Interference Subspace Adjustment in Biomagnetic Signal Separation
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Solution Overview
Problem
Current magnetic imaging methods, such as MEG and MRI, face challenges in accurately eliminating external interference signals, which are often significantly larger than the biomagnetic fields of interest, leading to suboptimal shielding factors and sensitivity to calibration errors.
Innovation Solution
The method involves generating two calculated signal subspaces using the Signal Space Separation (SSS) technique, where one subspace represents the useful signal and the other interference signals, with adjustments made to the interference subspace by adding intensive interference components and singular value decomposition to form a linearly independent basis, effectively improving the shielding factor and reducing calibration errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a magnetically shielded room is used to damp external interference signals, then the shielding factor is improved, but the device complexity and cost increase, and the room may introduce additional magnetic interference from its walls
Solution Approach 1:
The patent replaces the mechanical/physical shielded room structure with a mathematical signal processing method. The SSS technique uses signal space decomposition and projection to eliminate interference components from measurement signals without requiring physical shielding, thereby avoiding the complexity and potential interference sources of magnetically shielded rooms while achieving equivalent or superior interference rejection
Solution Approach 2:
The patent introduces reference sensors as intermediaries that measure only interference signals. These reference measurements serve as a mediator between the environmental interference and the measurement sensors, enabling the system to identify and remove interference components through mathematical operations without needing physical shielding
2Loss of information
If reference sensors are used to measure interference signals, then the interference estimation is improved, but measurement precision deteriorates due to the need to extrapolate interference field data from different locations
Solution Approach 1:
The patent extends the measurement space by adding reference sensors that provide interference information from an additional spatial dimension. By combining measurements from both the measurement sensors and reference sensors, the system creates a more complete picture of the interference field, enabling accurate interpolation and extrapolation through mathematical methods rather than relying on assumptions about field uniformity
3Object-affected harmful factors
If the SSS method is used to separate useful signals from interference, then the shielding factor is improved, but sensitivity to calibration errors increases
Solution Approach 1:
The patent incorporates feedback mechanisms where the system continuously monitors measurement signals and reference signals, uses this information to update interference models in real-time, and adjusts the signal separation process accordingly. This feedback loop reduces sensitivity to calibration errors by adapting to actual measured conditions rather than relying solely on predetermined calibration parameters
Solution Approach 2:
The patent performs preliminary measurements using reference sensors to characterize the interference field before processing the actual measurement signals. This preliminary action allows the system to pre-compute interference models and projection operators, reducing the impact of calibration errors during the actual measurement process by having already adapted to the specific interference environment
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the shielding factor from approximately 150 to 1000, achieving better accuracy in measuring biomagnetic signals over a wide frequency band with reduced calibration errors and improved stability, similar to a thicker shielded room without the physical limitations.
Implementation Method 1
measurement sensors and a data processing logic arranged to generate two calculated signal subspaces by means of a SSS method
Data Source
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AI summary
The present invention introduces a method for adjusting interference signal estimates provided by multi-channel 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. In addition, it is taken into account that only those forms of interference of the measured interference components are included which are not yet present in the calculated SSS model. Finally, an adjusted interference subspace is formed, by means of which signal processing and the analysis of the useful signals can be continued. In the invention, the incorrectly functioning signal channels can also be taken into account and equated with the external interferences. In one embodiment, the above-described process can also be performed for the signals of the internal basis, i.e. for the signals of interest.