Biomedical subjects

Won-Jin Moon

Publications and source records attributed to Won-Jin Moon.

10 recordsLinked to original sources

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

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

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↗

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

Diffusion abnormality of deep gray matter in external capsular hemorrhage.

BACKGROUND AND PURPOSE: To our knowledge, diffusion abnormality of the unaffected deep gray matter during striatocapsular hemorrhage has not been previously described in the literature. We report the presence of the diffusion abnormality separated from hematoma in patients with external capsular (lateral striatocapsular) hemorrhage and suggest the plausible mechanisms of diffusion signal intensity change. METHODS: We retrospectively reviewed MR images in 28 consecutive patients with spontaneous striatocapsular hemorrhage and evaluated signal intensity changes at sites separated from the hemorrhage and the lesions on diffusion-weighted (DW) images. Apparent diffusion coefficients (ADCs) of the lesions were measured, and volume changes in the deep gray matter were assessed at follow-up. RESULTS: On DW images, hyperintensity of deep gray matter was found in nine patients (25%). In all patients with DW imaging abnormality, the hemorrhage was located in the external capsule, and the interval from hemorrhagic ictus to MR imaging study was 8-54 days. Hyperintensity of the deep gray matter was seen in the caudate (n = 8), putamen (n = 7), thalamus (n = 5), and substantia nigra (n = 2). Mean relative ADC ratios of the diffusion abnormality were 0.76 +/- 0.10 in the caudate, 0.79 +/- 0.07 in the putamen, and 0.85 +/- 0.11 in the thalamus. DW imaging abnormality disappeared with mild atrophy in two patients who underwent follow-up imaging. CONCLUSION: External capsular hemorrhage may be uncommonly accompanied by diffusion abnormality in the striatum or thalamus at follow-up, and the lesion should not be misdiagnosed as new-onset infarction. Secondary neuronal degeneration may play an important role in the development of diffusion abnormality.

Adolescent↗

PubMed2005

Prospective analysis of cerebral infarction after carotid endarterectomy and carotid artery stent placement by using diffusion-weighted imaging.

BACKGROUND AND PURPOSE: Small emboli arising from a friable plaque during carotid endarterectomy (CEA) and carotid artery stent placement (CAS) constitute a potentially important cause of periprocedural ischemic complications. To evaluate the frequency and significance of cerebral ischemic lesions of embolic origin after CEA and CAS, we examined patients with moderate to severe carotid stenosis by using diffusion-weighted (DW) imaging. METHODS: Twenty-four patients undergoing 26 CEAs and 20 patients undergoing 22 CAS were prospectively studied with pre- and post-treatment DW imaging of the brain within 7 days (mean, 2.3 days) before and within 7 days (mean, 3.2 days) after treatment. DW images were analyzed by two neuroradiologists blinded to the clinical results after CEA and CAS. Any new hyperintense lesion on DW image was interpreted as a post-treatment ischemic lesion. We compared post-treatment ischemic lesions with change in neurologic status, presence of plaque ulcerations, and severity of stenosis and compared the frequency of overall post-treatment complications between the two procedures. RESULTS: In 25 (96%) of 26 CEAs, post-operative brain DW images were unchanged. In one patient (4%), a new single asymptomatic hyperintensity was observed in the striatocapsule on the surgical side. In 14 (64%) of 22 CAS procedures, post-operative brain DW images were unchanged. In eight CAS cases (36%), new hyperintensities were seen on DW images. Among them, two were symptomatic with a major neurologic deficit lasting more than 7 days. Post-treatment brain or retinal major stroke rates were 4% (n = 1) for CEA and 14% (n = 3) for CAS. Overall symptomatic complication rates were 19.2% and 13.6%, respectively. CONCLUSION: Rate of ischemic brain lesions was significantly lower after CEA than after CAS, although most of these brain lesions were silent. Also, CEA is a safer procedure carrying a lower risk of post-operative cerebral ischemia. CAS, however, may be a comparable procedure considering the total complication rate and can be a more reliable procedure with advances in neuroprotective means.

Adult↗

PubMed2004

Microstructure of metal-filled carbon nanotubes.

Catalysts are usually required to produce carbon nanotubes (CNTs) and play important roles during the growth process. Any catalysts that remain after processing are expected to add extra properties and removal of the catalysts is usually required to achieve the original properties of CNTs. Recently, CNTs have been filled incidentally by catalysts, such as Pb, Sn, Ni and Bi. This has led to success in obtaining additional properties and a few models have been proposed to describe the encapsulating mechanisms. In the present study, CNTs were filled with palladium by a microwave plasma-assisted chemical vapor deposition method. Detailed structural and compositional investigations of these metal-filled CNTs were carried out by transmission electron microscopy to elucidate the growth mechanisms.

Journal Article↗

PubMedDate not supplied

Orbital lymphoma and subacute or chronic inflammatory pseudotumor: differentiation with two-phase helical computed tomography.

OBJECTIVE: The differentiation between orbital lymphoma and subacute or chronic inflammatory pseudotumor (SCIPT) may be difficult clinically and radiologically. The aim of this study was to evaluate the enhancement characteristics of orbital lymphoma and SCIPT with two-phase helical computed tomography (CT) and delayed coronal CT and to determine whether attenuation measurements on CT can be used to differentiate between the 2 diseases. METHODS: Nineteen histopathologically proven orbital lymphomas and 9 SCIPTs were examined with two-phase helical CT. After injecting 90 mL contrast material at a rate of 3 mL/s, early- and late-phase axial CT scans were obtained with scanning delays of 30 and 90 seconds, respectively. Delayed coronal scans were obtained with delays of 4-9 minutes. Attenuation of the lesions at each phase was measured quantitatively. Relative percentages of contrast enhancement (CE) were calculated to determine the cutoff value for differentiating SCIPT from lymphoma. RESULTS: The CT attenuation change over time was significantly different between orbital lymphoma and SCIPT (P < 0.05). Increased CT attenuation between early- and late-phase axial scans was seen in 42% (n = 8) of lymphoma cases, and decreased CT attenuation was seen in 58% (n = 11). In 17 lymphomas (90%), the CT attenuation decreased between late-phase axial and delayed coronal scans. Conversely, in 7 SCIPTs (78%), the CT attenuation increased gradually over time from early-phase axial to delayed coronal scans. The relative percentage of CE at the delayed coronal scan had a cutoff value of -6.97%, a sensitivity of 84%, and a specificity of 100%. CONCLUSION: Different characteristics of attenuation change on two-phase helical CT and delayed coronal CT can be helpful in differentiating between orbital lymphoma and SCIPT.

Adult↗

PubMedDate not supplied

Multiphasic perfusion CT in acute middle cerebral artery ischemic stroke: prediction of final infarct volume and correlation with clinical outcome.

OBJECTIVE: To assess the utility of multiphasic perfusion CT in the prediction of final infarct volume, and the relationship between lesion volume revealed by CT imaging and clinical outcome in acute ischemic stroke patients who have not undergone thrombolytic therapy. MATERIALS AND METHODS: Thirty-five patients underwent multiphasic perfusion CT within six hours of stroke onset. After baseline unenhanced helical CT scanning, contrast-enhanced CT scans were obtained 20, 34, 48, and 62 secs after the injection of 90 mL contrast medium at a rate of 3 mL/sec. CT peak and total perfusion maps were obtained from serial CT images, and the initial lesion volumes revealed by CT were compared with final infarct volumes and clinical scores. RESULTS: Overall, the lesion volumes seen on CT peak perfusion maps correlated most strongly with final infarct volumes (R(2)=0.819, p<0.001, slope of regression line=1.016), but individual data showed that they were less than final infarct volume in 31.4% of patients. In those who showed early clinical improvement (n=6), final infarct volume tended to be overestimated by CT peak perfusion mapping and only on total perfusion maps was there significant correlation between lesion volume and final infarct volume (R(2)=0.854, p=0.008). The lesion volumes depicted by CT maps showed moderate correlation with baseline clinical scores and clinical outcomes (R=0.445-0.706, p< or = 0.007). CONCLUSION: CT peak perfusion maps demonstrate strong correlation between lesion volume and final infarct volume, and accurately predict final infarct volume in about two-thirds of the 35 patients. The lesion volume seen on CT maps shows moderate correlation with clinical outcome.

Acute Disease↗

PubMedDate not supplied

Assessment of tissue viability using diffusion- and perfusion-weighted MRI in hyperacute stroke.

OBJECTIVE: The aim of this study was to investigate the relationship between the diffusion and perfusion parameters in hyperacute infarction, and we wanted to determine the viability threshold for the ischemic penumbra using diffusion- and perfusion-weighted imaging (DWI and PWI, respectively). MATERIALS AND METHODS: Both DWI and PWI were performed within six hours from the onset of symptoms for 12 patients who had suffered from acute stroke. Three regions of interest (ROIs) were identified: ROI 1 was the initial lesion on DWI; ROI 2 was the DWI/PWI mismatch area (the penumbra) that progressed onward to the infarct; and ROI 3 was the mismatch area that recovered to normal on the follow-up scans. The ratios of apparent diffusion coefficient (ADC), the relative cerebral blood volume (rCBV), and the time to peak (TTP) were calculated as the lesions' ROIs divided by the contralateral mirror ROIs, and these values were then correlated with each other. The viability threshold was determined by using the receiver operating characteristic (ROC) curves. RESULTS: For all three ROIs, the ADC ratios had significant linear correlation with the TTP ratios (p < 0.001), but not with the rCBV ratios (p = 0.280). There was no significant difference for the ADC and rCBV ratios within the ROIs. The mean TTP ratio/TTP delay between the penumbras' two ROIs showed a significant statistical difference (p < 0.001). The cutoff value between ROI 2 and ROI 3, as the viability threshold, was a TTP ratio of 1.29 (with a sensitivity and specificity of 86% and 73%, respectively) and a TTP delay of 7.8 sec (with a sensitivity and specificity of 84% and 72%, respectively). CONCLUSION: Determining the viability thresholds for the TTP ratio/delay on the PWI may be helpful for selecting those patients who would benefit from the various therapeutic interventions that can be used during the acute phase of ischemic stroke.

Acute Disease↗