Biomedical subjects

Paola Coan

Publications and source records attributed to Paola Coan.

3 recordsLinked to original sources

PubMed2006

Evaluation of imaging performance of a taper optics CCD; FReLoN' camera designed for medical imaging.

The purpose of this work was to assess the imaging performance of an indirect conversion detector (taper optics CCD; FReLoN' camera) in terms of the modulation transfer function (MTF), normalized noise power spectrum (NNPS) and detective quantum efficiency (DQE). Measurements were made with a synchrotron radiation laminar beam at various monochromatic energies in the 20-51.5 keV range for a gadolinium-based fluorescent screen varying in thickness; data acquisition and analysis were made by adapting to this beam geometry protocols used for conventional cone beams. The pre-sampled MTFs of the systems were measured using an edge method. The NNPS of the systems were determined for a range of exposure levels by two-dimensional Fourier analysis of uniformly exposed radiographs. The DQEs were assessed from the measured MTF, NNPS, exposure and incoming number of photons. The MTF, for a given screen, was found to be almost energy independent and, for a given energy, higher for the thinnest screen. At 33 keV and for the 40 (100) microm screen, at 10% the MTF is 9.2 (8.6) line-pairs mm(-1). The NNPS was found to be different in the two analyzed directions in relation to frequency. Highest DQE values were found for the combination 100 microm and 25 keV (0.5); it was still equal to 0.4 at 51.5 keV (above the gadolinium K-edge). The DQE is limited by the phosphor screen conversion yield and by the CCD efficiency. At the end of the manuscript the results of the FReLoN characterization and those from a selected number of detectors presented in the literature are compared.

Diagnostic Imaging↗

PubMed2005

Phase-contrast X-ray imaging combining free space propagation and Bragg diffraction.

The combination of X-ray 'propagation-based' and 'analyzer-based' phase-contrast imaging with a perfect crystal-analyzer is investigated. The image pattern produced using this 'hybrid' imaging technique presents peculiar features that can be interpreted as a mixture of the two independent phase-contrast signals. A quantitative analysis has been performed in terms of signal-to-noise ratio for the three techniques considered in this paper. Results show that in the 'hybrid imaging' technique this parameter has a weaker dependence on the angular alignment of the crystal analyser with respect to the 'analyser-based' imaging. This pioneering experiment indicates that this hybrid imaging technique might permit simultaneous advantage of the specific features of the two imaging methods to be taken.

Absorption↗

PubMed2005

Quantitative comparison between two phase contrast techniques: diffraction enhanced imaging and phase propagation imaging.

Two x-ray phase contrast imaging techniques are compared in a quantitative way for future mammographic applications: diffraction enhanced imaging (DEI) and phase propagation imaging (PPI). DEI involves, downstream of the sample, an analyser crystal acting as an angular filter for x-rays refracted by the sample. PPI simply uses the propagation (Fresnel diffraction) of the monochromatic and partially coherent x-ray beam over large distances. The information given by the two techniques is assessed by theoretical simulations and compared at the level of the experimental results for different kinds of samples (phantoms and real tissues). The imaging parameters such as the energy, the angular position of the analyser crystal in the DEI case or the sample to detector distance in the PPI case were varied in order to optimize the image quality in terms of contrast, visibility and figure of merit.

Breast Neoplasms↗