanced detection. A fixed gain balanced detector (BD) was employed in the system for detecting the low sample light without amplifier. Compared to conventional SEM detection method, our BD-SEM device has two significant advantages, one is its capability of suppressing common-mode noise and thermal noise, resulting in the lateral resolution better than direct detection, the other is that it can amplify the signal intensity which is particularly helpful for tissue reflectance imaging. The lateral resolution was measured by imaging a USAF resolution target. The images of onion cells were obtained. The data showed that both the lateral resolution and signal noise ratio are better than non-BD method. The method presented in this work is helpful for developing miniature endoscopic probe for in vivo tissue visualization with high acquisition speed and high imaging quality.
KEYWORDS: Blood vessels, Optical coherence tomography, Signal to noise ratio, Blood circulation, In vivo imaging, Tissue optics, Tissues, Optical engineering, 3D image processing, Associative arrays
We present a cube data correlation-based correlation mapping optical coherence tomography (cube-cmOCT) method to reconstruct small blood vessel maps. In the cube-cmOCT method, the two adjacent cube data are correlated to extract blood flow information. Both phantom experiments and in vivo experiments were performed to demonstrate the advantage of the proposed method in improving the SNR of blood vessel maps without increasing the window size in the xz plane and offering a clear image of the small blood vessels almost missed by the conventional cmOCT method.
A new full-field optical coherence tomography system with high-resolution has been developed for imaging of cells and tissues. Compared with other FF-OCT (Full-field optical coherence tomography, FF-OCT) systems illuminated with optical fiber bundle, the improved Köhler illumination arrangement with a halogen lamp was used in the proposed FF-OCT system. High numerical aperture microscopic objectives were used for imaging and a piezoelectric ceramic transducer (PZT) was used for phase-shifting. En-face tomographic images can be obtained by applying the five-step phase-shifting algorithm to a series of interferometric images which are recorded by a smart camera. Three-dimensional images can be generated from these tomographic images. Imaging of the chip of Intel Pentium 4 processor demonstrated the ultrahigh resolution of the system (lateral resolution is 0.8μm ), which approaches the theoretical resolution 0.7 μm× 0.5 μm (lateral × axial). En-face images of cells of onion show an excellent performance of the system in generating en-face images of biological tissues. Then, unstained pig stomach was imaged as a tissue and gastric pits could be easily recognized using FF-OCT system. Our study provides evidence for the potential ability of FFOCT in identifying gastric pits from pig stomach tissue. Finally, label-free and unstained exvivo human liver tissues from both normal and tumor were imaged with this FFOCT system. The results show that the setup has the potential for medical diagnosis applications such liver cancer diagnosis.
The axial resolution is an important parameter in Optical Coherence Tomography (OCT). In OCT a
broadband light source is used to achieve high axial resolution imaging. However the dispersion results
in a broadening of the coherence envelope. The dispersion mismatch between reference and sample
arms then needs to be minimized to achieve optimal axial resolution for OCT. In this work we propose
a new numerical dispersion compensation method to obtain ultrahigh resolution in SDOCT, in which
wavelet transform instead of Fourier transform is used to obtain the signal in different frequency
domain. And a series of the phase signals of different interfaces of the sample can be obtained. Under
the homogeneous medium approxiamtion, the phase signal is a linear function of the wave number.
Thus based on linearization of the phase signal of different interface and the wave number, the axial
resolution can be improved.
A different real-time self-wavelength calibration method for spectral domain optical coherence tomography is presented in which interference spectra measured from two arbitrary points on the tissue surface are used for calibration. The method takes advantages of two favorable conditions of optical coherence tomography (OCT) signal. First, the signal back-scattered from the tissue surface is generally much stronger than that from positions in the tissue interior, so the spectral component of the surface interference could be extracted from the measured spectrum. Second, the tissue surface is not a plane and a phase difference exists between the light reflected from two different points on the surface. Compared with the zero-crossing automatic method, the introduced method has the advantage of removing the error due to dispersion mismatch or the common phase error. The method is tested experimentally to demonstrate the improved signal-to-noise ratio, higher axial resolution, and slower sensitivity degradation with depth when compared to the use of the zero-crossing method and applied to two-dimensional cross-sectional images of human finger skin.
Doppler optical coherence tomography (DOCT) is an extension of optical coherence tomography (OCT) for measuring
blood flow dynamics simultaneously with the microscopic structures at high spatial and velocity resolution. In this paper,
we analyze the effects of parameters of the DOCT system on the optical transfer function (OTF) which finally affects the
accuracy of the velocity estimation. Experimental data are given to show the effects. The methods of overcoming the
effects are also pointed out.
The significance of beam condition for scattered light from random tissue is analyzed for a practical optical imaging system with a finite numerical aperture. It is shown that in the transmitted illumination case, the information carrying part of the spectrum of the scattered light is proportional to the square of the spatial frequency of the spatial correlation function of the scattering potential of the medium. The result may be helpful in interpreting images obtained with microscopes in biological studies.
Optical Coherence Tomography (OCT) is a noninvasive cross-sectional imaging modality capable of measuring tissue morphology and function high spatial resolution. The amplitude of the intero-metric heterodyne signal provides a profile of sample reflectivity related to its microstructure and its phase may enable bi-directional blood flowing imaging, termed Color Doppler OCT (CDOCT). In order to evaluate and improve the imaging properties as well as find the appropriate image-processing algorithms, several theoretical models of OCT of biological tissue have been proposed. Most of these models are based on the consideration of both the single scattering and multiple scattering processes of the light within the tissues. However, all these models omitted the effects of moving scatterers on measured backscattering signal. We show that inclusion of this effect is more realized and is of great importance in the calculation and interpretation of the heterodyne signal, evaluation of the system performance as well as calculating the maximum imaging depth of the OCT scanners. The analytical results and a sample result is given.
3D image processing is an important problem of modern science and technology research. With the development of optical technology, the laser confocal scanning microscope (LCSM) system has been used successfully as advanced 3D image instrument in the medical research domain. This paper is primarily to discuss mathematical morphology method of processing 3D image combining with 3D cell image formed by LCSM system. Paper begins from 2D mathematical morphology and specializes various 3D mathematical morphology theories. It offers a series of mathematical morphology methods of 3D image processing about its various cases. At last we use these methods to process the 3D cell image formed by the laser confocal scanning microscope system.
Laser heterodyne interferometry is a kind of photoelectric phase measuring technique, it measures the optical path difference between the reference wavefront and the measured wavefront directly and needs not to deal with the interference figure. This technique can give very high phase measuring precision and can be used in dynamic optical phenomenon. This paper studies the basic principles of laser heterodyne interferometer, and the heterodyne interferometry has successfully been applied to the field of photoelastic properties of selected optical materials. A new method of measuring some parameters of photoelastic is presented. A device which brings atmosphere to bear on the optical materials has been developed to measure the change of refractive index at different pressures, and the relationship between the given pressure and the corresponding change of refractive index has been obtained through a series of experiments. Also, a careful analysis is given to the result of the experiments. At last, a feasible scheme is discussed on applying laser heterodyne interferometry to the measurement of refractive change.
Optical coherence microcopy (OCM) is a new method for optical and near-infrared imaging of biological tissues. This method is based on the detection of least-back-scattering light that maintain coherence and has thus spend shortest time that its path-length difference (Delta) L falling within the coherence length Lc of the low-coherence source. This paper points out that there are also a special part of multiple scattering light which has the sufficient small part length differences (Delta) L falling within the coherence Lc. The effects of this part of multiple scattering light can be divided into two categories. One is nonlinear effects and the other is speckle effects.
At the optical processing domain, the three-dimension reconstruction of information is an important problem of research. At the last few years, the laser confocal scanning microscope (LCSM) system was researched and has been used successfully as advanced optical instrument in the biological and medical research range. This paper primarily research the 3-D image reconstruction of the cell using its 2-D section image formed by the laser confocal scanning microscopy. First, the paper rests on the LCSM system characteristic of forming image to analyze the image noise and remove it. Then we extract the information of 2-D section image edge, and we use these informations to reconstruct the 3-D image of cell surface by method of B-Spline.
Low coherence optical tomography (OCT) is a novel technique with high resolution for rapid, noninvasive imaging in living biological tissues. With this technique, a thin 'optical section' within a thick biological specimen can be obtained. Using a combination of the principles of low-coherence interferometry and confocal microscopy, OCT can provide micron-scale tomographic imaging of internal tissue microstructures. In OCT, enhanced optical sectioning performance in biological tissues (highly scattering media) is achieved through high detection sensitivity and high contrast rejection of out-of-focus light. In this paper, basic principle and recent advances in optical coherence tomography are described. The emphasis is to analyze some key problems in OCT setup. Light attenuation and scanning system are studied in detail. A theoretical model for low-coherence optical tomography in highly scattering media (biological tissues) is given. The authors will show that OCT images may be significantly affected by multiple scattering associated with the refractive index inhomogeneities found in scattering media such as biological tissues. At last, a conclusion suggests that OCT is a very promising technique for clinical application because of its simple theory and low cost.
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