Phase unwrapping : geometric distortions correction on MRI

Magnetic Resonance Imaging has entered clinical practice about fifteen years ago, and has become one of the most widely used imaging modality. MRI suffers from important geometric distortions, leading to pixel shifts and intensity variations in the acquired images. Correction of these distortions is clearly required in stereotactic surgery using frame-based registrations or neuro-navigation. These distortions can be corrected using the phase of signal or image. However, as in Inverse Synthetic Aperture Radar (ISAR), the phase of the signal is obtained modulo 2 π. The goal of Phase unwrapping is to retrieve the initial phase of the signal. After a brief summary of related works and applications mainly using ISAR data, this paper presents a new algorithm for phase unwrapping. This algorithm is fast, robust to noise and takes into account the discontinuities of the acquired object. It is based upon the notion of homogeneous region. This homogeneity is defined by phase jumps and no parameters have to be determined a priori. Experiments on noisy phantoms exhibit good robustness to noise. An application to the correction of MRI of the head is presented.Les images du corps humain acquises par résonance magnétique sont une des modalités les plus utilisées à des fins cliniques depuis une quinzaine d'années. Elles souffrent cependant de distorsions géométriques importantes sous forme de décalages de pixels et de variations d'intensité. Ces distorsions doivent être corrigées pour utiliser ces imagés dans des applications de neuro-navigation ou de neuro-chirurgie stéréotaxiques. Une des solutions pour la correction exploite les images de phase issues de l'imageur. Cependant, comme en Interférométrie Radar à Ouverture Synthétique (ISAR), cette phase est codée modulo 2 π. Le déroulement de phase a pour objectif de retrouver la phase réelle du signal. Après un rapide bilan des outils existants, principalement dans le domaine ISAR, nous proposons dans cet article un algorithme de déroulement de phase original, rapide, robuste au bruit et qui prend en compte les discontinuités réelles de l'objet imagé. Il est basé sur la notion de région homogène du point de vue des sauts de phase et ne nécessite pas la détermination de paramètres. Les tests sur des fantômes bruités démontrent la bonne robustesse au bruit. Cet algorithme est ensuite utilisé pour la correction d'images IRM et illustre le bon déroulement de la phase

The dependence of the anomalous J/psi suppression on the number of participant nucleons

The observation of an anomalous J/psi suppression in Pb-Pb collisions by the NA50 Collaboration can be considered as the most striking indication for the deconfinement of quarks and gluons at SPS energies. In this Letter, we determine the J/psi suppression pattern as a function of the forward hadronic energy E-ZDC measured in a Zero Degree Calorimeter (ZDC). The direct connection between EZDC and the geometry of the collision allows us to calculate, within a Glauber approach, the precise relation between the number of participant nucleons N-part and E-ZDC. Then, we check if the experimental data can be better explained by a sudden or a smooth onset of the anomalous J/psi suppression as a function of the number of participants. (C) 2001 Elsevier Science B.V. All rights reserved.info:eu-repo/semantics/publishedVersio

Centrality Behaviour of J/ψ\psi Production in Na50

The J/$\psi$ production in 158 A GeV Pb-Pb interactions is studied, in the dimuon decay channel, as a function of centrality, as measured with the electromagnetic or with the very forward calorimeters. After a first sharp variation at mid centrality, both patterns continue to fall down and exhibit a curvature change at high centrality values. This trend excludes any conventional hadronic model and is in agreement with a deconfined quark-gluon phase scenario. We report also preliminary results on the measured charged multiplicity, as given by a dedicated detector.Comment: 5 pages, 7 figures (in eps) talk given at XXXI International Symposium on Multiparticle Dynamics, Sep. 1-7, 2001, Datong China URL http://ismd31.ccnu.edu.cn

Evaluation of machine-learning methods for ligand-based virtual screening

Machine-learning methods can be used for virtual screening by analysing the structural characteristics of molecules of known (in)activity, and we here discuss the use of kernel discrimination and naive Bayesian classifier (NBC) methods for this purpose. We report a kernel method that allows the processing of molecules represented by binary, integer and real-valued descriptors, and show that it is little different in screening performance from a previously described kernel that had been developed specifically for the analysis of binary fingerprint representations of molecular structure. We then evaluate the performance of an NBC when the training-set contains only a very few active molecules. In such cases, a simpler approach based on group fusion would appear to provide superior screening performance, especially when structurally heterogeneous datasets are to be processed

Urgent need to clarify the definition of chronic critical limb ischemia - a position paper from the European Society for Vascular Medicine

Chronic critical lower limb ischemia (CLI) has been defined as ischemia that endangers the leg. An attempt was made to give a precise definition of CLI, based on clinical and hemodynamic data (Second European Consensus). CLI may be easily defined from a clinical point of view as rest pain of the distal foot or gangrene or ulceration. It is probably useful to add leg ulcers of other origin which do not heal because of severe ischemia, and to consider the impact of frailty on adverse outcome. From a hemodynamic viewpoint there is no consensus and most of the existing classifications are not based upon evidence. We should thus propose a definition and then validate it in a prospective cohort in order to define the patients at major risk of amputation, and also to define the categories of patients whose prognosis is improved by revascularisation. From today\u27s available data, it seems clear that the patients with a systolic toe pressure (STP) below 30 mmHg must be revascularised whenever possible. However other patients with clinically suspected CLI and STP above 30 mmHg must be evaluated and treated in specialised vascular units and revascularisation has to be discussed on a case by case basis, taking into account other data such as the WiFi classification for ulcers.In conclusion, many useful but at times contradictory definitions of CLI have been suggested. Only a few have taken into account evidence, and none have been validated prospectively. This paper aims to address this and to give notice that a CLI registry within Europe will be set up to prospectively validate, or not, the previous and suggested definitions of CLI

Wool sheep and purple snails - Long‐term continuity of animal exploitation in ancient Meninx (Jerba/Tunisia)

Archaeological research at the ancient city of Meninx in Jerba, Tunisia, carried out by the Institut National du Patrimoine Tunisie and Ludwig Maximilian University of Munich (LMU) produced more than 10,000 faunal specimens and shed light on subsistence activities spanning from the fourth century BCE until the seventh century CE. Despite its highly diverse fauna totalling at least 69 species of mammals, birds, reptiles, fish and molluscs, domestic livestock formed the mainstay of the economy at Meninx. Throughout site occupation and compared with contemporaneous sites in coastal Tunisia and Libya, sheep were of prime importance at Meninx. Diachronic demographic profiling illustrates an emphasis on the production of wool for making textiles. Together with the ubiquitous presence of crushed banded dye‐murex (Hexaplex trunculus) shells implying exploitation of purple dyes, we assume that both activities were integrated into a single chaîne opératoire for making purple‐dyed fabrics that were traded across the Mediterranean from Punic until Late Roman times. Zooarchaeological findings also suggest that during the Byzantine Period, this major economic activity came to a standstill, with people returning to more self‐sufficient subsistence strategies. An intersite comparison furthermore revealed that high proportions of ovicaprines are a typical feature of Punic–Roman sites in Jerba. But even at the height of Roman power in the region, autochthonous husbandry traditions continued to exist on the island, as illustrated by the fauna from Henchir Bourgou