Biomedical subjects

Gérard Gimenez

Publications and source records attributed to Gérard Gimenez.

5 recordsLinked to original sources

PubMed2006

MRI intensity nonuniformity correction using simultaneously spatial and gray-level histogram information.

A novel approach for correcting intensity nonuniformity in magnetic resonance imaging (MRI) is presented. This approach is based on the simultaneous use of spatial and gray-level histogram information. Spatial information about intensity nonuniformity is obtained using cubic B-spline smoothing. Gray-level histogram information of the image corrupted by intensity nonuniformity is exploited from a frequential point of view. The proposed correction method is illustrated using both physical phantom and human brain images. The results are consistent with theoretical prediction, and demonstrate a new way of dealing with intensity nonuniformity problems. They are all the more significant as the ground truth on intensity nonuniformity is unknown in clinical images.

Algorithms↗

PubMed2006

Alveolar recruitment assessed by positron emission tomography during experimental acute lung injury.

OBJECTIVES: To compare changes in aerated lung volumes measured by positron emission tomography (PET) and inflation volume-pressure curve (V-P) of the respiratory system, and to evaluate the reliability of PET to assess alveolar recruitment. DESIGN AND SETTING: Experimental study in six anesthetized and mechanically ventilated pigs in a PET facility in an experimental university laboratory. INTERVENTIONS: Lung injury was induced by oleic acid. Animals were randomly studied in four conditions: PEEP 0cmH(2)O (ZEEP) in supine position (SP), PEEP 10cmH(2)O in SP, ZEEP in prone position (PP) and PEEP in PP, each applied for 30min. MEASUREMENTS AND RESULTS: With PET aerated lung volume was obtained from pulmonary density analysis using transmission scan (VA(trans)) and from nitrogen-13 kinetics on emission scan (VA(em)). Changes in VA(trans) and VA(em) were computed as the difference in aerated volume between conditions. VA(trans) and VA(em) did not differ between SP and PP, on either ZEEP or PEEP, suggesting no modification in relaxation volume of the respiratory system induced by posture. Changes in VA(trans) or VA(em) were significantly correlated with changes in aerated volume assessed from superimposed V-P curves (R (2)=0.74 and 0.75, respectively). Alveolar recruitment assessed by PET was significantly correlated with both PaO(2) (R (2)=0.61) and PaCO(2) (R (2)=0.40) variations induced by PEEP. CONCLUSIONS: PET is a new reliable tool of scientific interest to image lung volume and alveolar recruitment during acute lung injury.

Animals↗

PubMed2006

Computation of transmitted and received B1 fields in magnetic resonance imaging.

Computation of B1 fields is a key issue for determination and correction of intensity nonuniformity in magnetic resonance images. This paper presents a new method for computing transmitted and received B1 fields. Our method combines a modified MRI acquisition protocol and an estimation technique based on the Levenberg-Marquardt algorithm and spatial filtering. It enables accurate estimation of transmitted and received B1 fields for both homogeneous and heterogeneous objects. The method is validated using numerical simulations and experimental data from phantom and human scans. The experimental results are in agreement with theoretical expectations.

Algorithms↗

PubMed2006

Creation and application of a simulated database of dynamic [18f]MPPF PET acquisitions incorporating inter-individual anatomical and biological variability.

During the process of validation of a new tracer, estimation of performance and validation of processing algorithms have to be investigated with data sets representative of the ground truth. Because this ground truth is hardly accessible in positron emission tomography (PET), validations of processing algorithms often rely on the use of simulated data sets. Considering that Monte Carlo simulators are very time consuming and are not very easy to use, the building of publicly available databases of simulated PET volumes are becoming highly desirable. We present here the methodology employed for the creation of a database of simulated dynamic [18F]MPPF-PET data, including inter-individual anatomical and biological variability which meets the criteria of a gold standard database as defined by Lehmann: reliance, equivalence, independence, relevance, significance. The assessment of the realism of the built database against actual MPPF PET data is also presented here. Whereas the database was specifically created for the investigations of quantification of activity and binding of ligand-receptor with the [18F]MPPF PET tracer, it may serve the community with countless purposes. The full strength of this database, does not only stem from the knowledge of important information such as the true activity map and underlying anatomical data, but also from the possibility to fully control the biological difference between sets of simulated PET data. Indeed, time activity curves included in the simulated data sets are controlled by a multicompartmental model of ligand-receptor exchanges. This latter feature is of a great interest in the context of the improvement of the detectability of biological variation in PET.

Brain↗

PubMed2003

Characterization of PVA cryogel for intravascular ultrasound elasticity imaging.

The present study characterizes the mechanical properties of polyvinyl alcohol (PVA) cryogel in order to show its utility for intravascular elastography. PVA cryogel becomes harder with an increasing number of freeze-thaw cycles, and Young's modulus and Poisson's ratio are measured for seven samples. Mechanical tests were performed on cylindrical samples with a pressure column and on a hollow cylinder with the calculation of an intravascular elastogram. An image of the Young's modulus was obtained from the elastogram using cylinder geometry properties. Results show the mechanical similitude of PVA cryogel with the biological tissues present in arteries. A good agreement between Young's modulus obtained from pressure column and from elastogram was also observed.

Biomimetic Materials↗