-
[show abstract]
[hide abstract]
ABSTRACT: The Rhesus monkey is a useful model for examining age-related as well as other neurological and developmental effects on the brain, because of the extensive neuroanatomical homology to the human brain, the reduced occurrence of neurological diseases such as Alzheimer's disease, and the possibility of obtaining relevant behavioral data and post-mortem tissue for histological analyses. In this study, cortical thickness measurements based on a cortical surface modeling technique were applied for the first time to investigate cortical thickness patterns in the rhesus monkey brain, and were used to evaluate regional age related effects across a wide range of ages. Age related effects were observed in several cortical areas, in particular in the somato-sensory and motor cortices, where a robust negative correlation of cortical thickness with age was observed, similar to that found in humans. In contrast, results for monkeys compared with humans show significant interspecies differences in cortical thickness patterns in the frontal and the inferior temporal regions.
Neurobiology of aging 01/2012; 33(1):200.e23-31. · 5.94 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Regional atrophy of gray matter (GM) in Alzheimer's disease (AD) is well known; however, the relationship between macroscopic and microscopic changes of cerebral white matter (WM) is uncertain. The aim of this study was to investigate the pattern of GM, WM atrophy, and microscopic WM changes in the same individuals with AD. All subjects (10AD and 15 healthy controls [HC]) underwent a MRI scanning at 1.5 T, including a 3-dimensional volumetric scan and diffusion tensor imaging (DTI). We performed statistical parametric mapping (SPM) with DTI to evaluate the patterns of the microscopic WM changes, as well as voxel-based morphometry (VBM) for GM and WM volume changes between patients with AD and HC. GM atrophy was detected, mainly in posterior regions, and WM atrophy was similarly distributed, but less involved on VBM analysis. Unlike WM atrophy on VBM analysis, microscopic WM changes were shown in the medial frontal, orbitofrontal, splenium of the corpus callosum, and cingulum on DTI analysis with SPM. We demonstrated that the pattern of macroscopic WM atrophy was similar to GM atrophy, while microscopic WM changes had a different pattern and distribution. Our findings suggest that WM atrophy may preferentially reflect the secondary changes of GM atrophy, while microscopic WM changes start earlier in frontal areas before GM and WM atrophy can be detected macroscopically.
Journal of the neurological sciences 03/2011; 302(1-2):89-95. · 2.32 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Over the past decade, the importance of probing the anatomy of the brain has reemerged as an important field of neuroscience. In combination with functional imaging techniques, the rapid advancement of neuroimaging techniques—such as magnetic resonance imaging—and their growing applicability in studying brain morphometry has led to great advances in neuroscience research. Considering the requirements of the diverse technologies—from image processing to statistics—in performing morphometry of the brain, it is critical to have an overall understanding of this subject. The major objective of this review is to provide a practical introduction to this field. The review starts by covering basic concepts and techniques that are commonly used in morphometry of structural magnetic resonance imaging and then extends to further technical perspectives. © 2010 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 20, 117–125, 2010
International Journal of Imaging Systems and Technology 05/2010; 20(2):117 - 125. · 0.78 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Recent studies have demonstrated regional segregations on several peripheral white matter (WM) regions, which may imply different anatomical or functional characteristics [Cereb Cortex 17(4) 2007 816-25; Neuroimage 37(2) 2007 599-610; J Cogn Neurosci 16(7) 2004 1227-33]. Nonetheless, little is known about overall patterns of peripheral WM across the regions. In this study, diffusion tensor imaging with 2-mm isovoxel resolution and cortical surface mapping were combined to determine peripheral WM structure. Fractional anisotropy (FA) mapping showed consistent regional patterns across the young normal subjects while significant high or low FA values were shown in the motor-somatosensory cortex, prefrontal cortex, temporal, and medial occipital cortex. By adopting both region of interest and connectivity analysis, results were then discussed with structural network properties as well as WM maturation process.
Magnetic Resonance Imaging 05/2010; 28(8):1175-82. · 1.99 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The seizure network may be different between temporal lobe epilepsy with hippocampal sclerosis (TLE+HS) and without HS (TLE-HS). Chronic seizure activity may alter the diffusion properties of a seizure network. The thalamus is known to have an anatomical connection to the medial temporal area and to play a role in seizure modulation. This study aimed to evaluate differences in thalamic changes between TLE+HS and TLE-HS with diffusion tensor imaging (DTI).
Nine patients with TLE+HS and nine patients with TLE-HS were included in the study. All patients underwent surgery with good seizure outcomes. Hippocampal sclerosis was verified pathologically. Sixteen right-handed, normal subjects were enrolled as controls. DTI was acquired using 3.0 T MRI. The mean diffusivity (MD) and fractional anisotropy (FA) were calculated in the center of the bilateral thalamus with the DTIstudio program.
The MD of bilateral thalami increased in both TLE groups compared to controls (p<0.05), while FA values did not differ from controls. The MD of the thalamus ipsilateral to the epileptogenic side was higher in the TLE+HS group than in the TLE-HS group (p=0.007). Onset age, seizure duration, seizure frequency and total seizure number were not correlated with FA and MD changes (p>0.05).
Bilateral thalamic diffusion properties are altered in temporal lobe epilepsy. The presence of hippocampal sclerosis enhances the change ipsilaterally.
Epilepsy research 03/2010; 90(1-2):21-7. · 2.48 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We assessed sex differences in fractional anisotropy (FA) and mean diffusion (MD) of temporal lobe white matter (TLWMFA, TLWMMD), TLWM asymmetry, and the relationship between TLWM asymmetry and FA and MD of the corpus callosum (CCFA, CCMD) using diffusion tensor tractography. We found sex differences in the MD of both inferior longitudinal fasciculus (ILF); however, it disappeared after statistical adjustments for intracranial volume and CCMD variability. FA of the superior longitudinal fasciculus (SLFFA) and FA and MD of the ILF (ILFFA, ILFMD) showed leftward asymmetry. In females, the asymmetry indices of SLFFA and the MD of the SLF were significantly correlated with CCFA and CCMD, respectively, which may be related to sex differences in the hemispheric specialization for language.
Neuroreport 12/2009; 21(1):73-7. · 1.66 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In comparison to temporal lobe epilepsy (TLE) patients with hippocampal sclerosis (TLE-HS), TLE patients without HS (TLE-NH) have a similar clinical course but may result in worse surgical outcome. We investigated whether the clinical features related to the lack of HS in TLE patients (TLE-NH) can be explained by water diffusion abnormalities throughout diffusion tensor imaging (DTI) by voxel-based analysis.
Nineteen patients with TLE-HS (left/right TLE 12:7), 18 patients with TLE-NH (left/right TLE 10:8), and 20 controls were included in the study. By statistical parametric mapping (SPM2), the diffusion properties specific to disease characteristics (TLE-HS vs. TLE-NH) were analyzed.
In TLE-HS, we found the areas of increased mean diffusivity (MD) in their ipsilateral temporal and extratemporal areas including the hippocampus, parahippocampal, and frontoparietal regions. Left TLE-HS showed a characteristic MD increase in the ipsilateral posterior cingulum, isthmus of corpus callosum, and contralateral occipital and temporal regions, which was not observed in right TLE-HS group. In left TLE-NH, two regions of increased MD were observed in the ipsilateral posterior fornix (within fusiform gyrus) and posterior cingulum. Right TLE-NH did not show any increased MD.
In left TLE-NH, we could find the water diffusion change along the posterior cingulum, which was quite different from the extensive abnormality from TLE-HS. In addition, there was a lesion-side-specific distribution (left predominant) of pathology in mesial TLE. This provides a possibility that TLE-NH is a heterogeneous or entity different from TLE-HS.
Epilepsia 10/2009; 51(4):529-35. · 3.96 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Because of the complex nature of the human brain, a full understanding of its various group specific variation factors such as volume, shape, and location related to age, gender, ethnic, and disease might be provided in both structural and functional neuroimaging studies. To serve this purpose, a novel approach for characterizing the group variability information using group specific labeled probabilistic maps was introduced in this article. An automatic labeling technique was applied to encode group specific probabilistic information for each region of interests (ROIs) covering the overall cortical region and a probabilistic pattern analytic method was proposed to assess the difference in the spatial extent between 70 schizophrenics and 70 controls in the common space. From our proposed method, we found major differences in 17 ROIs that had shown large variation in schizophrenics. Most of these ROIs were in the frontal and the temporal lobe and only three ROIs were in the parietal and the occipital lobe. The ROIs highlighted through our proposed method could be connected with previous morphological findings on schizophrenia and it also might be considered in functional analysis. As a result, our method could provide intuitive information on group difference relevant to the overall anatomical variability in the substructural level. Thus, it could be used as a prompting system to search and examine the regions of the brain that are worthy of further precise analysis by various sub-cortical region based group studies in assessing specific patterns related to diseases. © 2008 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 18, 310–324, 2008
International Journal of Imaging Systems and Technology 12/2008; 18(5‐6):310 - 324. · 0.78 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Analyzing gray matter diffusion properties can be challenging due to possible measurement biases originating from averaging of gray matter (GM) and cerebrospinal fluid (CSF) signals. Therefore, a better characterization of CSF contamination effects in different cortical regions is required in order to disentangle actual changes in microstructure of GM itself from changes due to other effects such as macroscopic morphological changes. We propose a localized analysis framework for the CSF contamination effect on GM mean diffusivity measurement and applied this framework to measurements on 15 subjects. Our proposed modeling framework was compared to fluid-attenuated inversion recovery (FLAIR) DTI technique from the same subjects. The results of our studies suggest that GM mean diffusivity value was significantly biased by the CSF contamination effect, and that the amount of contamination strongly depended on the local morphology of the peripheral brain. Expected biases had their maxima in the motor and the somatosensory association cortex, and their minima in mid and inferior temporal areas of the brain where the cortical thicknesses are particularly pronounced. We conclude from our studies that regional differences in tissue compounding ratio must be taken into account when assessing localized GF diffusivity differences.
NeuroImage 09/2008; 44(1):136-44. · 5.89 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: To determine the anatomy of a standard brain reflecting well-defined group characteristics based on probabilistic information from group-specific anatomical variations.
We constructed a group-specific tissue probabilistic map for 20 subjects and used it to extract voxel-wise probabilistic information for each subject through regional spatial normalization using Automated Image Registration software (AIR 5.2.5). Extracted probabilistic information was then used to determine standard properties of the subjects. For comparison, we employed an empirical scoring function - a measure of entropy - in ordering the data set. A brain with minimum entropy was then selected for a group standard. The evaluation of our proposed method was performed using two different selection schemes: deformation analysis and similarity index measurements.
This method showed highly correlated result with previous method by Kochunov et al., with fewer computational tasks.
This method can thus be used to determine an appropriate standard model to compare with disease-affected brains.
Magnetic Resonance Imaging 10/2005; 23(7):809-15. · 1.99 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The language pathways consist of ventral and dorsal systems connected via the uncinate fasciculus and arcuate fasciculus, respectively. Seizures in medial temporal lobe epilepsy (mTLE) affect both tracts. Previous studies, however, have focused on the arcuate fasciculus to explain the language disturbance in mTLE. In contrast, we compared changes in both the uncinate and arcuate fasciculi using diffusion tensor imaging.
Thirteen patients with left mTLE and 12 with right mTLE were studied. The Wada test showed left dominance for language in all these patients. Sixteen healthy right-handed subjects were also studied. The mean fractional anisotropy and mean apparent diffusion coefficient with their lateralization index of two fasciculi were compared between hemispheres and between subjects.
The mean apparent diffusion coefficient of the arcuate and uncinate fasciculi in both left- and right-mTLE patients increased bilaterally compared with that in healthy subjects. In left mTLE, the fractional anisotropy of the uncinate fasciculus was lower ipsilaterally (P = 0.002) and was significantly lateralized contralaterally (P < 0.001) compared with control subjects, whereas the fractional anisotropy of the arcuate fasciculus showed no lateralization (P = 0.577). In right mTLE, such a difference was not prominent.
The seizure network affects both arcuate and uncinate fasciculi bilaterally in both left- and right-mTLE patients. The change is most prominent in the left uncinate fasciculus in left mTLE.
World Neurosurgery 75(3-4):509-16. · 0.68 Impact Factor
