Juan A. Pomarico

Speckle interferometry applied to pharmacodynamic studies: evaluation of parasite motility

The work reported here describes the application of the optical technique known as dynamic speckle interferometry to evaluate the motility of nematode parasites exposed to different anthelmintic drugs. This technique, a well proven tool for assessing the time evolution of different phenomena, is here successfully used to quantify parasite motility in pharmacodynamic assays. The characterization of the pharmacological properties of anthelmintic drugs is critical to optimize their use in parasite control. Besides, the evaluation of nematode motility is a relevant indicator of the pharmacodynamic effect of anthelmintic drugs. The application of this approach to study the motility of Haemonchus contortus (used as a model of nematode parasites) larvae exposed to different drugs is presented, showing its usefulness.

General Expression for the Voigt Function That is of Special Interest for Applied Spectroscopy

The purpose of this work is twofold. First we obtain a series expansion for the Voigt function that is valid for all values of the dimensionless parameter a (a measure of the ratio between the Lorentzian and Gaussian widths). Furthermore, the resulting coefficients are independent of the generalized coordinate b (the wavelength measured in units of the Gaussian width). In the second place, we fit an experimental “shaped bell” curve to a Voigt profile using certain theoretical restrictions that relate the maximum height and the full width at half-maximum.

Solution of the direct problem in turbid media with inclusions using Monte Carlo simulations implemented in graphics processing units: new criterion for processing transmittance data

The study of light propagation in diffusive media requires solving the radiative transfer equation, or eventually, the diffusion approximation. Except for some cases involving simple geometries, the problem with immersed inclusions has not been solved. Also, Monte Carlo (MC) calculations have become a gold standard for simulating photon migration in turbid media, although they have the drawback large processing times. The purpose of this work is two-fold: first, we introduce a new processing criterion to retrieve information about the location and shape of absorbing inclusions based on normalization to the background intensity, when no inhomogeneities are present. Second, we demonstrate the feasibility of including inhomogeneities in MC simulations implemented in graphics processing units, achieving large acceleration factors ( approximately 10(3)), thus providing an important tool for iteratively solving the forward problem to retrieve the optical properties of the inclusion. Results using a cw source are compared with MC outcomes showing very good agreement.

An efficient screening approach to be used in plasma modeling and ion-surface collision experiments

In this work we show that the Layzer theory for atomic calculations provides a theoretical framework and also a powerful computational approach if correct rules for the calculation of the screening parameters are given. Using the virial as a model for potential energy and splitting of two-body operators as sum of onebody operators, a neat definition of screening is given, satisfying diverse physically indispensable properties. Many different experimental and theoretical results are reproduced with high accuracy, with no fitting procedure involving energy levels or numerical potentials. A C++ code and an executable file are available upon request.

Study of inhomogeneities in turbid media: experimental and numerical results

Near Infrared diffuse transmission of light through tissue is a tool for noninvasive imaging for diagnostic purposes. Most of the research has been focused over breast cancer imaging; however, major efforts have been done in cerebral tomography and topography imaging, as well as small animal organs imaging systems. In this work, we investigate the transmitted light profiles when scattering and absorbing cylindrical inhomogeneities are submerged at different depths inside slabs of turbid media. We analyze the transilluminance profiles when the phantom is scanned using both, CW and time resolved detection. The study of the spatial profiles obtained with CW light, shows an apparently contradictory effect when the absorption coefficient of the inclusion is higher than that of the bulk. In this case, the intensity profiles displays a peak of higher intensity where the inclusion is located, as it would be expected for a less absorbing inclusion. The experiments were compared and analyzed with a theoretical model for cylindrical inclusions and Monte Carlo simulations implemented in a Graphic Processing Unit (GPU).

Retrieval of the optical properties in a semiinfinite three layers phantom: theory, experiments, and simulations

In this work we introduce a theoretical model for light propagation in multilayered, turbid cylinders with an infinitely thick bottom layer, which can be applied to the study of biological systems such as the human head. Our approach was validated with experiments on a three-layered phantom and with Monte Carlo simulations. We show that the absorption and the reduced scattering coefficient of the deepest layer can be retrieved within reasonable errors.

CW fluorescence imaging of tissue-like media in reflectance geometry

In the present contribution we investigate images of CW diffusely remitted light registered by a CCD camera imaging a turbid medium containing an absorbent and fluorescent lesion, during illumination by a point-like source. We show that a normalization technique using local background signals reconstructed from experimental data is useful to increase the contrast of both the absorption and the fluorescence channel. Using this technique, results on phantoms are given which demonstrate that lesions with clinically-realistic fluorophore and absorber concentrations can be detected. Results are compared with theoretical calculations as well.

Whole Field Reflectance Optical Tomography

Optical imaging through highly scattering media such as biological tissues is a topic of intense research, especially for biomedical applications. Diverse optical systems are currently under study and development for displaying the functional imaging of the brain and for the detection of breast tumors. From the theoretical point of view, a suitable description of light propagation in tissues involves the Radiative Transfer Equation, which considers the energetic aspects of light propagation. However, this equation cannot be solved analytically in a closed form and the Diffusion Approximation is normally used. Experimentally it is possible to use Transmission or Reflection geometries and Time Resolved, Frequency Modulated or CW sources. Each configuration has specific advantages and drawbacks, depending on the desired application. In the present contribution, we investigate the reflected light images registered by a CCD camera when scattering and absorbing inhomogeneities are located at different depths inside turbid media. This configuration is of particular interest for the detection and optical characterization of changes in blood flow in organs, as well as for the detection and characterization of inclusions in those cases for which the transmission slab geometry is not well suited. Images are properly normalized to the background intensity and allow analyzing relative large areas (typically 5 × 5 cm2) of the tissue. We tested the proposal using Numerical Monte Carlo simulations implemented in a Graphic Processing Unit (Video accelerating Card). Calculations are thus several orders of magnitude faster than those run in CPU. Experimental results in phantoms are also given.