Magnetic resonance line scan diffusion imaging of the brain, with diffusion weighting between 5 and 5,000 sec/mm(2), was performed in healthy subjects and patients with a 1.5-T machine. For each voxel, biexponential signal decay fits produced two apparent diffusion constants and respective signal amplitudes. Images based on these parameters show potential for use in the differentiation of gray and white matter, edema, and tumor.

No abstract

The aim of this work was to use probabilistic diffusion tractography to examine the organization of the human insular cortex based on the similarities of its remote projections. Forty right-handed healthy subjects (33.8 ± 12.7 years old) with no history of neurological injury were included in the study. After the spatial standardization of diffusion tensor images, insular cortical masks were delineated based on the Harvard-Oxford Cortical Atlas and were used to initiate fibertracking. Cluster analysis by the k-means algorithm was employed to partition the insular voxels into two groups that featured the most distinct distribution of connections. In order to perform volumetric comparisons, the assigned label maps were transformed back to space of the subjects' native anatomical MR images. The outlines of the change in connectivity profile did not respect the known cytoarchitectural subdivisions and were shown to be independent from the gyral anatomy. Interhemispheric asymmetry in the volumes of connectivity-based subdivisions was observed putatively marking a leftward functional dominance of the anterior insula and its reciprocally interconnected targets which influences the size of insular area where similar connections are represented. The fractional anisotropy values were not significantly different between the hemipsheres or connectivity-based clusters; however, the mean diffusivity was higher in the anterior insula in both hemispheres.

No abstract

Although several methods have been developed to automatically delineate subcortical gray matter structures from MR images, the accuracy of these algorithms has not been comprehensively examined. Most of earlier studies focused primarily on the hippocampus. Here, we assessed the accuracy of two widely used non-commercial programs (FSL-FIRST and Freesurfer) for segmenting the caudate and putamen. T1-weighted 1 mm3 isotropic resolution MR images were acquired for thirty healthy subjects (15 females). Caudate nucleus and putamen were segmented manually by two independent observers and automatically by FIRST and Freesurfer (v4.5 and v5.3). Utilizing manual labels as reference standard the following measures were studied: Dice coefficient (D), percentage volume difference (PVD), absolute volume difference as well as intraclass correlation coefficient (ICC) for consistency and absolute agreement. For putamen segmentation, FIRST achieved higher D, lower PVD and higher ICC for absolute agreement with manual tracing than either version of Freesurfer. Freesurfer overestimated the putamen, while FIRST was not statistically different from manual tracing. The ICC for consistency with manual tracing was similar between the two methods. For caudate segmentation, FIRST and Freesurfer performed more similarly. In conclusion, Freesurfer and FIRST are not equivalent when comparing to manual tracing. FIRST was superior for putaminal segmentation.

It is generally believed that the apparent diffusion coefficient (ADC) changes measured by diffusion-weighted imaging (DWI) in brain pathologies are related to alterations in the water compartments. The aim of this study was to elucidate the role of compartmentalization in DWI via biexponential analysis of the signal decay due to diffusion. DWI experiments were performed on mouse brain over an extended range of b-values (up to 10000 mm -2 s) under intact, global ischemic, and cold-injury conditions. DWI was additionally applied to centrifuged human erythrocyte samples with a negligible extracellular space. Biexponential signal decay was found to occur in the cortex of the intact mouse brain. During global ischemia, in addition to a drop in the ADC in both components, a shift from the volume fraction of the rapidly diffusing component to the slowly diffusing one was observed. In cold injury, the biexponential signal decay was still present despite the electron-microscopically validated disintegration of the membranes. The biexponential function was also applicable for fitting of the data obtained on erythrocyte samples Diffusion-weighted imaging (DWI) and measurements of the apparent diffusion coefficient (ADC) play important roles in clinical diagnosis. Alterations in the ADC of water occur in many pathological conditions, such as stroke (1,2), diffuse axonal injury (3), tumors (4), and epilepsy (5). Nevertheless, despite the widespread use of DWI, the underlying mechanisms that cause these changes in ADC are still unclear. Many theories have been put forward to explain the phenomenon, including: 1) water shifts from the extracellular space to the more viscous intracellular space (2,6,7); 2) a loss of cytoplasmic streaming and/or an increased intracellular viscosity results in a drop in ADC (8,9); 3) the extracellular space becomes more tortuous during such a water shift (10 -12); and 4) water goes through a transition from a sol state to a gel state (13).It is clear that, with exception of the latter theory, the physiological compartments appear to be involved. Van Zijl et al. (14) reported evidence suggesting that complete separation of the intra-and extracellular spaces in cell cultures was feasible by means of DW spectroscopy. However, the work of Niendorf et al. (15) on rat brain indicated that the correspondence between the water populations determined in vivo by localized DW spectroscopy and the extra-and intracellular compartments is not straightforward. Nevertheless, several studies involving experimental models (15-17) have indicated that the changes in these volume fractions, as assessed by NMR, follow the alterations in the water compartments in the brain. It becomes more difficult to understand the diffusion properties of water molecules in nervous tissue when the b-value range is extended over 10000 mm -2 s, where more than two exponentially decaying components can be determined (18).The results of the above-cited studies indicate that the origin of the water signal and the multiexponential funct...

No abstract

No abstract