Biomedical subjects

Glauber T Silva

Publications and source records attributed to Glauber T Silva.

8 recordsLinked to original sources

PubMed2006

Image formation in vibro-acoustography with depth-of-field effects.

We study the image formation of vibro-acoustography systems based on a concave sector array transducer taking into account depth-of-field effects. The system point-spread function (PSF) is defined in terms of the acoustic emission of a point-target in response to the dynamic radiation stress of ultrasound. The PSF on the focal plane and the axis of the transducer are presented. To extend the obtained PSF to the 3D-space, we assume it is a separable function in the axial direction and the focal plane of the transducer. In this model, an image is formed through the 3D convolution of the PSF with an object function. Experimental vibro-acoustography images of a breast phantom with lesion-like inclusions were compared with simulated images. Results show that the experimental images are in good agreement with the proposed model.

Elasticity↗

PubMed2006

Dynamic radiation force of acoustic waves on solid elastic spheres.

The present study concerns the dynamic radiation force on solid elastic spheres exerted by a plane wave with two frequencies (bichromatic wave) considering the nonlinearity of the fluid. Our approach is based on solving the wave scattering for the sphere in the quasilinear approximation within the preshock wave range. The dynamic radiation force is then obtained by integrating the component of the momentum flux tensor at the difference of the primary frequencies over the boundary of the sphere. Results reveal that effects of the nonlinearity of the fluid play a major role in dynamic radiation force leading it to a parametric amplification regime. The developed theory is used to calculate the dynamic radiation force on three different solid spheres (aluminum, silver, and tungsten). Resonances are observed in the spectrum of the force on the spheres. They have larger amplitude and better shape than resonances present in static radiation force.

Journal Article↗

PubMed2006

Parametric amplification of the dynamic radiation force of acoustic waves in fluids.

We report on parametric amplification in dynamic radiation force produced by a bichromatic acoustic beam in a fluid. To explain this effect we develop a theory taking into account the nonlinearity of the fluid. The theory is validated through an experiment to measure the dynamic radiation force on an acrylic sphere. Results exhibit an amplification of 66 dB in water and 80 dB in alcohol as the difference of the frequencies is increased from 10 Hz to 240 kHz.

Journal Article↗

PubMed2006

Multifrequency vibro-acoustography.

Elasticity imaging is a burgeoning medical imaging field. Many methods have been proposed that impart a force to tissue and measure the mechanical response. One method, vibro-acoustography, uses the ultrasound radiation force to harmonically vibrate tissue and measure the resulting acoustic emission field with a nearby hydrophone. Another method, vibrometry, uses the ultrasound radiation force accompanied with a measurement of the resulting velocity or displacement of the vibrating tissue or object has also been used for different applications. An extension of the vibro-acoustography method using a multifrequency stress field to vibrate an object is described. The objective of this paper is to present the image formation theory for multifrequency vibro-acoustography. We show that the number of low-frequency components created by this multifrequency method scales with the square of the number of ultrasound sources used. We provide experimental validation of the point-spread function of the multifrequency stress field and show examples of both vibrometry and vibro-acoustography imaging applications. This method holds the potential for a large gain of information with no increase in scanning time compared to conventional vibro-acoustography systems.

Acoustics↗

PubMed2005

Dynamic ultrasound radiation force in fluids.

The subject of this paper is to present a theory for the dynamic radiation force produced by dual-frequency ultrasound beams in lossless and nondispersive fluids. An integral formula for the dynamic radiation force exerted on a three-dimensional object by a dual-frequency beam is obtained stemming from the fluid dynamics equations. The static radiation force due to a monochromatic wave appears as a particular case of this theory. Dependence of the dynamic radiation force to nonlinear effects of the medium is analyzed. We calculate the dynamic radiation force exerted on solid elastic spheres of two different materials by a low-amplitude dual-frequency plane wave. The static and dynamic radiation forces exhibited approximately same magnitude. Resonance patterns observed in the dynamic radiation force are similar to those present in the static radiation force.

Journal Article↗

PubMed2005

Measurement of dynamic and static radiation force on a sphere.

Dynamic radiation force from ultrasound has found increasing applications in elasticity imaging methods such as vibro-acoustography. Radiation force that has both static and dynamic components can be produced by interfering two ultrasound beams of slightly different frequencies. This paper presents a method to measure both static and dynamic components of the radiation force on a sphere suspended by thin threads in water. Due to ultrasound radiation force, the sphere deflects to an equilibrant position and vibrates around it. The static radiation force is estimated from the deflection of the sphere. The dynamic radiation force is estimated from the calculated radiation impedance of the sphere and its vibration speed measured by a laser vibrometer. Experimental results on spheres of different size, vibrated at various frequencies, confirm the theoretical prediction that the dynamic and static radiation force on a sphere have approximately equal magnitudes [G. T. Silva, Phys. Rev. E 71, 056617 (2005)].

Acoustics↗

PubMed2005

Stress field forming of sector array transducers for vibro-acoustography.

This paper presents a study of the stress field forming of sector array transducers for vibro-acoustography applications. The system point-spread function (PSF) is given in terms of the dynamic radiation stress exerted on a point target by a dual ultrasound beam with slightly different frequencies. The radiation stress is calculated by assuming that the resulting ultrasound beam is a plane wave. The stress is proportional to the product of the velocity potential of each incident ultrasound beam. The beamforming and stress field forming of sector array transducers are analyzed through linear acoustics. An expression for the velocity potential produced by sector array transducers is derived. The vibro-acoustography PSF is evaluated numerically. A comparison between the PSF of a sector array and a confocal transducers is presented. The compared characteristics of the PSF are sidelobe levels, transverse, and in-depth spatial resolution. Indeed, one motivation to study sector transducers is the fact the depth-of-field of these transducers should be smaller than that of same size confocal transducers. An experimental setup was used to validate the theoretical PSF of sector array transducers. Results show that the measured PSF is in good agreement with the theoretical predications. Vibro-acoustography images of a breast-phantom by both transducers are presented and discussed.

Acoustics↗

PubMed2004

Linear arrays for vibro-acoustography: a numerical simulation study.

In this work, we study linear array beamforming for vibro-acoustography systems. The goal of this research is to assess the feasibility of vibro-acoustography imaging systems based on linear arrays for clinical applications. The vibro-acoustography transducer is designed with two arrays driven by two continuous-wave or tone-burst signals at slightly different frequencies. The system beamforming is modeled in a homogeneous and lossless fluid. In this model, the point-spread function (psf) of the system is obtained as the product of the spatial impulse function of each linear array. Three linear array configurations are analyzed for vibro-acoustography systems. Simulations considering 64 elements in each array are performed. Aspects related to clinical applications ofvibro-acoustography, such as system spatial resolution, sidelobes, grating lobes and image frame-rate are discussed. It is concluded that linear array transducers can produce acceptable spatial resolution for clinical applications.

Acoustics↗