Se-Hong Oh

Seven‐tesla magnetic resonance images of the substantia nigra in Parkinson disease

To investigate anatomical changes in the substantia nigra (SN) of Parkinson disease (PD) patients with age‐matched controls by using ultra‐high field magnetic resonance imaging (MRI).

Involvement of the anterior thalamic radiation in boys with high functioning autism spectrum disorders: A Diffusion Tensor Imaging study

BACKGROUND Autism has been hypothesized to reflect neuronal disconnection. Several recent reports implicate the key thalamic relay nuclei and cortico-thalamic connectivity in the pathophysiology of autism. Accordingly, we aimed to focus on evaluating the integrity of the thalamic radiation and sought to replicate prior white matter findings in Korean boys with high-functioning autism spectrum disorders (ASD) using Diffusion Tensor Imaging (DTI). METHODS We compared fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD) and radial diffusivity (RD) in 17 boys with ASD and 17 typically developing controls in the anterior thalamic radiation (ATR), superior thalamic radiation (STR), posterior thalamic radiation (PTR), corpus callosum (CC), uncinate fasciculus (UF) and inferior longitudinal fasciculus (ILF). RESULTS The two groups were group-matched on age, IQ, handedness and head circumference. In whole-brain voxel-wise analyses, FA was significantly reduced and MD was significantly increased in the right ATR, CC, and left UF in subjects with ASD (p<0.05, corrected). We found significantly lower FA in right and left ATR, CC, left UF and right and left ILF and significantly higher MD values of the CC in the ASD group in region of interest-based analyses. We also observed significantly higher RD values of right and left ATR, CC, left UF, left ILF in subjects with ASD compared to typically developing boys and significantly lower AD values of both ILF. Right ATR and right UF FA was significantly negatively correlated with total SRS score within the ASD group (r=-.56, p=.02). CONCLUSIONS Our preliminary findings support evidence implicating disturbances in the thalamo-frontal connections in autism. These findings highlight the role of hypoconnectivity between the frontal cortex and thalamus in ASD.

A fusion PET-MRI system with a high-resolution research tomograph-PET and ultra-high field 7.0 T-MRI for the molecular-genetic imaging of the brain.

We have developed a positron emission tomography (PET) and magnetic resonance imaging (MRI) fusion system for the molecular‐genetic imaging (MGI) of the in vivo human brain using two high‐end imaging devices: the HRRT‐PET, a high‐resolution research tomograph dedicated to brain imaging on the molecular level, and the 7.0 T‐MRI, an ultra‐high field version used for morphological imaging. HRRT‐PET delivers high‐resolution molecular imaging with a resolution down to 2.5 mm full width at half maximum (FWHM), which allows us to observe the brains molecular changes using the specific reporter genes and probes. On the other front, the 7.0 T‐MRI, with submillimeter resolution images of the cortical areas down to 250 μm, allows us to visualize the fine details of the brainstem areas as well as the many cortical and subcortical areas. The new PET–MRI fusion imaging system will provide many answers to the questions on neurological diseases as well as cognitive neurosciences. Some examples of the answers are the quantitative visualization of neuronal functions by clear molecular and genetic bases, as well as diagnoses of many neurological diseases such as Parkinsons and Alzheimers. The salient point of molecular‐genetic imaging and diagnosis is the fact that they precede the morphological manifestations, and hence, the early and specific diagnosis of certain diseases, such as cancers.

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.

An anatomic review of thalamolimbic fiber tractography: ultra-high resolution direct visualization of thalamolimbic fibers anterior thalamic radiation, superolateral and inferomedial medial forebrain bundles, and newly identified septum pellucidum tract.

BACKGROUND Images obtained through ultra-high-field 7.0-tesla magnetic resonance imaging with track-density imaging provide clear, high-resolution tractograms that have been hitherto unavailable, especially in deep brain areas such as the limbic and thalamic regions. This study is a largely pictorial description of the deep fiber tracts in the brain using track-density images obtained with 7.0-T diffusion-weighted imaging. METHODS To identify the fiber tracts, we selected 3 sets of tractograms and performed interaxis correlation between them. These tractograms offered an opportunity to extract new information in areas that have previously been difficult to examine using either in vivo or in vitro human brain tractography. RESULTS With this new technique, we identified 4 fiber tracts that have not previously been directly visualized in vivo: septum pellucidum tract, anterior thalamic radiation, superolateral medial forebrain bundle, and inferomedial forebrain bundle. CONCLUSIONS We present the high-resolution images as a tool for researchers and clinicians working with neurodegenerative and psychiatric diseases, such as Parkinson disease, Alzheimer disease, and depression, in which the accurate positioning of deep brain stimulation is essential for precise targeting of nuclei and fiber tracts.

Abnormal Activation of the Social Brain Network in Children with Autism Spectrum Disorder: An fMRI Study

Objective The aim of this study is to investigate abnormal findings of social brain network in Korean children with autism spectrum disorder (ASD) compared with typically developing children (TDC). Methods Functional magnetic resonance imaging (fMRI) was performed to examine brain activations during the processing of emotional faces (happy, fearful, and neutral) in 17 children with ASD, 24 TDC. Results When emotional face stimuli were given to children with ASD, various areas of the social brain relevant to social cognition showed reduced activation. Specifically, ASD children exhibited less activation in the right amygdala (AMY), right superior temporal sulcus (STS) and right inferior frontal gyrus (IFG) than TDC group when fearful faces were shown. Activation of left insular cortex and right IFG in response to happy faces was less in the ASD group. Similar findings were also found in left superior insular gyrus and right insula in case of neutral stimulation. Conclusion These findings suggest that children with ASD have different processing of social and emotional experience at the neural level. In other words, the deficit of social cognition in ASD could be explained by the deterioration of the capacity for visual analysis of emotional faces, the subsequent inner imitation through mirror neuron system (MNS), and the ability to transmit it to the limbic system and to process the transmitted emotion.

Distortion Correction in EPI at Ultra-High-Field MRI Using PSF Mapping with Optimal Combination of Shift Detection Dimension

Despite its wide use, echo‐planar imaging (EPI) suffers from geometric distortions due to off‐resonance effects, i.e., strong magnetic field inhomogeneity and susceptibility. This article reports a novel method for correcting the distortions observed in EPI acquired at ultra‐high‐field such as 7 T. Point spread function (PSF) mapping methods have been proposed for correcting the distortions in EPI. The PSF shift map can be derived either along the nondistorted or the distorted coordinates. Along the nondistorted coordinates more information about compressed areas is present but it is prone to PSF‐ghosting artifacts induced by large k‐space shift in PSF encoding direction. In contrast, shift maps along the distorted coordinates contain more information in stretched areas and are more robust against PSF‐ghosting. In ultra‐high‐field MRI, an EPI contains both compressed and stretched regions depending on the B0 field inhomogeneity and local susceptibility. In this study, we present a new geometric distortion correction scheme, which selectively applies the shift map with more information content. We propose a PSF‐ghost elimination method to generate an artifact‐free pixel shift map along nondistorted coordinates. The proposed method can correct the effects of the local magnetic field inhomogeneity induced by the susceptibility effects along with the PSF‐ghost artifact cancellation. We have experimentally demonstrated the advantages of the proposed method in EPI data acquisitions in phantom and human brain using 7‐T MRI. Magn Reson Med, 2012.

Probing signal phase in direct visualization of short transverse relaxation time component (ViSTa)

To demonstrate the phase evolutions of direct visualization of short transverse relaxation time component (ViSTa) matches with those of myelin water.

A Newly Identified Frontal Path from Fornix in Septum Pellucidum with 7.0T MRI Track Density Imaging (TDI) – The Septum Pellucidum Tract (SPT)

The high anatomical contrast achieved with the newly emerging MRI tractographic technique of super-resolution track density imaging (TDI) encouraged us to search for a new fiber tract in the septum pellucidum. Although this septum pellucidum tract (SPT) has been observed previously, its connections were unclear due to ambiguity and limited resolution of conventional MRI images. It is now possible to identify detailed parts of SPT with the increased resolution of TDI, which involves diffusion MRI imaging, whole-brain tractography, and voxel subdivision using the track-count information. Four healthy male subjects were included in the study. The experiment was performed with 7.0T MRI, following the guidelines of the institute’s institutional review board. Data were processed with the super-resolution TDI technique to generate a tractographic map with 0.18 mm isotropic resolution. The SPT was identified in all subjects. Based on additional seed tracking method with inter-axis correlation search, we have succeeded in identifying a new frontal lobe pathway in the SPT. We hypothesize that the tract is connected as a superior dorsal branch of the fornix that leads to the prefrontal cortex.

Whole brain g-ratio mapping using myelin water imaging (MWI) and neurite orientation dispersion and density imaging (NODDI)

Abstract MR g‐ratio, which measures the ratio of the aggregate volume of axons to that of fibers in a voxel, is a potential biomarker for white matter microstructures. In this study, a new approach for acquiring an in‐vivo whole human brain g‐ratio map is proposed. To estimate the g‐ratio, myelin volume fraction and axonal volume fraction are acquired using multi‐echo gradient echo myelin water imaging (GRE‐MWI) and neurite orientation dispersion and density imaging (NODDI), respectively. In order to translate myelin water fraction measured in GRE‐MWI into myelin volume fraction, a new scaling procedure is proposed and validated. This scaling approach utilizes geometric measures of myelin structure and, therefore, provides robustness over previous methods. The resulting g‐ratio map reveals an expected range of g‐ratios (0.71–0.85 in major fiber bundles) with a small inter‐subject coefficient of variance (less than 2%). Additionally, a few fiber bundles (e.g. cortico‐spinal tract and optic radiation) show different constituents of myelin volume fraction and axonal volume fraction, indicating potentials to utilize the measures for deciphering fiber tracking. Graphical abstract Figure. No caption available. HighlightsA new g‐ratio mapping method that combined GRE‐MWI with NODDI proposed.Translation of myelin water fraction into myelin volume fraction developed.Axonal volume fraction and myelin volume fraction varied among white fiber bundles.