Elekta Oy


Elekta Oy

Time filter
Source Type

Airaksinen K.,University of Helsinki | Butorina A.,Moscow State University of Psychology and Education | Pekkonen E.,University of Helsinki | Nurminen J.,University of Helsinki | And 4 more authors.
Clinical Neurophysiology | Year: 2012

Objective: Parkinsonian patients have abnormal oscillatory activity within the basal ganglia-thalamocortical circuitry. Particularly, excessive beta band oscillations are thought to be associated with akinesia. We studied whether cortical spontaneous activity is modified by deep brain stimulation (DBS) in advanced Parkinson's disease and if the modifications are related to the clinical symptoms. Methods: We studied the effects of bilateral electrical stimulation of subthalamic nucleus (STN) on cortical spontaneous activity by magnetoencephalography (MEG) in 11 Parkinsonian patients. The artifacts produced by DBS were suppressed by tSSS algorithm. Results: During DBS, UPDRS (Unified Parkinson's Disease Rating Scale) rigidity scores correlated with 6-10. Hz and 12-20. Hz somatomotor source strengths when eyes were open. When DBS was off UPDRS action tremor scores correlated with pericentral 6-10. Hz and 21-30. Hz and occipital alpha source strengths when eyes open. Occipital alpha strength decreased during DBS when eyes closed. The peak frequency of occipital alpha rhythm correlated negatively with total UPDRS motor scores and with rigidity subscores, when eyes closed. Conclusion: STN DBS modulates brain oscillations both in alpha and beta bands and these oscillations reflect the clinical condition during DBS. Significance: MEG combined with an appropriate artifact rejection method enables studies of DBS effects in Parkinson's disease and presumably also in the other emerging DBS indications. © 2012 International Federation of Clinical Neurophysiology.

Agency: European Commission | Branch: H2020 | Program: MSCA-ITN-ETN | Phase: MSCA-ITN-2014-ETN | Award Amount: 3.88M | Year: 2015

The European Brain Council (EBC) has recommended the disorders of the brain to be prioritised for funding. The purpose of this ChildBrain ETN is 1) to train young scientists, Early Stage Researchers (ESRs), to utilise evidence-based neuroscientific knowledge for helping children, especially those at high risk for dropout due to neurocognitive disorders, to meet future educational and societal demands. The network aims 2) to develop new, innovative brain imaging-based tools through research and industry to be applied by researchers and clinical sector end users for 3) increasing understanding and improving diagnosis and treatment of neurocognitive disorders, as well as enhancing targeted educational programs. To accomplish these goals, we aim 4) to form a cross-disciplinary and trans-sectorial European network of experts. Three research and two training work packages (WPs) are planned to reach these goals. The Childhood neurodevelopmental disorders WP comprises new research and training on the neural underpinnings of dyslexia, ADHD, epilepsy, and hearing loss and creates links to healthcare industry and special education. The Brain development WP will focus on understanding the systems-level brain development at the level of the individual child. The Brain research methods WP will develop new multi-modal data analysis methodologies that are essential for children and will also further brain research in adults. The academic, industrial and private sector partners will work across these themes, offering the ESRs project-specific collaboration, secondments, workshops, summer school and courses on scientific, transferable and entrepreneurial skills, as well as supervision. The ChildBrain ETN will produce a new generation of scientists with the theoretical, technological, and entrepreneurial skills necessary for making breakthroughs in the understanding of brain development and childhood neurocognitive disorders.

Agency: European Commission | Branch: H2020 | Program: RIA | Phase: FETOPEN-1-2014 | Award Amount: 4.00M | Year: 2016

By combining accurate magnetic measurements of neural activity with near-simultaneous high-definition measurements of cerebral structure provided by novel methods in ultra-low-field magnetic resonance imaging (ULF MRI ) we will be able to image the dynamics of human brain function at unprecedented resolution and reliability. BREAKBEN will achieve a revolution in neuroimaging; we aim at breaking the barrier for measurement of neuronal currents by ULF MRI (neural current imaging; NCI) as well as breaking the nonuniqueness barrier for magnetoencephalography (MEG) by combining it with ULF MRI and accurately presented a priori information. A key aspect in utilizing the a priori information is injected current density imaging (CDI), which will inform us about the individual conductivity structure of the head. Using novel verification and validation approaches, we will demonstrate the unique advantages of these multimodal techniques. These breakthroughs will result in completely different workflows in brain imaging, also suitable for clinical use. We believe that we are at the edge of a qualitative technology jump with ULF MRI, its applications and combinations. This will lead to a wealth of new applications and revolutionize the way we do magnetism-based measurements of the nervous system. Europe has the unique chance to lead this revolution.

Vesanen P.T.,Aalto University | Nieminen J.O.,Aalto University | Zevenhoven K.C.J.,Aalto University | Dabek J.,Aalto University | And 10 more authors.
Magnetic Resonance in Medicine | Year: 2013

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. © 2012 Wiley Periodicals, Inc.

Nurminen J.,Hospital District of Helsinki and Uusimaa | Nurminen J.,Aalto University | Taulu S.,Elekta Oy | Nenonen J.,Elekta Oy | And 3 more authors.
IEEE Transactions on Biomedical Engineering | Year: 2013

Recently, the signal space separation (SSS) method, based on the multipole expansion of the magnetic field, has become increasingly important in magnetoencephalography (MEG). Theoretical arguments and simulations suggest that increasing the asymmetry of the MEG sensor array from the traditional, rather symmetric geometry can significantly improve the performance of the method. To test this concept, we first simulated addition of tangentially oriented standard sensor elements to the existing 306-channel Elekta Neuromag sensor array, and evaluated and optimized the performance of the new sensor configuration. Based on the simulation results, we then constructed a prototype device with 18 additional tangential triple-sensor elements and a total of 360 channels. The experimental results from the prototype are largely in agreement with the simulations. In application of the spatial SSS method, the 360-channel device shows an approximately 100% increase in software shielding capability, while residual reconstruction noise of evoked responses is decreased by 20%. Further, the new device eliminates the need for regularization while applying the SSS method. In conclusion, we have demonstrated in practice the benefit of reducing the symmetry of the MEG array, without the need for a complete redesign. © 1964-2012 IEEE.

Airaksinen K.,University of Helsinki | Makela J.P.,University of Helsinki | Taulu S.,Elekta Oy | Ahonen A.,Elekta Oy | And 3 more authors.
Human Brain Mapping | Year: 2011

Motor symptoms of Parkinson's disease (PD) can be relieved by deep brain stimulation (DBS). The mechanism of action of DBS is largely unclear. Magnetoencephalography (MEG) studies on DBS patients have been unfeasible because of strong magnetic artifacts. An artifact suppression method known as spatiotemporal signal space separation (tSSS) has mainly overcome these difficulties. We wanted to clarify whether tSSS enables noninvasive measurement of the modulation of cortical activity caused by DBS. We have studied auditory and somatosensory-evoked fields (AEFs and SEFs) of advanced PD patients with bilateral subthalamic nucleus (STN) DBS using MEG. AEFs were elicited by 1-kHz tones and SEFs by electrical pulses to the median nerve with DBS on and off. Data could be successfully acquired and analyzed from 12 out of 16 measured patients. The motor symptoms were significantly relieved by DBS, which clearly enhanced the ipsilateral auditory N100m responses in the right hemisphere. Contralateral N100m responses and somatosensory P60m responses also had a tendency to increase when bilateral DBS was on. MEG with tSSS offers a novel and powerful tool to investigate DBS modulation of the evoked cortical activity in PD with high temporal and spatial resolution. The results suggest that STN-DBS modulates auditory processing in advanced PD. © 2010 Wiley-Liss, Inc.

Airaksinen K.,University of Helsinki | Makela J.P.,University of Helsinki | Nurminen J.,University of Helsinki | Luoma J.,University of Helsinki | And 3 more authors.
Clinical Neurophysiology | Year: 2015

Objective: Cortico-muscular coherence (CMC) is thought to reflect the interplay between cortex and muscle in motor coordination. In Parkinson's disease (PD) patients, levodopa has been shown to enhance CMC. This study examined whether subthalamic nucleus (STN) deep brain stimulation (DBS) affects the CMC in advanced PD. Methods: Magnetoencephalography (MEG) and electromyography (EMG) measurements were done simultaneously both with DBS on and off to determine the CMC during wrist extension. The spatiotemporal signal space separation (tSSS) was used for artifact suppression. Results: CMC peaks between 13 and 25. Hz were found in 15 out of 19 patients. The effect of DBS on CMC was variable. Moreover, the correlation between CMC and motor performance was inconsistent; stronger CMC did not necessarily indicate better function albeit tremor and rigidity may diminish the CMC. Patients having CMC between 13 and 25. Hz had the best motor scores at the group level. Conclusions: DBS modifies the CMC in advanced PD with large interindividual variability. Significance: DBS does not systematically modify CMC amplitude in advanced PD. The results suggest that some components of the CMC may be related to the therapeutic effects of DBS. © 2014 International Federation of Clinical Neurophysiology.

Zhdanov A.,Aalto University | Zhdanov A.,University of Helsinki | Wilenius J.,University of Helsinki | Paetau R.,University of Helsinki | And 2 more authors.
Epilepsy Research | Year: 2013

Introduction: Magnetoencephalography (MEG) measures magnetic fields generated by neuronal currents. MEG is complementary to EEG. Considerable body of evidence indicates that ictal MEG recordings can provide useful information for pre-surgical evaluation of epilepsy patients alongside the more established long-term ictal video-EEG. Ictal MEG is recorded in some epilepsy surgery centers. However, a wider adoption of ictal MEG is hampered by lack of tools for synchronized video-MEG recording similar to those of video-EEG. Methods: We have augmented MEG with a synchronized behavioral video-recording system. To estimate its additional value in ictal recordings, we retrospectively analyzed recordings of 10 epilepsy patients with and without the video. Results: In six patients out of ten, adding the video substantially changed the resulting interpretations. In all six cases the effect was considerable: the number of detected seizures changed by more than 50%. Conclusions: Synchronized video and audio recording capabilities are important for effective ictal MEG recordings of epilepsy patients. © 2013.

Vesanen P.T.,Aalto University | Nieminen J.O.,Aalto University | Zevenhoven K.C.J.,Aalto University | Dabek J.,Aalto University | And 3 more authors.
IEEE Transactions on Magnetics | Year: 2012

In the context of biomagnetism, a magnetically shielded room (MSR) is designed for shielding against external magnetic fields. Recently, several applications, such as combined structural magnetic resonance imaging (MRI) and functional magnetoencephalography (MEG), have emerged that require applying relatively strong magnetic fields inside the MSR. These magnetic fields induce eddy currents and magnetize the MSR walls that are made of materials with high permeability and conductivity. These eddy currents and magnetization generate secondary magnetic fields inside the room that disturb, e.g., combined MEG-MRI by affecting sample spins and by exceeding the available dynamic range of the magnetic field sensors. In this work, static and dynamic magnetic fields applied inside an MSR are studied both theoretically and experimentally. Using a spherical model, analytical expressions are derived for the amplitudes and time constants of the various secondary magnetic field modes. These predictions are validated by comparison with experimental measurements in a rectangular MSR. The results of this study facilitate, e.g., the design of coils compatible with an MSR; a self-shielded coil is presented that decreases the secondary magnetic fields to a small fraction. © 2006 IEEE.

Taulu S.,Elekta Oy | Nenonen J.,Elekta Oy | Ahonen A.,Elekta Oy
Brain Topography | Year: 2010

We have combined Signal Space Separation and beamformers (SSS beamformer). The SSS beamformer was tested by simulation in the presence of simulated brain noise. The SSS beamformer performs at least as well as the conventional beamformer, provided that the expansion order is sufficiently high. For beamformer outputs which depend on power or power difference normalized by the projected noise, the spatial resolution of the SSS beamformer is significantly better than that of the conventional beamformers if the sources are deeper, and about the same as that of the conventional beamformer when the sources are superficial. For beamformer outputs which depend on the ratio of powers, the spatial resolutions of the SSS and conventional beamfomers are the same. The sensor noise covariance matrix in the SSS basis is non-diagonal. The SSS beamformers with diagonalized noise covariance matrix exhibit better spatial resolution than that with nondiagonal noise covariance matrix. The SSS beamformers are computationally more efficient than the conventional beamformers. © Springer Science+Business Media, LLC 2010.

Loading Elekta Oy collaborators
Loading Elekta Oy collaborators