1. Soumyajit Sarkar, Murali K, Anindita Chandra, Susweta Das, Hari M Varma” Spatio-temporal Simulation of Laser Speckles using Stochastic Differential Equations” Accepted in IEEE Journal of selected topics in quantum electronics (2025)
  2. Ria Paul, Soumyajit Sarkar, Susweta Das, Shruti D. Marathe, Murali K, Nixon M. Abraham, Hari M Varma “Optimized laser speckle based imaging system and methods for deep tissue cerebral blood flow imaging in small rodents” Under review (2025)
  3. Soumyajit Sarkar, Murali K, and Hari M. Varma, “Tunable dynamical tissue phantom for laser speckle imaging,” Biomed. Opt. Express 15 (2024), 4737-4748.
  4. Murali, K., and Hari M. Varma. “Laser speckle simulation tool based on stochastic differential equations for bio imaging applications.” Biomedical Optics Express 13.12 (2022): 6745-6762. 
  5. Paul, Ria, K. Murali, and Hari M. Varma. “High-density diffuse correlation tomography with enhanced depth localization and minimal surface artefacts.” Biomedical Optics Express 13.11 (2022): 6081-6099.
  6. Paul, Ria, K. Murali, Sumana Chetia, and Hari M. Varma. “A simple algorithm for diffuse optical tomography (DOT) without matrix inversion.” Biomed. Phys. Eng. Express  8 (2022) 045001
  7. Murali, K. and Hari M. Varma “Multi-speckle diffuse correlation spectroscopy to measure cerebral blood flow.” Biomedical optics express 11 (2020): 6699–6709.
  8. Murali, K., A. K. Nandakumaran, and Hari M. Varma. “On the equivalence of speckle contrast-based and diffuse correlation spectroscopy methods in measuring in vivo blood flow.” Optics Letters 45.14 (2020): 3993-3996.
  9. Murali, K., A. K. Nandakumaran, Turgut Durduran, and Hari M. Varma. “Recovery of the diffuse correlation spectroscopy data-type from speckle contrast measurements: towards low-cost, deep-tissue blood flow measurements.” Biomedical optics express 10, no. 10 (2019): 5395-5413.
  10. Dragojević, Tanja, Hari M. Varma, Joseph L. Hollmann, Claudia P. Valdes, Joseph P. Culver, Carles Justicia, and Turgut Durduran. “High-density speckle contrast optical tomography (SCOT) for three dimensional tomographic imaging of the small animal brain.” NeuroImage 153 (2017): 283-292.
  11. Dragojević, Tanja, Danilo Bronzi, Hari M. Varma, Claudia P. Valdes, Clara Castellvi, Federica Villa, Alberto Tosi, Carles Justicia, Franco Zappa, and Turgut Durduran. “High-speed multi-exposure laser speckle contrast imaging with a single-photon counting camera.” Biomedical optics express 6, no. 8 (2015): 2865-2876.
  12. Valdes, Claudia P., Hari M. Varma, Anna K. Kristoffersen, Tanja Dragojevic, Joseph P. Culver, and Turgut Durduran. “Speckle contrast optical spectroscopy, a non-invasive, diffuse optical method for measuring microvascular blood flow in tissue.” Biomedical optics express 5, no. 8 (2014): 2769-2784.
  13. de la Rosa, Xavier, Alvaro Cervera, Anna K. Kristoffersen, Claudia P. Valdés, Hari M. Varma, Carles Justicia, Turgut Durduran, Ángel Chamorro, and Anna M. Planas. “Mannose-binding lectin promotes local microvascular thrombosis after transient brain ischemia in mice.” Stroke 45, no. 5 (2014): 1453-1459.
  14. Varma, Hari M., Claudia P. Valdes, Anna K. Kristoffersen, Joseph P. Culver, and Turgut Durduran. “Speckle contrast optical tomography: A new method for deep tissue three-dimensional tomography of blood flow.” Biomedical optics express 5, no. 4 (2014): 1275-1289.
  15. Nandakumaran, Akambadath Keerthiyil, Hari M. Varma, and R. M. Vasu. “Analysis of the inverse problem associated with diffuse correlation tomography.” Journal| MESA 3, no. 1 (2012): 79-97.
  16. Varma, Hari M., Kuriyakkattil P. Mohanan, Nuutti Hyvönen, Akambadath K. Nandakumaran, and Ram M. Vasu. “Ultrasound-modulated optical tomography: recovery of amplitude of vibration in the insonified region from boundary measurement of light correlation.” JOSA A 28, no. 11 (2011): 2322-2331.
  17. Varma, Hari M., B. Banerjee, D. Roy, A. K. Nandakumaran, and R. M. Vasu. “Convergence analysis of the Newton algorithm and a pseudo-time marching scheme for diffuse correlation tomography.” JOSA A 27, no. 2 (2010): 259-267.
  18. Varma, H. M., B. Banerjee, A. K. Nandakumaran, R. M. Vasu, and D. Roy. “Pseudo-time marching schemes for inverse problems in structural health assessment and medical imaging.” Current science (2009): 1220-1226.
  19. Varma, Hari M., A. K. Nandakumaran, and R. M. Vasu. “Study of turbid media with light: Recovery of mechanical and optical properties from boundary measurement of intensity autocorrelation of light.” JOSA A 26, no. 6 (2009): 1472-1483.
  20. Varma, Hari M., R. Mohan Vasu, and A. K. Nandakumaran. “Direct reconstruction of complex refractive index distribution from boundary measurement of intensity and normal derivative of intensity.” JOSA A 24, no. 10 (2007): 3089-3099.
  • Susweta Das, Soumyajit Sarkar, Murali K, U S Srinivasan, Hari M Varma, “Direct non-invasive measurement of blood flow changes in the Anterior Cerebral Artery using Diffuse Correlation Spectroscopy” Paper 13302-48, Clinical and Translational Neurophotonics, SPIE PhotonicWest 26 Jan 2025, SanFrancisco, US.
  • Soumyajit Sarkar, Murali K., Anindita Chandra, Susweta Das, Hari M. Varma, “Modeling the spatio-temporal statistics of laser speckles using stochastic differential equation”. Paper 13318-35, Dynamics and Fluctuations in Biomedical Photonics XXII, SPIE PhotonicWest 26 Jan 2025, SanFrancisco, US.
  • Murali Krishnamoorthy; Soumyajit Sarkar; Susweta Das and  Hari Varma, “A Stochastic optimization approach to laser speckle contrast imaging for a better estimation of blood flow (JTu2A.200)” CLEO 2024, Charlotte Convention Center, Charlotte, North Carolina, USA,  5-10 May 2024.

  • Susweta Das , Ria Paul , Soumyajit Sarkar , Makrand Rakshe , Prasanna Gandhi, and Hari M Varma, “A microfluidic based cerebral perfusion phantom for laser speckle imaging in small animals, Oral Presentation, European Conferences on Biomedical Optics 2023, Munich, Germany, 25-29 June,2023

  • Soumyajit Sarkar, Murali K, and Hari M Varma, “Development of a tunable dynamical tissue phantom for laser speckle imaging of blood flow, Oral Presentation, European Conferences on Biomedical Optics 2023, Munich, Germany, 25-29 June,2023

  • Soumyajit Sarkar, Mohammad Zaffar, and Hari M Varma, “Laser speckle correlation microscopy system to image microvasculature perfusion, Poster Presentation, European Conferences on Biomedical Optics 2023, Munich, Germany, 25-29 June,2023

  • Soumyajit Sarkar, Murali K, and Hari M Varma, “A stochastic differential equation-based Monte Carlo simulation to model light propagation in dynamic turbid media.”, Poster Presentation, European Conferences on Biomedical Optics 2023, Munich, Germany, 25-29 June,2023

  • Sivakumar Panneer Selvam , Murali K , Soumyajit Sarkar , Sibi Raj Bhaskaran , and Hari M Varma, “A deep learning approach to enhance the temporal resolution of laser speckle imaging system for blood flow measurement”, Poster Presentation, European Conferences on Biomedical Optics 2023, Munich, Germany, 25-29 June,2023

  • Ria Paul, Susweta Das, Soumyajit Sarkar, Mohammad Zaffar,  and Hari M Varma, “Fiber-conduit based Laser Speckle Contrast Imaging device for point of care diagnostics”, Poster Presentation, European Conferences on Biomedical Optics 2023, Munich, Germany,  25-29 June,2023

  • Ria Paul, Soumyajit Sarkar, Shruti D. Marathe, Murali K, Susweta Das, Nixon M. Abraham, and Hari M Varma, “Functional imaging of olfactory bulb and somatosensory cortex in mice using small-animal blood flow imaging platform” Oral Presentation “Dynamics and Fluctuations in Biomedical Photonics XX, SPIE Photonic West, San Francisco, 28th-2 January 2023.

  • Hari M Varma “Diffuse autocorrelation and speckle contrast based cerebral blood flow imaging: A theoretical and experimental analysis. “ Invited Talk, CLEO 2023, San Jose California, May 2023.

  • Paul, R., Murali, K, and Hari M Varma, A Spatially Weighted Filter Design for High Density Diffuse Correlation Tomography : Biophotonics Conference : Biomedical Optics 24-27 April, 2022 Fort Lauderdale, Florida, United States
  • Murali, K, and Hari M Varma. , A stochastic differential equation based algorithm to simulate laser speckles for deep-tissue blood flow imaging applications: Biophotonics Conference: Biomedical Optics 24-27 April, 2022 Fort Lauderdale, Florida, United States
  • Murali, K., and Hari M Varma Exploring different source configurations for laser speckle-based blood flow measurement system. In European Conference on Biomedical Optics (pp. EM1A-23) (2021, June). Optical Society of America.
  • Paul, R., Murali, K., Chetia, S., and Hari M Varma. A simple algorithm for diffuse optical tomography (DOT) without matrix inversion. In European Conference on Biomedical Optics (pp. EM1A-21). (2021, June) Optical Society of America.
  • Murali, K., and Hari M. Varma. “A low frame rate camera based Diffuse Correlation Spectroscopy (DCS) system to measure blood flow in human adult brain.” In Optical Tomography and Spectroscopy, pp. STu4D-7. Optical Society of America, 2020. (Oral Presentation by first author)
  • Murali, K., A. K. Nandakumaran, Turgut Durduran, and Hari M. Varma. “An in-expensive diffuse correlation spectroscopy system using low frame rate camera.” In Optical Tomography and Spectroscopy, pp. OTu2D-4. Optical Society of America, 2018. (Oral Presentation by first author)
 
  • Claudia P. Valdes, Hari M. Varma, Tanja Dragojevi ́, Anna K. Kristoffersen , Clara Castellvi ,Carles Justicia , Joseph P. Culver, and Turgut Durduran , “Deep tissue blood flow imaging with speckle contrast optical tomography”, EB 103-62 oral presentation (30 minutes) 24 June 2015,European conference on Biomedical Optics, Munich, Germany. (Second authorship shared with first author)
  • Tanja Dragojević , Danilo Bronzi , Hari M. Varma , Claudia P. Valdes , Clara Castellvi , Alberto Tosi , Franco Zappa , Carles Justicia , Turgut Durduran, “Multi-exposure, continuous laser speckle contrast imaging of mouse brain enabled by a novel single photon avalanche diode (SPAD) array” (oral presentation 10 minutes) XXVIIth International Symposium on Cerebral Blood Flow, Metabolism and Function & XIIth International Conference June 27-30, 2015, Vancouver, Canada.
  • Tanja Dragojević , Danilo Bronzi , Hari M. Varma , Claudia P. Valdes , Clara Castellvi , Alberto Tosi ,Franco Zappa , Carles Justicia , Turgut Durduran, “Single shot multi-exposure laser speckle contrast imaging with a novel single photon avalanche diode (SPAD) array”, oral presentation (30 minutes) 24 June 2015, European conference on Biomedical Optics, Munich, Germany
  • M. Varma, C. P. Valdes, A. K. Kristoffersen, J. P. Culver, and T. Durduran, “Laser Speckle based tomographic imaging of deep tissue blood flow,” ( Oral presentation, Functional Near Infrared Spectroscopy 2014, Ecole Polytechnique Montreal October 10-12 2014)
  • H. M. Varma, C. P. Valdes, A. K. Kristoffersen, J. P. Culver, and T. Durduran, “Speckle contrast optical tomography (SCOT): Reconstructing the three dimensional distribution of blood flow in deep tissues,” (Oral presentation, Biomedical Optics (BIOMED), Optical Society of America (OSA) 2014 ).
  • P. Valdes, H. M. Varma, A. K. Kristoffersen, J. P. Culver, and T. Durduran, “Multi-Exposure and Multi-Distance Speckle Contrast Spectroscopy for Measuring Blood Flow in Deep Tissues,”(Poster presentation, Biomedical Optics (BIOMED), Optical Society of America (OSA) 2014 ).
  • P. Valdes, H. M. Varma, A. K. Kristoffersen, J. P. Culver, and T. Durduran, “Speckle contrast measurements for blood f low imaging in deep tissues,” (23rd International Commission for Optics (ICO) conference, Santiago de Compostela 26-29 August 2014)
  • Nandakumaran, H. M. Varma, and R. M. Vasu, Direct reconstruction of complex refractive index distribution from boundary measurements,” Proceedings in Applied Mathematics and Mechanics , 7, 2010017-2010018 (2007)

    • Hari M Varma, Ria Paul, Soumyajit Sarkar, Susweta Das. “Modular and portable blood flow imaging system for small animals as a whole or in part”,   (Indian Patent 2024) (Applied,pending)

    • Ria Paul, Susweta Das, Soumyajit Sarkar, Mohammad Zaffar, Hari M Varma, “A point-of-care diagnostic system based on laser speckle contrast imaging (lsci) using an image conduit,”  (Indian Patent 2024) (Applied,pending)

    • Soumyajit Sarkar, Murali K, and Hari M Varma, “Tunable phantoms for mimicking flow dynamics in turbid media” (Indian Patent 2024) (Applied,pending)

    • Murali K and  Hari M Varma: “A scanless optical tomographic system” (2022) (Indian Patent) (GRANTED)

    • Murali K and  Hari M Varma: “Systems and methods for high density diffusing wave spectroscopy” (2019-20) (Indian Patent) (PENDING)

    • Turgut Durduran, Claudia Valdes, Anna Kristoffersen, Hari Varma, Joseph Culver “Speckle contrast optical tomography” EP2888994 A1, Europe/US patent applicant: FundacióInstitut de CiènciesFotòniques, Washington University (GRANTED)

Invited talks

  • Hari M Varma“A novel approach based on stochastic calculus for laser speckle imaging” BRICS (Brazil, Russia, India and China) Workshop on Biophotonics – 2024, October 3-5, Manipal University, India.
  • Hari M Varma “ Laser speckle based  bio-imaging“ 5-day Faculty Development Program (FDP – 2024) on “The New Era of Bioengineering: Innovations and Applications”, organized by the Bioengineering Program in the Department of Chemical Engineering at Dr. Vishwanath Karad MIT World Peace University (MIT-WPU). 
  • Hari M Varma “Non invasive blood flow imaging using laser speckles” Synergy Series, Indian College of Radiology and Imaging (ICRI) meets IIT Hyderabad,  6th July 2023.
  • Hari M Varma “Diffuse autocorrelation and speckle contrast based cerebral blood flow imaging: A theoretical and experimental analysis. “ Invited Talk, Advances in Neuroimaging, Conference on Laser and Electro-Optics (CLEO 2023), San Jose California, May 2023.
  • Hari M varma “Bio-imaging using noise: Application of laser speckles for deep tissue blood flow imaging” BRICS workshop on Biophotonics, 2023 (online among different BRICS countries
  • Hari M Varma “Laser speckle contrast based three dimensional tomographic imaging of deep tissue blood flow.” Indigo policy on September 22 & 23, 2016 at IISc, Bangalore.
  • Hari M Varma “Advances in Scientific and Industrial Instrumentation (ASCII-2019): national seminar conducted by the Department of Instrumentation, Cochin University of Science and Technology. “”Diffuse optical tomography: methods and applications” 15-02-2019.

Workshop

  • AICTE ATAL sponsored Faculty Development Program : Sardar Patel Institute of Technology , Mumbai. “ Quantitative  methods in medical imaging” 24/11/2020
    DBT STAR college scheme “ Webinar series on pure and applied mathematics” Vimala college Thrissur, Kerala “ The role of mathematics in medical imaging”, 15 December ,2020. 
  • IEEE EMB Webinar on  “Diffuse optics for in vivo imaging”, IEEE EMBS SBC, IIT Kharagpur, 11 September, 2020.
  • Department of Instrumentation, CUSAT: Students induction program: “A roadmap for an academic career”. 03/12/2020. 
  • One day workshop on optical imaging. Department of Instrumentation and Applied Physics, Indian Institute of Science, “A method to achieve inexpensive diffuse-correlation spectroscopy system” 29/07/2019

We develop systems and methods for light based bio imaging applications. We primarily focus on utilizing light as a probe for non invasive in vivo brain imaging in animals and humans.