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