[Show abstract][Hide abstract] ABSTRACT: Magnetoacoustic tomography with magnetic induction (MAT-MI) is an imaging technique under development to achieve imaging of electrical impedance contrast in biological tissues with spatial resolution close to ultrasound imaging. However, previously reported MAT-MI experimental results are obtained either from low salinity gel phantoms, or from normal animal tissue samples. In this study, we report the experimental study on the performance of the MAT-MI imaging method for imaging in vitro human liver tumor tissue. The present promising experimental results suggest the feasibility of MAT-MI to image electrical impedance contrast between the cancerous tissue and its surrounding normal tissues.
[Show abstract][Hide abstract] ABSTRACT: Understanding the neural mechanisms responsible for human social
interactions is difficult, since the brain activities of two or more
individuals have to be examined simultaneously and correlated with the
observed social patterns. We introduce the concept of hyper-brain
network, a connectivity pattern representing at once the information
flow among the cortical regions of a single brain as well as the
relations among the areas of two distinct brains. Graph analysis of
hyper-brain networks constructed from the EEG scanning of 26 couples of
individuals playing the Iterated Prisoner's Dilemma reveals the
possibility to predict non-cooperative interactions during the
decision-making phase. The hyper-brain networks of two-defector couples
have significantly less inter-brain links and overall higher modularity
- i.e. the tendency to form two separate subgraphs - than couples
playing cooperative or tit-for-tat strategies. The decision to defect
can be "read" in advance by evaluating the changes of connectivity
pattern in the hyper-brain network.
[Show abstract][Hide abstract] ABSTRACT: The current gold standard for the localization of the cortical regions responsible for the initiation and propagation of the ictal activity is through the use of invasive electrocorticography (ECoG). This method is utilized to guide surgical intervention in cases of medically intractable epilepsy by identifying the location and extent of the epileptogenic focus. Recent studies have proposed mechanisms in which the activity of epileptogenic cortical networks, rather than discrete focal sources, contributes to the generation of the ictal state. If true, selective modulation of key network components could be employed for the prevention and termination of the ictal state.
Here, we have applied graph theory methods as a means to identify critical network nodes in cortical networks during both ictal and interictal states. ECoG recordings were obtained from a cohort of 25 patients undergoing presurgical monitoring for the treatment of intractable epilepsy at the Mayo Clinic (Rochester, MN, U.S.A.).
One graph measure, the betweenness centrality, was found to correlate with the location of the resected cortical regions in patients who were seizure-free following surgical intervention. Furthermore, these network interactions were also observed during random nonictal periods as well as during interictal spike activity. These network characteristics were found to be frequency dependent, with high frequency gamma band activity most closely correlated with improved postsurgical outcome as has been reported in previous literature.
These findings could lead to improved understanding of epileptogenesis. In addition, this theoretically allows for more targeted therapeutic interventions through the selected modulation or disruption of these epileptogenic networks.
[Show abstract][Hide abstract] ABSTRACT: Magnetoacoustic tomography with magnetic induction (MAT-MI) is an emerging approach for noninvasively imaging electrical impedance properties of biological tissues. The MAT-MI imaging system measures ultrasound waves generated by the Lorentz force, having been induced by magnetic stimulation, which is related to the electrical conductivity distribution in tissue samples. MAT-MI promises to provide fine spatial resolution for biological tissue imaging as compared to ultrasound resolution. In the present study, we first estimated the imaging spatial resolution by calculating the full width at half maximum (FWHM) of the system point spread function (PSF). The actual spatial resolution of our MAT-MI system was experimentally determined to be 1.51 mm by a parallel-line-source phantom with Rayleigh criterion. Reconstructed images made from tissue-mimicking gel phantoms, as well as animal tissue samples, were consistent with the morphological structures of the samples. The electrical conductivity value of the samples was determined directly by a calibrated four-electrode system. It has been demonstrated that MAT-MI is able to image the electrical impedance properties of biological tissues with better than 2 mm spatial resolution. These results suggest the potential of MAT-MI for application to early detection of small-size diseased tissues (e.g. small breast cancer).
PLoS ONE 01/2011; 6(8):e23421. · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Inattention to current activity is ubiquitous in everyday situations. Mind wandering is an example of such a state, and its related brain areas have been examined in the literature. However, there is no clear evidence regarding neural rhythmic activities linked to mind wandering. Using a vigilance task with thought sampling and electroencephalography recording, the current study simultaneously examined neural oscillatory activities related to subjectively reported and behaviorally indexed mind wandering. By implementing time-frequency analysis, we found that subjectively reported mind wandering, relative to behaviorally indexed, showed increased gamma band activity at bilateral frontal-central areas. By means of beamformer source imaging, we found subjectively reported mind wandering within the gamma band to be characterized by increased activation in bilateral frontal cortices, supplemental motor area, paracentral cortex and right inferior temporal cortex in comparison to behaviorally indexed mind wandering. These findings dissociate subjectively reported and behaviorally indexed mind wandering and suggest that a higher degree of executive control processes are engaged in subjectively reported mind wandering.
PLoS ONE 01/2011; 6(9):e23124. · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The equivalent current density (ECD) model has been previously used in the cardiac electrical imaging technique for non-invasively reconstructing the global activation sequence (AS) in the normal heart. However, its performance in estimating AS in the heart with structural defects remains uncertain. This study aims to evaluate its feasibility in two common cardiac structure diseases--ischemia and infarction, by performing forward simulation using a cellular automaton heart model. The AS was derived from ECD and quantitatively compared to the true AS simulated with the heart model by calculating correlation coefficient (CC) and relative error (RE). In ischemia condition, the ECD model returns a CC (0.97) and RE (0.13), comparable with those of normal heart. In infarction condition, it is also able to identify area of infarction and reconstruct global AS at the excitable myocardium with CC of 0.97 and RE of 0.12. The present pilot simulation results suggest the feasibility of applying ECD model in the pathological heart, which would help the investigation of pathology mechanism and clinical management of cardiac diseases. Noninvasive 3-dimensional (3-D) imaging of cardiac electrical activities is important for facilitating basic cardiovascular research and management of cardiac diseases (1-5). The equivalent current density (ECD) model based 3-D cardiac electrical imaging (3-DCEI) approach has been proposed for the inverse reconstruction of 3-D ventricular activation (5). It is based on the principle that the activation time of normal heart tissue is corresponding to the instant when the time course of ECD reaches maximum at every myocardial site (5). This method has been evaluated in a healthy animal model (6), but it remains unclear that whether it is applicable to heart tissues with structural defects. The purpose of the present study is to test the feasibility of estimating activation sequence (AS) from the time course of ECD in hearts with ischemia and infarction, by means of forward simulation. The ventricular activation was simulated by a cellular automaton heart model and defined as the 'true' activation sequence. The current density at every myocardial unit was constructed accordingly and the activation time for each cellular unit was determined by picking up the time instant corresponding to the peak magnitude of ECD. The estimated AS from ECD time course was then quantitatively compared with the 'true' AS from the cellular automaton heart model.
[Show abstract][Hide abstract] ABSTRACT: Brain-computer interfaces (BCIs) allow a user to interact with a computer system using thought. However, only recently have devices capable of providing sophisticated multi-dimensional control been achieved non-invasively. A major goal for non-invasive BCI systems has been to provide continuous, intuitive, and accurate control, while retaining a high level of user autonomy. By employing electroencephalography (EEG) to record and decode sensorimotor rhythms (SMRs) induced from motor imaginations, a consistent, user-specific control signal may be characterized. Utilizing a novel method of interactive and continuous control, we trained three normal subjects to modulate their SMRs to achieve three-dimensional movement of a virtual helicopter that is fast, accurate, and continuous. In this system, the virtual helicopter's forward-backward translation and elevation controls were actuated through the modulation of sensorimotor rhythms that were converted to forces applied to the virtual helicopter at every simulation time step, and the helicopter's angle of left or right rotation was linearly mapped, with higher resolution, from sensorimotor rhythms associated with other motor imaginations. These different resolutions of control allow for interplay between general intent actuation and fine control as is seen in the gross and fine movements of the arm and hand. Subjects controlled the helicopter with the goal of flying through rings (targets) randomly positioned and oriented in a three-dimensional space. The subjects flew through rings continuously, acquiring as many as 11 consecutive rings within a five-minute period. In total, the study group successfully acquired over 85% of presented targets. These results affirm the effective, three-dimensional control of our motor imagery based BCI system, and suggest its potential applications in biological navigation, neuroprosthetics, and other applications.
PLoS ONE 01/2011; 6(10):e26322. · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Brain-computer interfaces (BCIs) are devices that allow for thought-based control of computer systems. However, sophisticated control of multi-dimensional BCIs has only recently been achieved in non-invasive systems. The design of these systems has focused on giving users fast, autonomous control that is both intuitive and accurate. Through the use of electroencephalographic recording techniques, sensorimotor rhythms induced from motor imaginations may be captured and a control signal may be characterized. Here we have trained two subjects with an interactive and continuous protocol to modulate their sensorimotor rhythms to control three-dimensions of motion of a virtual helicopter to reach randomly positioned and oriented rings. The subject group acquired 88% of presented targets and achieved as many as 11 consecutive rings in a five-minute period. Subjects learned to fly quickly, continuously and accurately through golden rings positioned and oriented randomly throughout a 3D virtual space.
Neural Engineering (NER), 2011 5th International IEEE/EMBS Conference on; 01/2011
[Show abstract][Hide abstract] ABSTRACT: Localization of the initial site of cardiac ectopic activity has direct clinical benefits for treating focal cardiac arrhythmias. The aim of the present study is to experimentally evaluate the performance of the equivalent moving dipole technique on noninvasively localizing the origin of the cardiac ectopic activity from the recorded body surface potential mapping (BSPM) data in a well-controlled experimental setting. The cardiac ectopic activities were induced in four well-controlled intact pigs by either single-site pacing or dual-site pacing within the ventricles. In each pacing study, the initiation sites of cardiac ectopic activity were localized by estimating the locations of a single moving dipole (SMD) or two moving dipoles (TMDs) from the measured BSPM data and compared with the precise pacing sites (PSs). For the single-site pacing, the averaged SMD localization error was 18.6 ± 3.8 mm over 16 sites, while the averaged distance between the TMD locations and the two corresponding PSs was slightly larger (24.9 ± 6.2 mm over five pairs of sites), both occurring at the onset of the QRS complex (10-25 ms following the pacing spike). The obtained SMD trajectories originated near the stimulus site and then traversed across the heart during the ventricular depolarization. The present experimental results show that the initial location of the moving dipole can provide the approximate site of origin of a cardiac ectopic activity in vivo, and that the migration of the dipole can portray the passage of an ectopic beat across the heart.
IEEE Transactions on Information Technology in Biomedicine 12/2010; · 1.98 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Magnetoacoustic tomography with magnetic induction (MAT-MI) is a hybrid imaging modality proposed to image electrical conductivity contrast of biological tissue with high spatial resolution. This modality combines magnetic excitations with ultrasound detection through the Lorentz force based coupling mechanism. However, previous studies have shown that MAT-MI method with single type of magnetic excitation can only reconstruct the conductivity boundaries of a sample. In order to achieve more complete conductivity contrast reconstruction, we proposed a multiexcitation MAT-MI approach. In this approach, multiple magnetic excitations using different coil configurations are applied to the object sequentially and ultrasonic signals corresponding to each excitation are collected for conductivity image reconstruction. In this study, we validate the new multiexcitation MAT-MI method for three-dimensional (3D) conductivity imaging through both computer simulations and phantom experiments. 3D volume data are obtained by utilizing acoustic focusing and cylindrical scanning under each magnetic excitation. It is shown in our simulation and experiment results that with a common ultrasound probe that has limited bandwidth we are able to correctly reconstruct the 3D relative conductivity contrast of the imaging object. As compared to those conductivity boundary images generated by previous single-excitation MAT-MI, the new multiexcitation MAT-MI method provides more complete conductivity contrast reconstruction, and therefore, more valuable information in possible clinical and research applications.
Journal of Applied Physics 12/2010; 108(12):124702. · 2.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Training improves performance on most visual tasks. Such perceptual learning can modify how information is read out from, and represented in, later visual areas, but effects on early visual cortex are controversial. In particular, it remains unknown whether learning can reshape neural response properties in early visual areas independent from feedback arising in later cortical areas. Here, we tested whether learning can modify feedforward signals in early visual cortex as measured by the human electroencephalogram. Fourteen subjects were trained for >24 d to detect a diagonal grating pattern in one quadrant of the visual field. Training improved performance, reducing the contrast needed for reliable detection, and also reliably increased the amplitude of the earliest component of the visual evoked potential, the C1. Control orientations and locations showed smaller effects of training. Because the C1 arises rapidly and has a source in early visual cortex, our results suggest that learning can increase early visual area response through local receptive field changes without feedback from later areas.
Journal of Neuroscience 11/2010; 30(45):15080-4. · 6.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The aim of this study is to investigate the use of interictal spikes to localize epileptogenic brain from noninvasive scalp EEG recordings in patients with medically intractable epilepsy.
Source reconstructions were performed using a high density electrode montage and a low density electrode montage by means of a distributed source modeling method. The source of interictal spike activity was localized using both a realistic geometry boundary element method (BEM) head model and 3-shell spherical head model.
In the analysis of 7 patients, the high density electrode montage was found to provide results more consistent with the suspected region of epileptogenic brain identified for surgical resection using intracranial EEG recordings and structural MRI lesions, as compared to the spatial low density electrode montage used in routine clinical practice. Furthermore, the realistic geometry BEM head model provided better source localization.
Our results indicate the merits of using high density scalp EEG recordings and realistic geometry head modeling for source localization of interictal spikes in patients with partial epilepsy.
The present results suggest further improvement of source localization accuracy of epileptogenic brain from interictal EEG recorded using high density scalp electrode montage and realistic geometry head models.
Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology 11/2010; 122(6):1098-105. · 3.12 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present in this study, an acoustic source reconstruction method using focused transducer with B-mode imaging for magnetoacoustic tomography with magnetic induction (MAT-MI). MAT-MI is an imaging modality proposed for noninvasive conductivity imaging with high spatial resolution. In MAT-MI, acoustic sources are generated in a conductive object by placing it in a static and a time-varying magnetic field. The acoustic waves from these sources propagate in all directions and are collected with transducers placed around the object. The collected signal is then used to reconstruct the acoustic source distribution and to further estimate the electrical conductivity distribution of the object. A flat piston transducer acting as a point receiver has been used in earlier MAT-MI systems to collect acoustic signals. In this study, we propose to use B-mode scan scheme with a focused transducer that gives a signal gain in its focus region and improves the MAT-MI signal quality. A simulation protocol that can take into account different transducer designs and scan schemes for MAT-MI imaging is developed and used in our evaluation of different MAT-MI system designs. It is shown in our computer simulations that as compared to the earlier approach, the MAT-MI system using B-scan with a focused transducer allows MAT-MI imaging at a closer distance and has improved system sensitivity. In addition, the B-scan imaging technique allows reconstruction of the MAT-MI acoustic sources with a discrete number of scanning locations, which greatly increases the applicability of the MAT-MI approach, especially when a continuous acoustic window is not available in real clinical applications. We have also conducted phantom experiments to evaluate the proposed method, and the reconstructed image shows a good agreement with the target phantom.
[Show abstract][Hide abstract] ABSTRACT: In the present study, a physical-model based three-dimensional (3-D) cardiac electrical imaging (3-DCEI) technique was evaluated with the aid of 3-D intra-cardiac mapping from 200 intramural sites during norepinephrine (NE) induced ventricular arrhythmias in the rabbit heart. Body surface potentials and intramural bipolar electrical recordings using plunge-needle electrodes were simultaneously measured in a closed-chest condition in a healthy rabbit. The non-invasively imaged activation sequence correlated well with invasively measured counterparts, with an averaged correlation coefficient of 0.70, and a relative error of 0.30. The sites of initial activation were well localized to be within ~5mm from the initiation sites determined from intra-cardiac mapping. The present experimental results suggest that the 3-DCEI approach can reconstruct 3-D ventricular global activation sequence and localize the origin of activation during focal ventricular arrhythmias.
[Show abstract][Hide abstract] ABSTRACT: Magnetoacoustic tomography with magnetic induction (MAT-MI) is an imaging approach proposed to conduct noninvasive electrical conductivity imaging of biological tissue with high spatial resolution. In the present study, based on the analysis of the relationship between the conductivity distribution and the generated MAT-MI acoustic source, we propose a new multi-excitation MAT-MI approach and the corresponding reconstruction algorithms. In the proposed method, multiple magnetic excitations using different coil configurations are employed and ultrasound measurements corresponding to each excitation are collected to derive the conductivity distribution inside the sample. A modified reconstruction algorithm is also proposed for the multi-excitation MAT-MI imaging approach when only limited bandwidth acoustic measurements are available. Computer simulation and phantom experiment studies have been done to demonstrate the merits of the proposed method. It is shown that if unlimited bandwidth acoustic data is available, we can accurately reconstruct the internal conductivity contrast of an object using the proposed method. With limited bandwidth data and the use of the modified algorithm we can reconstruct the relative conductivity contrast of an object instead of only boundaries at the conductivity heterogeneity. Benefits that come with this new method include better differentiation of tissue types with conductivity contrast using the MAT-MI approach, specifically for potential breast cancer screening application in the future.
IEEE transactions on medical imaging. 10/2010; 29(10):1759-67.
[Show abstract][Hide abstract] ABSTRACT: Films like Firefox, Surrogates, and Avatar have explored the possibilities of using brain-computer interfaces (BCIs) to control machines and replacement bodies with only thought. Real world BCIs have made great progress toward that end. Invasive BCIs have enabled monkeys to fully explore 3-D space using neuroprosthetics. However, noninvasive BCIs have not been able to demonstrate such mastery of 3-D space. Here, we report our work, which demonstrates that human subjects can use a noninvasive BCI to fly a virtual helicopter to any point in a 3-D world. Through use of intelligent control strategies, we have facilitated the realization of controlled flight in 3-D space. We accomplished this through a reductionist approach that assigns subject-specific control signals to the crucial components of 3-D flight. Subject control of the helicopter was comparable when using either the BCI or a keyboard. By using intelligent control strategies, the strengths of both the user and the BCI system were leveraged and accentuated. Intelligent control strategies in BCI systems such as those presented here may prove to be the foundation for complex BCIs capable of doing more than we ever imagined.
IEEE transactions on neural systems and rehabilitation engineering: a publication of the IEEE Engineering in Medicine and Biology Society 09/2010; 18(6):581-9. · 2.42 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Magnetoacoustic tomography with magnetic induction (MAT-MI) is a recently introduced imaging modality for noninvasive electrical impedance imaging, with ultrasound imaging resolution and a contrast reflecting the electrical conductivity properties of tissues. However, previous MAT-MI systems can only image samples that are much more conductive than real human or animal tissues. To image real biological tissue samples, a large-current-carrying coil that can give stronger magnetic stimulations and stronger MAT-MI acoustic signals is employed in this study. The conductivity values of all the tissue samples employed in this study are also directly measured using a well calibrated four-electrode system. The experimental results demonstrated the feasibility to image biological tissues with electrical conductivity contrast below 1.0 S∕m using the MAT-MI technique with safe level of electromagnetic energy applied to tissue samples.
[Show abstract][Hide abstract] ABSTRACT: We present in this study an ultrasound B-scan based imaging approach for magnetoacoustic tomography with magnetic induction (MAT-MI) to reconstruct electrical conductivity distribution. In MAT-MI acoustic waves are generated in the sample by placing it in a static and a time-varying magnetic field. The acoustic waves from these sources propagate in all directions. In the present approach these acoustic signals are collected with a focused ultrasound transducer which confines the collected signal to that from sources along a line. The focused transducer also gives signal gain in the focus region improving the MAT-MI signal quality. The time-resolved acoustic signals are back projected to form a one-dimensional (1D) image of the source distribution along the line. The complete cross-section of the object is obtained by acquiring 1D images along multiple directions in the cross-sectional plane. A simulation model of the image reconstruction method is developed with ultrasound simulations using the Field II program. The present reconstruction results suggest that acoustic source imaging in MAT-MI can be achieved using the much practical ultrasound B scan imaging technique. The developed method is applied to MAT-MI in experiments. This method should allow combining MAT-MI with clinical ultrasound imaging methods and broadening the potential applicability of the technique.
Journal of Physics Conference Series 05/2010; 224(1):012076.
[Show abstract][Hide abstract] ABSTRACT: Magnetoacoustic tomography with magnetic induction (MAT-MI) is an approach proposed to do non-invasive electrical conductivity imaging of biological tissue using magnetic induction and ultrasound measurements. In the present study, based on the analysis of the relationship between the conductivity distribution and the generated MAT-MI acoustic source, we propose a new multi-excitation algorithm to achieve better reconstruction of the conductivity distribution. In this algorithm, multiple magnetic excitations using different coil configurations are employed and the ultrasound measurements corresponding to each excitation are collected to derive the conductivity distribution inside the sample. The corresponding modified algorithm is also proposed for MAT-MI imaging when only limited bandwidth acoustic measurements data are available. Computer simulations have been done to demonstrate the performance of the proposed algorithm. It is shown that using this algorithm and unlimited bandwidth data, we can accurately reconstruct the internal conductivity contrast of the object. With limited bandwidth data and using the modified algorithm we can also reconstruct the relative conductivity contrast of the object instead of only the boundaries at the conductivity heterogeneity. Benefits come with this new algorithm include better differentiation of different tissue types with conductivity contrast using MAT-MI approach, specifically for the potential breast cancer screening application in the future.
Journal of Physics Conference Series 05/2010; 224(1):012035.
[Show abstract][Hide abstract] ABSTRACT: In the present study, the cascaded interactions between stimuli and neural and hemodynamic responses were modeled using linear systems. These models provided the theoretical hypotheses that were tested against the electroencephalography (EEG) and blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) data recorded from human subjects during prolonged periods of repeated visual stimuli with a variable setting of the inter-stimulus interval (ISI) and visual contrast. Our results suggest that (1) neural response is nonlinear only when ISI<0.2 s, (2) BOLD response is nonlinear with an exclusively vascular origin when 0.25<ISI<4.2 s, (3) vascular response nonlinearity reflects a refractory effect, rather than a ceiling effect, and (4) there is a strong linear relationship between the BOLD effect size and the integrated power of event-related synaptic current activity, after modeling and taking into account the vascular refractory effect. These conclusions offer important insights into the origins of BOLD nonlinearity and the nature of neurovascular coupling, and suggest an effective means to quantitatively interpret the BOLD signal in terms of neural activity. The validated cross-modal relationship between fMRI and EEG may provide a theoretical basis for the integration of these two modalities.