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Biomedical subjects

Toshinori Kato

Publications and source records attributed to Toshinori Kato.

10 recordsLinked to original sources
PubMed2006

TMS orientation for NIRS-functional motor mapping.

Functional near-infrared spectroscopic imaging (NIRS imaging) has the potential to elucidate the relationship between neuronal activity and oxygenation responses. However, its signal specificity to the functional cortex is sometimes spoiled by its rough spatial resolution. In this study we incorporated transcranial magnetic stimulation (TMS) motor mapping into an NIRS imaging study to enhance spatial specificity to the functional cortex. Distinctive biphasic responses in the cortical oxygenation status were observed in the center of the primary motor cortex during a motor task. The early response phase, occurring within 1 to 3 seconds after task initiation, represents a cortical deoxygenation which consists of a significant increase in deoxygenated hemoglobin concentration (HbR) and a nonsignificant decreasing tendency in oxygenated hemoglobin concentration (HbO(2)). The delayed response phase represents an excess of incoming blood flow, which appears as an increase in HbO(2)/total Hb (tHb) and a decrease in HbR following the early response. In the surrounding area, cortical oxygenation change showed a monophasic response consisting of an increase in HbO(2)/tHb and a decrease in HbR. Combining TMS mapping with NIRS imaging enabled us to specify the cortex with the strongest functional activity.

Adult↗
PubMed2005

Motor-related intracortical steal phenomenon detected by multichannel functional near-infrared spectroscopy imaging.

BACKGROUND: Patients with severe cerebral ischemia may lose autoregulation to increase cerebral blood flow following neural activity. Although the steal phenomenon under conventional cerebral blood flow study has been known as a high-risk factor for stroke, the cerebral oxygen hemodynamics in ischemic patients during functional activation has not been thoroughly investigated. In this study, we present rare cases with intracortical steal phenomenon during motor tasks detected by multichannel functional near-infrared spectroscopy before and after surgery. METHODS: The relative concentration change of oxygenated, deoxygenated and total hemoglobin in and around the primary sensorimotor cortex during contralateral hand grasping was investigated in 11 patients with severe internal carotid artery stenosis. RESULTS: In 3 patients, the concentration of total hemoglobin around the primary sensorimotor cortex significantly decreased in response to motor stimulation and returned to baseline soon after termination of the motor task. This phenomenon partially disappeared postoperatively in all patients who underwent surgery. The remaining 8 patients showed no signs of total hemoglobin decrease in and around the sensorimotor cortex. In 9 patients, lack of decrease in deoxygenated hemoglobin in the center of the primary motor cortex during the motor task was observed and 3 of them showed significant increase in deoxygenated hemoglobin. CONCLUSIONS: We have demonstrated that in some patients with severe ischemia, an abnormal motor-related steal phenomenon can be observed. This phenomenon can be modulated by surgical intervention and might imply the severity of ischemia.

Aged↗
PubMed2005

Evolution of subarachnoid space in normal fetuses using magnetic resonance imaging.

OBJECTIVE: The purpose of this study was to measure the fetal subarachnoid spaces at different sites of the brain using magnetic resonance (MR) images and analyze them in relation to gestational age. METHODS: Fetal MR images were obtained from 158 fetuses between 18 and 39 weeks of gestation who later showed no neurological problems. We bilaterally measured the distance between the superoanterior gyrus and the cranium as the frontal subarachnoid space (FSS) and the distance between the cortex in the parieto-occipital sulcus and the cranium as the parietal subarachnoid space (PSS). We also measured the cisterna magna between the cerebellar vermis and the cranium. Each of these was analyzed in relation to gestational age. RESULTS: The width of the FSS began to decrease significantly at 32 weeks of gestation (P < 0.05). The width of the PSS started to decrease significantly at 34 weeks of gestation (P < 0.05). There was no difference between the right and left sides (P < 0.05). The size of the cisterna magna showed a positive correlation with gestational age (P < 0.05). CONCLUSION: Measurement of the subarachnoid space is potentially useful for evaluating fetal development.

Cisterna Magna↗
PubMed2004

Theoretical evaluation of accuracy in position and size of brain activity obtained by near-infrared topography.

Near-infrared (NIR) topography can obtain a topographical distribution of the activated region in the brain cortex. Near-infrared light is strongly scattered in the head, and the volume of tissue sampled by a source-detector pair on the head surface is broadly distributed in the brain. This scattering effect results in poor resolution and contrast in the topographic image of the brain activity. In this study, a one-dimensional distribution of absorption change in a head model is calculated by mapping and reconstruction methods to evaluate the effect of the image reconstruction algorithm and the interval of measurement points for topographic imaging on the accuracy of the topographic image. The light propagation in the head model is predicted by Monte Carlo simulation to obtain the spatial sensitivity profile for a source-detector pair. The measurement points are one-dimensionally arranged on the surface of the model, and the distance between adjacent measurement points is varied from 4 mm to 28 mm. Small intervals of the measurement points improve the topographic image calculated by both the mapping and reconstruction methods. In the conventional mapping method, the limit of the spatial resolution depends upon the interval of the measurement points and spatial sensitivity profile for source-detector pairs. The reconstruction method has advantages over the mapping method which improve the results of one-dimensional analysis when the interval of measurement points is less than 12 mm. The effect of overlapping of spatial sensitivity profiles indicates that the reconstruction method may be effective to improve the spatial resolution of a two-dimensional reconstruction of topographic image obtained with larger interval of measurement points. Near-infrared topography with the reconstruction method potentially obtains an accurate distribution of absorption change in the brain even if the size of absorption change is less than 10 mm.

Algorithms↗
PubMed2004

Assessment of cortical gyrus and sulcus formation using magnetic resonance images in small-for-gestational-age fetuses.

OBJECTIVES: The purpose was to compare the development of gyrus and sulcus formation (GSF), an indicator of brain maturation, in small-for-gestational-age (SGA) fetuses using magnetic resonance (MR) imaging, with those of appropriate-for-gestational-age (AGA) fetuses. METHODS: The 160 infants with a normal neurological outcome were divided into two groups on the basis of their body weight at delivery; 37 SGA infants (Group SGA) and 123 AGA infants (Group AGA). Fetal MR images, which were obtained from 28 to 39 gestational weeks in Group SGA and from 18 to 39 gestational weeks in Group AGA, were classified into the 8 stages of development for GSF established by Abe et al. (2003), and comparison was made between the two groups retrospectively in their neurological development in relation to gestational age. RESULTS: In Group SGA, images were classified into stages 3 to 8 (P < 0.001). The gestational age of the cases determined for each stage between Groups SGA and AGA did not differ significantly, with respect to the development of GSF, despite differences in fetal estimated body weights. CONCLUSION: In SGA fetuses, evaluation of fetal GSF using MR images during the third trimester may be useful for predicting neurological prognoses postpartum.

Adult↗
PubMed2004

Semiquantitative assessment of myelination using magnetic resonance imaging in normal fetal brains.

OBJECTIVES: To evaluate the development of myelination in normal fetuses quantitatively using magnetic resonance (MR) imaging in relation to gestational age (GA). METHODS: Fetal MR images were obtained from 101 fetuses between 26 and 39 weeks of gestation with no neurological problems. Regions of interest were designated in frontal lobe, corona radiata, optic radiation, thalamus, pons, cerebellar vermis, and vitreous body. The signal intensity ratio (SIR) was calculated by the signal intensity of each of these designated areas to that of the vitreous body and analyzed in relation to GA. RESULTS: The SIR of the frontal lobe did not vary significantly with GA. The SIR of the corona radiata and the optic radiation decreased significantly with GA (P < 0.05); after 34 weeks of gestation, they decreased sharply. The SIR of the thalamus, the pons, and the cerebellar vermis was significantly smaller than that of the cerebral white matter at 26 weeks of gestation (P < 0.05) and decreased significantly with GA (P < 0.05). CONCLUSION: Changes in the SIR approximately corresponded to the time-course of progression of myelination in the previous histopathological reports. Semiquantitative evaluation on MR images may allow prenatal diagnosis of a delay or deficit of myelination.

Brain↗
PubMed2003

Evaluation of hippocampal infolding using magnetic resonance imaging.

To investigate developmental morphological variation of the hippocampal formation, we evaluated the degree of hippocampal infolding in cross-sectional oblique coronal images of the cerebral peduncle and the superior cerebellar peduncle. We defined the hippocampal infolding angle as the angle between the vertical midline and the straight line connecting the medial superior margin of the subiculum with the lateral margin of the cornu ammonis. The angle increased slightly with age, and was larger in the superior cerebellar peduncle than in the cerebral peduncle and larger in the right superior cerebellar peduncle than in the left superior cerebellar peduncle. This suggests that this angle and its variation with age and location merit our attention in morphological evaluation of the hippocampal formation.

Adolescent↗
PubMed2003

Assessment of cortical gyrus and sulcus formation using MR images in normal fetuses.

OBJECTIVES: The purpose of this study was to estimate the development of the gyrus and sulcus formation in normal fetuses on the basis of the neuroanatomical findings using MR images in relation to gestational age. METHODS: The MR images were obtained from 109 normal fetuses from 18 to 39 weeks of gestation with no neurological problems. The MR images were classified into 8 stages of development for the gyrus and sulcus formation in the frontal and temporal lobes on the basis of the neuroanatomical findings reported by Chi et al. (1977) and Dorovini-Zis and Dolman (1977). We examined retrospectively the relationship between our classification and gestational age in comparison with the five-stage classification proposed by McArdle et al. (1987). RESULTS: There were significant differences in the gestational age among the 8 groups (P < 0.001). Multiple comparison of individual groups revealed significant differences in the gestational age among the groups (P < 0.05). Images from 28 to 34 weeks of gestation were classified into 4 stages in our classification, while being covered by one stage in McArdle's classification. CONCLUSION: Our classification is useful for the assessment of fetal cerebral maturation during the third trimester of pregnancy and may contribute to the prenatal diagnosis of developmental delay of the gyrus and sulcus formation.

Cerebral Cortex↗
PubMed2002

Paradoxical correlation between signal in functional magnetic resonance imaging and deoxygenated haemoglobin content in capillaries: a new theoretical explanation.

Signal increases in functional magnetic resonance imaging (fMRI) are believed to be a result of decreased paramagnetic deoxygenated haemoglobin (deoxyHb) content in the neural activation area. However, discrepancies in this canonical blood oxygenation level dependent (BOLD) theory have been pointed out in studies using optical techniques, which directly measure haemoglobin changes. To explain the discrepancies, we developed a new theory bridging magnetic resonance (MR) signal and haemoglobin changes. We focused on capillary influences, which have been neglected in most previous fMRI studies and performed a combined fMRI and near-infrared spectroscopy (NIRS) study using a language task. Paradoxically, both the MR signal and deoxyHb content increased in Broca's area. On the other hand, fMRI activation in the auditory area near large veins correlated with a mirror-image decrease in deoxyHb and increase in oxygenated haemoglobin (oxyHb), in agreement with canonical BOLD theory. All fMRI signal changes correlated consistently with changes in oxyHb, the diamagnetism of which is insensitive to MR. We concluded that the discrepancy with the canonical BOLD theory is caused by the fact that the BOLD theory ignores the effect of the capillaries. Our theory explains the paradoxical phenomena of the oxyHb and deoxyHb contributions to the MR signal and gives a new insight into the precise haemodynamics of activation by analysing fMRI and NIRS data.

Biophysical Phenomena↗