Fiber bundle coupler is a key part in a probe-based endomicroscope used to couple laser in each core of the fiber bundles precisely when the laser scan unit is performing a high speed confocal scanning. Common fiber connector is usually used in communication application with single fiber core. But for image transmitting, common connector such as SMA must be manually adjusted in 5 axes to locate all fiber cores of the bundle. A micron precision fiber bundle coupler is introduced in this article. This coupler is special designed for an endomicroscope. This coupler can locate the position of the fiber cores of a bundle in micro precision in all 3 dimensions with the help of the mechanical structure and focusing mechanism. The coupler has a plug and a socket component. A polished fiber bundle is installed in the center of the plug. A connection core is located in the center of the socket component to make sure the plug and the coupling objective can stay in a same axis, so that the fiber bundle can also located in the same axis. A number of arms distributed symmetrically can be pushed by the operating cover to apply a constant pressure on the plug through a spring to lock the plug. The coupling objective can move along the axis inside the connection core by a linear actuator. An image evaluation algorithm can help the actuator to find a proper location to achieve auto focus. The coupler can work smoothly and automatically. It is very easy for clinical use.
We present a decoupled fluorescence Monte Carlo (dfMC) model for the direct computation of the fluorescence in turbid media. By decoupling the excitation-to-emission conversion and transport process of the fluorescence from the path probability density function and associating the corresponding parameters involving the fluorescence process with the weight function, the dfMC model employs the path histories of the excitation photons and the corresponding new weight function to directly calculate the fluorescence. We verify the model’s accuracy using phantom experiments and compare it with that of the perturbation fluorescence Monte Carlo model. The results indicate that the model is accurate for the direct fluorescence calculation and, thus, has great potential for application in fluorescence-based in vivo tomography.
Vasoactive drugs are normally utilized to elevate mean artery pressure and maintain adequate organ perfusion in clinical treatment. During the injection, morphological changes and the subsequent oxygen supply alteration in the brain, e.g., possible hypoxia, are prone to introduce serious damage and even dysfunction to the brain. Therefore, multiparameter monitoring of cerebral microvasculature is necessary during drug injection. An optical-resolution photoacoustic microscopy was used to assess the effects of norepinephrine on microvasculature in the brain cortex of mice. In our experiments, the diameter, total hemoglobin (HbT) and oxygen saturation (SO 2 ) of single cerebral microvessels during tail vein injection of norepinephrine were analyzed. Following the injection, vasoconstriction was observed, and HbT and SO 2 were decreased in turn. The vessel diameter and HbT recovered back to the base value without further injection, while the SO 2 remained low throughout the observation period. Arterioles showed more acute constriction but a smaller decline in HbT during the injection compared with venules, while SO 2 in arterioles increased slightly without further drug injection but not in venules. Our results suggested that photoacoustic microscopy may become a new method for early and comprehensive evaluation of the effect of drugs on microvasculature in brain.
Finite element method is a general approach for diffuse optical tomography, and the accuracy of which is closely related
to the type of elements used. In this paper, we investigate the differences between linear element and quadratic triangular
element in the forward problem of diffuse optical tomography. The results show that quadratic element is a better
compromise between high accuracy and low time consumption compared to the linear element. This means high order
element is a better choice for the diffuse optical tomography.
The study of dual-modality technology which combines microcomputed tomography (micro-CT) and fluorescence molecular tomography (FMT) has become one of the main focuses in FMT. However, because of the diversity of the optical properties and irregular geometry for small animals, a reconstruction method that can effectively utilize the high-resolution structural information of micro-CT for tissue with arbitrary optical properties is still one of the most challenging problems in FMT. We develop a micro-CT-guided non-equal voxel Monte Carlo method for FMT reconstruction. With the guidance of micro-CT, precise voxel binning can be conducted on the irregular boundary or region of interest. A modified Laplacian regularization method is also proposed to accurately reconstruct the distribution of the fluorescent yield for non-equal space voxels. Simulations and phantom experiments show that this method not only effectively reduces the loss of high-resolution structural information of micro-CT in irregular boundaries and increases the accuracy of the FMT algorithm in both forward and inverse problems, but the method also has a small Jacobian matrix and a short reconstruction time. At last, we performed small animal imaging to validate our method.
Low-resolution and ill-posedness are the major challenges in diffuse optical tomography(DOT)/fluorescence molecular
tomography(FMT). Recently, the multi-modality imaging technology that combines micro-computed tomography
(micro-CT) with DOT/FMT is developed to improve resolution and ill-posedness. To take advantage of the fine priori
anatomical maps obtained from micro-CT, we present an arbitrary boundary triangle mesh generation method for
FMT/DOT/micro-CT multi-modality imaging. A planar straight line graph (PSLG) based on the image of micro-CT is
obtained by an adaptive boundary sampling algorithm. The subregions of mesh are accurately matched with anatomical
structures by a two-step solution, firstly, the triangles and nodes during mesh refinement are labeled respectively, and
then a revising algorithm is used to modifying meshes of each subregion. The triangle meshes based on a regular model
and a micro-CT image are generated respectively. The results show that the subregions of triangle meshes can match
with anatomical structures accurately and triangle meshes have good quality. This provides an arbitrary boundaries
triangle mesh generation method with the ability to incorporate the fine priori anatomical information into DOT/FMT
reconstructions.
High-speed fluorescence molecular tomography (FMT) reconstruction for 3-D heterogeneous media is still one of the most challenging problems in diffusive optical fluorescence imaging. In this paper, we propose a fast FMT reconstruction method that is based on Monte Carlo (MC) simulation and accelerated by a cluster of graphics processing units (GPUs). Based on the Message Passing Interface standard, we modified the MC code for fast FMT reconstruction, and different Green's functions representing the flux distribution in media are calculated simultaneously by different GPUs in the cluster. A load-balancing method was also developed to increase the computational efficiency. By applying the Fréchet derivative, a Jacobian matrix is formed to reconstruct the distribution of the fluorochromes using the calculated Green's functions. Phantom experiments have shown that only 10 min are required to get reconstruction results with a cluster of 6 GPUs, rather than 6 h with a cluster of multiple dual opteron CPU nodes. Because of the advantages of high accuracy and suitability for 3-D heterogeneity media with refractive-index-unmatched boundaries from the MC simulation, the GPU cluster-accelerated method provides a reliable approach to high-speed reconstruction for FMT imaging.
We have developed a new third-order approximation model of Mueller matrix for spatial characterization of the
polarization effects in backscattering from highly scattering media. Using the Stokes-Mueller formalism and scattering
amplitudes calculated with Mie theory, we are able to numerically determined matrix elements. Specific features of the
2D Mueller matrix components corresponding to light backscattered from polystyrene micosphere suspensions are
characterized and compared with the experimental data for different size of scatterers, the scattering coefficient and the
anisotropy factor g. The results show good agreement in both azimuthal and radial direction.
The polarization properties of light backscattered from the Intralipid suspensions are investigated for different input
polarized light. The Stokes vector of the diffuse backscattered light exiting the sample is measured by use of CCD
experimental setup. The backscattering intensity and the degree of polarization are calculated from each Stokes vector.
Especially, the emphasis is on the influence of linearly polarized light with different input azimuth angle, the circularly
polarized light with the different rotary direction on the backscattering intensity and the degree of polarization of the
turbid media. Furthermore, both the relations of the backscattering intensity with the media concentration and the degree
of polarization with the media concentration for different input polarization state, different input azimuth angle are
presented. These experimental results have shown that the degree of polarization and the intensity of light backscattered
from a turbid media are sensitive to the input polarization state and the media concentration.
Polarized light scattering spectroscopy (LSS) is sensitive to the cell nuclear morphological changes in the various forms of epithelial dysplasia. Extensive studies illustrate it is a promising in situ technique to detect precancerous and early cancerous changes in the epithelial tissue. To determine the density and size distribution of cell nuclei with spectra, generally, Mie theory-based inverse model is adopted. This model is of multiple parameters, multiple extreme values and nonlinear. The determination of all unknown parameters needs to solve a nonlinear inverse problem. Other than least-square fitting used by previous studies, in this paper, we developed a novel method - float genetic algorithm (FGA) to determine the particle size distribution and refractive index for LSS. Our results showed that, relative errors of three estimated statistical quantities: diameter, standard deviation and refractive index are less than 5% for different additive Gauss noise levels with 70 iteration epochs. The errors gradually decrease with iteration epoch increases. Moreover, comparing with Newton-type iteration method coupled with a Marquardt-Tikhanov regularization scheme, FGA avoids the problems of local extreme value and selection of initial value and regularization parameters, thus obtains the advantages of high precision, stability and robustness.
In this paper, we have developed a Monte Carlo algorithm that simulates the wavelength dependent, elastic scattering spectroscopy of the polarization light in preinvasive cancer tissue. Using stokes vector formalism and scattering amplitudes calculated with Mie theory. The simulation results show the backscattering spectroscopy is sensitive to cellular and nuclear size.
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