Young-Don Son

Super-resolution track-density imaging of thalamic substructures: Comparison with high-resolution anatomical magnetic resonance imaging at 7.0T

The thalamus is one of the most important brain structures, with strong connections between subcortical and cortical areas of the brain. Most of the incoming information to the cortex passes through the thalamus. Accurate identification of substructures of the thalamus is therefore of great importance for the understanding of human brain connectivity. Direct visualization of thalamic substructures, however, is not easily achieved with currently available magnetic resonance imaging (MRI), including ultra‐high field MRI such as 7.0T, mainly due to the limited contrast between the relevant structures. Recently, improvements in ultra‐high field 7.0T MRI have opened the possibility of observing thalamic substructures by well‐adjusted high‐resolution T1‐weighted imaging. Moreover, the recently developed super‐resolution track‐density imaging (TDI) technique, based on results from whole‐brain fiber‐tracking, produces images with sub‐millimeter resolution. These two methods enable us to show markedly improved anatomical detail of the substructures of the thalamus, including their detailed locations and directionality. In this study, we demonstrate the role of TDI for the visualization of the substructures of the thalamic nuclei, and relate these images to T1‐weighted imaging at 7.0T MRI. Hum Brain Mapp 34:2538–2548, 2013.

Observation of Glucose Metabolism in the Thalamic Nuclei by Fusion PET/MRI

The anatomy of the thalamus and its connectivity with surrounding areas are known. Localized metabolic activities at the thalamic substructural level have not been measured in vivo in human brains because of limited resolution and contrast. Methods: The energy metabolism and fine anatomic structures of the thalamus were measured simultaneously in 5 healthy subjects using a PET/MRI fusion imaging system. Measured metabolism in individual thalamic nuclei was quantified by corresponding PET/MRI images. Results: Substructures of the thalamus were clearly distinguished in 7.0-T MRI images, and the corresponding metabolic activities measured by PET were integrated by the PET/MRI system. The medial dorsal thalamic nucleus consistently showed the highest glucose uptake among the thalamic nuclei. Conclusion: These results demonstrate that substructure-specific metabolic activities in the thalamus can be measured with a PET/MRI system consisting of an ultra-high-resolution PET component and an ultra-high-field MRI component.

Association of harm avoidance with dopamine D2/3 receptor availability in striatal subdivisions: a high resolution PET study.

We examined the relationship between the personality trait of harm avoidance (HA) and the dopamine D(2/3) receptor availability in striatal subdivisions using high resolution positron emission tomography (PET) with [(11)C]raclopride. Twenty-one healthy subjects completed 3T magnetic resonance imaging and high resolution PET scans with [(11)C]raclopride in order to measure D(2/3) receptor availability in subregions of the striatum. The D(2/3) receptor availability was obtained on the basis of the Logan graphical method. The Temperament and Character Inventory was used to measure the biogenetic temperament of HA. The analysis revealed that the HA score had significant negative correlations with D(2/3) receptor availability in the pre-commissural dorsal caudate and post-commissural putamen, suggesting that HA is associated with D(2/3) receptor availability in the associative and sensorimotor subdivisions of the striatum, which are mainly involved in cognition and locomotion. Further research is required to determine if pathological states have similar dopaminergic mechanisms in specific striatal subdivisions.

Substructural Hippocampal Glucose Metabolism Observed on PET/MRI

The hippocampus is one of the best-known neural structures in the brain and has been of interest in observing the substructures and their metabolic functions. However, it has been difficult to distinguish its substructures and functions in vivo because of its small size. Methods: 18F-FDG PET and high-resolution MRI of the hippocampus were performed on 5 healthy subjects using a PET/MRI system. The metabolism of each hippocampal substructure was measured in vivo on the basis of the MR images. Results: The dentate gyrus and cornu ammonis 4 showed the highest glucose uptake in the healthy subjects. Conclusion: Measuring glucose metabolism in the substructures of the hippocampus could provide a new tool for the future investigation of related brain diseases or functional studies, such as Alzheimer disease or memory and learning studies.

Effects of age on dopamine D2 receptor availability in striatal subdivisions: a high-resolution positron emission tomography study.

The purpose of the present study was to examine the relationship between age and dopamine D(2) receptor availability in striatal subdivisions of young and middle-aged healthy subjects using high-resolution positron emission tomography (PET) with [(11)C]raclopride to better characterize the nature of age-related decrements in striatal D(2) receptor availability. Twenty-four healthy volunteers completed 3-Tesla magnetic resonance imaging and high-resolution [(11)C]raclopride PET scans. The analyses using linear and exponential models revealed that age had a significant negative correlation with D(2) receptor availability in the post-commissural putamen (postPU) and that D(2) receptor binding in the postPU decreased significantly more with age than in the ventral striatum, suggesting subregional differences in age-related changes in D(2) receptor binding. The postPU, which belongs to the sensorimotor striatum, may be particularly vulnerable to the effects of age in young and middle-aged subjects.

Glucose metabolism of the midline nuclei raphe in the brainstem observed by PET-MRI fusion imaging.

UNLABELLED The brainstem contains various important monoaminergic neuronal centers, including the raphe nuclei which contain serotonergic neurons. The raphe nuclei, however, are not easily identifiable and located by conventional neuroimaging. METHODS Fluorodeoxyglucose positron emission tomography (PET) and magnetic resonance imaging (MRI) were performed in seven healthy subjects using a new PET-MRI, which consists of a high-resolution research tomograph (HRRT) PET and 7.0 T-MRI. Glucose metabolism of raphe nuclei was semiquantitatively measured and identified along the midline brainstem region in vivo. RESULTS Midline nuclei clustered in four groups appeared to be the raphe nuclei and could be clearly visualized; specifically, we identified the groups as the dorsal raphe, raphe reticularis centralis superior, raphe pontis, and raphe magnus group. CONCLUSION FDG imaging of the midline raphe nuclei in vivo could potentially be an important tool for investigating brain diseases as well as conducting functional brain studies in the context of sleep disorders, depression, and neurodegenerative disease.

The effects of caffeine ingestion on cortical areas: Functional imaging study☆ , ☆☆

The effect of caffeine as a cognitive enhancer is well known; however, caffeine-induced changes in the cortical regions are still not very clear. Therefore, in this study, we conducted an investigation of the activation and deactivation with blood-oxygenation-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) and of metabolic activity change with positron emission tomography (PET) in the human brain. Fourteen healthy subjects performed a visuomotor task inducing attention with 3T MRI, and PET imaging was also carried out in seven subjects to determine the cerebral glucose metabolic changes of caffeine at rest. The result by fMRI showed increased BOLD activation in the left cerebellum, putamen, insula, thalamus and the right primary motor cortex, and decreased BOLD deactivation in the posterior medial and the left posterior lateral cortex. Also, the resting state PET data showed reduced metabolic activity in the putamen, caudate nucleus, insula, pallidum and posterior medial cortex. The common cortical regions between fMRI and PET, such as putamen, insula and posterior medial cortex, where significant changes occurred after caffeine ingestion, are well known to play an important role in cognitive function like attention. This result suggests that the effect of caffeine as a cognitive enhancer is derived by modulating the attentional areas.

Dopamine D 2/3 receptor availability and human cognitive impulsivity: a high-resolution positron emission tomography imaging study with [ 11 C]raclopride

Objective Human impulsivity is a complex multidimensional construct encompassing cognitive, emotional, and behavioural aspects. Previous animal studies have suggested that striatal dopamine receptors play a critical role in impulsivity. In this study, we investigated the relationship between self-reported impulsiveness and dopamine D2/3 receptor availability in striatal subdivisions in healthy subjects using high-resolution positron emission tomography (PET) with [11C]raclopride. Methods Twenty-one participants completed 3-T magnetic resonance imaging and high-resolution PET scans with [11C]raclopride. The trait of impulsiveness was measured using the Barratt Impulsiveness Scale (BIS-11). Partial correlation analysis was performed between BIS-11 scores and D2/3 receptor availability in striatal subregions, controlling for the confounding effects of temperament characteristics that are conceptually or empirically related to dopamine, which were measured by the Temperament and Character Inventory. Results The analysis revealed that the non-planning (p = 0.004) and attentional (p = 0.007) impulsiveness subscale scores on the BIS-11 had significant positive correlations with D2/3 receptor availability in the pre-commissural dorsal caudate. There was a tendency towards positive correlation between non-planning impulsiveness score and D2/3 receptor availability in the post-commissural caudate. Conclusion These results suggest that cognitive subtrait of impulsivity is associated with D2/3 receptor availability in the associative striatum that plays a critical role in cognitive processes involving attention to detail, judgement of alternative outcomes, and inhibitory control.

Increased Basal Forebrain Metabolism in Mild Cognitive Impairment: An Evidence for Brain Reserve in Incipient Dementia

Cholinergic dysfunction is well known to significantly contribute to the cognitive decline in Alzheimers disease (AD). However, it has not been clarified whether the cholinergic dysfunction is a primary event or a retrograde event secondary to neuronal loss of the cholinergic targets. Analysis of the in vivo neuronal activity of the basal forebrain in the early stages of AD could yield more information about this issue. In the present study, uptake of [18F]-fluorodeoxyglucose (FDG) in the basal forebrain was measured in 13 patients with mild cognitive impairment (MCI), 20 with early AD, and 14 healthy subjects using high-resolution research tomograph-PET. The FDG uptake was compared among the groups and correlated with the Mini Mental Status Examination (MMSE) score. The MCI patients showed significantly higher FDG uptake in the basal forebrain than the healthy subjects and the AD patients, and those did not developed dementia after 2 years showed even higher uptake than those developed dementia. The basal forebrain metabolism showed an inverted-U relationship with MMSE score in highly educated subjects, and cross-voxel analysis over the whole brain in MCI patients revealed a significant correlation in uptake between the basal forebrain and the fronto-temporal cortices. These findings indicate that in MCI patients, neuronal activity in the basal forebrain is initially increased over that in normal aging and then decreased only with further cognitive decline. The increase is consistent with a secondary compensation against neurodegeneration at target areas, and may provide brain reserve against functional impairments at incipient stages of dementia.

Decreased regional gray matter volume in suicide attempters compared to suicide non-attempters with major depressive disorders

OBJECTIVE This study investigated regional gray matter (GM) volume differences between suicide attempters and suicide non-attempters with major depressive disorder (MDD) and their relationship with psychological risk factors for suicidality. METHODS MDD patients with and without a suicide attempt history (n=19 in each group) participated. The Hamilton Depression Rating Scale, Clinical Global Impression (severity subscale), Scale for Suicide Ideation (SSI), Risk-Rescue Rating (RRR), Beck Hopelessness Scale (BHS), Barrett Impulsivity Scale, Eysenck Personality Questionnaire, and Ways of Coping Checklist (WCCL) were administered. T1-weighted structural magnetic resonance imaging scans were acquired to evaluate changes in GM volume. Voxel-based morphometry was performed using the SPM 8 software package. Two-sample t-tests were used during second-level group comparison analysis; partial correlation analysis controlling for gender and age identified associations between regional GM volume and psychological measures. RESULTS Suicide attempters exhibited significantly decreased GM volume in the left angular gyrus (p<0.001, uncorrected) and right cerebellum (p<0.001, uncorrected). GM volume in the left angular gyrus was inversely correlated with BHS scores (r=-0.55, p<0.01) and positively correlated with the Seeking Social Support subscale of the WCCL (r=0.43, p<0.01). CONCLUSION These findings provide evidence of a neural basis of suicidal behaviors in MDD. In particular, reduced GM volume in the left angular gyrus may be a neurobiological marker of suicidality in depressed patients.