Dr. Ahhyun Stephanie Nam Profile

Dr. Ahhyun Stephanie Nam

at Wellman Ctr for Photomedicine

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Author

Publications (10)

SPIE Journal Paper | 17 April 2023 Open Access

Development of polarization-sensitive optical coherence tomography imaging platform and metrics to quantify electrostimulation-induced peripheral nerve injury in vivo in a small animal model

Guillermo Monroy, Mohsen Erfanzadeh, Michael Tao, Damon DePaoli, Ilyas Saytashev, Ahhyun Stephanie Nam, Harmain Rafi, Kasey Kwong, Katherine Shea, Benjamin Vakoc, Srikanth Vasudevan, Daniel Hammer

NPh, Vol. 10, Issue 02, 025004, (April 2023) https://doi.org/10.1117/12.10.1117/1.NPh.10.2.025004

KEYWORDS: Nerve, Optical coherence tomography, Coherence imaging, Animals, Nervous system, Injuries, Biological imaging, Optical imaging, Image segmentation, Tissue optics

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SignificanceNeuromodulation devices are rapidly evolving for the treatment of neurological diseases and conditions. Injury from implantation or long-term use without obvious functional losses is often only detectable through terminal histology. New technologies are needed that assess the peripheral nervous system (PNS) under normal and diseased or injured conditions.AimWe aim to demonstrate an imaging and stimulation platform that can elucidate the biological mechanisms and impacts of neurostimulation in the PNS and apply it to the sciatic nerve to extract imaging metrics indicating electrical overstimulation.ApproachA sciatic nerve injury model in a 15-rat cohort was observed using a newly developed imaging and stimulation platform that can detect electrical overstimulation effects with polarization-sensitive optical coherence tomography. The sciatic nerve was electrically stimulated using a custom-developed nerve holder with embedded electrodes for 1 h, followed by a 1-h recovery period, delivered at above-threshold Shannon model k-values in experimental groups: sham control (SC, n = 5, 0.0 mA / 0 Hz), stimulation level 1 (SL1, n = 5, 3.4 mA / 50 Hz, and k = 2.57), and stimulation level 2 (SL2, n = 5, 6.8 mA / 100 Hz, and k = 3.17).ResultsThe stimulation and imaging system successfully captured study data across the cohort. When compared to a SC after a 1-week recovery, the fascicle closest to the stimulation lead showed an average change of +4 % / − 309 % (SL1/SL2) in phase retardation and −79 % / − 148 % in optical attenuation relative to SC. Analysis of immunohistochemistry (IHC) shows a +1 % / − 36 % difference in myelin pixel counts and −13 % / + 29 % difference in axon pixel counts, and an overall increase in cell nuclei pixel count of +20 % / + 35 % . These metrics were consistent with IHC and hematoxylin/eosin tissue section analysis.ConclusionsThe poststimulation changes observed in our study are manifestations of nerve injury and repair, specifically degeneration and angiogenesis. Optical imaging metrics quantify these processes and may help evaluate the safety and efficacy of neuromodulation devices.

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Proceedings Article | 15 March 2023 Presentation

Automated peripheral nerve tissue classification based on PS-OCT derived multimodal volumes (Conference Presentation)

Ilyas Saytashev, Shivam Amin, Yong-Chul Yoon, Stephanie Nam, Benjamin Vakoc, Daniel Hammer

Proceedings Volume PC12382, PC123820K (2023) https://doi.org/10.1117/12.2653143

KEYWORDS: Nerve, Tissues, Safety, Optical coherence tomography, Polarization, In vivo imaging, Image segmentation, Image classification, Electrodes, Axons

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Proceedings Article | 9 March 2023 Presentation

A 32-beam, circular-ranging OCT system for video-rate, volumetric, laparoscopic imaging

Yongjoo Kim, Yong-Chul Yoon, Hyun-Sang Park, Tae Shik Kim, Ahhyun Nam, Danielle Harper, Norman Lippok, Rafael Lomeli-Navarro, Benjamin Vakoc

Proceedings Volume PC12367, PC123670K (2023) https://doi.org/10.1117/12.2653025

KEYWORDS: Imaging systems, Laparoscopy, Optical coherence tomography, Signal to noise ratio, Tissues, Scanners, Polarization, Picosecond phenomena, Optical scanning systems, Optical fibers

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Proceedings Article | 7 March 2022 Presentation

Optical coherence tomography assessment of choroidal blood flow enabled by dynamic forward scattering

Ahhyun Stephanie Nam, Boy Braaf, Benjamin Vakoc

Proceedings Volume PC11941, PC1194114 (2022) https://doi.org/10.1117/12.2609191

KEYWORDS: Optical coherence tomography, Scattering, Signal analyzers, Sclera, Pathogens, Modulation, Hemodynamics, Eye, Blood circulation, Associative arrays

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Proceedings Article | 7 March 2022 Presentation

Polarization-assisted layer identification during the lumbar puncture procedure

Danielle Harper, Yongjoo Kim, Alejandra Gómez-Ramírez, Ahhyun Stephanie Nam, Benjamin Vakoc

Proceedings Volume PC11963, PC1196305 (2022) https://doi.org/10.1117/12.2607897

KEYWORDS: Polarization, Fluoroscopy, X-rays, Tissues, Surgery, Spine, Skin, Sensors, Optical coherence tomography, Fiber lasers

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Proceedings Article | 10 March 2020 Presentation

Wide-field intraoperative polarization sensitive and angiographic optical coherence tomography of in vivo non-human primate peripheral nerve (Conference Presentation)

Mohsen Erfanzadeh, Ahhyun Nam, Marek Hansdorfer, Kasey Kwong, Mark Randolph, Robert Redmond, Benjamin Vakoc

Proceedings Volume 11251, 112510M (2020) https://doi.org/10.1117/12.2544939

KEYWORDS: Nerve, Optical coherence tomography, Angiography, In vivo imaging, Polarization, Tissue optics, Picosecond phenomena, Axons, Molecules, Birefringence

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Proceedings Article | 14 March 2018 Presentation

Optical coherence tomography angiography based biomarkers to assess the safety of peripheral nerve electrostimulation (Conference Presentation)

Srikanth Vasudevan, Ahhyun Nam, Benjamin Vakoc, Daniel Hammer

Proceedings Volume 10481, 1048115 (2018) https://doi.org/10.1117/12.2291646

KEYWORDS: Nerve, Optical coherence tomography, Safety, Electrodes, Injuries, Optical imaging, Relays, Nervous system, Arteries, Blood

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Proceedings Article | 19 April 2017 Presentation

Assessment of vascularization and myelination following peripheral nerve repair using angiographic and polarization sensitive optical coherence tomography (Conference Presentation)

Ahhyun Nam, Isabel Chico-Calero, Jeena Easow, Martin Villiger, Jonathan Welt, Jonathan Winograd, Mark Randolph, Robert Redmond, Benjamin Vakoc

Proceedings Volume 10053, 100530M (2017) https://doi.org/10.1117/12.2254910

KEYWORDS: Photomedicine, Nerve, Optical coherence tomography, Angiography, Injuries, Polarization, Picosecond phenomena, Visualization, Microscopes, Birefringence

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Proceedings Article | 27 April 2016 Presentation

Label-free in-vivo measurement of lymph flow velocity using Doppler optical coherence tomography (Conference Presentation)

Cedric Blatter, Eelco F. Meijer, Ahhyun Nam, Dennis Jones, Timothy Padera, Benjamin Vakoc

Proceedings Volume 9719, 97190O (2016) https://doi.org/10.1117/12.2213223

KEYWORDS: Lymphatic system, In vivo imaging, Doppler tomography, Optical coherence tomography, Signal detection, Biology, Blood, Microfluidics, Biological research, Photomedicine

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Proceedings Article | 26 April 2016 Presentation

Angiographic imaging using an 18.9 MHz swept-wavelength laser that is phase-locked to the data acquisition clock and resonant scanners (Conference Presentation)

Serhat Tozburun, Cedric Blatter, Meena Siddiqui, Ahhyun Nam, Benjamin Vakoc

Proceedings Volume 9697, 969708 (2016) https://doi.org/10.1117/12.2214775

KEYWORDS: Angiography, Laser scanners, 3D scanning, Data acquisition, Imaging systems, Clocks, Doppler tomography, Photomedicine, Calibration, Computing systems

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Showing 5 of 10 publications

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