G. de Marco

A Comparative Study of Perfusion Measurement in Brain Tumours at 3 Tesla MR: Arterial Spin Labeling versus Dynamic Susceptibility Contrast-Enhanced MRI

Purpose: To prove the feasibility of arterial spin labeling (ASL) to explore brain tumors by comparing dynamic susceptibility contrast-enhanced MRI to ASL at 3T MR. Materials and Methods: Twenty-seven patients were included presenting 9 gliomas, 10 metastases and 8 meningiomas. All were explored by a pseudo-continuous ASL and dynamic susceptibility contrast-enhanced T2* perfusion sequence. Two neuroradiologists analyzed the cerebral blood flow (CBF) maps to assess feasibility, examination quality and quantitative comparison. The Spearman nonparametric correlation test and the Bland-Altman graphic test were used to analyze our quantitative results. Results: 92% of ASL CBF maps were informative. ASL detected all lesions as well as dynamic susceptibility contrast-enhanced MRI. Both sequences provide relative quantitative CBF values closely correlated. Conclusion: On a 3T MR unit, ASL is a good alternative to dynamic susceptibility contrast-enhanced MRI when contrast medium is contraindicated or intravenous injection is not possible. Its results on relative CBF parameters are similar to contrast-injected perfusion.

Alertness in young healthy subjects: An fMRI study of brain region interactivity enhanced by a warning signal

An effective connectivity study was carried out on 16 young, healthy subjects performing an alertness task. The objective of this study was to develop and to evaluate a putative network model of alertness by adapting structural equation modeling to fMRI data. This study was designed to evaluate the directed interactivity of an attentional network during intrinsic and phasic alerting tasks. On the basis of theoretical hypotheses, clinical observations, behavioral data and neuroimaging studies, it was hypothesized that neural circuits in the right hemisphere including the dorsolateral prefrontal cortex (DLPFC), anterior cingulate cortex, inferior parietal cortex and the thalamus were involved. The results of this study support the existence of a common network of activated areas with significant path coefficient differences between intrinsic and phasic alertness. Functional interactivity was significantly reinforced during the phasic alertness task and appeared to preferentially involve activity in the DLPFC region, whereas the path coefficients of the model were well-balanced during intrinsic alertness. This study highlights the predominant role of the DLPFC region in maintenance of a state of alertness and in temporal preparation during an alertness task.

Changes in effective connectivity during incidental and intentional perception of fearful faces.

The present fMRI study examined effective connectivity within an emotional network composed of three brain areas: Amygdala (AMY), Anterior Cingulate Cortex (AAC) and Orbito-Frontal (OFC) in processing fearful faces. Two tasks: an incidental perception (gender identification) and an intentional detection (effortful discrimination) task were performed by 14 and 10 young healthy volunteers, respectively. Participants were scanned while viewing fearful, neutral and ambiguous facial expressions. Effective connectivity was assessed using Structural Equation Modeling (SEM). Results show that the hypothetical network fits the experimental data for both tasks and in both hemispheres. The comparison between Tasks 1 and 2 reveals significant differences in strength and direction of the connectivity patterns for the left and to a less stringent threshold for the right hemisphere. The path coefficients analysis suggests that the fearful information generated in AMY, reaches the OFC through the ACC in incidental perception, while in intentional perception, the route followed is in a reverse direction from OFC to ACC. Our findings confirm a differential brain connectivity between incidental and intentional processing of fearful faces.

Predicting the outcome of grade II glioma treated with temozolomide using proton magnetic resonance spectroscopy

Background:This study was designed to evaluate proton magnetic resonance spectroscopy (1H-MRS) for monitoring the WHO grade II glioma (low-grade glioma (LGG)) treated with temozolomide (TMZ).Methods:This prospective study included adult patients with progressive LGG that was confirmed by magnetic resonance imaging (MRI). Temozolomide was administered at every 28 days. Response to TMZ was evaluated by monthly MRI examinations that included MRI with volumetric calculations and 1H-MRS for assessing Cho/Cr and Cho/NAA ratios. Univariate, multivariate and receiver-operating characteristic statistical analyses were performed on the results.Results:A total of 21 LGGs from 31 patients were included in the study, and followed for at least n=14 months during treatment. A total of 18 (86%) patients experienced a decrease in tumour volume with a greater decrease of metabolic ratios. Subsequently, five (28%) of these tumours resumed growth despite the continuation of TMZ administration with an earlier increase of metabolic ratios of 2 months. Three (14%) patients did not show any volume or metabolic change. The evolutions of the metabolic ratios, mean(Cho/Cr)n and mean(Cho/NAA)n, were significantly correlated over time (Spearman ρ=+0.95) and followed a logarithmic regression (P>0.001). The evolutions over time of metabolic ratios, mean(Cho/Cr)n and mean(Cho/NAA)n, were significantly correlated with the evolution of the mean relative decrease of tumour volume, mean(ΔVn/Vo), according to a linear regression (P<0.001) in the ‘response/no relapse’ patient group, and with the evolution of the mean tumour volume (meanVn), according to an exponential regression (P<0.001) in the ‘response/relapse’ patient group. The mean relative decrease of metabolic ratio, mean(Δ(Cho/Cr)n/(Cho/Cr)o), at n=3 months was predictive of tumour response over the 14 months of follow-up. The mean relative change between metabolic ratios, mean((Cho/NAA)n−(Cho/Cr)n)/(Cho/NAA)n, at n=4 months was predictive of tumour relapse with a significant cutoff of 0.046, a sensitivity of 60% and a specificity of 100% (P=0.004).Conclusions:The 1H-MRS profile changes more widely and rapidly than tumour volume during the response and relapse phases, and represents an early predictive factor of outcome over 14 months of follow-up. Thus, 1H-MRS may be a promising, non-invasive tool for predicting and monitoring the clinical response to TMZ.

Differences in effective connectivity between dyslexic children and normal readers during a pseudoword reading task: an fMRI study.

PURPOSE This fMRI study investigated phonological and lexicosemantic processing in dyslexic and in chronological age- and reading level-matched children in a pseudoword reading task. MATERIALS AND METHODS The effective connectivity network was compared between the three groups using a structural model including the supramarginal cortex (BA 40; BA: Brodmann area), fusiform cortex (BA 37) and inferior frontal cortex (BA 44/45) areas of the left hemisphere. RESULTS The results revealed differences in connectivity patterns. In dyslexic patients, in contrast with chronological age- and reading level-matched groups, no causal relationship was demonstrated between BA 40 and BA 44/45. However, a significant causal relationship was demonstrated between BA 37 and BA 44/45 both in dyslexic children and in the reading level-matched group. CONCLUSIONS These findings were interpreted as evidence for a phonological deficit in developmental dyslexia.

Dynamic contrast-enhanced T2*-weighted MR imaging: A peritumoral brain oedema study

BACKGROUND AND PURPOSE Glioma and meningioma are the two most common types of primary brain tumor. The aim of the present study was to analyze, using dynamic susceptibility contrast MR perfusion imaging, the effect of angiogenesis on peritumoral tissue. METHODS In this prospective study, conducted from December 2003 to March 2005, out of 18 patients recruited, 12 were included (six with meningioma, six with glioblastoma). Using rates of maximum signal drop (MSD), we drew regions of interest (ROI) starting near the lesion, and gradually moving outwards to areas of distant edema in axial and sagittal planes at 10, 20 and 30 mm from the tumor. We also drew ROI on the contralateral brain white matter to obtain a normal baseline for comparison (relative MSD; rMSD). RESULTS In regions of peritumoral T2 hypersignals, we observed a decrease in rMSD with distance from glioblastoma due to reduced angiogenesis, and an increase in rMSD with distance from meningioma, probably due to a reduced mass effect. CONCLUSION In our study, dynamic susceptibility contrast MR perfusion imaging, using MSD as a parameter, revealed differences between meningioma and glioblastoma peritumoral tissue due to changes in angiogenesis.

Brain functional modeling, what do we measure with fMRI data?

The description of specific circuits in networks should allow a more realistic definition of dynamic functioning of the central nervous system which underlies various brain functions. After introducing the programmed and acquired networks and recalling the concepts of functional and effective connectivity, we presented biophysical and physiological aspects of the BOLD signal. Then, we briefly presented a few data-driven and hypothesis-driven methods; in particular we described structural equation modeling (SEM), a hypothesis-driven approach used to explore circuits within networks and model spatially and anatomically interconnected regions. We compared the SEM method with an alternative hypothesis-driven method, dynamic causal modeling (DCM). Finally, we presented independent components analysis (ICA), an exploratory data-driven approach which could be used to complete the directed brain interactivity studies. ICA combined with SEM/DCM may allow extension of the statistical and explanatory power of fMRI data.

Mathematical Modeling of Metabolism and Hemodynamics

We provide a mathematical study of a model of energy metabolism and hemodynamics of glioma allowing a better understanding of metabolic modifications leading to anaplastic transformation from low grade glioma.This mathematical analysis allows ultimately to unveil the solution to a viability problem which seems quite pertinent for applications to medecine.

Diffusion tensor changes in epileptogenic hippocampus of TLE patients

PURPOSE Diffusion tensor imaging (DTI) can provide quantitative information of brain abnormalities in patients with temporal lobe epilepsy (TLE) that are not detectable with conventional magnetic resonance imaging (MRI). METHODS Seventeen patients with medically TLE were selected for the study. The patients and ten healthy subjects underwent 25 directions DTI acquisition. The patients were separated into two groups based on the MRI findings: eight TLE MRI-negative patients with no signal abnormalities on conventional MRI and nine TLE patients with hippocampal sclerosis (HS). Fractional anisotropy (FA), mean diffusivity (MD), and the three diffusivities (lambda(1), lambda(2) and lambda(3)) were measured in bilateral hippocampi of controls, MRI-negative, and HS patients. Comparisons between the three groups were performed for hippocampi ipsi- and contralateral to epileptogenic zone. RESULTS The ipsilateral hippocampus of MRI-negative patients presented statistical increased anisotropy and no significant difference in diffusivities versus controls. Significant differences in anisotropy and diffusivities were detected between the ipsilateral hippocampus of HS when compared with controls. CONCLUSION DTI depicted hippocampal abnormalities in TLE patients with a normal conventional MRI different from those found in patients with HS. Diffusivity and anisotropy indices provide significant differences inside hippocampus and should be jointly considered to improve the DTI measurements specificity in TLE patients.

Cerebrospinal fluid MR dynamics and risk of falls in the elderly.

RATIONALE AND OBJECTIVES To investigate the relationship between CSF dynamics and risk of falls of unknown origin in the elderly. POPULATION AND METHODS Phase contrast MR studies allowed CSF aqueductal flow quantification on 23 community-dwelling older people initially explored for mild cognitive impairment. Mobility assessment included report of falls, talking walking test, stance test, one leg standing test, up and go test, and measurement of fast gait speed. RESULTS History of falls was associated with larger aqueduct, steeper diastolic slopes higher ratios RDV/SD of diastolic volume/CSF systole duration (p</=0.0006). Amplitude CSF parameters, diastolic slopes and RDV/SD appeared correlated with the aqueduct area (p<0.01). CONCLUSIONS These preliminary data suggest that disturbances of CSF dynamics could play a role in mobility decline with aging especially in falls of unknown origin.