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

Inversion of circular means and the wave equation on convex planar domains

We study the problem of recovering the initial data of the two dimensional wave equation from values of its solution on the boundary \partial \Om of a smooth convex bounded domain \Om \subset \R^2. As a main result we establish back-projection type inversion formulas that recover any initial data with support in \Om modulo an explicitly computed smoothing integral operator \K_\Om. For circular and elliptical domains the operator \K_\Om is shown to vanish identically and hence we establish exact inversion formulas of the back-projection type in these cases. Similar results are obtained for recovering a function from its mean values over circles with centers on \partial \Om. Both reconstruction problems are, amongst others, essential for the hybrid imaging modalities photoacoustic and thermoacoustic tomography.Comment: [14 pages, 2 figures

Understanding Lipase Action and Selectivity

In this article, a survey of recent lipase research, with special emphasis on molecular structure-function relationships, is presented. Determination of crystallographic structures of lipases from microbial and mammalian origin has shed light on the molecular mechanism of lipase catalyzed acyl ester hydrolysis. A catalytic triad similar to serine proteases is responsible for the cleavage of substrate ester bonds, involving the formation of an acyl-enzyme intermediate. Comparative structural studies revealed a common three dimensional fold and a superimposable topology of the catalytic machinery in lipases, esterases, and other hydrolytic enzymes. Availability of three dimensional structures is the basis for .understanding the mechanism of lipase catalysis and for elucidation of the molecular interactions that result in variant selectivities towards triacylglycerols and their analogs

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

Ueber den Nachweis von Vergiftungen durch Belladonna

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Mesoscopic modelling of enamel interaction with mid-infrared sub-ablative laser pulses

Using a finite element approach the authors model the influence of enamel's microstructure and water distribution on the temperature and stress at the centre of the laser spot, for a CO2 laser working at 10.6 μm, with 0.35 μs pulse duration and sub-ablative intensity. The authors found that the distribution of water in enamel significantly influences the stress generated at the end of one laser pulse: much lower (two orders of magnitude) stress values occur in models with homogeneously distributed water than in models with 0.27 vol.% water located in pores or 4 vol.% in layers. The amount of water in enamel has a strong influence on the stress distribution, but not on the maximum stress values reached. However, different water contents do not influence the temperature distribution in enamel. These results suggest that adequate modelling of the ablation mechanisms in enamel, as in other highly inhomogeneous materials, must include their structure at the mesoscopic scale