Elekta Ab (publ)

Neuromag Oy

Elekta Neuromag Oy

Commissariat a L'energie Atomique

Elekta Ab

Juha T Simola

Samu Taulu

Matti J Kajola

Antti I Ahonen

Visa A Vilkman

Jukka E Knuutila

Lauri Parkkonen

Claude Fermon

Myriam Pannetier

Petteri Laine

Juha Tuoriniemi

Heikki Rakkolainen

Jukka Nenonen

The present invention introduces a method, device and a computer program for removing artifacts present in individual channels of a multichannel measurement device. At first, a basis is generated defining an n-dimensional subspace of the N-dimensional signal space, where n is smaller than N, where using in the definition of the n-dimensional basis a physical model of a Signal Space Separation method, or a statistical model based on the statistics of recorded N-dimensional signals. Thereafter, a combined (n+m)-dimensional basis is formed by adding m signal vectors to the n-dimensional basis, each of these m signal vectors representing a signal present only in a single channel of the N-channel device. After this the recorded N-dimensional signal vector is decomposed into n+m components in the combined basis, and finally, components corresponding to the m added vectors in the combined basis are subtracted from the recorded N-dimensional signal vector.

Method and device for recognizing and removing undesired artifacts in multichannel magnetic field or electric potential measurements

The present invention introduces a method, apparatus and computer program for magnetic resonance imaging or magnetoencephalography applications in order to control currents of a coil assembly (), and thus achieving desired magnetic fields precisely in the measuring volume (). The approach is an algebraic method where a field vector is generated for the test currents of each coil (). Vector and matrix algebra is applied and a linear set of equations is formed. Field components and their derivatives up to the desired order can be taken into account. Principal component analysis or independent component analysis can be applied for determination of the dominant external interference components. By checking the condition value for the matrix (), it is possible to investigate whether a reasonable solution of currents for desired magnetic fields is possible to achieve. Finally, solved currents can be installed into a current supply unit () feeding the coils of the assembly (). The invention can be applied as an active compensation feature for different interference shapes in the MEG application (), or for the precise creation of the fields and gradients in the MRI application ().

Method for designing coil systems for generation of magnetic fields of desired geometry, a magnetic resonance imaging or magnetoencephalography apparatus with a coil assembly and a computer program

The present invention introduces a method for adjusting interference signal estimates provided by multichannel biomagnetic field measurements. A so-called Signal Space Separation method (SSS) is applied in the calculatory analysis of the measurement signals, providing for the division of the sources causing the fields in objects of interest and external interferences. When the signal basis representing the interferences has been estimated, this interference signal estimate is adjusted by measuring the fields without the object to be measured and without changing the sensor assembly. Interference components obtained in this manner are analyzed in such a way as to include only the most significant interference components. An adjusted interference subspace is formed, by means of which signal processing and the analysis of the useful signals can be continued.

Method for adjusting interference signal space in biomagnetic field measurements

The present invention introduces a method for processing multichannel measurement data achieved especially in MEG and EEG measurements. The method uses a signal space separation (SSS) method and the orthogonality of lead fields in order to calculate linear transformation from physical measurement channels to virtual channels. The geometry related to the measurement arrangement is dissipated and the number of virtual channels is clearly lower than the number of physical sensors. The concept of total information can be applied for such transformed measurement data due to orthogonality. The method offers simplified post-processing of the biomagnetic data, such as for source modelling. The total information can also be interpreted as a robust quantity describing the physiological state of a patient.

Analysis of multi-channel measurement data using orthogonal virtual channels

The present invention discloses a joint structure between the wall elements of a light-weight magnetically shielded room. In the joint structure, the end of the aluminum plate of the element is stepped and its surface roughened. In addition to this, the aluminum plate is coated, for example, with tin to improve the electrical contact. The joint includes &#x3bc; metal plates which are used to make a magnetic contact between the &#x3bc; metal plates of the elements. The compression force achieved by means of bolts is transmitted to the joint by means of an aluminum moulding. The non-continuous compression force is balanced over the entire joint area by using presser rubbers. The joint structure is protected by means of supporting profiles which are used to electrically couple the thinner aluminum plate of the sandwich type wall element to the thinner aluminum plate of an adjacent element. The thinner aluminum plate and the supporting profile can also be coated, for example, with tin to improve the contact.

Joint structure between the wall elements of a magnetically shielded room

The present invention recognises and eliminates from a biomagnetic measurement signal interferences whose source is disposed in the direct vicinity of an object being measured. The invention utilises the SSS method that can be used to separate from one another the signals associated with the internal and external sources of a set of measurement sensors by calculating two series developments. The sources to be examined in the invention and disposed in the so-called intermediate space produce a component to both of the developments, and can, therefore, be detected by means of an analysis to be performed in a time domain. This division into components can be made using the Principal Component Analysis (PCA), the Independent Component Analysis (ICA) or the Singular Value Decomposition. Finally, the clarified interferences in the intermediate space can be eliminated from the measured signal using, for example, the linear algebraic orthogonal projection.

Method and device for interference suppression in electromagnetic multi-channel measurement

The present invention describes a method enabling one to shield a device that measures weak biomagnetic signals from strong magnetic interference fields. The measurement sensors are provided with a feedback compensation loop, the difference signal of which is obtained from the measurement sensors themselves. As the actuator of the feedback function, one or more coils are responsible for eliminating, the external interference fields in the region of the sensors. Difference signals can be generated as a linear combination from the signals of two or more sensors. In the control logic, the SSS method can be used to numerically separate the biomagnetic signal being measured from the signals produced by the sources&#x2014;compensation coils and interference sources&#x2014;disposed outside the measurement region. The interference suppression can be enhanced by placing the assembly of sensors and the actuators within a magnetically shielding room.

Method for interference suppression in a measuring device

A method and device by means of which an irrotational, sourceless vector field can be expressed by a number of physically reasonable basis vectors. In the method and device for processing a multi-channel measurement of magnetic fields of the present invention, measured signals can be unambiguously divided into signals of the irrotational, sourceless vector field that are caused by an interesting object or external interferences, as well as into a signal caused by the nonideality of the measuring device. The invention is based on the combining of two very fundamental mathematical regularities and applying in the processing of signal vectors of a multi-channel measuring device that measures an irrotational, sourceless vector field. The invention is based on the Maxwell's equations of an irrotational, sourceless vector field, as well as on the convergence characteristics of series developments.

Method and device for processing a multi-channel measurement of magnetic fields

The device for sensing a magnetic field comprises a closed superconducting pick-up loop () having a path width (d) etched out of a single layer superconducting thin film and provided with a constriction () having a width (w) of narrow dimension smaller than the path width (d). The closed superconducting pick-up loop () constitutes a flux-to-field transformer (FFDT). At least one magnetoresistive element () is placed on top of or below the superconducting thin film, is isolated from the superconducting thin film by a thin insulating layer and is located so that an active part of the magnetoresistive element () is at the location of the constriction () and has a width equal to or less than the width of the constriction (). The active part of the magnetoresistive element () is oriented so that the bias current in this active part is directed essentially along the constriction (), orthogonally to the width of narrow dimension.

Device for sensing a magnetic field

The invention relates to a wall element for a magnetically shielded room and to a magnetically shielded room. The wall element comprises at least one first layer () which is formed of metal plate having a high electrical conductivity, and at least two layers, a second layer () and a third layer (), which consist of metal plates having a high magnetic permeability. The layers () are superimposed one on top of another in surface contact with each other without any separating air gaps, so that each first layer () having a high electrical conductivity lies between each second () and third layers () having a high permeability substantially in surface contact with the second and third layers, the layers together forming a compact structure in which the product (&#x3c3;&#xd7;&#x3bc;) of electrical conductivity (&#x3c3;) and permeability (&#x3bc;) is maximized so as to minimize the penetration depth of magnetic interference.

Wall element for magnetically shielded room and magnetically shielded room

A method and apparatus is described for making multichannel signal measurements of weak signals in noisy environments, wherein the elimination of background interference signals from the multichannel signal measurement is performed. The method is based on an adaptive compensation technique in which the large interfering background signals are first recorded. By a statistical analysis of this multichannel measurement, independent components of the interference are determined. The apparatus is provided with compensator elements which are coupled to individual sensors for both collection and distribution of information on the interference signals during the measurement. In this way the output of a device can be made immune to the large amplitude interference components present in the device's environment. This reduces the dynamic range requirement for the data transport and storage systems.

Method and apparatus for eliminating background interference signals from multichannel signal measurements

A sensor element of thin film components and fiber glass, and a support structure of fiber glass; when sensor elements are attached to the support structure, a sensor system for magnetoencephalographic measurements is formed. A substrate containing a planar signal coil and a SQUID is attached on a circuit board of fiber glass using a spring cut on the edge of a body plate. On the sensor element, is a small but mechanically stable connector or several such connectors (5); when the sensor element is plugged in receptacles (6) on the support structure (7), the element settles in a well defined orientation. Support structure (7) is made of a fiber glass shell following the shape of the bottom (10) dewar vessel, adapted to the shape of the head. The receptacles (6) are attached to the glass fiber shell by springs (9) made of thin fiber glass plate such that an array covering the whole skull as evenly as possible is formed when the sensor elements are plugged to the receptacles. The spring is cut to enable rotation only around an arbitrary axis in the plane of the spring and a translation only in a direction perpendicular to the plane of the spring. When this support structure is inserted in the dewar, individual sensor elements lean against the dewar bottom (10) by aid of three feet (11), pressed by springs (9), settling perpendicularly to the normal of the dewar bottom passing through the center of the sensor element.

Compact magnetometer probe and an array of them covering the whole human

A superconducting device for measuring weak magnetic fields, especially those generated by the human brain and detected simultaneously over the whole skull. The superconducting magnetometer or gradiometer elements of the device are attached with connectors to a cross-connection/support element which, in turn, is attached to a connecting element containing the electric components necessary for connecting the SQUIDs to the room temperature electronics. The connecting element is attached to a neck plug for the dewar flask. The neck plug is made of a stiff thermal insulation to prevent convection and a ribbon cable containing parallel twisted pairs. The latter element is self-supporting and forms an integral part of the magnetometer support structure. The cables in the neck plug have been made out of wires having a relatively high resistance in order to minimize the heat leak between room temperature and the cryogenic environment of the magnetometers. The excess noise caused by the resistive leads may be compensated by increasing the SQUID gain using positive feedback.

Multi-channel magnetic flux detector comprising a magnetometer modular

A reliable superconducting contact for superconducting thin film components, based on soft superconducting materials, and a method for making the contacts. A wire blank is squeezed to a thin plate and then this plate is cut into slabs used in the bonding. The ends of the slabs are longitudinally cut so that double or multiple parallel joints can be made. The slabs have elastic, bent central portions for absorbing stresses and stiff ends having a U-beam shape joined to the components. The U-beam shape may be formed by the soldering tool used to make the joints. The ribbon-like character, thinness and other features of the bonding slab permit a precise control of the bonding temperature, reduce the strain and bending forces caused by thermal contraction, and prevent the contact from peeling off while cooling the superconducting component to the operational temperature.

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Helsinki, Finland

Juha T Simola