Device for detecting magnetic signals generated by a beating heart

Abstract

The invention relates to a device for detecting magnetic signals generated by a beating heart (M), comprising at least two nitrogen-vacancy centre, NV, magnetometer units (S1, S2), which are arranged in a geometric arrangement relative to one another and are connected to a signal processing unit (200), wherein the device is designed to detect a magnetic field strength (R1, R2) and field direction (R1, R2) by means of each of the at least two NV magnetometer units (S1, S2), and, by means of the signal processing unit (200), to determine at least one field vector having an effective magnetic field strength and an effective field direction from the magnetic field strengths and field directions detected by the at least two NV magnetometers.

Description

[0001] Description

[0002] Title for capturing which is from a the heart are generated

[0003] The present invention relates to a device for detecting magnetic signals generated by a beating heart

[0004] Background of the invention

[0005] Optically pumped quantum sensors or those based on NV centers in diamond are particularly suitable for measuring very small magnetic field strengths. DE 10 2022 204 526.2 describes a magnetometer that uses optically pumped and optically detected magnetic resonance (ODMR). This method exploits the fact that the energy levels of certain spin states of unpaired electrons split under the influence of an external magnetic field, the so-called Zeeman effect.

[0006] The splitting of energy levels results in altered transitions during relaxation from excited states, which can then be measured, for example, by optical excitation and frequency-dependent detection of the resulting fluorescence radiation, or by observing optical properties such as light absorption. The measured optical parameters can then be used to determine the magnetic field strength.

[0007] Disclosure of the invention

[0008] According to the invention, a device for detecting magnetic signals generated by a beating heart is proposed, having the features of claim 1. Advantageous embodiments are the subject of the subclaims and the following description.

[0009] A magnetocardiogram (MCG for short) is the recording and display of the heart's magnetic field, which is generated by the electrophysiological activity of the heart muscle cells. The invention presents a contactless, passive method for long-term, high-resolution monitoring of the human heart. This is achieved using nitrogen vacancy magnetometers (so-called NV magnetometers) in a geometric arrangement for vector gradiometry.

[0010] In detail, a device for detecting magnetic signals generated by a beating heart is now presented, which device has at least two NV magnetometer units arranged in a geometric arrangement relative to one another and connected to a signal processing unit. The device is configured to detect a magnetic field strength and field direction using each of the at least two NV magnetometer units, and to determine, using the signal processing unit, at least one field vector comprising an effective magnetic field strength and an effective field direction from the magnetic field strengths and field directions detected by the at least two NV magnetometer units. Both a wireless and a wired connection between the sensor system and the signal processing unit is provided. Such a device can also be referred to as a magnetocardiograph.

[0011] Diamond NV magnetometers are based on the reading of magnetic resonances from specific defect centers in diamond, particularly nitrogen vacancies (NV), which occur as impurities in the carbon lattice of diamond and can also be deliberately introduced. If the NV center is optically excited in the ground state, for example, by irradiating a pump laser beam with a suitable wavelength (in this case in the green wavelength range, e.g., at 532 nm for off-resonance excitation), the electrons are lifted from the triplet ground state to the excited triplet state and relax, emitting fluorescent light in the red wavelength range at 650 - 800 nm (637 nm = zero phonon line). Since the probability for non-spin-conserving transitions from the spin state increases with the spin quantum number m s =±1 is larger, continuous excitation pumping ensures that the NV centers are mostly in the spin state m s=0 hyperpolarized.

[0012] Between the m s = 0 and m s =±1 spin states in the ground state, there is an energy difference, which in this case is about 2.87 GHz. Therefore, if microwave radiation is irradiated into the diamond in addition to the optical excitation, a dip in the red fluorescence occurs at this resonance frequency of 2.87 GHz, since the spin-polarized electrons are deflected by the microwave field from the m s = 0 in the m s =±1 ground state and from there by the pump light into the m s =±1 excited state. From there, however, mainly non-radiative transitions and weak infrared fluorescence transitions occur via the singlet state, while fluorescence in the red region disappears.

[0013] If an external magnetic field is present, the so-called Zeeman effect causes the splitting of the otherwise equally energetic m s=±1 triplet levels into energetically equidistant Zeeman levels. When the fluorescence is plotted against a frequency spectrum of the microwave excitation, two dips are observed in the fluorescence spectrum, the frequency spacing of which is proportional to the magnetic field strength of the external magnetic field. The magnetic field sensitivity is primarily defined by the minimum resolvable frequency shift and can reach 1 pTA / Hz or less. Since the NV center in single-crystal diamond has four possible arrangements in the crystal lattice, the presence of a directed magnetic field causes the NV centers present in the crystal to react with varying degrees to the external magnetic field depending on their position within the crystal. Ideally, this results in four pairs of fluorescence minima appearing in the spectrum, from whose shape and position relative to each other, both the magnetic field strength (magnitude) and the direction of the external magnetic field can be clearly determined.To enable vector magnetic field measurements, the device comprises a device for generating a substantially homogeneous bias magnetic field in the region of the magnetometer units or their sensor media, whereby the bias magnetic fields of different NV magnetometer units differ. This can be a Helmholtz coil arrangement, with at least the sensor medium arranged within the Helmholtz coil arrangement (each magnetometer unit has its own bias field). Other devices can also be used, such as a simple coil, an elongated coil, permanent magnet solutions such as in a Hallbach array, etc.

[0014] By using a number of vector magnetometer units in a geometric arrangement and gradiometer interconnection, these magnetometer units have different orientations to the heart's magnetic field. Through the gradiometer interconnection, i.e., essentially vector arithmetic of the measured object, the position and strength of the magnetic field exciter (heart) can be determined. Since the much stronger background field is essentially the same in both magnetometer units (same strength and orientation), it can be eliminated. This eliminates the need for magnetic shielding, allowing magnetic field measurements in everyday environments. A further advantage over classic gradiometer arrangements with one-dimensional magnetometers is the compact design of the gradiometer arrangement enabled by this, since no distant reference magnetometer is required.The invention is therefore particularly suitable for the unshielded measurement of weak magnetic fields. Technical details of gradiometer solutions that can also be used within the scope of the present invention are disclosed in DE 102022201690.4 and are intended to be incorporated herein.

[0015] Heart signals have a magnetic signature with an amplitude of (only) 1 to 2-digit picotesla (pT) at a distance of a few centimeters, whereas, for example, the Earth's magnetic field in Central Europe is about 50 pT (microtesla), i.e. a factor of 10 6 stronger. However, even such small field strengths can be resolved with high precision over the long term using the proposed technology.

[0016] High-resolution detection of the precise cardiac signal allows for the detection of a variety of diseases, such as permanent atrial fibrillation and paroxysmal atrial fibrillation. This can prevent a heart attack and, subsequently, a stroke (especially after an undetected heart attack). Furthermore, the invention is suitable for the early detection of ST-elevation myocardial infarction, other types of elevation myocardial infarction, pulmonary embolism, AV nodal retrieval tachycardia, ventricular extrasystoles, and even very rare pathogenic diseases such as arrhythmogenic right ventricular tachycardia, which can otherwise only be detected through gene sequencing.

[0017] A particular advantage of NV sensors is the directional or vector information. Unlike other technologies, this is inherent in NV sensors. Therefore, there is no need to introduce interference through modulation techniques or use less favorable projections, nor is there a need to use multiple separate sensors. Thus, the vector and gradiometric information are available at exactly the same location (diamond size, i.e., single-digit mm). A3 and below) and not separated by a few cm to many cm like with other technologies. With NV magnetometer units, which can determine not only the field strength but also the direction of the magnetic field, improved suppression of a background field and thus better detection of signals that are heavily overlaid by interference signals is possible. This is based on two mechanisms: firstly, the signal is not as susceptible to tilting of the sensors relative to each other (in a standard gradiometer application, tilting of the 1D magnetometer leads to a different projection of the measuring or interference field) and this can be compensated for, which is particularly relevant for non-rigid installation combined with localization, e.g. in a mattress. Secondly, the interference field can have a different spatial direction than the field to be measured. This facilitates the separation of signal and background.

[0018] The directional information can be used to record channels equivalent to ECG channels, especially when gradiometer arrays consisting of at least two NV magnetometer units with different main extension planes are used. A vector and / or scalar difference between different NV magnetometer units in an array can be calculated to detect or eliminate background noise. The calculation of time derivatives of the signals can also be used. The vector information allows for the precise (not just projection, but direct) correction / separation of background / interference signals. This particularly solves the problem that, with conventional gradiometers consisting of one-dimensional magnetic field sensors, these sensors must be very precisely aligned in angle. With vector information, this is no longer necessary, since the interference fields are completely known.

[0019] It is also possible to use the gradiometric direction differences or the various vector signals, or both, to generate information equivalent to various ECG channels (direction- and spatially resolved signals from the heart). In one embodiment, the signal processing unit is configured to determine multiple field vectors, each comprising a magnetic field strength and a field direction, from the magnetic field strengths and field directions detected by the at least two NV magnetometer units.

[0020] In particular, spatial resolution of the heart can be achieved by several individual magnetometer units in an array located near the heart, with a straight projection of the heart onto the array covering several NV magnetometer units. This spatially detects the 3D pattern of the heart's magnetic field (multiple field vectors). Depending on the implementation, this yields actual 2D and 3D images of the heart, allowing for much more in-depth analyses than previously possible.

[0021] After the data has been processed, the signal is analyzed. Particular attention is paid to certain terms that indicate specific problem signals or healthy signals. If these indicators deviate from the norm to a certain extent, an interference signal can be generated, which can trigger an alarm or forward the signal to a doctor.

[0022] Only precise resolution of the cardiac signal enables the detection of pathological patterns. In the case of highly noisy or poorly resolved signals, the shifts of the heart's various PQRST complexes relative to each other or over time, fluctuations in their amplitude, deformations, or small disturbances are not detectable. However, the resolution of these criteria is important, as the aforementioned problems can lead to complexes being confused (e.g., interpreting an elevated and shifted T wave as an R wave, which, however, frequently occurs in a "healthy" heart) and false alarms. In particular, the vector information also allows for the localization of the heart's position and thus the determination of the source and the explicit evaluation of data from the correct direction. This can also be used, in particular, to measure individual parts of the heart or other objects and specifically assign signals to them.Thus, the information content is higher compared to an ECG because the heart is spatially resolved, allowing various abnormalities to be assigned to specific physical areas. This allows for more precise diagnoses. Furthermore, there are signals that are only visible in the CKG but not in the ECG, particularly in these directional signals, which provide additional information, for example, when one heart chamber is "lagging behind" the other. The CKG signal is particularly informative here, as the artifacts appear in different directions or are spatially separated and can thus be precisely identified.

[0023] Another advantage of NV sensors is their size, especially the size of the sensor medium. For this application, the active measurement volume should be small compared to the object being measured (the heart), otherwise the area coverage would result in integration over large portions of the signal, and the signal might disappear because the integral is zero. The smaller the active measurement volume compared to the heart, the better the signal detection. NV sensors have a very small active sensor volume. This small size also allows the sensors to be used in a geometric arrangement. In particular, very high-resolution arrangements are possible due to the very small active sensor volume.

[0024] For this application, a sampling rate higher than the cardiac signal is required to resolve it, especially higher than 50 Hz. A range of 200 Hz to 400 Hz is considered particularly advantageous. Higher is always better for resolution, but increases the sensitivity requirements.

[0025] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0026] The invention is illustrated schematically in the drawing using exemplary embodiments and is described below with reference to the drawing.

[0027] Short description of the drawings

[0028] Figure 1 shows in a schematic block view the essential components of an NV center magnetometer as can be used in the context of the invention.

[0029] Figure 2 shows, in various figures a) to c), each in a schematic block view, possible geometric arrangements of NV magnetometer units of a device for detecting magnetic signals according to one embodiment.

[0030] Figure 3 shows a schematic block view of a measuring principle of NV vector gradiometry, as it can be used in an embodiment of the invention.

[0031] Embodiment(s) of the invention

[0032] Figure 1 schematically shows the essential components of an NV center magnetometer. Initially, a diamond 110 with nitrogen vacancies (NV) serves as the sensor medium. The optical excitation of the NV centers can be achieved by a suitable light source 120, such as an LED or a pump laser. For example, a frequency-doubled Nd:YAG laser or a semiconductor laser in the green range of approximately 510-532 nm is suitable, e.g., at 532 nm for off-resonance excitation. Alternatively, LEDs in suitable wavelength ranges can also be used. Depending on the arrangement, the light from the light source 120 can be irradiated into the diamond 110 via suitable optical elements 122, such as mirrors, beam splitters, focusing optics such as lenses, and optionally via fiber optic elements.In addition, the excitation light can be emitted continuously or in pulsed mode by the laser, so that, for example, time windows can be kept free for interference-free fluorescence light measurements.

[0033] Furthermore, the magnetometer can comprise a microwave source 150 capable of generating an electromagnetic field in the sensor medium over a bandwidth covering the desired resonance frequency, i.e., in the region of the NV centers of the diamond 110. A microwave resonator structure can be used to homogeneously distribute the generated microwaves across the volume of the measurement area in the diamond. The resonator structure or the microwave source 150 is preferably tuned to the frequency of the electron spin resonances. To enable vector magnetometry, an additional static bias magnetic field 140 is generated. This makes the measurement intrinsically vectorial. Various spatial directions in the crystal structure are used for this purpose. A Helmholtz coil, for example, is suitable for generating such a magnetic field 140, in which a substantially homogeneous magnetic field can be generated in a limited area using a pair of coils.

[0034] The resulting fluorescent light 112 from the diamond 110 can in turn be guided via suitable optical elements 134, such as optical filters, beam splitters, lenses, and / or fiber optic elements, to a first photodetector 130, which is sensitive at least in the range of the fluorescence wavelength. The first photodetector 130 can also be arranged directly on the diamond 110. A second photodetector 132 is arranged such that it can detect at least a portion of the excitation light from the light source 120, which can be coupled out, for example, by a beam splitter, a filter, or a partially transparent element. This detector signal 132 of the excitation light can be used as a reference signal, for example, to eliminate background signals and to highlight the resonance signal of interest by modulating the excitation light using a lock-in amplifier.Additionally or alternatively, this reference signal can be used to account for fluctuations in the excitation light. Appropriate circuits 160, such as a preamplifier, a logarithmic amplifier, a lock-in amplifier, signal filters, or others, are thus provided to receive the signals from the first and second photodetectors and preprocess the signals appropriately for further evaluation. Finally, the preprocessed fluorescence signal can be evaluated by a signal processing unit 170, e.g., using a suitable microcontroller or processor, to obtain the desired parameters of the detected magnetic field from the signal, in particular the magnetic field strength and the direction of the magnetic field.

[0035] It is understood that such a device may also comprise additional units not shown, such as communication units or interfaces for outputting the measurement results. Such a device may also advantageously be integrated into an ASIC or FPGA.

[0036] In order to be usable in an everyday environment, magnetic fields that do not originate from desired weak sources should be eliminated from the measurement as far as possible, especially the Earth's magnetic field in the range of 10' 5 Tesla (a few microtesla). In contrast, cardiac magnetic fields are in the range of 10-100 times 10' 12 Tesla (Picotesla).

[0037] The elimination of background magnetic fields can be achieved by a gradiometer arrangement during magnetic field measurement according to exemplary embodiments. A gradiometer is generally a sensor unit capable of measuring not only the field strength but also the field gradient.

[0038] For this purpose, at least two individual magnetometer units S1, S2, ..., Sn, S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1m, ..., SnmS11, S21, ..., Sn1, S12, S22, ..., Sn2, S1m, ..., Snm can be used, which are arranged at spatially different locations. As an example, a sensor unit that uses two or more NV center magnetometers in a gradiometer arrangement is described below in conjunction with Figure 2.

[0039] Figure 2 shows, in various images a) to c), possible geometric arrangements of NV magnetometer units of a device for detecting magnetic signals according to one embodiment. Figure a) shows, in a side view, an arrangement of at least two NV magnetometer units S1, S2, ..., Sn in any arrangement relative to one another in a plane (perpendicular to the plane of the drawing, ie only the first row is visible). Figure b) shows, in a side view, two NV magnetometer units S1, S2, whose sensor media are sections of the same diamond crystal 110. Figure c) shows, in a side view, a number (n times m) of NV magnetometer units S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1m, ..., Snm in any three-dimensional arrangement. Further layers (not shown) are arranged behind the plane of the drawing, so that overall a type of cubic lattice is formed.In this case, at least one NV magnetometer unit (not shown), which is located, for example, in one of the rear layers, is not arranged in the plane (plane of the drawing) in which other NV magnetometer units S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1m, ... Snm are arranged.

[0040] Furthermore, M denotes a signal source, here a heart, and O denotes an optional surface (in particular body skin) which limits the accessibility to or reachability of the magnetic field source M.

[0041] In embodiments of the invention, more than two NV magnetometer units can form a gradiometer (but at least two). With each additional NV magnetometer unit, the background field can be better determined, and the location and strength of the exciter can be better separated from the background.

[0042] In other embodiments of the invention, two NV magnetometer units can also form a gradiometer, whereby—depending on the number of NV magnetometer units—a total of several gradiometers are formed and record the signal of interest. From this, an effective measurement signal can then be formed, particularly by the signal processing unit, for example, by averaging, summation, etc.

[0043] A distance d between two NV magnetometer units S1, S2, ... or more precisely their sensor media corresponds to the distance between the locations where simultaneous magnetic field measurements are performed. As long as the distance between the measurement locations is relatively small, it can be assumed that the strength of an additional background magnetic field B envis approximately the same magnitude at both locations. In contrast, the weak magnetic field B of interest will decrease significantly with increasing distance from the magnetic field source M. Furthermore, the different orientation of the magnetic field of the pathogen (e.g., heart) allows for a clear separation from the background field, even at short distances.

[0044] By arranging two NV magnetometer units at different distances and angles from the source or the heart, the background field can be eliminated or determined using vector arithmetic, allowing the small magnetic field of interest to be determined and its source to be characterized (location and orientation). This can be further improved by a distant magnetometer that is far enough away that the weak magnetic field of interest has dropped below the detection threshold. With such a configuration, local changes in the background field can be compensated for by the at least two nearby magnetometers. For this purpose, for example, two NV magnetometer units can be arranged one above the other in an axial gradiometer configuration, so that an NV magnetometer unit of a first layer forms a gradiometer with an underlying NV magnetometer unit of a second, underlying layer.The background field can also be determined by placing another NV magnetometer unit at a large distance, e.g. at least 1 m, from the two NV magnetometer units.

[0045] One concept of the invention is to measure the field vectorially and simultaneously from different positions using multiple NV magnetometer units. As long as this arrangement is close to the signal source M to be measured, the field of the signal source is measured in different directions with the individual vector sensors. This distribution of the measured field vectors is characteristic and allows conclusions to be drawn about the source regarding strength, position, and orientation.To detect weak signals compared to the background, the assumption of a homogeneous background field across the geometric arrangement of NV magnetometer units (this is generally assumed here, since the distance between the source of the disturbance and the sensor medium is assumed to be much greater than that of the signal to be measured and the sensor medium) allows the calculation of the individual field vectors, since the disturbance field vector can be assumed to be the same, and thus simple vector arithmetic is sufficient to extract the signal vector. Using a geometric arrangement also compensates for inhomogeneities in the background.

[0046] As shown in Figure 3, the different measurement positions of the NV magnetometer units S1, S2 determine the field vector in different directions. Since the background field Z1 is the same for both NV magnetometer units, this allows for the strength and orientation of the source to be calculated. By measuring the signal / field in different directions (the amplitude and orientation of the source field depends on the position of the individual sensor relative to the source), noise in the background field can be further suppressed (fluctuations orthogonal to the measurement signal are suppressed). This allows for noise suppression superior to the conventional gradiometer approach.

[0047] For example, M1 to Mn are at least one magnetic field component, and Z1 to Zn are at least one interference component (e.g., the Earth's magnetic field), which can be static or temporally variable. Corresponding NV magnetometer units S1 to Sn (extendable according to Figure 1) measure resulting components R1 to Rn, which contain the interference signal. NV magnetometer unit S1 measures component R1, consisting of the first interference Z1 and the signal M1 at the location of S1, and NV magnetometer unit S2 measures component R2, consisting of the second interference Z2 and the signal M2 at the location of S2, etc. From this, a signal insensitive to the interference components can be determined using vector arithmetic. Figure 3 shows a schematic block diagram of a measurement principle of NV vector gradiometry, as can be used in one embodiment of the invention, for two NV magnetometer units S1 and S2. An evaluation can proceed as follows:

[0048] Two vector-valued signals R1 and R2 are measured. These contain signal components M1 and MT, as well as noise components Z1 and Z2=Z1, which are identical for the measuring ranges. The gradiometer measurement signal is then calculated as follows:

[0049] As described by equation (1), the signal no longer contains any noise components, provided these are uniform across the measurement ranges. Furthermore, the measurement signal is vectorial, allowing, for example, the assignment of direction ("Where does the signal come from?"), the differentiation of different signals, and the correlation of multiple signals from different sensors in an array (imaging process).

[0050] The result in Equation 1 can be expressed as a magnitude and a direction. This is particularly advantageous when the source lies between the magnetometer units (or in a plane passing through the center of both), thus opposing the magnetic field.

[0051] By using three or more magnetometer units (geometric arrangement), a system of equations can be set up that allows the individual magnetic fields at the magnetometer units to be determined.

[0052] A further advantage is that conventional gradiometers measure the difference between two scalar sensors connected in series. Performance depends on one sensor measuring only the background field (measured values ​​(scalar) are simply subtracted from each other). Furthermore, in this case, the difference between the sensors is always smaller than the actual measured value (< M). The approach described here can determine the measured signal at different angles to the background signal by arranging the sensors at different solid angles (even projected onto a plane). This increases the signal-to-noise ratio and thus the sensitivity (in the ideal symmetrical case, with two sensors, the magnetic fields are exactly opposite).

[0053] Another advantage of a vector gradiometer is that it can be built significantly smaller than conventional gradiometers. Here, a reference sensor is positioned so that its distance from the signal source is so great that the signal at the reference sensor is significantly smaller. This requires the distance between the sensors to be significantly greater than the distance between the source and the measuring sensor. By utilizing vector information, all magnetometer units can be mounted close to the source, eliminating the need for a distant reference sensor.

[0054] Through calibration, an assumption regarding the distances to the signal origin, or a reference sensor far from the source that characterizes the background field, a "map"—that is, a spatial resolution of the measurement signal (3D)—can be generated. A sensor array intrinsically provides a 2D resolution. If a sensor array is not used in a single plane, a 2D resolution can be achieved.

[0055] The distance d between the sensor heads within a gradiometer unit, in this case the distance between the two sensor diamonds, can range from mm to several cm, for example, between 0.5 cm and 2 cm. Good results have been achieved for values ​​in this range, for example, for measuring biomagnetic fields in the picotesla range. However, as long as sufficient independence of the signals from the background fields is achieved, larger or smaller distances or other gradiometer configurations, such as sensors arranged side by side, can also be used. If the distance between the individual sensor heads is too large, particularly in the presence of local background fields (electrical cables, etc.), this can lead to interference.) the background field may no longer be identical at both locations; if the distance between the sensor heads is too small, however, the difference between the field strengths of the magnetic field to be measured between the two locations may be too small. The selection of the appropriate distance between the two sensors of a gradiometer unit therefore preferably also depends on the type and orientation of the magnetic field source of interest and the expected field strength. The distance of the sensor unit from the magnetic field source can also be in the mm to cm range.

[0056] The signal processing in this case has the particular task of making the signal independent of external magnetic field disturbances. Wherever electrical charges move or magnetic or magnetizable materials move, the ambient noise changes. This must be separated from the signal through appropriate signal processing to make the signal measurable.

[0057] Particularly good signal processing also enables the improvement of signal resolution and thus the detection of rarer and more difficult to detect artifacts and associated clinical pictures.

[0058] Many ambient signals occur at a specific frequency. Through the power grid, signals are particularly noticeable at, for example, 50 Hz or 60 Hz and higher harmonics. Filtering these typical frequencies is highly advantageous, as it significantly reduces noise. In particular, the performance of gradiometer units can be significantly improved. For example, a band-stop filter or notch filter can be used at the frequency of an AC power supply (e.g., 50 Hz) and / or harmonics (e.g., 100 Hz, 150 Hz, etc.) to filter the measured signal.

[0059] Furthermore, high-pass filters can be advantageously used to filter out particularly low frequencies, e.g., less than 1 Hz, and / or low-pass filters to filter out particularly high frequencies, e.g., greater than 200 Hz, from the measured signal. Particularly high and particularly low are related to frequencies typically found in a cardiac signal (i.e., typically approximately 60 to 180 Hz).

[0060] In addition, additional specific filters can be incorporated to filter out interference frequencies tailored to a specific environment, such as typical field frequencies or field patterns from technical devices. This can also vary for different application areas. For example, interference frequencies in hospitals differ from interference frequencies in private homes.

Claims

Claims 1. A device for detecting magnetic signals generated by a beating heart (M), comprising at least two nitrogen vacancy center (NV) magnetometer units (S1, S2, ..., Sn, S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1m, ..., Snm) arranged in a geometric arrangement relative to one another and connected to a signal processing unit (170, 200), wherein the device is configured to detect a magnetic field strength (R1, R2) and field direction (R1, R2) by means of each of the at least two NV magnetometer units (S1, S2, ..., Sn, S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1m, ..., Snm), and to determine at least one field vector comprising an effective magnetic Field strength and an effective field direction from the signals determined by the at least two NV magnetometer units (S1, S2, ..., Sn, S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1m, ...Snm) recorded magnetic field strengths and field directions.

2. Device according to claim 1, wherein the geometric arrangement is a two-dimensional arrangement in which the at least two NV magnetometer units (S1, S2, ..., Sn, S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1m, ... Snm) are arranged in a plane.

3. Apparatus according to claim 1, wherein the at least two NV magnetometer units (S1, S2, ..., Sn, S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1m, ... Snm) comprise at least four NV magnetometer units and wherein the geometric arrangement is a three-dimensional arrangement in which at least one of the at least four NV magnetometer units is not arranged in a plane in which at least three other of the at least four NV magnetometer units are arranged. Device according to one of the preceding claims, wherein each of the at least two NV magnetometer units (S1, S2, Sn, S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1m, ... Snm) has a diamond crystal or a section of a diamond crystal with nitrogen vacancy centers as the sensor medium (110), wherein the device is configured to detect the magnetic field strength and field direction by reading out a spin resonance in the sensor medium (110) that is dependent on the magnetic field strength. The device according to claim 4, further comprising at least one excitation light source (120) for radiating light (124) into the sensor medium (110), at least one microwave source (150) for generating a resonant field in the sensor medium, and at least one photodetector (130) for detecting resonance-dependent fluorescent light (112) from the sensor medium (110). The device according to claim 5, wherein the at least two NV magnetometer units (S1, S2, ...), Sn, S11 , S21 , ... , Sn1 , S12, S22, ... , Sn2, S1m, ... Snm) are assigned the same excitation light source (120) and / or the same microwave source (150). Device according to one of claims 4 to 6, wherein the sensor medium of the at least two NV magnetometer units (S1, S2, ... , Sn, S11 , S21 , ... , Sn1 , S12, S22, ... , Sn2, S1m, ... Snm) each comprises a section of the same diamond crystal (110). Device according to one of claims 4 to 7, wherein the distance (d) between the sensor media (110) of the at least two NV magnetometer units (S1, S2, ..., Sn, S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1m, ..., Snm) is between 1 and 30 millimeters, preferably between 5 and 20 millimeters. Device according to one of claims 4 to 8, further comprising at least one device (140) for generating a substantially homogeneous bias magnetic field at the location of the sensor media (110) of the at least two NV magnetometer units (S1, S2, Sn, S11, S21, Sn1, S12, S22, Sn2, S1m, ... Snm), wherein the bias magnetic fields of different NV magnetometer units (S1, S2, ..., Sn, S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1m, ... Snm) are different. Device according to one of the preceding claims, further comprising a band-stop filter or notch filter with a filter frequency at the frequency of an AC power supply or harmonics thereof, and / or a low-pass filter and / or a high-pass filter for filtering the detected signal. Device according to one of the preceding claims, wherein the signal processing unit (170, 200) is configured to generate a plurality of field vectors, each comprising a magnetic field strength and a field direction, from the signals measured by means of the at least two NV magnetometer units (S1, S2, ..., Sn, S11 , S21 , ... , Sn1 , S12, S22, ... , Sn2, S1m, ... Snm) to determine the magnetic field strengths and field directions.

Images