Position-dependent cardiac stimulation monitoring

Abstract

The invention relates to a method for determining at least one monitoring parameter for monitoring cardiac stimulation during a magnetic resonance imaging (MRI) scan of a patient, a MRI scanner, and a computer program. According to the method, the patient is positioned in the MRI scanner. The patient's cardiac position relative to the MRI scanner is determined. The at least one monitoring parameter is determined based on a monitoring model as a function of the patient's cardiac position.

Description

[0001] The invention relates to a method for determining at least one monitoring parameter for monitoring cardiac stimulation during a magnetic resonance measurement of a patient, a magnetic resonance device and a computer program product.

[0002] In medical technology, magnetic resonance imaging (MRI), also known as magnetic resonance tomography (MRI), is characterized by high soft tissue contrast. A magnetic resonance measurement is performed using a magnetic resonance device, which contains a magnet unit. The magnet unit typically comprises a main magnet to generate a primary magnetic field and a gradient coil unit to generate a gradient magnetic field within the examination area of ​​the magnetic resonance device. The examination area is usually located in a magnetic bore of the magnet unit, in which a patient is positioned during the MRI measurement. To generate magnetic resonance signals during an MRI measurement, radio-frequency (RF) pulses are transmitted into the examination area according to a magnetic resonance sequence.

[0003] The gradient magnetic fields generated during magnetic resonance imaging (MRI) can cause nerve stimulation in the patient, particularly of the heart. To prevent harm to the patient due to excessive nerve stimulation, the generated gradient magnetic fields are typically monitored within a cylindrical monitoring volume, as specified in IEC 60601-2-33. This monitoring volume has a cylindrical axis aligned with the patient's axis, a radius of 0.20 m, and a length equal to the length of the gradient coil unit. The monitoring process, described, for example, in Hebrank FX, Gebhardt M. SAFE model - A new method for predicting peripheral nerve stimulation in MRI; Proceedings of the 8th Annual Meeting of ISMRM; Denver. 2000; p.The SAFE model, described in 2007, ensures that predetermined limits, such as a maximum time-dependent change in the magnetic field (dB / dt), are not exceeded throughout the entire monitoring volume. This can significantly limit the performance of the magnetic resonance measurement.

[0004] The object of the present invention can be considered to be to minimize the performance limitations of magnetic resonance measurements caused by monitoring cardiac stimulation, without thereby accepting an increased risk to the patient. This object is achieved by the features of the independent claims. Advantageous embodiments are described in the dependent claims.

[0005] A method, particularly computer-implemented, for determining at least one monitoring parameter for monitoring cardiac stimulation, especially cardiac nerve stimulation, during magnetic resonance imaging (MRI) of a patient is proposed. The patient is positioned in the MRI scanner. The patient's cardiac position relative to the MRI scanner is determined. The at least one monitoring parameter is then determined based on a monitoring model that considers the patient's cardiac position.

[0006] Determining the patient's heart position relative to the magnetic resonance imaging (MRI) device and / or determining at least one monitoring parameter based on a monitoring model as a function of the patient's heart position can be performed, in particular, by means of a determination unit. The determination unit can, for example, comprise one or more processors, particularly programmable ones, and / or one or more memory modules. The monitoring model can, in particular, be stored in memory and loaded from memory to execute the procedure.

[0007] The monitoring model can, for example, include the SAFE model described in Hebrank FX, Gebhardt M. SAFE model - A new method for predicting peripheral nerve stimulation in MRI; Proceedings of the 8th Annual Meeting of ISMRM; Denver. 2000; p. 2007. The at least one monitoring parameter is, in particular, a parameter of this SAFE model. Such a monitoring parameter could, for example, be a scaling factor that describes the maximum strength of a gradient magnetic field from a gradient coil in a given volume.

[0008] The patient positioning can be performed and / or assisted by an operator of the magnetic resonance imaging (MRI) device. Preferably, the patient is positioned in a magnetic port of the MRI device so that at least part of the patient, in particular the patient's heart, is located within the magnetic port. For example, the patient is placed on a patient table, which is then moved (together with the patient) into a magnetic port of the MRI device.

[0009] Preferably, the patient assumes an examination position by being positioned in the magnetic resonance imaging (MRI) device. Preferably, the patient also remains in this examination position during any subsequent MRI scan.

[0010] The heart position can be determined, in particular, relative to a reference position, especially a reference point, of the magnetic resonance device. The heart position can also be determined, in particular, relative to a gradient coil unit of the magnetic resonance device.

[0011] The at least one monitoring parameter can, for example, include a monitoring volume and / or a derived and / or dependent monitoring value. A possible derived and / or dependent monitoring value could be, for example, a scaling factor that describes the maximum strength of a gradient magnetic field of the gradient coil unit within the monitoring volume. Advantageously, smaller scaling factors are determined for smaller monitoring volumes that are closer to the isocenter. These smaller scaling factors are then advantageously used as monitoring parameters for adapted parameterization of the cardiac stimulation monitoring, which can be implemented, in particular, using the SAFE model as the monitoring model.

[0012] Advantageously, by considering the heart's position when determining at least one monitoring parameter, unnecessary safety margins that limit the performance of magnetic resonance measurements can be avoided. Advantageously, the monitoring volume can be reduced compared to the state of the art by adapting it to the actual position of the patient's heart. Advantageously, a general, position-independent determination of the monitoring volume can be avoided.

[0013] Preferably, a magnetic resonance measurement is performed, wherein the magnetic resonance measurement is monitored using at least one monitoring parameter. The monitoring can be performed, for example, with a cardiac stimulation monitor that is parameterized according to the at least one monitoring parameter.

[0014] Advantageously, monitoring cardiac stimulation during magnetic resonance imaging (MRI) using at least one monitoring parameter is suitable for limiting stimulation of the patient's heart. Advantageously, monitoring cardiac stimulation during MRI can increase patient safety.

[0015] Advantageously, the performance of a monitored magnetic resonance measurement can be increased. Advantageously, the magnetic resonance measurement can be performed faster and / or safety-related measurement interruptions can be avoided. Advantageously, magnetic resonance sequences with higher gradient activity can be used, e.g., resulting in a greater strength of a gradient magnetic field generated according to the magnetic resonance sequence, and / or allowing higher slew rates of the gradient magnetic field, which can lead to shorter rise times, especially when a constant gradient strength is required.

[0016] One possible embodiment of the method provides that, during the magnetic resonance measurement, the patient's heart position relative to the magnetic resonance device is repeatedly determined, and at least one monitoring parameter is determined, in particular adjusted, based on the monitoring model as a function of the repeatedly determined heart position of the patient.

[0017] Preferably, the (re-)determination of the heart position and, if necessary, a change in at least one monitoring parameter are performed continuously and / or continuously during the magnetic resonance imaging (MRI) scan. Advantageously, this allows the monitoring of cardiac stimulation to be adapted to any changes in heart position. A change in heart position can be caused, for example, by movement of the patient and / or a patient table supporting the patient.

[0018] Another possible embodiment of the method provides that the magnetic resonance device includes a gradient coil unit, wherein the monitoring model comprises a location-dependent strength of a gradient magnetic field (gradient strength) that can be generated by the gradient coil unit. For example, the location-dependent strength of a gradient magnetic field that can be generated by the gradient coil unit is the location-dependent strength of the gradient magnetic field that is generated when a certain current flows through at least one gradient coil of the gradient coil unit.

[0019] The gradient strength can be, in particular, the amplitude of the gradient magnetic field. The gradient strength can be specified, for example, in the unit mT / m.

[0020] The gradient coil unit can, for example, comprise three gradient coils that can generate gradient magnetic fields in different directions, particularly directions perpendicular to each other. A first of the three gradient coils (e.g., the x-gradient coil) can, for example, generate a gradient magnetic field along a first direction (e.g., an x-direction). A second of the three gradient coils (e.g., the y-gradient coil) can, for example, generate a gradient magnetic field along a second direction (e.g., a y-direction). A third of the three gradient coils (e.g., the z-gradient coil) can, for example, generate a gradient magnetic field along a third direction (e.g., a z-direction). For example, the position-dependent strength of the gradient magnetic field that can be generated by the z-gradient coil is the achievable strength of the gradient magnetic field as a function of a position in the z-direction. (This also applies analogously to the x- and y-directions.)

[0021] A gradient coil can, in particular, comprise two partial gradient coils operated in pairs with the same current but opposite polarity. Preferably, one partial gradient coil increases the magnetic field by a certain amount, while the opposing partial gradient coil decreases it by the same amount. The overall magnetic field can thus be changed.

[0022] Preferably, the heart, particularly in cardiac magnetic resonance imaging, is positioned at or near the isocenter of the magnetic resonance imaging (MRI) system. The main magnetic field of the MRI system typically exhibits particularly high homogeneity at the isocenter.

[0023] Preferably, the center point of the gradient coil unit is located at the isocenter. Preferably, the gradient coils of the gradient coil unit are arranged symmetrically with respect to the isocenter. Preferably, the centers of the gradient coils of the gradient coil unit are each located at the isocenter. However, a magnetic resonance device with an asymmetrical arrangement of the gradient coils is also conceivable.

[0024] Typically, the strength of the gradient magnetic field (especially the gradient magnetic field generated by the z-gradient coil) exhibits a zero crossing at the isocenter, and the technically achievable field strength is lower than in the outer region of the gradient coil. Therefore, the spatially dependent strength of the gradient magnetic field that can be generated by the gradient coil unit is typically relatively low at the isocenter.

[0025] This allows the requirements for monitoring cardiac stimulation to be reduced particularly effectively if the determination of the heart position reveals that the patient's heart is located at or near the isocenter.

[0026] Another possible embodiment of the method provides that, in order to determine at least one monitoring parameter, a spatial area (monitoring area) is determined based on the heart position, in which a predetermined stimulation should not be exceeded, wherein the at least one monitoring parameter is determined depending on the determined spatial area.

[0027] The spatial area can be, in particular, a volume, especially a room volume. The specified stimulation can be, in particular, nerve stimulation. The specified stimulation can be, in particular, stimulation of the patient's heart. The specified stimulation can, for example, be defined by a standard.

[0028] Advantageously, the monitoring area encompasses the patient's heart position. Advantageously, the monitoring area is smaller than the monitoring volume to be monitored according to standard IEC 60601-2-33, which was described previously. Advantageously, even a less precise determination of the heart position is sufficient to significantly reduce the monitoring volume compared to the specification of standard IEC 60601-2-33. Advantageously, the performance limitations are only applied to the reduced monitoring volume. Advantageously, the requirements for monitoring, or at least for one monitoring parameter, can thus be selected in such a way that the monitoring is less restrictive.

[0029] Preferably, at least one control value is determined for controlling the magnetic resonance device, wherein the monitoring of the cardiac stimulation includes monitoring of the at least one control value. For example, the at least one control value can relate to a current flow through the gradient coil unit, in particular through the gradient coil unit.

[0030] Advantageously, monitoring at least one control value can ensure that a predetermined stimulation level, especially in the monitoring range, is not exceeded.

[0031] One possible embodiment of the method involves determining the heart's position using a magnetic resonance imaging (MRI) scan of the patient. Advantageously, MRI scans are particularly well-suited for imaging the patient's internal organs, including the heart. Furthermore, MRI scans are especially well-suited for imaging soft tissues, including the heart. Therefore, the heart's position can be reliably determined using an MRI scan.

[0032] The magnetic resonance signals required for the reconstruction of the magnetic resonance image can be acquired using the magnetic resonance device after the patient has been positioned in the magnetic resonance device.

[0033] Preferably, the magnetic resonance image is acquired before the main magnetic resonance measurement, and at least one measurement parameter of the main measurement is adjusted based on the magnetic resonance image. The adjustment of the at least one measurement parameter can be carried out, in particular, by an operator of the magnetic resonance device. For example, the operator is shown the magnetic resonance image, whereupon they adjust the at least one measurement parameter of the main measurement based on the magnetic resonance image.

[0034] A magnetic resonance imaging (MRI) scan can involve performing several MRI scans, in particular a pre-scan and a subsequent main scan. The MRI signals necessary for the MRI image, which is used to determine the heart's position, can be acquired in such a pre-scan using the MRI scanner. This pre-scan might, for example, be a localizer scan, which is used to select a slice to be scanned in the main scan as a measurement parameter for the main scan. For instance, the slice orientation for the main scan is planned based on the localizer scan data. This planning can be done manually or automatically.

[0035] Advantageously, the preliminary measurement is carried out as part of the magnetic resonance examination anyway, so that the acquisition of the magnetic resonance image, which is used to determine the heart position, can be carried out in a time-efficient manner.

[0036] Another possible embodiment of the method involves determining the heart position using a camera image of the patient. The camera image can be captured with a camera. In particular, the camera can be a 3D camera designed to capture, and especially to generate, three-dimensional images. Preferably, the camera is an optical camera. Preferably, the camera is designed to detect visible light and / or UV radiation and / or infrared radiation. Preferably, the camera is designed to detect electromagnetic wavelengths in a wavelength range between 400 and 780 nm.

[0037] The camera can be positioned inside or outside the magnetic opening. In particular, the camera is positioned on an inner wall of the magnetic opening. Advantageously, the camera has a field of view that includes the isocenter of the magnetic resonance device.

[0038] Advantageously, the patient's external shape can be captured using a camera image. Based on this external shape, the heart's position can then be determined with sufficient accuracy. Advantageously, a body model describing the heart's position within the body is used to determine the heart's position from a camera image. A general, non-patient-specific body model can be used that still allows for a sufficiently accurate determination of the heart's position.

[0039] Another possible embodiment of the method involves determining the heart position using a pilot tone signal. The pilot tone signal can be received, for example, by a high-frequency antenna unit. The high-frequency antenna unit can, in particular, comprise one or more local coils. The high-frequency antenna unit can also be configured to receive magnetic resonance signals. For example, a pilot tone transmitter generates a transmit signal, which interacts with the patient, and the resulting pilot tone signal is then received. Preferably, the transmit signal has a frequency other than the Larmor frequency of the magnetic resonance device. Advantageously, the high-frequency antenna unit has multiple receiving antennas for receiving the pilot tone signal.

[0040] The patient's beating heart can cause location-dependent magnetic field variations on the order of nanotesla. This effect can be used, in particular, to trigger cardiac measurements by modulating the pilot tone signal with these effects. Especially when the pilot tone signal is acquired with multiple receiving antennas (which, for example, are part of a local coil positioned directly next to the patient), the heart position can advantageously be determined from the pilot tone signal. Advantageously, the position of the local coil relative to the magnetic resonance device is known, for example, by means of a Hall sensor arranged on or within the local coil.

[0041] Furthermore, a magnetic resonance device is proposed which is designed to perform a previously described method for determining at least one monitoring parameter for monitoring cardiac stimulation during a magnetic resonance measurement of a patient.

[0042] The advantages of the proposed magnetic resonance device essentially correspond to the advantages of the method for determining at least one monitoring parameter for monitoring cardiac stimulation during a magnetic resonance measurement of a patient, which have been described in detail above. Features, advantages, or alternative embodiments mentioned herein can also be transferred to the other claimed items and vice versa.

[0043] In addition to the components that a magnetic resonance device typically includes, the magnetic resonance device may in particular include a camera, for example a 3D camera.

[0044] The magnetic resonance device can, in particular, comprise a system control unit configured to determine the patient's heart position relative to the magnetic resonance device and at least one monitoring parameter based on a monitoring model that depends on the patient's heart position. In particular, the system control unit can include a determination unit as described above.

[0045] Furthermore, a computer program product is proposed that comprises a program and can be directly loaded into the memory of a programmable system control unit of a magnetic resonance device. The product includes program resources, such as libraries and auxiliary functions, for executing a previously proposed method for determining at least one monitoring parameter for monitoring cardiac stimulation during a magnetic resonance imaging (MRI) scan of a patient when the computer program product is executed in the system control unit of the MRI device. The computer program product may comprise software with source code that still needs to be compiled and bound or that only needs to be interpreted, or executable software code that only needs to be loaded into the system control unit for execution.

[0046] The proposed method can advantageously be executed quickly, identically, and robustly by the computer program product. The computer program product is preferably configured to execute the proposed method steps via the system control unit. The system control unit possesses the necessary prerequisites, such as sufficient main memory, a suitable graphics card, or a suitable logic unit, so that the respective method steps can be executed efficiently.

[0047] The computer program product is stored, for example, on a computer-readable medium or on a network or server, from where it can be loaded into the processor of a local system control unit, which may be directly connected to the magnetic resonance device or be formed as part of the magnetic resonance device. Furthermore, control information of the computer program product may be stored on an electronically readable data carrier. The control information of the electronically readable data carrier may be designed such that, when the data carrier is used in a system control unit of a magnetic resonance device, it executes a proposed procedure.

[0048] Examples of electronically readable data carriers include a DVD, a magnetic tape, or a USB flash drive, on which electronically readable control information, in particular software, is stored. If this control information is read from the data carrier and stored in a system control unit of the magnetic resonance device, all proposed embodiments of the previously described methods can be carried out.

[0049] Further advantages, features, and details of the invention will become apparent from the exemplary embodiments described below and from the drawings. Corresponding parts are designated with the same reference numerals in all figures.

[0050] They show: Fig. 1. A magnetic resonance device in a schematic representation, Fig. 2 a diagram of a procedure for determining at least one monitoring parameter for monitoring cardiac stimulation during a magnetic resonance imaging (MRI) scan of a patient, Fig. 3 a diagram of an extended procedure for determining at least one monitoring parameter for monitoring cardiac stimulation during magnetic resonance imaging of a patient, Fig. 4 a representation of a location-dependent strength of a gradient magnetic field that can be generated using the gradient coil unit.

[0051] In Fig. Figure 1 schematically depicts a magnetic resonance device 10. The magnetic resonance device 10 comprises a magnetic unit 11, which includes a main magnet 12 for generating a strong and, in particular, time-constant main magnetic field 13. The magnetic resonance device 10 also includes a magnetic opening 14 for receiving a patient 15. In this example, the magnetic opening 14 is cylindrical and is cylindrically surrounded by the magnetic unit 11 in one circumferential direction. However, other magnet shapes, e.g., an open magnet, are also conceivable. The patient 15 can be inserted into the magnetic opening 14 of the magnetic resonance device 10 by means of a patient positioning device 16 and thus positioned within the magnetic resonance device 10. For this purpose, the patient positioning device 16 has a patient table 17 that is movably designed within the magnetic opening 14.

[0052] The magnet unit 11 further comprises a gradient coil unit 18 for generating magnetic field gradients, which are used for spatial encoding during imaging. The gradient coil unit 18 can include multiple gradient coils, which are not shown individually here. In particular, each of the multiple gradient coils can generate a gradient magnetic field in a spatial direction, e.g., a z-gradient coil in the z-direction and a y-gradient coil in the y-direction. The gradient coil unit 18 is controlled by a gradient control unit 19 of the magnetic resonance device 10.

[0053] The magnet unit 11 further comprises a high-frequency antenna unit 20, which in the present embodiment is designed as a body coil permanently integrated into the magnetic resonance device 10. The high-frequency antenna unit 20 is controlled by a high-frequency antenna control unit 21 of the magnetic resonance device 10 and transmits high-frequency magnetic resonance sequences into an examination space that is essentially formed by the area of ​​the magnet opening 14 of the magnetic resonance device 10. This excites atomic nuclei in the main magnetic field 13 generated by the main magnet 12. Magnetic resonance signals are generated by the relaxation of the excited atomic nuclei. The high-frequency antenna unit 20 is designed to receive the magnetic resonance signals.

[0054] The magnetic resonance imaging (MRI) device 10 includes a system control unit 22 for controlling the main magnet 12, the gradient control unit 19, and the high-frequency antenna control unit 21. The system control unit 22 centrally controls the MRI device 10, for example, by performing a predetermined imaging magnetic resonance sequence. The system control unit 22 also includes an evaluation unit (not shown) for evaluating the magnetic resonance signals acquired during the MRI scan. Furthermore, the MRI device 10 includes a user interface 23 connected to the system control unit 22. Control information, such as imaging parameters, and reconstructed MRI images can be displayed on a display unit 24, for example, on at least one monitor, via the user interface 23 for medical personnel.Furthermore, the user interface 23 has an input unit 25 by means of which information and / or parameters can be entered by the medical operating personnel during a measurement process.

[0055] Furthermore, the magnetic resonance device 10 includes a camera 26, which is arranged here on an inner wall of the magnet opening 14. However, the camera could also be arranged at another location, in particular outside the magnet opening 14. The camera 26 is designed to capture camera images, including images of the patient 15 when the patient is located in the magnet opening 14.

[0056] The camera images can be provided to an investigation unit 27, which is part of the system control unit 22. With the help of the investigation unit, the following can be done: Fig. 2. The procedures shown are for determining at least one monitoring parameter for monitoring cardiac stimulation during a magnetic resonance measurement of a patient 15, in particular S20 and / or S30.

[0057] In S10, the patient 15 is positioned in the magnetic resonance device 10, specifically within the magnet opening 14. In S20, the heart position of the patient 15, positioned in the magnetic resonance device 10, is determined relative to the magnetic resonance device 10. In S30, at least one monitoring parameter is determined based on a monitoring model as a function of the heart position of the patient 15. Preferably, any inaccuracies, particularly measurement inaccuracies, in determining the heart position in S20 are taken into account.

[0058] Preferably, monitoring of cardiac stimulation is carried out even before the determination of at least one monitoring parameter depending on the heart position in S30, in which conventional monitoring parameters are applied, e.g. according to the standard IEC 60601-2-33.

[0059] In Fig. 3 is an extended procedure shown, whereby the following is based on the opposite Fig. Two additional aspects are addressed. In this process, an image of patient 15 is acquired in S15 after the patient has been positioned in the magnetic resonance device 10. The determination of the heart position in S20 can be performed using the image acquired in S15. This image could, for example, be a camera image acquired with camera 26.

[0060] Furthermore, it is conceivable that a magnetic resonance image is acquired in S15 prior to the main magnetic resonance measurement. The determination of the heart position can then be performed using the magnetic resonance image of patient 15 acquired in S15.

[0061] In S35, the main measurement of the magnetic resonance measurement is performed, with the main measurement being monitored using at least one monitoring parameter. Advantageously, at least one measurement parameter of the main measurement can also be adjusted based on the image acquired in S15, in particular a magnetic resonance image acquired in S15.

[0062] It is conceivable that a current image (S15), a determination of the current heart position (S20), and an update of at least one monitoring parameter (S30) during the magnetic resonance measurement (S35) could be repeatedly performed in order to adapt the monitoring to possible changes in the heart position of the patient (15). For example, it is conceivable that the heart position relative to the magnetic resonance device could change due to movement of the patient (15) and / or movement of the patient table (17).

[0063] Further aspects will be discussed using… Fig. 4 explained. During a magnetic resonance examination of the heart, the patient's heart 28 is usually positioned at the isocenter of the magnet unit 11. The position of the isocenter along the z-direction is defined here by axis B. Gz marked. B GzThe strength of a gradient magnetic field in the z-direction that can be generated by means of the gradient coil unit 18, in particular a z-gradient coil of the gradient coil unit 18. At different z-positions, the strength of the gradient magnetic field B Gz Different values ​​are observed, meaning the strength is location-dependent. Preferably, this information is part of the monitoring model used to determine at least one monitoring parameter in S30.

[0064] The in Fig. The fourth example shown refers to the z-direction or the z-gradient coil. However, a corresponding generalization to the x-direction or the x-gradient coil and the y-direction or the y-gradient coil is also possible.

[0065] Conventionally, especially according to standard ICE 60601-2-33, a monitoring volume V is used. normspecified, which does not take into account the actual position of the heart 28. In this comparatively large monitoring volume V norm can the strength of the gradient magnetic field B Gz They exhibit comparatively high values. Consequently, the monitoring parameters for monitoring cardiac stimulation must also be chosen accordingly restrictively.

[0066] The gradient magnetic field B Gz exhibits a zero crossing at the isocenter and rises again towards the outside until it reaches its maximum value B. Gz,max , before it falls again. If the heart 28 of patient 15 is located close to the isocenter, the heart is also exposed to a comparatively small gradient magnetic field B. GzThe risk of excessive cardiac stimulation by the gradient magnetic field is therefore low. Consequently, at least one monitoring parameter in S30 can be adjusted so that the corresponding monitoring of cardiac stimulation is less restrictive. Advantageously, this avoids unnecessary, excessive restriction of gradient activity during a magnetic resonance imaging (MRI) scan, particularly the main scan in S35.

[0067] In particular, a spatial area V can be determined based on the heart position identified in S20. relevant The target stimulation level is determined, ensuring that a predetermined level is not exceeded. Advantageously, in S30, at least one monitoring parameter is determined as a function of the identified spatial range V. relevant determined.

[0068] For example, the strength of the gradient magnetic field B is determined. Gz in spatial area V relevantmaximum exhibits which in Fig. 4 as B Gz,relevant is specified. Advantageously, at least one monitoring parameter is determined under the boundary condition that the gradient magnetic field B Gz the value B Gz,relevant does not exceed this value. This allows for less restrictive monitoring, especially since, in the worst-case scenario, a larger value for the maximum strength of the gradient magnetic field would have to be assumed without considering the actual heart position. In particular, B Gz,relevant an input value for the monitoring model applied in S30.

[0069] Finally, it should be noted once again that the methods described in detail above, as well as the illustrated magnetic resonance device, are merely exemplary embodiments which can be modified in various ways by those skilled in the art without departing from the scope of the invention. Furthermore, the use of the indefinite articles "a" or "an" does not preclude the possibility that the features in question may be present multiple times. Likewise, the term "unit" does not preclude the possibility that the components in question consist of several interacting sub-components, which may also be spatially distributed. Regardless of the grammatical gender of a particular term, persons of male, female, or other gender identities are included. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited non-patent literature

[0000] Hebrank FX, Gebhardt M. SAFE model - A new method for predicting peripheral nerve stimulation in MRI; Proceedings of the 8th Annual Meeting of ISMRM; Denver. 2000; p. 2007 [0003, 0007] Standard IEC 60601-2-33

[0058] Standard ICE 60601-2-33

[0065]

Claims

[1] Method for determining at least one monitoring parameter for monitoring cardiac stimulation during a magnetic resonance imaging (MRI) scan of a patient, the method comprising: - Positioning the patient in a magnetic resonance imaging (MRI) device, - Determining the patient's heart position relative to the magnetic resonance device, - Determination of at least one monitoring parameter using a monitoring model depending on the patient's heart position. [2] The method of claim 1, wherein the method further comprises: Performing the magnetic resonance measurement, whereby the magnetic resonance measurement is monitored using at least one monitoring parameter. [3] Method according to claim 2, wherein during the magnetic resonance measurement the heart position of the patient relative to the magnetic resonance device is repeatedly determined and at least one monitoring parameter is determined, in particular adapted, based on the monitoring model as a function of the repeatedly determined heart position of the patient. [4] Method according to one of the preceding claims, wherein the magnetic resonance device comprises a gradient coil unit, wherein the monitoring model comprises a location-dependent strength of a gradient magnetic field that can be generated by means of the gradient coil unit. [5] Method according to any of the preceding claims, wherein the determination of the at least one monitoring parameter comprises a monitoring model depending on the heart position of the patient: Determining a spatial area within which a predetermined stimulation level should not be exceeded, based on the heart's position, where at least one monitoring parameter is determined depending on the determined spatial area. [6] Method according to any of the preceding claims, wherein the heart position is determined using a magnetic resonance image of the patient. [7] Method according to claim 6, where the magnetic resonance image is acquired before a main measurement of the magnetic resonance measurement, where at least one measurement parameter of the main measurement is set based on the magnetic resonance image. [8] Method according to any of the preceding claims, wherein the determination of the heart position is carried out using a camera image of the patient. [9] Method according to any of the preceding claims, wherein the determination of the heart position is carried out using a pilot tone signal. [10] Magnetic resonance device, wherein the magnetic resonance device is configured to carry out a method according to any of the preceding claims. [11] Computer program product comprising a program that can be directly loaded into a memory of a programmable system control unit of a magnetic resonance device, comprising program means for executing a method according to any one of claims 1 to 9 when the program is executed in the system control unit of the magnetic resonance device.

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