Dr. A. K. Sood Profile

Dr. A. K. Sood

at Indian Institute of Science

SPIE Involvement:

Author

Publications (10)

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

Read Abstract +

DOWNLOAD PAPER

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

Read Abstract +

DOWNLOAD PAPER

Proceedings Article | 1 May 2007 Paper

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

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

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

Read Abstract +

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

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

Read Abstract +

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

Read Abstract +

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.

DOWNLOAD PAPER

Proceedings Article | 7 July 2006 Paper

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

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

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

Read Abstract +

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

DOWNLOAD PAPER

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

Read Abstract +

DOWNLOAD PAPER

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

Read Abstract +

DOWNLOAD PAPER

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

Read Abstract +

Showing 5 of 10 publications

View contact details

UPDATE YOUR PROFILE

Is this your profile? Update it now.

Sign into your SPIE.org account

Don’t have a profile and want one?

Create an account on SPIE.org

Keywords/Phrases

Search In:

Publication Years