905 research outputs found
Equivalent Circuit-Based Analysis of CMUT Cell Dynamics in Arrays
Cataloged from PDF version of article.Capacitive micromachined ultrasonic transducers (CMUTs) are usually composed of large arrays of closely packed cells. In this work, we use an equivalent circuit model to analyze CMUT arrays with multiple cells. We study the effects of mutual acoustic interactions through the immersion medium caused by the pressure field generated by each cell acting upon the others. To do this, all the cells in the array are coupled through a radiation impedance matrix at their acoustic terminals. An accurate approximation for the mutual radiation impedance is defined between two circular cells, which can be used in large arrays to reduce computational complexity. Hence, a performance analysis of CMUT arrays can be accurately done with a circuit simulator. By using the proposed model, one can very rapidly obtain the linear frequency and nonlinear transient responses of arrays with an arbitrary number of CMUT cells. We performed several finite element method (FEM) simulations for arrays with small numbers of cells and showed that the results are very similar to those obtained by the equivalent circuit model
Rayleigh-Bloch waves in CMUT arrays
Cataloged from PDF version of article.Using the small-signal electrical equivalent circuit of a capacitive micromachined ultrasonic transducer (CMUT) cell, along with the self and mutual radiation impedances of such cells, we present a computationally efficient method to predict the frequency response of a large CMUT element or array. The simulations show spurious resonances, which may degrade the performance of the array. We show that these unwanted resonances are due to dispersive Rayleigh-Bloch waves excited on the CMUT surface-liquid interface. We derive the dispersion relation of these waves for the purpose of predicting the resonance frequencies. The waves form standing waves at frequencies where the reflections from the edges of the element or the array result in a Fabry-Pérot resonator. High-order resonances are eliminated by a small loss in the individual cells, but low-order resonances remain even in the presence of significant loss. These resonances are reduced to tolerable levels when CMUT cells are built from larger and thicker lates at the expense of reduced bandwidth. © 2014 IEEE
Simultaneous use of Individual and Joint Regularization Terms in Compressive Sensing: Joint Reconstruction of Multi-Channel Multi-Contrast MRI Acquisitions
Purpose: A time-efficient strategy to acquire high-quality multi-contrast
images is to reconstruct undersampled data with joint regularization terms that
leverage common information across contrasts. However, these terms can cause
leakage of uncommon features among contrasts, compromising diagnostic utility.
The goal of this study is to develop a compressive sensing method for
multi-channel multi-contrast magnetic resonance imaging (MRI) that optimally
utilizes shared information while preventing feature leakage.
Theory: Joint regularization terms group sparsity and colour total variation
are used to exploit common features across images while individual sparsity and
total variation are also used to prevent leakage of distinct features across
contrasts. The multi-channel multi-contrast reconstruction problem is solved
via a fast algorithm based on Alternating Direction Method of Multipliers.
Methods: The proposed method is compared against using only individual and
only joint regularization terms in reconstruction. Comparisons were performed
on single-channel simulated and multi-channel in-vivo datasets in terms of
reconstruction quality and neuroradiologist reader scores.
Results: The proposed method demonstrates rapid convergence and improved
image quality for both simulated and in-vivo datasets. Furthermore, while
reconstructions that solely use joint regularization terms are prone to
leakage-of-features, the proposed method reliably avoids leakage via
simultaneous use of joint and individual terms.
Conclusion: The proposed compressive sensing method performs fast
reconstruction of multi-channel multi-contrast MRI data with improved image
quality. It offers reliability against feature leakage in joint
reconstructions, thereby holding great promise for clinical use.Comment: 13 pages, 13 figures. Submitted for possible publicatio
X-Chromosomal short tandem repeat loci in the Turkish population
In this study, we aimed to demonstrate the importance and utility of polymorphic short tandem repeat (STR) found on the human X chromosome and to provide the first allelic frequency data of X-STR (X chromosomal) loci in the Turkish population. Blood samples were taken from unrelated individuals (135 males and 129 females) from different regions of the country. Primers were designed according to gene bank data (www.gdb.org) and synthesised by the Köln Blutgruppen Institute. The primers amplified the following loci on the X chromosome: DXS8377, DXS101, DXS6789, STRX-1 and HUMHPRTB. Our data showed that two loci, DXS8377 and DX101, had the highest number of alleles (18) and the polymorphism information content (PIC) values of these loci were 0.9 and 0.87, respectively and were higher than those of other loci. In the other loci examined, 11 (STRX1), 10 (DXS6789) and 9 (HPRTB) alleles were detected and the PIC values of these loci were 0.78, 0.68 and 0.70, respectively. The highest (0.899) and lowest (0.674) rate of heterozygosity was found in the DXS8377 and HPRTB loci, respectively. In all loci, the power of discrimination for female (PDF) values were higher than the power of discrimination for male (PDM) values. The locus with the highest PDF value was DXS8377 (0.9841). The mean exclusion change (MEC) value of this locus also proved to be the highest for both fathermother- child and father-child. The locus with the lowest MEC value was DXS6789. To use calculations of probabilities of genetic results for forensic purposes, allelic frequencies in individuals in the community should be determined. Our study provides the first data from the Turkish population.Key words: X chromosomal (X-STR), forensic genetics, forensic sciences, DNA, kinship testing, paternity
Novel OCT mosaicking pipeline with Feature- and Pixel-based registration
High-resolution Optical Coherence Tomography (OCT) images are crucial for
ophthalmology studies but are limited by their relatively narrow field of view
(FoV). Image mosaicking is a technique for aligning multiple overlapping images
to obtain a larger FoV. Current mosaicking pipelines often struggle with
substantial noise and considerable displacement between the input sub-fields.
In this paper, we propose a versatile pipeline for stitching multi-view
OCT/OCTA \textit{en face} projection images. Our method combines the strengths
of learning-based feature matching and robust pixel-based registration to align
multiple images effectively. Furthermore, we advance the application of a
trained foundational model, Segment Anything Model (SAM), to validate
mosaicking results in an unsupervised manner. The efficacy of our pipeline is
validated using an in-house dataset and a large public dataset, where our
method shows superior performance in terms of both accuracy and computational
efficiency. We also made our evaluation tool for image mosaicking and the
corresponding pipeline publicly available at
\url{https://github.com/MedICL-VU/OCT-mosaicking}
TELPACK: An Advanced teletraffic analysis package
Performance evaluation of computer and communication networks gives rise to teletraffic problems of potentially large dimensionality. We briefly summarize a unifying system theoretic approach to efficient solution of a diversity of such problems, and introduce TELPACK, a publicly available software that implements this approach
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