Abstract: Context and objectives In the context of fluorescence diffuse optical tomography, the time-resolved approach was shown to improve the reconstruction quality compared to the continuous-wave approach when adopting the transmittance configuration. However, the improvement seriously decreases in the presence of noise. The scope of this paper is to investigate the additional value of the time-resolved approach in the reflectance configuration. Material and methods A comparative study between time-resolved and continuous-wave reconstructions is provided in the reflectance configuration. Reconstructions are performed from synthetic measurements in a slab geometry assuming Poisson noise statistics. Results and discussion In the reflectance configuration, the reconstruction quality, expressed in terms of the global reconstruction error or in terms of the localization and quantification of a local inclusion, is shown to be sensibly higher when the time-resolved approach is considered rather than the continuous-wave one. This behavior is observed for which the maximum number of detected photons is around 106. Conclusion In the reflectance configuration, considering realistic level of signal the time-resolved approach is shown to outperform continuous-wave approach.
Abstract: We report on the experimental demonstration of a fast reconstruction method for multiview fluorescence diffuse optical tomography by using a wavelet-based data compression. We experimentally demonstrate that the use of data compression combined with the multiview approach makes it possible to perform a fast reconstruction of high quality. A structured illumination approach, guided by the compression scheme, has been adopted to further reduce the acquisition time. The reconstruction algorithm is based on the finite element method, and hence is suitable for samples of any arbitrary shape.
Abstract: A simple and fast time-domain method for localizing inclusions, fluorescent optical probes or absorbers, is presented. The method offers new possibilities for situations where complete tomographic measurements are not permitted by the examined object, for example in endoscopic examination of the human prostate or the oesophagus. Feasibility has been envisioned with a phantom study conducted on a point-like fluorochrome embedded in a diffusing medium mimicking the optical properties of biological tissues.
Abstract: In the context of fluorescence diffuse optical tomography, determining the optimal way to exploit the time-resolved information has been receiving much attention and different features of the time-resolved signals have been introduced. In this article, the authors revisit and generalize the notion of feature, considering the projection of the measurements onto some basis functions. This leads the authors to propose a novel approach based on the wavelet transform of the measurements.
Abstract: A method to perform fast 3-D optical reconstruction, based on structured light, in thick samples is demonstrated and experimentally validated. The experimental and reconstruction procedure, based on Finite Elements Method, used to reconstruct absorbing heterogeneities, with arbitrary arrangement in space, is discussed. In particular we demonstrated that a 2D sampling of the source Fourier plane is required to improve the imaging capability.
Abstract: We present a fast reconstruction method for fluorescence optical tomography with structured illumination. Our approach is based on the exploitation of the wavelet transform of the measurements acquired after wavelet-patterned illuminations. This method, validated on experimental data, enables us to significantly reduce the acquisition and computation times with respect to the classical scanning approach. Therefore, it could be particularly suited for in vivo applications.
Abstract: This paper addresses the inverse problem of time-resolved (fluorescence) diffuse optical tomography from temporal moments of the measurements. A methodology that enables one to provide fairly comparable reconstructions is presented. The proposed reconstruction methodology is applied to infinite medium synthetic phantoms in the transmission geometry. Reconstructions are performed for moment orders increasing from 0 to 3. The reconstruction quality is shown to be increasing when higher moment orders are added. However, the value of the highest useful moments order strongly depends on the number of photons that can be acquired. In particular, it can be considered that the benefit of using higher order moments vanishes when fewer than 10(8) photons are detected. The evolution of the reconstruction quality with respect to the optical properties of the medium and fluorescence lifetime is also shown.
Abstract: The problem of fluorescence diffuse optical tomography consists in localizing fluorescent markers from near-infrared light measurements. Among the different available acquisition modalities, the time-resolved modality is expected to provide measurements of richer information content. To extract this information, the moments of the time-resolved measurements are often considered. In this paper, a theoretical analysis of the moments of the forward problem in fluorescence diffuse optical tomography is proposed for the infinite medium geometry. The moments are expressed as a function of the source, detector and markers positions as well as the optical properties of the medium and markers. Here, for the first time, an analytical expression holding for any moments order is mathematically derived. In addition, analytical expressions of the mean, variance and covariance of the moments in the presence of noise are given. These expressions are used to demonstrate the increasing sensitivity of moments to noise. Finally, the newly derived expressions are illustrated by means of sensitivity maps. The physical interpretation of the analytical formulae in conjunction with their map representations could provide new insights into the analysis of the information content provided by moments.
Abstract: Photon density and photon flux are widely used to model the measurable quantity in diffuse optical tomography problems. However, it is not these two quantities that are actually measured, but rather the radiance accepted by the detection system. We provide a theoretical analysis of the model deviations related to the choice of the measurable quantity-either photon density or flux. By using the diffusion approximation to the radiative transfer equation and its solution with extrapolated boundary conditions, an exact analytical expression of the measurable quantity has been obtained. This expression has been employed as a reference to assess model deviation when considering the photon density or the photon flux as the measurable quantity. For the case of semi-infinite geometry and for both continuous wave and time domains, we show that the photon density approximates the measurable quantity better than the photon flux. We also demonstrate that the validity of this approximation strongly depends on the optical parameters.
Abstract: Despite the widespread use of electrochemical sensing techniques, the determination of the physical parameters from the current response of rapid voltammetric measurements has been difficult for two reasons: large capacitance contributions overwhelm the current response of transient measurements and the reaction dynamics are inherently nonlinear and nonstationary. In this work, we present a signal processing methodology that in combination with a large-amplitude/high-frequency voltage waveform method, ac voltammetry, is able to determine the underlying physical parameters in heterogeneous electrochemical reaction-diffusion processes. Through a large number of numerical calculations, we explore the effect of kinetic, thermodynamic, and mass transport parameters on two components of the current response, the even and the odd. We study the even component directly whereas for the odd component, which is considerably influenced by capacitance, we use the Hilbert transform, which is suitable for the analysis of nonstationary and nonlinear data sets, to minimize the capacitance contribution. The theoretical analysis is applied to measurements of well-characterized electrochemical reactions, Ru(NH3)6(2+/3+) and Fe(CN)6(4-/3-), using two different electrode materials, glassy carbon and platinum, and the physical parameters deduced are in excellent agreement with published results.
Abstract: Fluorescence Diffuse Optical Tomography with structured light is demonstrated using multiple views. Reconstructions from simulated and experimental data sets is carried out. Multiple view approach improves the spatial resolution of reconstruction.
Abstract: Diffuse optical tomography (DOT) and Fluorescence mediated tomography (FMT) are powerful in-vivo optical imaging techniques but they are affected by long acquisition and computational times. Recently, the use of structured light has been proposed in order to reduce the acquisition time and also the computational time of the inverse problem. Additionally, it has been proposed to compress the measured data set to reduce the reconstruction time. Here we present our experimental approach, describing the instrument for structured illumination and wide field detection and we discuss the advantages to use a finite elements based approach. Then, we introduce the use of spatial wavelets. Our method is based on the projection of a small number of wavelet patterns (Haar and Battle-Lemarie wavelets). The detected images are wavelet transformed and the information content is compressed to achieve fast 3D reconstruction. Experimental results are presented, showing fast reconstruction of complex absorbing/fluorescent objects in thick diffusive samples. Implications for fast small animal imaging are discussed.
Abstract: This paper deals with the problem of time-resolved fluorescence diffuse optical tomography. We propose a new reconstruction scheme based on a multi-resolution approximation of the time-resolved signals. The underlying basis functions are exponential B-splines that are matched to the decay of fluorescence signals. We illustrate the applicability of the method on phantom data.
Abstract: Within the diffusion approximation, we recently shown that the classical measurable quantity models can lead to significant deviations. Here, the impact of these deviations on the reconstruction quality is evaluated.
Abstract: The present paper is devoted to a comparison between time- resolved fluorescence diffuse optical tomography and continuous wave fluorescence diffuse optical tomography. Both of these techniques aim at reconstructing 3D biodistribution of fluorescent markers embedded in biological tissues. The study is restricted in the time domain to the exploitation of the first three temporal moments of measurements. The temporal benefits in terms of reconstruction have been shown to depend strongly on the optical parameters of the medium investigated as well as the fluorescence lifetime.
Abstract: This paper aims at determining fluorescence lifetimes and optical properties leading to reconstruction benefits when employing the time-resolved method rather than the continuous wave method.
Abstract: The present paper is devoted to fluorescence diffuse optical tomography by using time resolved signals for the reconstruction of the 3D biodistribution of fluorescent probes embedded in biological tissues. The focus is made on the reconstruction of a methodology for an efficient exploitation of the time resolved data. The study is restricted to the examination of the three first moments of signals acquired in cylindrical geometry. The interest of temporal information upon cw information has been shown especially when only a limited number of views is available.
