Trond Varslot

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We derive a new image reconstruction method for distributed apertures operating in complex environments. The aperture elements can be distributed spatially in an arbitrary fashion, can be several hundred wavelengths apart, and can involve transmission from multiple elements simultaneously. Moreover, the object to be imaged can be either in the near-field or(More)
The reconstruction of images in photoacoustic tomography is reliant on specifying the speed of sound within the propagation medium. However, for in vivo imaging, this value is not normally accurately known. Here, an autofocus approach for automatically selecting the sound speed is proposed. This is based on maximizing the sharpness of the reconstructed(More)
We derive an optimal transmit waveform for filtered backprojection-based synthetic-aperture imaging. The waveform is optimal in terms of min-imising the mean square error (MSE) in the resulting image. Our optimization is performed in two steps: First, we consider the minimum-mean-square-error (MMSE) for an arbitrary but fixed waveform, and derive the(More)
A multiple-frequency inverse scattering method that uses eigenfunctions of a scattering operator is extended to image large-scale and high-contrast objects. The extension uses an estimate of the scattering object to form the difference between the scattering by the object and the scattering by the estimate of the object. The scattering potential defined by(More)
PURPOSE In this paper we show that optimization-based autofocus may be used to overcome the instabilities that have, until now, made high-resolution theoretically-exact tomographic reconstruction impractical. To our knowledge, this represents the first successful use of theoretically-exact reconstruction in helical micro computed tomography (micro-CT)(More)
  • T Varslot, B Yazıcı, C.-E Yarman, M Cheney, L Scharf
  • 2007
The idea of preconditioning transmit waveforms for optimal clutter rejection in radar imaging is presented. Waveform preconditioning involves determining a map on the space of transmit waveforms, and then applying this map to the waveforms before transmission. The work applies to systems with an arbitrary number of transmit-and receive-antenna elements, and(More)
A fast implementation of bilateral filtering is presented, which is based on an optimal expansion of the filter kernel into a sum of factorized terms. These terms are computed by minimizing the expansion error in the mean-square-error sense. This leads to a simple and elegant solution in terms of eigenvectors of a square matrix. In this way, the bilateral(More)
In this paper we analyze the problem of optimal waveform design for synthetic-aperture radar (SAR) imaging through a dispersive medium. We use a scalar model for wave propagation , together with the single-scattering approximation, and we assume that measurements are polluted with thermal noise whose statistics are known. For image formation, we use a(More)
The reference scan method is a simple yet powerful method for measuring spatial drift of the x-ray spot during a low-cone-angle μ-CT experiment. As long as the drift is smooth, and occurring on a time scale that is long compared to the acquisition time of each projection, this method provides a way to compensate for the drift by applying 2D in-plane(More)
We present a new image reconstruction method for distributed apertures operating in complex environments with additive non-stationary noise. Our method is capable of exploiting information that we might have about: multipath scattering in the environment; statistics of the objects to be imaged; statistics of the additive non-stationary noise. The aperture(More)
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