Method for monitoring an absorption, magnetic resonance device and computer program product

Abstract

Method for monitoring the absorption of transmission power emitted into a patient by a transmitter unit of a magnetic resonance device, wherein the method comprises - Providing absorption data that describe a patient-nonspecific, location-dependent absorption sensitivity of the transmitted power, - Positioning the patient in an irradiation area of ​​the magnetic resonance device, in which the transmission power is to be irradiated into the patient, - Capturing the patient's anatomy within the radiation field, - Mapping the absorption data to the patient's anatomy, - Performing a magnetic resonance measurement of the patient, whereby the transmitted power absorbed by the patient is monitored during the magnetic resonance measurement based on the associated absorption data, - Recording position data, where the position data describe a position of the patient in the radiation area relative to the transmitting unit of the magnetic resonance device during the performance of the magnetic resonance measurement, wherein the transmitting unit is part of a local coil, whereby in the event of excessive patient movement and / or coil displacement the magnetic resonance measurement is aborted.

Description

[0001] The invention relates to a method for monitoring absorption, a magnetic resonance device and a computer program product.

[0002] In medical technology, magnetic resonance imaging (MRI), also known as magnetic resonance tomography, is characterized by high soft tissue contrast. Typically, a human or animal patient is positioned on a table within the imaging area of ​​a magnetic resonance scanner. During an MRI scan, a transmitter unit delivers radio frequency (RF) pulses into the patient. These pulses excite nuclear spins within the patient, generating magnetic resonance signals. The MRI scanner receives these signals and uses them to reconstruct magnetic resonance images.

[0003] For signal excitation in magnetic resonance devices with ultra-high magnetic fields, especially 7 Tesla or higher, local coils in the form of transmit-receive coils are typically used. This means that such a transmit-receive coil is designed to both send and receive RF signals. Generally, these local coils are fixed in position relative to the patient table. They are typically rigid and / or designed for a specific body region (e.g., head and joints such as knee, shoulder, hand and foot, or torso / abdomen) to provide optimal transmission efficiency and field homogeneity.

[0004] The transmitter unit of the local coil often comprises several transmitting antennas. To homogenize the transmission field, these multiple antennas can be driven in parallel with adjustable phase and amplitude (parallel transmit, pTx). The appropriate transmit pulse shapes generate a complex sequence of heat inputs into the patient's tissue. Accurate knowledge of the local field properties is required to predict the resulting specific absorption rate (SAR).

[0005] Conventionally, a worst-case approach is used for SAR calculations of these coils. Typically, SAR simulations are performed with different body models and variations (e.g., using morphing and position variation) and a sufficient number of RF excitation profiles. In particular, resulting SAR hotspots can be calculated and compressed into matrices containing so-called virtual observation points (VOPs) for real-time monitoring during magnetic resonance imaging. Such an approach is disclosed, for example, in US20120256626A1.

[0006] This generally optimizes and ensures the safety of SAR monitoring for the patient population under consideration, but unnecessarily limits the measurement of an individual patient. The time required for the measurement can therefore be significantly increased.

[0007] In research settings, individual anatomical measurements of subjects can be performed, followed by segmentation of the resulting data. This data can then be used for SAR simulation and the calculation of an individual matrix. However, due to the high time and labor costs involved, this approach is not feasible in clinical practice.

[0008] The publication US 2016 / 0091583A1 discloses a patient-specific estimation of a specific absorption rate (SAR). The publication US 2011 / 0043205A1 discloses a real-time estimation of local and global SAR. The publication MELIADO, EF [et al.]: A deep learning method for image-based subject-specific local SAR assessment. In: Magnetic Resonance in Medicine, 2020, Vol. 83: 695-711 discloses a deep learning method for image-based subject-specific SAR estimation.

[0009] The object of the present invention can be considered to be, in particular, to enable safe monitoring of the SAR during a magnetic resonance measurement while maintaining a short measurement time.

[0010] The problem is solved by the features of the independent claims. Advantageous embodiments are described in the dependent claims.

[0011] Accordingly, a method for monitoring the absorption of (high-frequency) transmission power radiated into a patient by a transmitter unit of a magnetic resonance device is proposed. Absorption data are provided, in particular to a system control unit of the magnetic resonance device, which describe a patient-independent, location-dependent absorption sensitivity of the transmitted transmission power. Preferably, the absorption data take into account a spatial profile of the transmission power. The absorption data can, for example, be stored in a memory, particularly a non-volatile one, and transmitted to the system control unit. The patient is positioned within an irradiation area of ​​the magnetic resonance device where the transmission power is to be irradiated into the patient.For example, the patient is positioned on a patient positioning device and moved to the isocenter of the magnetic resonance imaging (MRI) scanner. Furthermore, the patient's anatomy within the radiation field is recorded, particularly using a data acquisition unit. The absorption data are then correlated with the patient's anatomy, specifically by the system control unit. A magnetic resonance imaging (MRI) scan of the patient is then performed, during which the transmitted power absorbed by the patient is monitored based on the absorption data correlated with the patient's anatomy, again specifically by the system control unit. During the MRI scan, magnetic resonance signals are typically acquired, from which one or more magnetic resonance images can be reconstructed.

[0012] Preferably, the transmission power radiated into the patient during the magnetic resonance measurement is monitored based on the absorption data assigned to the patient's anatomy.

[0013] The absorption of the transmission power radiated into the patient by the transmitter unit of the magnetic resonance device corresponds in particular to the specific absorption rate (SAR), i.e., the monitoring is SAR monitoring. Preferably, the monitoring of the transmission power absorbed by the patient during the magnetic resonance measurement, based on the associated absorption data, thus includes SAR monitoring. Advantageously, by assigning the (patient-nonspecific) absorption data to the patient's (patient-specific) anatomy, the monitoring can be more individually tailored to the patient without having to completely recalculate absorption data. Instead, general absorption data can be used, which are then individually adjusted. This advantageously reduces unnecessary safety margins and shortens the time required to perform the magnetic resonance measurement.

[0014] Monitoring the patient's absorbed transmit power can include, in particular, monitoring the shape, amplitude, and / or rate of RF transmit pulses emitted by the transmitting unit. The transmitting unit can include at least one transmitting antenna. Specifically, an RF transmit pulse can be generated by applying an electrical voltage to the at least one transmitting antenna. Monitoring can be performed in real time during the magnetic resonance imaging (MRI) scan; that is, the evaluation of the data required for monitoring is quasi-instant or requires only a short time. If necessary, the MRI scan can be terminated if the patient's absorbed transmit power exceeds a predefined limit.

[0015] Preferably, the absorption data takes into account a free variation of the transmitting unit's transmission profile in amplitude and / or phase. Preferably, the transmitting unit comprises multiple transmitting antennas. For example, the transmitting unit is configured as an N-channel array transmitting coil. Preferably, each transmitting antenna is configured to transmit a pulse independently of the other transmitting antennas. Advantageously, the multiple transmitting antennas allow the transmitting profile to be freely determined in amplitude and / or phase. In particular, the transmitting unit is configured to transmit a pTx pulse.

[0016] The SAR typically depends on the patient's anatomy, particularly the patient's load. In the case of a single-channel transmitting coil, the SAR can preferably be described by a scalar. In the case of an N-channel array transmitting coil, the SAR can preferably be described by a vector.

[0017] When transmitting power into the patient using a transmitter unit with multiple antennas, it is particularly advantageous to create at least one SAR matrix based on the associated absorption data. This SAR matrix can, in particular, include virtual observation points. Advantageously, previously calculated SAR hotspots are compressed within these virtual observation points.

[0018] The absorption data are not specific to the patient undergoing the magnetic resonance imaging (MRI) scan. Specifically, the absorption data may represent a wide range of patient types, a group of patient types, or a patient population. Furthermore, the absorption data may reflect a worst-case scenario; for example, the data may be generated based on an unfavorable condition. Advantageously, the absorption data can ensure that, regardless of the individual patient's characteristics, the absorption of the transmitted power does not pose a risk to the patient.

[0019] Preferably, the absorption data are generated in advance, particularly before positioning the patient, for example by simulation and / or based on pre-generated measurement data. To generate this measurement data, magnetic resonance measurements can be performed on a large number of patients, for example.

[0020] Absorption sensitivity can, in particular, be the assumed sensitivity of the absorption of the transmitted power within the patient's body. Specifically, there may be points within the radiation field where the transmitted power is absorbed more strongly and other points where it is absorbed less strongly.

[0021] The transmitting unit can, in particular, be part of a local coil. The coverage area can, in particular, be determined by the local coil. For example, the coverage area is located in a space that is at least partially surrounded by the local coil. For example, the local coil is a head coil with an upper and a lower section, and the coverage area is located between the upper and lower sections when the local coil is operational. The local coil can also, for example, be a knee coil and / or a foot coil that at least partially surround the coverage area. However, the local coil can also be, for example, a spinal coil and / or a coil ceiling that does not surround the coverage area. Positioning the patient within the coverage area of ​​the magnetic resonance device can, for example, involve positioning the patient's head in a head coil.

[0022] The recorded anatomy of the patient may, for example, include a spatial contour and / or shape and / or extent and / or extension of at least a part of the patient's body.

[0023] Assigning absorption data to the patient's anatomy can, in particular, involve assigning a value for the absorption sensitivity of the transmitted power to a point and / or area within the irradiation area. Specifically, at least one SAR matrix can be created taking the assigned absorption data into account. The SAR matrix can, in particular, contain a SAR for each voxel related to a specific mass of a local volume (e.g., a 10g local SAR), which can be generated for all relevant linear combinations of a transmit vector (e.g., NxN linear combinations for an N-channel transmitting system).

[0024] Performing magnetic resonance imaging of the patient may include, in particular, the application of an imaging magnetic resonance sequence and / or the reception of imaging magnetic resonance signals.

[0025] Monitoring the transmitted power can include, in particular, comparing the power absorbed by the patient with a predetermined reference value, especially a limit value. If this limit is exceeded, the magnetic resonance imaging (MRI) scan can be aborted and / or a warning can be issued, particularly to an operator of the MRI scanner.

[0026] Another embodiment of the method provides that during the magnetic resonance measurement, the transmission power is radiated by means of several transmitting antennas of the transmitting unit, wherein the absorption data take into account a transmission profile in amplitude and / or phase generated by the several transmitting antennas. In particular, the transmission profile can be generated by a linear combination of the respective amplitudes and / or phases of the several transmitting antennas, for example N amplitudes and N phases of N transmitting antennas.

[0027] Another embodiment of the method provides that the absorption data includes virtual observation points (VOPs) for monitoring the transmit power absorbed by the patient, with each observation point representing at least one voxel, in particular a voxel cluster.

[0028] Preferably, at least one voxel is assigned a peak sensitivity for a local specific absorption rate. Preferably, each voxel cluster defines a virtual observation point with a peak sensitivity to a local specific absorption rate for the voxel cluster. Preferably, generating virtual observation points involves compressing a patient model into a plurality of voxel clusters. In particular, voxels in a model can be collected and assigned to a cluster of voxels represented by one of the virtual observation points. Further possible aspects and advantages of the concept of monitoring the absorption of the transmitted power delivered into the patient using virtual observation points can be found in US 8653818 B2.

[0029] Another embodiment of the method involves assigning the absorption data to the patient's anatomy using a neural network, preferably one that has been previously trained. For example, such a neural network is based on pattern recognition. This advantageously allows for a particularly accurate and / or reliable assignment.

[0030] Another embodiment of the method provides that the position data describes the position of the transmitting unit of the magnetic resonance device before and / or during the magnetic resonance measurement. For example, the position data describes the position of a local coil that includes the transmitting unit.

[0031] Another embodiment of the method provides that the method further includes the acquisition of position data, wherein the position data describes a position of the patient in the irradiation area relative to the transmitting unit of the magnetic resonance device before and / or during the performance of the magnetic resonance measurement.

[0032] Advantageously, the recorded positional data allows for a particularly precise and / or reliable correlation of absorption data with the patient's anatomy. In particular, monitoring the absorption of the transmission power emitted into the patient by the transmitter unit of the magnetic resonance device can account for any changes in position during the magnetic resonance measurement based on the recorded positional data.

[0033] Preferably, the magnetic resonance device comprises a separate sensor unit for acquiring position data. Preferably, this sensor unit independently of a receiver unit of the magnetic resonance device for receiving magnetic resonance signals, acquires the position of the transmitting unit and / or the position of the patient within the radiation field relative to the transmitting unit.

[0034] Advantageously, the separate sensor unit allows for particularly fast and / or reliable correlation of absorption data with the patient's anatomy. Furthermore, any changes in the patient's position are taken into account immediately or with only a minimal delay, thus ensuring a particularly high level of patient safety. In particular, acquiring position data using a separate sensor unit eliminates the need for time-consuming measurement and / or evaluation of magnetic resonance signals to determine the position.

[0035] Preferably, the acquisition of position data does not include the acquisition of magnetic resonance signals. Preferably, the acquisition of position data includes the acquisition of optical signals. For example, the sensor unit comprises a camera, in particular a 3D camera.

[0036] Advantageously, the recorded positional data allows for a particularly quick and / or reliable assignment of the absorption data to the patient's anatomy.

[0037] Another embodiment of the method provides that the method further includes comparing position data, in particular the detected position of the patient in the irradiation area relative to the transmitting unit of the magnetic resonance device, with patient registration data and / or magnetic resonance device data.

[0038] The location data can be used, in particular, to detect any (intentional or unintentional) discrepancies with the patient registration data. Such a discrepancy could potentially lead to an excessive SAR dose. This risk can be advantageously reduced by reconciling the data with two independent sources.

[0039] The magnetic resonance device data may, for example, include information on whether a local coil, which in particular includes the transmitting unit, is connected to the magnetic resonance device.

[0040] Another embodiment of the method provides that acquiring the patient's anatomy within the radiation field includes acquiring magnetic resonance signals using the magnetic resonance device. Acquiring the patient's anatomy within the radiation field can preferably be achieved by acquiring a scout image prior to performing the (actual) magnetic resonance measurement, during which the transmitted power absorbed by the patient is monitored using the associated absorption data.

[0041] Another embodiment of the method provides that the patient's anatomy within the radiation field is captured in a monitoring mode that considers a worst-case scenario of absorption of the transmitted power by the patient. In particular, this monitoring mode does not include any patient-specific monitoring, or at least not patient-specific monitoring based on absorption data associated with the patient's anatomy. Thus, such a monitoring mode differs from the monitoring performed during the (actual) magnetic resonance imaging (MRI) scan.

[0042] Furthermore, a magnetic resonance device is proposed which is configured to perform a previously described method for monitoring the absorption of a transmission power radiated into a patient by a transmitting unit of a magnetic resonance device.

[0043] The advantages of the magnetic resonance device according to the invention essentially correspond to the advantages of the method according to the invention for monitoring the absorption of a transmission power radiated into a patient by a transmitter unit of a magnetic resonance device, which are described in detail below. Features, advantages, or alternative embodiments mentioned here can also be transferred to the other claimed items and vice versa.

[0044] Furthermore, a computer program product is proposed which comprises a program and can be directly loaded into a memory of a programmable system control unit of a magnetic resonance device and includes program means, e.g. libraries and auxiliary functions, to execute a method according to the invention for monitoring the absorption of a transmit power radiated into a patient by a transmitting unit of a magnetic resonance device when the computer program product is executed in the system control unit of the magnetic resonance device.

[0045] The computer program product can 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. The computer program product enables the inventive method to be executed quickly, identically, and robustly. The computer program product is configured so that it can execute the inventive method steps via the system control unit. The system control unit must have 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.

[0046] 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 for the computer program product may be stored on an electronically readable data carrier.

[0047] The control information of the electronically readable data carrier can be configured such that, when the data carrier is used in a system control unit of a magnetic resonance device, it performs a method according to the invention. Examples of electronically readable data carriers are a DVD, a magnetic tape, or a USB flash drive on which electronically readable control information, in particular software, is stored. When this control information is read from the data carrier and stored in a system control unit of the magnetic resonance device, all embodiments of the methods described above can be carried out according to the invention. The invention can also be based on the aforementioned computer-readable medium and / or the aforementioned electronically readable data carrier.

[0048] 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.

[0049] They show: Fig. 1. A magnetic resonance device in a schematic representation, Fig. 2 a method for monitoring absorption.

[0050] In Fig. Figure 1 schematically depicts a magnetic resonance imaging (MRI) device 10. The MRI 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 MRI device 10 also includes a patient receiving area 14 for receiving a patient 15. In the present embodiment, the patient receiving area 14 is cylindrical and is cylindrically surrounded in one circumferential direction by the magnetic unit 11. However, a different configuration of the patient receiving area 14 is conceivable. The patient 15 can be moved into the patient receiving area 14 by means of a patient positioning device 16 of the MRI device 10. For this purpose, the patient positioning device 16 has a patient table 17 that is movably designed within the patient receiving area 14.

[0051] The magnetic 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 is controlled by a gradient control unit 19 of the magnetic resonance device 10. The magnetic unit 11 also includes 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, by means of its transmitter unit, transmits high-frequency magnetic resonance sequences into an irradiation area, which here is located in the patient acquisition area 14 of the magnetic resonance device 10. This results in a transmission power being irradiated into the irradiation area, which is at least partially absorbed by the patient 15.This causes the main magnetic field 13 generated by the main magnet 12 to excite atomic nuclei. Relaxation of the excited atomic nuclei generates magnetic resonance signals. The high-frequency antenna unit 20 is designed to receive these magnetic resonance signals.

[0052] Furthermore, the magnetic resonance device can include one or more local coils arranged close to the patient 15. A head coil 27, a spinal coil 28, a ceiling coil 29, a knee coil, and a foot coil 31 are shown as examples. (However, usually not so many local coils are used simultaneously.) The local coils are controlled by the high-frequency antenna control unit 21, although for clarity, only the head coil 27 is shown connected to the high-frequency antenna control unit 21. Local coils often comprise only a receiver unit for receiving magnetic resonance signals. However, the local coils shown here also include a transmitter unit through which power can be transmitted into the patient 15.Especially in magnetic resonance devices with a high main magnetic field 13 of, for example, more than 5 Tesla, the radiation of the magnetic resonance sequences is often not carried out by a body coil permanently installed in the magnetic resonance device, but by local coils with a transmitter unit; usually such local coils also include a receiver unit for receiving magnetic resonance signals.

[0053] The magnetic resonance 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 magnetic resonance device 10, for example, by performing a predetermined imaging gradient echo sequence. Furthermore, the system control unit can run a computer program to monitor the absorption of the transmission power radiated into a patient 15 by a transmitter unit of the magnetic resonance device 10. The system control unit 22 also includes an evaluation unit (not shown) for evaluating the magnetic resonance signals acquired during the magnetic resonance examination. Finally, the magnetic resonance device 10 includes a user interface 23 connected to the system control unit 22.Control information, such as imaging parameters and reconstructed magnetic resonance images, can be displayed on a display unit 24, for example, on at least one monitor, of 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 personnel during a measurement procedure.

[0054] Furthermore, the magnetic resonance device 10 comprises a sensor unit in the form of a camera 26, in particular a 3D camera, with which the position of the local coils 27, 28, 29, 30, 31 with their transmitter units and / or the patient 15 can be detected. The camera 26 can detect the position data in the form of optical signals. The camera 26 has a detection range (indicated by the dashed lines) that is suitable for detecting the position of the local coils 27, 28, 29, 30, 31 and thus also of the transmitter units arranged in the local coils 27, 28, 29, 30, 31. (Advantageously, data is provided to the system control unit 22 to derive the position of the transmitting units arranged in the local coils 27, 28, 29, 30, 31 from the position of the local coils 27, 28, 29, 30, 31. This data can, for example, include information about the, in particular geometric, structure of the local coils 27, 28, 29, 30, 31.)These position data are therefore acquired independently of the acquisition of the magnetic resonance signals, which can be acquired using receiver units of the body coil and / or the local coils 27, 28, 29, 30, 31. The position data acquired by the camera 26 are transmitted to the system control unit 22 for further evaluation.

[0055] In Fig. Figure 2 shows an exemplary method for monitoring the absorption of a transmission power radiated into a patient 15 by a transmitter unit of a magnetic resonance device 10.

[0056] In S10, the patient 15 is positioned within the radiation field of the magnetic resonance device 10, where the transmission power is to be directed into the patient 15. Depending on the transmitter unit used, the radiation field can vary. For example, if the transmitter unit of the body coil permanently installed in the magnetic resonance device 10 is used, a comparatively large radiation field typically results in the patient reception area 14. If, for example, a local coil 27, 28, 29, 30, 31 is the active coil and its transmitter unit is used, a comparatively small, locally concentrated radiation field typically results. For example, when using the knee coil 30, the radiation field is usually only within the small area at the knee of the patient 15 that is surrounded by the knee coil 30.

[0057] Position data is acquired in S20, where the position data describes the position of the transmitting unit of the magnetic resonance device 10 before and / or during the magnetic resonance measurement. This can be done, for example, with the help of the camera 26. This allows the position of the active transmitting coil, for example, the knee coil 30, to be determined.

[0058] In S30, the acquired position data, in particular the determined position of the active coil, are compared with patient registration data and / or magnetic resonance device data. Patient registration data includes, for example, patient-specific data such as age, sex, weight, and / or height of the patient 15, which were entered into a data acquisition system connected to the magnetic resonance device 10 before the magnetic resonance examination. Magnetic resonance device data includes, for example, data that describe the state and / or properties of the magnetic resonance device 10. The data comparison enables a consistency check of the position data, the patient registration data, and / or the magnetic resonance device data. For example, the consistency check may reveal that the active coil is not connected to or plugged into the magnetic resonance device 10.

[0059] If an error and / or inconsistency is detected during the comparison, a corrective action can be taken in S40, for example, by the operator of the magnetic resonance device 10. For instance, a coil that was initially not connected can be correctly connected to the magnetic resonance device, after which the position data is acquired again in S20.

[0060] Upon successful consistency verification in S30, the anatomy of patient 15 within the irradiation area can be acquired in S50. For this purpose, overview data can be measured, for example. The anatomy of patient 15 can be acquired by recording magnetic resonance signals using the magnetic resonance device 10. In particular, at least one magnetic resonance image can be generated from the acquired magnetic resonance signals, from which the anatomy of patient 15 can be determined. To ensure a high level of patient safety, the acquisition of the patient's anatomy can be performed in a monitoring mode that considers a worst-case scenario of absorption of the irradiated transmission power by the patient. Such a monitoring mode can, in particular, be a so-called "protected mode" that includes the worst-case scenario for all body regions and models.

[0061] While considering the worst-case scenario may reduce the performance of the magnetic resonance device 10, ideally the patient's anatomy 15 is only acquired once, so this does not significantly restrict the overall magnetic resonance examination of the patient 15.

[0062] In S60, the system control unit is provided with 22 absorption data points that describe a patient-independent, location-dependent absorption sensitivity of the transmitted power. The absorption data can, for example, include virtual observation points. Each observation point can, in particular, represent a voxel cluster. A peak sensitivity for a local specific absorption rate can be assigned to the voxel cluster.

[0063] In S70, the system control unit 22 assigns the absorption data to the anatomy of patient 15. This assignment can be carried out in particular by means of a neural network.

[0064] If an error occurs in S50, S60 or S70, a corrective action can also be taken in S45, for example by an interaction of the operating personnel of the magnetic resonance device 10.

[0065] In S80, the assigned absorption data are adopted, possibly after confirmation by the operating personnel. In S90, a magnetic resonance measurement of patient 15 is performed, during which the transmitted power absorbed by patient 15 is monitored using the assigned absorption data.

[0066] During the magnetic resonance imaging (MRI) scan, position data is recorded in S90. Specifically, the position of the active transmitting coil, for example, the knee coil 30, is determined. Based on this position data, the patient 15 can be monitored during the MRI scan in order to abort the scan in case of excessive patient movement and / or coil displacement. If, for example, the deviation of the actual position of the active transmitting coil from the target position exceeds a predetermined limit, the MRI scan is aborted in S100. This can advantageously increase patient safety. Otherwise, the MRI scan ends as scheduled in S110.

[0067] The determination of the active transmitting coil's position in S20 and S90, together with the subsequent evaluation of the position data, can be considered a first safety layer for the magnetic resonance imaging (MRI) examination of patient 15. The measurement of the overview data in S50 with the active transmitting coil, the mapping of the absorption data provided in S60 in S70, and the subsequent SAR monitoring in S90 can be considered a second safety layer for the MRI examination of patient 15. Advantageously, these safety layers are independent of each other, thus ensuring patient safety in clinical practice.

[0068] By individualizing SAR monitoring based on the patient's body anatomy, worst-case cost overruns can be avoided, allowing, for example, more measurement slices to be acquired and / or the measurement time to be reduced. Advantageously, the proposed method can also be easily retrofitted into existing MR systems, for example, by implementing suitable software and / or hardware, such as a 3D camera.

[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.

Claims

[1] Method for monitoring the absorption of a transmission power emitted into a patient by a transmitter unit of a magnetic resonance device, the method comprising - Providing absorption data that describe a patient-nonspecific, location-dependent absorption sensitivity of the transmitted power, - Positioning the patient in an irradiation area of ​​the magnetic resonance device, in which the transmission power is to be irradiated into the patient, - Capturing the patient's anatomy within the radiation field, - Mapping the absorption data to the patient's anatomy, - Performing a magnetic resonance measurement of the patient, whereby the transmitted power absorbed by the patient is monitored during the magnetic resonance measurement based on the associated absorption data, - Recording position data, where the position data describe a position of the patient in the radiation area relative to the transmitting unit of the magnetic resonance device during the performance of the magnetic resonance measurement, wherein the transmitting unit is part of a local coil, whereby in the event of excessive patient movement and / or coil displacement the magnetic resonance measurement is aborted. [2] Method according to claim 1, wherein during the magnetic resonance measurement the transmission power is radiated by means of several transmitting antennas of the transmitting unit, wherein the absorption data take into account a transmission profile generated by the several transmitting antennas, in particular an amplitude and / or phase. [3] Method according to one of claims 1 or 2, wherein the absorption data comprise virtual observation points for monitoring the transmitted power absorbed by the patient, each observation point representing at least one voxel, in particular a voxel cluster. [4] Method according to claim 3, wherein the at least one voxel is assigned a peak sensitivity for a local specific absorption rate. [5] Method according to any of the preceding claims, wherein the mapping of the absorption data to the patient's anatomy is carried out using a neural network. [6] Method according to any of the preceding claims, the procedure further includes the recording of position data, where the position data describes the position of the transmitting unit of the magnetic resonance device before and / or during the magnetic resonance measurement. [7] Method according to any of the preceding claims, wherein the position data describe a position of the patient in the irradiation area relative to the transmitting unit of the magnetic resonance device before performing the magnetic resonance measurement. [8] Method according to any one of claims 5 to 7, wherein the acquisition of position data comprises the acquisition of optical signals, in particular by means of a camera. [9] Method according to any one of claims 5 to 8, wherein a movement of the patient and / or the transmitting unit is determined based on the position data, wherein the magnetic resonance measurement is aborted if the movement exceeds a predetermined limit value. [10] Method according to any one of claims 5 to 9, wherein the method further comprises: Comparing the recorded position data with patient registration data and / or magnetic resonance device data. [11] Method according to claim 9, wherein the magnetic resonance device data includes information on whether a local coil, which in particular includes the transmitting unit, is connected to the magnetic resonance device. [12] Method according to one of the preceding claims, wherein the detection of the patient's anatomy in the radiation area comprises the detection of magnetic resonance signals by the magnetic resonance device. [13] Method according to one of the preceding claims, wherein the detection of the patient's anatomy in the irradiation area is carried out in a monitoring mode that takes into account a worst-case absorption of the irradiated transmit power by the patient. [14] Magnetic resonance device configured to perform a method according to any of the preceding claims. [15] 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 12 when the program is executed in the system control unit of the magnetic resonance device.

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