Measuring device for detecting an electrophysiological process

Abstract

The invention relates to a measuring device (1) for detecting an electrophysiological process, comprising an ultrasonic device (3) for transmitting and receiving ultrasonic waves (8, 9) and comprising a magnetic field detection device (2, 4) for detecting a magnetic field. The ultrasonic device (3) and the magnetic field detection device (2, 4) are positioned relative to each other such that the magnetic field detected by the magnetic field detection device (2, 4) can be spatially associated with an ultrasonic image which can be constructed from the ultrasonic waves emitted and received by the ultrasonic device (3). The invention also relates to a method for detecting the electrophysiological process with the aid of the measuring device.

Description

[0001] Description

[0002] title

[0003] Measuring device for recording an electrophysiological process

[0004] The present invention relates to a measuring device for detecting an electrophysiological process, as well as a method for detecting an electrophysiological process with the aid of the measuring device.

[0005] State of the art

[0006] Medical imaging of biomagnetic fields is currently in an early stage of development. To obtain spatial information from biomagnetic fields using established imaging techniques, two-dimensional magnetometer arrays are combined with a conventional X-ray system (Shirai, Y., Hirao, K., Shibuya, T., Okawa, S., Hasegawa, Y., Adachi, Y., ... & Kawabata, S. (2019). Magnetocardiography using a magnetoresistive sensor array. International heart journal, 60(1), 50-54). This allows, for example, the spatial assignment of an infarcted cardiac area to a portion of the left ventricle. In the field of magnetoencephalography (MEG), combinations with magnetic resonance imaging (MRI) are known. For example, Alem et al. (Alem, O., Hughes, KJ, Buard, I., Cheung, TP, Maydew, T., Griesshammer, A., ... & Knappe, S. (2023). An integrated full-head OPM-MEG system based on 128 zero-field sensors.Frontiers in Neuroscience, 17, 1190310) compared the source densities determined using the beamformer algorithm (see Hillebrand, A., & Barnes, GR (2005). Beamformer analysis of MEG data. International review of neurobiology, 68, 149-171) with the coronal reconstruction of a clinical MRI image.

[0007] Transthoracic echocardiography is an established, cost-effective, radiation- and contrast-free anatomical and functional imaging technique with wide, low-threshold availability (see Mitchell, C., Rahko, PS, Blauwet, LA, Canaday, B., Finstuen, JA, Foster, MC, ... & Velazquez, EJ (2019). Guidelines for performing a comprehensive transthoracic echocardiographic examination in adults: recommendations from the American Society of Echocardiography. Journal of the American Society of Echocardiography, 32(1), 1-64). It can be used, in particular, to assess the geometry and contraction of the myocardial tissue, as well as the blood flow in the atria and ventricles.

[0008] Currently, magnetocardiography is the only non-contact method for electrophysiological examination of the heart muscle. Other functional imaging techniques include local mechanical cardiac activity (ultrasound), blood supply to the heart muscle (gadolonium enhancement in MRI), and glucose uptake by the heart muscle (myocardial perfusion SPECT). While ultrasound is insufficiently sensitive for small infarct areas in the early stages, MRI and SPECT examinations provide contrast-enhanced images. The size of the devices precludes bedside imaging. Therefore, it is not possible to assess the consequences of an early-stage myocardial infarction in the emergency room.

[0009] Magnetic field sensors based on NV diamonds have been the subject of research for several years. These are based on diamond crystals whose crystal lattices contain 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 directly adjacent to 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 3 A2 into an excited state 3 E induced. From the excited state 3 E relaxes the NV center back to the ground state by emitting fluorescence radiation in a wavelength range between 650 nm and 750 nm 3 A2.

[0010] The ground state 3 A2 has three magnetic substates with ms =0, m s =±1 . The states with m s =0 and m s =±1 are distinguished 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 in the ground state 3 A2 exposed to microwave radiation with a frequency of 2.87 GHz, the NV center oscillates between the m s =0, 3 A2 - Ground 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 , 3E state. From there, it relaxes back to the ground state, predominantly without radiation. If the intensity of the fluorescence radiation is measured as a function of the frequency of the microwave radiation, a sudden drop in the intensity of the fluorescence radiation (a so-called peak) occurs at a frequency of 2.87 GHz. The drop in the intensity of the fluorescence radiation can be explained by the fact that - when microwave radiation with a frequency of 2.87 GHz is applied - fewer NV centers in the m s =0, 3 A2 ground state are available, which are optically excited and emit fluorescence radiation into the m s =±1 , 3 A2 ground state can relax.

[0011] In an external magnetic field, the m s =±1 , 3 A2 -ground state into two states with spin quantum number m s =1 and m s=-1 (Zeemann effect). If the intensity of the fluorescence radiation is now 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 on the magnetic flux density of the external magnetic field.

[0012] NV magnetic field sensors are vector-valued and have a compact design.

[0013] It is an object of the invention to provide a measuring device and a method with which biomagnetic fields, such as those arising as a result of an electrophysiological process, can be spatially detected and combined with imaging techniques that do not have the disadvantages of the prior art.

[0014] Disclosure of the invention

[0015] The present invention relates to a measuring device for detecting an electrophysiological process according to claim 1, as well as a method for detecting an electrophysiological process with the aid of the measuring device according to claim 9. Advantageous embodiments of the invention are the subject of the subclaims and the description.

[0016] The invention provides a measuring device for detecting an electrophysiological process, comprising an ultrasound device for transmitting and receiving ultrasound waves and a magnetic field detection device for detecting a magnetic field. The ultrasound device and the magnetic field detection device are arranged relative to one another such that a spatial region detectable using the ultrasound waves transmitted and received by the ultrasound device and a spatial region detectable by the magnetic field detection device at least partially overlap. An ultrasound image can be generated from the propagation times and intensities of the reflected ultrasound waves. The ultrasound device and the magnetic field detection device are arranged relative to one another such that a value characteristic of the detected magnetic field, e.g., a magnetic flux density, can be assigned to at least one image coordinate of the ultrasound image.In this way, a specific spatial area, e.g. a specific area of ​​an organ, can be assigned to the detected magnetic field.

[0017] With the help of the measuring device, a magnetic field can be detected, for example, generated by an electrophysiological process. The electrophysiological process can be, for example, the contraction or expansion of a muscle. Secondly, the ultrasound waves can be reflected, absorbed, or scattered by a carrier of the electrophysiological process that causes the detected magnetic field, e.g., a muscle. The ultrasound waves can also be reflected, absorbed, or scattered by the environment of the carrier of the electrophysiological process. The ultrasound image that can be constructed from the received ultrasound waves is then an image of the carrier and / or the environment of the carrier of the electrophysiological process.Since the arrangement of the magnetic field generating device and the ultrasound device relative to each other is known and the magnetic field generating device and the ultrasound device can detect the same spatial area, it is possible to spatially assign the magnetic field generated by the electrophysiological process to the carrier and / or the environment of the carrier of the electrophysiological process by which the detected magnetic field was caused.

[0018] The measuring device according to the invention thus makes it possible to combine an imaging method and a magnetic field measurement, thus assigning the detected magnetic fields to a specific spatial region, e.g., a specific area of ​​an organ, such as the heart. It is compact in design, allowing it to be easily transported and used, for example, at the patient's bedside.

[0019] In one embodiment of the invention, the ultrasound device comprises a plurality of piezo crystals for transmitting and receiving ultrasonic waves. The plurality of piezo crystals enables the generation of an ultrasound image with a particularly high resolution. In particular, the plurality of piezo crystals is arranged in a row. The piezo crystals can be arranged in a plane or along a convexly curved surface.

[0020] In one embodiment of the invention, the magnetic field detection device comprises at least two magnetic field sensors arranged around the plurality of piezoelectric crystals. The magnetic field sensors are arranged, in particular, at a row start and a row end of the row of piezoelectric crystals. At least one of the magnetic field sensors can be designed as an NV magnetic field sensor. NV magnetic field sensors have a compact design while being very sensitive. The use of NV magnetic field sensors in the measuring device makes it possible to design it as sensitive and compact.

[0021] In one embodiment of the invention, the magnetic field detection device is designed as a gradiometer arrangement with at least two magnetic field sensors, e.g., two NV magnetic field sensors. This takes advantage of the fact that—assuming the interference signal source is far enough away—the intensity of any interference signals detected by the respective magnetic field sensors hardly differs. The gradiometer arrangement makes it possible to identify and selectively filter out interference signals in a magnetic field signal detected by the magnetic field detection device. The provision of the gradiometer arrangement thus improves the signal-to-noise ratio of the magnetic field detection device. In one further development of the invention, the measuring device has an evaluation device configured to spatially assign the magnetic field signal detected by the magnetic field detection device to a region of the ultrasound image.The evaluation device is particularly configured to assign a value specific to the detected magnetic field, e.g., a value for the magnetic flux density, to at least one pixel of the ultrasound image. This makes it possible to assign the magnetic field generated by an electrophysiological process to a specific region of an organ, e.g., the heart, and thus to detect regions that are not visible in the ultrasound image.

[0022] In a further development of the invention, the evaluation device is configured to temporally evaluate the magnetic field signal detected by the magnetic field detection device. In this way, the contraction and expansion of a muscle, such as the heart, can be visualized.

[0023] With the help of NV magnetic field sensors, not only the magnitude but also the direction of the magnetic field to be detected can be determined. If the magnetic field detection device comprises at least one NV magnetic field sensor, then with the help of the above-mentioned evaluation device not only the magnitude but also the direction of the magnetic field to be detected can be detected. The above-mentioned gradiometer arrangement of at least two NV magnetic field sensors is particularly advantageous in this regard. The measuring device according to this embodiment of the invention is thus configured to determine the temporal progression of the magnitude and direction of the magnetic field to be detected. This can be useful, for example, when detecting the magnetic field generated by the heart muscle(s), since not only the magnitude but also the direction of this so-called cardiac magnetic field changes over time.The temporal analysis of the magnetic field signal thus acquired opens up new diagnostic possibilities, for example, in the diagnosis of a heart attack. Furthermore, NV magnetic field sensors are compact and small, so they can be easily mounted on the sensor head.

[0024] In a further development of the invention, the evaluation device is configured to reconstruct the source density of the detected magnetic field, in particular using a beamformer method. The beamformer method is a method for determining the position of sources in wave fields. Using the beamformer method, it is possible to identify different sources of the detected magnetic field. For example, muscles located close to one another can be individually identified based on the magnetic field they generate.

[0025] The invention also relates to a method for detecting an electrophysiological process using a measuring device having one or more of the aforementioned features, comprising the steps of: a. emitting ultrasonic waves, wherein the emitted ultrasonic waves are reflected by an object, b. receiving the reflected ultrasonic waves, c. generating an ultrasound image from properties of the reflected and received ultrasound waves, d. detecting a magnetic field, wherein the detected magnetic field is arranged in a spatial region that overlaps with a spatial region that can be detected by the emitted and received ultrasonic waves, e. spatially assigning the detected magnetic field to the ultrasound image.

[0026] The properties of the reflected and received ultrasound waves can include, in particular, propagation times and intensities. The method makes it possible to depict an electrophysiological process in a specific spatial region, in which, for example, a portion of an organ is located. In particular, the temporal progression of the magnetic field can also be recorded, allowing, for example, a muscle movement to be depicted.

[0027] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0028] The invention is illustrated schematically in the drawings using exemplary embodiments and is described below with reference to the drawings. Brief description of the drawings

[0029] Figure 1 shows an embodiment of a measuring device for detecting a physiological process according to an embodiment of the invention;

[0030] Figure 2 shows the measuring device in an application case;

[0031] Figure 3 shows a human heart that can be examined with the measuring device.

[0032] Embodiments of the invention

[0033] Figure 1 shows a measuring device 1 for recording an electrophysiological process, comprising a magnetic field detection device 2, a row of piezoelectric crystals 18 serving as an ultrasound device 3 and capable of transmitting and / or receiving ultrasonic waves, and a measuring head 5 on which the piezoelectric crystals 18 and the magnetic field detection device 2 are arranged. The magnetic field detection device 2 comprises two magnetic field sensors 4, in particular two NV magnetic field sensors, which are arranged such that they do not obscure a surface of the piezoelectric crystals 18 via which the piezoelectric crystals 18 transmit and receive ultrasonic waves. Likewise, the piezoelectric crystals 18 do not obscure a sensitive surface of the two magnetic field sensors 4 via which the magnetic field sensors 4 can detect a magnetic field. The two magnetic field sensors 4 can be arranged, for example, at the beginning and end of a row of the row of piezoelectric crystals 18.The arrangement of the magnetic field sensors 4 and the piezo crystals 18 is designed such that a reconstruction of a source density of the detected magnetic field at a predefined distance from the magnetic field sensors 4 is possible. This can be done, for example, by using a so-called beamformer algorithm. The source of the detected magnetic field can be moving electrical charges, for example in an electrophysiological process. Figure 2 shows an application of the measuring device 1 on an organ 6, e.g. a heart. Ultrasound waves 8 are emitted by the ultrasound device 3 and partially reflected, absorbed and / or scattered by the organ 6 and the surrounding tissue. Some of the ultrasound waves 8 are absorbed, while another part is reflected or scattered. The ultrasound waves 9 returning to the ultrasound device 3 can thus be attenuated compared to the emitted ultrasound waves 8.An ultrasound image can be generated from the attenuations and propagation times of the ultrasound waves 8, 9, which are reflected, absorbed, and / or scattered in the organ and / or the surrounding tissue. Within a predefined area 16, which at least partially covers, for example, a portion of the organ 6, a magnetic field with, in this case, concentrically extending magnetic field lines 17 can also be generated—for example, as a result of an electrophysiological process. This magnetic field can be detected by the magnetic field detection device 2. The generated ultrasound image can then be combined, in particular, with a temporal profile of the magnetic field detected by the magnetic field detection device 2 in the predefined area 16.

[0034] The advantage of the measuring device 1 will be explained below using the example of detecting an impending heart valve defect, which can occur as a complication of a myocardial infarction. As shown in Figure 3, certain connective tissue threads, the so-called chordae tendinae 14, are essential for the function of the heart valve of the left atrium 12 and left ventricle 10 (the so-called mitral valve 13). These are attached to the papillary muscles 11. If the papillary muscles 11 die due to a heart attack, the chordae tendinae 14 break from their anchorage, and the mitral valve 13 no longer closes completely. This severely limits cardiac performance and is life-threatening. The papillary muscles 11 can be clearly visualized using established ultrasound techniques. If the magnetic field in area 16 of the papillary muscles 11 can be reconstructed, an infarction in this area 16 can either be excluded or confirmed.If the infarct area extends to the papillary muscles 11, an artificial heart valve replacement can be inserted early, before failure of the mitral valve 13 occurs. This is not necessary if the infarct area is limited to a neighboring area, e.g., area 10. Alternatives include other applications in the field of medical ultrasound, e.g., transesophageal or intracardiac echocardiography, or the combination of magnetomyography and ultrasound. A combination with other ultrasound techniques, such as flow measurements based on the Doppler effect, is also possible.

Claims

Claims 1. A measuring device (1) for detecting an electrophysiological process, comprising an ultrasound device (3) for transmitting and receiving ultrasound waves (8, 9) and a magnetic field detecting device (2, 4) for detecting a magnetic field, wherein the ultrasound device (3) and the magnetic field detecting device (2, 4) are arranged relative to one another in such a way that the magnetic field detected by the magnetic field detecting device (2, 4) can be spatially assigned to an ultrasound image that can be constructed from the ultrasound waves transmitted and received by the ultrasound device (3).

2. Measuring device (1) according to claim 1, wherein the ultrasonic device (3) comprises a plurality of piezo crystals (3) for emitting and receiving ultrasonic waves (8, 9) 3. Measuring device (1) according to claim 2, wherein the plurality of piezo crystals (3) are arranged in a row.

4. Measuring device (1) according to claim 2 or 3, wherein the magnetic field detection device (2, 4) has at least two magnetic field sensors (4) which are arranged around the plurality of piezo crystals (3), in particular at a row start and a row end.

5. Measuring device (1) according to one of the preceding claims, wherein the magnetic field detection device (2) is designed as a gradiometer arrangement with at least two magnetic field sensors (4), in particular at least two NV magnetic field sensors.

6. Measuring device (1) according to one of the preceding claims, comprising an evaluation device (17) which is configured to spatially assign a magnetic field signal detected by the magnetic field detection device (2, 4) to a region in the ultrasound image detected by the ultrasound device (3).

7. Measuring device (1) according to claim 6, wherein the evaluation device (17) is configured to temporally evaluate the magnetic field signal detected by the magnetic field detection device (2, 4).

8. Measuring device (1) according to claim 6 or 7, wherein the evaluation device (17) is configured to determine a source density of the detected magnetic field, in particular with the aid of a beamformer algorithm.

9. A method for detecting an electrophysiological process using a measuring device (1) according to one of claims 1 to 8, comprising the steps of: a. emitting ultrasonic waves (8, 9), wherein the emitted ultrasonic waves (8) are reflected by an object, b. receiving the reflected ultrasonic waves (9), c. generating an ultrasound image from the reflected and received ultrasound waves (8, 9), d. detecting a magnetic field, e. spatially assigning the detected magnetic field to the ultrasound image.

10. The method according to claim 9, wherein a temporal progression of the magnetic field is detected.

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