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Biomedical subjects

J Lenoir

Publications and source records attributed to J Lenoir.

At least 19 recordsLinked to original sources
PubMed2005

New approaches to catheter navigation for interventional radiology simulation.

For over 20 years, interventional methods have improved the outcomes of patients with cardiovascular disease. However, these procedures require an intricate combination of visual and tactile feedback and extensive training periods. In this paper, we describe a series of novel approaches that have lead to the development of a high-fidelity simulation system for interventional neuroradiology. In particular we focus on a new approach for real-time deformation of devices such as catheters and guidewires during navigation inside complex vascular networks. This approach combines a real-time incremental Finite Element Model, an optimization strategy based on substructure decomposition, and a new method for handling collision response in situations where the number of contacts points is very large. We also briefly describe other aspects of the simulation system, from patient-specific segmentation to the simulation of contrast agent propagation and fast volume rendering techniques for generating synthetic X-ray images in real-time.

Algorithms↗
PubMed2004

A layered model of a virtual human intestine for surgery simulation.

In this paper, we propose a new approach to simulate the small intestine in a context of laparoscopic surgery. The ultimate aim of this work is to simulate the training of a basic surgical gesture in real-time: moving aside the intestine to reach hidden areas of the abdomen. The main problem posed by this kind of simulation is animating the intestine. The problem comes from the nature of the intestine: a very long tube which is not isotropically elastic, and is contained in a volume that is small when compared to the intestine's length. It coils extensively and collides with itself in many places. To do this, we use a layered model to animate the intestine. The intestine's axis is animated as a linear mechanical component. A specific sphere-based model handles contacts and self-collisions. A skinning model is used to create the intestine's volume around the axis. This paper discusses and compares three different representations for skinning the intestine: a parametric surface model and two implicit surface models. The first implicit surface model uses point skeletons while the second uses local convolution surfaces. Using these models, we obtained good-looking results in real-time. Some videos of this work can be found in the online version at doi: 10.1016/j.media.2004.11.006 and at www-imagis.imag.fr/Publications/2004/FLAMCFC04.

Algorithms↗
PubMed2000

A weak electrical current enhances intracellular delivery of therapeutic substances.

Cell membranes have electrical properties which can be measured and modified. Administering a weak electrical signal across a tissue is a technique which can be used to determine the quantity of water in the intracellular and extracellular compartments. Using this real-time method of bioelectrical impedance, it was found that a variety of stimuli (including an electrical current) can enhance the passage of water and other substances into the cell. We propose an inexpensive and safe technique which could be utilized to enhance delivery of a wide variety of therapeutic agents into cells for the enhanced delivery of antibiotics, chemotherapy or other therapeutic agents.

Animals↗
PubMed1983

The physiological surveillance of hemodialysis sessions by the continuous measurement of L.F. impedance of the circulating blood (Thomasset's method).

Everybody grants as a fact that hemodialysis disturbances are produced by volemia variations. During H-D the vascular sector is the necessary transit medium to withdraw excessive interstitial water. If this withdrawing is greater than the coming back of the interstitial water into the vascular sector, the plasmatic volume will be decreasing. Thus, to measure the variations of the plasmatic volume in circulating blood it is sufficient to effect a continuous measurement of these ones in a transducer having a definite volume. So, by the mean of an impedancemeter, 5 kHz impedance is continuously measured between the two electrodes of the transducer, because it is known (Thomasset's method) that at 5 kHz current uses only the plasma in order to pass from one electrode to another.

Humans↗
PubMed1981

Determination of body fluid compartments by impedance measurements: differences in the repartition of water between Duchenne muscular dystrophy and some neurological diseases.

Body fluid volumes were determined by impedance measurements in several groups of patients. Boys with Duchenne muscular dystrophy had decreased intracellular and extracellular fluid volumes. Patients with severe sequelae of poliomyelitis and with other severely disabling neurological diseases did not exhibit such profound alterations of their body fluid compartments.

Adolescent↗
PubMed1977

[Determination of the lean body mass in adult using the impedance method].

It deals with a new formula which gives the estimation of lean body mass (LBM) by the electric impedance measure at 1 MHz. According to the authors the weight of LBM is set up in two parts: the total water (TBW) conductive of electricity and an inert part (ILBM) which is a bad conductive one: the weight is an individual constant at the grown up. ILBM is calculated from simple morphological datums (H = height and C = wrist circonference). From which one concludes the formula: LBM = TBW + ILBM.

Adipose Tissue↗
PubMed1975

[Evaluation of sectorial fluid movement by measurement of the global impedance of the body. Study during hemodialysis and during treatment with major diuretics].

During courses of haemodialysis or treatment with powerful diuretics, the clinician at the present time bases his actions on blood pressure levels which reflects blood volume and on weight variation which is dependent on water loss. The authors show, in studying variations in total body impedance at 5kHz and 1kHz and their ratio R, that there exists another method of observation which complements the basic notions provided by blood pressure levels and baseline weight. They were thus able to detect the possible formation of cellular oedema due to excessively rapid osmotic depletion. The method makes possible the evaluation of these sectorial fluid transfers when they occur, even though they are not evident clinically. This easy to use method is perhaps less rapid than the usual means of observation but is nevertheless more rational and provides information on electrolyte balance.

Blood Volume↗
PubMed1975

Determination of body fluid compartments by electrical impedance measurements.

?The ratio of the LF and HF impedances appears to be an excellent and simple tool for investigation of liquid specimens, either of the total human body, taking into consideration global impedances, or of a particular organ, taking into consideration local impedances. We have sketched out in this communication a study of the global impedance ratio variations with age, but a large number of studies still remain to be undertaken in those cases of severe denutrition, as in all cases of metabolic illnesses. We can state that, in most cases, not only does the ratio decrease but that there is extreme difficulty in reestablishing normal values. Whatever action is undertaken, it seems that the intracellular liquid compartment remains insufficient with respect to that of the extracellular liquid compartment. It is as if the water will not enter in the cells or as if it were no longer retained within the cells. Finally, with this concept of impedance ratios of Zlf/Zhf a promising experimental method has been found which will, perhaps, enable better infestigations in a field which has often been left to one side.

Body Composition↗
PubMed1975

Investigation of electrical impedance variations of dog brain tissue during experimental metabolic disturbances.

Experiments were carried out on dogs using bielectrode probes having as adequate impedancemeter. The probe is introduced via a cranial opening into the grey matter. This gives the following: a low frequency reading which is related to the extra cellular fluid component; a high frequency reading which is related to the total overall liquids; and a proportionality ratio of these liquids in the explored volume. The impedance variations are functions of the nature and intessity of vascular disturbance. Variation of the low frequency impedance (5 kHz) is the most significant. The experimental prodedure consists of: 1) Abrupt and permanent circulatory arrest; 2) Circulatory reduction by haemorrhage followed by recovery (if necessary by means of blood transfusion); 3) Anoxia by CO inhalation, recovery affected by means of O2 inhalation; and 4) Hypoglycemic coma induced by intravenous injection of insulin. The changes in the biochemical state of the cerebral tissue give very large variations of the low frequency impedance. It is these variations which are to constitute the object of this communication.

Animals↗