Biomedical subjects

L Lamalle

Publications and source records attributed to L Lamalle.

10 recordsLinked to original sources

PubMed2006

[Functional magnetic resonance imaging in clinical practice].

In the last decade, functional MRI (fMRI) has become one of the most widely used functional imaging technique in neurosciences. However, its clinical applications remain limited. Despite methodological and practical issues, fMRI data has been validated by different techniques (magnetoencephalography, Wada test, electrical and magnetic stimulations, and surgical resections). In neurosurgical practice, fMRI can identify eloquent areas involved in motor and language functions, and may evaluate characteristics of postoperative neurological deficit including its occurrence, clinical presentation and duration. This may help to inform patients and to prepare postoperative care. fMRI may also identify epileptic foci. In neurological practice, fMRI may help to determine prognosis of recovery after stroke, appropriate medication, and rehabilitation. fMRI may help to identify patients at risk of developing Alzheimer disease. Finally, cerebrovascular reactivity imaging is an interesting approach that might provide new radiological insights of vascular function.

Brain↗

PubMed2004

Vessel size imaging using low intravascular contrast agent concentrations.

Vessel size index (VSI) measurements have been validated on rats bearing a glioma with high doses of contrast agent. The aim of this study was to evaluate the impact of using a reduced dose of contrast agent, necessary for clinical trials. Experiments were performed on rats at three doses of AMI-227 and clearly show higher VSI values at lower doses, whatever the region of interest (contralateral, peritumoral and intratumoral tissue). These results are in good correlation with Monte-Carlo simulations on healthy brain and suggest that only relative values can be obtained at clinical contrast agent doses and magnetic fields.

Animals↗

PubMed2004

In vivo assessment of tumoral angiogenesis.

Vessel size imaging (VSI) for brain tumor characterization was evaluated and the vessel size index measured by MRI (VSIMRI) was correlated with VSI obtained by histology (VSIhisto). Blood volume (BV) and VSI maps were obtained on 12 rats by simultaneous measurements of R2* and R2, before and after the injection of a macromolecular contrast agent, AMI-227. Immunostaining of collagen IV in vessels was performed. An expression was derived for evaluating VSI from stereologic measurements on histology data (VSIhisto). On BV and VSI images obtained from large-size tumors (n = 9), three regions could be distinguished and correlated well with histological sections: a high BV region surrounding the tumor, a necrotic area where BV is very low, and a viable tumor tissue region showing lower BV but higher VSI than the normal rat cortex, with the presence of larger vessels. The quantitative analysis showed a good correlation (Spearman rank's rho = 0.74) between VSIhisto and VSIMRI with a linear regression coefficient of 1.17. The good correlation coefficient supports VSI imaging as a quantitative method for tumor vasculature characterization.

Animals↗

PubMed2001

Vessel size imaging.

Vessel size imaging is a new method that is based on simultaneous measurement of the changes Delta R(2) and Delta R(2)(*) in relaxation rate constants induced by the injection of an intravascular superparamagnetic contrast agent. Using the static dephasing approximation for Delta R(2)(*) estimation and the slow-diffusion approximation for Delta R(2) estimation, it is shown that the ratio Delta R(2)/Delta R(2)(*) can be expressed as a function of the susceptibility difference between vessels and brain tissue, the brain water diffusion coefficient, and a weighted mean of vessel sizes. Comparison of the results with 1) the Monte Carlo simulations used to quantify the relationship between tissue parameters and susceptibility contrast, 2) the experimental MRI data in the normal rat brain, and 3) the histologic data establishes the validity of this approach. This technique, which allows images of a weighted mean of the vessel size to be obtained, could be useful for in vivo studies of tumor vascularization. Magn Reson Med 45:397-408, 2001.

Animals↗

PubMed2001

Methodology of brain perfusion imaging.

Numerous techniques have been proposed in the last 15 years to measure various perfusion-related parameters in the brain. In particular, two approaches have proven extremely successful: injection of paramagnetic contrast agents for measuring cerebral blood volumes (CBV) and arterial spin labeling (ASL) for measuring cerebral blood flows (CBF). This review presents the methodology of the different magnetic resonance imaging (MRI) techniques in use for CBV and CBF measurements and briefly discusses their limitations and potentials.

Animals↗

PubMed2001

Rat lung MRI using low-temperature prepolarized helium-3.

The purpose of this study was to evaluate the recently proposed technique of 3He prepolarization at low temperature and high field (Kober et al. Magn Reson Med 1999; 41:1084-1087) for fast imaging of the lung. Helium-3 was cooled to 2.4 K in a magnetic field of 8 Tesla to obtain a polarization of 0.26%. The polarized 3He was warmed up to room temperature and transferred to a rat, with a final polarization of about 0.1%, large enough for acquiring a 3D image of the rat lung in 30 s.

Animals↗

PubMed2001

Xenon-129 MR imaging and spectroscopy of rat brain using arterial delivery of hyperpolarized xenon in a lipid emulsion.

Hyperpolarized (129)Xe dissolved in a lipid emulsion constitutes an NMR tracer that can be injected into the blood stream, enabling blood-flow measurement and perfusion imaging. A small volume (0.15 ml) of this tracer was injected in 1.5 s in rat carotid and (129)Xe MR spectra and images were acquired at 2.35 T to evaluate the potential of this approach for cerebral studies. Xenon spectra consistently showed two resonances, at 194.5 ppm and 199.0 ppm relative to the gas peak. The signal-to-noise ratio (SNR) obtained for the two peaks was sufficient (ranging from 12 to 90) to follow their time courses. 2D transverse-projection xenon images were obtained with an in-plane resolution of 900 microm per pixel (SNR range 8-15). Histological analysis revealed no brain damage except in two rats that had received three injections.

Animals↗

PubMed2000

In vivo 129Xe NMR in rat brain during intra-arterial injection of hyperpolarized 129Xe dissolved in a lipid emulsion.

Hyperpolarized 129Xe was dissolved in a lipid emulsion and administered to anaesthetized rats by manual injections into the carotid (approximately 1-1.5 mL in a maximum time of 30 s). During injection, 129Xe NMR brain spectra at 2.35 T were recorded over 51 s, with a repetition time of 253 ms. Two peaks assigned to dissolved 129Xe were observed (the larger at 194 +/- 1 ppm assigned to intravascular xenon and the smaller at 199 +/- 1 ppm to xenon dissolved in the brain tissue). Their kinetics revealed a rapid intensity increase, followed by a plateau (approximately 15 s duration) and then a decrease over 5 s. This behaviour was attributed to combined influences of the T1 relaxation of the tracer, of radiofrequency sampling, and of the tracer perfusion rate in rat brain. Similar kinetics were observed in experiments carried out on a simple micro-vessel phantom. An identical experimental set-up was used to acquire a series of 2D projection 129Xe images on the phantom and the rat brain.

Animals↗

PubMed1995

A gating and triggering system dedicated to nuclear magnetic resonance studies of isolated perfused heart.

This work reports a low-cost and versatile electronic device designed to trigger NMR acquisitions from the cardiac cycle of an isolated perfused heart, or to perform electrical stimulation of the heart. The triggering is synchronised with the pressure curve of the perfused heart. The cardiac pacing is achieved from pulses of the NMR system, or by an internal pulse generator, in order to be operated separately from the NMR instrument.

Animals↗

PubMed1992

Optimization schemes for selective excitations: application to the DIGGER pulses.

In this work, two distinct approaches to the tailoring of selective radiofrequency (RF) pulses were applied to a cos-sinc pulse of the DIGGER sequence used in localized spectroscopy. Ideally, three such pulses combined with a gradient in each direction destroy the Mz component of the magnetization everywhere but in the volume of interest. In the first approach, the optimal RF amplitude modulation is found by minimizing the difference between the ideal and the computed Mz profiles. In the second strategy, the RF pulse envelope is adjusted by optimization of the tip angle profile. Computed slice profiles optimized by each of these methods have been compared to experimental results. Simulations as well as experiments show that the second approach, which optimizes tip angles, is the most efficient.

Magnetic Resonance Spectroscopy↗