Ryuta Ito

Cortical and subcortical vestibular response to caloric stimulation detected by functional magnetic resonance imaging

The posterior insula, central sulcus, and inferior parietal lobule including the intraparietal sulcus have been considered the vestibular cortex based on functional brain mapping in humans as well as experiments in lower primates. The same regions receive optokinetic, visual, and proprioceptive projections. We examined the cortical and subcortical projection of vestibular activity with visual and proprioceptive input eliminated during caloric stimulation (CS), using functional magnetic resonance imaging (fMRI). Single-shot gradient-echo echoplanar image (EPI) volumes were sensitive to BOLD contrast in oblique orientation. We adopted a pharmacokinetic model for analysis of imaging data from 10 subjects as a group. The insular gyrus, intraparietal sulcus, superior temporal gyrus, hippocampus, cingulate gyrus, and thalamus showed activation by CS. Cortical and subcortical activation during CS in the present study was observed within regions less precisely delineated by other methods. As intraparietal sulcus activation showed right hemispheric dominance, this region may have an oculomotor projection as well as the vestibular input.

Diffusion tensor brain MR imaging in X-linked cerebral adrenoleukodystrophy

Brain diffusion tensor MRI of 11 boys with X-linked adrenoleukodystrophy was performed. The authors determined quantitative isotropic apparent diffusion coefficient (ADCi) and fractional anisotropy (FA) values in the white matter. ADCi and FA values in the affected white matter were significantly different from those in normal-appearing white matter. Zonal ADCi and FA gradations, which might originate from well-established histopathologic zonal changes, existed within affected white matter.

DIFFUSION TENSOR BRAIN IMAGING AND TRACTOGRAPHY

Diffusion-tensor MR imaging is a promising tool to evaluate white-matter integrity by quantitative and graphic maps including neural fiber tractogram. Current challenges afoot are to obtain higher quality diffusion-weighted MR images (high SNR, isotropic voxel, and high spatial resolution), to create a robust mathematical framework to process the data, to construct a user-friendly computer-based algorithm, to reveal determinants of diffusion process, and to establish analytical methodology.

Stereopsis-processing regions in the human parieto-occipital cortex.

We performed fMRI on the human parieto-occipital cortex in order to identify the neural processing regions of stereopsis. Visual stimulation for stereopsis was performed with a random-dot stereogram displayed in the image guides of a new binocular visual stimulation device that we developed. Interestingly, regions from the dorsal portion of the occipital lobe to the superior parietal lobule were activated by binocular disparity, while the inferior parietal lobule was not activated. Moreover, these regions were shown as dominant in the right hemisphere. Functional brain mapping revealed that the processing regions of stereopsis were dorsally located in parieto-occipital cortex, and that the superior parietal lobule is an important region for neural processing of human stereopsis.

Estimation of Cerebral Perfusion Reserve by Blood Oxygenation Level—Dependent Imaging: Comparison with Single-Photon Emission Computed Tomography

Measurement of cerebrovascular reserve capacity predicts the risk of ischemic insult in patients with major vessel occlusion. Blood oxygenation level-dependent (BOLD) imaging has the potential to estimate reserve capacity of the cerebral circulation noninvasively based on changes in the signal that reflect differences in the magnetic susceptibility of intravascular oxyhemoglobin and deoxyhemoglobin. The authors examined the feasibility of using the BOLD technique to assess cerebrovascular reserve capacity in patients with cerebrovascular occlusive disease by comparing results with an established method of measuring CBF. Ten patients with severe or complete occlusion of the internal carotid artery were compared with 17 healthy subjects to evaluate regional differences and identify variables that indicate a change in the BOLD signal. Dilation of cerebral vessels was induced by breath holding, and the R2* change was examined with gradient-echo, echo-planar imaging. Before measuring the regional change in the BOLD signal, actual timing of “activated” and “rest” periods was corrected by shifting the phase of a sine-wave template to obtain the largest correlation coefficient. Percent signal change was calculated on a pixel-by-pixel basis and was compared with CBF measured by single-photon emission computed tomography (SPECT) before and after acetazolamide challenge. The degree of impairment and the distribution of impaired areas detected by the BOLD study correlated with the results of SPECT. Overall sensitivity and specificity of the BOLD technique by visual inspection were 100% and 98.4%, respectively. A negative response (decreased CBF) frequently was observed in areas of exhausted reserve capacity, suggesting that a “steal” phenomenon exists. The percent change and the ΔCBF were well correlated (P < 0.01). The mean percent change in most areas of impaired reserve capacity was more than 2 SD below the mean values in healthy subjects. The present method of semiquantitative BOLD analysis can be used to create a map of the cerebral hemodynamic state. Furthermore, the development of reliable, generally accessible techniques for evaluating cerebral hemodynamics opens the door for clinical studies to monitor and treat patients with compromised reserve. This study is an attempt to develop such analysis.

Maturational changes in diffusion anisotropy in the rat corpus callosum: Comparison with quantitative histological evaluation

To determine the main histological components that affect fractional anisotropy (FA) in postnatal development of the rat corpus callosum and compare FA values with histological changes evaluated quantitatively.

Cortical representation of hearing restoration in patients with sudden deafness

To characterize brain activity in response to auditory stimuli during recovery from acute hearing loss, fMRI was performed at two time points in 11 patients with sudden deafness in the right ear, and 10 subjects with normal hearing. In the acute phase, right-ear auditory stimulation induced only a small response in the auditory cortex, limited to the left hemisphere. In the recovery phase, the auditory response was more extensive than in the acute phase. Stimulation of the left ear induced a more extensive response in the left than right hemisphere in both acute and recovery phases, which differed from the pattern in normal subjects. The changes in cortical activation patterns were seen within 1 week of sudden deafness. Thus, alteration of cortical response in deafness occurs earlier than suggested by previous reports.

Common neural processing regions for dynamic and static stereopsis in human parieto-occipital cortices.

We performed functional magnetic resonance imaging to identify the neural processing regions in the parieto-occipital cortices for human dynamic and static stereopsis. The subjects were ten ophthalmologists professionally trained to do microscopic surgery. Visual stimuli for dynamic or static stereopsis were performed with solid stereograms displayed in the image guides of a binocular visual stimulation device that we developed. The dorsal occipital portion and the superior parietal lobule (i.e. dorsal parieto-occipital portion) were activated not only in static stereopsis, but also in dynamic stereopsis. The activation showed a right hemispherical dominancy. On the other hand, the temporo-occipital junction (i.e. human MT (middle temporal area) / MST (medial superior temporal area) complex) was activated in dynamic stereopsis. This demonstrates that the dorsal parieto-occipital portion is a common neural processing region for dynamic and static stereopsis.

Development of a new binocular visual stimulation device using image guides for functional MRI

Functional magnetic resonance imaging (fMRI) makes it possible to detect regions of neuronal activity in the brain. Moreover, this examination is quite non-invasive. Although fMRI is popularly employed in ophthalmology, it is sometimes impossible to give optimal visual stimulation to the subject because the space inside the MRI equipment is very small and has a strong magnetic field. Thus, there are strict limitations on visual stimulation devices. In order to resolve these problems, we developed a new binocular visual stimulation device for fMRI using image guides. This device consists of a pair of image guides, LCD projectors, C-mounted objective lenses, and eyepieces. The image guides and the eyepieces are diamagnetic. They can be attached to the surface or head coil unit of the MRI equipment without any magnetic influence on the fMRI signals. Since the images in both eyepieces are completely separated, binocular parallax stimulation can easily be given to a subject. This makes it possible to investigate stereopsis with fMRI. This device will be very useful for the fMRI investigation of the brain region related to visual function.

Metastatic adenocarcinoma presenting as a homogeneously high density mass on CT

We report a case of metastatic adenocarcinoma to the brain that appeared as a homogeneously hyperdense mass on CT. The lesion was initially diagnosed as an intracerebral hematoma. On serial CT scans, the high density lesion progressively enlarged. Pathology showed coagulation necrosis without hemorrhage or calcification. Analysis of the tumor revealed elevation of the protein content relative to the normal brain. We conclude that the high CT attenuation was due to the elevated protein content.