PubMed Health⌕ Search

Biomedical subjects

D Bar

Publications and source records attributed to D Bar.

At least 19 recordsLinked to original sources
PubMed2006

[Digital volume tomography using the NewTom system: advantages of this new technique in children].

In some cases, after preliminary clinical examination, medical imaging can provide indispensable complementary information for the care of young patients. Volume imaging using two- and three-dimensional reconstructions provides the most complete information possible. Problems involving the superposition of anatomical structures, which can occur with conventional X-rays, are a thing of the past, and this technique represents the future in this field. In high-density tissue such as bone or teeth, tomodensitometry is the preferred examination as it can give a three-dimensional approach to the study. However, because of the high radiation dose required, scanner is still a second intention examination. Development of digital volume tomography using NewTom system, designed for maxillofacial exploration, produces the same type of image for a very much reduced X-ray dose, and at low cost. Although the use of this new examining technique is developing rapidly in Europe and throughout the world since its recent introduction, France is lagging behind as to date there are only seven machines in the entire country. The main uses in children, illustrated by original clinical cases, relate to preoperative surgery planning, post-trauma diagnostic workups, orthodontic checkups, postoperative follow-up and TMJ examinations. The purpose of this article is to inform dental surgeons, paediatricians and doctors about this new medical imaging examination, which will most definitely have a place in the battery of diagnostic tools available to us. After weighing the advantages/risks involved, it should be possible to reduce the number of tomodensitometry exams in favour of this new examination technique in children according to the clinical examination data and diagnostic information required.

Child↗
PubMed2004

Phase transition in the bounded one-dimensional multitrap system.

We have previously discussed the diffusion limited problem of the bounded one-dimensional multitrap system where no external field is present, and pay special attention to the transmission of the diffusing particles through the imperfect traps. We discuss here the case in which an external field is included to each trap and find not only the transmission but also the energy associated with the diffusing particles in the presence and absence of such a field. From the energy we find the specific heat C(h) and show that for certain values of the parameters associated with the multitrap system it behaves in a manner which is suggestive of phase transition. Moreover, this phase transition is demonstrated not only through the conventional single peak at which the specific heat function is undifferentiable but also through the less frequent phenomenon of double peaks.

Journal Article↗
PubMed2003

Diffusion-limited reaction for the one-dimensional trap system.

We have previously discussed the one-dimensional multitrap system of finite range and found somewhat unexpected result that the larger is the number of imperfect traps the higher is the transmission through them. We discuss in this work the effect of a small number of such traps arrayed along either a constant or a variable finite spatial section. It is shown that under specific conditions, to be described in the following, the remarked high transmission may be obtained for this case also. Thus, compared to the theoretical large number of traps case these results may be experimentally applied to real phenomena.

Comment↗
PubMed2001

Diffusion-limited reaction in the presence of n traps.

We solve the problem of a one-dimensional array of n imperfect traps. These traps are physically represented by small regions of space (in the one-dimensional version we discuss here these traps are represented by small sections of the x axis) with a smaller diffusion constant than that outside them. Small physical particles of one kind diffuse outside and through these small sections. In this work we investigate the changes of the particles density incurred by the presence of these traps. We also check how this density behaves when the density of traps becomes very large.

Journal Article↗
PubMed2000

Gamma ray nuclear resonance absorption: an alternative method for in vivo body composition studies.

We have evaluated gamma ray nuclear resonance absorption (gamma-NRA) on nitrogen, a mature technology proposed and developed by Soreq NRC for detecting explosives, as an alternative to neutron activation for in vivo assaying of body nitrogen. The principles of the gamma-NRA method are outlined, and a test facility constructed at McMaster University's Accelerator Laboratory is described. The results of a feasibility study recently performed there on phantoms and animal tissue are presented and discussed. gamma-NRA is a full imaging technique that essentially constitutes element-specific absorptiometry--i.e., it can generate projections of the mass distribution for a specific element, along with a conventional radiograph of the patient. From the transmission profile of an individual scanned by 9.17 MeV gamma rays, local or whole body nitrogen content can be determined via the resonant attenuation undergone when the beam encounters regions of nitrogen concentration. The advantages of gamma-NRA over neutron activation are (a) radiation doses delivered to the body are at least one order of magnitude lower, thus allowing repeated measurements on individual patients and also rendering the method ethically acceptable for application to children; (b) gamma-NRA is inherently free from uncertainties related to nonuniform distributions of the element in question within the body; (c) it is applicable to patients of varying size and shape; and (d) it yields both nitrogen images and conventional radiographic images of the body.

Animals↗
PubMed1999

The premaxilla in Neandertal and early modern children: ontogeny and morphology.

This comparative study of maxillae in Neandertals, Qafzeh, and extant children examines two specific traits: the premaxillary suture (sutura incisiva) and the interincisive sinuses, proposing a new hypothesis about some features of the Neandertal mid-face. Morphologic study of the premaxillary suture at its different borders (i.e. the nasal aspect of the frontal process, nasal and palatal aspects of the palatal process of the maxilla) indicates a persistence of the suture among very young Neandertal children in comparison to the condition in extant ones. This suggests a longer independence of some parts of the premaxilla in Neandertals. To further examine this possibility, CT scans of two Neandertal children were analyzed: Roc de Marsal, estimated to be about 3 years, and Engis 2, estimated to be about 5-6 years. The results are quite different between the fossils. In the older, the premaxillary suture is represented only by a deep groove. In the younger it extends deep to the surface of the nasal process reaching the Parinaud's canal. Synostosis of the premaxillary suture was found to occur later in Neandertal children than in modern ones. Moreover, we observed the existence of two interincisive sinuses in the fossil children, whereas this is rare in modern children (present on only 2% of our sample of 0-6 year-old infants, n = 247). Persistence of an open premaxillary suture represents the potential for an extended period of growth of the Neandertal mid-face. Although no trace of the premaxillary suture remains in adult Neandertals, Neandertals present many features classically considered as consequences of this persistence. The two interincisive sinuses could be a consequence of the labio-lingual diameter of the incisors. The results presented here can be further investigated by additional studies on the cranial sutural system and by precise morphologic observations and CT scans of the mid-face of a larger sample of fossil children.

Adult↗
PubMed1982

Anomaly of the facial canal in a Mondini malformation with recurrent meningitis.

A patient with recurrent meningitis and congenital hearing loss was evaluated with tomography and metrizamide cisternography. Tomography showed an aberrant first portion of the facial nerve canal, while on cisternography, communication between the internal auditory canal and the dilated labyrinthine remnant was evident. The authors describe the radiographic findings and their significance and propose a mechanism for the formation of the anomalous facial nerve canal.

Child↗
PubMed1980

[Scannography apport in syringomyelic study. 40 syringolyelic cases (author's transl)].

Forty patients with a syringomyelic syndrome were studied by means of scannography of the cervical spine and cervico-occipital joint before and after intrathecal injection of metrizamide. metrizamide transit, and more particularly the opacification of the syringomyelic cyst by metrizamide were assessed by delayed passages. This study demonstrates the value of this technique both from the morphological and dynamic point of view.

Adult↗
PubMed1978

Jugular venous reflux in cerebral radionuclide angiography: an explanation.

A case of isotopic jugular venous reflux, reaching the opposite jugular vein, is described. Phlebography and aortography were simultaneously performed in this patient and showed the innominate vein narrowed and pinched between the sternal notch and the aortic arch. This narrowing depends on the position of the left arm.

Aged↗