Signal detection device for detecting magnetic fields

Abstract

In the United States, there are approximately 17,000 new cases of spinal cord injury (SCI) each year [according to the SCI Model Systems Network]. The United States has at least 43 specialized hospitals, including at least 18 NIDILRR Model SCI Centers nationwide and 25 Veterans Affairs SCI Centers.

Description

[0001] In the United States, there are approximately 17,000 new cases of spinal cord injury (SCI) each year [according to the SCI Model Systems Network]. The United States has at least 43 specialized hospitals, including at least 18 NIDILRR Model SCI Centers nationwide and 25 Veterans Affairs SCI Centers.

[0002] In Germany alone, there are approximately 140,000 SCI patients and 2,400 new spinal cord injuries per year [according to the German Spinal Cord Injury Association (FGQ)]. There are at least 28 specialized hospitals, including several university hospitals and occupational accident clinics [Der Querschnitt.de].

[0003] Little is known about the exact degree of paralysis and the temporal changes / improvement / deterioration in the post-traumatic rehabilitation phase of paraplegic patients.

[0004] A deeper understanding of the continuous post-traumatic neuromuscular recovery and its dynamic development will create a better understanding of a. Learning about the activity, recovery and function of the spinal muscles in the “threshold areas of injury”, b. Assessing and deciding on individual training, both in rehabilitation and throughout life, c. enable biofeedback for training d. for the maximum use of muscles and biosignals at the affected site for the best possible recovery of SCI patients, and e.g. for the preparation of innovations of new sensor tools and rehabilitation robots / home care devices to improve life with SCI.

[0005] Clinical diagnosis of the affected muscles, sensory perception, and functional feedback are currently typically used to determine the medical status after six months. There is no continuous, non-invasive, contactless tool for the detailed diagnosis of spinal muscle impairment over time.

[0006] The object of the present invention is to provide a device and a method that allow the measurement of muscle function in the back of a subject. This object is achieved by the signal acquisition device according to claim 1 and the method for acquiring magnetic fields according to claim 11. The dependent claims specify advantageous embodiments of the signal acquisition device according to the invention.

[0007] According to the invention, a signal acquisition device for detecting magnetic fields is provided, which can be generated particularly in the back muscles, or alternatively or additionally, for example, in the spinal canal or generally in nerve pathways of a subject. The signal acquisition device preferably comprises at least one magnetic field measuring device with at least one magnetic field sensor, wherein the magnetic field measuring device can, for example, be arranged to be positioned on the back of the subject at a distance from the back muscles, the spinal canal, or nerve pathways of the subject, which distance is preferably so small that the field strength of at least one magnetic field generated there is, at least temporarily, greater at the location of the magnetic field sensor than the sensitivity of the magnetic field sensor.The signal acquisition device can advantageously also include at least one position determination device configured to determine the position of the at least one magnetic field measuring device and / or the at least one magnetic field sensor, for example on the back of the subject, and to generate a position signal indicating the position. Furthermore, the signal acquisition device can advantageously include at least one evaluation device configured to receive a measurement signal from the at least one magnetic field measuring device and to receive the position signal, wherein the evaluation device can preferably be further configured to evaluate the measurement signal as a function of the position signal and to output a result of the evaluation.

[0008] A signal detection device may, for example, include one or more of the following elements: 1. a multitude of sensors, preferably maneuverable in six degrees of freedom, including but not limited to 1.1. Magnetic field sensors, 1.2. imaging sensors, 2. a system for positioning and tracking the sensors, 3. a device for sample placement (e.g. a chair / bed for positioning a human test subject), 4. an EM (electromagnetic field) shielding device, 5. a calibration system.

[0009] The signal acquisition device can be used, for example, to determine or track the position, type and development of spinal paralysis or the position, type and development of excitable cells in a tissue, i.e., for (but not limited to): 1. Diagnostics of neurological patients (e.g. spinal cord injuries, brachial plexus injuries, neuropathies, etc.) 2. Short- and long-term monitoring of cardiac and / or neurological diseases, 3. Human-machine interfaces (based on muscles, nerves or brain) 4. Prenatal fetal activity, 5. Diagnostics of electrical circuits, 6. Analysis of material defects / inhomogeneities (e.g. welding, seams, scans).

[0010] The following description applies to the case where magnetic fields of the back muscles are measured. However, magnetic fields of the spinal canal, spinal cord, or other nerve tracts can also be measured instead or in addition.

[0011] The magnetic field sensors can advantageously be nitrogen vacancy quantum sensors (NV sensors). The NV sensor measuring unit can comprise one or more sensor heads or magnetic field measuring devices containing the measuring sensors and advantageously includes a central electronic unit or evaluation device that provides the necessary excitation signals for the sensor heads and acquires and analyzes the measurement data from the sensor heads.

[0012] The sensor head, e.g., a magnetic field measuring device, can advantageously be designed as a gradiometer with two magnetic field-sensitive elements (magnetic field sensors) arranged variably in distance and position. This allows the differentiation between endogenous signals (nerve or muscle magnetic field signals) with a strong gradient and stray fields with no or a significantly lower gradient. The magnetic field sensor closer to the source (e.g., muscle or nerve) can collect the field amplitude from the body and the stray fields, while optionally, the magnetic field sensor at a greater distance from the source collects only the stray field amplitudes. Subtracting the signals from both magnetic field sensors thus yields the pure magnetic signal of interest, which is generated, for example, by activated nerves or muscles.

[0013] The magnetic field sensors or sensor heads can, for example, comprise NV (nitrogen-vacancy) doped diamond, which can be excited by laser light and / or microwave fields. The laser light preferably has an optical power of 10 mW to 1 W, particularly preferably 300 mW collimated to a beam diameter of 10 µm to 500 µm. The laser light can be generated by a laser diode in the sensor head or in the magnetic field measuring device, or fed into the sensor head or magnetic field measuring device from a central electronics box via optical fibers (multimode or, preferably, single-mode or polarization-maintaining fibers). In the sensor head or magnetic field measuring device of the gradiometer, the laser light can advantageously be split by an optical beam splitter to excite both diamonds in the gradiometer. The microwave field can be generated by a generator within the magnetic field measuring device or magnetic field measuring device.of the sensor head or can be fed in remotely from the central electronic unit.

[0014] In the magnetic field measuring device or sensor head, the diamond fluorescence of each diamond can advantageously be detected using a photodiode. The photodiode signals can be converted into voltage signals, for example via a transimpedance amplifier, and then subtracted. Subsequently, the difference between the two signals can be amplified using a so-called balanced detection method.

[0015] Alternatively, the gradiometer can, for example, also have two separate magnetic field sensors or sensor heads, each with a single diamond. The signals from the individual magnetic field sensors or sensor heads can be subtracted or split, for example, to obtain a gradiometric signal for common-mode noise suppression. In this case, the signal from one or more sensor heads or magnetic field sensors can be used to suppress the common-mode noise of multiple sensor heads or magnetic field sensors, thus creating a power-efficient gradiometric array. A balanced detection scheme can, for example, be implemented in each sensor head or magnetic field sensor to compensate for laser intensity noise.

[0016] By using a multitude of microwave oscillations that address the magnetic resonances along each of the four possible NV defect orientations within the diamond crystal, the magnetic field vector can be extracted in addition to the magnetic field strength value. When each of the diamonds within the gradiometer is addressed with this multitude of microwave oscillations, the sensory instrument can also extract magnetic field vector gradient information. This additional vector information is a further measure for extracting useful information about muscle activity and distinguishing it from ambient noise. The required multitude of microwave oscillations for vector-based measurements can be generated, for example, with a variety of signal-defined radio (SDR) sources.

[0017] By using an array of sensors (a system with multiple gradiometric sensor heads), the extraction of relevant events (e.g., muscle reinnervation after a spinal cord injury) can be significantly improved. Ideally, the sensor heads are arranged as shown in the accompanying figures. Collecting the sensor data from all sensor heads in the central electronics unit improves the reduction of background noise by distinguishing between common modes present in all sensor heads and individual signal differences. Furthermore, the array aspect enables additional signal analysis strategies, such as waveform or pattern recognition, using the entire array dataset.

[0018] The use of neural networks and / or machine learning in conjunction with suitable algorithms can also be part of the system to improve the capabilities for a correct diagnosis.

[0019] Another advantageous aspect of the invention is the extraction of the sensor's local position relative to the subject's body. Considering this aspect can also improve the quality of the results.

[0020] To obtain precise information about the sensor's positioning relative to the body, camera or video recordings (general or coarse positioning) can be used in conjunction with ultrasound or radar images (providing information about the distance between the skin and the sensor). To improve the extraction of relevant data for the described purpose (measuring the degree of re-enervation), the system advantageously offers the possibility of directly relating the sensor position to the position and size of the relevant muscles or nerves by using anatomical-physiological data from an MRI or similar imaging technique. This anatomical-physiological data can be arranged, for example, in a mathematical model such as a finite element model, a continuum mechanics model, or others.

[0021] The imaging sensors can, for example, include or be ultrasonic sensors (various modalities, e.g., B- or A-mode), radar, lidar and / or cameras (e.g., visible or infrared light) and provide information about the anatomy of the subject, object or specimen.

[0022] Imaging and magnetic sensors can be advantageously used to control a positioning system. For example, they could be used to align local geometries with reference geometries, ensuring correct (re)positioning of the sensor heads or magnetic field sensors, even over time, and to compensate for patient movements (such as heartbeat, respiration, and / or motion artifacts).

[0023] For example, an ultrasound probe can be used to identify a specific body region that corresponds to subject-specific 3D models, such as those derived from MRI, CT, or ultrasound scans. Alternatively, radar / Lidar or cameras can be used to position the sensors at a known distance from anatomical landmarks. Magnetic sensors could also contribute to the positioning system by detecting known magnetic fields (e.g., from electromagnets or permanent magnets) that are coupled / associated with specific anatomical landmarks on the person's body.

[0024] To enable the described merging of sensor data from individual sensor heads or magnetic field sensors, time synchronization of the measurement signals from all sensors is advantageous. Such time synchronization can be achieved, for example, by using a precise clock, such as a thermally controlled quartz oscillator, an atomic clock on a chip scale, and / or a silicon-based micromechanical oscillator. These can be housed in the electronics unit or evaluation device that distributes this signal to all sensor heads or magnetic field sensors, for example, via electrical cables. To further reduce magnetic noise from the environment, additional sensors can be advantageously positioned further away from the magnetic field measuring device (e.g., 1 m to 5 m). These allow for the pre-subtraction of strong noise sources before the sensor data is processed using pattern recognition algorithms.

[0025] These measurements can be combined with other measurement techniques to correlate exact signal levels with anatomical landmarks for spatial diagnostics and repeatability, such as medical ultrasound.

[0026] The device for sample placement, i.e., the storage device, can advantageously take the form of a chair or a bed into which a living organism (e.g., a human being) can be placed. The apparatus preferably ensures a comfortable position for extended periods and is advantageously magnetically transparent or causes only known distortions of the magnetic field.

[0027] When imaging devices such as ultrasound are used, the device is preferably shaped and constructed in such a way that it does not interfere with the measurement (i.e., it is either transparent to the physical quantity being measured (e.g., in the case of ultrasound, the device material may have a similar impedance to the skin of the test subject), or it only causes known distortions of the measured physical quantity).

[0028] The signal acquisition device can advantageously include an electromagnetic shielding device that reduces magnetic interference fields to a manageable level, so that the readout of the magnetic field sensors is not impaired. The electromagnetic shielding device can, for example, take the form of a single- or multi-layer tube in which the entire system is housed. Alternatively, a single- or multi-layer shielding device of a suitable shape can be provided to protect specific areas of the signal acquisition device, such as the sensor heads or magnetic field sensors. A single- or multi-layer shielding device can also be provided to shield specific areas of the environment so that stray magnetic fields do not reach the sensors. The shielding can be optimized for the respective application using a calibration system (see below).

[0029] A calibration system may advantageously include one or more magnetic sensors (either the sensors already mentioned or special sensors) that monitor the magnetic field in the environment with and without the installed device at various points in time and space. The calibration system may be coupled with one or more phantom devices that generate a magnetic field with a known position, amplitude, and frequency. These phantom devices may, for example, but are not required to be, permanent magnets, alone or in combination with electromagnets. The electromagnets may, for example, include voltage / current generators and metal wires.The phantom devices can advantageously also include components that cause a mechanical disturbance of the electromagnetic system, for example, but not limited to, magnetically transparent hammers that strike metal threads to generate a displacement wave that propagates through space at a known speed. The output of the phantom device can advantageously be similar in amplitude and frequency to the signal to be detected. Fig. Figure 1 shows a simple diagram in which the vertical spine is represented by the visible spinal processes, the longitudinally running erector spinae muscles, and the nerves and muscles leading laterally. In the center: a horizontal spinal cord injury (SCI). Fig. Figure 2 shows a horizontal section through the spine with spinal cord and spinous processes, the erector spinae muscles on the side, and skin interfaces, e.g., two NV sensors with e.g., two individual sensors brought out each, and a PC for recording measurement data. Fig. 3: shows the anatomy of the subject in two partial images. Fig. 2 with spinal cord and intercostal nerves, each with a multitude of movable (e.g., 6D) individual sensors and their units in the areas of the healthy / affected erector spinae muscles, as well as arrays thereof, in various array settings "laterally" (sensor unit) to, for example, neck / shoulder / arm muscle areas, "laterally" (sensor unit) to, for example, a nerve that lies very close to the surface (intercostal nerve, which can fire but does not show muscle activity). Fig. Figure 4 shows two views of the subject in two partial images: a top view lying on the analysis table / sitting in a wheelchair backrest, and a side view in cross-section. The individual sensors and devices are located under the subject and can be moved; a laptop for data acquisition and analysis is positioned next to them. Fig. Figure 5 shows a sandwich diagram in cross-section with the spinous processes and muscles on top, skin layer, bed and sensor interface, and individual sensors to the NV unit. Fig. Figure 6 shows another simple diagram with a single sensor array and a central processing unit. Fig. Figure 7 shows examples of a gradiometer with variable geometry. Fig. Figure 8 shows a gradiometer with variable geometry with potential applications for neuromuscular diagnosis.

[0030] The invention provides a patient-safe examination infrastructure that includes all the software and hardware interfaces that experts in neurorehabilitation and data analysis could desire.

[0031] It preferably features flexible and comfortable (and adjustable) head, neck, chest, torso and limb support / seating / bed modules that allow experiments to be conducted in bed or in a seated position.

[0032] The support / backrest surface underneath advantageously has movable, non-contact NV sensor modules that can be positioned relatively freely by the examiner. These can be two or more units, primarily aimed at the erector spinae muscles running laterally and parallel to the spine.

[0033] The shoulder-arm muscle complex and perhaps even the nerves in this area may also be located within the adjustable sensor range.

[0034] The system is visually appealing and inspires confidence in patients.

[0035] The NV sensor units themselves are technically safe and encapsulated. Technical service is offered by QANT.

[0036] It is possible to connect the device according to the invention with commercially available or custom-made cinematographs / rehabilitation devices / external measuring modules.

[0037] It is possible to use the system for monitoring vital parameters (e.g. magnetocardiography, respiratory analysis).

[0038] The system advantageously enables contactless, non-radiative, continuous paralysis level diagnostics for neuroscience as a testing system. It offers better spatial resolution than electromyography signals (of the same affected muscles). It is psychologically unobtrusive under the patient's bed and can optionally be combined with training and directly measurable muscle effects.

[0039] A gradiometric NV sensor preferably comprises a small sensor head and a central control unit. Multiple sensor heads can be integrated into a single control unit. Joint data analysis, synchronized over time, supported by AI and triggers, is possible. Technical implementation for actuators is described.

Claims

[1] Signal detection device for detecting magnetic fields generated in the body of a subject, in particular the back muscles of a subject, comprising at least one magnetic field measuring device with at least one magnetic field sensor, wherein the magnetic field measuring device is arranged to be positioned on the body of the subject, in particular on the back of the subject, at a distance from the body of the subject, in particular at a distance from the back muscles of the subject, which distance is so small that a field strength of at least one magnetic field generated in the body of the subject, in particular in the back muscles of the subject, at the location of the magnetic field sensor is at least temporarily greater than a sensitivity of the magnetic field sensor. [2] Signal detection device according to the preceding claim, characterized by, that the signal detection device is set up to detect magnetic fields generated in the nerve fibers and / or spinal canal and / or back muscles of the subject, [3] Signal detection device according to any of the preceding claims, further comprising at least a position determination device which is configured to determine the position of the at least one magnetic field measuring device and / or the at least one magnetic field sensor on the body of the subject, in particular on the back of the subject, and to generate a position signal indicating the position, further comprising an evaluation device which is configured to receive a measurement signal from the at least one magnetic field measuring device and to receive the position signal, wherein the evaluation device is further configured to evaluate the measurement signal depending on the position signal and to output a result of the evaluation. [4] Signal acquisition device according to the preceding claim, wherein the result of the evaluation indicates the position, type and development of spinal paralysis or indicates the position, type and development of excitable cells in a tissue, for example using the position of the magnetic field measuring device and the measured signals. [5] Signal acquisition device according to one of the preceding claims, wherein the at least one magnetic field measuring device comprises a plurality of magnetic field sensors forming at least one gradiometer, wherein the gradiometer is configured to determine at least one gradient of the magnetic field generated in the body, in particular in the back muscles, wherein the evaluation device is configured to distinguish, on the basis of the gradient, the magnetic field generated in the body, in particular in the back muscles, from magnetic fields that originate outside the body of the subject. [6] Signal acquisition device according to one of the preceding claims, wherein the at least one magnetic field measuring device comprises a plurality of magnetic field sensors forming a gradiometer, wherein the magnetic field sensors are movable relative to each other within the gradiometer. [7] Signal acquisition device according to one of the preceding claims, wherein at least one of the at least one magnetic field sensors is a nitrogen vacancy sensor (NV sensor) or an optically pumped magnetometer (OPM). [8] Signal acquisition device according to one of the preceding claims, wherein the magnetic field measuring device has at least two nitrogen vacancy sensors, nitrogen vacancy sensors, or NV sensors which are excited by means of a laser, wherein the magnetic field measuring device has a laser source and also has at least one beam splitter with which a laser beam generated by the laser source can be directed onto the at least two nitrogen vacancy sensors, nitrogen vacancy sensors, or NV sensors. [9] Signal acquisition device according to one of the preceding claims, further comprising at least a displacement device which is configured to displace at least one magnetic field measuring device on the body of the subject, in particular on the back of the subject, preferably based on the position signal. [10] Signal acquisition device according to one of the preceding claims, further comprising at least a magnetic field shield arranged such that, when the magnetic field measuring device is arranged as intended on the body of the subject, in particular on the back of the subject, it shields at least partially or substantially completely in at least one direction all magnetic fields that are not generated by the body of the user. [11] Signal acquisition device according to one of the preceding claims, further comprising a storage device in which the subject can be stored in a predetermined position, wherein the at least one magnetic field measuring device is arranged in an area of ​​the storage device in which, when the subject is stored in the storage device as intended, the body of the subject, in particular the back of the subject, is located, wherein the storage device preferably comprises a chair or a bed. [12] Signal acquisition device according to one of the preceding claims, wherein the position determination device comprises at least one camera, at least one LIDAR, at least one radar and / or at least one ultrasonic sensor with which the position of the at least one magnetic field sensor on the body of the subject, in particular on the back of the subject, can be determined. [13] Method for detecting magnetic fields generated in the back muscles of a subject, wherein a magnetic field measuring device with at least one magnetic field sensor is arranged on the body of the subject, in particular on the back of the subject, at a distance from the body of the subject, in particular from the back muscles of the subject, which distance is so small that a field strength of at least one magnetic field generated in the body of the subject, in particular in the back muscles of the subject, is at least temporarily greater at the location of the magnetic field sensor than a sensitivity of the magnetic field sensor, wherein, in addition, a position of the at least one magnetic field measuring device and / or the at least one magnetic field sensor on the body of the subject, in particular on the back of the subject, is determined, and a position signal indicating the position is generated.A measurement signal is evaluated by at least one magnetic field measuring device depending on the position signal, and a result of the evaluation is output.

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