Tomohiko Masumoto

Topography of the human corpus callosum using diffusion tensor tractography

Objective: To evaluate the crossing fiber trajectory through the corpus callosum using distortion-corrected diffusion tensor tractography in the human brain. Methods: After correcting distortion associated with large-diffusion gradients, T2-weighted echo planar images (EPIs) acquired from 10 right-handed healthy men were coregistered into T2-weighted fast spin echo images using linear through sixth-order nonlinear, 3-dimensional, polynomial warping functions. The optimal transformation parameters were also applied to the distortion-corrected diffusion-weighted EPIs. Diffusion tensor tractography through the corpus callosum was reconstructed, employing the “1 or 2 regions of interest” method. Results: Compared with the lines through the genu, those through the rostrum ran more inferiorly and seemed to enter the orbital gyrus. Those lines entering posterior temporal white matter (tapetum) crossed through the ventral portion of the splenium and were clearly distinguished from lines that reached parieto-occipital white matter (forceps major). Conclusion: Diffusion tensor tractography is a feasible noninvasive tool to evaluate commissural fiber trajectory.

Temporal changes of the apparent diffusion coefficients of water and metabolites in rats with hemispheric infarction: experimental study of transhemispheric diaschisis in the contralateral hemisphere at 7 tesla.

The purpose of the present study was to clarify the temporal changes of the apparent diffusion coefficients (ADCs) of cerebral metabolites during early focal ischemia using stimulated echo acquisition mode with short echo time at a 7 T magnet to assess the pathophysiology of the reduction in diffusion properties observed both in the ischemic cerebral hemisphere and in the contralateral hemisphere. The ADCs of metabolites in the infarcted hemisphere 1 hour and 3 hours after the onset of ischemia decreased with 25% and 29% for choline-containing compounds (Cho), 16% and 26% for creatine and phosphocreatine (Cre), and 19% and 19% for N-acetylaspartate (NAA), respectively, compared with the ADC values 2 hours later in the contralateral hemisphere. There were decreases in the ADC of Cho, Cre, and NAA with 21%, 7%, and 18% 8 hours later, respectively, in the noninfarcted hemisphere, which suggested transhemispheric diaschisis in rats with focal cerebral ischemia. The present study proposed that the diffusion characteristics of the brain metabolites might offer new insights into circulatory and metabolic alteration in the cerebral intracellular circumstance.

Corticospinal tracts by diffusion tensor tractography in patients with arteriovenous malformations.

Objective: To visualize the corticospinal tract (CST) in patients with arteriovenous malformations (AVMs) by using diffusion tensor tractography (DTT) and to confirm the clinical reliability of DTT in patients with AVMs. Methods: We performed DTT in 24 patients who had their AVMs near the CST. Tracts and AVMs were shown simultaneously, providing information on their spatial relationships. We also counted numbers of voxels in the DTT-CST at the level of the AVM. Results: DTT was visualized in 23 patients. In all 9 patients with hemiparesis, their DTT-CSTs were involved in the AVM or its surrounding lesion. Their volume of DTT-CST at the affected side was significantly decreased when compared with the contralateral side (P = 0.0469). All 14 patients whose DTT-CSTs were free from lesion had no hemiparesis. Conclusions DTT was safe and clinically applicable in patients with AVMs. DTT is recommended when an AVM is located near the corticospinal tract.

Evaluation of ventriculomegaly using diffusion tensor imaging: correlations with chronic hydrocephalus and atrophy

OBJECT Ventriculomegaly is a common imaging finding in many types of conditions. It is difficult to determine whether it is related to true hydrocephalus or to an atrophic process by using only imaging procedures such as MR imaging after traumatic injury, stroke, or infectious disease. Diffusion tensor (DT) imaging can distinguish the compression characteristics of white matter, indicating that increased diffusion anisotropy may be related to white matter compression. In this preliminary study, the authors compared the DT imaging findings of ventriculomegaly with those of chronic hydrocephalus or atrophy to clarify the potential of diffusion anisotropy in the identification of hydrocephalus. METHODS Ten patients with chronic hydrocephalus, 8 patients with atrophy (defined by conventional devices and surgical outcome), and 14 healthy volunteers underwent DT imaging. Images were acquired before and after shunting or once in cases without shunting. The fractional anisotropy (FA) values at many points around the lateral ventricle were evaluated. RESULTS The FA patterns around the lateral ventricle in the chronic hydrocephalus and atrophy groups were different. Especially in the caudate nucleus, FA was increased in the chronic hydrocephalus group compared with the atrophy group. Furthermore, the FA values returned to normal levels after shunt placement. CONCLUSIONS Assessment of the FA value of the caudate nucleus may be an important, less invasive method for distinguishing true hydrocephalus from ventriculomegaly. Further research in a large number of patients is needed to verify the diagnostic ability of this method.

Visual Field Damage in Normal-tension Glaucoma Patients With or Without Ischemic Changes in Cerebral Magnetic Resonance Imaging

PurposeTo compare the pattern of visual field damage between normal-tension glaucoma (NTG) patients with signs indicative of ischemic changes and those NTG patients without signs of ischemic changes, using brain magnetic resonance imaging (MRI), in a single center, cross-sectional study.MethodsIn 94 consecutive NTG patients who were younger than 61 years old, brain MRI images were obtained using fluid-attenuated inversion recovery pulse sequences. The presence of signs indicative of ischemic changes in brain MRI images was decided separately by two neuroradiologists masked to the diagnosis and stage of glaucoma. Visual field testing was performed using the 30-2 program of the Humphrey Visual Field Analyzer. Between the patients with signs indicative of ischemic changes in brain MRI (ischemic group) and those without MRI signs (nonischemic group), total deviation (TD) at each test point less the average of TDs of the 30-2 program ([TD − TDmean])—was compared at each test point.ResultsSigns indicative of ischemic changes in brain MRI were found in 32 of the 94 patients (34.0%). Age, blood pressure, refraction, intraocular pressure, the average of TDs, mean deviation, and corrected pattern standard deviation were not significantly different between the ischemic (N = 32) and nonischemic (N = 62) groups (P > 0.2). [TD − TDmean] in the ischemic group was significantly smaller than that in the nonischemic group at 6 nonedge contiguous test points in the inferior pericentral to nasal field (P = 0.005–0.047).ConclusionNTG patients with signs indicative of ischemic changes in brain MRI had a relatively deeper depression in the inferior pericentral visual field.

Three-dimensional susceptibility-weighted imaging at 3 T using various image analysis methods in the estimation of grading intracranial gliomas

OBJECT Although three-dimensional (3D), high-spatial resolution susceptibility-weighted imaging (SWI) appears to be valuable in the evaluation of central nervous system gliomas, several evaluation methods are proposed in the literature. The purpose of this study was to evaluate the use of 3D SWI for grading intracranial gliomas with various analysis methods. MATERIALS AND METHODS Twenty-three patients suspected of having gliomas participated in this study. SWI was performed in addition to conventional MR sequences. In 15 cases, post-gadolinium enhanced SWI was also obtained. Imaging evaluation criteria were conventional grade, hypointensity ratio in the tumor-dominant structure of hypointensity on SWI (hemorrhage or vascular structure) and presence of abnormal enhancement surrounding the tumor. RESULTS Mean grading scores of conventional grade showed no statistically significant difference among WHO grades. Mean grading scores of hypointensity ratios in the tumor were higher for WHO Grades 3 and 4 than for lower grade tumors (P=.05, Mann-Whitney U test). Hemorrhagic foci were more frequently seen in the higher grade tumor. Post-contrast susceptibility-weighted images of five of 11 WHO Grade 3 and 4 cases showed bright enhancement surrounding the tumor, suggesting a breakdown of the blood-brain barrier. CONCLUSIONS SWI at 3 T may be a useful method to analyze the structural characteristics of gliomas and to evaluate pathology in vivo. Assessment of hypointensity ratios in the glioma was the most preferable method in grading glioma. However, more studies, specifically concerning a suitable method for image analysis, are needed to establish SWI at 3 T as a useful tool in clinical routine.

Primary face motor area as the motor representation of articulation

No clinical data have yet been presented to show that a lesion localized to the primary motor area (M1) can cause severe transient impairment of articulation, although a motor representation for articulation has been suggested to exist within M1. Here we describe three cases of patients who developed severe dysarthria, temporarily mimicking speech arrest or aphemia, due to a localized brain lesion near the left face representation of the human primary motor cortex (face-M1). Speech was slow, effortful, lacking normal prosody, and more affected than expected from the degree of facial or tongue palsy. There was a mild deficit in tongue movements in the sagittal plane that impaired palatolingual contact and rapid tongue movements. The speech disturbance was limited to verbal output, without aphasia or orofacial apraxia. Overlay of magnetic resonance images revealed a localized cortical region near face-M1, which displayed high intensity on diffusion weighted images, while the main portion of the corticobulbar fibers arising from the lower third of the motor cortex was preserved. The cases suggest the existence of a localized brain region specialized for articulation near face-M1. Cortico-cortical fibers connecting face-M1 with the lower premotor areas including Brocas area may also be important for articulatory control.

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

PurposeThe aim of this study was to develop ex vivo diffusion tensor (DT) flexible phantoms.Materials and methodsMaterials 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.ResultsWe 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.ConclusionThe 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.

MR imaging of ischemic penumbra

Cerebral ischemic stroke is one of the most fatal diseases despite current advances in medical science. Recent demonstration of efficacy using intravenous and intra-arterial thrombolysis demands therapeutic intervention tailored to the physiologic state of the individual tissue and stratification of patients according to the potential risks for therapies. In such an era, the role of the neuroimaging becomes increasingly important to evaluate the extent and location of tissues at risk of infarction (ischemic penumbra), to distinguish it from unsalvageable infarcted tissues or doomed hemorrhagic parenchyma. In this review, we present briefly the current role and limitation of computed tomography and conventional magnetic resonance imaging (MRI). We also present the possible applications of advanced MR techniques, such as diffusion and perfusion imaging, concentrating on the delineation or detection of ischemic penumbra.

Moyamoya disease: evaluation of postoperative revascularization using multiphase selective arterial spin labeling MRI.

Purpose The purpose of this study was to evaluate cerebral blood flow through the bypass in operated patients with Moyamoya disease using multiphase selective arterial spin labeling (ASL) technique. Materials and Methods Fifteen surgically treated cerebral hemispheres from 11 patients with Moyamoya disease were included. Selective ASL examinations were performed during the early postoperative period (mean, 5.5 days) on 4 hemispheres and late postoperative period (mean, 332.7 days) on 15 hemispheres. The labeling slab was positioned at the bypassed external carotid artery and 5 slices in each of the 10 sequential phases were acquired using a 3-T scanner. Results Two of 4 early postoperative ASL examinations and all late postoperative ASL examinations demonstrated blood flow through the bypass. The remaining 2 early postoperative ASL examinations showed absence of blood flow; however, blood flow improved on follow-up examinations. Conclusion Multiphase selective ASL technique can provide information about the dynamics of postoperative blood flow through the bypass in Moyamoya disease.