Rationale
The behavioral effects of nicotine and the role of the beta2-containing nicotinic receptors in these behaviors are well documented. However, the behaviors altered by nicotine rely on the ...functioning on multiple brain circuits where the high-affinity beta2-containing nicotinic receptors (β2*nAChRs) are located.
Objectives
We intend to see which brain circuits are activated when nicotine is given in animals naïve for nicotine and whether the β2*nAChRs are needed for its activation of the blood oxygen level dependent (BOLD) signal in all brain areas.
Materials and methods
We used functional magnetic resonance imaging (fMRI) to measure the brain activation evoked by nicotine (1 mg/kg delivered at a slow rate for 45 min) in anesthetized C57BL/6J mice and beta2 knockout (KO) mice.
Results
Acute nicotine injection results in a significant increased activation in anterior frontal, motor, and somatosensory cortices and in the ventral tegmental area and the substantia nigra. Anesthetized mice receiving no nicotine injection exhibited a major decreased activation in all cortical and subcortical structures, likely due to prolonged anesthesia. At a global level, beta2 KO mice were not rescued from the globally declining BOLD signal. However, nicotine still activated regions of a meso-cortico-limbic circuit likely via alpha7 nicotinic receptors.
Conclusions
Acute nicotine exposure compensates for the drop in brain activation due to anesthesia through the meso-cortico-limbic network via the action of nicotine on β2*nAChRs. The developed fMRI method is suitable for comparing responses in wild-type and mutant mice.
Introduction Gliomas are the most common primary brain tumors, whose aggressive forms are glioblastomas (high grade gliomas). Common treatment of glioblastomas is concomitant chemotherapy and ...radiotherapy (RT). Volumes considered for RT are defined from T1 weighted images to which security (but not optimal) margins are added to cover possible tumoral infiltration. In this context, metabolite quantification could be a precious marker to obtain a better delineation of the tumor invasion and a characterization of RT adverse effects in normal brain tissue and in tumor. Metabolic information is brought by spectroscopy imaging. However, intra and inter-subjects comparison could only be achieved with normalized signal CSI maps. The aim of this study is validate a fast method of normalization and to determine quantification in tumors based on CSI normalization for water content. Material and methods 3 sequences (T2*, XEP1 and DESPOT1 2) for the water content determination and CSI sequence were acquired at 3T (Siemens Verio system), on a phantom containing NAA and different concentrations of deuterium and on five healthy volunteers, using a 32-channel receiver head coil. CSI data normalization was realized using the method 3 correcting non-water suppressed CSI by proton-density ( ρ ) MRI. Results Phantom: T1, ρ and absolute concentration of NAA were found similar to theoretical calculations. Volunteers A good agreement was achieved between T1, ρ and absolute concentration of metabolites between published values and mean values found on volunteers in different regions. A patient analysis is in work-in-progress. Conclusion This combination yields to a real benefit for water spectrum correction and could be applied in clinical protocol to obtain signal normalization of metabolites (acquisition time = 9 mn) even in the presence of brain disorder which water content cannot be directly known.
Objectives
The Iseult MRI is an actively shielded whole-body magnet providing a homogeneous and stable magnetic field of 11.7 T. After nearly 20 years of research and development, the magnet ...successfully reached its target field strength for the first time in 2019. This article reviews its commissioning status, the gradient–magnet interaction test results and first imaging experience.
Materials and methods
Vibration, acoustics, power deposition in the He bath, and field monitoring measurements were carried out. Magnet safety system was tested against outer magnetic perturbations, and calibrated to define a safe operation of the gradient coil. First measurements using parallel transmission were also performed on an ex-vivo brain to mitigate the RF field inhomogeneity effect.
Results
Acoustics measurements show promising results with sound pressure levels slightly above the enforced limits only at certain frequency intervals. Vibrations of the gradient coil revealed a linear trend with the B
0
field only in the worst case. Field monitoring revealed some resonances at some frequencies that are still under investigation.
Discussion
Gradient-magnet interaction tests at up to 11.7 T are concluded. The scanner is now kept permanently at field and the final calibrations are on-going to pave the road towards the first acquisitions on volunteers.
We are conducting a $377^{\circ 2}$ proper motion survey in the ~V and I bands in order to determine the cool white dwarf contribution to the Galactic dark matter. Using the $250^{\circ 2}$ for which ...we possess three epochs, and applying selection criteria designed to isolate halo-type objects, we find no candidates in a $5500\,{\rm pc}^3$ effective volume for old, fast MV=17 white dwarfs. We check the detection efficiency by cross-matching our catalogue with Luyten's NLTT catalogue. The halo white dwarf contribution cannot exceed 5% (95% C.L.) for objects with and . The same conclusion applies to a 14 Gyr halo composed of white dwarfs with hydrogen atmosphere, as modeled by Chabrier.
We present the type Ia rate measurement based on two EROS supernova search campaigns (in 1999 and 2000). Sixteen supernovae identified as type Ia were discovered. The measurement of the detection ...efficiency, using a Monte Carlo simulation, provides the type Ia supernova explosion rate at a redshift ~0.13. The result is $0.125^{+0.044+0.028}_{-0.034-0.028}\ h_{70}^2$ SNu where 1 SNu = 1 SN / $10^{10}\ {L}_{\odot}^B$ / century. This value is compatible with the previous EROS measurement CITE, done with a much smaller sample, at a similar redshift. Comparison with other values at different redshifts suggests an evolution of the type Ia supernova rate.
One of the promises of Ultra High Field (UHF) MRI scanners is to bring finer spatial resolution in the human brain images due to an increased signal to noise ratio. However, at such field strengths, ...the spatial non-uniformity of the Radio Frequency (RF) transmit profiles challenges the applicability of most MRI sequences, where the signal and contrast levels strongly depend on the flip angle (FA) homogeneity. In particular, the MP-RAGE sequence, one of the most commonly employed 3D sequences to obtain T1-weighted anatomical images of the brain, is highly sensitive to these spatial variations. These cause deterioration in image quality and complicate subsequent image post-processing such as automated tissue segmentation at UHF. In this work, we evaluate the potential of parallel-transmission (pTx) to obtain high-quality MP-RAGE images of the human brain at 7 T. To this end, non-selective transmit-SENSE pulses were individually tailored for each of 8 subjects under study, and applied to an 8-channel transmit-array. Such RF pulses were designed both for the low-FA excitation train and the 180 degree inversion preparation involved in the sequence, both utilizing the recently introduced kT-point trajectory. The resulting images were compared with those obtained from the conventional method and from subject-specific RF-shimmed excitations. In addition, four of the volunteers were scanned at 3 T for benchmarking purposes (clinical setup without pTx). Subsequently, automated tissue classification was performed to provide a more quantitative measure of the final image quality.
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