Maximum-likelihood absorption tomography

Maximum-likelihood methods are applied to the problem of absorption tomography. The reconstruction is done with the help of an iterative algorithm. We show how the statistics of the illuminating beam can be incorporated into the reconstruction. The proposed reconstruction method can be considered as a useful alternative in the extreme cases where the standard ill-posed direct-inversion methods fail.Comment: 7 pages, 5 figure

Thermodynamics of Meissner effect and flux pinning behavior in the bulk of single crystal La2 xSrxCuO4 x 0.09

We have studied the evolution of magnetic flux pinning behavior in the Meissner phase and the mixed state for the high- T c single-crystal La 2 − x Sr x CuO 4 ( x = 0.09 ) superconductor using the polarized neutron imaging method with varying magnetic field and temperature. In the Meissner state expulsion of magnetic field (switched on during the measurements) is visualized, and the signatures of a mixed state with increasing temperature are observed. However, for flux pinning behavior in the range 5 K ≤ T ≤ 15 K and H ext = 63.5 mT (switched off during the measurements), the evolution of the fringe pattern indicates magnetic flux pinning inside the bulk of the sample. At 25 K ≤ T ≤ 32 K , a continuous decrease in inhomogeneously distributed pinned magnetic flux is observed, with the sample reaching a normal conducting state at T c ( ≈ 32 K). The flux pinning behavior is also explored as a function of H ext at T = 5 K . As expected, with increasing H ext an increase in fringe density is observed, indicating an increase in magnetic flux pinning in the bulk of the sample. A comparison between calculated and experimentally visualized pinned magnetic fluxes shows good agreement. This implies quantification of pinned magnetic flux inside the sample, which is not possible with any other technique for bulk samples

Phase based x ray scattering A preliminary study to detect cancer cells in a very early stage

Purpose This theoretical work contains a detailed investigation of the potential and sensitivity of phase based x ray scattering for cancer detection in biopsies if cancer is in a very early stage of development. Methods Cancer cells in their early stage of development differ from healthy ones mainly due to their faster growing cell nuclei and the enlargement of their densities. This growth is accompanied by an altered nucleus plasma relation for the benefit of the cell nuclei, that changes the physical properties especially the index of refraction of the cell and the one of the cell nuclei. Interaction of radiation with matter is known to be highly sensitive to small changes of the index of refraction of matter; therefore a detection of such changes of volume and density of cell nuclei by means of high angular resolved phase based scattering of x rays might provide a technique to distinguish malignant cells from healthy ones if the cell cell nucleus system is considered as a coherent phase shifting object. Then one can observe from a thin biopsy which represents a monolayer of cells no multiple scattering that phase based x ray scattering curves from healthy cells differ from those of cancer cells in their early stage of development. Results Detailed calculations of x ray scattering patterns from healthy and cancer cell nuclei yield graphs and numbers with which one can distinguish healthy cells from cancer ones, taking into account that both kinds of cells occur in a tissue within a range of size and density. One important result is the role and the influence of the lateral coherence width of the radiation on the scattering curves and the sensitivity of phase based scattering for cancer detection. A major result is that a larger coherence width yields a larger sensitivity for cancer detection. Further import results are calculated limits for critical sizes and densities of cell nuclei in order to attribute the investigated tissue to be healthy or diseased. Conclusions With this proposed method it should be in principle possible to detect cancer cells in apparently healthy tissues in biopsies and or in samples of the far border region of abscised or excised tissues. Thus this method could support established methods in diagnostics of cancer suspicious samples. 2014 American Association of Physicists in Medicine. [http dx.doi.org 10.1118 1.4871616

Calculation of scattering patterns from phase shifting objects using the Radon Transform

In the case of neutron (and X-ray) scattering by objects that are about 105times larger than the wavelength, the objects can be considered as (inhomogeneous) phase-shifting media. In contrast with small-angle scattering, the scattering patterns from phase-shifting objects are calculated by the superposition of coherent partial waves that penetrate the object. In order to determine the scattering patterns from large complicated objects, it is proposed to use the two-dimensional Radon transform of the objects and Fraunhofer diffraction. This approach is much easier than using the small-angle scattering treatment, as is shown in this paper.</jats:p

Corrigendum Calculation of scattering patterns from phase shifting objects using the Radon transform

The affiliations for the authors of J. Appl. Cryst. (2011), 44, 1157–1163 are corrected.</jats:p

Radiography and tomography with polarized neutrons

Neutron imaging became important when, besides providing impressive radiographic and tomographic images of various objects, physical, quantification of chemical, morphological or other parameters could be derived from 2D or 3D images. The spatial resolution of approximately 50 mm and less yields real space images of the bulk of specimens with more than some cm3 in volume. Thus the physics or chemistry of structures in a sample can be compared with scattering functions obtained e.g. from neutron scattering. The advantages of using neutrons become more pronounced when the neutron spin comes into play. The interaction of neutrons with magnetism is unique due to their low attenuation by matter and because their spin is sensitive to magnetic fields. Magnetic fields, domains and quantum effects such as the Meissner effect and flux trapping can only be visualized and quantified in the bulk of matter by imaging with polarized neutrons. This additional experimental tool is gaining more and more importance. There is a large number of new fields that can be investigated by neutron imaging, not only in physics, but also in geology, archeology, cultural heritage, soil culture, applied material research, magnetism, etc. One of the top applications of polarized neutron imaging is the large field of superconductivity where the Meissner effect and flux pinning can be visualized and quantified. Here we will give a short summary of the results achieved by radiography and tomography with polarized neutron