Dr. Héctor A. García Profile

Dr. Héctor A. García

at Univ. of Wisconsin-Madison

SPIE Involvement:

Author

Publications (6)

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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