Prof. R. M. Vasu Profile

Prof. R. M. Vasu

Professor at Indian Institute of Science

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Author

Publications (29)

Proceedings Article | 1 April 2016 Paper

An evolutionary Bayesian search scheme for ultrasound modulated optical tomography

Mamatha Venugopal, Debasish Roy, Ram Mohan Vasu

Proceedings Volume 9790, 97900M (2016) https://doi.org/10.1117/12.2214730

KEYWORDS: Ultrasonography, Optical tomography, Ultrasound tomography, Inverse problems, Light scattering, Scattering, Bayesian inference, Image restoration, Stochastic processes, Diffusion, Inverse optics

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SPIE Journal Paper | 23 December 2014

Quantitative estimation of density variation in high-speed flows through inversion of the measured wavefront distortion

Biswajit Medhi, Gopalkrishna Hegde, Kalidevapura Polareddy Jagannath Reddy, Debasish Roy, Ram Mohan Vasu

OE, Vol. 53, Issue 12, 124107, (December 2014) https://doi.org/10.1117/12.10.1117/1.OE.53.12.124107

KEYWORDS: Wavefronts, Data modeling, Refractive index, Stochastic processes, Wavefront distortions, Tomography, Visualization, Optical engineering, Cameras, Signal processing

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Proceedings Article | 20 March 2014 Paper

Intense acoustic burst ultrasound modulated optical tomography for elasticity mapping of soft biological tissue mimicking phantom: a laser speckle contrast analysis study

M. Suheshkumar Singh, K. Rajan, R. Vasu

Proceedings Volume 9040, 90401S (2014) https://doi.org/10.1117/12.2035065

KEYWORDS: Acoustics, Ultrasonography, Tissue optics, Speckle, Modulation, Tissues, Laser tissue interaction, Soft tissue optics, Scattering, CCD cameras

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SPIE Journal Paper | 19 February 2013 Open Access

Flux density calibration in diffuse optical tomographic systems

Samir Kumar Biswas, Kanhirodan Rajan, Ram Vasu

JBO, Vol. 18, Issue 02, 026023, (February 2013) https://doi.org/10.1117/12.10.1117/1.JBO.18.2.026023

KEYWORDS: Calibration, Sensors, Tissue optics, Data analysis, Tissues, Data modeling, Absorption, Imaging systems, Scattering, Photons

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SPIE Journal Paper | 22 June 2012 Open Access

Quantitative estimation of mechanical and optical properties from ultrasound assisted optical tomography data

Mayanglambam Singh, Kanhirodan Rajan, Ram Vasu, Debasish Roy

JBO, Vol. 17, Issue 10, 101507, (June 2012) https://doi.org/10.1117/12.10.1117/1.JBO.17.10.101507

KEYWORDS: Ultrasonography, Scattering, Optical properties, Optical tomography, Modulation, Photons, Transducers, Light scattering, Biological research, Monte Carlo methods

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Proceedings Article | 3 March 2012 Paper

Linearization and reconstruction of nonlinear diffuse optical tomographic image

K. Rajan, R. Vasu, S. Biswas

Proceedings Volume 8313, 83133X (2012) https://doi.org/10.1117/12.911182

KEYWORDS: Tissue optics, Inverse optics, Data modeling, Nonlinear optics, Diffusion, Reconstruction algorithms, Optical properties, Inverse problems, Tomography, Diffuse optical tomography

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Proceedings Article | 25 February 2012 Paper

Ultrasound assisted optical tomography: estimation of phase shift experienced by photon on transit through US insonified region for detection of breast tumor

R. Vasu, Suheshkumar Singh, Rajan Kanhirodan

Proceedings Volume 8320, 832015 (2012) https://doi.org/10.1117/12.910876

KEYWORDS: Phase shifts, Ultrasonography, Light scattering, Scattering, Anisotropy, Monte Carlo methods, Breast, Tumors, Modulation, Ultrasonics

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SPIE Journal Paper | 1 November 2008 Open Access

Detection of optical and mechanical property inhomogeneities in tissue mimicking phantoms using an ultrasound assisted optical probe

C. Usha Devi, R. S. Bharat Chandran, Ram Vasu, Ajay Sood

JBO, Vol. 13, Issue 06, 064025, (November 2008) https://doi.org/10.1117/12.10.1117/1.3041169

KEYWORDS: Modulation, Absorption, Tissue optics, Transducers, Scattering, Ultrasonography, Optical properties, Acoustics, Tissues, Biomedical optics

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Proceedings Article | 7 May 2007 Paper

Efficient noise tolerant reconstructions in diffuse optical tomography through computation of Jacobian in wavelet domain

B. Kanmani, R. Vasu

Proceedings Volume 6535, 65350Y (2007) https://doi.org/10.1117/12.740968

KEYWORDS: Wavelets, Reconstruction algorithms, Absorption, Optical properties, Diffuse optical tomography, Tissue optics, Scattering, Near infrared, Image restoration, Numerical simulations

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SPIE Journal Paper | 1 May 2007 Open Access

Measurement of visco-elastic properties of breast-tissue mimicking materials using diffusing wave spectroscopy

C. Usha Devi, R. S. Bharat Chandran, Ram Vasu, Ajay Sood

JBO, Vol. 12, Issue 03, 034035, (May 2007) https://doi.org/10.1117/12.10.1117/1.2743081

KEYWORDS: Particles, Tissues, Polymers, Light scattering, Scattering, Spectroscopy, Spectroscopes, Breast, Elastography, Dynamic light scattering

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Proceedings Article | 1 May 2007 Paper

Elasticity mapping of tissue mimicking phantoms by remote palpation with a focused ultrasound beam and intensity autocorrelation measurements

R. S. Bharat Chandran, C. Usha Devi, A. Sood, R. Vasu

Proceedings Volume 6535, 65350R (2007) https://doi.org/10.1117/12.740958

KEYWORDS: Modulation, Transducers, Ultrasonography, Tissue optics, Absorption, Photons, Tissues, Elastography, Particles, Optical tomography

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Proceedings Article | 1 May 2007 Paper

Ultrasound assisted optical elastography for measurement of tissue stiffness: contribution to the measurement from scattering coefficient variation

R. S. Bharat Chandran, A. Sood, R. Vasu, C. Usha Devi

Proceedings Volume 6535, 65350X (2007) https://doi.org/10.1117/12.740965

KEYWORDS: Modulation, Tissue optics, Scattering, Ultrasonography, Absorption, Elastography, Photons, Light scattering, Transducers, Monte Carlo methods

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SPIE Journal Paper | 1 March 2007 Open Access

Mechanical property assessment of tissue-mimicking phantoms using remote palpation and optical read-out for amplitude of vibration and refractive index modulation

C. Usha Devi, R. S. Bharat Chandran, Ram Vasu, Ajay Sood

JBO, Vol. 12, Issue 02, 024028, (March 2007) https://doi.org/10.1117/12.10.1117/1.2718938

KEYWORDS: Modulation, Transducers, Photons, Tissue optics, Scattering, Absorption, Refractive index, Light scattering, Particles, Ultrasonography

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A coherent light beam is used to interrogate the focal region within a tissue-mimicking phantom insonified by an ultrasound transducer. The ultrasound-tagged photons exiting from the object carry with them information on local optical path length fluctuations caused by refractive index variations and medium vibration. Through estimation of the force distribution in the focal region of the ultrasound transducer, and solving the forward elastography problem for amplitude of vibration of tissue particles, we observe that the amplitude is directed along the axis of the transducer. It is shown that the focal region interrogated by photons launched along the transducer axis carries phase fluctuations owing to both refractive index variations and particle vibration, whereas the photons launched perpendicular to the transducer axis carry phase fluctuations arising mainly from the refractive index variations, with only smaller contribution from vibration of particles. Monte-Carlo simulations and experiments done on tissue-mimicking phantoms prove that as the storage modulus of the phantom is increased, the detected modulation depth in autocorrelation is reduced, significantly for axial photons and only marginally for the transverse-directed photons. It is observed that the depth of modulation is reduced to a significantly lower and constant value as the storage modulus of the medium is increased. This constant value is found to be the same for both axial and transverse optical interrogation. This proves that the residual modulation depth is owing to refractive index fluctuations alone, which can be subtracted from the overall measured modulation depth, paving the way for a possible quantitative reconstruction of storage modulus. Moreover, since the transverse-directed photons are not significantly affected by storage modulus variations, for a quantitatively accurate read-out of absorption coefficient variation, the interrogating light should be perpendicular to the focusing ultrasound transducer axis.

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Proceedings Article | 7 July 2006 Paper

Elimination of cross-talk in diffuse optical tomographic reconstructions through a weighted update procedure: results of simulation study

B. Kanmani, R. Vasu

Proceedings Volume 6164, 61640S (2006) https://doi.org/10.1117/12.696398

KEYWORDS: Scattering, Absorption, Reconstruction algorithms, Optical properties, Protactinium, Sensors, Matrices, Tomography, Optical tomography, Light scattering

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Proceedings Article | 7 July 2006 Paper

Computationally efficient optical tomographic reconstructions through waveletizing the normalized quadratic perturbation equation

Puneet Bansal, R. Vasu, B. Kanmani

Proceedings Volume 6164, 61640R (2006) https://doi.org/10.1117/12.696394

KEYWORDS: Wavelets, Reconstruction algorithms, Optical properties, Tomography, Absorption, Diffusion, Optical tomography, Algorithm development, Image restoration, Linear filtering

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Proceedings Article | 7 July 2006 Paper

Elastic property estimation using ultrasound assisted optical elastography through remote palpation-A simulation study

A. Sood, C. Usha Devi, R. Vasu, R. S. Bharat Chandran

Proceedings Volume 6164, 61640Q (2006) https://doi.org/10.1117/12.696392

KEYWORDS: Tissues, Ultrasonography, Tissue optics, Transducers, Modulation, Photons, Elastography, Acoustics, Monte Carlo methods, Wave propagation

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We propose an effective elastography technique in which an acoustic radiation force is used for remote palpation to generate localized tissue displacements, which are directly correlated to localized variations of tissue stiffness and are measured using a light probe in the same direction of ultrasound propagation. The experimental geometry has provision to input light beam along the ultrasound propagation direction, and hence it can be prealigned to ensure proper interception of the focal region by the light beam. Tissue-mimicking phantoms with homogeneous and isotropic mechanical properties of normal and malignant breast tissue are considered for the study. Each phantom is insonified by a focusing ultrasound transducer (1 MHz). The focal volume of the transducer and the ultrasound radiation force in the region are estimated through solving acoustic wave propagation through medium assuming average acoustic properties. The forward elastography problem is solved for the region of insonification assuming the Lame's parameters and Poisson's ratio, under Dirichlet boundary conditions which gives a distribution of displacement vectors. The direction of displacement, though presented spatial variation, is predominantly towards the ultrasound propagation direction. Using Monte Carlo (MC) simulation we have traced the photons through the phantom and collected the photons arriving at the detector on the boundary of the object in the direction of ultrasound. The intensity correlations are then computed from detected photons. The intensity correlation function computed through MC simulation showed a modulation whose strength is found to be proportional to the amplitude of displacement and inversely related to the storage (elastic) modulus. It is observed that when the storage modulus in the focal region is increased the computed displacement magnitude, as indicated by the depth of modulation in the intensity autocorrelation, decreased and the trend is approximately exponential.

SPIE Journal Paper | 1 July 2006 Open Access

Errata: Application of ultrasound-tagged photons for measurement of amplitude of vibration of tissue caused by ultrasound: theory, simulation, and experiments

R. Vasu, C. Usha Devi, A. Sood

JBO, Vol. 11, Issue 04, 049802, (July 2006) https://doi.org/10.1117/12.10.1117/1.2220572

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SPIE Journal Paper | 1 May 2006 Open Access

Application of ultrasound-tagged photons for measurement of amplitude of vibration of tissue caused by ultrasound: theory, simulation, and experiments

C. Devi, Ram Vasu, Ajay Sood

JBO, Vol. 11, Issue 03, 034019, (May 2006) https://doi.org/10.1117/12.10.1117/1.2209012

KEYWORDS: Modulation, Tissue optics, Absorption, Photons, Ultrasonography, Tissues, Refractive index, Particles, Scattering, Sensors

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SPIE Journal Paper | 1 July 2005 Open Access

Design, fabrication, and characterization of a tissue-equivalent phantom for optical elastography

C. Amma, Ram Vasu, A. Sood

JBO, Vol. 10, Issue 04, 044020, (July 2005) https://doi.org/10.1117/12.10.1117/1.2003833

KEYWORDS: Tissues, Acoustics, Breast, Tissue optics, Scattering, Ultrasonography, Elastography, Optical properties, Signal attenuation, Transducers

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Proceedings Article | 9 June 2005 Paper

Experimental determination of optical and mechanical properties of an optical elastography phantom

C. Amma, R. Vasu, A. Sood

Proceedings Volume 5772, (2005) https://doi.org/10.1117/12.636893

KEYWORDS: Tissue optics, Geometrical optics, Scattering, Elastography, Tissues, Optical properties, Light scattering, Anisotropy, Breast, Polymers

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Proceedings Article | 9 June 2005 Paper

Diffuse optical tomography through solving a system of quadratic equations without re-estimating the derivatives: the "Frozen-Newton" method; reconstruction from experimental data

R. Padmaram, B. Kanmani, R. Vasu

Proceedings Volume 5772, (2005) https://doi.org/10.1117/12.636880

KEYWORDS: Reconstruction algorithms, Optical properties, Absorption, Sensors, Scattering, Nonlinear optics, Algorithm development, Chemical elements, Image restoration, Inverse problems

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SPIE Journal Paper | 1 September 2004 Open Access

Reconstruction of optical properties of low-scattering tissue using derivative estimated through perturbation Monte-Carlo method

Yalavarthy Phaneendra Kumar, Ram Vasu

JBO, Vol. 9, Issue 05, (September 2004) https://doi.org/10.1117/12.10.1117/1.1778733

KEYWORDS: Optical properties, Reconstruction algorithms, Scattering, Absorption, Sensors, Tissue optics, Data modeling, Monte Carlo methods, Computer simulations, Solids

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Proceedings Article | 29 July 2004 Paper

Perturbation Monte-Carlo-based derivative estimation for imaging transport regime tissue optical properties

Kirtish Karlekar, Ram Vasu, Yalavarthy Phaneendra Kumar

Proceedings Volume 5486, (2004) https://doi.org/10.1117/12.571442

KEYWORDS: Optical properties, Scattering, Photons, Reconstruction algorithms, Tissue optics, Tissues, Absorption, Light scattering, Sensors, Monte Carlo methods

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Proceedings Article | 14 July 2004 Paper

Diffuse tomographic imaging after estimation of location and approximate value of the object inhomogeneities through backprojection of the data

Ram Vasu, Kanmani Buddhi

Proceedings Volume 5475, (2004) https://doi.org/10.1117/12.568556

KEYWORDS: Reconstruction algorithms, Scattering, Optical properties, Absorption, Sensors, Tomography, Point spread functions, Data modeling, Diffusion, Finite element methods

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Proceedings Article | 1 August 2003 Paper

Imaging in turbid media by modified filtered back projection method using data from Monte Carlo simulation

Ashwani Aggarwal, Ram Vasu

Proceedings Volume 5047, (2003) https://doi.org/10.1117/12.484108

KEYWORDS: Photons, Tissue optics, Monte Carlo methods, X-rays, Image filtering, Tissues, Fourier transforms, Sensors, Near infrared, Tomography

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Proceedings Article | 30 October 2001 Paper

Direct measurement of phase of foreward-scattered light using polarization heterodyne interferometer

Ram Vasu, S. Asokan, G. Ganesh Chandan

Proceedings Volume 4596, (2001) https://doi.org/10.1117/12.447354

KEYWORDS: Phase measurement, Heterodyning, Photons, Polarization, Scattering, Interferometers, Light scattering, Refractive index, Interferometry, Reconstruction algorithms

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Proceedings Article | 17 May 1999 Paper

Wavelet-based multiresolution extended Kalman filter approach to the reconstruction problem of curved-ray optical tomography

Ram Vasu, Naren Naik

Proceedings Volume 3642, (1999) https://doi.org/10.1117/12.348424

KEYWORDS: Wavelets, Reconstruction algorithms, Filtering (signal processing), Optical tomography, Refractive index, Refraction, Discrete wavelet transforms, Data modeling, Tomography, Error analysis

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Proceedings Article | 29 April 1999 Paper

Extended-Kalman-filter-based reconstruction approach to curved ray optical tomography

Ram Vasu, Naren Naik

Proceedings Volume 3729, (1999) https://doi.org/10.1117/12.346775

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SPIE Journal Paper | 1 June 1994

Deblurring in a noncoherent optical processing system: pupil function synthesis and experimental implementation

Ram Vasu, V. Boopathi

OE, Vol. 33, Issue 06, (June 1994) https://doi.org/10.1117/12.10.1117/12.168862

KEYWORDS: Point spread functions, Optical transfer functions, Optical signal processing, Filtering (signal processing), Modulation, Optical filters, Fourier transforms, Image processing, Demodulation, Phase retrieval

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Showing 5 of 29 publications

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