Validation of GOMOS Ozone Measurements Using Data Assimilation

International audienceAn assimilation system allowing combining the forecasts of a CTM with observations is used to assess the quality of GOMOS ozone measurements. Only a sub-sample of all GOMOS observations performed so far were available in the validation dataset that was available to the ACVT community. This allowed us to find that the average precision of GOMOS local O3 density retrievals is of the order of 5% in the low stratosphere. It has not been possible to draw any significant conclusions on the bias using this dataset and further investigations are require

Alternative usage of 5' exons in the chicken nerve growth factor gene: refined characterization of a weakly expressed gene

Article dans revue scientifique avec comité de lecture. internationale.International audienceNerve growth factor (NGF) is the prototype member of the neurotrophin family. Identification of transcript structures and promoter regions is described here in view of clarifying the molecular basis of chicken NGF gene regulation. Chicken NGF complementary DNA (cDNA) was amplified from heart and brain mRNA using the single-strand ligation to cDNA (SLIC) procedure. Several cloning and sequencing rounds were necessary to elucidate the diversity of NGF transcripts. The chicken NGF gene was shown to possess, in addition to its unique 3′ coding exon, five 5′ exons grouped into two clusters that have been entirely sequenced. The first cluster encompasses three leader exons (1a, 1b and 1c) and is separated from the second cluster by a ~15 kilobases (kb) intronic sequence. "Exon walking" based on reverse transcription–polymerase chain reaction (RT–PCR) allowed to ascertain the length of the three leader exons. The second cluster contains exons 2 and 3, separated from each other by a ~2.4 kb intron, and lies ~0.5 kb upstream from coding exon 4. Combination of several mechanisms, such as differential usage of leader and internal exons, alternative transcription start inside exon 1b, second donor and acceptor sites in exon 1c and 4, respectively, leads to the production of at least 21 different transcripts. This remarkable diversity may represent a common feature largely underestimated for other weakly expressed genes. Preliminary RT–PCR expression study in a panel of chicken tissues shows that transcripts containing exon 1b are present in most tissues tested. Transcripts containing exon 1a are represented mainly in heart and reproductive organs, whereas transcripts containing exon 1c are mostly represented in peripheral organs other than heart. Complementary data are published as a Web supplement available at http://www.loria.fr/~devignes/NGF/index.html

Imagerie hybride TEP/IRM dans le bilan des pathologies neurodégénératives : retour d’expérience

International audienceObjectifsL’imagerie hybride TEP/IRM permet de combiner de façon précise l’information moléculaire fournie par la TEP avec une grande variété de séquences IRM. L’acquisition des deux examens en une session unique minimise les désagréments pour le patient tout en maximisant les informations collectées grâce à la fusion spatiale et temporelle des deux modalités. Dans ce travail, nous discuterons, à partir de cas cliniques, l’apport des deux modalités IRM et TEP dans le bilan des pathologies neuro-dégénératives, notamment la maladie d’Alzheimer (MA), la démence fronto-temporale (DFT), l’aphasie primaire progressive (APP), la démence à corps de Lewy (DCL), l’atrophie corticale postérieure (ACP) et le déficit cognitif léger (MCI).Matériels et méthodesCent vingt-trois patients ont été adressés dans le service entre le 2/10/15 et le 12/01/16 pour un bilan de troubles cognitifs. Les acquisitions ont été réalisées avec le TEP/IRM SIGNA (GE Healthcare) qui combine une technologie TEP temps de vol avec des photomultiplicateurs au silicium et une IRM 3T. Le protocole IRM a compris des acquisitions 3DFLAIR, 3DSWAN, 3DT1 et axiales diffusion. L’acquisition TEP-FDG (2 MBq/kg) centrée sur le cerveau a été réalisée simultanément aux séquences IRM en un pas de lit de 16 minutes (champ de vue axial de 24,4 cm). Les reconstructions étaient réalisées avec l’algorithme Vue Point FX (8 itérations, 28 sous-ensembles, fréquence de coupure 3 mm) incluant correction de résolution spatiale et le temps de vol. La correction de l’atténuation était basée sur un atlas TD.RésultatsLes images TEP et IRM sont de qualité très satisfaisante pour une durée d’examen d’environ 30 minutes. Il n’a pas été identifié d’artéfact de correction lié à l’atlas gênant l’interprétation. Dans les formes jeunes de MA, d’ACP et de DCL, la TEP-FDG montrait souvent des anomalies marquées du métabolisme alors que l’IRM était normale ou montrait une atrophie non spécifique. Dans les formes plus focales (DFT, démence sémantique), les anomalies IRM et TEP étaient généralement associées. Les lésions vasculaires (leucopathies, microsaignements, séquelles d’AVC) sont facilement détectées sur les nouvelles séquences de susceptibilité magnétique (3D SWAN) ; la TEP met en évidence une éventuelle composante dégénérative associée, voire le retentissement (désafférentation) d’une lésion sous corticale.ConclusionsLa fusion des images TEP de haute résolution spatiale avec le 3DT1 permet d’améliorer la confiance diagnostique, en faisant la part entre un effet de volume partiel en cas d’atrophie ou lésion et un véritable déficit fonctionnel. L’interprétation simultanée par le médecin nucléaire et le neuroradiologue apporte au clinicien un résultat diagnostique optimisé, en particulier dans les cas complexes

Dose Reduction in Brain [18F]FDG PET/MRI: Give It Half a Chance

International audienc

Use of FDG-PET/CT for systemic assessment of suspected primary central nervous system lymphoma: a LOC study

International audienc

Hybrid [18F]-F-DOPA PET/MRI Interpretation Criteria and Scores for Glioma Follow-up After Radiotherapy

International audienceObjective18F‑fluoro-L‑3,4‑dihydroxyphenylalanine positron emission tomography (F‑DOPA PET) is used in glioma follow-up after radiotherapy to discriminate treatment-related changes (TRC) from tumor progression (TP). We compared the performances of a combined PET and MRI analysis with F‑DOPA current standard of interpretation.MethodsWe included 76 consecutive patients showing at least one gadolinium-enhanced lesion on the T1‑w MRI sequence (T1G). Two nuclear medicine physicians blindly analyzed PET/MRI images. In addition to the conventional PET analysis, they looked for F‑DOPA uptake(s) outside T1G-enhanced areas (T1G/PET), in the white matter (WM/PET), for T1G-enhanced lesion(s) without sufficiently concordant F‑DOPA uptake (T1G+/PET), and F‑DOPA uptake(s) away from hemorrhagic changes as shown with a susceptibility weighted imaging sequence (SWI/PET). We measured lesions’ F‑DOPA uptake ratio using healthy brain background (TBR) and striatum (T/S) as references, and lesions’ perfusion with arterial spin labelling cerebral blood flow maps (rCBF). Scores were determined by logistic regression.Results53 and 23 patients were diagnosed with TP and TRC, respectively. The accuracies were 74% for T/S, 76% for TBR, and 84% for rCBF, with best cut-off values of 1.3, 3.7 and 1.25, respectively. For hybrid variables, best accuracies were obtained with conventional analysis (82%), T1G+/PET (82%) and SWI/PET (81%). T1G+/PET, SWI/PET and rCBF ≥ 1.25 were selected to construct a 3-point score. It outperformed conventional analysis and rCBF with an AUC of 0.94 and an accuracy of 87%.ConclusionsOur scoring approach combining F‑DOPA PET and MRI provided better accuracy than conventional PET analyses for distinguishing TP from TRC in our patients after radiation therapy

Retrieval of atmospheric parameters from GOMOS data

International audienceThe Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument on board the European Space Agency's ENVISAT satellite measures attenuation of stellar light in occultation geometry. Daytime measurements also record scattered solar light from the atmosphere. The wavelength regions are the ultraviolet-visible band 248-690 nm and two infrared bands at 755-774 nm and at 926-954 nm. From UV-Visible and IR spectra the vertical profiles of O3, NO2, NO3, H2O, O2 and aerosols can be retrieved. In addition there are two 1 kHz photometers at blue 473-527 nm and red 646-698 nm. Photometer data are used to correct spectrometer measurements for scintillations and to retrieve high resolution temperature profiles as well as gravity wave and turbulence parameters. Measurements cover altitude region 5-150 km. Atmospherically valid data are obtained in 15-100 km. In this paper we present an overview of the GOMOS retrieval algorithms for stellar occultation measurements. The low signal-to-noise ratio and the refractive effects due to the point source nature of stars have been important drivers in the development of GOMOS retrieval algorithms. We present first the Level 1b algorithms that are used to correct instrument related disturbances in the spectrometer and photometer measurements The Level 2 algorithms deal with the retrieval of vertical profiles of atmospheric gaseous constituents, aerosols and high resolution temperature. We divide the presentation into correction for refractive effects, high resolution temperature retrieval and spectral/vertical inversion. The paper also includes discussion about the GOMOS algorithm development, expected improvements, access to GOMOS data and alternative retrieval approaches

Hybrid [18F]-F-DOPA PET/MRI Interpretation Criteria and Scores for Glioma Follow-up After Radiotherapy

International audienceObjective18F‑fluoro-L‑3,4‑dihydroxyphenylalanine positron emission tomography (F‑DOPA PET) is used in glioma follow-up after radiotherapy to discriminate treatment-related changes (TRC) from tumor progression (TP). We compared the performances of a combined PET and MRI analysis with F‑DOPA current standard of interpretation.MethodsWe included 76 consecutive patients showing at least one gadolinium-enhanced lesion on the T1‑w MRI sequence (T1G). Two nuclear medicine physicians blindly analyzed PET/MRI images. In addition to the conventional PET analysis, they looked for F‑DOPA uptake(s) outside T1G-enhanced areas (T1G/PET), in the white matter (WM/PET), for T1G-enhanced lesion(s) without sufficiently concordant F‑DOPA uptake (T1G+/PET), and F‑DOPA uptake(s) away from hemorrhagic changes as shown with a susceptibility weighted imaging sequence (SWI/PET). We measured lesions’ F‑DOPA uptake ratio using healthy brain background (TBR) and striatum (T/S) as references, and lesions’ perfusion with arterial spin labelling cerebral blood flow maps (rCBF). Scores were determined by logistic regression.Results53 and 23 patients were diagnosed with TP and TRC, respectively. The accuracies were 74% for T/S, 76% for TBR, and 84% for rCBF, with best cut-off values of 1.3, 3.7 and 1.25, respectively. For hybrid variables, best accuracies were obtained with conventional analysis (82%), T1G+/PET (82%) and SWI/PET (81%). T1G+/PET, SWI/PET and rCBF ≥ 1.25 were selected to construct a 3-point score. It outperformed conventional analysis and rCBF with an AUC of 0.94 and an accuracy of 87%.ConclusionsOur scoring approach combining F‑DOPA PET and MRI provided better accuracy than conventional PET analyses for distinguishing TP from TRC in our patients after radiation therapy