A novel MR-guided brain therapy device operating at 1 MHz has been designed and constructed. The system has been installed and tested in a clinical 1.5 T Philips Achieva MRI. Skull bone distortions induced on the ultrasonic beam are corrected using the concept of time reversal focusing. Prior to the treatment, a 3D CT scan of the patient head is performed and used as entry parameters for three-dimensional finite differences simulations that compute the propagation of the wave field through the human skull. The simulated phase distortions are then used as inputs for transcranial corrections. Temperature elevations during the treatment are imaged using MRI thermometry thus ensuring the control and safety of this therapeutic approach. First experiments are performed on four human cadavers and the promising results allow us to envision a first clinical investigation of this therapeutic approach in a near future. First targeted applications correspond to the non-invasive treatment of brain metastases and neurologic disorders such as the essential tremor. (C) 2010 Published by Elsevier Masson SAS.

Many methods have been proposed to extract pressure gradient maps from magnetic resonance (MR) images. They were based on the resolution of the haemodynamic model of Navier–Stokes and needed the flow acceleration to be known. Most used velocity data acquisition and computed acceleration from temporal and spatial derivatives of the velocity field. However, MR sequences have been developed in order to acquire the acceleration field directly. Here we compared direct MR measurements of acceleration field components with those calculated from MR velocity acquisitions. Two experimental phantoms were used to separately evaluate the inertial and convective components of the acceleration. Mathematical simulation of the convective phantom further explained the origin of the noise generated by the spatial and temporal derivatives of the velocity data, and the misregistration artefacts due to MR sequences. We found that direct measurement of the acceleration field generates less noise and fewer artefacts than calculation from velocity derivatives.

The objective of this study was to identify the cerebral correlates of the early phase, and of low to moderate levels, of penile tumescence using for the first time a volumetric measure of the penile response. We hypothesized that (i) regions whose response had been found correlated with circumferential penile responses in previous studies would be identified with volumetric plethysmography and (ii) that other brain regions, including the amygdalae, would be found using the more sensitive volumetric measurement. In ten healthy males, functional magnetic resonance imaging (fMRI) was used to study brain responses to sexually stimulating photographs and to various categories of control photographs. Both ratings of perceived erection and penile plethysmography demonstrated an erectile response to the presentation of sexually stimulating photographs. Regions where the BOLD signal was correlated with penile volumetric responses included the right medial prefrontal cortex, the right and left orbitofrontal cortices, the insulae, the paracentral lobules, the right ventral lateral thalamic nucleus, the right anterior cingulate cortex and regions involved in motor imagery and motor preparation (supplementary motor areas, left ventral premotor area). This study suggests that the development of low levels of penile tumescence in response to static sexual stimuli is controlled by a network of frontal, parietal, insular and cingulate cortical areas and that penile tumescence reciprocally induces activation in somatosensory regions of the brain.

A family of velocity-selective pulses consisting of a series of RF hard pulses followed by bipolar gradients was designed. The succession of required pulses was deduced using a k-space approach within a small tip-angle approximation. Fourier transform of the desired velocity excitation determined the flip-angle series, and the corresponding position in the generalized k-space identified the bipolar-gradient first moments. Spins from any velocity class can be selected. To illustrate this approach we designed and experimentally tested a velocity-slice selection that is analogous to standard spatial-slice selection but involves excitation of spins moving at a chosen velocity (velocity-slice center) and within a given interval (velocity-slice thickness). The assumed approximation does not limit the design to small angles, because velocity selection still holds for angles up to 90 degrees. Velocity slices were experimentally selected, centered on velocities ranging from -1 m s(-1) to 1 m s(-1) with a velocity-slice thickness of 0.4 m s(-1). The experimental velocity-slice profile was assessed and the flow was quantified.

BACKGROUND AND PURPOSE:Brain hypervascular diseases are complex and induce hemodynamic disturbances on brain parenchyma, which are difficult to accurately evaluate by using perfusion-weighted (PWI) MR imaging. Our purpose was to test and to assess the best AIF estimation method among 4 patients with brain hypervascular disease and healthy volunteers.METHODS:Thirty-three patients and 10 healthy volunteers underwent brain perfusion studies by using a 1.5T MR imaging scanner with gadolinium-chelate bolus injection. PWI was performed with the indicator dilution method. AIF estimation methods were performed with local, regional, regional scaled, and global estimated arterial input function (AIF), and PWI measurements (cerebral blood volume [CBV] and cerebral blood flow [CBF]) were performed with regions of interest drawn on the thalami and centrum semiovale in all subjects, remote from the brain hypervascular disease nidus. Abnormal PWI results were assessed by using Z Score, and evaluation of the best AIF estimation method was performed by using a no gold standard evaluation method.RESULTS:From 88% to 97% of patients had overall abnormal perfusion areas of hypo- (decreased CBV and CBF) and/or hyperperfusion (increased CBV and CBF) and/or venous congestion (increased CBV, normal or decreased CBF), depending on the AIF estimation method used for PWI computations. No gold standard evaluation of the 4 AIF estimates found the regional and the regional scaled methods to be the most accurate.CONCLUSION:Brain hypervascular disease induces remote brain perfusion abnormalities that can be better detected by using PWI with regional or regional scaled AIF estimation methods.

Cette étude décrit le développement en cours d’un simulateur morphofonctionnel des voies aériennes supérieures et proximales chez l’homme pour l’aide au diagnostic, au geste médicochirurgical et à l’administration de médicaments par inhalation. Ce travail pluridisciplinaire met en synergie des outils et des connaissances variées en imagerie médicale, modélisation physique et numérique en passant par la physiopathologie et la validation expérimentale, lesquels sont structurés autour de cinq sous-projets distincts décrits succinctement : (I) explorations sur patient ; (II) données et concepts anatomofonctionnels ; (III) modélisations physique et numérique ; (IV) simulateur morphofonctionnel des voies respiratoires et (V) validation in vivo. Cette étude fait partie du projet coopératif intitulé R-MOD, financé par Air Liquide et le ministère de la recherche. Air Liquide est le coordinateur du projet.

Measurements of pressure variations within the cardiac chambers could provide important information for clinical assessments of cardiovascular function. In this work an MRI method for evaluating spatial distributions of intracardiac relative pressure is presented. We first calculated pressure gradients from MR maps of blood acceleration by applying the NS equation. We then used an original algorithm to compute pressure distribution in a region of interest (ROI) by minimizing the pressure gradient curl so that the result in a given pixel is independent of the integration path. The method was assessed in five healthy volunteers by means of MR 2D maps of the blood acceleration in the left ventricle (LV) during ejection and filling phases. The pressure variations calculated from acceleration mapping fit the known physiological variations better than those based on velocity maps acquired in the same volunteers. Furthermore, the optimization algorithm presented here produced the same results as iterative algorithms proposed by other authors, but in much less time and without requiring adjustable parameters or boundary conditions.

Changes in cerebral blood oxygenation and flow during activation of human brain can be measured using functional magnetic resonance imaging (fMRI) data acquired during periodic sensory stimulation. Ideally, spatial and temporal correlations in the acquired data should all be taken into account to derive statistical parametric maps (SPM) and to identify significant changes in fMRI signal. This paper proposes a multivariate statistical model for brain activation detection accounting for both the spatial and temporal correlations. This model considers a space-time variant error and a spatial Markov random field process is used to yield an unbiased estimate of the SPM. As the number of pixels is large enough, the asymptotic theory is used to derive a threshold allowing the identification of activated areas in the SPM. The method is illustrated on sensorimotor experiments performed on normal subjects using 1.5T gradient-echo MRI.

L’exposé à pour objectif de montrer comment la coopération entre : les lois de la mécanique des fluides, les principes de la physique de l’IRM, le développement de séquences d’acquisitions dédiées et la mise en œuvre de méthodes de traitement du signal adaptées ouvre l’accès aux paramètres de I hémodynamique cardiaque et artérielle sur l’homme. L’accent portera sur l’amélioration de la qualité des images de vélocimétrie, sur l’intérêt d’une mesure directe de l’accélération par codage de phase ainsi que sur l’estimation locale des gradients de pression dans les cavités auriculo-ventriculaires et dans la lumière aortique. Enfin il sera montré comment l’estimation de la vitesse de propagation du flux au travers des valves mitrale et aortique laisse espérer l’accès à une cartographie de la pression centrale des voies de remplissage et d’éjection du ventricule gauche.

Seizures, which may be the main expression of cerebral arteriovenous malformations (CAVM) can be difficult to control medically. Our goal was to use perfusion-weighted imaging (PWI) in correlation with clinical data to detect abnormal areas of the cerebrum related to a particular type of CAVM (proliferative angiopathy) and to study the pathophysiology. We use PWI, with a bolus injection of contrast medium, to investigate seven patients with proliferative angiopathy and fits producing language disturbance. Perfusion parameters were calculated using the first-pass moment theory. Five patients had perimalformative and/or contralateral abnormal areas with relative hyperperfusion (cerebral blood volume +20.7+/-16.2%, blood flow 92.5+/-68.8 ml/min/100 g). Areas of hypoperfusion and venous congestion were detected in two patients. One patient who underwent MRI after a severe focal deficit had no significant haemodynamic abnormality.

The management of Brain Arteriovenous Malformations continues to be challenged by a lack of understanding and control of pathophysiological processes implied in the clinical symptoms. New data from functional MRI with diffusion-weighted, perfusion-weighted and neuronal activation highlight abnormal brain areas near or remote to the AVM nidus. Moreover, these techniques are able to show hemodynamic and neuronal adaptative phenomena involved in brain plasticity. They reflect the instantaneous hemodynamic brain conditions that may help to correlate the clinical symptoms with the anatomical and functional substratum and to influence any invasive therapy.

Évaluer en IRM de perfusion les anomalies de l’hémodynamique cérébrale induites par des malformations artérioveineuses en utilisant la théorie de dilution des indicateurs et l’analyse factorielle Quarante patients porteurs de malformation artérioveineuses cérébrales et 10 sujets sains ont été exploré sur 3 centres en France et au Canada en IRM de perfusion à l’aide de séquence EPI écho de gradient et injection de chélate de Gadolinium en Bolus. Les données issues de la perfusion ont été quantitativement traitées à l’aide de 2 logiciels propriétaires afin d’établir des images paramétriques de Volume et de Débit Sanguin Cérébral (VSC et DSC). Quatre régions d’intérêt ont été positionnées dans le cortex et la substance blanche chez tous les sujets, et les résultats obtenus chez les patients ont été comparés à ceux de même topographie obtenus chez les sujets sains par coefficient de corrélation et en utilisant une nouvelle méthode d’évaluation sans Gold Standard. Tous les patients ont présenté des anomalies de perfusion à type d’hyperperfusion autour de la zone du nidus (DSC = 300 +/- 150 ml/min/100 g versus 60 +/− 5 ml/min/100 g dans le cortex). Seulement 7 d’entre eux ont présenté des anomalies de perfusion à distance de la zone nidale, à type d’hypoperfusion (DCS = 30 +/− 15 ml/min/100 g dans le cortex) ou de congestion veineuse (VSC = 8 +/− 2 ml/100 g, DSC = 60 +/− 20 ml/min/100 g dans le cortex) dans le cortex et la substance blanche adjacente. Ces zones anormales ont été immédiatement repérées en Analyse factorielle, alors qu’elles ne sont apparues qu’après un post-traitement élaboré en dilution des indicateurs. L’analyse factorielle est une méthode rapide et efficace révélant immédiatement les anomalies de perfusion cérébrales qui ne sont visibles par méthode conventionnelle qu’après post-traitement élaboré.

L’enjeu actuel de la prise en charge des malformations artérioveineuses cérébrales réside dans la connaissance approfondie et la maîtrise des processus physiopathologiques sou tendant leurs principales manifestations cliniques. Des nouvelles données recueillies en imagerie fonctionnelle cérébrale de diffusion, de perfusion et d’activation permettent de mettre en évidence certaines zones de souffrance parenchymateuse cérébrale au contact ou à distance de ces zones lésionnelles. De plus, ces techniques permettent d’explorer les phénomènes adaptatifs hémodynamiques et neuronaux constituant la plasticité cérébrale. Enfin, elles fournissent un véritable « instantané » de l’état hémodynamique cérébral permettant de moduler les thérapeutiques invasives et de suivre l’évolution de la symptomatologie clinique corrélée au substratum anatomo-fonctionnel.

Anionic iron oxide nanoparticles are efficiently internalized into macrophages where they concentrate within micrometric endosomes, conferring on them a high magnetic susceptibility. The uptake of anionic maghemite nanoparticles by macrophages was quantified by an electron spin resonance (ESR) experiment. MR spin‐echo sequences were performed with various TEs and TRs. The contrast enhancement was compared between two types of agarose phantoms with the same equivalent ferrite concentrations but containing either dispersed isolated nanoparticles or magnetically labeled macrophages. It is shown that the intracellular confinement of maghemite nanoparticles within micrometric endosomes results in a significant decrease of the longitudinal relaxivity and a moderate decrease of the transverse relaxivity compared to the relaxivities of the dispersed isolated nanoparticles. As a consequence, the signature of endosomal magnetic labeling consists of a negative contrast on T1‐weighted images in the whole ferrite concentration range, whereas the presence of extracellular isolated nanoparticles can result in a positive enhancement. Magn Reson Med 49:646–654, 2003. © 2003 Wiley‐Liss, Inc.

A method for reconstructing magnetic resonance angiography (MRA) volumes from successive acquisitions is described. The method is based on double oblique acquisitions of highly anisotropic MRA volumes, each of which corresponds to reduced k-space filling. These partial k-spaces are then combined to obtain a 3D k-space adapted to the frequency spread of the angiographic image of the stenosis. The SNR-resolution compromise of MRA is thus improved by focusing the acquisition on the most relevant k-space regions. The reconstruction is performed directly in k-space by averaging the partial k-spaces. The feasibility of the method was demonstrated in studies on a Lucite stenosis phantom, on MRAs of carotid arteries using three bolus injections, and on MRAs of renal arteries using a single contrast injection.

Background: Little is still known concerning subcutaneous adipose tissue and cellulite, and controversial questions are still under discussion.Aims: Magnetic resonance imaging and spectroscopy were used to address two unresolved questions relating to the anatomy and physiology of subcutaneous adipose tissue.Methods: Using high spatial resolution magnetic resonance imaging we characterized the topography of the dermo- hypodermal junction, and the three-dimensional architecture of the subcutaneous fibrous septae. Using proton spectroscopy, we measured water and lipid fractions within a fat lobule, and T-1 and T-2 values of the detected compounds. All these data were analysed according to sex and presence of cellulite.Results: MR imaging quantified deeper indentations of adipose tissue into the dermis, and evidenced for the first time a great increase in the thickness of the inner fat layer in women with cellulite. Moreover, 3D reconstruction of the fibrous septae network showed a higher percentage of septae in a direction perpendicular to the skin surface in women with cellulite; but our study also depicted the tortuous aspect of this network. MR proton spectroscopy could not show any differences related to sex or presence of cellulite concerning T-1 and T-2 relaxation times of the detected compounds within a fat lobule, neither the unsaturated lipid fraction, the saturated lipid fraction, nor the water fraction.Conclusions: Magnetic resonance imaging showed that the 3D architecture of fibrous septae couldn't be modelled simply as perpendicular planes for women and tilted planes at 45degrees for men. MR spectroscopy did not confirm the hypothesis of increased water content in the adipose tissue of women with cellulite as suggested by others, except if such water would be located in the connective septae.