Biomedical subjects

Sun I Kim

Publications and source records attributed to Sun I Kim.

At least 19 recordsLinked to original sources

PubMed2006

Pattern classification using principal components of cortical thickness and its discriminative pattern in schizophrenia.

We proposed pattern classification based on principal components of cortical thickness between schizophrenic patients and healthy controls, which was trained using a leave-one-out cross-validation. The cortical thickness was measured by calculating the Euclidean distance between linked vertices on the inner and outer cortical surfaces. Principal component analysis was applied to each lobe for practical computational issues and stability of principal components. And, discriminative patterns derived at every vertex in the original feature space with respect to support vector machine were analyzed with definitive findings of brain abnormalities in schizophrenia for establishing practical confidence. It was simulated with 50 randomly selected validation set for the generalization and the average accuracy of classification was reported. This study showed that some principal components might be more useful than others for classification, but not necessarily matching the ordering of the variance amounts they explained. In particular, 40-70 principal components rearranged by a simple two-sample t-test which ranked the effectiveness of features were used for the best mean accuracy of simulated classification (frontal: (left(%)|right(%))=91.07|88.80, parietal: 91.40|91.53, temporal: 93.60|91.47, occipital: 88.80|91.60). And, discriminative power appeared more spatially diffused bilaterally in the several regions, especially precentral, postcentral, superior frontal and temporal, cingulate and parahippocampal gyri. Since our results of discriminative patterns derived from classifier were consistent with a previous morphological analysis of schizophrenia, it can be said that the cortical thickness is a reliable feature for pattern classification and the potential benefits of such diagnostic tools are enhanced by our finding.

Adult↗

PubMed2006

Spatial accuracy of fMRI activation influenced by volume- and surface-based spatial smoothing techniques.

As improvements in cortical surface modeling allowed accurate cortical topology in brain imaging studies, surface-based methods for the analysis of functional magnetic resonance imaging (fMRI) were introduced to overcome the topological deficiency of commonly used volume-based methods. The difference between the two methods is mainly due to the smoothing techniques applied. For practical applications, the surface-based methods need to quantitatively validate the accuracy of localizing activation. In this study, we evaluated the spatial accuracy of activation detected by the volume- and surface-based methods using simulated blood oxygenation level-dependent (BOLD) signals and MRI phantoms focusing on the influence of their smoothing techniques. T1- and T2-weighted phantoms were acquired from BrainWeb () and used to extract cortical surfaces and to generate echo planar imaging (EPI) data. Simulated BOLD signals as the gold standard of activation in our experiment were applied to the surfaces and projected to the volume space with random noise. Three-dimensional isotropic Gaussian kernel smoothing and two-dimensional heat kernel smoothing were applied to the volume- and surface-based methods. Sensitivity and 1-specificity, which are truly and falsely detected activations, and similarity measures, which are spatially and statistically similar for the gold standard and detected activations, were calculated. In the results, the surface-based method showed the sensitivity and similarity scores of about 12% higher than the volume-based method. In conclusion, the surface-based method guarantees better spatial accuracy for the localization of BOLD signal sources within the cortex than the volume-based method.

Brain↗

PubMed2006

How does distortion correction correlate with anisotropic indices? A diffusion tensor imaging study.

PURPOSE: The purpose of this study was to determine a suitable registration algorithm for diffusion tensor imaging (DTI) using conventional preprocessing tools [statistical parametric mapping (SPM) and automated image registration (AIR)] and to investigate how anisotropic indices for clinical assessments are affected by these distortion corrections. MATERIALS AND METHODS: Brain DTI data from 15 normal healthy volunteers were used to evaluate four spatial registration schemes within subjects to correct image distortions: noncorrection, SPM-based affine registration, AIR-based affine registration and AIR-based nonlinear polynomial warping. The performance of each distortion correction was assessed using: (a) quantitative parameters: tensor-fitting error (Ef), mean dispersion index (MDI), mean fractional anisotropy (MFA) and mean variance (MV) within 11 regions of interest (ROI) defined from homogeneous fiber bundles; and (b) fiber tractography through the uncinate fasciculus and the corpus callosum. Fractional anisotropy (FA) and mean diffusivity (MD) were calculated to demonstrate the effects of distortion correction. Repeated-measures analysis of variance was used to investigate differences among the four registration paradigms. RESULTS: AIR-based nonlinear registration showed the best performance for reducing image distortions with respect to smaller Ef (P<.02), MDI (P<.01) and MV (P<.01) with larger MFA (P<.01). FA was decreased to correct distortions (P<.0001) whether the applied registration was linear or nonlinear and was lowest after nonlinear correction (P<.001). No significant differences were found in MD. CONCLUSION: In conventional DTI processing, anisotropic indices of FA can be misestimated by noncorrection or inappropriate distortion correction, which leads to an erroneous increase in FA. AIR-based nonlinear distortion correction would be required for a more accurate measurement of this diffusion parameter.

Adult↗

PubMed2006

Swelling behavior of chitosan hydrogels in ionic liquid-water binary systems.

The swelling behavior of chitosan hydrogels in ionic liquid-water binary systems was studied using hydrophilic room-temperature ionic liquids (RTILs) to elucidate the swelling mechanism of chitosan hydrogels. No penetration of RTIL into a dry chitosan material was observed. Swelling was achieved by soaking in water-RTIL binary mixtures, with larger swelling observed at higher water contents. In one instance, the binary mixture was acidic and produced larger than expected swelling due to the dissociation of the amine groups in the chitosan. The equilibrium binary system content behavior of the chitosan hydrogels depended upon the amount of free water, which is a measure of the number of water molecules that do not interact with the ionic liquid. After evaporation of water, remnant RTIL remained in the chitosan network and hardness testing indicated a plasticization effect, suggesting that the RTIL molecularly mixed with the chitosan. Chitosan hydrogels containing only RTIL were prepared by dropping pure RTIL onto a fully preswollen hydrogel followed by water evaporation. This method may be a useful means for preparing air-stable swollen chitosan gels.

Calorimetry, Differential Scanning↗

PubMed2006

Shape deformation of the insula in schizophrenia.

Schizophrenia has been conceptualized to be a neurodevelopmental disorder. Neuroimaging evidence was generally findings of volumetric reductions in various brain structures. The shape analysis of the insula can uncover unique structural deformity in the neurodevelopmental disorder, which cannot be revealed from a simple volume measurement. The objective of this study was to demonstrate a subtle change of the insula in schizophrenia using our special shape analysis technique. Subjects were 23 patients with schizophrenia and 23 normal healthy subjects. A landmark-based structural and surface shape analysis of the insula was performed using high-spatial resolution magnetic resonance imaging. A characteristic finding was that the frontotemporal sides of the right insula were deformed in the patients with schizophrenia compared with normal controls. This deformation can be associated with abnormal development of the frontal and temporal lobes in schizophrenia.

Adult↗

PubMed2006

An MRI study of structural variations in schizophrenia using deformation field morphometry.

Magnetic resonance imaging (MRI) has an important role in investigating the changes in brain structure that are associated with schizophrenia. In this study, MRI scans of patients diagnosed with schizophrenia (37 males; 19 females; 17-42 years of age) were compared with those of an age- and sex-matched group of normal subjects (37 males; 19 females; 18-40 years of age). Based on the images of the healthy control subjects, we constructed a representative average brain template. Automated image analysis techniques were used to measure differences in the regional nonlinear deformation fields between the two groups. A deformation field, which measures the spatial transformation to deform a template of brain anatomy to each individual data, was obtained as a three-dimensional displacement vector in each voxel. There was a significantly greater magnitude of the deformation fields in the superior frontal and parietal lobes as well as in the cingulate gyrus connecting both lobes of the patients with schizophrenia than in those of healthy controls, suggesting that these cerebral regions have a significantly higher structural variability in schizophrenia.

Adolescent↗

PubMed2006

A novel quantitative cross-validation of different cortical surface reconstruction algorithms using MRI phantom.

Cortical surface reconstruction is important for functional brain mapping and morphometric analysis of the brain cortex. Several methods have been developed for the faithful reconstruction of surface models which represent the true cortical surface in both geometry and topology. However, there has been no explicit comparison study among those methods because each method has its own procedures, file formats, coordinate systems, and use of the reconstructed surface. There has also been no explicit evaluation method except visual inspection to validate the whole-cortical surface models quantitatively. In this study, we presented a novel phantom-based validation method of the cortical surface reconstruction algorithm and quantitatively cross-validated the three most prominent cortical surface reconstruction algorithms which are used in Freesurfer, BrainVISA, and CLASP, respectively. The validation included geometrical accuracy and mesh characteristics such as Euler number, fractal dimension (FD), total surface area, and local density of points. CLASP showed the best geometric/topologic accuracy and mesh characteristics such as FD and total surface area compared to Freesurfer and BrainVISA. In the validation of local density of points, Freesurfer and BrainVISA showed more even distribution of points on the cortical surface compared to CLASP.

Algorithms↗

PubMed2006

Gender difference analysis of cortical thickness in healthy young adults with surface-based methods.

We have examined gender differences of cortical thickness using a 3-D surface-based method that enables more accurate measurement in deep sulci and localized regional mapping compared to volumetric analyses. Cortical thickness was measured using a direct method for calculating the distance between corresponding vertices from inner and outer cortical surfaces. We normalized cortical surfaces using 2-D surface registration and performed diffusion smoothing to reduce the variability of folding patterns and to increase the power of the statistical analysis. In stereotaxic space, significant localized cortical thickening in women was found extensively in frontal, parietal and occipital lobes, including the superior frontal gyrus (SFG), superior parietal gyrus (SPG), inferior frontal gyrus (IFG) and postcentral gyrus (PoCG) in the left hemisphere and mostly in the parietal lobe, including the SPG in the right hemisphere. In the temporal lobe, small regions of the left and right caudal superior temporal gyrus (STG) and the left temporal pole showed significantly greater cortical thickness in women. The temporal lobe shows relatively less significant thickening than other lobes in both hemispheres. In native space, significantly greater cortical thickness in women was detected in left parietal region, including SPG and PoCG. No significant local increases of cortical thickness were observed in men in both spaces. These findings suggest statistically significant cortical thickening in women in localized anatomical regions, which is consistent with several previous studies and may support a hypothesis of sexual dimorphism.

Adolescent↗

PubMed2006

Increased water diffusivity in the frontal and temporal cortices of schizophrenic patients.

Schizophrenia has been suggested to be the result of both macroscopic and microscopic abnormalities in the brain. Although no definitive clinico-pathological correlations have been found to reconcile the many facets inherent in this disorder, the recent development of the magnetic resonance diffusion tensor imaging (DTI) has allowed us to gather useful information regarding the microcircuitry of the brain. Specifically, the apparent diffusion coefficient (ADC) reflects the degree of diffusion barriers and heterosynaptic communication for the brain neurotransmitter. Nineteen patients with DSM-IV schizophrenia and 21 age- and sex-matched control subjects participated in DTI, and the severity of the patients' symptoms was evaluated according to the Positive and Negative Syndrome Scale (PANSS). The ADC values were determined and compared between patients and control subjects via voxel-based morphometry. The results show an increased ADC in the bilateral fronto-temporal regions of the schizophrenic patients, as compared with those of the control subjects. In addition, the ADC values in the area of the right insular were correlated with the negative syndromes from the PANSS. Our findings of increased water diffusivity in the fronto-temporal regions of schizophrenic patients and the correlation between negative symptom scales and the ADC in the right insular region indicate that damaged brain microcircuitry might contribute to the pathophysiology of schizophrenia. These findings contribute towards integrating micro and macrostructural abnormalities and syndromes of schizophrenia.

Adult↗

PubMed2006

Fractal dimension in human cortical surface: multiple regression analysis with cortical thickness, sulcal depth, and folding area.

Fractal dimension (FD) has been widely used to provide a quantitative description of structural complexity in the cerebral cortex. FD is an extremely compact measure of shape complexity, condensing all details into a single numeric value. We interpreted the variation of the FD in the cortical surface of normal controls through multiple regression analysis with cortical thickness, sulcal depth, and folding area related to cortical complexity. We used a cortical surface showing a reliable representation of folded gyri and manually parcellated it into frontal, parietal, temporal, and occipital regions for regional analysis. In both hemispheres the mean cortical thickness and folding area showed significant combination effects on cortical complexity and accounted for about 50% of its variance. The folding area was significant in accounting for the FD of the cortical surface, with positive coefficients in both hemispheres and several lobe regions, while sulcal depth was significant only in the left temporal region. The results may suggest that human cortex develops a complex structure through the thinning of cortical thickness and by increasing the frequency of folds and the convolution of gyral shape rather than by deepening sulcal regions. Through correlation analysis of FD with IQ and the number of years of education, the results showed that a complex shape of the cortical surface has a significant relationship with intelligence and education. Our findings may indicate the structural characteristics that are revealed in the cerebral cortex when the FD in human brain is increased, and provide important information about brain development.

Adult↗

PubMed2006

Pilot study for assessing the behaviors of patients with schizophrenia towards a virtual avatar.

This study examined whether a virtual avatar could be perceived as a real human by patients with mental disease, especially schizophrenia, as well as whether a virtual avatar could be applied to acquiring patients' behavior characteristics in a short conversation situation. The virtual avatar has been used for various applications which need to communicate with other person or to train or educate by showing humanlike behavior. Recently, many researches have shown that the virtual avatar technology has been enhanced and the avatar could be perceived like real human. A virtual avatar, standing in a virtual room, was designed for this study. Tasks to approach, initiate a talk, and answer to avatar's questions was assigned to the 11 patients with schizophrenia. As behavioral parameters in the virtual environment, the interpersonal distance and the verbal response time were acquired. In addition, the Positive and Negative Syndrome Scale (PANSS) for patients was administered in order to investigate the relationship between patients' symptomatic characteristics and behavior parameters. The interpersonal distance was negatively correlated with the negative syndrome scale, a subscale of PANSS, which is consistent with previous research reporting the relationship between interpersonal distance and a real person's image. The verbal response time, however, was not correlated with any other subscale of PANSS. After analyzing subitems of the negative syndrome of PANSS, two positive correlations were found: one was with blunted affect and the other was with poor rapport. We concluded that the virtual avatar could be perceived as a real human by schizophrenic patients and the avatar could draw the schizophrenic patients' behavior characteristics.

Adult↗

PubMed2006

A proton MRSI study of brain N-acetylaspartate level after 12 weeks of citalopram treatment in drug-naive patients with obsessive-compulsive disorder.

OBJECTIVE: Reductions in the level of N-acetylaspartate within subcortical structures of patients with obsessive-compulsive disorder (OCD) have been reported in several studies. However, there have been, as yet, no reports regarding N-acetylaspartate levels in the prefrontal cortex of adult drug-naive OCD patients. The authors used proton magnetic resonance spectroscopic imaging ((1)H-MRSI) to investigate regional N-acetylaspartate level abnormalities and changes after 12 weeks of pharmacotherapy with citalopram in drug-naive OCD patients. METHOD: Thirteen drug-naive OCD patients and 13 age- and sex-matched healthy comparison subjects were included in this study. N-acetylaspartate levels (obtained from ratios of N-acetylaspartate with creatine, choline, and creatine plus choline) in the prefrontal cortex, parietal cortex, anterior cingulate, posterior cingulate, frontal white matter, and parietal white matter were measured by (1)H-MRSI. In OCD patients, measurements were taken before and after 12 weeks of citalopram treatment. Correlations between N-acetylaspartate concentrations in regions of interest and clinical measures were also assessed. RESULTS: Drug-naive OCD patients exhibited significantly lower N-acetylaspartate levels in the prefrontal cortex, frontal white matter, and anterior cingulate at baseline than did comparison subjects. Significant increases in N-acetylaspartate level were detected in the prefrontal cortex and frontal white matter in OCD patients after 12 weeks of citalopram treatment. CONCLUSIONS: These data suggest that reductions in neuronal viability occur in the frontal region of OCD patients and that these reductions may be partly reversible.

Adult↗

PubMed2006

Gelastic seizures involving the right parietal lobe.

Gelastic seizures have been described in various epilepsies arising from the temporal or frontal lobes, although the most commonly encountered form is related to the presence of an hypothalamic hamartoma. We report a patient with gelastic seizures involving the right parietal lobe. Our patient, a 32-year-old man, underwent video-EEG monitoring, interictal and ictal brain SPECTs during gelastic seizures. Subtraction ictal SPECT co-registered to MRI (SISCOM), was performed to localize any ictal hyperperfusion during these gelastic seizures. The seizures consisted of brief staring followed by smiling and laughing. Electroencephalography during the gelastic seizures showed rhythmic sharp waves in the right parietal lobe. SISCOM showed ictal hyperperfusion in the right parietal lobe and medial portions of right cerebellum. Our findings suggest that the right parietal lobe may actively participate in the particular epileptogenic network generating gelastic seizures.

Adult↗

PubMed2005

Surprising shrinkage of expanding gels under an external load.

Hydrogels are fascinating and useful in that they can show large volume changes in response to various stimuli, such as temperature or chemical environment. Here we report the peculiar observation that chemically crosslinked hydrogels that normally expand owing to a change in electrolyte pH can be made to shrink in certain circumstances. Specifically, these hydrogels contract when tested at a constant compressive force and subjected to a pH change that causes expansion in the absence of the applied load. When tested under tension, the gels always expand. Although the effects of external stress on the swelling of gels is known, the concomitant change in gel mechanical properties during pH switching was found to be a more dominant effect in our studies. However, existing mechanical models used to predict dimensional changes in actuator materials could not explain both the tensile and compression results. In addition, we show that the friction between metal plates of the apparatus and the gel is a key factor in explaining the contractile actuation under compressive loads. The observations reported in this paper are important for the successful design and use of hydrogel actuators in devices such as valves for microfluidics.

Cross-Linking Reagents↗

PubMed2005

Representative brain selection using a group-specific tissue probability map.

PURPOSE: To determine the anatomy of a standard brain reflecting well-defined group characteristics based on probabilistic information from group-specific anatomical variations. MATERIALS AND METHODS: 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. RESULTS: This method showed highly correlated result with previous method by Kochunov et al., with fewer computational tasks. CONCLUSION: This method can thus be used to determine an appropriate standard model to compare with disease-affected brains.

Adult↗

PubMed2005

Automated 3-D extraction and evaluation of the inner and outer cortical surfaces using a Laplacian map and partial volume effect classification.

Accurate reconstruction of the inner and outer cortical surfaces of the human cerebrum is a critical objective for a wide variety of neuroimaging analysis purposes, including visualization, morphometry, and brain mapping. The Anatomic Segmentation using Proximity (ASP) algorithm, previously developed by our group, provides a topology-preserving cortical surface deformation method that has been extensively used for the aforementioned purposes. However, constraints in the algorithm to ensure topology preservation occasionally produce incorrect thickness measurements due to a restriction in the range of allowable distances between the gray and white matter surfaces. This problem is particularly prominent in pediatric brain images with tightly folded gyri. This paper presents a novel method for improving the conventional ASP algorithm by making use of partial volume information through probabilistic classification in order to allow for topology preservation across a less restricted range of cortical thickness values. The new algorithm also corrects the classification of the insular cortex by masking out subcortical tissues. For 70 pediatric brains, validation experiments for the modified algorithm, Constrained Laplacian ASP (CLASP), were performed by three methods: (i) volume matching between surface-masked gray matter (GM) and conventional tissue-classified GM, (ii) surface matching between simulated and CLASP-extracted surfaces, and (iii) repeatability of the surface reconstruction among 16 MRI scans of the same subject. In the volume-based evaluation, the volume enclosed by the CLASP WM and GM surfaces matched the classified GM volume 13% more accurately than using conventional ASP. In the surface-based evaluation, using synthesized thick cortex, the average difference between simulated and extracted surfaces was 4.6 +/- 1.4 mm for conventional ASP and 0.5 +/- 0.4 mm for CLASP. In a repeatability study, CLASP produced a 30% lower RMS error for the GM surface and a 8% lower RMS error for the WM surface compared with ASP.

Algorithms↗

PubMed2005

Sex differences in the human corpus callosum: diffusion tensor imaging study.

In order to assess underlying structural differences between the male and female corpus callosum, the fractional anisotropy and volume of the corpus callosum, and also its T1 signal intensity, were measured. The corpus callosum of the 15 normal women and 15 normal men was drawn on the mid-sagittal T1-weighted image, for determining its volume and signal intensity, and this region of interest was projected onto the coregistered fractional anisotropy image, in order to obtain the value for the corpus callosum. We found increased T1 signal intensity and decreased fractional anisotropy in the female corpus callosum, as compared with that of the male. Despite the long-standing debates, the corpus callosum remains a region of sex differences.

Adult↗

PubMed2005

Quantitative analysis of group-specific brain tissue probability map for schizophrenic patients.

We developed group-specific tissue probability map (TPM) for gray matter (GM), white matter (WM) and cerebrospinal fluid (CSF) on the common spatial coordinates of an averaged brain atlas derived from normal controls (NC) and from schizophrenic patients (SZ). To identify differences in group-specific TPMs, we used quantitative evaluation methods based on differences in probabilistic distribution as a global criterion, and the mean probability and the similarity index (SI) by lobe as regional criteria. The SZ group showed more spatial variation with a lower mean probability than NC subjects. And, for the right temporal and left parietal lobes, the SI between each group was lower than the other lobes. It can be said that there were significant differences in spatial distribution between controls and schizophrenic patients at those areas. In case of female group, although group differences in the volumes of GM and WM were not significant, global difference in the probabilistic distribution of GM was more prominent and the SI was lower and its descent rate was greater in all lobes, compared with the male group. If these morphological differences caused by disease or group-specific features were not considered in TPM, the accuracy and certainty of specific group studies would be greatly reduced. Therefore, suitable TPM is required as a common framework for functional neuroimaging studies and an a priori knowledge of tissue classification.

Adult↗