Method and system for providing position information of an object

Abstract

Method for providing position information of an object (31) in a patient tunnel (14) of a magnetic resonance imaging (MRI) scanner (100), comprising: positioning (40) the object (31) outside the patient tunnel (14); moving (41) the object (31) into the patient tunnel (14) along an axis of symmetry of a B0 field magnet (12) of the MRI scanner (100); acquiring (42) a magnetic resonance signal for a predefined slice (32) during the movement of the object (31) into the patient tunnel (14); determining (43) the position information of the object (31) based on the acquired magnetic resonance signal.

Description

[0001] The present invention relates to a method and a system for providing position information of an object in a patient tunnel of a magnetic resonance imaging scanner, a system for providing such position information and a corresponding computer program element.

[0002] Magnetic resonance imaging (MRI) scanners are imaging devices that use a strong external magnetic field to align the nuclear spins of a sample and then stimulate them to precess around this alignment using an alternating magnetic field. The precession, or return of the spins from this excited state to a lower-energy state, in turn generates an alternating magnetic field that can be received by antennas. Using magnetic gradient fields, a spatial encoding can be applied to the signals, allowing the received signal to be assigned to a volume element. The received signal is then processed, and a three-dimensional image of the sample is generated.

[0003] During magnetic resonance imaging (MRI), the radiofrequency fields used can cause the patient to heat up. To ensure patient safety, limits have been established for the specific absorption rate (SAR), particularly for the head, the exposed body, and the whole body. To monitor these limits, models have been developed that can allocate the absorbed power to different parts of the patient's body. For example, a cylindrical model is known to be used, in which the patient's anatomy can be approximated using cylinders for the head, torso, and legs, and the absorbed power for each cylinder can be calculated or estimated for a homogeneous magnetic field.For the most accurate modeling possible, it is necessary to know the positions of body parts, especially the head, of a patient in relation to the isocenter of the magnetic resonance imaging (MRI) scanner. For example, to determine a patient's head position, it is known to measure it manually. This head position is measured in relation to a patient table, the position of which is known and on which the patient lies.

[0004] In this context, it has become apparent that there is a further need to provide a method and a system with which positional information of an object, in particular the head position of a patient, can be provided in a patient tunnel of a magnetic resonance imaging scanner.

[0005] In the publications KOKEN P. [et al.]: Towards Automatic Patient Positioning and Scan Planning Using Continuously Moving Table Imaging. Proc. Intl. Soc. Mag. Reson. Med. 16 (2008) 971 and KOKEN P. [et al.]: Towards Automatic Patient Positioning and Scan Planning Using Continuously Moving Table MR Imaging. In: Magnetic Resonance in Medicine, Vol. 62, 2009, p. 1067-1072, a method for the automatic positioning of a patient using continuous imaging while moving a patient table is disclosed.

[0006] It is an object of the present invention to provide a method and a system with which position information of an object, in particular a head position of a patient, can be provided in a patient tunnel of a magnetic resonance tomograph.

[0007] These and other problems, which will be mentioned in the following description or which may be recognized by a person skilled in the art, are solved by the subject matter of the independent claims. The dependent claims further develop the central idea of ​​the present invention in a particularly advantageous manner.

[0008] According to the invention, a method for providing position information of an object in a patient tunnel of a magnetic resonance imaging scanner is provided, comprising: Positioning the object outside the patient tunnel; Moving the object into the patient tunnel, along an axis of symmetry of a B0 field magnet of the magnetic resonance imaging scanner; Acquiring a magnetic resonance signal for a predefined layer while the object is moving into the patient tunnel; Determining the object's position information based on the captured magnetic resonance signal.

[0009] In other words, the present invention proposes using a magnetic resonance imaging (MRI) scanner to acquire signals in a predefined slice during the movement of the object into the patient tunnel. This allows the system to determine when the object reaches the predefined slice during this movement, since a strong MRI signal is only detected once the object has moved into the predefined slice. As soon as the object can be detected in the predefined slice, it is known that the object is located at the position of the predefined slice, and its position relative to the axis of symmetry of the B0 field magnet can then be determined. This procedure can be used, for example, to determine the head position of a patient when the patient is moved into the patient tunnel in a so-called head-down position.A head-first position means that the patient is moved headfirst into the patient tunnel. In such a case, a strong magnetic resonance signal is generated as soon as the head reaches the predefined slice. If, on the other hand, the patient is moved feet-first into the patient tunnel, a so-called "feet-first" arrangement, the foot position can be determined accordingly. Additionally, the head position can also be determined in a "feet-first" arrangement by detecting when, or at what position, no magnetic resonance signal can be detected. In other words, when the patient's body moves out of the predefined slice. Since the proposed method essentially provides a profile of a patient during entry into the tunnel, the positions or areas of other body parts can also be determined.In this regard, it is only necessary to further evaluate the magnetic resonance signal and, in particular, to correlate / align it with the patient's body shape.

[0010] The proposed procedure allows, in particular, the determination of a patient's head and / or foot position. These positions can then be used to model the specific absorption rates. This enables a comparatively accurate modeling of the specific absorption rates, regardless of whether a patient is correctly positioned on the examination table and also independent of potential measurement errors during manual measurement of a patient's head or foot position. Furthermore, the proposed procedure can be integrated relatively easily into standard workflows during a patient examination, since the examination table on which the patient is positioned is typically moved into the patient tunnel at the beginning of the examination anyway.The proposed procedure can be carried out during this movement of the patient table, so that the examination time is not increased, or not significantly increased.

[0011] The term "patient tunnel" is to be understood broadly in this context. In particular, it refers to the interior of the "tube" typical of most magnetic resonance imaging (MRI) scanners, but it can also refer to the sensitive area suitable for imaging within any type of MRI scanner.

[0012] The term "object" is to be understood broadly in this context. In particular, an object is understood to be a human or animal body or a part thereof. An object can be, for example, a patient's head, a patient's feet, and / or any identifiable / distinguishable part of a patient's body, such as the neck, knees, or the like.

[0013] The term "positional information" for an object is to be understood broadly here and can be specified, for example, by a point on the Z-coordinate axis or as a range on the Z-coordinate axis. For instance, the positional information could be the beginning of a patient's head on the Z-coordinate axis. Alternatively or additionally, a range within which the patient's head is located can be specified, with a Z-coordinate for the beginning of the head and a Z-coordinate for the end of the head. The end of a patient's head could, for example, be determined by detecting a neck region where the magnetic resonance signal typically begins to decline.

[0014] The term "arranging the object" is to be understood broadly in this context and includes, in particular, positioning a patient on a patient table. Moving the object into the patient tunnel preferably occurs through a continuous movement of the patient table into the patient tunnel, although non-continuous movements are also included in this context.

[0015] Spatial coding is typically based on an XYZ coordinate system. The Z-axis is usually defined, as in this case, as the axis of symmetry of a B0 field magnet of the magnetic resonance imaging (MRI) scanner, passing through a patient tunnel of the B0 field magnet in the preferred direction of the B0 field. In the standard MRI scanner setup, the Z-axis is horizontally oriented and runs centrally through the opening of the B0 field magnet's windings and through an acquisition area of ​​the B0 field magnet. The object being scanned is usually positioned parallel to the Z-axis on a movable patient table within the patient tunnel. Together with the Z-axis, an X-axis and a Y-axis define a space, with the coordinate axes preferably being orthogonal to each other, and the X-axis being horizontally oriented and the Y-axis vertically oriented.

[0016] Preferably, during a sequence for acquiring the magnetic resonance signal for the predefined layer, or during the execution of the disclosed method, no gradients are switched in the layer plane, i.e., in the plane perpendicular to the layer selection direction. "Gradients" here refers in particular to a linear gradient field that can be added for spatial coding. Specifically, no readout gradients or phase-coding gradients are switched. These gradients are also referred to below as X- and Y-gradients, respectively, since in preferred embodiments they are aligned at least approximately along the X- and Y-coordinate axes (or vice versa). Thus, only a one-dimensional (1D) data set is acquired from the layer at any given time, as no spatial coding takes place within the layer.Since only 1D spatial information in the Z-coordinate axes is required, the X and Y gradients can remain deactivated; that is, they do not need to be used for this method. This avoids the noise associated with X and Y gradient switching. Furthermore, fewer or no currents are induced in the object, so the method does not result in any additional SAR (Signal Acceleration Ratio). Signal noise from X and Y gradient switching is also avoided.

[0017] Preferably, the Z-gradient switching of the magnetic resonance imaging (MRI) scanner is performed for a predefined duration with a constant amplitude, wherein the amplitude is preferably between 1 and 4 mT / m, particularly preferably between 1.5 and 3 mT / m, and most preferably between 2.0 and 2.5 mT / m. Preferably, the Z-gradient is set to a constant amplitude for the entire duration of the sequence. This eliminates the need for further Z-gradient switching in the present method after a constant Z-amplitude has been applied, thus preventing signal noise and the associated noise pollution from switching.

[0018] Preferably, the object is moved into the patient tunnel at a speed between 0.5 cm / s and 5 cm / s, more preferably at a speed between 1.0 cm / s and 3.5 cm / s, and particularly preferably at a speed of 2.0 cm / s. Preferably, the object is placed on a patient table that can be moved into the patient tunnel. Moving the object into the patient tunnel at such a speed can be achieved, in particular, by a corresponding control of an actuating mechanism of the patient table.

[0019] Preferably, the predefined layer is at least substantially transverse and selected to be at least substantially orthogonal to the object's direction of movement. "At least substantially" here means, in particular, that the layer's orientation can deviate from the transverse or orthogonal plane by up to ±10°, preferably up to ±5°. A transverse layer can preferably be excited by applying a high-frequency pulse while simultaneously switching on a Z-gradient. The layer selection gradient can also include slight X- and / or Y-gradients.

[0020] The predefined layer is preferably located centrally, i.e., at Z=0, because the B0 magnetic field is particularly homogeneous at this position, resulting in a particularly flat layer. However, the position can deviate from this; for example, the layer can be located between Z=-20 cm and Z=+20 cm. Positioning the layer at the edge of the sensitive area allows for detection when the object enters this area. The layer thickness can be, for example, between 2 mm and 2 cm. Since the sequence only serves to detect the presence of an object, the layer thickness is not critical. The layer thickness can be selected, in particular, to minimize the energy required for the high-frequency excitation. The layer thickness is preferably chosen to be between approximately 2 and 20 mm, more preferably between approximately 5 and 15 mm, and most preferably approximately 10 mm.

[0021] Preferably, a radiofrequency excitation with only one radiofrequency pulse is performed per repetition time (TR). In other words, preferably only a single radiofrequency pulse is used per repetition time. This radiofrequency pulse can be chosen to be comparatively weak, so that the radiofrequency power is negligible with regard to patient heating, and the specific absorption rates therefore do not need to be monitored for the implementation of the present method. For example, the radiofrequency pulse can have a relatively small bandwidth. Preferably, however, the phase of the radiofrequency pulse varies from TR to TR.

[0022] The sequence for acquiring the magnetic resonance signal can be very simple, e.g. one radio frequency pulse per repetition time (TR), followed by an acquisition window (TA).

[0023] Preferably, the acquisition window (TA) is between approximately 2 and 15 ms, preferably between approximately 3 and 10 ms, and most preferably is approximately 4 ms. The repetition time (TR) is preferably between 500 ms and 2000 ms, more preferably between 800 ms and 1500 ms, and most preferably is approximately 1000 ms.

[0024] As already explained above, the position information can indicate the beginning or end of the object along the axis of symmetry of the B0 field magnet of the magnetic resonance imaging scanner. However, the present disclosure is not limited to this. Preferably, the object is a patient's head or foot, and the position information indicates the head and / or foot position of the patient, preferably the beginning or end of the head or foot along the Z-coordinate axis.

[0025] A preferred application of the present method is the determination of a patient's head position in order to provide the most accurate possible (cylindrical) model of the patient, thus enabling the monitoring of the respective limits for absorbed power. However, the present invention is not limited to this application. Rather, the positional data determined by the present invention can also be used for other applications where the position of a patient's anatomy is required. For example, consistency checks can also be performed using the determined positional data and corresponding data processing steps. It can be determined, for instance, whether a patient's profile corresponds to typical human anatomy.

[0026] Preferably, the object's position information is determined or converted in relation to the patient table so that this position information can be easily used to control the patient table. Typically, an additional XYZ coordinate system is introduced for this purpose, aligned with the patient table. For example, the Z-axis is aligned along the longitudinal axis of the patient table, the X-axis is preferably horizontal, and the Y-axis is preferably vertical, with the coordinate axes being orthogonal to each other. Such a patient table-aligned coordinate system is also known in practice as a "Table Coordinate System" (TCS).

[0027] The present invention further relates to a system for providing positional information of an object in a patient tunnel of a magnetic resonance imaging (MRI) scanner, comprising: a processing circuit; a storage medium; and a data interface; wherein the storage medium comprises a computer program with instructions which, when the program is executed, cause the processing circuit to perform the method described above, wherein the data interface is configured to receive the magnetic resonance signal for a central transverse layer of the object. The above descriptions of the disclosed method apply accordingly to the system.

[0028] Furthermore, the present invention relates to a computer program element with instructions that, when executed on data processing equipment of a data processing environment, are set up to perform the steps of the above-mentioned method in a above-mentioned system.

[0029] All embodiments described herein can be combined with one another, unless explicitly stated otherwise. Further features, advantages, and applications of the present invention will become apparent from the following description, the exemplary embodiment, and the figures. These show: Fig. 1 a conventional magnetic resonance imaging (MRI) machine; Fig. Figure 2 shows a schematic representation of a system according to the invention for providing position information of an object in a patient tunnel of a magnetic resonance device; Fig. Figure 3 shows a schematic representation of a method according to the invention for providing position information of an object in a patient tunnel of a magnetic resonance device; Fig. Figure 4 shows a schematic representation of a patient on a patient table; Fig. Figure 5 shows a schematic representation of a patient on a patient table; Fig. Figure 6 shows exemplary different sequence parameters that can be used to carry out a method according to the invention, and Fig. Figure 7 shows an example of a recorded magnetic resonance signal.

[0030] In Fig. Figure 1 shows a conventional magnetic resonance imaging (MRI) device. The MRI device comprises a field generation unit 11, which has a main magnet 12 (B0 magnet) with one or more permanent magnets, electromagnets, or superconducting magnets for generating a strong and, in particular, homogeneous main magnetic field 13 (B0 magnetic field). The MRI device 1 also includes a patient tunnel 14 for imaging a patient 15. In the illustrated embodiment, the patient tunnel 14 is cylindrical and enclosed in one circumferential direction by the main magnet 12. However, other configurations of the patient tunnel 14 are also conceivable. The patient tunnel 14 can essentially correspond to an image acquisition area of ​​the MRI device 1.

[0031] In the Fig. In the example shown, patient 15 can be positioned in the patient tunnel 14 using a patient positioning device 16 of the magnetic resonance imaging (MRI) device 1. The patient positioning device 16 has a horizontally movable patient table 17 for this purpose.

[0032] The field generation unit 11 comprises a gradient system with at least one gradient coil 18 for generating a magnetic gradient field, which is used for spatial encoding during a magnetic resonance imaging (MRI) scan. The gradient coil 18 is controlled by a gradient control unit 19 of the MRI scanner 1. It is conceivable that the gradient system includes several gradient coils 18 for generating magnetic gradient fields along different spatial directions, preferably orthogonal to each other.

[0033] The field generation unit 11 also comprises a high-frequency system with a high-frequency coil, which in the present embodiment is designed as a body coil 20 permanently integrated into the magnetic resonance imaging (MRI) device 1. The body coil 20 is designed to excite nuclear spins located in the main magnetic field 13 generated by the main magnet 12. The body coil 20 is controlled by a high-frequency control unit 21 of the MRI device 1 and emits high-frequency excitation pulses into the image acquisition area, which is essentially formed by the patient acquisition area 14 of the MRI device 1. The body coil 20 can also be configured to receive magnetic resonance signals and form a receiving unit or part of a receiving unit of the MRI device 1.

[0034] The magnetic resonance imaging (MRI) device 1 includes a control unit 22 for controlling the MRI device 1, in particular the gradient control unit 19 and the radio frequency control unit 21. The control unit 22 is specifically designed to coordinate the execution of an imaging sequence, such as a GRE (radiant echo) sequence, a TSE (turbo spin echo) sequence, or a UTE (ultra-short echo time) sequence. Furthermore, the control unit 22 comprises a processing unit 28 for evaluating magnetic resonance signals acquired during an MRI scan with an imaging sequence.

[0035] The magnetic resonance imaging (MRI) device 1 can include a user interface 23, which has a signal connection to the control unit 22. Control information, such as imaging parameters of the MRI scan, can be displayed on a display unit 24, for example, on at least one monitor, of the user interface 23. The display unit 24 can be designed, in particular, to provide a graphical user interface displaying a relevant body region of the patient 15. Furthermore, the user interface 23 includes an input unit 25, by means of which parameters of a MRI scan can be entered or changed by a user.

[0036] The magnetic resonance device 1 may include further components, such as a local coil 26. The local coil 26 may be positioned in an application-appropriate position on a diagnostically or therapeutically relevant body region of the patient 15. The local coil 26 preferably has a plurality of antenna elements configured to detect magnetic resonance signals from the relevant body region of the patient 15 and transmit them to the processing unit 28 and / or the control unit 22. For this purpose, the local coil may be connected to the high-frequency control unit 21 and the control unit 22 by means of an electrical connecting cable 27 or another signal connection. Analogous to the body coil 20, the local coil 26 may also be configured to excite nuclear spins in the jaw region 31 of the patient 15. The local coil 26 may be controlled for this purpose by the high-frequency control unit 21.

[0037] Typically, the field generation unit 11 and a magnet holding structure are enclosed by a housing 30. The housing 30 can be designed to protect components of the magnetic resonance device 1 from external influences and / or to provide touch protection for a patient 15.

[0038] Fig. Figure 2 shows an embodiment of a system 50 according to the invention for providing position information of an object 31 in a patient tunnel 14 of a magnetic resonance imaging (MRI) scanner 100. The system 50 comprises a processing circuit 60, a storage medium 70, and a data interface 80. The storage medium 70 comprises a computer program with instructions which, when the program is executed, cause the processing circuit 60 to perform a method according to the invention, wherein the data interface 80 is configured to receive the magnetic resonance signal for a predefined layer, preferably a central transverse layer selected orthogonal to the direction of movement of the object 31, during the movement of the object 31 into the patient tunnel 14.

[0039] Fig. Figure 3 shows a schematic representation of a method for providing position information of an object 31 in a patient tunnel 14 of a magnetic resonance tomograph 100.

[0040] In a first step 40, a patient 15 is positioned outside the patient tunnel 14, for example on a Fig. 1 shown patient positioning device 16 with a movable patient table 17. Such an arrangement of a patient 15 on a patient table 17 is in Fig. Figure 4 shows the embodiment shown. In the illustrated embodiment, the position of the patient's head 31 is to be determined, for example, by the initial position of the head 31 along the Z-axis in the direction of entry. This represents a preferred application of the disclosed method. Knowing the position of the patient's head 31 allows for the creation of a comparatively accurate (cylindrical) model of the patient 15, which can then be used to monitor the respective limits for the absorbed power. The patient table 17 is movably mounted along the Z-axis, so that the patient 15 can be moved into the patient tunnel 14 in a single step 41 along with the movement of the patient table 17. In the illustrated embodiment, the patient table 17, and thus the patient 15, is moved into the patient tunnel 14 at a speed of 2.0 cm / s.

[0041] In a further step 42, a magnetic resonance signal for a predefined layer 32 is acquired during the movement of the patient 15 and his head 31 into the patient tunnel 14. As in the Fig. 4 and Fig. As shown in Figure 5, the predefined layer 32 is preferably a central transverse layer 32, which is chosen orthogonal to the direction of movement of the patient 15.

[0042] The preferred sequence parameters are in Fig. Figure 6 is shown only as an example. The present invention is not limited to this.

[0043] The Z-gradient (see GS GRZ) of the magnetic resonance imaging scanner 100 is set to a constant amplitude of approximately -2.3 T. The X-gradient (see GF GRX) and the Y-gradient (see GP GRY) are not switched.

[0044] The acquisition window (see ADC) is approximately 4 ms. In the preferred embodiment, the repetition time (TR) is approximately 1000 ms. Thus, with an entry speed of 2 cm / s of the patient 15 into the patient tunnel 14 and a repetition time (TR) of 1 s, the position of the patient 15's head 31 can be determined with an accuracy of 1 cm. It has been found that such accuracy is sufficient to provide a comparatively accurate (cylindrical) model of the patient 15. The sequence parameters mentioned here as examples, as well as the speed at which the patient 15 is moved into the patient tunnel 14, can be adjusted accordingly to provide different accuracies in position determination.

[0045] As in Fig. As shown in Figure 6, high-frequency excitation is achieved with only a single high-frequency pulse (see RFD). This high-frequency pulse can be chosen to be comparatively high, so that the high-frequency power is negligible with regard to patient heating, and the specific absorption rates therefore do not need to be monitored for the implementation of the present procedure.

[0046] In Fig. Figure 7 shows an example of a magnetic resonance signal that was generated during the entry of the vehicle into the Fig. 4 and Fig.The magnetic resonance signal of patient 15, shown in Figure 5, was acquired in patient tunnel 14 for the central transverse slice 32. The Y-axis represents the magnetic resonance signal normalized to 1 for the central transverse slice 32, and the Z-axis represents the Z-coordinate in the table coordinate system (TCS) aligned with the patient table. As can be seen from the acquired magnetic resonance signal, no magnetic resonance signal is detected for the range from Z = -40 cm to Z = -30 cm; a magnetic resonance signal can only be detected from Z = -30 cm onwards. After patient 15 was moved into patient tunnel 14 in the head-down position, i.e., with his head 31 leading, the increase in the magnetic resonance signal at Z = -30 cm represents the head position of patient 15. Thus, in step 43, the position of the head 31, here indicated by the beginning of the head 31, can be determined based on the recorded magnetic resonance signal.If the sole purpose is to determine the head position of patient 15 in order to model specific absorption rates, the procedure could essentially end at coordinate Z = -30 cm. Alternatively or additionally, the complete profile of patient 15 can be recorded, for example, to determine the positions of other body parts / areas of patient 15, to perform consistency checks if necessary, or to make volume estimates or similar calculations based on such a patient profile.

[0047] The present invention is not limited to the embodiment described above, as long as it is encompassed by the subject matter of the following claims. It should be further noted that the terms "comprising" and "comprising" do not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude a plurality. It should also be noted that features or steps described with reference to the embodiments above may also be used in combination with other features.

[0048] Furthermore, it should be noted that regardless of the grammatical gender of a particular term, persons with male, female or other gender identities are included.

Claims

[1] Method for providing position information of an object (31) in a patient tunnel (14) of a magnetic resonance imaging scanner (100), comprising: Positioning (40) the object (31) outside the patient tunnel (14); Moving (41) the object (31) into the patient tunnel (14), along an axis of symmetry of a B0 field magnet (12) of the magnetic resonance imaging scanner (100); Acquisition (42) of a magnetic resonance signal for a predefined layer (32) during the movement of the object (31) into the patient tunnel (14), wherein no switching of gradients in the layer plane is performed during a sequence for acquiring the magnetic resonance signal for the predefined layer; Determine (43) the position information of the object (31) based on the acquired magnetic resonance signal. [2] Method according to claim 1, wherein during a sequence for acquiring the magnetic resonance signal for the predefined slice a slice selection gradient of the magnetic resonance tomograph (100) is applied for a predefined duration with a constant amplitude, wherein the amplitude is preferably between 1 and 4 mT / m, particularly preferably between 1.5 and 3 mT / m and particularly preferably between 2.0 and 2.5 mT / m, and wherein the predefined duration is preferably at least one repetition time of the sequence and preferably the entire duration of the sequence. [3] Method according to one of the preceding claims, wherein the movement (41) of the object (31) into the patient tunnel (14) is carried out at a speed between 0.5 cm / s and 5 cm / s, preferably at a speed between 1.0 cm / s and 3.5 cm / s and particularly preferably at a speed of 2.0 cm / s. [4] Method according to any of the preceding claims, wherein the predefined layer (32) is an at least substantially transverse layer (32) which is selected at least substantially orthogonal to the direction of movement of the object (31). [5] Method according to one of the preceding claims, wherein the predefined layer (32) has a layer thickness between 2 and 20 mm, particularly preferably between 5 and 15 mm, particularly 10 mm. [6] Method according to one of the preceding claims, wherein a high-frequency excitation with only one high-frequency pulse is performed for each repetition time (TR). [7] Method according to any of the preceding claims, wherein the acquisition window (TA) is between 2 and 15 ms, preferably between 3 and 10 ms and particularly preferably 4 ms. [8] Method according to any of the preceding claims, wherein the repetition time (TR) is between 500 ms and 2000 ms, preferably between 800 ms and 1500 ms and most preferably 1000 ms. [9] Method according to one of the preceding claims, wherein the position information indicates the beginning or the end of the object (31) along the axis of symmetry of the B0 field magnet (12) of the magnetic resonance tomograph (100). [10] Method according to any of the preceding claims, wherein the object (31) is a head (31) or a foot of a patient (15) and the position information indicates the head or foot position of the patient (15), preferably the beginning or the end of the head (31) or the foot along the axis of symmetry of the B0 field magnet (12) of the magnetic resonance imaging scanner (100). [11] Method according to any of the preceding claims, wherein the position information of the object (31) is determined in relation to a patient table (17). [12] System (50) for providing position information of an object (31) in a patient tunnel (14) of a magnetic resonance imaging scanner (100), comprising: a processing circuit (60); a storage medium (70); and a data interface (80); wherein the storage medium (70) comprises a computer program with instructions which, When the program is executed, the processing circuit (60) is caused to execute the method according to one of claims 1 to 11, wherein the data interface (80) is set up to receive the magnetic resonance signal for a predefined layer during the movement of the object (31) into the patient tunnel (14). [13] Computer program element comprising instructions that, when executed on computer equipment in a computer environment, are configured to perform the steps of the method according to any one of claims 1 to 11 in a system according to claim 12.

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