Biomedical subjects

Sun I Kim

Publications and source records attributed to Sun I Kim.

At least 37 records · Page 2Linked to original sources

PubMed2005

Asymmetry analysis of deformable hippocampal model using the principal component in schizophrenia.

The hippocampus is thought to play an important role in learning and memory processing, and impairments in memory, attention, and decision making are found commonly in schizophrenia. Although many studies have reported decreases in hippocampal volume in the left hemisphere in schizophrenia, regionally specific hippocampal volume loss has not been revealed consistently using volume analysis. Recently, many studies have analyzed shape asymmetry using 3-D models; however, inconsistent results have been reported, mainly due to methodologic differences. We therefore used an active, flexible, deformable shape model for surface parameterization, and compared shape asymmetry based on principal component analysis (PCA) in the hippocampi of schizophrenic patients with those of the normal controls. Although the overall pattern of the statistical results did not change according to the number of principal components, the reconstructed results based on six major components were much more distinguishable. Although the left hemispheric hippocampal volume was larger than the right hemispheric was in this study, the difference was not significant. In shape asymmetry analysis, the right hemisphere hippocampus was bilaterally larger than the left hemisphere hippocampus was in the head of the superior CA1 and smaller in the tail and head of the inferior CA1. The asymmetry in the schizophrenia group was statistically smaller than that in the control group through reduction of the left hemisphere hippocampus volume.

Adult↗

PubMed2005

Interindividual reproducibility of glutamate quantification using 1.5-T proton magnetic resonance spectroscopy.

The goal of this study was to measure the interindividual reproducibility of glutamate quantification in 1.5-T (1)H MRS of human brains. To determine the effective echo time (TE) for glutamate quantification, spectra from a phantom and 12 participants were obtained with TE = 30, 35, 40, and 144 ms (repetition time (TR) = 2000 ms and volume of interest = 4 cm(3)). The average Cramer-Rao lower bounds for glutamate quantification using LCModel was lowest in two experiments when TE = 40 ms.Twenty-one subjects participated in experiments that measured interindividual reproducibility of glutamate quantification. Spectra were acquired with TR = 6000 ms and TE = 40 ms. Results showed that the coefficients of variance were 11.0 and 13.1% in the anterior cingulate cortex and insula, respectively. This suggests that glutamate can be reproducibly measured from 1.5-T (1)H MRS with long TR, effective TE, and the LCModel.

Adult↗

PubMed2005

Mechanisms of virtual reality exposure therapy: the role of the behavioral activation and behavioral inhibition systems.

J. A. Gray's (1975) theory distinguishes between two motivational systems, which he refers to as the behavioral activation system (BAS) and the behavioral inhibition system (BIS). D. C. Fowles (1980) has shown that heart rate responses reflect activity of the BAS, and electrodermal responses reflect activity of the BIS. Both BAS and BIS are reliably activated during in-vivo exposure to fearful situations (F. H. Wilhelm & W. T. Roth, 1998). However, due to the constraints imposed by virtual reality (VR), we hypothesized that VR exposure to fearful situations would activate the BIS alone. To test this hypothesis, a VR free-standing elevator simulation was presented to participants selected for high and low fear of heights. As predicted, the high-anxious group strongly responded electrodermally (effect size d = 1.53), but showed only minimal HR elevations during exposure (d = 0.12), and little other cardiovascular or respiratory changes. The low-anxious control group showed little electrodermal and HR reactivity (d = 0.28 and 0.12). A comparison with data from a previous study demonstrated that this pattern was in stark contrast to the large electrodermal and cardiovascular response observed during situational in-vivo exposure outside the laboratory. We conclude that the BIS, but not BAS, is selectively activated during VR exposure, causing discordance between self-report and commonly used physiological measures of anxiety. Results are discussed within the framework of E. B. Foa & M. J. Kozak's (1986) emotional processing theory of fear modification, suggesting different mechanisms underlying VR and in-vivo exposure treatments.

Adolescent↗

PubMed2005

Experimental results of affective valence and arousal to avatar's facial expressions.

The objectives of this study were to propose a method of presenting dynamic facial expressions to experimental subjects, in order to investigate human perception of avatar's facial expressions of different levels of emotional intensity. The investigation concerned how perception varies according to the strength of facial expression, as well as according to an avatar's gender. To accomplish these goals, we generated a male and a female virtual avatar with five levels of intensity of happiness and anger using a morphing technique. We then recruited 16 normal healthy subjects and measured each subject's emotional reaction by scoring affective arousal and valence after showing them the avatar's face. Through this study, we were able to investigate human perceptual characteristics evoked by male and female avatars' graduated facial expressions of happiness and anger. In addition, we were able to identify that a virtual avatar's facial expression could affect human emotion in different ways according to the avatar's gender and the intensity of its facial expressions. However, we could also see that virtual faces have some limitations because they are not real, so subjects recognized the expressions well, but were not influenced to the same extent. Although a virtual avatar has some limitations in conveying its emotion using facial expressions, this study is significant in that it shows that a new potential exists to use or manipulate emotional intensity by controlling a virtual avatar's facial expression linearly using a morphing technique. Therefore, it is predicted that this technique may be used for assessing emotional characteristics of humans, and may be of particular benefit for work with people with emotional disorders through a presentation of dynamic expression of various emotional intensities.

Adult↗

PubMed2005

Virtually driving: are the driving environments "real enough" for exposure therapy with accident victims? An explorative study.

There is a small but growing body of research supporting the effectiveness of computer-generated environments in exposure therapy for driving phobia. However, research also suggests that difficulties can readily arise whereby patients do not immerse in simulated driving scenes. The simulated driving environments are not "real enough" to undertake exposure therapy. This sets a limitation to the use of virtual reality (VR) exposure therapy as a treatment modality for driving phobia. The aim of this study was to investigate if a clinically acceptable immersion/presence rate of >80% could be achieved for driving phobia subjects in computer generated environments by modifying external factors in the driving environment. Eleven patients referred from the Accident and Emergency Department of a general hospital or from their General Practitioner following a motor vehicle accident, who met DSM-IV criteria for Specific Phobia-driving were exposed to a computer-generated driving environment using computer driving games (London Racer/Midtown Madness). In an attempt to make the driving environments "real enough," external factors were modified by (a) projection of images onto a large screen, (b) viewing the scene through a windscreen, (c) using car seats for both driver and passenger, and (d) increasing vibration sense through use of more powerful subwoofers. Patients undertook a trial session involving driving through computer environments with graded risk of an accident. "Immersion/presence" was operationally defined as a subjective rating by the subject that the environment "feels real," together with an increase in subjective units of distress (SUD) ratings of >3 and/or an increase of heart rate of >15 beats per minute (BPM). Ten of 11 (91%) of the driving phobic subjects met the criteria for immersion/presence in the driving environment enabling progression to VR exposure therapy. These provisional findings suggest that the paradigm adopted in this study might be an effective and relatively inexpensive means of developing driving environments "real enough," to make VR exposure therapy a viable treatment modality for driving phobia following a motor vehicle accident (MVA).

Accidents, Traffic↗

PubMed2005

Development of Korean standard brain templates.

We developed age, gender and ethnic specific brain templates based on MR and Positron-Emission Tomography (PET) images of Korean normal volunteers. Seventy-eight normal right-handed volunteers (M/F=49/29) underwent 3D T1-weighted SPGR MR and F-18-FDG PET scans. For the generation of standard templates, an optimal target brain that has the average global hemispheric shape was selected for each gender. MR images were then spatially normalized by linear transformation to the target brains, and normalization parameters were reapplied to PET images. Subjects were subdivided into 2 groups for each gender: the young/midlife (<55 yr) and the elderly groups. Young and elderly MRI/PET templates were composed by averaging the spatially normalized images. Korean templates showed different shapes and sizes (mean length, width, and height of the brains were 16.5, 14.3 and 12.1 cm for man, and 15.6, 13.5 and 11.4 cm for woman) from the template based on Caucasian (18.3, 14.2, and 13.3 cm). MRI and PET templates developed in this study will provide the framework for more accurate stereotactic standardization and anatomical localization.

Adolescent↗

PubMed2004

Gray matter abnormalities in paranoid schizophrenia and their clinical correlations.

Numerous imaging studies have shown structural brain abnormalities in schizophrenia. Recently, voxel-based morphometry enabled whole brain analysis beyond the regions of interest (ROI). Regional gray matter concentrations of magnetic resonance (MR) images from 35 patients with paranoid schizophrenia were compared with those from 35 age- and sex-matched controls, and their clinical correlations were explored using voxel-based morphometry. Gray matter concentrations in the patients were significantly reduced in the left insular and dorsolateral prefrontal regions, and bilaterally in the medial frontal, anterior cingulate, inferior frontal and superior temporal regions. On the other hand, gray matter concentrations in the bilateral cerebellum and right striatum were significantly increased in the patients compared with controls. A negative correlation between the score for the severity of 'lack of insight and judgment' and gray matter concentrations in the left posterior and right anterior cingulate and bilateral inferior temporal regions including the lateral fusiform gyri was found. These results suggest the important roles of the paralimbic structures in the pathophysiology of schizophrenia and the involvement of the perceptual and monitoring systems in the mechanism of insight.

Adult↗

PubMed2004

Recurrence quantification analysis of sleep electoencephalogram in sleep apnea syndrome in humans.

The aim of this study is to elucidate whether the results of recurrence quantification analysis (RQA) of sleep EEGs in sleep apnea syndrome are valuable for analyzing sleep EEGs in sleep apnea syndrome. We investigated the ability of RQA to discriminate sleep stages and to characterize the different behaviors of sleep EEGs in sleep apnea syndrome. RQA was applied to EEG signals during sleep stages 1, 2, slow wave sleep (SWS), REM and the stage 'awake.' The sleep EEG signals were obtained from the MIT-BIH polysomnographic database. To examine the differences in the RQA measures for all sleep stages, one-way analysis of variance (ANOVA) and post hoc analysis were performed. From the results, all sleep stages could be distinctly discriminated by means of the RQA measure of %RATIO. We observed that stage 1 and REM had fewer recurrences, and that stage 2 was more autocorrelated than the other stages. The different dynamic behaviors of wakefulness and sleep EEG were also observed. Of significant interest was the observation that RQA was able to distinguish stage 1 from REM. In conclusion, we suggest that the information obtained from RQA of sleep EEGs in sleep apnea syndrome is valuable for its analysis, and that RQA constitutes a useful tool for analyzing sleep EEGs in subjects with sleep apnea syndrome.

Computing Methodologies↗

PubMed2004

Electrical behavior of polymer hydrogel composed of poly(vinyl alcohol)-hyaluronic acid in solution.

Interpenetrating polymer networks (IPN), as polymer hydrogels composed of poly(vinyl alcohol) (PVA) and hyaluronic acid (HA), which exhibited electrical sensitive behavior were prepared. The swelling behavior of the IPN/HA IPN was studied by immersing the gel in various concentrations of aqueous NaCl solutions and various pH buffer solutions. The response of the PVA/HA IPN to electric fields stimuli was also investigated. When swollen IPN was placed between a pair of electrodes, and an electric field applied, it exhibited bending behavior. The PVA/HA IPN also displayed stepwise bending behavior, depending on the magnitude of the electric stimulus. Also, for use in biosensors application, their bending behavior was studied in Hank's solution at pH 7.4.

Biocompatible Materials↗

PubMed2004

Validation of automatically measured monophasic action potential recordings.

This study devised an automatic monophasic action potential (MAP) measurement program, and compared the computer-measured MAP durations with those measured manually by two independent observers in order to facilitate the analysis of MAP data obtained during a clinical electrophysiology study. The results were compared at various cycle lengths and during pharmacologic or physiologic interventions. This program identified the onset, plateau, and baseline accurately using the MAP data. The automatically measured MAP durations at the 90% repolarization level (MAPd) strongly correlated with those measured manually (r = 0.99). The MAPd shortened in parallel as the pacing cycle length was progressively shortened from 800 to 600, 400 and 300 ms.

Action Potentials↗

PubMed2004

Nonlinear-analysis of human sleep EEG using detrended fluctuation analysis.

Quantification of the fractal scaling properties of human sleep EEG dynamics was sought and each normal sleep stage was compared with that of sleep apnea. The fractal scaling exponents that quantify power-law correlations were computed using detrended fluctuation analysis. Six healthy subjects, aged 30-35 years, participated and six recordings of the apnea were acquired from MIT/BIH polysomnography database. The data were 8-h baseline recordings (23:00-07:00 h). The EEG signals from the C4-A1 derivation were acquired with a resolution of 250 Hz. The sleep stages were visually scored for 30 s epochs, according to the criteria of Rechtschaffen and Kales. The mean scaling exponents increased from the awake stage to stages 1, 2 and 3-4, but decreased during rapid eye movement (REM) sleep. The scaling exponents of the apnea were lower than those of the healthy subject for all the stages. The scaling exponents could be attributed to the fractal nature of EEG, which would be more appropriate for describing the complexity of EEG due to its assumption of non-stationarity.

Adult↗

PubMed2004

Deformable model with surface registration for hippocampal shape deformity analysis in schizophrenia.

Changes to the hippocampal structure have been reported as consistent structural abnormalities in schizophrenic patients and have been related to the learning and memory deficits in such patients. Although many magnetic resonance (MR) imaging studies have focused on the hippocampal volume, local structural changes were difficult to discriminate from normal neuroanatomical variations. 3D shape deformation analysis of the brain structure may reflect localized schizophrenic abnormalities. A deformable model, evolved from the ellipsoid to hippocampal surface, with 2562 vertexes, was developed to analyze the left and right hippocampus shapes in 22 schizophrenic patients and 22 healthy age and gender matched controls. One of the most critical issues in the shape analysis is the determination of homologous points between two objects. To determine more accurate corresponding points, an alignment procedure, consisting of coarse and fine steps, following a deformation process, was applied. The performance of the alignment process was tested using artificial data, to get the alignment error to within 3 degrees for each angle. A volume analysis indicated the hippocampal volume to be bilaterally reduced in schizophrenic patients compared to the normal controls, with a shape analysis showing a deformity pattern of the hippocampal surface. Bilateral inward deformities in the anterior and posterior hippocampus and a unilateral outward deformity in the right anterior hippocampus were observed, respectively.

Adult↗

PubMed2004

Neurofeedback training with virtual reality for inattention and impulsiveness.

In this research, the effectiveness of neurofeedback, along with virtual reality (VR), in reducing the level of inattention and impulsiveness was investigated. Twenty-eight male participants, aged 14-18, with social problems, took part in this study. They were separated into three groups: a control group, a VR group, and a non-VR group. The VR and non-VR groups underwent eight sessions of neurofeedback training over 2 weeks, while the control group just waited during the same period. The VR group used a head-mounted display (HMD) and a head tracker, which let them look around the virtual world. Conversely, the non-VR group used only a computer monitor with a fixed viewpoint. All participants performed a continuous performance task (CPT) before and after the complete training session. The results showed that both the VR and non-VR groups achieved better scores in the CPT after the training session, while the control group showed no significant difference. Compared with the other groups, the VR group presented a tendency to get better results, suggesting that immersive VR is applicable to neurofeedback for the rehabilitation of inattention and impulsiveness.

Adolescent↗

PubMed2004

Nicotine craving and cue exposure therapy by using virtual environments.

Smokers who are exposed to cues associated with smoking show cardiovascular reactivity and an increase in smoking urges as compared to when they are presented with neutral cues. Cue exposure therapy (CET), which refers to the repeated exposure to drug-related cues in order to extinguish this learned association, has increasingly been proposed as a potential treatment of addictive behaviors, including tobacco smoking. The result of our pilot study suggests that a cue elicited using a virtual environment (VE) is more effective than other cue exposure devices. The VE was composed of craving environments (virtual bar) and objects (an alcoholic drink, a packet of cigarettes, a lighter, an ashtray, a glass of beer, and advertising posters) that are likely to trigger craving, a smoking avatar, and an audio environment that included the noisy sound and music of a restaurant. Sixteen late-adolescent males who smoked at least 10 cigarettes a day were recruited to participate in the VE-CET study. The CET virtual bar program consisted of six sessions, and the participants were exposed repeatedly to each session using different questions and procedures. Although the effects of CET did not yield significant reductions in all of the dependent variables, the craving for cigarettes was gradually decreased during the course of the sessions. This tendency was closely related to the reduction in the smoking count between the morning before the experiment and the start of the experiment. Based on these preliminary results, it appears that VE-CET maybe a useful tool to use in treatment programs to help reduce craving in those who are nicotine dependent.

Adolescent↗

PubMed2004

A virtual reality assessment and training system for unilateral neglect.

Patients with unilateral neglect have problems reporting, responding, or orienting to novel or meaningful stimuli that is presented to the side opposite to that of a brain lesion. This creates a serous problem in regards to daily living activities. However, the established methods for assessing and training of unilateral neglect patients have several deficits. Recently, virtual reality (VR) technologies have been used as an assessment and treatment tool for rehabilitation. Hence, this study designed a VR system to assess and train unilateral neglect patients. In addition, the suitability and feasibility of our VR system for unilateral neglect patients was verified.

Activities of Daily Living↗

PubMed2004

Analysis of the hemispheric asymmetry using fractal dimension of a skeletonized cerebral surface.

We investigated hemispheric asymmetry using the fractal dimension (FD) of the skeletonized cerebral surface. Sixty-two T1-weighted magnetic resonance imaging volumes from normal Korean adults were used. The skeletonization of binary volume data, which corresponded to the union of the gray matter and cerebrospinal flow classified by fuzzy clustering, was performed slice by slice in the sagittal direction, and then skeletonized slices were integrated into the three-dimensional (3-D) hemisphere. Finally, the FD of the 3-D skeletonized cerebral surface was calculated using the box-counting method. We measured the FD of the skeletonized cerebral surface and the volumes of intracranial gray matter and white matter for the whole hemispheres and obtained the hemispheric asymmetries of each measurement. The FD, the gray matter, and the white matter volumes for the whole hemispheres decreased in the old group. The asymmetry of the FD revealed a significant right-greater-than-left asymmetry showed rightward, but did not change according to age and gender. None of the intracranial gray matter or white matter volumes showed any significant asymmetric changes. It could be said that the FD of the skeletonized cerebral surface is a novel measure of cerebral asymmetry.

Adolescent↗

PubMed2004

The development of a VR system for the cognitive & behavioral assessment of schizophrenia.

Patients with schizophrenia have many trouble in their life due to their thinking disorders such as delusion or hallucination. It is because they have a deficit in the ability which to systematize and integrate information. Therefore, they cannot integrate or systematize properly the integrated stimuli occurring frequently in a real situation. In this study, we suggest a virtual reality system for the assessment of their ability to integrate, memorize and react to integrated stimuli. The virtual reality system we developed provided multimodal stimuli, such as visual and auditory stimuli or visuo-spatial integration, and the patients was assessed and compared their thought flexibility and working memory abilities based on multi-modal manner by making the patient experience and react to multimodal stimuli. From this study, we could conclude that the VR could provide a patient with various stimuli in an immersive environment and allow the assessment of cognitive ability, and the identification of the relationships between cognitive functions.

Case-Control Studies↗

PubMed2003

Morphometric abnormality of the insula in schizophrenia: a comparison with obsessive-compulsive disorder and normal control using MRI.

The insula is increasingly the subject of great interest in psychiatric disorders of neurodevelopmental origin because of its anatomical location, wide interconnectivity, and variety of functions. This study explores the possible morphometric change of the insula in schizophrenia and obsessive-compulsive disorder (OCD), and its potential relationship to clinical symptoms. The insula was traced on all coronal slices of magnetic resonance images of three age- and sex-matched diagnostic groups, which consisted of 21 patients with schizophrenia, 21 patients with OCD and 21 normal volunteers. The volumetric measures of the insula were compared among the three groups, and their relationships to the symptom severity were investigated. Volumetric reduction of the left insula was observed in the schizophrenia group, but not in the OCD group. These results confirm the involvement of deficient insular function in the pathophysiology of schizophrenia.

Adult↗