1-11Method for performing a magnetic resonance measurement, magnetic resonance device and computer program product

Abstract

The invention relates to a method for performing a magnetic resonance measurement taking into account a minimum distance of a patient from the inner wall of the magnet opening, a magnetic resonance device, and a computer program product. The method comprises determining an initial minimum distance of the patient from the inner wall of the magnet opening, determining an initial maximum transmission power based on the initial minimum distance, determining an initial measurement protocol based on the initial maximum transmission power, and starting the magnetic resonance measurement according to the initial measurement protocol.

Description

[0001] The invention relates to a method for carrying out a magnetic resonance measurement taking into account a minimum distance of a patient from the inner wall of the magnet opening, a magnetic resonance device and a computer program product.

[0002] In medical technology, imaging using magnetic resonance (MR), also known as magnetic resonance imaging (MRI), is characterized by high soft tissue contrast. A magnetic resonance measurement is performed using a magnetic resonance device that has a magnet unit. The magnet unit usually comprises a main magnet for generating a main magnetic field and a gradient coil unit for generating a gradient magnetic field in an examination region of the magnetic resonance device. The examination region is usually located in a magnet bore of the magnet unit, in which a patient is positioned during the magnetic resonance measurement. High-frequency (HF) waves are used to generate magnetic resonance signals during a magnetic resonance measurement.Radio-frequency (RF) pulses are radiated into the examination area, particularly into the patient, according to a measurement protocol, in particular a magnetic resonance sequence. This irradiation generates a B1 field. The magnetic resonance signals are received as measurement data by the magnetic resonance device and used to reconstruct magnetic resonance images.

[0003] The radiation from the RF pulses can cause the patient's body to heat up. To ensure that heating occurs only to a degree that is harmless to the patient, a maximum permissible specific absorption rate (SAR) is usually specified and taken into account in magnetic resonance measurements. Particularly high local heating can occur near the inner wall of the magnet opening.

[0004] The document DE 102012205236 A1 describes a method according to which a distance between a patient and a wall of a magnetic resonance imaging scanner is determined and, based on the distance, an electromagnetic field is adjusted for a subsequent examination of the patient.

[0005] The object of the present invention can be considered to enable a magnetic resonance measurement that is safe for the patient and at the same time efficient. This object is achieved by the features of the independent claims. Advantageous embodiments are described in the dependent claims.

[0006] Accordingly, a computer-implemented method for performing a magnetic resonance measurement of a patient using a magnetic resonance device is proposed. The magnetic resonance device comprises a magnet opening, within which at least a part of the patient is positioned during the magnetic resonance measurement, and a radio-frequency antenna unit configured to emit a transmission power. In a step a), an initial minimum distance of the patient from the inner wall of the magnet opening is determined. In a step b), an initial maximum transmission power is determined based on the initial minimum distance. In a step c), an initial measurement protocol is determined based on the initial maximum transmission power. In a step d), the magnetic resonance measurement is started according to the initial measurement protocol.

[0007] Preferably, the minimum distance, in particular the initial minimum distance, of the patient to the inner wall of the magnet opening is the shortest (geometric) distance between the surface of the patient and the surface of the inner wall of the magnet opening.

[0008] Preferably, the minimum distance, in particular the initial minimum distance, is dependent on a location-dependent heating potential on the inner wall of the magnet opening. Preferably, the minimum distance, in particular the initial minimum distance, is the shortest (geometric) distance between the surface of the patient and particularly strongly heated sections of the surface of the inner wall of the magnet opening. For example, several sections are located along a central axis of the magnet opening (in the z-direction) which are designed to heat the patient to different intensities. For example, the surface of the inner wall of the magnet opening has a spatial heating profile, in particular depending on a position in the z-direction. Preferably, the spatial heating profile indicates a location-dependent heating potential, in particular the extent to which the patient can be heated depending on a position on the surface of the inner wall of the magnet opening.Preferably, the minimum distance, in particular the initial minimum distance, is determined as a function of the spatial heating profile of the surface of the inner wall of the magnet opening.

[0009] This advantageously allows for the often occurring circumstance that heating occurs particularly strongly at two hotspots at the beginning and end of a body coil that is fixed close to the inner wall of the magnet opening to be taken into account.

[0010] The prior art discloses a variety of methods that can be used to determine the minimum distance, in particular the initial minimum distance. For example, determining the minimum distance comprises detecting an optical signal and / or a magnetic resonance signal, based on which the minimum distance is determined. For example, the minimum distance is determined using 2D or 3D camera monitoring, light barrier monitoring, or magnetic resonance imaging. The minimum distance can be determined, in particular, using a minimum distance determination unit, which may, for example, comprise one or more cameras or one or more light barriers.

[0011] The determination of the maximum transmission power, in particular the initial maximum transmission power, based on the current minimum distance can be performed, for example, using a model, in particular depending on the distance of the patient, in particular the patient's tissue, from the radio-frequency antenna unit. In particular, the determination of the maximum transmission power can be performed using one or more stored tables that were previously generated, for example, using simulation calculations. The determination of the current maximum transmission power can be performed, in particular, using a transmission power determination unit.

[0012] Said transmission power is, in particular, a (temporally) averaged and / or (temporally) averaged transmission power. The transmission power is preferably a transmission power of the magnetic resonance device, in particular of a radio-frequency antenna unit of the magnetic resonance device, which is transmitted during the magnetic resonance measurement.

[0013] In particular, the B1 field generated by the high-frequency antenna unit and / or B1 2 -field must be taken into account. In particular, the transmission power averaged over a specific period of time, e.g., 10 seconds and / or 6 minutes, can be taken into account. The transmission power is determined in particular by the RF pulses to be applied according to the measurement protocol. The maximum transmission power is advantageously a transmission power whose application does not pose a risk to the patient.

[0014] The determination of the measurement protocol, in particular the initial measurement protocol, can in particular be based on a predefined base measurement protocol that is adapted to generate the initial measurement protocol. The measurement protocol, in particular the initial measurement protocol, can in particular comprise a plurality of pulses, in particular RF pulses and / or gradient pulses. The measurement protocol, in particular the initial measurement protocol, can in particular comprise one or more MR pulse sequences. The determination of the measurement protocol, in particular the initial measurement protocol, can in particular comprise an adaptation of RF pulses and / or gradient pulses, in particular of a predefined base measurement protocol. The determination of the measurement protocol can in particular be carried out by means of a measurement protocol determination unit.

[0015] The minimum distance determination unit, the transmission power determination unit and / or the measurement protocol determination unit can in particular comprise one or more processors and / or one or more memory modules.

[0016] Advantageously, the initial minimum distance of the patient to the inner wall of the magnet opening is the actual minimum distance of the patient to the inner wall of the magnet opening, especially immediately before starting the magnetic resonance measurement. Advantageously, the initial measurement protocol is adapted to the initial, especially actual, minimum distance of the patient to the inner wall of the magnet opening, and in particular, optimized for this purpose.

[0017] Advantageously, it is possible to avoid using a theoretical and / or assumed minimum distance of the patient from the inner wall of the magnet opening as a basis for determining an applicable measurement protocol; this is because such a basis may require a more conservative estimate than actually necessary, which in turn may result in lower performance of the magnetic resonance measurement. Advantageously, the maximum transmission power can be adjusted according to the measurement protocol to improve the performance of the magnetic resonance measurement. Advantageously, the method enables adaptation of a magnetic resonance examination, in particular a magnetic resonance measurement, to changed B1 limits to prevent local overheating.

[0018] A possible embodiment of the method further comprises the following steps: In step e), a current minimum distance of the patient to the inner wall of the magnet opening is determined during the (already started or ongoing) magnetic resonance measurement. In step f), a current maximum transmission power is determined based on the current minimum distance. In step g), an adapted measurement protocol is determined based on the current maximum transmission power. In step h), the magnetic resonance measurement is continued according to the adapted measurement protocol.

[0019] The possible features previously disclosed for determining the initial minimum distance can also be applied to determining the current minimum distance, and vice versa. For example, the current minimum distance can also be determined using the minimum distance determination unit.

[0020] The possible features previously disclosed for determining the initial maximum transmission power can also be applied to determining the current maximum transmission power, and vice versa. For example, the current maximum transmission power can also be determined using the transmission power determination unit.

[0021] The possible features previously disclosed for determining the initial measurement protocol can also be applied to determining the adapted measurement protocol, and vice versa. For example, the adapted measurement protocol can also be determined using the measurement protocol determination unit.

[0022] The current minimum distance can be determined continuously, in particular quasi-continuously (i.e., with only minimal interruptions and / or interruptions resulting from technical limitations). The current minimum distance can also be determined at specific time intervals. For example, the current minimum distance is determined every 10 seconds.

[0023] The minimum distance, in particular the initial and / or current minimum distance, can be determined in particular from measurement data. The measurement data can in particular be measurement data that describe the position of the patient's body in the magnet opening. The measurement data can, for example, comprise measurement data acquired by means of a camera and / or light barriers. The measurement data can, for example, comprise magnetic resonance signals, in particular magnetic resonance images reconstructed from magnetic resonance signals. The measurement data used to determine the minimum distance can be recorded at a point in time, preferably the current and / or last point in time. However, it is also conceivable that measurement data recorded in a previous time interval are taken into account for determining the minimum distance, in particular the initial and / or current minimum distance.For example, determining the minimum distance may involve averaging the measured data. For example, determining the minimum distance may involve interpolating and / or extrapolating and / or predicting the minimum distance.

[0024] Advantageously, the measurement protocol is dynamically adjusted based on the determined current minimum distance. This allows for optimized performance throughout the entire magnetic resonance measurement. Furthermore, it is advantageously possible to ensure that the magnetic resonance measurement is performed safely.

[0025] For example, if the patient or a part of the patient's body (e.g., their arm) moves closer to the inner wall of the magnet opening during the magnetic resonance measurement, thus decreasing the minimum distance, the maximum transmission power is preferably also reduced and the measurement protocol is adjusted accordingly. However, if the patient or a part of the patient's body (e.g., their arm) moves away from the inner wall of the magnet opening during the magnetic resonance measurement, thus increasing the minimum distance, the maximum transmission power is preferably increased and the measurement protocol is adjusted accordingly.

[0026] A possible embodiment of the method provides that the method after step e) further comprises checking in step e1) whether a difference between the current minimum distance and the initial minimum distance exceeds a predetermined distance threshold, and steps f), g) and h) are carried out depending on whether the check in step e1) shows that the difference between the current minimum distance and the initial minimum distance exceeds the predetermined distance threshold.

[0027] Advantageously, steps f), g), and h) can be omitted if the difference does not exceed the specified distance threshold. This dependency can therefore also mean that steps f), g), and h) are not executed at all if the distance threshold is not exceeded. In particular, it can be avoided that an adjusted measurement protocol must be determined for every slightest change in the minimum distance. Advantageously, the distance threshold is specified in such a way that steps f), g), and h) are only performed if the change in the minimum distance is sufficiently significant, making an adjustment of the measurement protocol appropriate.

[0028] A possible embodiment of the method provides that the method after step f) further comprises checking in step f1) whether the current maximum transmission power would be exceeded if the magnetic resonance measurement were carried out according to the initial measurement protocol, wherein steps g) and h) are carried out depending on whether the check in step f1) shows that the current maximum transmission power would be exceeded if the magnetic resonance measurement were carried out according to the initial measurement protocol.

[0029] Advantageously, steps g) and h) can be omitted if the current maximum transmission power would not be exceeded even without changing the measurement protocol. Advantageously, an adjusted measurement protocol is only determined if this is necessary to avoid excessive transmission power.

[0030] A possible embodiment of the method provides that, after step f), the method further comprises checking, in step f2), the degree of deviation by which the current maximum transmission power deviates from the initial maximum transmission power when performing the magnetic resonance measurement according to the measurement protocol. Steps g) and h) are executed depending on whether the degree of deviation exceeds a predetermined deviation threshold.

[0031] Advantageously, steps g) and h) can be omitted if the specified deviation threshold is not exceeded. Advantageously, an adjusted measurement protocol is only generated if the maximum transmission power changes sufficiently.

[0032] One possible embodiment of the method provides that determining the adapted measurement protocol includes changing at least one repetition time of the initial measurement protocol. Advantageously, increasing the repetition time can reduce the transmission power.

[0033] The repetition time (often referred to as TR) is typically the time between two excitation pulses (RF pulses). Within the TR interval, signals can be acquired with one or more echo times and with one or more phase encodings (depending on the measurement technique). TR is one of the measurement parameters that determine contrast. The acquisition time (TA) is usually directly proportional to TR.

[0034] One possible embodiment of the method provides that determining the adjusted measurement protocol comprises changing the number of echoes in an echo train of the initial measurement protocol. Advantageously, reducing the number of echoes in an echo train can reduce the transmission power.

[0035] An echo train is generated particularly in multi-echo sequences. For example, in a fast spin-echo or turbo spin-echo pulse sequence, an echo train comprises a series of rephasing 180° RF pulses and their corresponding echoes.

[0036] One possible embodiment of the method provides that determining the adapted measurement protocol comprises changing a flip angle of at least one RF pulse of the initial measurement protocol. Advantageously, reducing the flip angle can reduce the transmission power.

[0037] A flip angle can be defined, in particular, as an excitation angle for a pulse sequence. It is typically the angle, relative to the direction of the main magnetic field, into which a net magnetization is rotated by applying an RF pulse. In gradient-echo sequences, flip angles between 0° and 90° are typically used; in spin-echo sequences, a 90° pulse followed by a series of 180° pulses are used; and in inversion-recovery sequences, an initial 180° pulse followed by a 90° and a 180° pulse is used.

[0038] Preferably, determining the adapted measurement protocol involves the use, in particular the introduction, of a variable flip angle profile (VFA). For example, in a TSE and / or SPACE sequence, a VFA typically describes the refocusing pulses across the echo train. With VFA, these pulses are modified across the echo train, e.g., decreasing progressively over the course of the echo train (i.e., 180° only at the beginning of the echo train, then decreasing progressively less). This advantageously reduces the average transmit power. Depending on the determined limits, the VFA could be adjusted to comply with the limits.

[0039] A possible embodiment of the method provides that steps e), f), g) and h), and optionally e1), f1) and / or f2), are carried out repeatedly during the (ongoing) magnetic resonance measurement.

[0040] Preferably, the previous current maximum transmission power is treated as the initial maximum transmission power and / or a previous adjusted measurement protocol is treated as the initial measurement protocol.

[0041] For example, the measurement protocol is repeatedly adjusted during a magnetic resonance measurement to accommodate a changing minimum distance between the patient and the inner wall of the magnet opening, or to accommodate a resulting change in the maximum transmit power. Advantageously, a safe and efficient magnetic resonance measurement can be performed throughout the entire magnetic resonance measurement.

[0042] Furthermore, a magnetic resonance apparatus is proposed that is configured to carry out a method described above. The magnetic resonance apparatus may, in particular, comprise a minimum distance determination unit, a transmission power determination unit, and / or a measurement protocol determination unit.

[0043] The advantages of the proposed magnetic resonance device essentially correspond to the advantages of the previously described method for performing a magnetic resonance measurement of a patient, which are explained in detail above. Features, advantages, or alternative embodiments mentioned herein can also be applied to the other claimed subject matter, and vice versa.

[0044] Furthermore, a computer program product is proposed, which comprises a program and is directly loadable into a memory of a programmable system control unit of a magnetic resonance apparatus and has program means, e.g., libraries and auxiliary functions, for executing a proposed method when the computer program product is executed in the system control unit of the magnetic resonance apparatus. The computer program product can comprise software with a source code that still needs to be compiled and linked or that only needs to be interpreted, or an executable software code that only needs to be loaded into the system control unit for execution.

[0045] The computer program product advantageously allows the proposed method to be executed quickly, identically repeatably, and robustly. The computer program product is preferably configured to execute the proposed method steps using the system control unit. The system control unit has the necessary prerequisites, such as a suitable RAM, 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 stored on a network or server, from where it can be loaded into the processor of a local system control unit, which can be directly connected to the magnetic resonance device or formed as part of the magnetic resonance device. Furthermore, control information of the computer program product can be stored on an electronically readable data carrier. The control information of the electronically readable data carrier can be configured to carry out a proposed method when the data carrier is used in a system control unit of a magnetic resonance device.

[0047] Examples of electronically readable data storage media include a DVD, a magnetic tape, or a USB stick on which electronically readable control information, in particular software, is stored. If this control information is read from the data storage media and stored in a system control unit of the magnetic resonance device, all proposed embodiments of the methods described above can be implemented.

[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 provided with the same reference numerals in all figures.

[0049] They show: Fig. 1 a magnetic resonance device in a schematic representation, Fig. 2 a possible method for performing a magnetic resonance measurement, Fig. 3 a detailed representation of the magnet opening, Fig. 4-6 further variants of a procedure for performing a magnetic resonance measurement.

[0050] In Fig. 1, a magnetic resonance apparatus 10 is shown schematically. The magnetic resonance apparatus 10 comprises a magnet unit 11 having a main magnet 12 for generating a strong and, in particular, temporally constant main magnetic field 13. In addition, the magnet unit 11 comprises a magnet opening 14 for accommodating a patient 15. The patient 15 is supported within the magnet opening 14, at least partially during a magnetic resonance measurement. In the present exemplary embodiment, the magnet opening 14 is cylindrical and is surrounded in a circumferential direction by the magnet unit 11. The magnet opening 14 can have the shape of a circular cylinder, but cross-sectional shapes other than a circle are also conceivable, e.g., an oval, in particular an ellipse. The magnet opening 14 is delimited by an inner wall W of the magnet opening.The patient 15 can be moved into the patient receiving area 14 by means of a patient support device 16 of the magnetic resonance device 10. For this purpose, the patient support device 16 comprises a patient table 17 designed to be movable in the z-direction within the magnet opening 14.

[0051] The magnet unit 11 further comprises a gradient coil unit 18 for generating magnetic field gradients 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 magnet unit 11 also comprises a radio-frequency antenna unit 20, which in the present exemplary embodiment is designed as a body coil permanently integrated into the magnetic resonance device 10. The radio-frequency antenna unit 20 is controlled by a radio-frequency antenna control unit 21 of the magnetic resonance device 10 and radiates transmission power in the form of RF pulses into the examination region, which is essentially formed by the magnet opening 14 of the magnetic resonance device 10. As a result, the main magnetic field 13 generated by the main magnet 12 excites atomic nuclei.Magnetic resonance signals are generated by the relaxation of the excited atomic nuclei. The radio-frequency antenna unit 20 is designed to receive the magnetic resonance signals.

[0052] The magnetic resonance apparatus 10 has a system control unit 22 for controlling the main magnet 12, the gradient control unit 19, and the radio-frequency antenna control unit 21. The system control unit 22 centrally controls the magnetic resonance apparatus 10, for example, by executing a measurement protocol. The system control unit 22 also includes an evaluation unit (not shown in detail) for evaluating the magnetic resonance signals acquired during the magnetic resonance examination. Furthermore, the magnetic resonance apparatus 10 includes a user interface 23 connected to the system control unit 22. Control information, such as imaging parameters, as well as 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 operating personnel during the magnetic resonance measurement.

[0053] In Fig. Figure 2 shows a sequence of a possible computer-implemented method for performing a magnetic resonance measurement of the patient 15 using the magnetic resonance device 10. Before the start of the magnetic resonance measurement, an initial minimum distance of the patient 15 to the inner wall W of the magnet opening 14 is determined in S1. Fig. Figure 3 shows in more detail the minimum distance dm of the patient 15 to the inner wall W of the magnet opening 14. The viewing direction is the z-direction, which is oriented perpendicular to the plane spanned by the x-direction and the y-direction. The magnet opening 14 is circularly cylindrical in shape and has a radius r2. The part of the patient (here, his arm on the right side) that has the smallest distance to the inner wall W of the magnet opening 14 (i.e., the minimum distance dm) is located at a radius r1.

[0054] In S2, an initial maximum transmission power is determined based on the initial minimum distance dm. In particular, it can be provided that the maximum transmission power, especially the initial maximum transmission power, is lower the closer the patient is to the inner wall of the magnet opening, i.e., the smaller dm is.

[0055] This is preferably the maximum transmission power that the radio frequency antenna unit 20 should emit during the magnetic resonance measurement, i.e. this transmission power should not be exceeded during the magnetic resonance measurement in order to avoid endangering the patient.

[0056] In S3, an initial measurement protocol is determined based on the initial maximum transmission power. Measurement protocols, in particular the initial measurement protocol, can be centrally controlled by the system control unit 22 of the magnetic resonance apparatus 10. The initial measurement protocol is preferably designed such that the initial maximum transmission power is not exceeded.

[0057] In S4, the magnetic resonance measurement is started according to the initial measurement protocol. This can be done automatically or manually by the operating personnel.

[0058] In S5, a current minimum distance of the patient 15 to the inner wall W of the magnet opening 14 is determined during the ongoing magnetic resonance measurement. For example, the patient 15 could move their arm, causing the minimum distance dm to change; then the current minimum distance differs from the initial minimum distance.

[0059] In S6, the current maximum transmission power is determined based on the current minimum distance. This determination can be performed in a similar way to the determination of the initial maximum transmission power based on the initial minimum distance.

[0060] If the current minimum distance decreases compared to the initial minimum distance, this can preferably lead to a lower current maximum transmission power. If the current minimum distance increases compared to the initial minimum distance, this can preferably lead to a higher current maximum transmission power.

[0061] In S7, an adjusted measurement protocol is generated based on the current maximum transmission power. For example, with an increased current maximum transmission power, the performance of the magnetic resonance measurement can be improved, particularly the speed and / or resolution of the magnetic resonance measurement. Conversely, with a reduced current maximum transmission power, the measurement protocol can be adjusted to reduce the risk of harm to the patient.

[0062] In S8, the magnetic resonance measurement is then continued according to the adapted measurement protocol.

[0063] Optionally, S5, S6, S7 and S8 can be performed repeatedly during the magnetic resonance measurement.

[0064] In the Fig. 4, the procedure is as per Fig. 2 is expanded in that a check is carried out in S6,1 to determine whether a difference between the current minimum distance and the initial minimum distance exceeds a predetermined distance threshold value; only if the distance threshold value is exceeded is the magnetic resonance measurement continued in accordance with S6, S7, S8 in a modified manner, in particular with a modified measurement protocol. Otherwise, without changing the measurement protocol, a current minimum distance can be repeatedly determined in S5 and compared in S6,1 with an earlier minimum distance (which then corresponds to the initial minimum distance in the sense mentioned above). A pause can be provided between two such checks, or the check can be carried out continuously. Even after performing steps S6, S7, S8, a current minimum distance can be repeatedly determined in S5 and compared in S6,1 with an earlier minimum distance (which then corresponds to the initial minimum distance in the sense mentioned above).

[0065] In the Fig. 5, the procedure is as per Fig. 2 is expanded in that in S7,1 a check is carried out to determine whether the current maximum transmission power would be exceeded if the magnetic resonance measurement were carried out according to the initial measurement protocol; only if the current maximum transmission power would be exceeded is the magnetic resonance measurement continued according to S7, S8 in a modified manner, in particular with a modified measurement protocol. Otherwise, a (new) current minimum distance can be determined repeatedly in S5 without changing the measurement protocol, and in S6 a (new) current maximum transmission power is determined based on the current minimum distance. A pause can be provided between two such checks, or the check can be carried out continuously. Even after steps S7, S8 have been carried out, the method can be continued repeatedly with S5.

[0066] In the Fig. 6, the procedure is as per Fig. 2 is expanded in that in S7,2 a check is carried out to determine the degree of deviation by which the current maximum transmission power deviates from the initial maximum transmission power when the magnetic resonance measurement is carried out according to the measurement protocol; only if the degree of deviation exceeds the specified deviation threshold is the magnetic resonance measurement continued according to S7, S8 in a modified manner, in particular with a modified measurement protocol. Otherwise, a (new) current minimum distance can be repeatedly determined in S5 without changing the measurement protocol, and in S6 a (new) current maximum transmission power is determined based on the current minimum distance. A pause can be provided between two such checks, or the check can be carried out continuously. The method can also be repeatedly continued with S5 after steps S7, S8 have been carried out.

[0067] The procedures according to the Fig. 4, Fig. 5 and Fig. 6, in particular steps S6,1, S7,1 and / or S7,2, can also be combined with one another.

[0068] Determining the adapted measurement protocol in S7 can involve various adjustments, particularly depending on the sequence type used in the measurement protocol. A mean transmission power is preferably considered, as this is often the critical limitation over time.

[0069] Particularly high (average) transmit powers are typically applied using spin-echo-based sequences, such as spin-echo (SE), turbo-spin-echo (TSE), half-Fourier acquisition single-shot turbo spin-echo (HASTE), sampling perfection with application-optimized contrast using different flip angle evolution (SPACE), or BLADE. The following adaptations are particularly suitable for such sequences or measurement protocols. i. Extending the repetition time or using more concatenations (or concats for short). This increases the measurement time, but reduces the average transmit power while maintaining the same contrast. Concatenations can be advantageously used to measure more slices or to prevent crosstalk when the slice spacing is small. ii. Shortening the echo train without reducing the repetition time or the number of concats. iii. Introducing a variable flip angle curve that requires a lower average transmit power. iv. Reducing all pulse amplitudes or clipping the transmit power so that the second maximum transmit power is maintained. However, this is not preferred, as reducing the pulses can significantly impact image quality, especially image contrast, and may render the measurement data unusable.

[0070] It is also conceivable that possible strategies for adaptation are already stored in the measurement protocol.

[0071] The proposed method can advantageously react to a possible patient movement and thus prevent the risk of overheating, while still avoiding very conservative initial limits.

[0072] It is also conceivable to increase the transmit power during the measurement - for example, if it is determined that the minimum distance of the patient to the bore wall has increased significantly.

[0073] Advantageously, the method enables the adaptation of a magnetic resonance measurement, which starts with a first (initial) maximum transmission power and during which the (average) transmission power is adjusted to a second (current) maximum transmission power. Patient safety is thereby advantageously ensured. Advantageously, the magnetic resonance measurement is adjusted such that a generally unchanged image quality, especially contrast, is generated with the respective maximum transmission power.

[0074] Finally, it should be noted once again that the methods described in detail above, as well as the magnetic resonance device illustrated, are merely exemplary embodiments that can be modified in a variety of ways by a person skilled in the art without departing from the scope of the invention. Furthermore, the use of the indefinite articles "a" or "an" does not exclude the possibility that the features in question may be present in multiple instances. Likewise, the term "unit" does not exclude the possibility that the components in question may consist of several interacting subcomponents, which may also be spatially distributed. Regardless of the grammatical gender of a particular term, this includes persons with male, female, or other gender identities.

Claims

[1] Computer-implemented method for performing a magnetic resonance measurement of a patient by means of a magnetic resonance device, wherein the magnetic resonance device comprises a magnet opening within which at least a part of the patient is positioned during the magnetic resonance measurement, and comprises a radio-frequency antenna unit which is designed to emit a transmission power, the method comprising the following steps a) Determination of an initial minimum distance of the patient to the inner wall of the magnet opening, b) Determining an initial maximum transmission power based on the initial minimum distance, c) Determining an initial measurement protocol based on the initial maximum transmission power, d) Starting the magnetic resonance measurement according to the initial measurement protocol, e) Determining a current minimum distance of the patient to the inner wall of the magnet opening during the magnetic resonance measurement, f) Determining a current maximum transmission power based on the current minimum distance, f2) Check the degree of deviation of the current maximum transmission power from the initial maximum transmission power when performing the magnetic resonance measurement according to the measurement protocol, g) Determining an adapted measurement protocol based on the current maximum transmission power, h) Continuing the magnetic resonance measurement according to the adapted measurement protocol, wherein steps g) and h) are carried out depending on whether the deviation measure exceeds a predetermined deviation threshold. [2] Method according to claim 1, wherein the initial minimum distance and possibly the current minimum distance are dependent on a location-dependent heating potential on the inner wall of the magnet opening. [3] A method according to any one of the preceding claims, wherein the method further comprises, after step e), e1) Checking whether a difference between the current minimum distance and the initial minimum distance exceeds a predetermined distance threshold, wherein steps f), g) and h) are carried out depending on whether the check in step e1) shows that the difference between the current minimum distance and the initial minimum distance exceeds the predetermined distance threshold. [4] A method according to any one of the preceding claims, wherein the method further comprises, after step f), f1) Checking whether the current maximum transmission power would be exceeded if the magnetic resonance measurement were carried out in accordance with the initial measurement protocol, wherein steps g) and h) are carried out depending on whether the check in step f1) shows that the current maximum transmission power would be exceeded if the magnetic resonance measurement were carried out in accordance with the initial measurement protocol. [5] Method according to one of the preceding claims, wherein determining the adapted measurement protocol comprises changing at least one repetition time of the initial measurement protocol. [6] Method according to one of the preceding claims, wherein determining the adapted measurement protocol comprises changing a number of echoes of an echo train of the initial measurement protocol. [7] Method according to one of the preceding claims, wherein determining the adapted measurement protocol comprises changing a flip angle of at least one RF pulse of the initial measurement protocol. [8] Method according to one of the preceding claims, wherein determining the adapted measurement protocol comprises using a variable flip angle profile. [9] Method according to one of the preceding claims, wherein steps e), f), g) and h) are carried out repeatedly during the (ongoing) magnetic resonance measurement. [10] Magnetic resonance apparatus adapted to carry out a method according to any one of the preceding claims. [11] Computer program product comprising a program and being directly loadable into a memory of a programmable system control unit of a magnetic resonance apparatus, with program means for carrying out 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 apparatus.

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