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Shigeki Aoki

Publications and source records attributed to Shigeki Aoki.

At least 19 recordsLinked to original sources
PubMed2007

Human brain structural change related to acute single exposure to sarin.

OBJECTIVE: This study aimed to identify persistent morphological changes subsequent to an acute single-time exposure to sarin, a highly poisonous organophosphate, and the neurobiological basis of long-lasting somatic and cognitive symptoms in victims exposed to sarin. METHODS: Thirty-eight victims of the 1995 Tokyo subway sarin attack, all of whom had been treated in an emergency department for sarin intoxication, and 76 matched healthy control subjects underwent T1-weighted and diffusion tensor magnetic resonance imaging (DTI) in 2000 to 2001. Serum cholinesterase (ChE) levels measured immediately and longitudinally after the exposure and the current severity of chronic reports in the victims were also evaluated. RESULTS: The voxel-based morphometry exhibited smaller than normal regional brain volumes in the insular cortex and neighboring white matter, as well as in the hippocampus in the victims. The reduced regional white matter volume correlated with decreased serum cholinesterase levels and with the severity of chronic somatic complaints related to interoceptive awareness. Voxel-based analysis of diffusion tensor magnetic resonance imaging further demonstrated an extensively lower than normal fractional anisotropy in the victims. All these findings were statistically significant (corrected p < 0.05). INTERPRETATION: Sarin intoxication might be associated with structural changes in specific regions of the human brain, including those surrounding the insular cortex, which might be related to elevated subjective awareness of internal bodily status in exposed individuals.

Adult↗
PubMed2006

Flexible ex vivo phantoms for validation of diffusion tensor tractography on a clinical scanner.

PURPOSE: The aim of this study was to develop ex vivo diffusion tensor (DT) flexible phantoms. MATERIALS AND METHODS: Materials were bundles of textile threads of cotton, monofilament nylon, rayon, and polyester bunched with spiral wrapping bands and immersed in water. DT images were acquired on a 1.5-Tesla clinical magnetic resonance scanner using echo planar imaging sequences with 15 motion probing gradient directions. DT tractography with seeding and a line-tracking method was carried out by software originally developed on a PC-based workstation. RESULTS: We observed relatively high fractional anisotropy on the polyester phantom and were able to reconstruct tractography. Straight tracts along the bundle were displayed when it was arranged linearly. It was easy to bend arcuately or bifurcate at one end; and tracts followed the course of the bundle, whether it was curved or branched and had good agreement with direct visual observation. Tractography with the other fibers was unsuccessful. CONCLUSION: The polyester phantom revealed a diffusion anisotropic structure according to its shape and would be utilizable repeatedly under the same conditions, differently from living central neuronal system. It would be useful to validate DT sequences and to optimize an algorithm or parameters of DT tractography software. Additionally, the flexibility of the phantom would enable us to model human axonal projections.

Anisotropy↗
PubMed2006

Aging in the CNS: comparison of gray/white matter volume and diffusion tensor data.

This study investigated the global and regional effects of aging on brain volume, mean diffusivity (MD), and fractional anisotropy (FA) in 73 normal female subjects using voxel-based analysis. On a global scale, gray matter volume and FA were negatively correlated, whereas MD was positively correlated with age. Voxel-wise analyses showed brain volume and FA were negatively correlated predominantly in anterior structures, whereas MD was positively correlated in the cortical gray matter and periventricular white matter. Volume preservation was observed in the cingulate gyrus and subjacent white matter. FA increase was observed in the putamen. Voxel-based direct comparisons of volume and diffusion properties showed FA was more strongly negatively correlated in the fronto-temporal white matter, compared with volume and MD. Stronger positive correlation of MD was observed in the thalamus, caudate nucleus, and midbrain and stronger negative correlation of brain volume was observed in the frontal lobe and basal ganglia, compared with the other. These results indicate that diffusion properties and brain volume are complementary markers to the effects of aging.

Adult↗
PubMed2006

[Utility of axial images in an early Alzheimer disease diagnosis support system (VSRAD)].

In recent years, voxel-based morphometry (VBM) has become a popular tool for the early diagnosis of Alzheimer disease. The Voxel-Based Specific Regional Analysis System for Alzheimer's Disease (VSRAD), a VBM system that uses MRI, has been reported to be clinically useful. The able-bodied person database (DB) of VSRAD, which employs sagittal plane imaging, is not suitable for analysis by axial plane imaging. However, axial plane imaging is useful for avoiding motion artifacts from the eyeball. Therefore, we created an able-bodied person DB by axial plane imaging and examined its utility. We also analyzed groups of able-bodied persons and persons with dementia by axial plane imaging and reviewed the validity. After using the DB of axial plane imaging, the Z-score of the intrahippocampal region improved by 8 in 13 instances. In all brains, the Z-score improved by 13 in all instances.

Alzheimer Disease↗
PubMed2006

[Examination of an imaging method in early Alzheimer disease diagnosis support system (VSRAD)].

The use of voxel-based morphometry (VBM) has recently become a popular tool for the early diagnosis of Alzheimer disease. The Voxel-Based Specific Regional Analysis System for Alzheimer's Disease (VSRAD) is a clinically useful VBM that employs MRI. However, there has been insufficient information about the influence of the image pickup apparatus and imaging conditions in terms of the value calculated by the sensitivity correction. We therefore reviewed this problem in a volunteer who provided consent. We were able to confirm reproducibility under the same conditions. When changing the image pickup apparatus and conditions, the average Z-score of 0.18+/-0.21 became larger, and the change in Z-score increased when imaging was done in the axial plane. Further, the average Z-score of 0.06+/-0.21 for sensitivity correction use was high on average by 0.19+/-0.16 for phased-array uniformity enhancement (PURE) and low for surface coil intensity correction (SCIC).

Adult↗
PubMed2006

Voxel-based diffusion tensor analysis reveals aberrant anterior cingulum integrity in posttraumatic stress disorder due to terrorism.

Recent functional neuroimaging work has suggested that interregional functional connectivity between the anterior cingulate cortex (ACC), other limbic, and prefrontal regions may be involved in the pathophysiology of posttraumatic stress disorder (PTSD). However, less attention has been paid to the white matter network. Voxel-based analysis enables an exploration of morphological or functional changes throughout the entire brain. Here we undertook the first application of this technology to diffusion tensor data in patients with PTSD. Participants were 9 victims of the Tokyo subway sarin attack with PTSD and 16 matched victims of the same traumatic event without PTSD. The voxel-based analysis showed a significant fractional anisotropy increase in the left anterior cingulum, subjacent to the left ACC gray matter where we previously found a volume decrement, in PTSD subjects. Moreover, the severity was positively, but not significantly associated with the fractional anisotropy of the left anterior cingulum in the victims with PTSD, using the region of interest defined in the native space with the inverse normalization technique. The present study demonstrated further evidence of abnormalities of both the ACC, a structure that is pivotally involved in attention, emotional regulation, and fear conditioning, and of subjacent white matter in the pathology of PTSD.

Adult↗
PubMed2006

Line scan diffusion tensor MRI at low magnetic field strength: feasibility study of cervical spondylotic myelopathy in an early clinical stage.

PURPOSE: To implement line scan diffusion tensor MR imaging (LSDTI) on a 0.2 Tesla MR imager, and investigate the findings in the spinal cord of patients with cervical spondylotic myelopathy in an early clinical stage. MATERIALS AND METHODS: Fourteen patients with clinical symptoms of cervical myelopathy underwent LSDTI. The signal-to-noise ratio (SNR) in the spinal cord and cerebrospinal fluid (CSF) was evaluated. The apparent diffusion coefficient (ADC) and fractional anisotropy (FA) were measured. We classified the ROIs into two groups: 1) unaffected (no clinical symptoms and no abnormality on conventional images) and 2) affected (some clinical symptoms but no abnormal signal on conventional images). Three-dimensional (3D) fiber-tracking was also studied. RESULTS: The isotropic ADC values (10(-3)mm2/sec) were 1.28 +/- 0.11 in group 1 and 1.59 +/- 0.23 in group 2. The FAs were 0.55 +/- 0.07 in group 1, and 0.47 +/- 0.11 in group 2. The ADC value in group 2 increased (P < .001, Mann-Whitney U-test) and the FA in group 2 decreased (P = 0.24) on average, compared to those in group 1. 3D fiber-tracking was successful in 64% (9/14) of the cases. CONCLUSION: LSDT images at low field strength may be a sensitive method for elucidating the structural characteristics of spinal cord pathology in vivo. However, clinical correlation and a long-term follow-up study will be needed.

Adolescent↗
PubMed2006

Brachial plexus injury: clinical manifestations, conventional imaging findings, and the latest imaging techniques.

Brachial plexus injury (BPI) is a severe neurologic injury that causes functional impairment of the affected upper limb. Imaging studies play an essential role in differentiating between preganglionic and postganglionic injuries, a distinction that is crucial for optimal treatment planning. Findings at standard myelography, computed tomographic (CT) myelography, and conventional magnetic resonance (MR) imaging help determine the location and severity of injuries. MR imaging sometimes demonstrates signal intensity changes in the spinal cord, and enhancement of nerve roots and paraspinal muscles at MR imaging indicates the presence of root avulsion injuries. New techniques including MR myelography, diffusion-weighted neurography, and Bezier surface reformation can also be useful in the evaluation and management of BPI. MR myelography with state-of-the-art technology yields remarkably high-quality images, although it cannot replace CT myelography entirely. Diffusion-weighted neurography is a cutting-edge technique for visualizing postganglionic nerve roots. Bezier surface reformation allows the depiction of entire intradural nerve roots on a single image. CT myelography appears to be the preferred initial imaging modality, with standard myelography and contrast material-enhanced MR imaging being recommended as additional studies. Work-up will vary depending on the equipment used, the management policy of peripheral nerve surgeons, and, most important, the individual patient.

Brachial Plexus↗
PubMed2005

The magnetic resonance Matas test: Feasibility and comparison with the conventional intraarterial balloon test occlusion with SPECT perfusion imaging.

PURPOSE: To evaluate a new MR Matas test that uses a form of contrast-enhanced MR angiography (MRA) with temporary manual occlusion of the common carotid artery whose internal carotid artery (ICA) is to be permanently sacrificed. MATERIALS AND METHODS: The MR Matas test was performed on eight patients using an open type MR imager (Signa Profile 0.2 Tesla ver. 7.5, GE-YMS, Tokyo, Japan). Conventional balloon occlusion Matas test and single-photon emission computed tomography (SPECT) of the brain were performed in all cases within a week before or after the MR Matas test. RESULTS: The MR Matas test was successful in all eight patients without any complications. The image quality of the MR Matas test was generally sufficient to confirm cross-flow from the patent side to the occluded side in comparison with selective intraarterial digital subtraction angiography (IADSA) except in one case. CONCLUSION: Brain perfusion information using MR Matas test is comparable to brain SPECT.

Aged↗
PubMed2005

Line-scan diffusion tensor MR imaging at 0.2 T: feasibility study.

PURPOSE: To investigate and measure apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values using data obtained with line-scan diffusion-weighted imaging (DWI) of human brains on a 0.2 Tesla MR imager. MATERIALS AND METHODS: Diffusion-tensor imaging (DTI) was performed on eight healthy volunteers. The signal-to-noise ratios (SNRs) of white matter and cerebrospinal fluid were measured. ADC and FA were also measured from the data obtained from all subjects. Three-dimensional corticospinal fiber tracts were reconstructed from the DT images and a qualitative evaluation was done. RESULTS: The total scan time was 52 minutes 30 seconds for 18 slices with full-tensor images covering the whole brain. The ADCs and FAs show the appropriate values, in comparison with values obtained at high field strength in previous studies. Corticospinal fibers were demonstrated more clearly on images obtained at 0.2 T than at 1.5T. CONCLUSION: DTI at low field strength may be feasible for clinical use to estimate the white matter of brain with limited coverage, which often may be sufficient.

Adult↗
PubMed2005

Delayed automatic detection of change in speech sounds in adults with autism: a magnetoencephalographic study.

OBJECTIVE: Autism is a form of pervasive developmental disorder in which dysfunction in interpersonal relationships and communication is fundamental. This study evaluated neurophysiological abnormalities at the basic level of language processing, i.e. automatic change detection of speech and non-speech sounds, using magnetoencephalographic recording of mismatch response elicited by change in vowels and tones. METHODS: The auditory magnetic mismatch field (MMF) was evaluated in 9 adults with autism and 19 control subjects using whole-head magnetoencephalography. The MMF in response to the duration change of a pure tone or vowel /a/ and that in response to across-phoneme change between vowels /a/ and /o/, were recorded. RESULTS: The groups were not significantly different in MMF power under any conditions. However, the autism group showed a left-biased latency prolongation of the MMF particularly under the across-phoneme change condition, and this latency delay was significantly associated with greater symptom severity. CONCLUSIONS: These results suggest that adults with autism are associated with delayed processing for automatic change detection of speech sounds. These electrophysiological abnormalities at the earliest level of information processing may contribute to the basis for language deficits observed in autism. SIGNIFICANCE: These results provide the first evidence for delayed latency of phonetic MMF in adults with autism.

Acoustic Stimulation↗
PubMed2005

Functional identification of the primary motor area by corticospinal tractography.

OBJECTIVE: For quick and stable identification of the primary motor area (PMA), diffusion tensor imaging (DTI) data were acquired and corticospinal tractography was mathematically visualized. METHODS: Data sets of DTI, anatomic magnetic resonance imaging, and functional magnetic resonance imaging with finger-tapping tasks were acquired during the same investigation in 30 patients with a brain lesion affecting the motor system. Off-line processing of DTI data was performed to visualize the corticospinal tract, placing a seed area in the cerebral peduncle of the midbrain, where the corticospinal tract is densely concentrated. Somatosensory evoked magnetic fields and intraoperative cortical somatosensory evoked potentials were recorded with electrical stimulation of the median nerve to confirm the results of the corticospinal tractography. RESULTS: Functional magnetic resonance imaging and somatosensory evoked magnetic fields failed to identify the PMA in eight patients (16.7%) and one patient (3.8%) investigated, respectively, because of cortical dysfunctions caused by brain lesions. DTI data were acquired within 3 minutes without patient tasks. Using the appropriate seed area and fractional anisotropy, corticospinal tractography successfully indicated the PMA location in all patients. The suspected PMA and central sulcus locations were confirmed by the cortical somatosensory evoked potentials. CONCLUSION: Corticospinal tractography enables identification of the PMA and is beneficial, particularly for patients who present with dysfunction of the PMA.

Adolescent↗
PubMed2005

Functional monitoring for visual pathway using real-time visual evoked potentials and optic-radiation tractography.

OBJECTIVE: It has been difficult to obtain anatomic and functional information about the visual pathway during neurosurgical operations. The aim of this study was to combine the information of the visual evoked potentials (VEPs) and the anatomic navigation of the optic radiation by diffusion tensor imaging-based tractography for functional monitoring of the visual pathway. METHODS: The subjects were two patients with brain lesions adjacent to the visual pathway. Diffusion tensor imaging-based tractography of the optic radiation was performed by selecting appropriate regions of interest and by fractional anisotropy. During surgery, cortical VEPs were recorded continuously under general anesthesia with sevoflurane. In Patient 2, the results of optic radiation tractography were imported to a neuronavigation system to better understand the spatial relationships between the lesions and the visual pathway (functional neuronavigation). RESULTS: In Patient 1, the lesion did not seem to be attached to the optic radiation, and VEP profiles remained stable during resection. In Patient 2, who had a lesion adjacent to the posterior horn of the lateral ventricle, VEPs suddenly diminished when resection reached the optic radiation as illustrated on the neuronavigation system. As a result, complete left hemianopia developed after surgery in Patient 2. CONCLUSION: We confirmed functional correlations of the results of diffusion tensor imaging-based tractography by monitoring intraoperative VEPs. The combination of continuous VEP and optic-radiation tractography is reliable to monitor the visual function and is helpful in performing neurosurgical planning near the visual pathway.

Adult↗
PubMed2005

Combined use of tractography-integrated functional neuronavigation and direct fiber stimulation.

OBJECT: The aim of this study was better preoperative planning and direct application to intraoperative procedures through accurate coregistration of diffusion-tensor (DT) imaging-based tractography results and anatomical three-dimensional magnetic resonance images and subsequent importation of the combined images to a neuronavigation system (functional neuronavigation). METHODS: Six patients with brain lesions adjacent to the corticospinal tract (CST) were studied. During surgery, direct fiber stimulation was used to evoke motor responses to confirm the accuracy of CST depicted on functional neuronavigation. In three patients, stimulation of the supposed CST elicited the expected motor evoked potentials. In the other three, stimulation at the resection borders more than 1 cm away from the supposed CST showed no motor response. All patients underwent appropriate tumor resection with preservation of the CST. CONCLUSIONS: Integration of the DT imaging-based tractography information into a traditional neuronavigation system demonstrated spatial relationships between lesions and the CST, allowing for the avoidance of tract injury during lesion resection. Direct fiber stimulation was used for real-time reliable white matter mapping, which served to adjust for any discrepancy between the neuronavigation system data and potentially shifted positions of the brain structures. The combination of these techniques enabled the authors to identify accurate positions of the CST during surgery and to accomplish optimal tumor resections.

Adult↗
PubMed2005

Integration of three-dimensional corticospinal tractography into treatment planning for gamma knife surgery.

OBJECT: In the radiosurgical treatment of critically located lesions, the effort to minimize the risk of complication is essential. In this study the integration of diffusion-tensor (DT) imaging-based tractography was clinically applied to treatment planning for gamma knife surgery (GKS). METHODS: Seven patients with cerebral arteriovenous malformations located adjacent to the corticospinal tract (CST) underwent this technique. Data provided by DT imaging were acquired before the frame was affixed to the patient's head and the CST of the DT tractography was created using our original software. Stereotactic three-dimensional imaging studies were obtained after frame fixation and then coregistered with the data from DT tractography. After image fusion of the two studies, the combined images were transported to a GKS treatment-planning workstation. The spatial relationship between the dose distribution and the CST was clearly demonstrated within the 2 hours it took to complete the entire imaging process. The univariate logistic regression analysis of transient or permanent motor complications revealed a significant independent correlation with the volume of the CST that received 25 Gy or more and with a maximum dose to the CST (p < 0.05). CONCLUSIONS: The integration of DT tractography into the GKS treatment planning was highly useful in confirming the dose to the CST during treatment planning.

Adult↗
PubMed2005

Intracranial extracerebral glioneuronal heterotopia. Case report and review of the literature.

The authors report a case of intracranial extracerebral glioneuronal heterotopia (IEGH) in an infant. Glioneuronal heterotopias are rare congenital disorders that arise in the head, face, spine, and thoracic cavity. They consist of nodular accumulations of neuronal and glial cells that have developed abnormally, ranging in size from small lesions to large masses. Among heterotopias, IEGHs are relatively rare. They cause various clinical symptoms, depending on their size and location. The neuroimaging studies, histological examinations, and intraoperative findings presented provide insight into the pathogenesis of this disorder. The findings support the separation and detachment theory, which proposes that IEGHs originate from a third telencephalon that erroneously forms between the 4th and 6th week of embryogenesis. More detailed case reports are necessary to understand fully the pathogenesis of IEGHs.

Adult↗
PubMed2005

Quantitative evaluation of the pyramidal tract segmented by diffusion tensor tractography: feasibility study in patients with amyotrophic lateral sclerosis.

PURPOSE: Diffusion tensor imaging can evaluate the cerebral white matter quantitatively using fractional anisotropy (FA) and also can extract a certain tract by tractography, but these two have been used separately and not combined. The purpose of this study was to assess the clinical feasibility of ROI analysis using diffusion tensor tractography (DTT) in patients with amyotrophic lateral sclerosis (ALS). MATERIALS AND METHODS: Sixteen patients with ALS (9 limb-onset type, 7 bulbar-onset type) and nine age-matched volunteers were studied. DTT of the corticobulbar tract (DTT-CBT) and corticospinal tract (DTT-CST) were visualized by free software (dTV/VOLUME-ONE). Regions-of-interest (ROIs) were semi-automatically placed on the tracts defined by DTT methods, and FA values within the ROIs were measured. RESULTS: Mean FA values of ALS patients in the ROIs along the DTT-CST (bulbar-onset: 0.574, limb-onset: 0.594) were significantly lower than those of controls (DTT-CST: 0.629) (p<0.05). The mean FA of DTT-CBT of the bulbar-onset type (0.509) was significantly lower than that of the limb-onset type (0.558) and that of volunteers (0.561). CONCLUSION: DTT could segmentate certain white matter tracts and evaluate them quantitatively. It could depict the subtle changes between subtypes of ALS as well as the changes between the patients and volunteers.

Amyotrophic Lateral Sclerosis↗