Fat quantification with MRI

MR technique offers the opportunity to non-invasively separate fat from water signal. This tutorial will provide an overview of methods to quantify fat with MRI, from T1 based or frequency selective methodologies to chemical shift induced imaging. Underlying principles, advantages and confounding factors will be presented

Chemical shift imaging from simultaneous acquisition of a primary and a stimulated echo

An imaging method is presented for obtaining chemical shift images from only one acquisition. Images are acquired with the same spatial resolution as in regular spin-echo imaging. The sequence is based on the simultaneous acquisition of a spin echo and a stimulated echo in a single pass. The use of 90 degrees radiofrequency pulse flip angles results in the same proton density, T2 and T1 weighting for the two echoes. Application of this sequence to chemical shift imaging is discussed for three fat suppression techniques (chopper, CHESS, and hybrid). Imaging was performed on phatoms and volunteers. The image quality was the same as those obtained by the chopper and the hybrid methods and the acquisition time was reduced by a factor of two

Présentation des plateformes SCIAM et IRM-PRIMEX

Présentation des plateformes SCIAM et IRM-PRIMEX Guillaume Mabilleau et Florence Franconi Université d’Angers, Institut de Biologie en Santé, 49933 Angers, France Le service commun d’imageries et d’analyses microscopiques (SCIAM) et la plateforme d’Imagerie par Résonance Magnétique (IRM) préclinique – PRIMEX sont deux services communs de la SFR ICAT 4208 de l’Université d’Angers. Le SCIAM dispose d’un ensemble dispose d’un microtomographe à rayons X (Bruker microCT 1076) permettant l’acquisition in vivo à des résolutions de 9, 18 et 36 µm et d’un irradiateur à rayons X (Faxitron CP-160). La plateforme PRIMEX dispose d’un imageur Biospec 70/20 Avance III (Bruker Biospin) opérant à un champ magnétique de 7 Tesla. Ces équipements sont particulièrement adaptés pour l’imagerie de la souris ou du rat. Un tour d’horizon du potentiel de ces équipements en préclinique sera présenté. Ces équipements permettent des explorations in vivo chez le petit animal pour des applications telles que la caractérisation anatomique ou fonctionnelle de modèle animaux en oncologie, neurologie, cardiologie… ou l’évaluation de l’efficacité de nouveaux traitements thérapeutiques. Des applications dans d’autres domaines sont aussi possibles (végétal, agroalimentaire, matériaux, ex vivo…). Ces deux plateformes sont ouvertes aux partenaires institutionnels et industriels. Elles proposent un accompagnement scientifique et technique à la conception de projets ainsi que des formations dans le domaine de l’IRM préclinique

Idazoxan does not prevent but worsens focal hypoxic-ischemic brain damage in neonatal Wistar rats

We examined the neuroprotective efficacy of a post-treatment with idazoxan (Idaz): an alpha2-adrenoceptor antagonist with activity at the I1- and I2-subtypes of the imidazoline receptor (I-receptor), in an experimental model of perinatal hypoxic-ischemic (HI) brain damage. Seventy-two, 7-day-old Wistar rats were subjected to permanent unilateral ligation of the common carotid artery and transient (2 hr) hypoxia (8% O(2)). The surviving animals were sub-divided into 3 groups: one "control" group received intraperitoneal (i.p.) injection of saline (Sigma; n = 21) and two "treated" groups received, 10 min post-HI, i.p. treatments with Idaz (I3: 3 mg/kg; n = 19) or (I8: 8 mg/kg; n = 20). Idaz effects were assessed by TTC-staining 72 hr post-HI for Sigma (n = 13), I3 (n = 11), and I8 (n = 12) groups and by MRI-examination 5 weeks post-HI for Sigma (n = 8), I3 (n = 8), and I8 (n = 6) groups. Total ratio of brain infarct areas were significantly (P < 0.01) different between Sigma and Idaz-treated rats: 20.9 +/- 4.0%, 35.6 +/- 5.9 % and 36.8 +/- 5.8% for Sigma, I3 and I8, respectively, when determined with TTC-staining and; 23.3 +/- 3.7%, 39.8 +/- 4.2%, and 43.2 +/- 10.1%, for Sigma, I3, and I8, respectively, when assessed by MRI. Our results suggest that Idaz, given as a post-HI treatment, does not exert neuroprotective effects but enhances the brain injury induced by focal neonatal cerebral HI. The deleterious mechanism may result from an overactivity of sympathetic tone and/or the immaturity of central I-receptors in newborn rats

Diffusion imaging with a multi-echo MISSTEC sequence

An imaging method is presented to measure the water-diffusion coefficient. The sequence (MISSTEC) uses the simultaneous acquisition of a spin echo and several stimulated echoes with the same intensity except for diffusion weighting. The optimal number of stimulated echoes was calculated to minimize the diffusion coefficient error (D). D values obtained in vitro and in vivo were in good agreement with those from the spin-echo sequence (IntraVoxel Incoherent Motion [IVIM] method). The total acquisition time is half that of the classic IVIM method

Optimisation de l'échantillonnage temporel pour la mesure précise de temps de relaxation T1 multiples en Imagerie par Résonance Magnétique (IRM)

L’imagerie par résonance magnétique est de plus en plus utilisée pour l’étude des risques liés à l’obésité par la quantification non invasive et non ionisante de la fraction lipidique. Toutefois, la différence importante entre les temps de relaxation longitudinale T1 de l’eau et des lipides peut conduire à une surestimation significative de la fraction lipidique pour les techniques basées sur le déplacement chimique comme IDEAL1. Il est donc important de connaitre précisément ces T1 pour optimiser les conditions d’acquisition et corriger les mesures. Ce travail vise à proposer une méthode d’optimisation de la stratégie de mesure des T1 d’un système biexponentiel (eau et lipide) par échantillonnage de la courbe de saturation-récupération. Théorie : Le calcul théorique d’une fonction basée sur les coefficients de variation de la mesure du T1 et représentative de la précision de la mesure, a été réalisé pour différents nombre de points d’échantillonnage, différentes répartitions des temps d’échantillonnage correspondants aux temps de répétition TR (espacement en loi de puissance) et différentes gamme d’échantillonnage (TRmin et TRmax). Pour chaque design, le gain de temps a été calculé par rapport au motif le plus long. Résultats et discussion : La minimisation de cette fonction a permis de définir un design optimisé de mesure conjointe des T1 des muscles et des lipides. Plus généralement, cette stratégie peut être adaptée pour optimiser les conditions d’acquisition en fonction des caractéristiques de l’échantillon afin d’obtenir la meilleure précision dans un temps donné et ainsi être appliquée à d’autres méthodes d’IRM quantitatives. 1-Iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL): application with fast spin-echo imaging. Reeder SB et al., Pelc NJ.Magn Reson Med. 2005; 54(3):636-44

In vitro expansion of U87-MG human glioblastoma cells under hypoxic conditions affects glucose metabolism and subsequent in vivo growth

Hypoxia is a characteristic feature of solid tumors leading to the over expression of hypoxia-inducible factor (HIF)-1α protein and therefore to a specific cellular behavior. However, even though the oxygen tension in tumors is low (<5 %), most of the cell lines used in cancer studies are grown under 21 % oxygen tension. This work focuses on the impact of oxygen conditions during in vitro cell culture on glucose metabolism using 1-13C-glucose. Growing U87-MG glioma cells under hypoxic conditions leads to a two- to threefold reduction of labeled glutamine and an accumulation of fructose. However, under both hypoxic and normoxic conditions, glucose is used for de novo synthesis of pyrimidine since the 13C label is found both in the uracil and ribose moieties. Labeling of the ribose ring demonstrates that U87-MG glioma cells use the reversible branch of the non-oxidative pentose phosphate pathway. Interestingly, stereotactic implantation of U87-MG cells grown under normoxia or mild hypoxia within the striatum of nude mice led to differential growth; the cells grown under hypoxia retaining an imprint of the oxygen adaptation as their development is then slowed down

Gender Differences among Sardinians with Alcohol Use Disorder

Sardinia is an Italian island in the Mediterranean characterized by secular isolation and the singular genetic characteristics of its inhabitants. Findings obtained in populations with diverse genetic make-up and cultural background indicate gender differences and/or similarities in drinking characteristics of patients with alcohol use disorder (AUD). Knowledge of these characteristics in AUD patients is useful to improve access to treatments. This paper investigated the drinking characteristics of 66 female and 282 male outpatients with AUD, born from 1937 to 1991, living in Sardinia, and compared their characteristics with those of AUD patients living in other countries. Most Sardinian patients were men, approximately 3 years younger than women; women consumed lower amounts of alcohol than men but did not differ from men in the severity of AUD. Men were more often single than women, while a higher proportion of women reported that their mother or spouse was affected by AUD. Anxiety and depression were more prevalent among women while a higher proportion of men were affected by substance use disorders. Women were older than men at the age of first drink, regular drinking, and onset of AUD, and progressed faster than men from regular use to AUD onset. Women did not differ from men in age at first request for care, and in the lapse from AUD onset to first request for care. Women and men waited for more than 8 and 9 years, respectively, before receiving medical treatment. Gender differences progressively decreased among younger patients. Although the scarce number of women in some cohorts limits the strength of these findings, drinking characteristics of Sardinian patients did not vary significantly from those of AUD patients living in other countries. These results suggest that the number of Sardinian women with AUD is increasing and services for treatment of AUD should (a) consider women’s specific needs, and (b) realize effective policies to reduce latency prior to accessing medical treatment for both men and women with AUD