Recent studies have revealed the importance of high-frequency brain signals (>70 Hz). One chal... more Recent studies have revealed the importance of high-frequency brain signals (>70 Hz). One challenge of high-frequency signal analysis is that the size of time-frequency representation of high-frequency brain signals could be larger than 1 terabytes (TB), which is beyond the upper limits of a typical computer workstation's memory (<196 GB). The aim of the present study is to develop a new method to provide greater sensitivity in detecting high-frequency magnetoencephalography (MEG) signals in a single automated and versatile interface, rather than the more traditional, time-intensive visual inspection methods, which may take up to several days. To address the aim, we developed a new method, accumulated source imaging, defined as the volumetric summation of source activity over a period of time. This method analyzes signals in both low- (1~70 Hz) and high-frequency (70~200 Hz) ranges at source levels. To extract meaningful information from MEG signals at sensor space, the si...
Epilepsy surgery is an option for patients with medically refractory epilepsy. To achieve a bette... more Epilepsy surgery is an option for patients with medically refractory epilepsy. To achieve a better outcome post surgery, it is very important to take various presurgical evaluations into account for determining an appropriate surgical plan. Over the past two decades, more comprehensive presurgical assessments and advanced techniques have become available. High-resolution magnetic resonance imaging (MRI) has been known as the best preoperative diagnosis for patients with lesional refractory neocortical epilepsy (NE). 1-3 Digital video electroencephalography (VEEG) provides us with a definitive diagnosis of seizure-like events, while intracranial VEEG (iVEEG) is commonly used to define the ictal onset zone (IOZ). However, surgical resection of the IOZ alone does not always yield a favorable operative outcome because iVEEG electrodes only record signals in their direct vicinity and are blind for other areas, making it difficult to judge whether the IOZ really represents the ictal generator or is the result of propagation from elsewhere. 4 However, in a number of reports, 5 it was pointed out that it is also difficult to judge whether spike foci represent the epileptogenic zone. Furthermore, Holmes et al. 6 reported that only unifocal interictal epileptiform discharges (IEDs) restricted to the seizure onset zone could be used as a marker for epileptogenicity, while others showed that (rapid) spike Seizure 20 (2011) 692-700
Electroencephalography and clinical neurophysiology, 1996
The topography of somatosensory evoked magnetic fields (SEFs) following stimulation of the upper ... more The topography of somatosensory evoked magnetic fields (SEFs) following stimulation of the upper and lower lips was investigated in 6 normal subjects. When the lateral side of the upper lip was stimulated, P20m and its counterpart, N20m, were identified in the hemisphere contralateral to the stimulated side. The equivalent current dipoles (ECDs) of N20m-P20m were considered to be located in lip area of the primary sensory cortex (SI). Middle latency deflections (N40m-P40m, N60m-P60m, and N80m-P80m) were identified in bilateral hemispheres. Their ECDs were located in the SI in both hemispheres. Long latency deflections (P110m-N110m) were recognized in both hemispheres, and their ECDs were located inferior to the SI, in an area considered to be the secondary sensory cortex (SII). When the midline of the lip was stimulated, similar short and middle latency deflections was also identified, but SII deflections (P110m-N110m) were decreased in amplitude. When the lower lip was stimulated, ...
Proceedings of the 2010 IEEE 36th Annual Northeast Bioengineering Conference, NEBEC 2010, 2010
This paper introduces a source localization technique that exploits the high temporal resolution ... more This paper introduces a source localization technique that exploits the high temporal resolution of neuronal magnetoencephalography (MEG) data to locate the originating sources within the head. A traditional frequency beamforming algorithm was adapted from its conventional application of providing frequency information to yield information on the spatial location of simulated neuronal signals. This novel technique incorporates actual MEG sensor locations
Recent studies have revealed the importance of high-frequency brain signals (>70 Hz). One chal... more Recent studies have revealed the importance of high-frequency brain signals (>70 Hz). One challenge of high-frequency signal analysis is that the size of time-frequency representation of high-frequency brain signals could be larger than 1 terabytes (TB), which is beyond the upper limits of a typical computer workstation's memory (<196 GB). The aim of the present study is to develop a new method to provide greater sensitivity in detecting high-frequency magnetoencephalography (MEG) signals in a single automated and versatile interface, rather than the more traditional, time-intensive visual inspection methods, which may take up to several days. To address the aim, we developed a new method, accumulated source imaging, defined as the volumetric summation of source activity over a period of time. This method analyzes signals in both low- (1~70 Hz) and high-frequency (70~200 Hz) ranges at source levels. To extract meaningful information from MEG signals at sensor space, the si...
Epilepsy surgery is an option for patients with medically refractory epilepsy. To achieve a bette... more Epilepsy surgery is an option for patients with medically refractory epilepsy. To achieve a better outcome post surgery, it is very important to take various presurgical evaluations into account for determining an appropriate surgical plan. Over the past two decades, more comprehensive presurgical assessments and advanced techniques have become available. High-resolution magnetic resonance imaging (MRI) has been known as the best preoperative diagnosis for patients with lesional refractory neocortical epilepsy (NE). 1-3 Digital video electroencephalography (VEEG) provides us with a definitive diagnosis of seizure-like events, while intracranial VEEG (iVEEG) is commonly used to define the ictal onset zone (IOZ). However, surgical resection of the IOZ alone does not always yield a favorable operative outcome because iVEEG electrodes only record signals in their direct vicinity and are blind for other areas, making it difficult to judge whether the IOZ really represents the ictal generator or is the result of propagation from elsewhere. 4 However, in a number of reports, 5 it was pointed out that it is also difficult to judge whether spike foci represent the epileptogenic zone. Furthermore, Holmes et al. 6 reported that only unifocal interictal epileptiform discharges (IEDs) restricted to the seizure onset zone could be used as a marker for epileptogenicity, while others showed that (rapid) spike Seizure 20 (2011) 692-700
Electroencephalography and clinical neurophysiology, 1996
The topography of somatosensory evoked magnetic fields (SEFs) following stimulation of the upper ... more The topography of somatosensory evoked magnetic fields (SEFs) following stimulation of the upper and lower lips was investigated in 6 normal subjects. When the lateral side of the upper lip was stimulated, P20m and its counterpart, N20m, were identified in the hemisphere contralateral to the stimulated side. The equivalent current dipoles (ECDs) of N20m-P20m were considered to be located in lip area of the primary sensory cortex (SI). Middle latency deflections (N40m-P40m, N60m-P60m, and N80m-P80m) were identified in bilateral hemispheres. Their ECDs were located in the SI in both hemispheres. Long latency deflections (P110m-N110m) were recognized in both hemispheres, and their ECDs were located inferior to the SI, in an area considered to be the secondary sensory cortex (SII). When the midline of the lip was stimulated, similar short and middle latency deflections was also identified, but SII deflections (P110m-N110m) were decreased in amplitude. When the lower lip was stimulated, ...
Proceedings of the 2010 IEEE 36th Annual Northeast Bioengineering Conference, NEBEC 2010, 2010
This paper introduces a source localization technique that exploits the high temporal resolution ... more This paper introduces a source localization technique that exploits the high temporal resolution of neuronal magnetoencephalography (MEG) data to locate the originating sources within the head. A traditional frequency beamforming algorithm was adapted from its conventional application of providing frequency information to yield information on the spatial location of simulated neuronal signals. This novel technique incorporates actual MEG sensor locations
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Papers by J. Xiang