Publications de Chandra Sekhar Seelamantula

HILBERT TRANSFORM RELATIONS IN FREQUENCY-DOMAIN OPTICAL-COHERENCE TOMOGRAPHIC IMAGING

Theo Lasser, Chandra Sekhar Seelamantula

Interferometric imaging techniques typically embed the object phase information in the magnitude during the measurement process. During reconstruction, the phase is recovered from the magnitude by certain approximations on the measured magnitude and underl ...

2013

A Shape-Template Based Two-Stage Corpus Callosum Segmentation Technique for Sagittal Plane T1-Weighted Brain Magnetic Resonance Images

Michaël Unser, Chandra Sekhar Seelamantula

We propose a semi-automatic technique to segment corpus callosum (CC) using a two-stage snake formulation: A restricted affine transform (RAT) constrained snake followed by an unconstrained snake in an iterative fashion. A statistical model is developed to ...

IEEE2013

Zero-crossing approach to high-resolution reconstruction in frequency-domain optical-coherence tomography

Marcel Leutenegger, Theo Lasser, Chandra Sekhar Seelamantula, Arno Pino Bouwens

We address the problem of high-resolution reconstruction in frequency-domain optical-coherence tomography (FDOCT). The traditional method employed uses the inverse discrete Fourier transform, which is limited in resolution due to the Heisenberg uncertainty ...

2012

Snakes With an Ellipse-Reproducing Property

Philippe Thévenaz, Michaël Unser, Chandra Sekhar Seelamantula, Ricard Delgado Gonzalo

We present a new class of continuously defined parametric snakes using a special kind of exponential splines as basis functions. We have enforced our bases to have the shortest possible support subject to some design constraints to maximize efficiency. Whi ...

IEEE2012

Local demodulation of holograms using the Riesz transform with application to microscopy

Christian Depeursinge, Michaël Unser, Nicolas Pavillon, Chandra Sekhar Seelamantula

We propose a Riesz transform approach to the demodulation of digital holograms. The Riesz transform is a higher-dimensional extension of the Hilbert transform and is steerable to a desired orientation. Accurate demodulation of the hologram requires a relia ...

Optical Society of America2012

Exact Complex-Wave Reconstruction in Digital Holography

Christian Depeursinge, Michaël Unser, Nicolas Pavillon, Chandra Sekhar Seelamantula

We address the problem of exact complex-wave reconstruction in digital holography. We show that, by confining the object-wave modulation to one quadrant of the frequency domain, and by maintaining a reference-wave intensity higher than that of the object, ...

OSA2011

A method and apparatus for enhanced spatial bandwidth wavefronts reconstructed from digital interferograms or holograms

Christian Depeursinge, Michaël Unser, Nicolas Pavillon, Chandra Sekhar Seelamantula

The present invention discloses a method and an apparatus to compute a complex wavefield, referred to as the object wave o, by means of measuring the intensity signal resulting from the interference of the said object wave with a second wave termed the ref ...

2010

A fast time-domain algorithm for the assessment of tissue blood flow in laser-Doppler flowmetry

Dimitri Nestor Alice Van De Ville, Chandra Sekhar Seelamantula

In this study, we derive a fast, novel time-domain algorithm to compute the nth-order moment of the power spectral density of the photoelectric current as measured in laser-Doppler flowmetry (LDF). It is well established that in the LDF literature these mo ...

Institute of Physics2010

A Time-Domain Wavelet-Based Approach for Fluorescence Diffuse Optical Tomography

Michaël Unser, Chandra Sekhar Seelamantula

Purpose: In the context of fluorescence diffuse optical tomography, determining the optimal way to exploit the time-resolved information has been receiving much attention and different features of the time-resolved signals have been introduced. In this art ...

AAPM2010

Performance Analysis of Reconstruction Techniques for Frequency-Domain Optical-Coherence Tomography

Michaël Unser, Chandra Sekhar Seelamantula

We address the issue of noise robustness of reconstruction techniques for frequency-domain optical-coherence tomography (FDOCT). We consider three reconstruction techniques: Fourier, iterative phase recovery, and cepstral techniques. We characterize the re ...

Institute of Electrical and Electronics Engineers2010

Suppression of the zero-order in off-axis digital holography through nonlinear filtering

Christian Depeursinge, Michaël Unser, Jonas Kühn, Nicolas Pavillon, Chandra Sekhar Seelamantula

We present experimental validation of a new reconstruction method for off-axis digital holographic microscopy (DHM). This method effectively suppresses the object auto-correlation — namely the zero-order term — from holographic data, thereby improving the ...

2009

A Nonlinear Technique for Automatic Twin-Image and Zero-Order Term Suppression in Digital Holographic Microscopy

Christian Depeursinge, Michaël Unser, Nicolas Pavillon, Chandra Sekhar Seelamantula

ITO2009

A Method for Generalized Sampling and Reconstruction of Finite-Rate-of-Innovation Signals

Michaël Unser, Chandra Sekhar Seelamantula

We address the problem of generalized sampling and reconstruction of finite-rate-of-innovation signals. Specifically, we consider the problem of sampling streams of Dirac impulses and propose a two-channel method that enables fast, local reconstruction und ...

LATP2009

Zero-Order-Free Image Reconstruction in Digital Holographic Microscopy

Christian Depeursinge, Michaël Unser, Nicolas Pavillon, Chandra Sekhar Seelamantula

We address the problem of zero-order-free image reconstruction in digital holographic microscopy. We show how the goal can be achieved by confining the object-wave modulation to one quadrant of the frequency domain, and by maintaining a reference-wave inte ...

IEEE2009

Time Resolved Fluorescence Diffuse Optical Tomography Using Multi-Resolution Exponential B-Splines

Michaël Unser, Chandra Sekhar Seelamantula

This paper deals with the problem of time-resolved fluorescence diffuse optical tomography. We propose a new reconstruction scheme based on a multi-resolution approximation of the time-resolved signals. The underlying basis functions are exponential B-spli ...

IEEE2009

Blocking artifacts in speech/audio: Dynamic auditory model-based characterization and optimal time-frequency smoothing

Chandra Sekhar Seelamantula

We revisit the problem of blocking artifacts and their suppression in generic frame-based speech/audio applications. We provide a perceptual characterization of the artifacts by using dynamic auditory models. We propose some short-time-Fourier-transform-ba ...

2009

A Generalized Sampling Method for Finite-Rate-of-Innovation-Signal Reconstruction

Michaël Unser, Chandra Sekhar Seelamantula

The problem of sampling signals that are not admisible within the classical Shannon framework has received much attention in the recent past. Typically, these signals have a parametric representation with a finite number of degrees of freedom per time unit ...

IEEE Institute of Electrical and Electronics Engineers2008

Parametric B-Spline Snakes on Distance Maps—Application to Segmentation of Histology Images

Philippe Thévenaz, Michaël Unser, François Aguet, Chandra Sekhar Seelamantula

We construct parametric active contours (snakes) for outlining cells in histology images. These snakes are defined in terms of cubic B-spline basis functions. We use a steerable ridge detector for obtaining a reliable map of the cell boundaries. Using the ...

EURASIP2008

Exact and Efficient Signal Reconstruction in Frequency-Domain Optical-Coherence Tomography

Michaël Unser, Rainer Leitgeb, Chandra Sekhar Seelamantula

We address the problem of tomogram reconstruction in frequency-domain optical-coherence tomography. We propose a new technique for suppressing the autocorrelation artifacts that are commonly encountered with the conventional Fourier-transform-based approac ...

OSA2008

Perception Studies on the Attributes of Synthetic Clear Speech for the Hard of Hearing

Chandra Sekhar Seelamantula

We make a case for ‘synthetic clear speech’ in the context of the persons with hearing impairment. We study the acoustic attributes of ‘clear speech’ that enable us to understand their importance in speech perception. Our perception experiments are motivat ...

IEEE2007