74 research outputs found
On the noise-resolution duality, Heisenberg uncertainty and Shannon's information
Several variations of the Heisenberg uncertainty inequality are derived on
the basis of "noise-resolution duality" recently proposed by the authors. The
same approach leads to a related inequality that provides an upper limit for
the information capacity of imaging systems in terms of the number of imaging
quanta (particles) used in the experiment. These results can be useful in the
context of biomedical imaging constrained by the radiation dose delivered to
the sample, or in imaging (e.g. astronomical) problems under "low light"
conditions
Signal-to-noise and spatial resolution in in-line imaging. 1. Basic theory, numerical simulations and planar experimental images
Signal-to-noise ratio and spatial resolution are quantitatively analysed in
the context of in-line (propagation based) X-ray phase-contrast imaging. It is
known that free-space propagation of a coherent X-ray beam from the imaged
object to the detector plane, followed by phase retrieval in accordance with
Paganin's method, can increase the signal-to-noise in the resultant images
without deteriorating the spatial resolution. This results in violation of the
noise-resolution uncertainty principle and demonstrates "unreasonable"
effectiveness of the method. On the other hand, when the process of free-space
propagation is performed in software, using the detected intensity distribution
in the object plane, it cannot reproduce the same effectiveness, due to the
amplification, during free-space propagation, of photon shot noise in the
object-plane intensity. We show that the performance of Paganin's method is
determined by just two dimensionless parameters: the Fresnel number and the
ratio of the phase shift to the logarithm of intensity in the object plane. The
relevant theoretical analysis is performed first, followed by computer
simulations and then by a brief test using experimental images collected at a
synchrotron beamline. More extensive experimental tests will be presented in
the second part of this paper.Comment: 26 pages, 2 figures, 2 tables, 56 reference
Phase-and-amplitude computer tomography
A tomographic technique is proposed for reconstruction under specified conditions of the three-dimensional distribution of complex refractive index in a sample from a single projection image per view angle, where the images display both absorption contrast and propagation-induced phase contrast. The algorithm achieves high numerical stability as a consequence of the complementary nature of the absorption and phase contrast transfer functions. The method is pertinent to biomedical imaging and nondestructive testing of samples exhibiting weak absorption contrast
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