Dr. Damber Thapa Profile

Dr. Damber Thapa

Postdoctoral Research Associate at Univ of Toronto

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Publications (12)

SPIE Journal Paper | 27 January 2024 Open Access

Quantitative photothermal analysis and multispectral imaging of dental structures: insights into optical and thermal properties of carious and healthy teeth

Elnaz Baradaran Shokouhi, Damber Thapa, Robert Welch, Koneswaran Sivagurunathan, Andreas Mandelis

JBO, Vol. 29, Issue 01, 015003, (January 2024) https://doi.org/10.1117/12.10.1117/1.JBO.29.1.015003

KEYWORDS: Enamels, Teeth, Thermography, Optical parametric oscillators, Semiconductor lasers, Multispectral imaging, Scattering, Tissues, Laser scattering, Dental caries

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SignificanceIn the analysis of two-layered turbid dental tissues, the outer finite-thickness layer is modeled by an optical transport coefficient distinct from its underlying semi-infinite substrate layer. The optical and thermophysical parameters of healthy and carious teeth across the various wavelengths were measured leading to the determination of the degree of reliability of each of the fitted parameters, with most reliable being thermal diffusivity and conductivity, enamel thickness, and optical transport coefficient of the enamel layer. Quantitative pixel-by-pixel images of the key reliable optical and thermophysical parameters were constructed.AimWe introduced a theoretical model of pulsed photothermal radiometry based on conduction-radiation theory and applied to quantitative photothermal detection and imaging of biomaterials. The theoretical model integrates a combination of inverse Fourier transformation techniques, avoiding the conventional cumbersome analytical Laplace transform method.ApproachTwo dental samples were selected for analysis: the first sample featured controlled, artificially induced early caries on a healthy tooth surface, while the second sample exhibited natural defects along with an internal filling. Using an Nd:YAG laser and specific optical parametric oscillator (OPO) wavelengths (675, 700, 750, and 808 nm), photothermal transient signals were captured from different points on these teeth and analyzed as a function of OPO wavelength. Measurements were also performed with an 808-nm laser diode for comparison with the same OPO wavelength excitation, particularly for the second sample with natural defects.ResultsThe findings demonstrated that the photothermal transient signals exhibit a fast-decaying pattern at shorter wavelengths due to their higher scattering nature, while increased scattering and absorption in the carious regions masked conductive and radiative contributions from the underlayer. These observations were cross-validated using micro-computed tomography, which also enabled the examination of signal patterns at different tooth locations.ConclusionsThe results of our study showed the impact of optical and thermal characteristics of two-layered turbid dental tissues via an inverse Fourier technique, as well as the interactions between these layers, on the patterns observed in depth profiles.

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Proceedings Article | 12 May 2022 Presentation

Handheld Point-of-Care Device for the Quantification of Anti-SARS-CoV-2 Antibodies

Damber Thapa, Nakisa Samadi, Nima Tabatabaei

Proceedings Volume PC11968, PC1196803 (2022) https://doi.org/10.1117/12.2607778

KEYWORDS: Point-of-care devices, Standards development, Thermography, Thermal sensing, Therapeutic antibodies, Plasma, Nanoparticles, Infrared sensors, Infrared radiation, Infrared imaging

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Proceedings Article | 5 March 2021 Presentation

Portable thermo-photonic device for highly sensitive detection and quantification of target analytes in lateral flow immunoassay

Damber Thapa, Nakisa Samadi, Nima Tabatabaei

Proceedings Volume 11651, 1165107 (2021) https://doi.org/10.1117/12.2580660

KEYWORDS: Target detection, Signal detection, Laser applications, Thermography, Point-of-care devices, Plasma, Particles, Nanoparticles, Infrared radiation, Gold

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Proceedings Article | 23 April 2020 Paper

Comparison of low cost and research grade active thermography platforms for detection of early dental caries

D. Thapa, N. Samadi, A. Parkhimchyk, N. Tabatabaei

Proceedings Volume 11354, 1135409 (2020) https://doi.org/10.1117/12.2555279

KEYWORDS: Dental caries, Cameras, Imaging systems, Teeth, Thermography, Infrared cameras, Image enhancement, Modulation, Phase shift keying, Optical coherence tomography

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Lock-in thermography (LIT) is a non-destructive testing technique with a broad spectrum of applications, spanning from detection of manufacturing defects in industrial samples to early diagnosis of diseases in hard and soft tissues. Nevertheless, commercialization and wide-spread adaption of LIT has long been impeded by the cost (usually $10k-$100k) and size of infrared cameras. In this paper, we demonstrate that this cost and size limitation can be overcome using cell-phone attachment infrared cameras/sensors. Developed low-cost and portable LIT systems use an intensity-modulated near infrared light for illumination while detecting thermal signatures by the low-cost cellphone attachment infrared camera (Seek thermal compact; Android). While the nominal frame rate of camera is less than 9fps, we have deciphered the communication protocol and frame information structure of the camera and set up packets of information and send them to the camera’s default endpoint address and, subsequently, acquire frame data from camera through a corresponding pipe. As such, the developed platform can control camera attributes through a simple USB interface while achieving a stable high frame rate of 33fps. To demonstrate performance of developed low-cost and portable system, two types of LIT experiments were conducted: (i) in response to the recent legalizations of marijuana in Canada, we interrogated photothermal responses of commercially available oral fluid latral flow immunoassays (LFAs), demonstrating reliable detection of THC (the psychoactive substance of cannabis) at concentrations as low as 2 ng/ml. (ii) To demonstrate ability of the system in early detection of dental caries, artificially induced early caries were created on healthy enamel surfaces and imaged with the low cost and portable system at different stages of formation. Results, suggest ability of the system in detection of caries at very early stages when neither x-ray nor visual-tactile inspection can detect them. Both sets of experiments clearly demonstrate the promise of the developed low-cost and portable LIT system in producing reliable LIT images, paving the way for translation of this technology to industry.

Proceedings Article | 13 April 2020 Presentation + Paper

Enhancement of sensitivity and detection limit of lateral flow immunoassays using lock-in thermography

D. Thapa, N. Samadi, N. Patel, N. Tabatabaei

Proceedings Volume 11361, 113610M (2020) https://doi.org/10.1117/12.2555274

KEYWORDS: Imaging systems, Thermography, Cameras, Modulation, Statistical analysis, Medicine, Image processing, Point-of-care devices, Infrared thermal wave imaging, Radiometry, Infrared imaging

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Proceedings Article | 8 February 2017 Paper

Wide-field fundus imaging with trans-palpebral illumination

Devrim Toslak, Damber Thapa, Yanjun Chen, Muhammet Kazim Erol, R. V. Paul Chan, Xincheng Yao

Proceedings Volume 10045, 100451X (2017) https://doi.org/10.1117/12.2252491

KEYWORDS: Eye, Photography, Sclera, Fiber optic illuminators, Imaging devices, Light sources, Retina, Cameras, Imaging systems

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SPIE Journal Paper | 19 December 2016 Open Access

In vivo super-resolution retinal imaging through virtually structured detection

Changgeng Liu, Yanan Zhi, Benquan Wang, Damber Thapa, Yanjun Chen, Minhaj Alam, Yiming Lu, Xincheng Yao

JBO, Vol. 21, Issue 12, 120502, (December 2016) https://doi.org/10.1117/12.10.1117/1.JBO.21.12.120502

KEYWORDS: Super resolution, In vivo imaging, Spatial frequencies, Retinal scanning, Image resolution, Retina, Eye, Spatial resolution, Signal to noise ratio, Microscopy

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SPIE Journal Paper | 23 June 2016 Open Access

Stimulus-evoked outer segment changes in rod photoreceptors

Xiaohui Zhao, Damber Thapa, Benquan Wang, Yiming Lu, Shaoyan Gai, Xincheng Yao

JBO, Vol. 21, Issue 06, 065006, (June 2016) https://doi.org/10.1117/12.10.1117/1.JBO.21.6.065006

KEYWORDS: Rods, Retina, Image segmentation, Cones, Visible radiation, Calibration, Microscopy, Near infrared, Tissues, Confocal microscopy

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Proceedings Article | 7 March 2016 Paper

Biophysical mechanism of transient retinal phototropism in rod photoreceptors

Xiaohui Zhao, Damber Thapa, Benquan Wang, Shaoyan Gai, Xincheng Yao

Proceedings Volume 9706, 97061O (2016) https://doi.org/10.1117/12.2209144

KEYWORDS: Retina, Rods, Microscopy, Optical coherence tomography, Confocal microscopy, Near infrared, Visible radiation, Molecules, Optical flow, Plasma

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Proceedings Article | 4 March 2016 Paper

Comparison of performance of some common Hartmann-Shack centroid estimation methods

C. Thatiparthi, A. Ommani, R. Burman, D. Thapa, N. Hutchings, V. Lakshminarayanan

Proceedings Volume 9693, 969321 (2016) https://doi.org/10.1117/12.2219857

KEYWORDS: Image processing, Wavefront sensors, Wavefronts, Optical aberrations, Signal processing, Eye models, Spherical lenses, Eye, Mirrors

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Proceedings Article | 17 July 2014 Open Access

Light and optics conceptual evaluation findings from first year optometry students

Damber Thapa, Vasudevan Lakshminarayanan

Proceedings Volume 9289, 928919 (2014) https://doi.org/10.1117/12.2070519

KEYWORDS: Visual optics, Physics, Active optics, Geometrical optics, Error analysis, Photonics, Refraction, Optical design, Ophthalmology, Visualization

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SPIE Journal Paper | 1 May 2014 Open Access

Comparison of super-resolution algorithms applied to retinal images

Damber Thapa, Kaamran Raahemifar, William Bobier, Vasudevan Lakshminarayanan

JBO, Vol. 19, Issue 05, 056002, (May 2014) https://doi.org/10.1117/12.10.1117/1.JBO.19.5.056002

KEYWORDS: Lawrencium, Super resolution, Image fusion, Image analysis, Image resolution, Blood vessels, Image registration, Motion estimation, Associative arrays, Eye

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