Spatial resolution enhancement of ultrasound images using neural networks

Spatial resolution in modern ultrasound imaging systems is limited by the high cost of large aperture transducer arrays, which require a large number of transducer elements and electronic channels. A new technique to enhance the spatial resolution of pulse-echo imaging systems is presented. The method attempts to build an image that could be obtained with a transducer array aperture larger than that physically available. We consider two images of the same object obtained with two different apertures, the full aperture and a subaperture, of the same transducer. A suitable artificial neural network (ANN) is trained to reproduce the relationship between the image obtained with the transducer full aperture and the image obtained with a subaperture. The inputs of the neural network are portions of the image obtained with the subaperture (low resolution image), and the target outputs are the corresponding portions of the image produced by the full aperture (high resolution image). After the network is trained, it can produce images with almost the same resolution of the full aperture transducer, but using a reduced number of real transducer elements. All computations are carried out on envelope-detected decimated images; for this reason, the computational cost is low and the method is suitable for real-time applications. The proposed method was applied to experimental data obtained with the ultrasound synthetic aperture focusing technique (SAFT), giving quite promising results. Realtime implementation on a modern, full-digital echographic system is currently being developed.     

Apodized fiber Bragg gratings manufactured with the phase plate process

We present a manufacturing method based on the dynamic use of phase plates to photowrite Bragg gratings. This process allows for control of the local value of the index modulation envelope in the grating. The application to apodized fiber Bragg gratings is discussed.     

A Surface Reconstruction Method Using Global Graph Cut Optimization

Surface reconstruction from multiple calibrated images has been mainly approached using local methods, either as a continuous optimization problem driven by level sets, or by discrete volumetric methods such as space carving. We propose a direct surface reconstruction approach which starts from a continuous geometric functional that is minimized up to a discretization by a global graph-cut algorithm operating on a 3D embedded graph. The method is related to the stereo disparity computation based on graph-cut formulation, but fundamentally different in two aspects. First, existing stereo disparity methods are only interested in obtaining layers of constant disparity, while we focus on high resolution surface geometry. Second, most of the existing graph-cut algorithms only reach approximate solutions, while we guarantee a global minimum. The whole procedure is consistently incorporated into a voxel representation that handles both occlusions and discontinuities. We demonstrate our algorithm on real sequences, yielding remarkably detailed surface geometry up to 1/10th of a pixel. Author has worked on this project during his Ph. D. at ARTIS     

Expressiveness of Probabilistic π-calculus

In this work we propose a probabilistic extension of the π-calculus. The main novelty is a probabilistic mixed choice operator, that is, a choice construct with a probability distribution on the branches, and where input and output actions can both occur as guards. We develop the operational semantics of this calculus, and then we investigate its expressiveness. In particular, we compare it with the sublanguage with the two separate choices, where input and output guards are not allowed together in the same choice construct. Our main result is that the separate choices can encode the mixed one. Further, we show that input-guarded choice can encode output-guarded choice and viceversa. In contrast, we conjecture that neither of them can encode the pair of the two separate choices.     

Molecular Orientational Ordering in Solid C60

Single-crystal X-ray diffraction studies of the orientational ordering in solid C₆₀ are reviewed. The temperature dependence of selected Bragg reflections was carefully examined, allowing to obtain original information on the first-order orientational ordering transition at T_o = 259K, the unusual behavior of both fundamental and superstructure reflections below T_o and the freezing in of the C₆₀ reorientations at T_g ≈ 85K. The diffuse intensity due to orientational disorder of the C₆₀ molecules at room temperature is found to be strongly modulated, both radially and azimuthally. showing that the molecular orientations are indeed correlated. The corresponding intensity distribution has been calculated within a mean-field theory for different microscopic models of inter molecular interactions. It should allow a better understanding of these interactions.     

Characterization of Campylobacter isolates recovered from clinically healthy pigs and from sporadic cases of campylobacteriosis in humans

Campylobacter spp. were recovered from 660 (77.6%) of 850 swine cecal contents at the abattoir and from 24 (8.6%) of 278 specimens from sporadic cases of human diarrhea during the same period in the same geographical area. Campylobacter coli represented 95.7% of Campylobacter isolates recovered from pigs and 8.3% of those isolated from humans. Genetic profiles were determined by pulsed-field gel electrophoresis (PFGE) using KpnI enzyme to characterize the isolates in combination with phenotypic assays to detect production of cytotoxins, enterotoxins, and hemolysins. Among a subset of isolates (n = 10), up to five colonies from the same animal were characterized by PFGE. In 5 (50%) of 10 of the isolates, more than one genetic profile was observed per pig. Among the 100 isolates from pigs selected for further analysis, 81 different genetic profiles were observed, whereas 20 different genetic profiles were found among the 24 isolates of human origin. Cytotoxicity on Chinese hamster ovary cells was observed in 11 (11%) of 98 isolates from pigs and in 5 (21%) of 24 Campylobacter isolates from humans. No enterotoxin production was detected in Campylobacter isolates in this study, but 17 (71%) of 24 human and 61 (63%) of 97 pig isolates showed hemolytic activity. The study of genotypic and phenotypic profiles of swine and human isolates revealed no epidemiological relationship between isolates. The low genomic relatedness observed between groups of isolates and the weak toxicity level of swine isolates suggest that the hazard of contamination of humans by Campylobacter associated with swine production is low.     

A P-matrix based model for SAW grating waveguides taking into account modes conversion at the reflection

Several models exist for analyzing the wave-guiding effect of a reflective grating. On the one hand, there are models based on scalar waveguide theory. These models consider that a device can be described as being made of several regions having different velocities. On the other hand, an extension of the coupling of modes (COM) model taking into account the transverse dimension has been developed. This paraxial COM model predicts that guidance is possible even when there is no velocity difference between the interior and the exterior of the grating region. Guidance, under such circumstances, is due only to differences in reflectivity between regions. Following from this insight, a new approach has been developed: guided modes and the continuum of radiating modes are first determined. At each period, reflections then are considered as occurring only in the reflective regions, so that the modes are truncated. Thus, at each reflection (and transmission), each mode is converted into a distribution of all modes. Dispersion curves very similar to those shown by other researchers are obtained by this method. They show, in particular, the existence of guided modes even when the wave velocity in all regions is identical. This model can be used to more easily analyze practical devices and exhibits a good agreement with experimental results.     

CMOS inverters based positive type second generation current conveyor

A new versatile class AB low-voltage second generation current conveyor based on CMOS inverters operating in transconductance mode is presented in this letter. Against traditional design based on CCII+, the circuit is able to operate at low supply voltages and offers numerous advantages like class AB operation, large voltage and current swing, synthesis from digital inverters. Simulation results from a typical 0.35 μm CMOS process had demonstrated the circuit capability to operate at high frequency over wide voltage and wide current swings. The proposed circuit operation has been acted from measurements with the HEF4069UBP from Philips semiconductors [1].