Use of a porous membrane for gas bubble removal in microfluidic channels: physical mechanisms and design criteria

We demonstrate and explain a simple and efficient way to remove gas bubbles from liquid-filled microchannels, by integrating a hydrophobic porous membrane on top of the microchannel. A prototype chip is manufactured in hard, transparent polymer with the ability to completely filter gas plugs out of a segmented flow at rates up to 7.4 microliter/s per mm2 of membrane area. The device involves a bubble generation section and a gas removal section. In the bubble generation section, a T-junction is used to generate a train of gas plugs into a water stream. These gas plugs are then transported towards the gas removal section, where they slide along a hydrophobic membrane until complete removal. The system has been successfully modeled and four necessary operating criteria have been determined to achieve a complete separation of the gas from the liquid. The first criterion is that the bubble length needs to be larger than the channel diameter. The second criterion is that the gas plug should stay on the membrane for a time sufficient to transport all the gas through the membrane. The third criterion is that the gas plug travel speed should be lower than a critical value: otherwise a stable liquid film between the bubble and the membrane prevents mass transfer. The fourth criterion is that the pressure difference across the membrane should not be larger than the Laplace pressure to prevent water from leaking through the membrane

Geometrie differentielle et vision par ordinateur: reconstruction des contours d'occultation de la surface d'un objet non-polyedrique

SIGLEINIST T 75129 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Model Based Detection of Tubular Structures in 3D Images

Detection of tubular structures in 3D images is an important issue for vascular detection in medical imaging. We present in this paper a new approach for centerline detection and reconstruction of 3D tubular structures. Several models of vessels are introduced for estimating the sensivity of the image second order derivatives according to elliptical cross-section, to curvature of the axis, or to partial volume e#ects. Our approach uses a multiscale analysis for extracting vessels of di#erent sizes according to the scale. For a given model of vessel, we derive an analytic expression of the relationship between the radius of the structure and the scale at which it is detected. The algorithm gives both centerline extraction and radius estimation of the vessels allowing their reconstruction. The method has been tested on both synthetic and real images, with encouraging results. This work was done in collaboration with GEMS

Reconstruction of Coronary Arteries from One Rotational X-ray Projection Sequence

Cardiovascular diseases remain the first death cause in developed countries. In most cases, exploration of possibly underlying coronary artery pathologies is performed using injected X-ray coronary angiography imaging modality. Current clinical routine in coronary angiography is directly conducted in 2-D from angiograms acquired from several static points of view. However, for diagnosis and treatment purposes, coronary arteries reconstruction is highly suitable. In this report, we propose a novel method to reconstruct coronary arteries from one single rotational X-ray projection sequence. The purpose of this study is to provide physicians with a 3-D model of coronary arteries, e.g. for absolute tridimensional measures for lesion assessment, instead of direct projective measures deducted from the images, which are highly dependent on the point of view. Our method is split in 3 sequential steps: (1) 3-D stereoscopic reconstruction of coronary arteries centerlines, including respiratory motion compensation, (2) coronary arteries 4-D motion computation, and (3) 3-D tomographic reconstruction of coronary arteries, involving compensation for respiratory and cardiac motions. We have successfully tested it on the datasets from a synthetic phantom and 16 patients

Model based detection of tubular structures in 3D images

Theme 3 - Interaction homme-machine, images, donnees, connaissances - Projet EpidaureAvailable from INIST (FR), Document Supply Service, under shelf-number : 14802 E, issue : a.1999 n.3736 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc

Quantitative Automated Assessment of Myocardial Perfusion at Cardiac Catheterization

Perfusion assessed in the cardiac catheterization laboratory predicts outcomes after myocardial infarction. The aim of this study was to investigate a novel method of assessing perfusion using digital subtraction angiography to generate a time-density curve (TDC) of myocardial blush, incorporating epicardial and myocardial perfusion. Seven pigs underwent temporary occlusion of the left anterior descending coronary artery for 60 minutes. Angiography was performed in the same projections before, during, and after occlusion. Perfusion parameters were obtained from the TDC and compared with Thrombolysis In Myocardial Infarction (TIMI) frame count and myocardial perfusion grade. In addition, safety and feasibility were tested in 8 patients after primary percutaneous coronary intervention. The contrast density differential between the proximal artery and the myocardium derived from the TDC correlated well with TIMI myocardial perfusion grade (R = 0.54, p \u3c0.001). The arterial transit time derived from the TDC correlated with TIMI frame count (R = 0.435, p = 0.011). Using a cutoff of 2.4, the density/time ratio, a ratio of density differential to transit time, had sensitivity and specificity of 100% for coronary arterial occlusion. The positive and negative predictive values were 100%. The generation of a TDC was safe and feasible in 7 patients after acute myocardial infarctions, but the correlation between TDC-derived parameters and TIMI parameters did not reach statistical significance. In conclusion, this novel method of digital subtraction angiography with rapid, automated, quantitative assessment of myocardial perfusion in the cardiac catheterization laboratory correlates well with established angiographic measures of perfusion. Further studies to assess the prognostic value of this technique are warranted. © 2008 Elsevier Inc. All rights reserved

Sensory gating in adult with attention-deficit/hyperactivity disorder: Event-evoked potential and perceptual experience reports comparisons with schizophrenia

International audienceno abstrac