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 (neuronal 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 method in using this 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.
SQUID-sensors tailored for ULF MRI can also be used for MEG, which makes it possible to measure both imaging modalities using the same sensor array. This eliminates manual steps of precisely aligning the anatomical model used for localizing brain activity and the MEG sensors. At the same time, also the associated errors are eliminated.
Ultra-low-field magnetic resonance imaging (ULF MRI) is a relatively new technique pioneered at UC Berkeley in the 2000s, where the nuclear magnetic resonance (NMR) is measured at kHz frequencies using ultra-sensitive magnetic-field sensor technology. Typically, the sensors are based on superconducting quantum-interference devices (SQUIDs) and operate at a 4.2 K temperature in liquid helium. ULF MRI provides a completely silent and safe method for acquiring 3D images, for instance, of the human head. With novel electronics and methods developed at Aalto University and PTB, ULF MRI also provides unique possibilities, for instance in current-density imaging (CDI).
Magnetoencephalography (MEG) is the measurement of the magnetic field generated by electric currents in neuronal activity. When a large number of highly sensitive magnetic field sensors is used, one obtains information about the location of the brain activity. A great deal of MEG expertise is concentrated in the Helsinki area. The MEG-MRI group at Aalto University continues the heritage of the famous Low-Temperature Laboratory at Aalto in applying superconductivity to brain imaging, and Elekta Oy in Helsinki is the leading manufacturer of MEG devices. The combination of MEG with ULF MRI and CDI can significantly improve the workflow and accuracy of localizing brain activity.
One important building block of superconducting electronics is the Josephson junction, in which a supercurrent passes through a non-superconducting barrier by means of quantum-mechanical tunneling. By connecting two Josephson junctions in parallel in a superconducting circuit, one forms a loop known as a superconducting quantum-interference device (SQUID). With a suitably adjusted circuit around it, the voltage measured over the SQUID oscillates as a function of magnetic flux through the SQUID loop. The oscillations are due to a quantum interference effect and are analogous to interference of waves in a two-slit experiment in classical physics.
Electric current flow in tissue affects the nuclear spins of hydrogen atoms, i.e. protons, in the tissue. The information recorded by the atomic nuclei can be accessed using NMR. However, a strong applied magnetic field drowns the effects in the perpendicular plane. Information is thus lost in two of three Cartesian directions. However, ultra-low-noise ULF MRI current-source electronics developed at Aalto allows fast switching of all magnetic fields during the imaging sequence, providing information in all three components. One of the aims of BREAKBEN is to succeed in measuring injected current density in the human head.
Solving the so-called inverse problem locates the brain activity that produced the measured multi-sensor signal. Accurate solutions require accurate MEG–MRI coregistration and knowledge of the conductivity map of the head. Imaging of injected currents in tissue can be used to determine the conductivity geometry of the head and to thereby allow accurate source localization.
Neuronal activity in the brain causes electric currents to flow in tissue. While these currents are very small, it may be possible to do neuronal current imaging (NCI) to detect electrical brain activity directly from NMR in a way similar to current-density imaging. Since the spatial origin of the signal can be encoded in the signal by means of MRI, the MEG inverse problem is bypassed, increasing the precision of localizing of brain activity.
Superconductivity is the phenomenon where a material, cooled below its critical temperature, loses its ability to resist electric current. Superconductivity is based on quantum-mechanical effects of so-called Cooper pairs formed by electrons and their interactions with the surrounding material. Besides levitating objects, maglev trains and fusion reactors, the phenomenon can also be used to build superconducting electronics that allows special components not available in conventional electronics. A typical superconducting material used niobium, which superconducts when immersed in liquid helium at a temperature of 4.2 kelvin. Superconductivity is also closely related to magnetism, and superconducting electronics can be made extremely sensitive to magnetic fields.