A Developmental Method for Evolving Large-Scale Spiking Neural Networks

Lin, Xianghong; Tian-wen, Zhang; Zhang, Gui-Cang

doi:10.3724/sp.j.1016.2012.02633

Cited by 3 publications

(2 citation statements)

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“…This is the first time, to the best of our knowledge, that shear waves were coupled with coherent light and furthermore related with CCD speckle-contrast statistics in a simulation framework. The simulation will be incorporated with ARFassisted ultrasound modulated optical tomography [17,18] to study the effect of ARF-generated shear waves on the image resolution. The method can also be generalized to other forms of electromagnetic waves if the speckle patterns can be detected.…”

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Tracking shear waves in turbid medium by light: theory, simulation, and experiment

Song

et al. 2014

Opt. Lett.

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Shear wave propagation provides rich information for material mechanical characterization, including elasticity and viscosity. This Letter reports tracking of shear wave propagation in turbid media by laser-speckle-contrast analysis. The theory is described, and a Monte Carlo simulation of light shear wave interaction was developed. Simulation and experiments on tissue-mimicking phantoms agree well and show tracking of shear wave at the phantom surface and at depth as well as multiple shear waves interacting within the object. The relationship between speckle contrast value and shear wave amplitude is also investigated. . Optical observation of tissue response to acoustic radiation force and associated shear wave generation was previously reported in [4,5]. In this Letter, we present a method to track the shear wave propagation in optically turbid media by laser speckle contrast analysis. Part of our experimental method was discussed in [6], where the shear wave speed was tracked in phantoms of varying elasticity. A coherent green laser was used, and the speckle patterns were received on a CCD camera. Transient shear waves were generated by acoustic radiation force a distance away from laser axis at depth in phantoms. The shear wave was tracked using the timeresolved CCD speckle-contrast difference. In this Letter, we first describe the theoretical basis of this experimental method, then a Monte Carlo simulation system is developed for the first time and verified by experiments. We also show shear wave imaging at the phantom edge using local speckle contrast analysis. In addition, multiple shear waves are simultaneously observed through speckle-contrast detection for the first time, and the relationship between CCD speckle-contrast difference and shear wave amplitude is also studied.Previous theoretical contributions that explain the interaction of ultrasound and (multiply) scattered light are available in the literature [7][8][9]. Generally, two mechanisms are thought to be responsible for the ultrasound modulation of light: first, the phase change due to displacement of optical scatterers by ultrasound; second, the phase change due to alteration of the optical refractive index by compression and rarefaction of ultrasound. However, when light interacts with a transient shear wave alone, there are two major differences: (1) the shear wave pressure is small, and therefore little alteration of optical refractive index occurs. As a consequence, the second modulation mechanism may be neglected; (2) the shear wave period is much longer than the ultrasound period and is comparable and most likely longer than the light integration time on the detector. Below we describe a framework that can be used to explain the mechanism of tracking shear waves with CCD speckle-contrast analysis.A stochastic explanation of CCD speckle analysis was provided [10,11]. The CCD speckle contrast is defined by C σ∕Ī, where σ andĪ are the standard deviation and the mean of CCD pixel intensities. From first-and second-order statistical analys...

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confidence: 99%

Tracking shear waves in turbid medium by light: theory, simulation, and experiment

Song

et al. 2014

Opt. Lett.

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“…Li et al [75] investigated the influence of amplitude modulated US on the speckle contrast in a parallel detection setup. In this case the US amplitude was modulated with a 250 Hz to 16 KHz cosine envelope.…”

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confidence: 99%