Biomedical subjects

David M Paganin

Publications and source records attributed to David M Paganin.

4 recordsLinked to original sources

PubMed2006

Effects of incident illumination on in-line phase-contrast imaging.

Effects of incident illumination on phase-contrast images obtained by means of free-space propagation are investigated under the "transport-of-intensity" approximation. Analytical expressions for image intensity distribution are derived in the cases of coherent quasi-plane and quasi-spherical incident waves, as well as for spatially incoherent and quasi-homogeneous sources and some other types of sources. Practical methods for measuring the relevant parameters of the incident radiation are discussed together with formulas allowing one to calculate the effect of these parameters on the image intensity distribution. The results are expected to be useful in quantitative in-line imaging, phase retrieval, and tomography with polychromatic and spatially partially coherent radiation. As an application we present a method for simultaneous "automatic" phase retrieval and spatial deconvolution in in-line imaging of homogeneous objects using extended polychromatic x-ray sources.

Algorithms↗

PubMed2005

Inferring the time-dependent complex Ginzburg-Landau equation from modulus data.

We present a formalism for inferring the equation of evolution of a complex wave field that is known to obey an otherwise unspecified -dimensional time-dependent complex Ginzburg-Landau equation, given field moduli over various closely spaced planes. The phase of the complex wave field is retrieved via a noninterferometric method, and all terms in the equation of evolution are determined using only the magnitude of the complex wave field. The formalism is tested using simulated data for a generalized nonlinear system with a single-component complex wave field. The method can be generalized to multicomponent complex fields.

Journal Article↗

PubMed2005

Analyser-based mammography using single-image reconstruction.

We implement an algorithm that is able to decode a single analyser-based x-ray phase-contrast image of a sample, converting it into an equivalent conventional absorption-contrast radiograph. The algorithm assumes the projection approximation for x-ray propagation in a single-material object embedded in a substrate of approximately uniform thickness. Unlike the phase-contrast images, which have both directional bias and a bias towards edges present in the sample, the reconstructed images are directly interpretable in terms of the projected absorption coefficient of the sample. The technique was applied to a Leeds TOR[MAM] phantom, which is designed to test mammogram quality by the inclusion of simulated microcalcifications, filaments and circular discs. This phantom was imaged at varying doses using three modalities: analyser-based synchrotron phase-contrast images converted to equivalent absorption radiographs using our algorithm, slot-scanned synchrotron imaging and imaging using a conventional mammography unit. Features in the resulting images were then assigned a quality score by volunteers. The single-image reconstruction method achieved higher scores at equivalent and lower doses than the conventional mammography images, but no improvement of visualization of the simulated microcalcifications, and some degradation in image quality at reduced doses for filament features.

Algorithms↗

PubMed2003

Wave-function reconstruction of complex fields obeying nonlinear parabolic equations.

We present a generalized Gerchberg-Saxton (GS) algorithm for reconstructing a (2+1)-dimensional complex scalar wave field which obeys a known nonlinear nondissipative parabolic differential equation, given knowledge of the wave-field modulus at three or more values of an evolution parameter such as time. This algorithm is used to recover the complex wave function of a (2+1)-dimensional Bose-Einstein condensate (BEC) from simulated modulus data. The Gross-Pitaveskii equation is used to model the dynamics of the BEC, with the modulus information being provided by a temporal sequence of simulated absorption images of the condensate. The efficacy of the generalized GS algorithm is examined for a wide range of simulation conditions, including strong nonlinearities, vortex states and Poisson noise. The general form of this algorithm, which allows one to reconstruct a time-dependent wave function, will be useful for studying the phase dynamics of topological defects in coherent quantum systems.

Journal Article↗