Time filter

Source Type

Sainte-Foy-lès-Lyon, France

Malik S.J.,Imperial College London | Keihaninejad S.,Imperial College London | Hammers A.,Neurodis Foundation | Hajnal J.V.,Imperial College London
Magnetic Resonance in Medicine | Year: 2012

Brain images acquired at 3T often display central brightening with spatially varying tissue contrast, caused by inhomogeneity in the transmit radiofrequency fields used for excitation. Tailored radiofrequency pulses can provide mitigation of radiofrequency field inhomogeneity, but previous designs have been unsuitable for 3D imaging in rapid pulse sequences. This article presents a nonselective pulse design based on a short (1 ms) 3D spiral k-space trajectory that covers low spatial frequencies. The resulting excitations are optimized to produce a uniform excitation within a specified volume of interest covering the whole brain. B1 mapping and pulse calculation times were reduced by optimizing in only five slices within the brain. The method has been tested with both single and parallel transmission: in phantom experiments, normalized root-mean-square error in excitation was 0.022 for single and 0.020 for parallel transmission. The corresponding results in vivo were 0.066 and 0.055 respectively. A pilot brain imaging study using the proposed pulses for excitation within the Alzheimer's disease neuroimaging initiative magnetization prepared rapid gradient echo (MP-RAGE) protocol, yielded excellent image quality with improved signal to noise ratio in peripheral brain regions and enhanced uniformity of contrast compared with standard excitation. Greatest performance enhancement was achieved using parallel transmission, but single channel transmission offers significant improvement over standard excitation pulses. Copyright © 2011 Wiley Periodicals, Inc. Source

Rheims S.,Idee | Rheims S.,French Institute of Health and Medical Research | Rubi S.,Hospital Clinic de Barcelona | Bouvard S.,Hospices Civils de Lyon | And 8 more authors.
Neuro-Oncology | Year: 2014

Background: Dysembryoplastic neuroepithelial tumors (DNTs) represent a prevalent cause of epileptogenic brain tumors, the natural evolution of which is much more benign than that of most gliomas. Previous studies have suggested that [11C]methionine positron emission tomography (MET-PET) could help to distinguish DNTs from other epileptogenic brain tumors, and hence optimize the management of patients. Here, we reassessed the diagnostic accuracy of MET-PET for the differentiation between DNT and other epileptogenic brain neoplasms in a larger population. Methods: We conducted a retrospective study of 77 patients with focal epilepsy related to a nonrapidly progressing brain tumor on MRI who underwent MET-PET, including 52 with a definite histopathology. MET-PET data were assessed by a structured visual analysis that distinguished normal, moderately abnormal, and markedly abnormal tumor methionine uptake and by semiquantitative ratio measurements. Results: Pathology showed 21 DNTs (40%), 10 gangliogliomas (19%), 19 low-grade gliomas (37%), and 2 high-grade gliomas (4%). MET-PET visual findings significantly differed among the various tumor types (P<.001), as confirmed by semiquantitative analyses (P<.001 for all calculated ratios), regardless of gadolinium enhancement on MRI. All gliomas and gangliogliomas were associated with moderately or markedly increased tumor methionine uptake, whereas 9/21 DNTs had normal methionine uptake. Receiver operating characteristics analysis of the semiquantitative ratios showed an optimal cutoff threshold that distinguished DNTs from other tumor types with 90% specificity and 89% sensitivity. Conclusions: Normal MET-PET findings in patients with an epileptogenic nonrapidly progressing brain tumor are highly suggestive of DNT, whereas a markedly increased tumor methionine uptake makes this diagnosis unlikely. © The Author(s) 2014. Source

Didelot A.,French Institute of Health and Medical Research | Didelot A.,University of Lyon | Didelot A.,Institute Federatif Des Neurosciences Of Lyon | Mauguiere F.,French Institute of Health and Medical Research | And 13 more authors.
Journal of Nuclear Medicine | Year: 2010

18F-4-(2′-methoxyphenyl)-1-[2′-(N-2-pyridinyl) -p-fluorobenzamido]-ethyl-piperazine (18F-MPPF) PET has proved to be a sensitive technique in the presurgical evaluation of patients with drugresistant temporal lobe epilepsy (TLE), but a significant proportion of visually detected abnormalities failed to be detected by standard statistical parametric mapping (SPM) analysis. This study aimed at describing a voxel-based method for computing interhemispheric asymmetric index (AI) using statistical software and applying and validating the clinical relevance of this method for analyzing asymmetries of 18F-MPPF PET images in patients with drug-resistant TLE. Methods: 18F-MPPF PET scans of 24 TLE patients who achieved an Engel class I outcome after epilepsy surgery and of 41 controls were analyzed visually, with standard SPM, and by computing voxel-based AIs. Both SPM methods were assessed using 2 different statistical thresholds (P< 0.05, corrected at the cluster level, and P< 0.05, familywise error (FWE) corrected at the voxel level). Sensitivity and specificity of each method were estimated and compared using McNemar tests. Results: The sensitivity of AI analysis to detect decreases of 18F-MPPF binding potential ipsilateral to the epileptogenic lobe was 92% (P< 0.05, corrected at the cluster level) and 96% (P< 0.05, familywise error corrected at the voxel level), whereas specificity (defined as the congruence between the localization of the voxel associated with the greatest z score and that of the epileptogenic zone) was 88% at both thresholds. AI analysis was significantly more sensitive (P< 0.05) and specific (P< 0.005) than standard SPM analysis, regardless of the applied threshold. AI analysis also proved to be more sensitive than visual analysis. Conclusion: AI analysis of 18F-MPPF PET was more sensitive and specific than previous methods of analysis. This noninvasive imaging procedure was especially informative for the presurgical assessment of patients presenting with clinical histories atypical of mesial TLE or with normal brain MRI results. Copyright © 2010 by the Society of Nuclear Medicine, Inc. Source

Yankam Njiwa J.,Neurodis Foundation | Gray K.R.,Imperial College London | Costes N.,CERMEP Imagerie du Vivant | Mauguiere F.,University of Lyon | And 2 more authors.
NeuroImage: Clinical | Year: 2015

Purpose We have previously shown that an imaging marker, increased periventricular [11C]flumazenil ([11C]FMZ) binding, is associated with failure to become seizure free (SF) after surgery for temporal lobe epilepsy (TLE) with hippocampal sclerosis (HS). Here, we investigated whether increased preoperative periventricular white matter (WM) signal can be detected on clinical [18F]FDG-PET images. We then explored the potential of periventricular FDG WM increases, as well as whole-brain [11C]FMZ and [18F]FDG images analysed with random forest classifiers, for predicting surgery outcome. Methods Sixteen patients with MRI-defined HS had preoperative [18F]FDG and [11C]FMZ-PET. Fifty controls had [18F]FDG-PET (30), [11C]FMZ-PET (41), or both (21). Periventricular WM signal was analysed using Statistical Parametric Mapping (SPM8), and whole-brain image classification was performed using random forests implemented in R (http://www.r-project.org). Surgery outcome was predicted at the group and individual levels. Results At the group level, non-seizure free (NSF) versus SF patients had periventricular increases with both tracers. Against controls, NSF patients showed more prominent periventricular [11C]FMZ and [18F]FDG signal increases than SF patients. All differences were more marked for [11C]FMZ. For individuals, periventricular WM signal increases were seen at optimized thresholds in 5/8 NSF patients for both tracers. For SF patients, 1/8 showed periventricular signal increases for [11C]FMZ, and 4/8 for [18F]FDG. Hence, [18F]FDG had relatively poor sensitivity and specificity. Random forest classification accurately identified 7/8 SF and 7/8 NSF patients using [11C]FMZ images, but only 4/8 SF and 6/8 NSF patients with [18F]FDG. Conclusion This study extends the association between periventricular WM increases and NSF outcome to clinical [18F]FDG-PET, but only at the group level. Whole-brain random forest classification increases [11C]FMZ-PET's performance for predicting surgery outcome. Source

Rizzo G.,University of Padua | Veronese M.,University of Padua | Veronese M.,Kings College London | Heckemann R.A.,Gothenburg University | And 5 more authors.
Journal of Cerebral Blood Flow and Metabolism | Year: 2014

Substantial efforts are being spent on postmortem mRNA transcription mapping on the assumption that in vivo protein distribution can be predicted from such data. We tested this assumption by comparing mRNA transcription maps from the Allen Human Brain Atlas with reference protein concentration maps acquired with positron emission tomography (PET) in two representative systems of neurotransmission (opioid and serotoninergic). We found a tight correlation between mRNA expression and specific binding with 5-HT1A receptors measured with PET, but for opioid receptors, the correlation was weak. The discrepancy can be explained by differences in expression regulation between the two systems: transcriptional mechanisms dominate the regulation in the serotoninergic system, whereas in the opioid system proteins are further modulated after transcription. We conclude that mRNA information can be exploited for systems where translational mechanisms predominantly regulate expression. Where posttranscriptional mechanisms are important, mRNA data have to be interpreted with caution. The methodology developed here can be used for probing assumptions about the relationship of mRNA and protein in multiple neurotransmission systems. © 2014 ISCBFM. Source

Discover hidden collaborations