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Biomedical subjects

J Meunier

Publications and source records attributed to J Meunier.

At least 37 records · Page 2Linked to original sources
PubMed2000

Coupling between flow and structure for a lamellar surfactant phase

The flow-structure relation of lamellar phases is studied using rheometry and cross-polarized microscopy under flow. The equilibrium phases show different defects. Low salinities lead to very viscous, "onion" phases, whereas at high salinity, a low viscosity plane lamellar phase is found. Under shear, the latter shows a sudden transition to a viscoelastic gel, with a texture and viscosity very similar to that of the onions. Gelation occurs after a certain delay time, increasing rapidly with salinity, by the nucleation of onions. This allows one to relate the delay time to the defect energy.

Journal Article↗
PubMed2000

The nociceptin (ORL1) receptor: molecular cloning and functional architecture.

Nociceptin and the ORL1 receptor share high sequence similarity with opioid peptides, particularly dynorphin A, and their receptors. However, nociceptin and dynorphin A may use distinct molecular pathways to bind and activate their cognate receptors. Activation of the kappa-opioid receptor by dynorphin A is thought to require interactions of its N-terminal hydrophobic domain (Y(1)GGF) with the receptor opioid binding pocket, located within the transmembrane helix bundle, while activation of the ORL1 receptor appears to require interactions of the positively charged core (R(8)KSARK) of nociceptin with the negatively charged second extracellular receptor loop.

Amino Acid Sequence↗
PubMed2000

Three-dimensional blind deconvolution of SPECT images.

Thanks to its ability to yield functionally rather than anatomically-based information, the three-dimensional (3-D) SPECT imagery technique has become a great help in the diagnostic of cerebrovascular diseases. Nevertheless, due to the imaging process, the 3-D single photon emission computed tomography (SPECT) images are very blurred and, consequently, their interpretation by the clinician is often difficult and subjective. In order to improve the resolution of these 3-D images and then to facilitate their interpretation, we propose herein to extend a recent image blind deconvolution technique (called the nonnegativity support constraint-recursive inverse filtering deconvolution method) in order to improve both the spatial and the interslice resolution of SPECT volumes. This technique requires a preliminary step in order to find the support of the object to be restored. In this paper, we propose to solve this problem with an unsupervised 3-D Markovian segmentation technique. This method has been successfully tested on numerous real and simulated brain SPECT volumes, yielding very promising restoration results.

Algorithms↗
PubMed2000

[Chemical weapons: antidotes. View about the real means, perspectives].

Chemical methods remain a credible threat in 1999. The doctrine for their use not only includes the battlefield but also domestic terrorism as was disclosed during the Tokyo metro attempt in 1995. International Treaties have not yet proven their efficacy. The arsenal of chemical weapons has changed little since the second World War but is now dispersed into many high-risk zones throughout the world. There has also been little change in antidotes: therapeutic prevention with pyridostigmine against organo-phosphorus compounds, protective treatment for seizure-induced brain lesions using anticonvulsants in association with oxime for acetylcholinesterase reactivation, and atropine are combined in a three-compartment syringe. Preventive measures against vesicants and other suffocating or toxic intracellular substances (CN, AsH(3), fluorocarbons.) can only be achieved with protective skin covering or protective breathing devices. There is no specific treatment and we often have to use symptomatic medications. Future perspectives include: phosphotriesterases as organo-phosphorus scavengers, huperzine as pretreatment and gacyclidine (GCK 11) which would effectively complete emergency multiple drug therapy against nerve agents. A new two-compartment syringe is now prepared with atropine, avisafone and HI6 or pralidoxine. A gel made of cyclodextrines for external and eventually internal use is under study.

Antidotes↗
PubMed1999

Automatic detection of hippocampal atrophy on magnetic resonance images.

An automatic method for identifying hippocampal atrophy on magnetic resonance (MR) images obtained from patients with clinical evidence of temporal lobe epilepsy (TLE) is described. The method is based on the analysis of image intensity differences between patients and controls within a volume of interest (VOI) centred on the hippocampus. The core of the method is a fully automatic signal intensity-based inter-subject image registration technique. In particular, a global affine registration to a reference image is performed, followed by a local affine registration within the VOI. A mask produced by manual segmentation of the mean hippocampus for 30 control subjects enabled investigations to be restricted to a specified region of the VOI approximately corresponding to the hippocampus. Normal variations of hippocampal signal intensity were computed from images obtained for the 30 control subjects. The manual method of hippocampal volumetry, currently an important component of the pre-surgical evaluation of patients with clinical evidence of medically intractable TLE, is used to determine the lower 1st percentile limits of normal hippocampal volume. Hippocampi with volumes below this limit are defined as atrophic. We investigated whether the automatic method can correctly distinguish between 15 patients with significant hippocampal atrophy according to absolute volumes and a further 14 controls. ROC curves enabled evaluation of sensitivity and specificity in respect of an intensity threshold. 100% specificity is required when determining suitability of patients for neurosurgery, resulting in levels of 50% and 70% sensitivity in detecting atrophy in the right and left hippocampus, respectively. We propose that the method can be developed as an automatic screening procedure.

Adolescent↗
PubMed1999

[Generic drugs and right of substitution. Relating to Article 29 of the 1999 *social Security Financing Act].

The 1999 Social Security Financing Act grants the right of substitution to pharmacists. If the prescriptor does not object, the pharmacist can replace a medicine by its generic. After reiterating that generic medicines are essentially similar but not strictly identical to the original or to each other, we analyze the discussions which took place at the National Assembly and Senate which should have resulted in some further modifications to the recently adopted legislative text.

Drug Prescriptions↗
PubMed1998

Delayed fracture of an inhomogeneous soft solid

The spontaneous fracture of polymer gels was studied. Contrary to crystalline solids, where fracture usually happens instantaneously at a well-defined breaking strength, the fracture of a polymer gel can occur with a delay. When a constant force was applied, the cracks nucleated and started to propagate after a delay that can be as long as 15 minutes, depending on the force. This phenomenon can be understood by calculating the activation energy for crack nucleation in arbitrary dimension and accounting for the inhomogeneity of the gel network in terms of its fractal dimension.

Journal Article↗
PubMed1998

Tissue motion assessment from 3D echographic speckle tracking.

The potential of ultrasonic image speckle tracking to characterize tissue dynamics has been illustrated and validated elsewhere. In this paper we wish to extend this speckle tracking methodology to 3D. To investigate the feasibility of such an approach we first model the image formation process and simulate the 3D speckle motion inherent to tissue linear transformations (translation, rotation and deformation). It is shown that tissue axial rotation and translation are perfectly correlated with the tissue speckle motion while tissue deformation and non-axial rotations corrupt the speckle pattern with a motion-induced noise and are therefore more difficult to track when large motions are concerned. Furthermore, in the framework of our model, our results indicate that short ultrasound pulses with low frequencies and small beamwidths are more desirable for a speckle tracking methodology. The feasibility of speckle tracking is illustrated with an optical flow algorithm. A theoretical study of the correlation between various linear transformations of the tissue and the corresponding ultrasonic speckle motions is also performed.

Algorithms↗
PubMed1995

Echographic image mean gray level changes with tissue dynamics: a system-based model study.

In echography, several groups have reported a systematic decrease in the total backscattering intensity or image mean gray level during myocardial contraction with a minimum at end-systole and maximum at end-diastole. In order to investigate this phenomenon, we use a three-dimensional inhomogeneous continuum model to mimic the tissue as a collection of cells that scatter the acoustic wave due to their individual impedance. The mathematical analysis clearly shows the relationship between the mean gray level changes and the size, orientation, and deformation of the cells that compose the tissue, as well as the frequency of the transducer. Using a myocardial model example, the mean gray level changes reported in the literature during contraction are described in terms of changes in orientation and deformation of cardiac fibers. The model is simple and should set the ground for further study and analysis of speckle pattern changes during tissue motion.

Echocardiography↗