Dr. Hector A. Garcia Profile

Dr. Hector A. Garcia

at Univ. Nacional del Centro de la Provincia de Buenos Aires

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Publications (10)

SPIE Journal Paper | 22 January 2025 Open Access

Analytical sensitivity factors from distributions of time of flight of photons for near-infrared spectroscopy studies in multilayered turbid media

Hector García, Demián A. Vera, Nicolás Carbone, María Waks-Serra, Juan Pomarico

JBO, Vol. 30, Issue 01, 015002, (January 2025) https://doi.org/10.1117/12.10.1117/1.JBO.30.1.015002

KEYWORDS: Simulations, Absorption, Photons, Turbidity, Factor analysis, Sensors, Biological research, Near infrared spectroscopy, Analytic models, Multilayers

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SPIE Journal Paper | 18 November 2024 Open Access

Combined dual-channel fluorescence depth sensing of indocyanine green and protoporphyrin IX kinetics in subcutaneous murine tumors

Madhusudan Kulkarni, Matthew Reed, Xu Cao, Héctor García, Marien Ochoa, Shudong Jiang, Tayyaba Hasan, Marvin Doyley, Brian Pogue

JBO, Vol. 30, Issue S1, S13709, (November 2024) https://doi.org/10.1117/12.10.1117/1.JBO.30.S1.S13709

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SignificanceFluorescence sensing within tissue is an effective tool for tissue characterization; however, the modality and geometry of the image acquisition can alter the observed signal.AimWe introduce a novel optical fiber-based system capable of measuring two fluorescent contrast agents through 2 cm of tissue with simple passive electronic switching between the excitation light, simultaneously acquiring fluorescence and excitation data. The goal was to quantify indocyanine green (ICG) and protoporphyrin IX (PpIX) within tissue, and the sampling method was compared with wide-field surface imaging to contrast the value of deep sensing versus surface imaging.ApproachThis was achieved by choosing filters for specific wavelengths that were mutually exclusive between ICG and PpIX and coupling these filters to two separate detectors, which allows for direct swapping of the excitation and emission channels by switching the on-time of each excitation laser between 780- and 633-nm wavelengths.ResultsThis system was compared with two non-contact surface imaging systems for both ICG and PpIX, which revealed that the fluorescence depth sensing system was superior in its ability to resolve kinetics differences in deeper tissues that would normally be dominated by strong signals from skin and other surface tissues. Specifically, the system was tested using pancreatic adenocarcinoma tumors injected into murine models, which were imaged at several time points throughout tumor growth to its ∼6-mm diameter. This demonstrated the system’s capability to track longitudinal changes in ICG and PpIX kinetics that result from tumor growth and development, with larger tumors showing sluggish uptake and clearance of ICG, which was not observable with surface imaging. Similarly, PpIX was quantified, which showed slower kinetics over different time points, and was further compared with the wide-filed imager. These results were further validated through depth measurements in tissue phantoms and model-based interpretation.ConclusionThis fluorescence depth sensing system can be used to sample the interior blood flow characteristics by ICG sensing of tissue as deep as 20 mm into the tissue with sensitivity to kinetics that are superior to surface imaging and may be combined with other imaging modalities such as ultrasound to provide guided deep fluorescence measurements.

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SPIE Journal Paper | 28 February 2024 Open Access

Retrieval of chromophore concentration changes in a digital human head model using analytical mean partial pathlengths of photons

Demián Vera, Héctor García, Nicolás Carbone, María Victoria Waks-Serra, Daniela Iriarte, Juan Pomarico

JBO, Vol. 29, Issue 02, 025004, (February 2024) https://doi.org/10.1117/12.10.1117/1.JBO.29.2.025004

KEYWORDS: Chromophores, Analytic models, Head, Absorption, Simulations, Sensors, Photons, Tissues, Brain, Reconstruction algorithms

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SignificanceContinuous-wave functional near-infrared spectroscopy has proved to be a valuable tool for assessing hemodynamic activity in the human brain in a non-invasively and inexpensive way. However, most of the current processing/analysis methods assume the head is a homogeneous medium, and hence do not appropriately correct for the signal coming from the scalp. This effect can be reduced by considering light propagation in a layered model of the human head, being the Monte Carlo (MC) simulations the gold standard to this end. However, this implies large computation times and demanding hardware capabilities.AimIn this work, we study the feasibility of replacing the homogeneous model and the MC simulations by means of analytical multilayered models, combining in this way, the speed and simplicity of implementation of the former with the robustness and accuracy of the latter.ApproachOxy- and deoxyhemoglobin (HbO and HbR, respectively) concentration changes were proposed in two different layers of a magnetic resonance imaging (MRI)-based meshed model of the human head, and then these changes were retrieved by means of (i) a typical homogeneous reconstruction and (ii) a theoretical layered reconstruction.ResultsResults suggest that the use of analytical models of light propagation in layered models outperforms the results obtained using traditional homogeneous reconstruction algorithms, providing much more accurate results for both, the extra- and the cerebral tissues. We also compare the analytical layered reconstruction with MC-based reconstructions, achieving similar degrees of accuracy, especially in the gray matter layer, but much faster (between 4 and 5 orders of magnitude).ConclusionsWe have successfully developed, implemented, and validated a method for retrieving chromophore concentration changes in the human brain, combining the simplicity and speed of the traditional homogeneous reconstruction algorithms with robustness and accuracy much more similar to those provided by MC simulations.

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Proceedings Article | 21 August 2023 Paper

Analytical photon measurement density functions in flat and spherical layered media

Demián Vera, Héctor García, Guido Baez, María Waks-Serra, Nicolás Carbone, Daniela Iriarte, Juan Pomarico

Proceedings Volume 12628, 126281K (2023) https://doi.org/10.1117/12.2667099

KEYWORDS: Spherical lenses, Monte Carlo methods, Tissue optics, Brain tissue, Brain, Windows, Simulations, Refractive index, Photon transport, Optical sensing

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Proceedings Article | 21 August 2023 Paper

Theoretical computation of photon mean partial pathlengths in multilayered turbid media

Demián Vera, Héctor García, Nicolás Carbone, María Waks-Serra, Daniela Iriarte, Juan Pomarico

Proceedings Volume 12628, 126281X (2023) https://doi.org/10.1117/12.2670453

KEYWORDS: Turbidity, Simulations, Optical properties, Optical computing, Multilayers, Analytic models, Source detector separation, Photodetectors, Monte Carlo methods, Head

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Proceedings Article | 9 December 2021 Paper

A comparison between flat and spherical models of the human head for NIR light propagation

Demián Vera, MarÍa Waks Serra, Héctor GracÍa, Guido Baez, Daniela Iriarte, Juan Pomarico

Proceedings Volume 11920, 119201H (2021) https://doi.org/10.1117/12.2615379

KEYWORDS: Spherical lenses, Data modeling, Near infrared, Head, Multilayers, Monte Carlo methods, Magnetic resonance imaging, Absorption, Skull, Photons

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Proceedings Article | 11 July 2019 Paper

Extended Kalman Filtering for the recovery of the absorption coefficients in layered turbid media

Guido Baez, Héctor García, Dirk Grosenick, Heidrun Wabnitz

Proceedings Volume 11074, 110742N (2019) https://doi.org/10.1117/12.2527043

KEYWORDS: Absorption, Scattering, Reflectivity, Optical properties

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Proceedings Article | 28 July 2017 Paper

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

H. García, D. Iriarte, J. Pomarico, D. Grosenick, R. Macdonald

Proceedings Volume 10412, 104120S (2017) https://doi.org/10.1117/12.2285446

KEYWORDS: Optical properties, Multilayers, Reflection

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Proceedings Article | 16 July 2015 Paper

Determination of the optical properties of multilayered phantoms by time-resolved reflectance measurements

H. García, D. Iriarte, J. Pomarico, D. Grosenick, R. Macdonald

Proceedings Volume 9538, 95381G (2015) https://doi.org/10.1117/12.2183459

KEYWORDS: Optical properties, Absorption, Reflectivity, Liquids, Solids, Tissues, Scattering, Diffusion, Multilayers, Head

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Proceedings Article | 3 November 2011 Paper

Whole field reflectance optical tomography

Nicolás Carbone, Héctor García, Héctor Di Rocco, Daniela Iriarte, Juan Pomarico, Héctor Ranea Sandoval

Proceedings Volume 8011, 80118J (2011) https://doi.org/10.1117/12.901946

KEYWORDS: Tissues, Optical properties, Scattering, Near infrared spectroscopy, Monte Carlo methods, Cameras, Reflectivity, Optical tomography, Optical imaging

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