224 research outputs found
Progress in real-time photoacoustic imaging using optical ultrasound detection
Optical phase contrast full field detection in combination with a CCD-camera can be used to record acoustic fields. This allows to obtain two-dimensional photoacoustic projection images in real-time. The present work shows an extension of the technique towards full three-dimensional photoacoustic tomography. The reconstruction of the initial three dimensional pressure distribution is a two step process. First of all, projection images of the initial pressure distribution are acquired. This is done by back propagating the observed wave pattern in frequency space. In the second step the inverse Radon transform is applied to the obtained projection dataset to reconstruct the initial three dimensional pressure distribution. An experiment is performed using a phantom sample which mimics the properties of biological samples to show the overall applicability of this technique for real-time photoacoustic imaging
Photoacoustic section imaging with integrating detectors
Photoacoustic section imaging is a method for visualizing structures with optical contrast in selected layers of an extended object. In order to avoid resolution limitations that are due to commonly used ultrasound detectors of finite size, we propose the use of extended, integrating cylindrical elements for focusing the acoustic detection into the selected section. Two imaging methods based on piezoelectric and optical detection are presented. Resolution limits and results on zebra fish are demonstrated
Reconstruction of a function from its spherical (circular) means with the centers lying on the surface of certain polygons and polyhedra
We present explicit filtration/backprojection-type formulae for the inversion
of the spherical (circular) mean transform with the centers lying on the
boundary of some polyhedra (or polygons, in 2D). The formulae are derived using
the double layer potentials for the wave equation, for the domains with certain
symmetries. The formulae are valid for a rectangle and certain triangles in 2D,
and for a cuboid, certain right prisms and a certain pyramid in 3D. All the
present inversion formulae yield exact reconstruction within the domain
surrounded by the acquisition surface even in the presence of exterior sources.Comment: 9 figure
Thermoacoustic tomography with detectors on an open curve: an efficient reconstruction algorithm
Practical applications of thermoacoustic tomography require numerical
inversion of the spherical mean Radon transform with the centers of integration
spheres occupying an open surface. Solution of this problem is needed (both in
2-D and 3-D) because frequently the region of interest cannot be completely
surrounded by the detectors, as it happens, for example, in breast imaging. We
present an efficient numerical algorithm for solving this problem in 2-D
(similar methods are applicable in the 3-D case). Our method is based on the
numerical approximation of plane waves by certain single layer potentials
related to the acquisition geometry. After the densities of these potentials
have been precomputed, each subsequent image reconstruction has the complexity
of the regular filtration backprojection algorithm for the classical Radon
transform. The peformance of the method is demonstrated in several numerical
examples: one can see that the algorithm produces very accurate reconstructions
if the data are accurate and sufficiently well sampled, on the other hand, it
is sufficiently stable with respect to noise in the data
On regularization methods of EM-Kaczmarz type
We consider regularization methods of Kaczmarz type in connection with the
expectation-maximization (EM) algorithm for solving ill-posed equations. For
noisy data, our methods are stabilized extensions of the well established
ordered-subsets expectation-maximization iteration (OS-EM). We show
monotonicity properties of the methods and present a numerical experiment which
indicates that the extended OS-EM methods we propose are much faster than the
standard EM algorithm.Comment: 18 pages, 6 figures; On regularization methods of EM-Kaczmarz typ
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