Generalized Pulse Spectrum Technique Research Articles

1B13 一般化パルススペクトル法を用いた蛍光トモグラフィーの三次元画像再構成(GS5:画像解析)

1B13 一般化パルススペクトル法を用いた蛍光トモグラフィーの三次元画像再構成(GS5:画像解析)

Combined hemoglobin and fluorescence diffuse optical tomography for breast tumor diagnosis: a pilot study on time-domain methodology.

A combined time-domain fluorescence and hemoglobin diffuse optical tomography (DOT) system and the image reconstruction methods are proposed for enhancing the reliability of breast-dedicated optical measurement. The system equipped with two pulsed laser diodes at wavelengths of 780 nm and 830 nm that are specific to the peak excitation and emission of the FDA-approved ICG agent, and works with a 4-channel time-correlated single photon counting device to acquire the time-resolved distributions of the light re-emissions at 32 boundary sites of tissues in a tandem serial-to-parallel mode. The simultaneous reconstruction of the two optical (absorption and scattering) and two fluorescent (yield and lifetime) properties are achieved with the respective featured-data algorithms based on the generalized pulse spectrum technique. The performances of the methodology are experimentally assessed on breast-mimicking phantoms for hemoglobin- and fluorescence-DOT alone, as well as for fluorescence-guided hemoglobin-DOT. The results demonstrate the efficacy of improving the accuracy of hemoglobin-DOT based on a priori fluorescence localization.

Time-domain fluorescence-guided diffuse optical tomography based on the third-order simplified harmonics approximation

Extensive efforts have been made to integrate diffuse optical tomography (DOT) with other imaging modalities, such as magnetic-resonance imaging and x-ray computerized tomography, for its performance improvement. However, the experimental apparatus is in general intricate and costly due to adoption of the physically distinct radiation regimes. In this study, a time-domain fluorescence-guided DOT methodology that incorporates a priori localization information provided by diffuse fluorescence tomography (DFT) is investigated in an attempt to optimize recovery of the optical property distributions. The methodology is based on a specifically designed multichannel time-correlated single-photon-counting DOT/DFT system as well as a featured-data image reconstruction scheme that is developed within the framework of the generalized pulse spectrum technique and employs the third-order simplified harmonics approximation to the radiative transfer equation as the forward model. We have validated the methodology using phantom experiments and demonstrated that, with the guidance of fluorescence a priori, the quantitativeness and spatial resolution of the recovered optical target can be considerably improved in terms of the absorption and scattering images.

An Inverse Electromagnetic Scattering Method for One-Dimensional Inhomogeneous Media

A frequency-domain inversion scheme for reconstructing the permittivity profile of one-dimensional inhomogeneous media is proposed. The generalized reflection coefficients and the generalized transmission coefficients of the inhomogeneous media are used as the input data of the inverse model. A Newton-like iterative algorithm known as the generalized pulse-spectrum technique with the Tikhonov regularization is applied to solve the inverse problem. Novel boundary conditions are proposed for the inverse problem and therefore the permittivity at the boundary of the inhomogeneous media is not required as prior knowledge. The choice of frequency points of the frequency-domain method is also investigated. Numerical examples are carried out to validate the inversion technique. Good agreements between the reconstructed profiles and the true profiles are shown.

Reduction of image artifacts induced by change in the optode coupling in time-resolved diffuse optical tomography

Tomographic images of the optical properties can be reconstructed using inversion algorithms for diffuse optical tomography (DOT); however, changes in the optode coupling that occurs while obtaining an object's measurements may often lead to the presence of artifacts in the reconstructed images. To reduce the number of artifacts induced by optode coupling, previous studies have introduced (unknown) coupling coefficients in reconstruction algorithms, which were found to be effective for continuous wave- and frequency-domain DOT. This study aims to investigate the effects of optode calibration on the reconstructed images of time-domain DOT. Here, coupling coefficients are incorporated into the time-domain DOT algorithm based on a modified generalized pulse spectrum technique. The images of the absorption coefficient are reconstructed in various numerical simulations, phantom experiments, and in vivo experiments of time-domain DOT. As a result, the artifacts resulting from changes in optode coupling are reduced in the reconstructed images of the absorption coefficient, thereby demonstrating that introduction of coupling coefficients is effective in time-domain DOT. Moreover, numerical simulations, phantom experiments, and in vivo studies have validated this algorithm.

An efficient Jacobian scaling method for time-domain optical mammography

Time-domain diffuse optical tomography can efficiently reconstruct optical parameters which can be further applied in diagnosing early breast cancer. Nevertheless, the performances of reconstructed imaging are badly influenced by different Jacobian magnitudes of absorption coefficient and reduced scattering coefficient. With the introudction of a relative data type based on generalized pulse spectrum technique, an efficient Jacobian scaling method is proposed. The interrelated simulated validation is also revealed for the enhancing performances.

Time-resolved diffuse optical tomography and its application to in vitro and in vivo imaging

This work reviews our research during the past several years on time-resolved (TR) near-infrared diffuse optical tomography (DOT). Following an introduction of the measuring modes, two proposed schemes of image reconstruction in TR-DOT are described: one utilizes the full TR data, and the other, referred to as the modified generalized pulse spectrum technique (GPST), uses the featured data extracted from the TR measurement. The performances of the two algorithms in quantitativeness and spatial resolution are comparatively investigated with 2-D simulated data. TR-DOT images are then presented for phantom experiments, which are obtained by using a 16-channel time-correlated single photon counting system, and the factors affecting the quantification of the reconstruction are discussed. Finally, in vitro and in vivo imaging examples are illustrated for validating the capibility of TR-DOT to provide not only the anatomical but also the physiological information of the objects.

A linear, featured-data scheme for image reconstruction in time-domain fluorescence molecular tomography

Fluorescence diffuse optical tomography (DOT) has attracted many attentions from the community of biomedical imaging, since it provides effective enhancement in imaging contrast. This modality is now rapidly evolving as a potential means of monitoring molecular events in small living organisms with help of molecule-specific contrast agents, referred to as fluorescence molecular tomography (FMT). FMT could greatly promote pathogenesis research, drug development, and therapeutic intervention. Although FMT in steady-state and frequency-domain modes have been heavily investigated, the extension to time-domain scheme is imminent for its several unique advantages over the others. By extending the previously developed generalized pulse spectrum technique for time-domain DOT, we propose a linear, featured-data image reconstruction algorithm for time-domain FMT that can simultaneously reconstruct both fluorescent yield and lifetime images of multiple fluorophores, and validate the methodology with simulated data.

Influences of Target Size and Contrast on Near Infrared Diffuse Optical Tomography – a Comparison Between Featured-data and Full Time-resolved Schemes

Our recent diffuse optical tomography experiments on human lower legs and forearms are presented using the time-resolved measuring system and image reconstruction algorithm based on the modified generalized pulse spectrum technique. It was shown that the spatial resolution and quantitativeness of the resultant images, was rather poor, and the interior blood vessels invisible in the absorption images. To clarify this issue, the influences of target contrast and size on the image reconstruction were investigated with simulated data. We have found that the quantitativeness of the reconstructed optical properties was prone to be spoiled by the small size ratio and high contrast of the interior targets to the background, and the incompleteness of information embedded in the featured data-types, evidently answers for the degradation of the image quality. It was shown in a further simulative investigation that the image quality could be substantially improved by making full use of the time-resolved data.

A widely convergent generalized pulse-spectrum technique for the inversion of two-dimensional acoustic wave equation

An algorithm of the generalized pulse-spectrum technique (GPST) is used for the inverse problems of two-dimensional acoustic wave equation, and a skill of saving computational cost is designed in choosing regularizing parameters. To overcome the defect of the local convergence of the GPST, a widely convergent GPST (WCGPST) is constructed. Numerical simulations are carried out to test the feasibility and to study the general characteristics of the WCGPST. It is found that the WCGPST is not only as robust as the standard GPST but also possessing widely convergent region.

Optical tomographic mapping of cerebral haemodynamics by means of time-domain detection: methodology and phantom validation

One of the primary applications of diffuse optical imaging is to localize and quantify the changes in the cerebral oxygenation during functional brain activation. Up to now, data from an optical imager are simply presented as a two-dimensional (2D) topographic map using the modified Beer–Lambert law that assumes homogeneous optical properties beneath each optode. Due to the highly heterogeneous nature of the optical properties in the brain, the assumption is evidently invalid, leading to both low spatial resolution and inaccurate quantification in the assessment of haemodynamic changes. To cope with these difficulties, we propose a nonlinear tomographic image reconstruction algorithm for a two-layered slab geometry that uses time-resolved reflected light. The algorithm is based on the previously developed generalized pulse spectrum technique, and implemented within a semi-three-dimensional (3D) framework to conform to the topographic visualization and to reduce computational load. We demonstrate the advantages of the algorithm in quantifying simulated changes in haemoglobin concentrations and investigate its robustness to the uncertainties in the cortical structure and optical properties, as well as the effects of random noises on image quality. The methodology is also validated by experiments using a solid layered phantom.

A Widely Convergent Generalized Pulse‐ Spectrum Methods for 2‐D Wave Equation Inversion

AbstractCombining the widely convergent homotopy method applied to the inversion process of operator identification with the Tikhonov regularization method for ill‐posed problem, a new Widely Convergent Generalized Pulse‐Spectrum Technique (WCGPST) for 2‐D wave equation inversion is constructed. And constraint inversion is preformed with data of well logs. Many numerical simulations and tests of anti‐noise indicate that this method is effective.

Semi-three-dimensional algorithm for time-resolved diffuse optical tomography by use of the generalized pulse spectrum technique.

Although a foil three-dimensional (3-D) reconstruction with both 3-D forward and inverse models provide, the optimal solution for diffuse optical tomography (DOT), because of the 3-D nature of photon diffusion in tissue, it is computationally costly for both memory requirement and execution time in a conventional computing environment. Thus in practice there is motivation to develop an image reconstruction algorithm with dimensional reduction based on some modeling approximations. Here we have implemented a semi-3-D modified generalized pulse spectrum technique for time-resolved DOT, where a two-dimensional (2-D) distribution of optical properties is approximately assumed, while we retain 3-D distribution of photon migration in tissue. We have validated the proposed algorithm by reconstructing 3-D structural test objects from both numerically simulated and experimental date. We demonstrate our algorithm by comparing it with the calibrated 2-D reconstruction that is in widespread use as a shortcut to 3-D imaging and proving that the semi-3-D algorithm outperforms the calibrated 2-D algorithm.

Imaging of in vitro chicken leg using time-resolved near-infrared optical tomography

Near-infrared optical imaging gains much attention because of its non-invasiveness and deep penetration depths into tissue. Here, we report near-infrared optical tomographic imaging of an in vitro chicken leg from time-resolved measurements. The in vitro chicken leg, dipped in a cylindrical container filled with diluted Intralipid-10% solution, was imaged with a multi-channel time-resolved imaging system. A two-dimensional reconstruction algorithm based on a modified generalized pulse spectrum technique has been developed to reconstruct the images of both the absorption and reduced scattering coefficients simultaneously and quickly. The results demonstrate that a simultaneous reconstruction of absorption and reduced scattering coefficients from time-resolved measurement has a potential to reveal the changes in the optical properties associated with not only the physiological information but also the anatomical structure of the organ.

Anatomical and Functional Images of in vitro and in vivo Tissues by NIR Time-domain Diffuse Optical Tomography.

Near infra-red (NIR) diffuse optical tomography (DOT) has gained much attention and it will be clinically applied to imaging breast, neonatal head, and the hemodynamics of the brain because of its noninvasiveness and deep penetration in biological tissue. Prior to achieving the imaging of infant brain using DOT, the developed methodologies need to be experimentally justified by imaging some real organs with simpler structures. Here we report our results of an in vitro chicken leg and an in vivo exercising human forearm from the data measured by a multi-channel time-resolved NIR system. Tomographic images were reconstructed by a two-dimensional image reconstruction algorithm based on a modified generalized pulse spectrum technique for simultaneous reconstruction of the µa and µs´. The absolute µa- and µs´-images revealed the inner structures of the chicken leg and the forearm, where the bones were clearly distinguished from the muscle. The Δµa-images showed the blood volume changes during the forearm exercise, proving that the system and the image reconstruction algorithm could potentially be used for imaging not only the anatomic structure but also the hemodynamics in neonatal heads.

A Newton-Raphson Iterative Scheme for Integrating Multiphase Production Data Into Reservoir Models

Summary This paper presents a new linearized iterative algorithm for building reservoir models conditioned to multiphase production data and geostatistical data. The significant feature of the proposed algorithm is that the computation of the sensitivity coefficients of production data, with respect to model parameters, can be avoided. This leads to dramatic reduction of computational cost. Instead of generating the sensitivity matrix as required for the least-squares algorithms, the proposed approach relies on solving the inversion equations, which are derived from the necessary conditions for a functional extremum. It is proved that the proposed method requires considerably less computational effort than the traditional algorithms such as the Gauss-Newton method, the Levenberg-Marquardt method, and the generalized pulse-spectrum technique (GPST). This is because the computation of the sensitivity coefficients makes the traditional algorithms computationally intensive. However, for the proposed linearized iterative scheme, the computational requirement only depends on the timesteps used in the reservoir simulator rather than the number of parameters or the number of observed data. The linearized iteration scheme converges quickly because the inversion equations can be solved through the Newton-Raphson method. At each iteration, the new approach requires solving the finite difference equations and the linear adjoint equations only once, respectively. Since the solver for the flow equations can be used to solve both the adjoint equations and the inversion equations, the proposed algorithm can be easily applied to commercial reservoir simulators. In this paper, two numerical examples for incorporating water oil rate data into geostatistical models are given to prove the efficiency of the proposed algorithm.

Efficient Algorithm for Solving Inverse Source Problems of a Nonlinear Diffusion Equation in Microwave Heating

Determination of the equivalent internal heat source from surface temperature measurements in microwave processing of materials is formulated as an inverse source problem of a nonlinear diffusion equation. The versatile generalized pulse-spectrum technique (GPST) inversion algorithm with the incorporation of multi-level grid method and hierarchical parallelism is developed for solving this type of inverse problems. Development of a simple 2D code has been completed. Numerical simulations are carried out to test the feasibility and capability of this improved GPST without the real measurement data. It is found that this new inversion algorithm not only does produce very good results but also is much more efficient and stable than its standard version.

A widely convergent generalized pulse-spectrum technique for the coefficient inverse problem of differential equations

A new algorithm of the generalized pulse-spectrum technique (GPST) is constructed for the solution of coefficient inverse problems of differential equations, and a skill of saving computational cost is designed in choosing regularizing parameters. To overcome the defect of the local convergence of the GPST, a widely convergent GPST is illustrated. Numerical simulations are carried out for solving the inverse problem of 1 − D seismic prospection to test the feasibility without real measurement data. The computational results show the method's effectiveness.

History Matching for Multiphase Reservoir Models On Shared Memory Supercomputers

A parallel algorithm using the generalized pulse spec trum technique and multilevel grid method for solving reservoir structural parameter identification problems is discussed here. The algorithm can be used to iden tify the reservoir's absolute permeability distributions by matching the computed pressure values with mea sured historical pressure values obtained at observa tion wells (history matching). Use of a multilevel grid improves the quality of the identified permeability dis tributions significantly. The whole parameter identifica tion process is very computationally intensive since a group of coupled nonlinear partial differential equa tions (PDEs) and a regularized least square problem must be solved repeatedly with different parameter values. Several hundred megabyte memory is required for reservoir models involving thousands of grid points. The block SOR scheme with red and black or dering and a parallel Householder transformation scheme were used to solve the algebraic equations resulting from the discretization of the PDEs. High speedup has been achieved by exploring parallefisnl, refining the whole program, rather than just the hot- spots, and utilizing the high-speed cache memory effi ciently.

An efficient numerical method for exterior and interior inverse problems of Helmholtz equation

The generalized pulse-spectrum technique (GPST), an efficient and versatile inversion algorithm, is used with adaptive grids to solve both exterior (scattering) and interior (cavity) boundary-shape inverse problems of two-dimensional Helmholtz equation. Numerical simulations of nontrivial examples are carried out to test the feasibility and to study the general characteristics of GPST without the real measurement data. It is found that GPST does efficiently produce very good results.