Fast Marching based Tissue Adaptive Delay Estimation for Aberration Corrected Delay and Sum Beamforming in Ultrasound Imaging

Conventional ultrasound (US) imaging employs the delay and sum (DAS) receive beamforming with dynamic receive focus for image reconstruction due to its simplicity and robustness. However, the DAS beamforming follows a geometrical method of delay estimation with a spatially constant speed-of-sound (SoS) of 1540 m/s throughout the medium irrespective of the tissue in-homogeneity. This approximation leads to errors in delay estimations that accumulate with depth and degrades the resolution, contrast and overall accuracy of the US image. In this work, we propose a fast marching based DAS for focused transmissions which leverages the approximate SoS map to estimate the refraction corrected propagation delays for each pixel in the medium. The proposed approach is validated qualitatively and quantitatively for imaging depths of upto ~ 11 cm through simulations, where fat layer induced aberration is employed to alter the SoS in the medium. To the best of authors' knowledge, this is the first work considering the effect of SoS on image quality for deeper imaging.Comment: 5 pages, 4 figure

Phase estimation methods and their application to holographic interferometry

Phase of the interference fringe pattern is known to convey important information in optical metrology. Typically, phase measurement using temporal techniques involves incorporating a piezoelectric device (PZT) in one arm of the interferometer for shifting the relative phase between the two interference beams. Although the precision in the measurement of phase achieved by this technique is one hundredth of the wavelength, the error arising due to the phase shifter itself is one of the potential bottlenecks in the successful measurement of the parameter of interest. The measurement process is also very sensitive to other systematic and random sources of errors that we may encounter during the experiment. To address these concerns, several algorithms have been proposed, but they have met with limited success as they allow only a limited number of error sources influencing the measurements to be minimized. The problem is exacerbated further when it comes to accommodating multiple PZTs in an optical configuration, such as, in holographic moiré. Incorporation of two PZTs is essential for the simultaneous estimation of multiple phase information in holographic moiré, such as, those corresponding to out-of-plane and in-plane displacement components. Recent introduction of high resolution methods in holographic moiré for the estimation of multiple phase information has been found to exhibit constraints while operating outside the linear region of the response of the piezoelectric device to the applied voltage. This research thesis thus addresses a significant issue of measuring phase efficiently in the presence of nonlinear response of the PZT to the applied voltage and at the same time contributes to compensating several other systematic sources of errors. For this we have designed methods based on signal processing approaches which have reputation of robust performers in the presence of random noise. The thesis presents simulation and experimental verification of the proposed methods to show their feasibility in practical situations. To the best of our knowledge, this is one of the first times that an attempt has been made to provide a robust signal processing approach for the estimation of multiple phase information in a topic of extreme significance such as that of optical metrology

An Integral Approach to Phase Shifting Interferometry Using a Super-Resolution Frequency Estimation Method

The objective of this paper is to describe an integral approach—based on the use of a super-resolution frequency estimation method—to phase shifting interferometry, starting from phase step estimation to phase evaluation at each point on the object surface. Denoising is also taken into consideration for the case of a signal contaminated with white Gaussian noise. The other significant features of the proposal are that it caters to the presence of multiple PZTs in an optical configuration, is capable of determining the harmonic content in the signal and effectively eliminating their influence on measurement, is insensitive to errors arising from PZT miscalibration, is applicable to spherical beams, and is a robust performer even in the presence of white Gaussian intensity noise

High-resolution frequency estimation technique for recovering phase distribution in interferometers

An integral approach to phase measurement is presented. First, the use of a high-resolution technique for the pixelwise detection of phase steps is proposed. Next, the robustness of the algorithm that is developed is improved by incorporation of a denoising procedure during spectral estimation. The pixelwise knowledge of phase steps is then applied to the Vandermonde system of equations for retrieval of phase values at each pixel point. Conceptually, our proposal involves the design of an annihilating filter that has zeros at the frequencies associated with the polynomial that describes the fringe intensity. The parametric estimation of this annihilating filter yields the desired spectral information embedded in the signal, which in our case represents the phase steps. The proposed method offers the advantage of extracting the interference phase of nonsinusoidal waveforms in the presence of miscalibration error of the piezoelectric transducer. In addition, in contrast to previously reported methods, this method does not require the application of selective phase steps between data frames for nonsinusoidal waveforms. © 2005 Optical Society of America OCIS codes: 120.3180, 120.5050. Phase shifting has now become a well-established technique in optical interferometry for the detection of interference phase. The technique functions b