Jonathan Vacher

Learn More
In order to improve the quality of positron tomographic imaging, a time-of-flight technique combined with a classical reconstruction method has been investigated. The decay time of NaI(Tl) and bismuth germanate (BGO) scintillators is too long for this application, and efficiency of the plastic scintillators is too low. Cesium fluoride appears to be a very(More)
This contribution deals with the Heeger-Bergen pyramid-based texture analysis/synthesis algorithm. It brings a detailed explanation of the original algorithm tested on many characteristic examples. Our analysis reproduces the original results, but also brings a minor improvement concerning non-periodic textures. Inspired by visual perception theories,(More)
Applying the recommended guidelines of the Instrumentation Group of the EEC Concerted Action, the sensitivity of an ECAT 933/4-16 scanner was determined. Several filters were used to reconstruct the images. On the images regions of interest (ROIs) were defined, and the ROI-counts were compared to the specific activity in the phantom. Whereas the uncorrected(More)
Perception is often described as a predictive process based on an optimal inference with respect to a generative model. We study here the principled construction of a generative model specifically crafted to probe motion perception. In that context, we first provide an axiomatic, biologically-driven derivation of the model. This model synthesizes random(More)
The kinetic reactions in N2-xCH4(C2H2) gas discharges with x less than 1% have been studied by emission spectroscopy in the afterglow of D.C. discharges and by mass spectroscopy from radiolysis ionization using alpha particles. The pressure range is from several Torr to 100 Torr. At the end of N2 D.C. discharges at room temperature, for a residence time(More)
Thermochemical data for several ion-molecule clustering of hydrocarbon ions with N2 or CH4 were obtained from clustering equilibria studies in gas mixtures irradiated by alpha-particles. High-pressure mass spectrometry was used to determine the enthalpy and entropy changes of clustering (delta H0 and delta S0, respectively) for the reactions X+(N2)n-1 +(More)
The interest of PET is now well established in medical research. Recently PET has proved to be also useful in the clinical domain e.g. for the diagnosis of epilepsy, myocardial disease etc... Its use has been so far limited by the cost of the radionuclide production and the cost of the PET itself. However, inexpensive, compact cyclotrons and centralized(More)