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- 2003 Conference Abstracts
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- 岡田知久
- Silent fMRI acquisition methods for large acoustic noise during scan
- Functional magnetic resonance imaging(fMRI)is now the method of choice for studying neural correlates of various tasks in normal subject as well as patients. This method,however,is inevitably coupled with the acoustic noise produced during the image acquisition process. This is a problem not only in auditory experiments but also in other cognitive tasks in general. The problems caused by such noise are modulation of auditory activation, impaired perception of auditory stimuli,and deterioration of task performance possibly due to stress from the abnormal circumstances. While both hardware and software solutions that can be implemented in scanners already installed. Their advantages and disadvantages diffre depending on the kinds of tasks involved,i.e.whether block design or event-related design, and they are disaussed with a view to better utilization.
- Bagarinao Epifanio
- Real time functional MRI using a PC cluster
- A system for the real-time analysis of functional magnetic resonance imaging (fMRI) time series is evaluated. The system exploits the advantages of parallel computing, coupled with an efficient general linear model (GLM) coefficient estimation algorithm, to overcome several issues constraining the analysis of the whole-brain fMRI data in real time. The highly parallel, voxel-wise processing of fMRI data motivated the use of a cluster of personal computers for parallel computation. Aside from gaining a significant increase in computational speed, the PC cluster provides a versatile way to handle the computational requirements of the system. The use of GLM in the supporting software allows substantial parametric analysis to be performed. Results of the real-time analysis of the whole-brain fMRI data of a normal subject performing a simple finger-tapping task demonstrated the capabilities of the system. For a real-time statistical analysis including real-time image reconstruction, realignment for motion correction, smoothing, GLM coefficient estimation, statistical analysis, and update of the displayed activation map, the time required to process the data for each image volume is about 1.034 s for a 64 x 64 x 30 image volume and 2.561 s for a 128 x 128 x 20 image volume, less than the TR set to 3s.
- 中井敏晴
- The effect of task block arrangement on the detectability of activation in fMRI
- The effect of task block arrangements on the detection of brain activation was investigated. Sessions of functional magnetic resonance imaging (fMRI) including the same number of two different task conditions but with different arrangements were compared. The two task conditions were, Ellipse-shaped black and white checkerboard flicker stimulation at 4.2 Hz covering the bilateral visual field, and the same flicker stimuli covering only the left visual field. In the rest blocks, the subjects looked at a fixation point. Four different task block arrangements were compared, 1)A0 (0A0A0A0) and B0 (0B0B0B0), 2) A0B0 (0A0B0A0B0A0B0), 3) AB0(0AB0AB0AB0) and 4) AB (0ABABAB). Bilateral V1, V2, V3 and the left V5 were activated by condition A, and the right V1 and V2 by B. The activation in the left visual field by A0 was larger than in the other three conditions. In a differential analysis between conditions A and B, activation in the left V3 and V5 was declined by AB0 or AB. When rest blocks were located in the post-stimulus undershoot phase, the % signal change of the BOLD signal was emphasized, which caused augmented significance in the detection of the activity. It was indicated that the outcome of the activation map was influenced by the arrangement of task blocks, even though the same number of task blocks were repeated within the sessions. In fMRI studies, task conditions should be carefully compared within or across sessions considering the characteristics of hemodynamic response functions.
- 岡田知久
- Facial recognition reactivates the primary visual cortex: an fnctional magnetic resonance imaging study in human
- In order to investigate how the brain represents sensory-specific information during memory retrieval, we examined functional magnetic resonance imaging's during a face-recognition task. When compared with activation associated with viewing of novel faces, recognition of faces presented 5 min before scanning activated the primary visual cortex, consistent with the hypothesis that retrieved facial information is coded by the reactivation of the brain regions engaged during sensory perception. This reactivation was not observed 14 weeks following initial presentation of the faces despite no significant difference in recognition rate between the two intervals. This suggests that accessing of visual information during memory retrieval is associated with the primary visual cortex, and that its activation is time-dependent ? probably related to the memory transformation or consolidation.
- 中井敏晴
- A study of subjective symptoms during functional magnetic resonance imaging at 3T
- The incidence of subjective symptoms during fMRI studies using a static magnetic field at 3T with a high power gradient coil system was examined. Ninety samples were obtained in the first investigation period, and 105 in the second period. Symptoms related to the static magnetic field that were ovserved were :dizziness,vertigo, and the seeing of flashing light. Dizziness was present in 2% of volunteers in the first investigation period and 10% in the second. Vertigo was present in 6% of volunteers in both periods. The seeing of flashing lights was present in 2% of volunteers in the first period and 3% in the second. Nausea, headache and tinnitus were not reported. Peripheral sensory stimulation was transient for a few seconds or at most under one minute and remained mild. It was present in 11% of volunteers in the first period and 6% in the second. No reports of pain, uncomfortabie sensations, or nerve stimulation other than sensory system stimulation were obtained. The most frequent regions of sensory nerve stimulation were the face and upper extrenities. Overall, sensory stimulation was more frequent using a fast spoiled gradient recalled echo(FSPGR) sequence than a EPI sequence. More than 40 % of the volunteers commented on the loudness of the acoustic noise. No significant relationship between the occurrence of subjective symptoms and the total scan time of the study, difficulty of task performance, or the scanner's noise was observed (p > 0.05). The volunteers' impression of the length of the study was significantly longer than the actual time if the scan time of the fMRI sessions was over 6 minutes. These results indicating the frequency of the subjective symptoms will help in improving the comfort of the volunteers and monitoring safety during fMRI studies using ultra high field MR scanners.
- 松尾香弥子
- Finger movements lighten the neural loads in the recognition of ideographic characters
- The role of finger writing movements in recognizing Japanese ideographic characters (Kanji) was investigated using functional magnetic resonance imaging at 3 T. A total of 12 healthy native Japanese-speaking volunteers were studied while counting the number of strokes in ideographic characters. In experiment 1, a representation of the pronunciation of an ideographic character was displayed using Japanese syllabic characters. Volunteers were required to count the strokes of the ideographic character corresponding to the displayed phonogram. This procedure included retrieval and generation of ideographic characters. In experiment 2, the ideographic character itself was displayed and the volunteers counted its strokes. This procedure focused on visuospatial imagery processes. Each experiment was conducted under two different motor conditions. One condition allowed the subject to use finger movements to count the strokes, while the other disallowed any finger movements. In both experiments, movement-allowed conditions duly activated the primary motor area. The phonogram-displayed and movement-disallowed condition induced an augmented activation in a part of the left premotor area, which was assumed to be Exner’s area. This area might have been activated by a demand for sequential generation of character graphemes that corresponded to the phonogram displayed. The ideographic-character-displayed and movement-disallowed condition activated the dorsal occipitoparietal areas and the primary visual area, which might be involved in the visuospatial mental imagery processes. These results suggest that execution of finger movements during stroke counting of ideographic characters lightens the neural loads for grapheme generation on Exner’s area and for the visuospatial imagery processes on the dorsal pathway.
- Bagarinao Epifanio
- Estimation of general linear model coefficients for real-time application
- An algorithm using an orthogonalization procedure to estimate the coefficients of general linear models (GLM) for functional magnetic resonance imaging (fMRI) calculations is described. The idea is to convert the basis functions or explanatory variables of a GLM into orthogonal functions using the usual Gram-Schmidt orthogonalization procedure. The coefficients associated with the orthogonal functions, henceforth referred to as auxiliary coefficients, are then easily estimated by applying the orthogonality condition. The original GLM coefficients are computed from these estimates. With this formulation, the estimates can be updated when new image data become available, making the approach applicable for real-time estimation. Since the contribution of each image data is immediatel incorporated into the estimated values, storing the data in memory during the estimation process becomes unnecessary, minimizing the memory requirements of the estimation process. By employing Cholesky decomposition, the algorithm is a factor of two faster than the standard recursive least-squares approach. Results of the analysis of an fMRI study using this approach showed the algorithm's potential for real-time application.
- 黒田輝
- Feasibility of internally referenced brain temperature imaging with a metabolite signal
- The feasibility of using a metabolite signal as an internal reference for self-referenced temprature distribution measurement was examined. Line scan echo-planar spectroscopic imaging(LSEPSI) was applied to obtain quick multi-voxel spectroscopic measurements and to avoid ossible spectral degradation from motion. Temperature distribution in a rabbit brain in vivo was successfully visualization by means of the chemical shift of water, which was measured by using naturally abundant( up to 10 mM) N-acetyl-aspartate( NAA ) as the reference signal. Unlike the phase-mapping approach, this technique does not require a pixel-by-pixel subtraction. Therefore, in theory, it is more resistant to inter-scan motion or changes in susceptibility. The spatial and temporal resolutions of this technique are 1.5立方cm and 4.5 min. A higher signal-to-noise ratio and optimization of the temperaturemapping capabilities.
- 大石健一
- Cortical motor areas in plantar response: an event-related functional MRI study in normal subjects
- The role of the cerebral cortices in normal plantar response was investigated with event-related functional magnetic resonance imaging (fMRI) at 3 Tesla in 12 right-handed normal subjects. During fMRI acquisition, the lateral (LS) and medial (MS) side of the left sole was mechanically stimulated every 16 s to evoke the plantar response under monitoring of the surface electromyogram. LS activated the contralateral elementary motor area (SMA) more intensively than MS. In contrast, no difference was found in the commonly activated areas including the contralateral primary sensorimotor area, bilateral secondary sensory areas and the thalamus. The results support the hypothesis that the normal plantar response is influenced by the cerebral cortices, and that the SMA likely participates in the regulation of the plantar reflex arc at the spinal level.
- 當間圭一郎
- The role of the human supplementary motor area in reactive motor operation
- The role of the supplementary motor area (SMA) in reactive motor operation was investigated with functional magnetic resonance imaging in 13 normal subjects. A visual cue was presented at a regular (1 Hz) or irregular (mean,1Hz) rate, and the subject pressed a button with the right index finger in a predictive or reactive manner. Brain regions associated with reactive movement were detected by comparing reactive with predictive movement tasks, and those with irregular movement by comparing irregular and regular cueing tasks. During regular cueing,the SMA showed greater activation for reactive than predictive movement. However, the SMA was equally activated between regular and irregular cueing once the subject reacted to the cue. The SMA is likely involved in reactive adjustment of movement to the external cue.
- 中井敏晴
- A functional magnetic resonance imaging study of internal modulation of an external visual cue for motor execution
- The strategy to perform a task differs according to how a cue is interpreted. In order to investigate the basic mechanisms of temporal regulation in the higher motor areas, the interaction between two different types of internal modulations of an external visual cue was evaluated using functional magnetic resonance imaging (fMRI). An opposing finger movement task guided by dot prompting was employed. In the intermittent tapping experiment, two taps per second and a rest for one second were alternatively repeated in the task blocks. In the constant tapping experiments, the volunteers performed finger movements at 0.5, 1 or 2 Hz. The activation in the primary sensory motor area correlated with the amount of movement. Activities in the supplementary motor area, left dorsal pre-motor area, left superior parietal lobule and right cerebellum depended on the demand for internal modulation. Activation in these areas was maximum for the intermittent task which was a combination of two different internal modulations, and minimum for the 1 Hz movement that did not require internal modulation. It was suggested that these four areas are directly involved in the generation of a complex movement sequence driven by a visual cue, and they are organized for performance. The translation of external pacing and initiation for self-pacing may share the same neuronal basis. Activation in the left supramarginal gyrus, bilateral frontal operticula and basal ganglia did not depend on the combination of the two internal modulations.
- 松尾香弥子
- Discrimination of Exner's area and the frontal eye field in humans-functional magnetic resonance imaging during language and saccade tasks
- In the left frontal lobe, Exner’s area (EXA), which is responsible for writing and reading, is located close to the frontal eye field (FEF),which is responsible for eye movements. To discriminate EXA from FEF anatomically and functionally, functional magnetic resonanceimaging was conducted in 12 healthy volunteers. The saccadic eye movement experiment activated a region defined as the FEF, whereas three language experiments that included translation between grapheme and phoneme activated another region defined as EXA. EXA was found to be located only 1.5 cm apart from the FEF in the Talairach brain template. By conducting the saccade and language experiments in the same individuals, this study was able to successfully separate EXA from FEF.