The Experts below are selected from a list of 201 Experts worldwide ranked by ideXlab platform

Peter D D Schwindt - One of the best experts on this subject based on the ideXlab platform.

  • non invasive functional brain imaging with an opm based Magnetoencephalography System
    PLOS ONE, 2020
    Co-Authors: Amir Borna, T R Carter, Anthony P Colombo, Julia M Stephen, Michael P Weisend, Samu Taulu, James R Mckay, Peter D D Schwindt
    Abstract:

    A non-invasive functional-brain-imaging System based on optically-pumped-magnetometers (OPM) is presented. The OPM-based Magnetoencephalography (MEG) System features 20 OPM channels conforming to the subject’s scalp. We have conducted two MEG experiments on three subjects: assessment of somatosensory evoked magnetic field (SEF) and auditory evoked magnetic field (AEF) using our OPM-based MEG System and a commercial MEG System based on superconducting quantum interference devices (SQUIDs). We cross validated the robustness of our System by calculating the distance between the location of the equivalent current dipole (ECD) yielded by our OPM-based MEG System and the ECD location calculated by the commercial SQUID-based MEG System. We achieved sub-centimeter accuracy for both SEF and AEF responses in all three subjects. Due to the proximity (12 mm) of the OPM channels to the scalp, it is anticipated that future OPM-based MEG Systems will offer enhanced spatial resolution as they will capture finer spatial features compared to traditional MEG Systems employing SQUIDs.

  • non invasive functional brain imaging with a novel Magnetoencephalography System
    arXiv: Medical Physics, 2018
    Co-Authors: Amir Borna, T R Carter, Anthony P Colombo, Jim Mckay, Julia M Stephen, Michael P Weisend, Samu Taulu, Peter D D Schwindt
    Abstract:

    A non-invasive functional-brain-imaging System based on optically-pumped-magnetometers (OPM) is presented. The OPM-based Magnetoencephalography (MEG) System features 20 OPM channels conforming to the subject's scalp. Due to proximity (12 mm) of the OPM channels to the brain, it is anticipated that this MEG System offers an enhanced spatial resolution as it can capture finer spatial features compared to traditional MEG Systems employing superconducting quantum interference device (SQUID). We have conducted two MEG experiments on three subjects: somatosensory evoked magnetic field (SEF) and auditory evoked magnetic field (AEF) using our OPM-based MEG System and a commercial SQUID-based MEG System. We have cross validated the robustness of our System by calculating the distance between the location of the equivalent current dipole (ECD) yielded by our OPM-based MEG System and the ECD location calculated by the commercial SQUID-based MEG System. We achieved sub-centimeter accuracy for both SEF and AEF responses in all three subjects.

  • a 20 channel Magnetoencephalography System based on optically pumped magnetometers
    Physics in Medicine and Biology, 2017
    Co-Authors: Amir Borna, T R Carter, Josh D Goldberg, Anthony P Colombo, Christopher Berry, Jim Mckay, Julia M Stephen, Michael P Weisend, Peter D D Schwindt
    Abstract:

    We describe a multichannel Magnetoencephalography (MEG) System that uses optically pumped magnetometers (OPMs) to sense the magnetic fields of the human brain. The System consists of an array of 20 OPM channels conforming to the human subject's head, a person-sized magnetic shield containing the array and the human subject, a laser System to drive the OPM array, and various control and data acquisition Systems. We conducted two MEG experiments: auditory evoked magnetic field and somatosensory evoked magnetic field, on three healthy male subjects, using both our OPM array and a 306-channel Elekta-Neuromag superconducting quantum interference device (SQUID) MEG System. The described OPM array measures the tangential components of the magnetic field as opposed to the radial component measured by most SQUID-based MEG Systems. Herein, we compare the results of the OPM- and SQUID-based MEG Systems on the auditory and somatosensory data recorded in the same individuals on both Systems.

Nobukazu Nakasato - One of the best experts on this subject based on the ideXlab platform.

  • Somatosensory evoked fields in comatose survivors after severe traumatic brain injury
    Clinical Neurophysiology, 2020
    Co-Authors: Masaki Iwasaki, Akitake Kanno, Nobukazu Nakasato, Keisaku Hatanaka, Ken-ichi Nagamatsu, Yoshihide Nagamine, Takashi Yoshimoto
    Abstract:

    Abstract Objective : To evaluate the cortical function quantitatively in patients in the chronic phase of severe traumatic brain injury. Methods : Thirteen patients with severe traumatic brain injury due to traffic accident followed by persistent consciousness disturbance and disability were studied. Somatosensory evoked magnetic fields (SEFs) for unilateral median nerve stimulation were measured using a whole-head Magnetoencephalography System. The latency and electrical current dipole (ECD) moment for the N20m, P30m, N45m and P60m components were calculated and compared with those of 14 age-matched healthy adults. Results : The peak latency of N20m was longer ( P P P Conclusions : These results can be explained by the hypothesis that diffuse brain injury induces decreased and delayed input of the somatosensory afferent and compensational amplification of the response in the primary somatosensory cortex. Middle-latency SEFs may be applicable as a cortical functional measure for patients with severe traumatic brain injury.

  • Effects of Visual Speech on Early Auditory Evoked Fields - From the Viewpoint of Individual Variance
    PLOS ONE, 2017
    Co-Authors: Izumi Yahata, Akitake Kanno, Nobukazu Nakasato, Tetsuaki Kawase, Hiroshi Hidaka, Shuichi Sakamoto, Ryuta Kawashima, Yukio Katori
    Abstract:

    The effects of visual speech (the moving image of the speaker's face uttering speech sound) on early auditory evoked fields (AEFs) were examined using a helmet-shaped Magnetoencephalography System in 12 healthy volunteers (9 males, mean age 35.5 years). AEFs (N100m) in response to the monosyllabic sound /be/ were recorded and analyzed under three different visual stimulus conditions, the moving image of the same speaker's face uttering /be/ (congruent visual stimuli) or uttering /ge/ (incongruent visual stimuli), and visual noise (still image processed from speaker's face using a strong Gaussian filter: control condition). On average, latency of N100m was significantly shortened in the bilateral hemispheres for both congruent and incongruent auditory/visual (A/V) stimuli, compared to the control A/V condition. However, the degree of N100m shortening was not significantly different between the congruent and incongruent A/V conditions, despite the significant differences in psychophysical responses between these two A/V conditions. Moreover, analysis of the magnitudes of these visual effects on AEFs in individuals showed that the lip-reading effects on AEFs tended to be well correlated between the two different audio-visual conditions (congruent vs. incongruent visual stimuli) in the bilateral hemispheres but were not significantly correlated between right and left hemisphere. On the other hand, no significant correlation was observed between the magnitudes of visual speech effects and psychophysical responses. These results may indicate that the auditory-visual interaction observed on the N100m is a fundamental process which does not depend on the congruency of the visual information.

  • Effects of Contralateral Noise on the 20-Hz Auditory Steady State Response - Magnetoencephalography Study
    PLOS ONE, 2014
    Co-Authors: Hajime Usubuchi, Akitake Kanno, Nobukazu Nakasato, Tetsuaki Kawase, Izumi Yahata, Ryuta Kawashima, Hiromitsu Miyazaki, Yukio Katori
    Abstract:

    The auditory steady state response (ASSR) is an oscillatory brain response, which is phase locked to the rhythm of an auditory stimulus. ASSRs have been recorded in response to a wide frequency range of modulation and/or repetition, but the physiological features of the ASSRs are somewhat different depending on the modulation frequency. Recently, the 20-Hz ASSR has been emphasized in clinical examinations, especially in the area of psychiatry. However, little is known about the physiological properties of the 20-Hz ASSR, compared to those of the 40-Hz and 80-Hz ASSRs. The effects of contralateral noise on the ASSR are known to depend on the modulation frequency to evoke ASSR. However, the effects of contralateral noise on the 20-Hz ASSR are not known. Here we assessed the effects of contralateral white noise at a level of 70 dB SPL on the 20-Hz and 40-Hz ASSRs using a helmet-shaped Magnetoencephalography System in 9 healthy volunteers (8 males and 1 female, mean age 31.2 years). The ASSRs were elicited by monaural 1000-Hz 5-s tone bursts amplitude-modulated at 20 and 39 Hz and presented at 80 dB SPL. Contralateral noise caused significant suppression of both the 20-Hz and 40-Hz ASSRs, although suppression was significantly smaller for the 20-Hz ASSRs than the 40-Hz ASSRs. Moreover, the greatest suppression of both 20-Hz and 40-Hz ASSRs occurred in the right hemisphere when stimuli were presented to the right ear with contralateral noise. The present study newly showed that 20-Hz ASSRs are suppressed by contralateral noise, which may be important both for characterization of the 20-Hz ASSR and for interpretation in clinical situations. Physicians must be aware that the 20-Hz ASSR is significantly suppressed by sound (e.g. masking noise or binaural stimulation) applied to the contralateral ear.

  • Auditory evoked magnetic fields in patients with absent brainstem responses due to auditory neuropathy with optic atrophy.
    Clinical Neurophysiology, 2011
    Co-Authors: Yusuke Takata, Akitake Kanno, Nobukazu Nakasato, Tetsuaki Kawase, Toshimitsu Kobayashi
    Abstract:

    Abstract Objective To examine whether auditory evoked fields (AEFs) can be used to objectively evaluate hearing in patients with absent auditory brainstem responses (ABRs) due to auditory neuropathy. Methods Subjects were 3 patients with auditory neuropathy, 1 male aged 29 years and 2 females aged 18 and 27 years, with absence of click evoked ABRs for bilateral ear stimuli at a level of 105 dB nHL. All patients also had optic atrophy. AEFs were measured with a helmet-shaped Magnetoencephalography System for 2.0 kHz tone bursts of 60 ms duration to the unilateral ear. Results Bihemispherical AEF responses were clearly recorded in all three patients for either left or right ear stimulus. Although the latencies of N100m were severely prolonged and amplitudes were considerably decreased compared to the normal range of N100m responses in our facilities, N100m latency of AEF was shorter in the contralateral hemisphere to the stimulated ear, as usually found in normal subjects, despite the abnormal delay in N100m latency in all conditions. Conclusions Presence and abnormality of auditory cortical responses can be evaluated by AEFs in patients with auditory neuropathy even under null responses in ABRs. Significance AEFs are useful to evaluate residual hearing in patients with auditory neuropathy.

  • Contralateral white noise attenuates 40-Hz auditory steady-state fields but not N100m in auditory evoked fields
    NeuroImage, 2011
    Co-Authors: Tetsuaki Kawase, Akitake Kanno, Nobukazu Nakasato, Atsuko Maki, Mika Sato, Toshimitsu Kobayashi
    Abstract:

    Abstract The different response characteristics of the different auditory cortical responses under conventional central masking conditions were examined by comparing the effects of contralateral white noise on the cortical component of 40-Hz auditory steady state fields (ASSFs) and the N100m component in auditory evoked fields (AEFs) for tone bursts using a helmet-shaped Magnetoencephalography System in 8 healthy volunteers (7 males, mean age 32.6 years). The ASSFs were elicited by monaural 1000 Hz amplitude modulation tones at 80 dB SPL, with the amplitude modulated at 39 Hz. The AEFs were elicited by monaural 1000 Hz tone bursts of 60 ms duration (rise and fall times of 10 ms, plateau time of 40 ms) at 80 dB SPL. The results indicated that continuous white noise at 70 dB SPL presented to the contralateral ear did not suppress the N100m response in either hemisphere, but significantly reduced the amplitude of the 40-Hz ASSF in both hemispheres with asymmetry in that suppression of the 40-Hz ASSF was greater in the right hemisphere. Different effects of contralateral white noise on these two responses may reflect different functional auditory processes in the cortices.

Takashi Yoshimoto - One of the best experts on this subject based on the ideXlab platform.

  • Somatosensory evoked fields in comatose survivors after severe traumatic brain injury
    Clinical Neurophysiology, 2020
    Co-Authors: Masaki Iwasaki, Akitake Kanno, Nobukazu Nakasato, Keisaku Hatanaka, Ken-ichi Nagamatsu, Yoshihide Nagamine, Takashi Yoshimoto
    Abstract:

    Abstract Objective : To evaluate the cortical function quantitatively in patients in the chronic phase of severe traumatic brain injury. Methods : Thirteen patients with severe traumatic brain injury due to traffic accident followed by persistent consciousness disturbance and disability were studied. Somatosensory evoked magnetic fields (SEFs) for unilateral median nerve stimulation were measured using a whole-head Magnetoencephalography System. The latency and electrical current dipole (ECD) moment for the N20m, P30m, N45m and P60m components were calculated and compared with those of 14 age-matched healthy adults. Results : The peak latency of N20m was longer ( P P P Conclusions : These results can be explained by the hypothesis that diffuse brain injury induces decreased and delayed input of the somatosensory afferent and compensational amplification of the response in the primary somatosensory cortex. Middle-latency SEFs may be applicable as a cortical functional measure for patients with severe traumatic brain injury.

  • Movement-Related Magnetic Fields to Tongue Protrusion
    NeuroImage, 2001
    Co-Authors: Nobukazu Nakasato, Akitake Kanno, Keisaku Hatanaka, Hidemi Itoh, Hiroko Nakahara, Takashi Yoshimoto
    Abstract:

    Movement-related magnetic fields (MRFs) associated with tongue protrusion were measured in five normal subjects using a helmet-shaped Magnetoencephalography System. Bihemispherical two-dipolar patterns appeared from approximately −2000 or −1000 to 0 ms to the trigger signal indicating when protrusion of the tongue tip reached the frontal part of the palate. Equivalent current dipoles (ECDs) for the MRFs were localized on the central sulcus, 14.4 ± 6.1 mm inferior (P < 0.0001) and 7.6 ± 6.9 mm anterior (P < 0.01) to the ECD for the N20m in the somatosensory evoked fields for median nerve stimuli. The ECD orientations of MRFs were anterior and perpendicular to the central sulcus. These results correspond to the movement-related potentials for tongue protrusion previously recorded from subdural electrodes in patients with epilepsy. Magnetoencephalography can be applied to analyze cortical functions related to tongue movement with high resolution in time and space in normal subjects.

  • Hemispheric asymmetry of the auditory evoked N100m response in relation to the crossing point between the central sulcus and Sylvian fissure
    Electroencephalography and Clinical Neurophysiology, 1998
    Co-Authors: Satoru Ohtomo, Akitake Kanno, Nobukazu Nakasato, Keisaku Hatanaka, Reizo Shirane, Kazuo Mizoi, Takashi Yoshimoto
    Abstract:

    The positions of the bilateral N100m sources of the auditory evoked magnetic fields (AEFs) were measured in relation to the central sulcus (CS) using an MRI-linked whole head Magnetoencephalography System in 20 right-handed normal male subjects. The location of the N20m source of the median nerve-stimulated somatosensory evoked magnetic fields (SEFs), in the left hemisphere was 3.9±5.4 mm (mean±SD) posterior to that in the right hemisphere (P

  • Interhemispheric asymmetry exists in female in the N100m source position of the auditory evoked magnetic fields
    Nō to shinkei Brain and nerve, 1998
    Co-Authors: Akitake Kanno, Nobukazu Nakasato, Satoru Fujiwara, Satoru Ohtomo, Keisaku Hatanaka, Reizo Shirane, Kyoko Suzuki, Takashi Yoshimoto
    Abstract:

    The N100m source of the auditory evoked magnetic fields (AEFs) is located more posterior in the left than the right hemisphere in male subjects. However, whether this asymmetry exists in female subjects is controversial. The present study, analyzed the N100m source positions of the AEFs due to monaural tone stimuli using a helmet-shaped 66-channel Magnetoencephalography System (CTF Systems) in 62 right-handed normal adults (24 females and 38 males). The best fit sphere was calculated for each subject from the head shape reconstructed from three-dimensional magnetic resonance images. N100m source positions were estimated using a double-dipole model. The contralateral N100m response to the stimulated ear was measured relative to the midpoint of the bilateral auricular points. Statistical analysis used a standardized head size for each subject based on the mean value of all subjects (r = 8.27 cm). In females, the N100m dipole positions were 0.00 +/- 1.02 cm anterior in the left hemisphere and 0.35 +/- 0.74 cm in the right (p < 0.02). In males, the N100m dipole positions were -0.31 +/- 0.81 cm (mean +/- standard deviation) anterior in the left hemisphere and 0.61 +/- 0.78 cm in the right (p < 0.0001). The interhemispheric difference in the N100m positions was 0.35 +/- 0.65 in females and 0.92 +/- 0.77 in males (p < 0.005). In conclusion, the left hemispheric N100m is located more posterior to the right in both genders. However, this functional asymmetry is more evident in males, like previous findings of more evident anatomical asymmetry in males.

  • Localizing the central sulcus by functional magnetic resonance imaging and Magnetoencephalography
    Clinical Neurology and Neurosurgery, 1997
    Co-Authors: Hiroaki Shimizu, Nobukazu Nakasato, Kazuo Mizoi, Takashi Yoshimoto
    Abstract:

    Abstract To further validate the potential of functional magnetic resonance imaging (fMRI) for localization of the sensorimotor cortex, fMRI was compared with somatosensory evoked fields (SEFs) in eight normal volunteers. A conventional 1.5 T MRI scanner and an MRI-linked 66-channel whole head Magnetoencephalography System were used. fMRI activated by unilateral hand squeeze movement indicated the highest activation on the central sulci that were localized by SEFs in all 16 contralateral hemispheres. This indicates that although the fMRI signal activation may originate from a vein running along the central sulcus, fMRI is reliable to detect the central sulcus. The pre-central gyrus also indicated some signal activation on fMRI implying better visualization of spatial distribution of activation. fMRI and SEFs are complementary methods for localizing the central sulcus.

J Penttila - One of the best experts on this subject based on the ideXlab platform.

  • hybrid ultra low field mri and Magnetoencephalography System based on a commercial whole head neuromagnetometer
    Magnetic Resonance in Medicine, 2013
    Co-Authors: Panu T Vesanen, Jaakko O Nieminen, Koos C J Zevenhoven, Juhani Dabek, Lauri Parkkonen, Andrey Zhdanov, Juho Luomahaara, Juha Hassel, J Penttila
    Abstract:

    Ultra-low-field MRI uses microtesla fields for signal encoding and sensitive superconducting quantum interference devices for signal detection. Similarly, modern Magnetoencephalography (MEG) Systems use arrays comprising hundreds of superconducting quantum interference device channels to measure the magnetic field generated by neuronal activity. In this article, hybrid MEG-MRI instrumentation based on a commercial whole-head MEG device is described. The combination of ultra-low-field MRI and MEG in a single device is expected to significantly reduce coregistration errors between the two modalities, to simplify MEG analysis, and to improve MEG localization accuracy. The sensor solutions, MRI coils (including a superconducting polarizing coil), an optimized pulse sequence, and a reconstruction method suitable for hybrid MEG-MRI measurements are described. The performance of the device is demonstrated by presenting ultra-low-field-MR images and MEG recordings that are compared with data obtained with a 3T scanner and a commercial MEG device. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.

  • Hybrid ultra‐low‐field MRI and Magnetoencephalography System based on a commercial whole‐head neuromagnetometer
    Magnetic Resonance in Medicine, 2012
    Co-Authors: Panu T Vesanen, Jaakko O Nieminen, Koos C J Zevenhoven, Juhani Dabek, Lauri Parkkonen, Andrey Zhdanov, Juho Luomahaara, Juha Hassel, J Penttila, Juha Simola
    Abstract:

    Ultra-low-field MRI uses microtesla fields for signal encoding and sensitive superconducting quantum interference devices for signal detection. Similarly, modern Magnetoencephalography (MEG) Systems use arrays comprising hundreds of superconducting quantum interference device channels to measure the magnetic field generated by neuronal activity. In this article, hybrid MEG-MRI instrumentation based on a commercial whole-head MEG device is described. The combination of ultra-low-field MRI and MEG in a single device is expected to significantly reduce coregistration errors between the two modalities, to simplify MEG analysis, and to improve MEG localization accuracy. The sensor solutions, MRI coils (including a superconducting polarizing coil), an optimized pulse sequence, and a reconstruction method suitable for hybrid MEG-MRI measurements are described. The performance of the device is demonstrated by presenting ultra-low-field-MR images and MEG recordings that are compared with data obtained with a 3T scanner and a commercial MEG device. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.

Andrey Zhdanov - One of the best experts on this subject based on the ideXlab platform.

  • hybrid ultra low field mri and Magnetoencephalography System based on a commercial whole head neuromagnetometer
    Magnetic Resonance in Medicine, 2013
    Co-Authors: Panu T Vesanen, Jaakko O Nieminen, Koos C J Zevenhoven, Juhani Dabek, Lauri Parkkonen, Andrey Zhdanov, Juho Luomahaara, Juha Hassel, J Penttila
    Abstract:

    Ultra-low-field MRI uses microtesla fields for signal encoding and sensitive superconducting quantum interference devices for signal detection. Similarly, modern Magnetoencephalography (MEG) Systems use arrays comprising hundreds of superconducting quantum interference device channels to measure the magnetic field generated by neuronal activity. In this article, hybrid MEG-MRI instrumentation based on a commercial whole-head MEG device is described. The combination of ultra-low-field MRI and MEG in a single device is expected to significantly reduce coregistration errors between the two modalities, to simplify MEG analysis, and to improve MEG localization accuracy. The sensor solutions, MRI coils (including a superconducting polarizing coil), an optimized pulse sequence, and a reconstruction method suitable for hybrid MEG-MRI measurements are described. The performance of the device is demonstrated by presenting ultra-low-field-MR images and MEG recordings that are compared with data obtained with a 3T scanner and a commercial MEG device. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.

  • Hybrid ultra‐low‐field MRI and Magnetoencephalography System based on a commercial whole‐head neuromagnetometer
    Magnetic Resonance in Medicine, 2012
    Co-Authors: Panu T Vesanen, Jaakko O Nieminen, Koos C J Zevenhoven, Juhani Dabek, Lauri Parkkonen, Andrey Zhdanov, Juho Luomahaara, Juha Hassel, J Penttila, Juha Simola
    Abstract:

    Ultra-low-field MRI uses microtesla fields for signal encoding and sensitive superconducting quantum interference devices for signal detection. Similarly, modern Magnetoencephalography (MEG) Systems use arrays comprising hundreds of superconducting quantum interference device channels to measure the magnetic field generated by neuronal activity. In this article, hybrid MEG-MRI instrumentation based on a commercial whole-head MEG device is described. The combination of ultra-low-field MRI and MEG in a single device is expected to significantly reduce coregistration errors between the two modalities, to simplify MEG analysis, and to improve MEG localization accuracy. The sensor solutions, MRI coils (including a superconducting polarizing coil), an optimized pulse sequence, and a reconstruction method suitable for hybrid MEG-MRI measurements are described. The performance of the device is demonstrated by presenting ultra-low-field-MR images and MEG recordings that are compared with data obtained with a 3T scanner and a commercial MEG device. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.