Biomedical subjects

Sarayu Ramachandran

Publications and source records attributed to Sarayu Ramachandran.

2 recordsLinked to original sources

PubMed2006

Operational verification of a 40-MHz annular array transducer.

An experimental system to take advantage of the imaging capabilities of a 5-ring polyvinylidene fluoride (PVDF)-based annular array is presented. The array has a 6-mm total aperture and a 12-mm geometric focus. The experimental system is designed to pulse a single element of the array and then digitize the received data of all array channels simultaneously. All transmit/receive pairs are digitized and then the data are post-processed with a synthetic-focusing technique to achieve an enhanced depth of field (DOF). The performance of the array is experimentally tested with a wire phantom consisting of 25-microm diameter wires diagonally spaced at 1-mm by 1-mm intervals. The phantom permitted the efficacy of the synthetic-focusing algorithm to be tested and was also used for two-way beam characterization. Experimental results are compared to a spatial impulse response method beam simulation. After synthetic focusing, the two-way echo amplitude was enhanced over the range of 8 to 19 mm and the 6-dB DOF spanned from 9 to 15 mm. For a wire at a fixed axial depth, the relative time delays between transmit/receive ring pairs agreed with theoretical predictions to within +/- 2 ns. To further test the system, B-mode images of an excised bovine eye were rendered.

Journal Article↗

PubMed2004

Adaptive spectral strain estimators for elastography.

In conventional elastography, internal tissue deformations, induced by external compression applied to the tissue surface, are estimated by cross-correlation analysis of echo signals obtained before and after compression. Conventionally, strains are estimated by computing the gradient of estimated displacement. However, gradient-based algorithms are highly susceptible to noise and decorrelation, which could limit their utility. We previously developed strain estimators based on a frequency-domain (spectral) formulation that were shown to be more robust but less precise compared to conventional strain estimators, In this paper, we introduce a novel spectral strain estimator that estimates local strain by maximizing the correlation between the spectra of pre- and postcompression echo signals using iterative frequency-scaling of the latter; we also discuss a variation of this algorithm that may be computationally more efficient but less precise. The adaptive spectral strain estimator combines the advantages of time- and frequency-domain methods and has outperformed conventional estimators in experiments and 2-D finite-element simulations.

Algorithms↗