Eduardo Tavares Costa

Ultrasound speckle reduction using modified gabor filters

B-mode ultrasound images are characterized by speckle artifact, which may make the interpretation of images difficult. One widely used method for ultrasound speckle reduction is the split spectrum processing (SSP), but the use of one-dimensional (1-D), narrow-band filters makes the resultant image experience a significant resolution loss. In order to overcome this critical drawback, we propose a novel method for speckle reduction in ultrasound medical imaging, which uses a bank of wideband 2-D directive filters, based on modified Gabor functions. Each filter is applied to the 2-D radio-frequency (RF) data, resulting in a B-mode image filtered in a given direction. The compounding of the filters outputs give rise to a final image in which speckle is reduced and the structure is enhanced. We have denoted this method as directive filtering (DF). Because the proposed filters have effectively the same bandwidth as the original image, it is possible to avoid the resolution loss caused by the use of narrow-band filters, as with SSP. The tests were carried out with both simulated arid real clinical data. Using the signal-to-noise ratio (SNR) to quantify the amount of speckle of the ultrasound images, we have achieved an average SNR enhancement of 2.26 times with simulated data and 1.18 times with real clinical data

Transthoracic cardiac ultrasonic stimulation induces a negative chronotropic effect

The objective of this study is to investigate cardiac bioeffects resulting from ultrasonic stimulation using a specific set of acoustical parameters. Ten Sprague-Dawley rats were anesthetized and exposed to 1-MHz ultrasound pulses of 3-MPa peak rarefactional pressure and approximately 1% duty factor. The pulse repetition frequency started slightly above the heart rate and was decreased by 1 Hz every 10 s, for a total exposure duration of 30 s. The control group was composed of five rats. Two-way analysis of variance for repeated measures and Bonferroni post hoc tests were used to compare heart rate and ejection fraction, which was used as an index of myocardial contractility. It was demonstrated for the first time that transthoracic ultrasound has the potential to decrease the heart rate by ~20%. The negative chronotropic effect lasted for at least 15 min after ultrasound exposure and there was no apparent gross damage to the cardiac tissue.

Measurement of transducer directivity function

A method for measuring the directivity function of transient fields with a new type of hydrophone that can be located at any convenient distance from the transducer is presented. Fields from planar and focused transducers, for both continuous wave and pulsed excitation, are measured via the new method, and the results compared against conventional measurements as well as against theoretical predictions. The directivity function for pulsed fields is best expressed as a complex directivity spectrum, and images of this fundamental transducer field characteristic are shown to encode a number of unexpected features. The definition and measurement of the directivity function, is not dependent on continuous wave or far-field conditions, and laboratory implementation of the theory is via a new type of hydrophone, with some unusual properties. It is concluded that precise and unambiguous measurement of transducer directivity patterns are straight forward to perform provided a relatively simple, but novel, technique is used. Images of the informative directivity spectrum may be obtained with ease.

Diffractive limited acoustic field of an apodized ultrasound transducer

The diffraction in the acoustic field of an ultrasound transducer can be modeled as the result of the interference of edge and plane waves generated from the periphery and the center of the piezoelectric element, respectively. Our objective in developing ultrasound transducers with apodized piezoelectric ceramic discs was to generate acoustical fields with reduced edge waves interference. Transducers were built with apodized ceramic discs (polarized more intensively in the central region than in the edges) and their mapped acoustic fields showed a distinct pattern when compared to those of conventional transducers. A polynomial equation describing the nonlinear poling field intensity, was used with the Rayleigh equation to simulate the nonuniform vibration amplitude distribution generated by the apodized transducers. Simulated acoustic fields were compared to experimental field mappings. The results of simulations and experimental tests showed reduction in the lateral spreading of acoustic fields produced by apodized transducers, compared to those produced by conventional transducers. The reduced presence of the lateral lobes in the apodized acoustic field is due to the minimized vibration of the disc periphery. The numerical and experimental results were in good agreement and showed that it was possible to reduce acoustic field diffraction through nonlinear polarization of the piezoelectric element.

Fatores que influenciam a massa óssea de crianças e adolescentes saudáveis mensurada pelo ultrassom quantitativo de falanges: revisão sistemática

Objective: To analyze the main factors that influence bone mass in children and teenagers assessed by quantitative ultrasound (QUS) of the phalanges. Data source: A systematic literature review was performed according to the PRISMA method with searches in databases Pubmed/Medline, SciELO and Bireme for the period 2001-2012, in English and Portuguese languages, using the keywords: children, teenagers, adolescent, ultrasound finger phalanges, quantitative ultrasound of phalanges, phalangeal quantitative ultrasound. Data synthesis: 21 articles were included. Girls had, in QUS, Amplitude Dependent Speed of Sound (AD-SoS) values higher than boys during pubertal development. The values of the parameters of QUS of the phalanges and dual-energy X-ray Absorptiometry (DXA) increased with the increase of the maturational stage. Anthropometric variables such as age, weight, height, body mass index (BMI), lean mass showed positive correlations with the values of QUS of the phalanges. Physical activity has also been shown to be positively associated with increased bone mass. Factors such as ethnicity, genetics, caloric intake and socioeconomic profile have not yet shown a conclusive relationship and need a larger number of studies. Conclusions: QUS of the phalanges is a method used to evaluate the progressive acquisition of bone mass during growth and maturation of individuals in school phase, by monitoring changes that occur with increasing age and pubertal stage. There were mainly positive influences variables of sex, maturity, height, weight and BMI, with similar data when compared to the gold standard method, the DXA.Objetivo:Analisar quais os principais fatores que influenciam na massa ossea de criancas e adolescentes avaliada pelo ultrassom quantitativo (QUS) de falanges.Fonte de dados:Foi realizada revisao sistematica da literatura, de acordo com o metodo Prisma, com buscas nas bases de dados do Pubmed/Medline, Bireme e Scielo, referente ao periodo de 2001 a 2012, nos idiomas ingles e portugues, utilizando os descritores children, adolescent, ultrassonography finger phalanges, quantitative ultrasound of phalanges, phalangeal quantitative ultrasound.Sintese dos dados:Foram incluidos 21 artigos. As meninas apresentaram no QUS valores de Amplitude Dependent Speed of Sound (AD-SoS) superiores aos meninos durante o desenvolvimento puberal. Os valores dos parâmetros do QUS de falanges aumentaram com o incremento do estadio maturacional, assim como ocorre com o Dual-energy X-ray Absorptiometry (DXA). Variaveis antropometricas, como idade, peso, estatura, indice de massa corporal (IMC) e massa magra, demonstraram correlacoes positivas com os valores do QUS de falanges. A atividade fisica tambem demonstrou estar positivamente relacionada ao aumento da massa ossea. Fatores como etnia, genetica, ingestao calorica e perfil socioeconomico ainda nao mostraram relacao conclusiva e necessitam um numero maior de estudos.Conclusoes:O QUS de falanges e um metodo indicado para avaliar a progressiva aquisicao da massa ossea durante o crescimento e a maturacao dos individuos em fase escolar, por acompanhar as alteracoes que ocorrem com o aumento da idade e do estadio puberal. Observouse influencia positiva, principalmente das variaveis de sexo, maturacao, estatura, peso e IMC, sendo seus dados semelhantes quando comparados ao metodo padrao-ouro, o DXA.

A programmable FPGA-based 8-channel arbitrary waveform generator for medical ultrasound research activities

In modern ultrasound imaging systems, digital transmit beamformer module typically generates accurate control of the amplitude of individual elements in a multielement array probe, as well as of the time delays and phase between them, to enable the acoustic beam to be focused and/or steered electronically. However, these systems do not provide the ultrasound researchers access to transmit front-end module. This paper presents the development of a digital transmit beamformer system for generating simultaneous arbitrary waveforms, specifically designed for research purposes. The proposed architecture has 8 independent excitation channels and uses an FPGA (Field Programmable Gated Array) device for electronic steering and focusing of ultrasound beam. The system allows operation in pulse-echo mode, with pulse repetition rate of excitation from 62.5 Hz to 8 kHz, center frequency from 500 kHz to 20 MHz, excitation voltage over 100 Vpp, and individual control of amplitude apodization, phase angle and time delay trigger. Experimental results show that this technique is suitable for generating the excitation waveforms needed for medical ultrasound imaging researches.

Design of a 128-channel FPGA-based ultrasound imaging beamformer for research activities

Medical ultrasound scanners are amongst the most sophisticated signal processing machines in use today. To support the complex analog and digital functions, multiple customized application-specific integrated circuits (ASIC) are typically used for the front-end and back-end processing, with limited programmability. Even with the recent advances in electronic technology, most of these systems do not provide the ultrasound researchers to have access to raw ultrasound radio-frequency (RF) data and several other important transmission and reception functions, which are available only to systems engineers. In this paper, we present the design and progresses of a 128-channel programmable, reconfigurable and modular FPGA-based ultrasound beamformer system specifically designed for medical imaging research. The transmitter beamformer can excite simultaneously 128-channel with arbitrary waveform, with individual enable control, amplitude apodization, phase angle and time delay for dynamic focusing on transmission. The receiver beamformer can handle simultaneous 128-channels acquisition with programmable sampling rate up to 50 MHz and 12-bit resolution. The proposed platform allows connection to linear and convex transducers array, up to 256 elements, or phased array transducers, up to 128 elements, and center frequency between 500 kHz and 20 MHz.

The effect on hemolysis of the raceway profile of roller pumps used in cardiopulmonary bypass.

This study aims at the influence on hemolysis of the differences between the maximum and minimum amplitudes of pressure in the outlet of three roller pump models adjusted by dynamic calibration method. Tests were performed with silicone tubes (½ × 3/16 inches) in fluid analogous to blood and fresh bovine blood from slaughterhouse. Tests with analogous solution to blood were performed varying the dynamic calibration pressure between 78 and 500 mm Hg. Tests with fresh bovine blood were performed with the three pumps simultaneously, and pressure differences and free hemoglobin in the plasma were measured during 360 minutes. Tests with both analogous solution to blood and fresh bovine blood showed differences of mean pressures of pump 2 related to pumps 1 and 3 (p < 0.01). The different models of roller pumps analyzed presented differences in pressure amplitudes (p < 0.01) and hemolysis (p < 0.01) adjusted for the same dynamic calibration pressure. Raceway profile of pump 2 resulted in smaller pressure amplitude, implying lower hemolysis rate compared with pumps 1 and 3.

Phase diversity for speckle reduction

B-mode ultrasound images are characterized by speckle artefact, which results from interference effects between returning echoes, and may make the interpretation of images difficult. Consequently, many methods have been developed to reduce this problematic feature. One widely used method, popular in both medical and non-destructive-testing applications, is a 1D method known as Split Spectrum Processing (SSP), or also as Frequency Diversity. Although this method was designed for speckle reduction applications, the final image experiences a resultant loss of resolution, impinging a trade-off between speckle reduction and resolution loss. In order to overcome this problem, we have developed a new method that is an extension of SSP to 2D data using directive filters, called Split Phase Processing (SPP). Instead of using 1D narrow band-pass filters as in the SSP method, we use 2D directive filters to split the RF ultrasound image in a set of wide band images with different phases. The use of such filters substantially avoids the resolution loss usually associated with SSP for speckle reduction, because they effectively have the same bandwidth as the original image. It is concluded that the Split Phase Processing, as introduced here, provides a significant improvement over the conventional Split Spectrum Processing.

Non-Uniform Piezoelectric Ceramic Polarisation: Minimising Ultrasound Field Diffraction

We have manipulated the poling process of piezoelectric ceramic discs in order to reduce the diffraction effects caused by edge waves in the acoustic field. FEM simulation was used to investigate the poling electric field format and the vibrational behaviour of apodised and non-apodised piezoelectric ceramic discs.