Biomedical subjects

Sylvester Chuang

Publications and source records attributed to Sylvester Chuang.

6 recordsLinked to original sources

PubMed2006

The role of magnetoencephalography in pediatric epilepsy surgery.

INTRODUCTION: Magnetoencephalography (MEG) is a new diagnostic imaging and brain mapping device that has been recently used in the context of pediatric epilepsy, epilepsy surgery, and neuronavigation. PRINCIPLES OF MAGNETOENCEPHALOGRAPHY: MEG allows for the placement of magnetic spike sources on a conventional magnetic resonance imaging scan, the so-called magnetic source imaging, so that the localization of epileptiform activity in a child can be determined. Considerable effort is placed on analyzing the configuration and number of spike waves by MEG that relate to a primary epileptiform discharge. Such MEG spike clusters are corroborated now by intraoperative invasive subdural grid monitoring that show good correlation in the majority of cases. Another important role of MEG relates to the mapping of critical regions of brain function using known paradigms for speech, motor, sensory, visual, and auditory brain cortex. FUTURE APPLICATIONS: When linked to standard neuronavigation devices, MEG brain mapping can be extremely helpful to the neurosurgeon approaching nonlesional epilepsy cases or lesional cases where the safest and most direct route to the surgical disease can be selected. As paradigms for brain mapping improve and as MEG software upgrades become more sensitive to analyzing all types of spike sources, MEG will play an increasingly important role in pediatric neurosurgery, especially for the child with intractable epilepsy.

Brain Mapping↗

PubMed2005

Volumetric localization of epileptic activities in tuberous sclerosis using synthetic aperture magnetometry.

BACKGROUND: Magnetoencephalography (MEG) is a novel noninvasive technique for localizing epileptic zones. Tuberous sclerosis complex (TSC) is often associated with medically refractory epilepsy with multiple epileptic zones. Surgical treatment of TSC requires accurate localization of epileptogenic tubers. OBJECTIVE: The objective of this study was to introduce a new MEG technique, synthetic aperture magnetometry (SAM), to volumetrically localize irritable zones and clarify the correlations between SAM, dipole modeling and anatomical tubers. MATERIALS AND METHODS: Eight pediatric patients with TSC confirmed by clinical and neuroimaging findings were retrospectively studied. MEG data were recorded using a whole-cortex CTF OMEGA system. Sleep deprivation was employed to provoke epileptiform activity. Irritable zones were localized using both dipole modeling and SAM. RESULTS: MRI detected 42 tubers in the eight patients. Dipole modeling localized 28 irritable zones, and 19 out of the 28 zones were near tubers (19/42, 45%). SAM found 51 irritable zones, and 31 out of the 51 zones were near tubers (31/42, 74%). Among the 51 irritable zones determined by SAM, thirty-five zones were in 1-35 Hz, nine zones were in 35-60 Hz, and seven zones were in 60-120 Hz. CONCLUSIONS: The new method, SAM, yielded very plausible equivalent sources for patients who showed anatomical tubers on MRI. Compared to conventional dipole modeling, SAM appeared to offer increased detection of irritable zones and beneficial volumetric and frequency descriptions.

Brain Mapping↗

PubMed2005

Auditory detection of motion velocity in humans: a magnetoencephalographic study.

To investigate the cerebral mechanisms of auditory detection of motion velocity in the human brain, neuromagnetic fields elicited by six moving sounds and one stationary sound were investigated with a whole-cortex magnetoencephalography (MEG) system. The stationary sound evoked only one clear response at a latency of 109+/-6 ms (first response, or M100), but the six moving sounds evoked two clear responses: an earlier response at a latency of 116+/-7 ms (M100) and a later response at a latency ranging from 180 to 760 ms (magnetic motion response, or MM). The latency and amplitude of the MM were inversely related to the velocity of the moving sounds (p<0.02). The magnetic source of MM was related to the velocity of the moving sounds (p<0.05). A dynamic neuromagnetic response, MM, was elicited by the moving sounds, which likely encoded the neural processing of auditory detection of motion velocity. A specific neural network that processes the motion velocity in the human brain probably includes the bilateral superior temporal cortices and the brainstem. The left posterior and lateral part of the auditory cortex may play a pivotal role in the auditory detection of motion velocity.

Acoustic Stimulation↗

PubMed2003

Volumetric localization of somatosensory cortex in children using synthetic aperture magnetometry.

BACKGROUND: Magnetic signal from the human brain can be measured noninvasively by using magnetoencephalography (MEG). OBJECTIVE: This study was designed to localize and reconstruct the neuromagnetic activity in the somatosensory cortex in children. MATERIALS AND METHODS: Twenty children were studied using a 151-channel MEG system with electrical stimulation applied to median nerves. Data were analyzed using synthetic aperture magnetometry (SAM). RESULTS: A clear deflection (M1) was clearly identified in 18 children (90%, 18/20). Two frequency bands, 30-60 Hz and 60-120 Hz, were found to be related to somatosensory cortex. Magnetic activity was localized in the posterior bank of the central sulcus in 16 children. The extent of the reconstructed neuromagnetic activity of the left hemisphere was significantly larger than that of the right hemisphere ( P<0.01). CONCLUSION: Somatosensory cortex was accurately localized by using SAM. The extent of the reconstructed neuromagnetic activity suggested that the left hemisphere was the dominant side in the somatosensory system in children. We postulate that the volumetric characteristics of the reconstructed neuromagnetic activity are able to indicate the functionality of the brain.

Adolescent↗

PubMed2003

Localization of auditory N1 in children using MEG: source modeling issues.

Techniques for localizing auditory (AEF) sources are a topic of on-going discussion and this is particularly pertinent in pediatric research. Smaller head sizes are: (1) subject to bilateral temporal lobe source interference from both temporal lobes; and (2) further from MEG sensors resulting in poorer signal-to-noise ratios. An additional consideration in children is that the components of the AEF have distinct contributions along the development spectrum resulting in an ever-changing morphology for the pediatric AEF. These factors present a complicated picture for dipole fitting and raise the question of the most effective fitting strategy. We examined the AEF localizations in five children from 151, 70 and 47 MEG channels of data. We found evidence that bilateral source interaction could result in localization errors along the medial-lateral axis of up to 1 cm. We suggest that any modeling strategy needs to sufficiently account for this interaction and more precise models allowing for multiple sources need to be developed.

Acoustic Stimulation↗

PubMed2002

Sound motion evoked magnetic fields.

OBJECTIVE: The aim of present study was to determine which brain regions are involved in the conscious perception of sound motion in humans. METHODS: Six kinds of sound stimuli were studied. Two static sound stimuli with durations of 100 or 1000 ms remained at a fixed position during the stimulation period. Four moving sound stimuli with duration of 100 or 1000 ms were moving from left to right, or right to left, during the stimulation period. Evoked magnetic fields were recorded using a 151-channel whole cortex magnetoencephalographic system. RESULTS: The response identified in all sound stimuli was M100. Responses identified only in moving sound stimuli were M180, M280 and M680. Contour maps and dipoles overlapped on magnetic resonance imaging indicated that both the M100 and M680 responses were generated in the superior temporal cortex (left and right), while M180 and M280 were generated in the parietal cortex (right). CONCLUSIONS: The results of this MEG study indicated that the right parietal cortex was involved in sound motion processing. We hypothesize that the right parietal cortex, in association with the left and right superior temporal cortex, forms a network to process sound motion information.

Acoustic Stimulation↗