Badal-Soler, A.; Kyprianou, I.; Banh, D.; Badano, A.; Sempau, J. IEEE transactions on medical imaging Vol. 28, num. 12, p. 1894-1901 DOI: 10.1109/TMI.2009.2021615 Data de publicació: 2009-12 Article en revista
We have developed a general-purpose Monte Carlo simulation code, called penMesh, that combines the accuracy of the radiation transport physics subroutines from PENELOPE and the flexibility of a geometry based on triangle meshes. While the geometric models implemented in most general-purpose codes-such as PENELOPE's quadric geometry-impose some limitations in the shape of the objects that can be simulated, triangle meshes can be used to describe any free-form (arbitrary) object. Triangle meshes are extensively used in computer-aided design and computer graphics. We took advantage of the sophisticated tools already developed in these fields, such as an octree structure and an efficient ray-triangle intersection algorithm, to significantly accelerate the triangle mesh ray-tracing. A detailed description of the new simulation code and its ray-tracing algorithm is provided in this paper. Furthermore, we show how it can be readily used in medical imaging applications thanks to the detailed anatomical phantoms already available. In particular, we present a whole body radiography simulation using a triangulated version of the anthropomorphic NCAT phantom. An example simulation of scatter fraction measurements using a standardized abdomen and lumbar spine phantom, and a benchmark of the triangle mesh and quadric geometries in the ray-tracing of a mathematical breast model, are also presented to show some of the capabilities of penMesh.
We quantify the variation in resolution due to
anisotropy caused by oblique X-ray incidence in indirect flat-panel
detectors for computed tomography breast imaging systems. We
consider a geometry and detector type utilized in breast computed
tomography (CT) systems currently being developed. Our
methods rely on MANTIS, a combined X-ray, electron, and optical
Monte Carlo transport open source code. The physics models
are the most accurate available in general-purpose Monte Carlo
packages in the diagnostic energy range. We consider maximum-
obliquity angles of 10 and 13 at the centers of the 30 and
40 cm detector edges, respectively, and 16 at the corner of the
detector. Our results indicate that blur is asymmetric and that the
resolution properties vary significantly with the angle (or location)
of incidence. Our results suggest that the asymmetry can be as
high as a factor of 2.6 between orthogonal directions. Anisotropy
maps predicted by MANTIS provide an understanding of the effect
that such variations have on the imaging system and allow more
accurate modeling and optimization of breast CT systems. These
maps of anisotropy across the detector could lead to improved
reconstruction and help motivate physics-based strategies for
computer detection of breast lesions.
Schelkens, P.; Munteanu, A.; Barbarien, J.; Galca, M.; Giro-Nieto, X.; Giro, X.; Cornelis, J. IEEE transactions on medical imaging Vol. 22, num. 3, p. 441-458 Data de publicació: 2003-03 Article en revista
A framework to analyze the propagation of measurement noise through backprojection reconstruction algorithms in electrical impedance tomography (EIT) is presented. Two
measurement noise sources were considered: noise in the current drivers and in the voltage detectors. The influence of the acquisition system architecture (serial/semi-parallel) is also discussed. Three variants of backprojection reconstruction are studied:
basic (unweighted), weighted and exponential backprojection.
The results of error propagation theory have been compared with those obtained from simulated and experimental data. This
comparison shows that the approach provides a good estimate of the reconstruction error variance. It is argued that the reconstruction error in EIT images obtained via backprojection can be approximately modeled as a spatially nonstationary Gaussian
distribution. This methodology allows us to develop a spatial characterization of the reconstruction error in EIT images.
For newly developed iterative Newton-Kantorovitch reconstruction techniques, the quality of the final image depends on both experimental and model noise. Experimental noise is inherent to any experimental acquisition scheme, while model noise refers to the accuracy of the numerical model, used in the reconstruction process, to reproduce the experimental setup. This paper provides a systematic assessment of the major sources of experimental and model noise on the quality of the final image. This assessment is conducted from experimental data obtained with a microwave circular scanner operating at 2.33 GHz. Targets to be imaged include realistic biological structures, such as a human forearm, as well as calibrated samples for the sake of accuracy evaluation. The results provide a quantitative estimation of the effect of experimental factors, such as temperature of the immersion medium, frequency, signal-to-noise ratio, and various numerical parameters.
Rius, J.; Pichot, C.; Jofre, L.; Bolomey, J.Ch.; Joachimowicz, N.; Broquetas, A.; Ferrando, M. IEEE transactions on medical imaging Vol. 11, num. 4, p. 457-469 DOI: 10.1109/42.192681 Data de publicació: 1992-12 Article en revista
A comparative study at 2.45 GHz concerning both measurement and reconstruction parameters for planar and cylindrical configurations is presented. For the sake of comparison, a numerical model consisting of two nonconcentric cylinders is considered and reconstructed using both geometries from simulated experimental data. The scattered fields and reconstructed images permit extraction of very useful information about dynamic range, sensitivity, resolution, and quantitative image accuracy for the choice of the configuration in a particular application. Both geometries can measure forward and backward scattered fields. The backscattering measurement improves the image resolution and reconstruction in lossy mediums, but, on the other hand, has several dynamic range difficulties. This tradeoff between forward only and forward-backward field measurement is analyzed. As differential temperature imaging is a weakly scattering problem, Born approximation algorithms can be used. The simplicity of Born reconstruction algorithms and the use of FFT make them very attractive for real-time biomedical imaging systems