Sensor system for detecting a medium

Abstract

The invention relates to a magnetic field sensor arrangement (1) for detecting a sagittal component of a cardiac magnetic field caused by an excitation of the Tawara branches (8, 9) and the myocardial portions (20, 21) of the heart, comprising at least four magnetic field sensors (2, 3, 4, 5), wherein a first and a second magnetic field sensor (2, 3) of the at least four magnetic field sensors are arranged along a first straight line (17) and a third and a fourth magnetic field sensor (4, 5) of the at least four magnetic field sensors (2, 3, 4, 5) are arranged along a second straight line (18) and wherein the first and the second straight line (17, 18) are at least approximately at right angles to one another.

Description

[0001] Description

[0002] title

[0003] Sensor system for detecting a medium

[0004] The present invention relates to a magnetic field sensor arrangement for detecting a cardiac magnetic field caused by excitation of the bundle branches and the myocardial parts of the heart, and to a method for operating such a magnetic field sensor arrangement.

[0005] State of the art

[0006] Numerous arrangements of magnetic field sensors for measuring biomagnetic signals have been described to date. These include, for example, gradiometers for magnetoencephalography (MEG) or magnetocardiography (MCG). SQUID-based systems are typically used in these applications, but their spatial arrangement is fixed. In contrast, magnetic field sensor arrangements based on optically pumped magnetic field sensors allow adaptation to the external physiognomy of, for example, the skull and thoracic mantle. However, current gradiometer systems for thoracic diagnostics only partially utilize the radial symmetry of the cardiac magnetic field during the excitation phase of the heart chambers.

[0007] Conventional magnetic field sensors, such as SQUID-based ones

[0008] Magnetic field sensors have edge lengths significantly greater than 1 cm and therefore only allow limited use of the underlying anatomy to increase the signal-to-noise ratio. Furthermore, conventional SQU ID magnetic field sensors are sensitive either only in the xy-direction (i.e., within the coronal plane) or in the z-direction. Optically pumped magnetic field sensors also only provide a maximum of two-dimensional sensitivity.

[0009] Information, although here too the directional dependence is significantly limited. For several years, magnetic field sensors based on NV diamonds have been the subject of research. These are based on diamond crystals whose crystal lattice exhibits defects in the form of NV centers. In an NV center, a nitrogen atom occupies the lattice site of a carbon atom, with a defect located in the immediate vicinity of the nitrogen atom – again on the lattice site of a carbon atom. If such a crystal lattice is irradiated with excitation radiation with a wavelength between 490 nm and 575 nm, an electronic transition from a ground state occurs in the crystal lattice. 3 A2 into an excited state 3 E induced. From the excited state 3 E relaxes the NV center back to its ground state by emitting fluorescence radiation in a wavelength range between 650 nm and 750 nm. 3 A2.

[0010] The basic state 3 A2 has three magnetic substates with m s =0, m s =±1 . The states with m s =0 and m s The values ​​=±1 differ by an energy difference of 2.87 GHz (zero field splitting). The excited state 3 E also has three magnetic substates with m s =0, m s =±1. If the NV center is now in the ground state 3 When exposed to microwave radiation at a frequency of 2.87 GHz, the NV center oscillates between the m s =0, 3 A2 - Basic state and the m s =±1 , 3 A2 ground state. Upon irradiation with the excitation radiation, the NV center is now partially removed from the m s =±1 , 3 A2 - Ground state in the excited m s =±1 , 3The electron is switched to the E-state. From there, it relaxes back to the ground state, predominantly without emitting radiation. If the intensity of the fluorescence radiation is measured as a function of the microwave frequency, a sudden drop in intensity (a so-called peak) occurs at a frequency of 2.87 GHz. This drop in fluorescence intensity can be explained by the fact that—when irradiated with microwave radiation at a frequency of 2.87 GHz—fewer NV centers are present in the m s =0, 3 A2 ground state is available, which can be optically excited and emit fluorescence radiation into the m s =±1 , 3 A2 -basal state can relax.

[0011] In an external magnetic field, the m s =±1 , 3 A2 -ground state in two

[0012] states with spin quantum number m s =1 and m s=-1 (Zeeman effect). If the intensity of the fluorescence radiation is measured while changing the frequency of the microwave radiation, two peaks are obtained. The frequencies at which these peaks occur depend on the size of the splitting of the m s =±1 , 3 A2 -ground state and thus depends on the field strength of the external magnetic field.

[0013] NV magnetic field sensors are vector-valued and have a compact design.

[0014] It is an object of the invention to provide a magnetic field sensor arrangement for detecting a cardiac magnetic field caused by excitation of the bundle branches and the myocardial parts of the heart, which has an improved signal-to-noise ratio.

[0015] Disclosure of the invention

[0016] The present invention relates to a magnetic field sensor arrangement for detecting a sagittal component of the bundle branches and the myocardial portions of the heart according to claim 1, and a method for operating such a magnetic field sensor arrangement according to claim 9. Advantageous embodiments of the invention are the subject of the dependent claims and the description.

[0017] The invention provides a magnetic field sensor arrangement for detecting a sagittal component of the cardiac magnetic field generated by excitation of the bundle branches and the myocardial portions of the heart. Cardiac excitation typically begins with atrial excitation and then progresses via the atrioventricular node and the two bundle branches to the apex of the heart. The proposed magnetic field sensor arrangement allows the cardiac magnetic field to be detected during systole, particularly during early and late systole.

[0018] During early systole, each of the two bundle branches generates a partial cardiac magnetic field that radiates circularly around its respective bundle branch. The sagittal component of the partial cardiac magnetic field of the right bundle branch points out of the thorax in the region between the bundle branches and into the thorax on the opposite side, i.e., in the region of the right ventricle. The sagittal component of the partial cardiac magnetic field of the left bundle branch points into the thorax in the region between the bundle branches and out of the thorax on the opposite side of the left bundle branch, i.e., in the region of the left ventricle.

[0019] In conventional magnetic field sensor arrangements, the magnetic field sensors are positioned such that positive values ​​for the magnetic flux density are obtained for the partial cardiac magnetic field located in the left ventricle during early systole, while negative values ​​are obtained for the partial cardiac magnetic field located in the right ventricle. Subtracting the positive values ​​from the negative values ​​results in good signal quality for early systole, as the amplitudes of the two partial cardiac magnetic fields effectively double.

[0020] However, in late systole, i.e., during the excitation phase of the myocardial components, this arrangement proves disadvantageous, as the positive and negative field components of the respective partial cardiac magnetic fields cannot be detected separately. Due to their size, the sensitive areas of conventional magnetic field sensors are arranged in such a way that both positive and negative field components impinge on a single sensitive area, at least partially canceling each other out. Consequently, the magnetic flux density of the respective partial cardiac magnetic fields cannot be detected in this manner.

[0021] The magnetic field sensor arrangement comprises at least four magnetic field sensors, wherein a first and a second magnetic field sensor of the at least four magnetic field sensors are arranged along a first straight line, and a third and a fourth magnetic field sensor of the at least four magnetic field sensors are arranged along a second straight line. The first and the second straight lines are arranged at an approximately right angle to each other, e.g., an angle between 80° and 100°. The magnetic field sensors have sensitive surfaces whose area is, in particular, less than 4 cm². 2 , preferably less than 1 cm 2The sensitive area can be the surface of the respective magnetic field sensor on which at least the sensitive medium is located. The sensitive area can, for example, have a square or circular cross-section. The sensitive areas of the first and second magnetic field sensors can each be arranged centrally along the first line, while the sensitive areas of the third and fourth magnetic field sensors can be arranged centrally along the second line.

[0022] With the magnetic field sensor arrangement according to the invention, the partial cardiac magnetic fields can now be detected during both early and late systole. The first and second magnetic field sensors can be arranged to detect the positive sagittal component of the partial cardiac magnetic field of the left bundle branch during early systole, while the third and fourth magnetic field sensors can be arranged to detect the negative sagittal component of the partial cardiac magnetic field of the right bundle branch.

[0023] The first magnetic field sensor can be positioned to detect the negative sagittal component of the partial cardiac magnetic field of the myocardial portions of the left ventricle during late systole, while the second magnetic field sensor can be positioned to detect the positive sagittal component of the partial cardiac magnetic field of the myocardial portions of the left ventricle during late systole. The third magnetic field sensor is positioned to detect the negative sagittal component of the partial cardiac magnetic field of the myocardial portions of the right ventricle, while the fourth magnetic field sensor is positioned to detect the positive sagittal component of the partial cardiac magnetic field of the myocardial portions of the right ventricle.

[0024] In a further development of the invention, the at least four magnetic field sensors are configured as NV magnetic field sensors. In this case, the magnetic field sensor comprises a diamond with NV centers (NV diamond), an excitation light source configured to emit excitation radiation for the electronic excitation of the NV centers, and a detector for detecting fluorescence radiation emitted as a result of the electronic excitation of the NV centers. The NV magnetic field sensor further comprises a microwave structure configured to generate a microwave field in the NV diamond, and a magnetic field generation device for generating a permanent magnetic field. The NV diamond, the excitation light source, the detector, the microwave structure, and the magnetic field generation device can be arranged on a printed circuit board.In particular, the NV diamond, the excitation light source, the detector, and the microwave structure can be arranged in a housing mounted on a printed circuit board. If the magnetic field generation device is designed as an arrangement of permanent magnets, for example, as an at least approximately circular arrangement of permanent magnets in a Halbach configuration with the NV diamond at the center, then the minimum area required for such an NV magnetic field sensor can, in principle, be determined by the distance of the permanent magnets from the NV diamond.

[0025] The sensitive area is, in particular, the area on which the NV diamond as the sensitive medium, the microwave structure, the excitation light source, and the magnetic field generation device are arranged. The sensitive area can also be the area on which the NV diamond, the microwave structure, and at least part of the magnetic field generation device are arranged.

[0026] The first and second lines can intersect, forming a sensor plane. At least four magnetic field sensors can be arranged within this sensor plane.

[0027] Alternatively, at least one of the at least four magnetic field sensors can be arranged such that a projection of its sensitive surface lies on the first or second straight line. In such an arrangement, at least one of the at least four magnetic field sensors cannot be located in the sensor plane.

[0028] A central axis runs between the second and third magnetic field sensors, such that the first and second magnetic field sensors are arranged on one side of the central axis and the third and fourth magnetic field sensors are arranged on the other side. The at least four magnetic field sensors of the magnetic field sensor arrangement are arranged in pairs symmetrically with the central axis as their mirror axis. In particular, the first magnetic field sensor is arranged in a mirror-symmetrical manner with respect to the fourth magnetic field sensor, and the second magnetic field sensor is arranged in a mirror-symmetrical manner with respect to the third magnetic field sensor. The central axis can lie in the sensor plane.

[0029] The central axis can be arranged at least approximately parallel to a cardiac axis running midway between the two Tawara arms. The magnetic field sensor arrangement can be oriented such that the first and second magnetic field sensors are located above the left side of the heart, particularly above the left myocardial portion, and the third and fourth magnetic field sensors are located above the right side of the heart, particularly above the right myocardial portion.

[0030] In a further development of the invention, the magnetic field sensor arrangement includes an evaluation device that is operatively connected to the magnetic field sensor arrangement and is configured to receive and process signals from magnetic field sensors arranged symmetrically with respect to the central axis. The evaluation device is specifically configured to calculate an evaluation signal (s) from the signals (s1, s2, s3, s4) received from the respective magnetic field sensors. In particular, the evaluation device is configured to subtract from each other the signals detected by magnetic field sensors that are arranged symmetrically with respect to the central axis – i.e., the signals of the first and fourth magnetic field sensors as well as the signals of the second and third magnetic field sensors – and to add the magnitudes of the differences thus formed (s = |s1 - s4| + |s2 - s3|).In this way, the signal-to-noise ratio can be increased in both early and late systole.

[0031] The invention also includes a method for operating the magnetic field sensor arrangement with one or more of the aforementioned features.

[0032] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing.

[0033] The invention is schematically illustrated in the drawing using exemplary embodiments and is described below with reference to the drawing.

[0034] Brief description of the drawings

[0035] Figure 1 shows a schematic representation of the human heart;

[0036] Figure 2 shows a conventional magnetic field sensor arrangement for measuring a right and left partial cardiac magnetic field during early systole; Figure 3 shows a conventional magnetic field sensor arrangement for measuring the right and left partial cardiac magnetic field during late systole;

[0037] Figure 4 shows a magnetic field sensor arrangement according to an embodiment of the invention for measuring the right and left partial cardiac magnetic field during early systole;

[0038] Figure 4 shows a magnetic field sensor arrangement according to an embodiment of the invention for measuring the right and left partial cardiac magnetic field during late systole;

[0039] Embodiments of the invention

[0040] Figure 1 shows a schematic representation of the human heart. Cardiac excitation typically begins with the excitation of the atria 14, 15 and then proceeds via the atrioventricular node 16 and the right bundle branches 8 and 9 to the apex of the heart. A cardiac axis 6 runs between the two bundle branches 8, 9. Figure 1 depicts the sagittal components of the cardiac magnetic field during early systole. Components pointing out of the plane of the drawing are indicated with a "+", and sagittal components pointing into the plane of the drawing with a "-".

[0041] During early systole, a partial cardiac magnetic field is generated that runs circularly around each of the respective bundle branches 8 and 9. The partial cardiac magnetic field around the right bundle branch 8 is oriented in the opposite direction to the partial cardiac magnetic field around the left bundle branch 9.

[0042] Figure 2 shows a conventional magnetic field sensor arrangement 7 for detecting the cardiac magnetic field. A first and a second magnetic field sensor 10, 12 are arranged on opposite sides of the cardiac axis 6. During early systole, the cardiac magnetic field is well detected by such a conventional magnetic field sensor 7. In particular, signals detected by a magnetic field sensor located above the right side of the heart are subtracted from signals detected by a magnetic field sensor located above the left side of the heart.

[0043] Figure 3 shows the same conventional magnetic field sensor arrangement 7 during late systole. It can be seen that during this excitation phase, sagittal components of the cardiac magnetic field pointing out of and into the plane of the drawing both intersect the same magnetic field sensor 10, 12. These components can cancel each other out, so that in this way, a measurement of the cardiac magnetic field during late systole is not possible.

[0044] Figure 4 shows a magnetic field sensor arrangement 1 according to the invention. A first magnetic field sensor 2 and a second magnetic field sensor 3 are arranged along a first straight line 17. A third magnetic field sensor 4 and a fourth magnetic field sensor 5 are arranged along a second straight line 18. The first and second straight lines 17, 18 intersect at a right angle. A central axis 19 runs between the second and third magnetic field sensors 3, 4. The first magnetic field sensor 2 is arranged at least approximately symmetrically with respect to the central axis 19 with respect to the third magnetic field sensor 4. The second magnetic field sensor 3 is arranged at least approximately symmetrically with respect to the central axis 19 with respect to the fourth magnetic field sensor 5. The magnetic field sensor arrangement 1 is arranged above a heart axis 6, such that the central axis 19 of the magnetic field sensor arrangement 1 runs at least approximately parallel to the heart axis 6.The four magnetic field sensors 2, 3, 4, 5 are arranged in a sensor plane, which includes the central axis 19 and the first and second lines 17, 18. Figure 4 shows the cardiac magnetic field during early systole, during which partial cardiac magnetic fields are formed, arranged circularly around the respective bundle branches 8, 9. The magnetic field sensor arrangement 1 according to the invention makes it possible to detect the two partial cardiac magnetic fields independently of each other. Signals received at the respective magnetic field sensors can be evaluated using an evaluation device 22.

[0045] Figure 5 shows the cardiac magnetic field during late systole. During late systole, partial cardiac magnetic fields are formed, each radiating circularly around the myocardial portions 20 and 21 of the heart. The magnetic field sensor arrangement 1 according to the invention is arranged such that the first magnetic field sensor 2 can detect sagittal components of a partial cardiac magnetic field radiating around the left myocardial portions 21 that point into the plane of the drawing. The second magnetic field sensor 3 is arranged such that it can detect sagittal components of the partial cardiac magnetic field radiating around the left myocardial portions 21 that point out of the plane of the drawing. Similarly, the third magnetic field sensor 4 is arranged such that it can detect sagittal components of the partial cardiac magnetic field radiating concentrically around the right myocardial portions 20 that point into the plane of the drawing.The fourth magnetic field sensor 5 is arranged so that it can detect sagittal components of the partial cardiac magnetic field that point out of the plane of the drawing and is arranged around the right myocardial portions 20.

[0046] The magnetic field sensor arrangement 1 can be operatively connected to an evaluation device 22. The evaluation device 22 is configured to receive and process signals from the respective magnetic field sensors 2, 3, 4, 5 (s1, s2, s3, and s4). In particular, the evaluation device 22 can be configured to subtract from each other those signals that are attributable to oppositely directed components of the respective partial cardiac magnetic fields and to add the magnitudes of the differences thus formed (s = |s1 - s4| + |s2 - s3|). In this way, the signal-to-noise ratio can be increased in both early and late systole.

Claims

Claims 1. Magnetic field sensor arrangement (1) for detecting a sagittal component of a cardiac magnetic field caused by excitation of the bundle branches (8, 9) and the myocardial portions (20, 21) of the heart, comprising at least four magnetic field sensors (2, 3, 4, 5), wherein a first and a second magnetic field sensor (2, 3) of the at least four magnetic field sensors is arranged along a first straight line (17) and a third and a fourth magnetic field sensor (4, 5) of the at least four magnetic field sensors (2, 3, 4, 5) is arranged along a second straight line (18) and wherein the first and the second straight line (17, 18) are arranged at an at least approximately right angle to each other.

2. Magnetic field sensor arrangement (1) according to claim 1, wherein the first straight line (17) and the second straight line (18) are arranged in a sensor plane.

3. Magnetic field sensor arrangement (1) according to one of the preceding claims, wherein the first magnetic field sensor (2) is arranged in a mirror-symmetrical manner to the fourth magnetic field sensor (5) and the second magnetic field sensor (3) is arranged in a mirror-symmetrical manner to the third magnetic field sensor (4), with a central axis (19) as the axis of symmetry.

4. Magnetic field sensor arrangement (1) according to claim 3, wherein the central axis (19) can be arranged at least approximately parallel to a heart axis (6) running centrally between the two Tawara legs (8, 9).

5. Magnetic field sensor arrangement (1) according to one of the preceding claims, wherein the at least four magnetic field sensors (2, 3, 4, 5) are designed as NV magnetic field sensors.

6. Magnetic field sensor arrangement (1) according to one of the preceding claims, wherein the first and second magnetic field sensors (2, 3) are arranged above the left myocardial portions (20) and the third and fourth magnetic field sensors (4, 5) are arranged above the right myocardial portions (21).

7. Magnetic field sensor arrangement (1) according to one of the preceding claims with an evaluation device (22) which is connected to the magnetic field sensor arrangement (1) is interconnected and set up to receive and process signals from the respective magnetic field sensors (2, 3, 4, 5).

8. Magnetic field sensor arrangement (1) according to claim 7, wherein the evaluation device (22) is configured to calculate an evaluation signal (s) from the signals (s1 , s2, s3, s4) received from the respective magnetic field sensors (2, 3, 4, 5).

9. Method for operating a magnetic field sensor arrangement (1) according to any one of claims 1 to 8.

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