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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.

Agency: Cordis | 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.

Agency: Cordis | 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.

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.

Nurminen J.,Medical Imaging Center | 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.

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