Hassan Rivaz

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This paper introduces two real-time elastography techniques based on analytic minimization (AM) of regularized cost functions. The first method (1D AM) produces axial strain and integer lateral displacement, while the second method (2D AM) produces both axial and lateral strains. The cost functions incorporate similarity of radio-frequency (RF) data(More)
This paper introduces a 2-D strain imaging technique based on minimizing a cost function using dynamic programming (DP). The cost function incorporates similarity of echo amplitudes and displacement continuity. Since tissue deformations are smooth, the incorporation of the smoothness into the cost function results in reduced decorrelation noise. As a(More)
Extending mutual information (MI), which has been widely used as a similarity measure for rigid registration of multi-modal images, to deformable registration is an active field of research. We propose a self-similarity weighted graph-based implementation of alpha-mutual information (alpha-MI) for nonrigid image registration. The new Self Similarity(More)
Displacement estimation is an essential step for ultrasound elastography and numerous techniques have been proposed to improve its quality using two frames of ultrasound RF data. This paper introduces a technique for calculating a displacement field from three (or multiple) frames of ultrasound RF data. To calculate a displacement field using three images,(More)
The clinical feasibility of 2D elastography methods is hindered by the requirement that the operator avoid out-of-plane motion of the ultrasound image during palpation, and also by the lack of volumetric elastography measurements. In this paper, we develop and evaluate a 3D elastography method operating on volumetric data acquired from a 3D probe. Our(More)
This paper presents a robust framework for freehand ultrasound elastography to cope with uncertainties of freehand palpation using the information from an external tracker. In order to improve the quality of the elasticity images, the proposed method selects a few image pairs such that in each pair the lateral and out-of-plane motions are minimized. It(More)
Tracked ultrasound elastography can be used for guidance in partial breast radiotherapy by visualizing the hard scar tissue around the lumpectomy cavity. For clinical success, the elastography method needs to be robust to the sources of decorrelation between ultrasound images, specifically fluid motions inside the cavity, change of the appearance of(More)
— Speckle detection is essential in many areas of quantitative ultrasound. In this work, speckle is characterized with R=SNR and S=skewness of the amplitude of the ultrasound signal data A. Different powers of A can be used to calculate R and S. Prager et al. [1] proposed a method for finding the optimum power value, which then was further scrutinized [2].(More)
—Out-of-plane motion in freehand 3D ultrasound can be estimated using the correlation of corresponding patches, leading to sensorless freehand 3D ultrasound systems. Previous work has shown that the motion estimation in a beef tissue is systematically underestimated by approximately 33% and that it can be improved to approximately 25% by limiting the(More)
The elevational distance between two ultrasound images can be obtained from the correlation between the two images, leading to sensorless freehand 3D ultrasound systems. Most of these systems rely on the correlation between patches of fully developed speckles (FDS). Previous work 1 has compared different FDS detectors and concluded that the elevational(More)