Approximate Extended Kalman Filter Research Articles

Detection of Single and Multiple Targets in Tissue Phantoms with Fluorescence-enhanced Optical Imaging: Feasibility Study

To evaluate the feasibility of reconstructing single and multiple targets by using fluorescence-enhanced tomography of a breast tissue phantom. Frequency-domain fluorescence measurements were performed in cup-shaped tissue phantoms of clinically relevant size (diameter, 10 cm) in which single or multiple 0.5-1.0-cm(3) targets that contained micromolar concentrations of indocyanine green with 1:0 and 100:1 target-to-background (T:B) contrast ratios had been embedded. Rapid acquisition of time-dependent fluorescent light measurements was performed at the phantom surface in response to point illumination of excitation light by using a gain-modulated intensified charge-coupled device detection system. Boundary surface measurements were used to tomographically reconstruct the interior targets located with various experimental conditions. Single 1.0-cm(3) targets located between 1.43 and 2.82 cm deep from the phantom surface at a T:B contrast ratio of 100:1 and three approximately 0.55-cm(3) targets located about 1.30 cm deep at a T:B contrast ratio of 1:0 were reconstructed with minimal or no artifacts by using boundary surface fluorescence measurements and an approximate extended Kalman filter algorithm. It is feasible to detect single or multiple fluorescent targets in tissue phantoms of clinically relevant size by using fluorescence-enhanced optical tomography.

Three‐dimensional fluorescence lifetime tomography

Near-infrared fluorescence tomography using molecularly targeted lifetime-sensitive, fluorescent contrast agents have applications for early-stage cancer diagnostics. Yet, although the measurement of fluorescent lifetime imaging microscopy (FLIM) is extensively used in microscopy and spectroscopy applications, demonstration of fluorescence lifetime tomography for medical imaging is limited to two-dimensional studies. Herein, the feasibility of three-dimensional fluorescence-lifetime tomography on clinically relevant phantom volumes is established, using (i) a gainmodulated intensified charge coupled device (CCD) and modulated laser diode imaging system, (ii) two fluorescent contrast agents, e.g., Indocyanine green and 3-3'-Diethylthiatricarbocyanine iodide differing in their fluorescence lifetime by 0.62 ns, and (iii) a two stage approximate extended Kalman filter reconstruction algorithm. Fluorescence measurements of phase and amplitude were acquired on the phantom surface under different target to background fluorescence absorption (70:1, 100:1) and fluorescence lifetime (1:1, 2.1:1) contrasts at target depths of 1.4-2 cm. The Bayesian tomography algorithm was employed to obtain three-dimensional images of lifetime and absorption owing to the fluorophores.

Fluorescence-enhanced optical imaging in large tissue volumes using a gain-modulated ICCD camera

A novel image-intensified charge-coupled device (ICCD) imaging system has been developed to perform 3D fluorescence tomographic imaging in the frequency-domain using near-infrared contrast agents. The imager is unique since it (i) employs a large tissue-mimicking phantom, which is shaped and sized to resemble a female breast and part of the extended chest-wall region, and (ii) enables rapid data acquisition in the frequency-domain by using a gain-modulated ICCD camera. Diffusion model predictions are compared to experimental measurements using two different referencing schemes under two different experimental conditions of perfect and imperfect uptake of fluorescent agent into a target. From these experimental measurements, three-dimensional images of fluorescent absorption were reconstructed using a computationally efficient variant of the approximate extended Kalman filter algorithm. The current work represents the first time that 3D fluorescence-enhanced optical tomographic reconstructions have been achieved from experimental measurements of the time-dependent light propagation on a clinically relevant breast-shaped tissue phantom using a gain-modulated ICCD camera.

Biomedical optical tomography using dynamic parameterization and Bayesian conditioning on photon migration measurements

Stochastic reconstruction techniques are developed for mapping the interior optical properties of tissues from exterior frequency-domain photon migration measurements at the air-tissue interface. Parameter fields of absorption cross section, fluorescence lifetime, and quantum efficiency are accurately reconstructed from simulated noisy measurements of phase shift and amplitude modulation by use of a recursive, Bayesian, minimum-variance estimator known as the approximate extended Kalman filter. Parameter field updates are followed by data-driven zonation to improve the accuracy, stability, and computational efficiency of the method by moving the system from an underdetermined toward an overdetermined set of equations. These methods were originally developed by Eppstein and Dougherty [Water Resources Res. 32, 3321 (1996)] for applications in geohydrology. Estimates are constrained to within feasible ranges by modeling of parameters as beta-distributed random variables. No arbitrary smoothing, regularization, or interpolation is required. Results are compared with those determined by use of Newton-Raphson-based inversions. The speed and accuracy of these preliminary Bayesian reconstructions suggest the near-future application of this inversion technology to three-dimensional biomedical imaging with frequency-domain photon migration.