Ms. Kristen T. Tgavalekos Profile

Kristen T. Tgavalekos

Doctoral Candidate at Tufts Univ

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Author

Publications (8)

Proceedings Article | 13 February 2018 Presentation + Paper

Measurements of coherent hemodynamics to enrich the physiological information provided by near-infrared spectroscopy (NIRS) and functional MRI

Angelo Sassaroli, Kristen Tgavalekos, Thao Pham, Nishanth Krishnamurthy, Sergio Fantini

Proceedings Volume 10487, 104870E (2018) https://doi.org/10.1117/12.2290040

KEYWORDS: Hemodynamics, Near infrared spectroscopy, Data acquisition, Cerebral blood flow, Wavelets, Functional magnetic resonance imaging, Magnetic resonance imaging, Tissue optics, Spectroscopy, Fourier transforms

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Proceedings Article | 18 February 2017 Paper

Coherent hemodynamics spectroscopy: initial applications in the neurocritical care unit

Kristen Tgavalekos, Angelo Sassaroli, Xuemei Cai, Joshua Kornbluth, Sergio Fantini

Proceedings Volume 10059, 100591F (2017) https://doi.org/10.1117/12.2251021

KEYWORDS: Near infrared spectroscopy, Cerebral blood flow, Hemodynamics, Mathematical modeling, Spectroscopy, Blood, Optical spectroscopy, Blood pressure, Imaging spectroscopy, Optical spectroscopy imaging, Autoregressive models, Data modeling, Tissue optics, Tissues

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Proceedings Article | 17 February 2017 Paper

Induced and spontaneous hemodynamic oscillations in cerebral and extracerebral tissue for coherent hemodynamics spectroscopy

Angelo Sassaroli, Xuan Zang, Kristen Tgavalekos, Sergio Fantini

Proceedings Volume 10059, 100591G (2017) https://doi.org/10.1117/12.2250930

KEYWORDS: Hemodynamics, Tissue optics, Spectroscopy, Brain, Tissues, Blood, Near infrared spectroscopy, Skull, Brain stimulation, Capillaries, Channel projecting optics, Phase measurement, Blood pressure

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We report preliminary results of a study for investigating the spatial homogeneity of induced and spontaneous oscillations in the concentration of oxyhemoglobin on the scalp/skull layer of two human subjects. Hemodynamic oscillations were induced by modulation of arterial blood pressure, which triggers the cerebral autoregulation mechanism. Induced hemodynamic oscillations are used in coherent hemodynamics spectroscopy to derive physiological parameters of interest for medical diagnostics. For example, our dedicated mathematical model translates typical near-infrared spectroscopy observables, like the amplitude and phase relationship of the oscillations of oxy- and deoxyhemoglobin concentrations into capillary and venous blood transit times, cutoff frequency of the autoregulation process, and other parameters related to microvascular blood volume. In this study, we focused on the phase relationship between the oscillations of oxyhemoglobin concentrations in three optical channels, two of which feature a short (5 mm) source-detector separation (sampling the scalp/skull only) and the third one features a long (30 mm) source-detector separation (sampling both extracerebral and cerebral tissues). The two main goals of the study were: a) to compare the coherence of induced and spontaneous oscillations; b) to assess if induced and spontaneous oscillations may be assumed to be uniform in the extracerebral layer. This was assessed by studying the phase relationship of oscillations in oxyhemoglobin concentration at the two short source-detector separations. About point a) we verified that induced oscillations have a higher incidence of coherence than spontaneous oscillations: 74% for induced oscillations, and 30% for spontaneous oscillations. About point b) the results show an overall trend for both spontaneous and induced oscillations to be homogeneous or “quasi-homogeneous” in the extracerebral tissue; however, we observed cases where a significant non-zero phase difference was measured, indicating spatial heterogeneity. We propose a method for taking into account the possible inhomogeneous behavior of the oscillations in the scalp/skull in order to increase the accuracy of measurements of cerebral hemodynamic oscillations.

SPIE Journal Paper | 21 June 2016 Open Access

Cerebral blood flow and autoregulation: current measurement techniques and prospects for noninvasive optical methods

Sergio Fantini, Angelo Sassaroli, Kristen Tgavalekos, Joshua Kornbluth

NPh, Vol. 3, Issue 03, 031411, (June 2016) https://doi.org/10.1117/12.10.1117/1.NPh.3.3.031411

KEYWORDS: Blood, Tissues, Brain, Near infrared spectroscopy, Cerebral blood flow, Arteries, Data modeling, Tissue optics, Ultrasonography, Traumatic brain injury

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SPIE Journal Paper | 28 March 2016 Open Access

Blood-pressure-induced oscillations of deoxy- and oxyhemoglobin concentrations are in-phase in the healthy breast and out-of-phase in the healthy brain

Kristen Tgavalekos, Jana Kainerstorfer, Angelo Sassaroli, Sergio Fantini

JBO, Vol. 21, Issue 10, 101410, (March 2016) https://doi.org/10.1117/12.10.1117/1.JBO.21.10.101410

KEYWORDS: Breast, Brain, Blood, Hemodynamics, Tissues, Blood circulation, Near infrared spectroscopy, Oxygen, Tissue optics, Capillaries

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Proceedings Article | 9 March 2016 Presentation + Paper

Non-invasive assessment of cerebral microcirculation with diffuse optics and coherent hemodynamics spectroscopy

Sergio Fantini, Angelo Sassaroli, Jana Kainerstorfer, Kristen Tgavalekos, Xuan Zang

Proceedings Volume 9690, 96900S (2016) https://doi.org/10.1117/12.2213139

KEYWORDS: Hemodynamics, Near infrared spectroscopy, Cerebral blood flow, Diffuse optical imaging, Brain, Blood pressure, Modeling, Tissues, Oxygen, Blood circulation, Capillaries

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Proceedings Article | 12 March 2015 Paper

Functional near-infrared spectroscopy for adaptive human-computer interfaces

Beste Yuksel, Evan Peck, Daniel Afergan, Samuel Hincks, Tomoki Shibata, Jana Kainerstorfer, Kristen Tgavalekos, Angelo Sassaroli, Sergio Fantini, Robert J. Jacob

Proceedings Volume 9319, 93190R (2015) https://doi.org/10.1117/12.2075929

KEYWORDS: Unmanned aerial vehicles, Brain-machine interfaces, Machine learning, Human-machine interfaces, Brain, Cognitive modeling, Data modeling, Calibration, Near infrared spectroscopy, Adaptive control

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Proceedings Article | 12 March 2015 Paper

Dynamic cerebral autoregulation measured with coherent hemodynamics spectroscopy (CHS)

Jana Kainerstorfer, Angelo Sassaroli, Kristen Tgavalekos, Sergio Fantini

Proceedings Volume 9319, 93190N (2015) https://doi.org/10.1117/12.2077816

KEYWORDS: Capillaries, Hemodynamics, Blood, Near infrared spectroscopy, Spectroscopy, Linear filtering, Autoregressive models, Time metrology, Data modeling, Cerebral blood flow

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Showing 5 of 8 publications

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