Dr. Heidy H. Sierra-Gil Profile

Dr. Heidy H. Sierra-Gil

Assistant Professor at Univ de Puerto Rico Mayagüez

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Author

Publications (24)

Proceedings Article | 19 March 2024 Presentation

A computational framework to analyze time and location-dependent NIRS readouts for detecting cytochrome c oxidase

Anastasia Goulopoulos, Michael Alvarez, Heidy Sierra, Walfre Franco

Proceedings Volume PC12822, PC128220A (2024) https://doi.org/10.1117/12.3003150

KEYWORDS: Near infrared spectroscopy, Mitochondria, Signal detection, Oxygen, 3D modeling, Tissues, Spectroscopy, Oxygenation, Tissue optics, Photoplethysmography

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Proceedings Article | 28 September 2023 Presentation + Paper

Using Monte Carlo simulated PPGs signals to train a deep learning model to predict hemoglobin levels

Michael Alvarez, Emmanuel Arzuaga, Heidy Sierra

Proceedings Volume 12655, 1265504 (2023) https://doi.org/10.1117/12.2677499

KEYWORDS: Blood oxygen saturation, Monte Carlo methods, Simulations, Education and training, Deep learning, Tissues, Signal generators, Skin, Blood

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Measuring Hemoglobin (Hb) levels is required for the assessment of different health conditions, such as anemia, a condition where there are insufficient healthy red blood cells to carry enough oxygen to the body’s tissues. Measuring Hb levels requires the extraction of a blood sample, which is then sent to a laboratory for analysis. This is an invasive procedure that may add challenges to the continuous monitoring of Hb levels. Noninvasive techniques, including imaging and photoplethysmography (PPG) signals combined with machine learning techniques, are being investigated for continuous measurements of Hb. However, the availability of real data to train the algorithms is limited to establishing a generalization and implementation of such techniques in healthcare settings. In this work, we present a computational model based on Monte Carlo simulations that can generate multispectral PPG signals that cover a broad range of Hb levels. These signals are then used to train a Deep Learning (DL) model to estimate hemoglobin levels. Through this approach, valuable insights about the relationships between PPG signals, oxygen saturation, and Hb levels are learned by the DL model. The signals were generated by propagating a source in a volume that contains the skin tissue properties and the target physiological parameters. The source consisted of plane waves using the 660 nm and 890 nm wavelengths. A range of 6 g/dL to 18 dL Hb values was used to generate 468 PPGs to train a Convolutional Neural Network (CNN). The initial results show high accuracy in detecting low levels of Hb. To the best of our knowledge, the complexity of biological interactions involved in measuring hemoglobin levels has yet to be fully modeled. The presented model offers an alternative approach to studying the effects of changes in Hb levels on the PPGs signal morphology and its interaction with other physiological parameters that are present in the optical path of the measured signals.

Proceedings Article | 19 May 2020 Presentation + Paper

Analyzing the effects of pixel-scale data fusion in hyperspectral image classification performance

Michael Alvarez, Carlos Theran, Emmanuel Arzuaga, Heidy Sierra

Proceedings Volume 11392, 1139205 (2020) https://doi.org/10.1117/12.2560106

KEYWORDS: Spatial resolution, Image fusion, Data fusion, Hyperspectral imaging, Image classification, Image enhancement, Resolution enhancement technologies, Multispectral imaging, Spectral resolution

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Proceedings Article | 19 May 2020 Presentation + Paper

Studying the effect of a decision fusion model on enhanced hyperspectral images

Carlos Theran, Michael Alvarez, Heidy Sierra, Emmanuel Arzuaga

Proceedings Volume 11392, 1139206 (2020) https://doi.org/10.1117/12.2560107

KEYWORDS: Data fusion, Image fusion, Hyperspectral imaging, Spatial resolution, Image classification, Data modeling, Fuzzy logic, Remote sensing, Neural networks, Buildings

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SPIE Journal Paper | 13 June 2019

Improving execution time for supervised sparse representation classification of hyperspectral images using the Moore–Penrose pseudoinverse

Fernando Arias, Heidy Sierra, Emmanuel Arzuaga

JARS, Vol. 13, Issue 02, 026512, (June 2019) https://doi.org/10.1117/12.10.1117/1.JRS.13.026512

KEYWORDS: Hyperspectral imaging, Image classification, Scene classification, Principal component analysis, Optimization (mathematics), Associative arrays, Reflectivity, Statistical methods, Classification systems, Sensors

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SPIE Journal Paper | 23 August 2017 Open Access

Reflectance confocal microscopy-guided laser ablation of basal cell carcinomas: initial clinical experience

Heidy Sierra, Oriol Yélamos, Miguel Cordova, Chih-Shan Jason Chen, Milind Rajadhyaksha

JBO, Vol. 22, Issue 08, 085005, (August 2017) https://doi.org/10.1117/12.10.1117/1.JBO.22.8.085005

KEYWORDS: Tumors, Laser ablation, Video, Confocal microscopy, Skin, Reflectivity, Tissues, Aluminum, Video processing, In vivo imaging

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Proceedings Article | 24 March 2017 Paper

Reflectance confocal microscopy-guided laser ablation of basal cell carcinomas: initial in vivo results

Heidy Sierra, Miguel Cordova, Oriol Yelamos, Chih-Shan Jason Chen, Milind Rajadhyaksha

Proceedings Volume 10060, 1006004 (2017) https://doi.org/10.1117/12.2254741

KEYWORDS: Laser ablation, Confocal microscopy, Reflectivity, In vivo imaging, Tissues, Tumors, Video, Skin, Aluminum, Er:YAG lasers

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Proceedings Article | 17 May 2016 Paper

Classification performance of a block-compressive sensing algorithm for hyperspectral data processing

Fernando Arias, Heidy Sierra, Emmanuel Arzuaga

Proceedings Volume 9840, 984005 (2016) https://doi.org/10.1117/12.2224542

KEYWORDS: Compressed sensing, Hyperspectral imaging, Sensors, Data acquisition, Data processing, Reconstruction algorithms, Image processing, Data storage, Image compression, Neural networks

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Proceedings Article | 27 April 2016 Presentation

Latest advances in confocal microscopy of skin cancers toward guiding patient care: a Mohs surgeon's review and perspective (Conference Presentation)

Kishwer Nehal, Milind Rajadhyaksha

Proceedings Volume 9689, 968907 (2016) https://doi.org/10.1117/12.2217675

KEYWORDS: Confocal microscopy, Mohs surgery, Skin cancer, Surgery, Skin, Melanoma, Biopsy, Reflectivity, In vivo imaging, Luminescence

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Proceedings Article | 22 April 2016 Paper

Induced structural defects in Ti-doped ZnO and its two-photon-excitation

Milton Martínez Julca, Ivonnemary Rivera , Jaime Santillan Mercado, Heidy Sierra, Oscar Perales-Pérez

Proceedings Volume 9722, 97221E (2016) https://doi.org/10.1117/12.2213750

KEYWORDS: Zinc oxide, Nanoparticles, Photodynamic therapy, Luminescence, Two photon excitation microscopy, Oxygen, Cancer, Oncology, Ultraviolet radiation, Biomedical optics, Picosecond phenomena, Titanium, Scanning electron microscopy, Zinc, Raman spectroscopy

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Proceedings Article | 21 March 2016 Paper

Laser ablation of basal cell carcinomas guided by confocal microscopy

Heidy Sierra, Miguel Cordova, Kishwer Nehal, Anthony Rossi, Chih-Shan Jason Chen, Milind Rajadhyaksha

Proceedings Volume 9689, 96890R (2016) https://doi.org/10.1117/12.2213280

KEYWORDS: Laser ablation, Confocal microscopy, Reflectivity, Er:YAG lasers, In vivo imaging, Aluminum, Tumors, Mohs surgery, Tissues, Skin

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Proceedings Article | 17 March 2016 Paper

Fluorescein as a contrast agent for confocal intra-operative imaging of basal cell carcinomas: a preliminary ex vivo study

Heidy Sierra, Qiaochu Qi, Angela Jiang, Nikash Taskar, Anthony Rossi, Milind Rajadhyaksha

Proceedings Volume 9703, 97030N (2016) https://doi.org/10.1117/12.2213719

KEYWORDS: Tumors, Tissues, Confocal microscopy, In vivo imaging, Luminescence, Mohs surgery, Reflectivity, Surgery, Skin, Natural surfaces

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Proceedings Article | 9 March 2016 Presentation + Paper

Compressive sensing in reflectance confocal microscopy of skin images: a preliminary comparative study

Fernando Arias, Heidy Sierra, Milind Rajadhyaksha, Emmanuel Arzuaga

Proceedings Volume 9713, 97130Z (2016) https://doi.org/10.1117/12.2213685

KEYWORDS: Skin, Reconstruction algorithms, Confocal microscopy, Image processing, Compressed sensing, Signal processing, Algorithm development, Image compression, Signal detection, Microscopes

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Proceedings Article | 12 March 2014 Paper

In vivo stepwise multi-photon activation fluorescence imaging of melanin in human skin

Zhenhua Lai, Zetong Gu, Saleh Abbas, Jared Lowe, Heidy Sierra, Milind Rajadhyaksha, Charles DiMarzio

Proceedings Volume 8949, 894919 (2014) https://doi.org/10.1117/12.2038310

KEYWORDS: Skin, Luminescence, In vivo imaging, Continuous wave operation, Near infrared, 3D acquisition, Microscopes, Polygon scanners, Optical filters, Imaging systems

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SPIE Journal Paper | 17 September 2013 Open Access

Confocal microscopy to guide Erbium:yttrium aluminum garnet laser ablation of basal cell carcinoma: an ex vivo feasibility study

Heidy Sierra, Bjorg Larson, Chih-Shan Chen, Milind Rajadhyaksha

JBO, Vol. 18, Issue 09, 095001, (September 2013) https://doi.org/10.1117/12.10.1117/1.JBO.18.9.095001

KEYWORDS: Laser ablation, Tissues, Confocal microscopy, Tumors, Aluminum, Skin, Mohs surgery, Laser tissue interaction, Garnet, Erbium

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Proceedings Article | 8 March 2013 Paper

Confocal microscopy to guide laser ablation of basal cell carinoma: a preliminary feasibility study

Bjorg Larson, Heidy Sierra, Jason Chen, Milind Rajadhyaksha

Proceedings Volume 8565, 856502 (2013) https://doi.org/10.1117/12.2005482

KEYWORDS: Tissues, Tumors, Laser ablation, Confocal microscopy, Laser tissue interaction, Skin, Er:YAG lasers, Mohs surgery, Natural surfaces, Reflectivity

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Proceedings Article | 21 February 2013 Paper

Analyzing subcellular structure with optical Fourier filtering based on Gabor filters

Nada Boustany, Heidy Sierra

Proceedings Volume 8592, 85920Q (2013) https://doi.org/10.1117/12.2004899

KEYWORDS: Optical filters, Image filtering, Cell death, Electronic filtering, LCDs, Light scattering, Digital filtering, Gaussian filters, Spatial filters, Optical spheres

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Label-free measurement of subcellular morphology can be used to track dynamically cellular function under various conditions and has important applications in cellular monitoring and in vitro cell assays. We show that optical filtering of scattered light by two-dimensional Gabor filters allows for direct and highly sensitive measurement of sample structure. The Gabor filters, which are defined by their spatial frequency, orientation and Gaussian envelope, can be used to track locally and in situ the characteristic size and orientation of structures within the sample. Our method consists of sequentially implementing a set of Gabor filters via a spatial light modulator placed in a conjugate Fourier plane during optical imaging and identifying the filters that yield maximum signal. Using this setup, we show that Gabor filtering of light forward-scattered by spheres yields an optical response which varies linearly with diameter between 100nm and 2000nm. The optical filtering sensitivity to changes in diameter is on the order of 20nm and can be achieved at low image resolution. We use numerical simulations to demonstrate that this linear response can be predicted from scatter theory and does not vary significantly with changes in refractive index ratio. By applying this Fourier filtering method in samples consisting of diatoms and cells, we generate false-color images of the object that encode at each pixel the size of the local structures within the object. The resolution of these encoded size maps in on the order of 0.36μm. The pixel histograms of these encoded images directly provide 20nm resolved “size spectra”, depicting the size distribution of structures within the analyzed object. We use these size spectra to differentiate the morphology of apoptosis-competent and bax/bak null apoptosis-resistant cells during cell death. We also utilize the sensitivity of the Gabor filters to object orientation to track changes in organelle morphology, and detect mitochondrial fission in cells undergoing apoptosis.

Proceedings Article | 2 February 2012 Paper

Direct and highly sensitive measurement of the spatial arrangement of microstructures within biological samples

Nada Boustany, Heidy Sierra, Robert Pasternack, Bryan Rabin

Proceedings Volume 8230, 82300O (2012) https://doi.org/10.1117/12.907100

KEYWORDS: LCDs, Optical spheres, Collagen, Image filtering, Scattering, Particles, Microscopes, Charge-coupled devices, Calibration, Light scattering

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Proceedings Article | 23 February 2011 Paper

Refractive index reconstruction of biological samples from multimodal phase microscopy

Heidy Sierra, Charles DiMarzio, Dana Brooks

Proceedings Volume 7904, 79040R (2011) https://doi.org/10.1117/12.875657

KEYWORDS: Refractive index, Digital image correlation, Refraction, Microscopy, Reconstruction algorithms, Image processing, Phase measurement, Image segmentation, Biological research, 3D image processing

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SPIE Journal Paper | 1 July 2010 Open Access

Acquiring 3-D information about thick objects from differential interference contrast images using texture extraction

Heidy Sierra, Dana Brooks, Charles DiMarzio

JBO, Vol. 15, Issue 04, 046021, (July 2010) https://doi.org/10.1117/12.10.1117/1.3475961

KEYWORDS: Digital image correlation, 3D image processing, Phase measurement, Luminescence, Image processing, Image segmentation, Microscopy, Image analysis, 3D modeling, Refraction

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Proceedings Article | 24 February 2010 Paper

Reconstructing features of thick objects from phase images

Heidy Sierra, Dana Brooks, Charles DiMarzio

Proceedings Volume 7570, 757005 (2010) https://doi.org/10.1117/12.842958

KEYWORDS: Refraction, Digital image correlation, Image processing, Microscopy, Glasses, Imaging systems, 3D image processing, Detection and tracking algorithms, Reconstruction algorithms, Visualization

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Proceedings Article | 4 March 2009 Paper

3D effects in DIC images of extended objects

Heidy Sierra, Charles DiMarzio, Dana Brooks

Proceedings Volume 7184, 71840D (2009) https://doi.org/10.1117/12.809836

KEYWORDS: 3D modeling, Digital image correlation, Point spread functions, 3D image processing, Microscopy, Geometrical optics, Image acquisition, Refraction, Process modeling, Microscopes

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Proceedings Article | 12 February 2008 Paper

Modeling images of phase information for three-dimensional objects

Heidy Sierra, Charles DiMarzio, Dana Brooks

Proceedings Volume 6861, 68610A (2008) https://doi.org/10.1117/12.763756

KEYWORDS: 3D modeling, Data modeling, Refraction, Optical spheres, Microscopy, 3D image processing, Point spread functions, Systems modeling, Microscopes, Phase measurement

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Proceedings Article | 23 September 2003 Paper

Spectral oversampling in hyperspectral imagery

Shawn Hunt, Heidy Sierra

Proceedings Volume 5093, (2003) https://doi.org/10.1117/12.488936

KEYWORDS: Image classification, Quantization, Hyperspectral imaging, Signal to noise ratio, Electronic filtering, Image filtering, Resolution enhancement technologies, Interference (communication), Reflectivity, Image resolution

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Showing 5 of 24 publications

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