Findings from previous magnetic resonance imaging studies of sex differences in gray matter have been inconsistent, with some showing proportionally increased gray matter in women and some showing no differences between the sexes. Regional sex differences in gray matter thickness have not yet been mapped over the entire cortical surface in a large sample of subjects spanning the age range from early childhood to old age. We applied algorithms for cortical pattern matching and techniques for measuring cortical thickness to the structural magnetic resonance images of 176 healthy individuals between the ages of 7 and 87 years. We also mapped localized differences in brain size. Maps of sex differences in cortical thickness revealed thicker cortices in women in right inferior parietal and posterior temporal regions even without correcting for total brain volume. In these regions, the cortical mantle is up to 0.45 mm thicker, on average, in women than in men. Analysis of a subset of 18 female and 18 male subjects matched for age and brain volume confirmed the significance of thicker gray matter in temporal and parietal cortices in females, independent of brain size differences. Further analyses were conducted in the adult subjects where gender differences were evaluated using height as a covariate, and similar sex differences were observed even when body size differences between the sexes were controlled. Together, these results suggest that greater cortical thickness in posterior temporal inferior parietal regions in females relative to males are independent of differences in brain or body size. Age-by-sex interactions were not significant in the temporoparietal region, suggesting that sex differences in these regions are present from at least late childhood and then are maintained throughout life. Male brains were larger than female brains in all locations, though male enlargement was most prominent in the frontal and occipital poles, bilaterally. Given the large sample and the large range of ages studied, these results help to address controversies in the study of central nervous system sexual dimorphisms.

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Spectral imaging is a technology that integrates conventional imaging and spectroscopy to get both spatial and spectral information from an object. Although this technology was originally developed for remote sensing, it has been extended to the biomedical engineering field as a powerful analytical tool for biological and biomedical research. This review introduces the basics of spectral imaging, imaging methods, current equipment, and recent advances in biomedical applications. The performance and analytical capabilities of spectral imaging systems for biological and biomedical imaging are discussed. In particular, the current achievements and limitations of this technology in biomedical engineering are presented. The benefits and development trends of biomedical spectral imaging are highlighted to provide the reader with an insight into the current technological advances and its potential for biomedical research.

The basal ganglia portions of cortico-striato-thalamo-cortical (CSTC) circuits have consistently been implicated in the pathogenesis of Tourette syndrome, whereas motor and sensorimotor cortices in these circuits have been relatively overlooked. Using magnetic resonance imaging, we detected cortical thinning in frontal and parietal lobes in groups of Tourette syndrome children relative to controls. This thinning was most prominent in ventral portions of the sensory and motor homunculi that control the facial, orolingual and laryngeal musculature that is commonly involved in tic symptoms. Correlations of cortical thickness in sensorimotor regions with tic symptoms suggest that these brain regions are important in the pathogenesis of Tourette syndrome.

A method for the spatial normalization and reorientation of diffusion tensor (DT) fields is presented. Spatial normalization of tensor fields requires an appropriate reorientation of the tensor on each voxel, in addition to its relocation into the standardized space. This appropriate tensor reorientation is determined from the spatial normalization transformation and from an estimate of the underlying fiber direction. The latter is obtained by treating the principal eigenvectors of the tensor field around each voxel as random samples drawn from the probability distribution that represents the direction of the underlying fiber. This approach was applied to DT images from nine normal volunteers, and the results show a significant improvement in signal-to-noise ratio (SNR) after spatial normalization and averaging of tensor fields across individuals. Diffusion tensor imaging (DTI) has emerged during the past several years as a potentially powerful way to map white matter fibers in vivo. DTI takes advantage of the microscopic diffusion of water molecules, which is less restricted along the axis of a fiber than along its transverse direction. DT images are usually acquired by applying at least six noncolinear gradient orientations, and thus measuring a symmetric tensor on each voxel. The principal axis of this tensor presumably coincides with the underlying fiber's orientation. One of the potential applications of this technique is the study of white matter architecture in the brain. In conventional MRI, such as T 1 -and T 2 -weighted images, white matter often appears as a homogeneous structure, even though it consists of many axonal bundles of various sizes and orientations. With the use of fiber orientation information, one can identify various axonal tracts within the homogeneous-looking white matter. This capability of DTI may be useful for studying effects of development, aging, and diseases on specific white matter tracts of interest.Despite the promise of this imaging method, the clinical utility of DTI is currently limited by several factors. For instance, even if tracts of interest can be identified visually, proper tools with which to quantify their locations, sizes, and shapes, and to compare them between normal and abnormal populations, are still in their infancy. DTI is also an inherently lengthy imaging technique that produces relatively higher levels of scanner noise. This is particularly a problem in non-cooperative patient populations, since scanning time must be kept to a minimum, which thus decreases noise. Image noise is also detrimental in fiber tractography, since its cumulative effect can cause significant deviations of a pathway tracked along a tensor field from its true position. Similar problems also arise in functional imaging and, particularly, positron emission tomography (PET) as a result of limited SNR. A widely used approach to mitigate the effects of noise in group analysis has been the use of statistical parametric mapping (SPM) (1,2), which usually consists of two steps. First, ima...

Changes in FC of the visual cortex are found in patients with POAG. These include alterations in connectivity between the visual cortex and associative visual areas along with disrupted connectivity between the primary and higher visual areas.

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These findings are consistent with the known plasticity of the dentate gyrus and with findings from previous imaging studies suggesting the presence of failed compensatory plasticity in adults with TS who have not experienced the usual decline in symptoms during adolescence.