1,721,221 research outputs found
A view into the brain of female children with autism pectrum disorder: Morphometric regional alterations detected by structural MRI mass-univariate and pattern classification analisys
No full textFemale children with autism spectrum disorder: An insight from mass-univariate
and pattern classification analyses.
Calderoni S, Retico A, Biagi L, Tancredi R, Muratori F, Tosetti M.
IRCCS Stella Maris Foundation, Viale del Tirreno 331, 56018 Calambrone, Pisa,
Italy; Division of Child Neurology and Psychiatry, University of Pisa, Pisa,
Italy.
Several studies on structural MRI in children with autism spectrum disorders
(ASD) have mainly focused on samples prevailingly consisting of males. Sex
differences in brain structure are observable since infancy and therefore caution
is required in transferring to females the results obtained for males. The
neuroanatomical phenotype of female children with ASD (ASDf) represents indeed a
neglected area of research. In this study, we investigated for the first time the
anatomic brain structures of a sample entirely composed of ASDf (n=38; 2-7years
of age; mean=53months; SD=18) with respect to 38 female age and non verbal IQ
matched controls, using both mass-univariate and pattern classification
approaches. The whole brain volumes of each group were compared using voxel-based
morphometry (VBM) with diffeomorphic anatomical registration through
exponentiated lie algebra (DARTEL) procedure, allowing us to build a
study-specific template. Significantly more gray matter (GM) was found in the
left superior frontal gyrus (SFG) in ASDf subjects compared to controls. The GM
segments obtained in the VBM-DARTEL preprocessing are also classified with a
support vector machine (SVM), using the leave-pair-out cross-validation protocol.
Then, the recursive feature elimination (SVM-RFE) approach allows for the
identification of the most discriminating voxels in the GM segments and these
prove extremely consistent with the SFG region identified by the VBM analysis.
Furthermore, the SVM-RFE map obtained with the most discriminating set of voxels
corresponding to the maximum Area Under the Receiver Operating Characteristic
Curve (AUC(max)=0.80) highlighted a more complex circuitry of increased cortical
volume in ASDf, involving bilaterally the SFG and the right temporo-parietal
junction (TPJ). The SFG and TPJ abnormalities may be relevant to the
pathophysiology of ASDf, since these structures participate in some core atypical
features of autism
Musculoskeletal MRI at 7 T: do we need more or is it more than enough?
Full text linkUltra-high field magnetic resonance imaging (UHF-MRI) provides important diagnostic improvements in musculoskeletal imaging. The higher signal-to-noise ratio leads to higher spatial and temporal resolution which results in improved anatomic detail and higher diagnostic confidence. Several methods, such as T2, T2*, T1rho mapping, delayed gadolinium-enhanced, diffusion, chemical exchange saturation transfer, and magnetisation transfer techniques, permit a better tissue characterisation. Furthermore, UHF-MRI enables in vivo measurements by low-γ nuclei (23Na, 31P, 13C, and 39K) and the evaluation of different tissue metabolic pathways. European Union and Food and Drug Administration approvals for clinical imaging at UHF have been the first step towards a more routinely use of this technology, but some drawbacks are still present limiting its widespread clinical application. This review aims to provide a clinically oriented overview about the application of UHF-MRI in the different anatomical districts and tissues of musculoskeletal system and its pros and cons. Further studies are needed to consolidate the added value of the use of UHF-MRI in the routine clinical practice and promising efforts in technology development are already in progress
BOLD response to spatial phase congruency in human brain
No full textHuman psychophysical observations, computational models, and the selectivity of neurons in primary visual cortex all suggest that an early step in visual processing is the detection of features such as lines and edges. However, previous fMRI experiments investigating the responses of early visual areas to phase coherence have led to apparently discordant results. We studied the human brain BOLD responses to structured periodic band-pass images of matched amplitude spectrum but of different phase spectra, arranged to create three distinct types of stimuli: pure edges; pure lines (matched global and local energy to the edges, but different phase); and random noise (random phase spectrum, hence no salient features, and a different spatial distribution of local energy from the lines and edges stimuli). Alternation of lines against edges did not activate primary visual cortex, but did activate two higher order visual areas. Alternation of these lines or edges against the random stimulus produced a strong activity in many visual areas, including primary visual cortex. Interestingly, the BOLD activity was higher for the edges and lines than for the random stimuli for a wide range of stimulus contrasts, indicating the presence of non-linear gain modulation in the cell response. These results show that phase congruency is coded at the level of primary visual cortex. We show that a stage of response gain modulation can explain our present and previous fMRI discordant results
Local SAR variability assessment at 7T via B1+ measurement and electromagnetic field simulation
No full textLa Spettroscopia Protonica a Risonanza Magnetica nella patologia neurologicadell’età evolutiva
No full textThe impact of white matter fiber orientation in single-acquisition quantitative susceptibility mapping
No full textThe aim of this work was to assess the impact of tissue structural orientation on quantitative susceptibility mapping (QSM) reliability, and to provide a criterion to identify voxels in which measures of magnetic susceptibility (chi) are most affected by spatial orientation effects. Four healthy volunteers underwent 7-T magnetic resonance imaging (MRI). Multi-echo, gradient-echo sequences were used to obtain quantitative maps of frequency shift (FS) and chi. Information from diffusion tensor imaging (DTI) was used to investigate the relationship between tissue orientation and FS measures and QSM. After sorting voxels on the basis of their fractional anisotropy (FA), the variations in FS and chi values over tissue orientation were measured. Using a K-means clustering algorithm, voxels were separated into two groups depending on the variability of measures within each FA interval. The consistency of FS and QSM values, observed at low FA, was disrupted for FA > 0.6. The standard deviation of. measured at high FA (0.0103 ppm) was nearly five times that at low FA (0.0022 ppm). This result was consistent through data across different head positions and for different brain regions considered separately, which confirmed that such behavior does not depend on structures with different bulk susceptibility oriented along particular angles. The reliability of single-orientation QSM anticorrelates with local FA. QSM provides replicable values with little variability in brain regions with FA < 0.6, but QSM should be interpreted cautiously in major and coherent fiber bundles, which are strongly affected by structural anisotropy and magnetic susceptibility anisotropy
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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