Methods for operating a magnetic resonance imaging (MRI) device, the MRI device, computer programs, and electronically readable data carriers

Abstract

The local coil device (5) for use on the examination table (1) has a magnetic field sensor (6) for measuring the main magnetic field of the magnetic resonance device (16) so as to determine the position information of the local coil device (5) by aligning with the main magnetic field map, wherein the method according to the invention is performed in order to check whether the function of the magnetic resonance sensor is correct.

Description

Technical Field

[0001] This invention relates to a method for operating a magnetic resonance imaging (MRI) device, the MRI device comprising:

[0002] - A main magnet unit, the main magnet unit having a main magnet for generating a main magnetic field and, in particular, a cylindrical patient receiving portion, wherein the field lines of the main magnetic field in a homogeneous volume within the patient receiving portion extend in the field direction.

[0003] - An examination bed for moving a patient into a patient receiving area along the z-direction corresponding to the longitudinal direction of the examination bed, wherein the examination bed is associated with a position determining device for determining the bed position along the z-direction.

[0004] - At least one local coil device for placement on a patient and / or examination bed, wherein the local coil device has a magnetic field sensor, particularly a Hall sensor, for measuring the magnetic field strength of at least the main magnetic field, and

[0005] - A control device configured to obtain first position information describing a first measurement position of a local coil device by aligning a first measurement value of a magnetic field sensor with a main magnetic field map at least outside the patient receiving area.

[0006] Furthermore, the present invention relates to a magnetic resonance device, a computer program, and an electronically readable data carrier. Background Technology

[0007] In magnetic resonance imaging (MRI), local coil devices with at least one local coil element that can be used for transmitting and / or receiving are also frequently used. These local coil devices can be freely positioned on the examination table and / or directly on the patient already placed on the examination table. A challenge is subsequently moving the examination table into the patient housing of the MRI apparatus such that the local coil device is positioned at the isocenter. The isocenter can be defined, for example, as the center of the patient housing and / or the center of the homogeneous volume (the two locations often coincide). The examination table is typically moved in a direction corresponding to its longitudinal direction, which may be referred to as the z-direction. In a cylindrical patient housing, the longitudinal direction of the examination table typically corresponds to the field direction of the main magnetic field in the homogeneous volume.

[0008] To achieve the most precise positioning possible in the local coil device, laser positioning devices have been proposed in the prior art. This involves, for example, first adjusting the inspection bed with the local coil device so that a laser mark indicates what should be placed at the isocenter, and then automatically moving the bed to place the marked point at the isocenter. For example, the marking laser can be externally fixed to the main magnet unit at a fixed position so that the distance from the isocenter in the z-direction is known. However, marking lasers with variable positions have also been proposed. These positioning methods have proven to be extremely costly.

[0009] Therefore, a method for using a magnetic field sensor as part of a local coil device is also proposed in the prior art. This magnetic field sensor measures a main magnetic field (B0 field), which here also includes stray fields outside the patient housing, at least measuring its magnetic field strength (preferably three-dimensionally, i.e., based on measurements in three mutually orthogonal directions). Outside the patient housing, i.e., where the local coil device is positioned at the patient, the main magnetic field has a characteristic variation curve that particularly allows for one-to-one correlation. This means that the location of the local coil device, at least in the z-direction, can be inferred from the measurements of the magnetic field sensor, especially in three dimensions, using the main magnetic field map (B0 map). This location information can be easily translated into a suitable movement path for the examination bed to place the local coil device at an isocenter (typically in the case of z=0). The determination of the location of the local coil device using such a magnetic field strength sensor is described in more detail, for example, in DE 10 2016 203 255A1.

[0010] For this purpose, it is known, for example, that a schematic diagram of at least the examination bed and the local coil device disposed thereon is displayed on a touchscreen, particularly at the main magnet unit adjacent to the patient receiving area. The operator can then select the local coil device with a simple click, which is then automatically placed in the isocenter (“Push-Button”, also known as “Select and Go”). This allows for significantly faster and more comfortable positioning.

[0011] Hall sensors, preferably three-dimensional Hall sensors, are typically used here as magnetic field sensors. Like any other electronic component, magnetic field sensors have a limited lifespan and may, over time, provide measurements that deviate from actual values ​​or even cease to function correctly altogether. It is known that if an MRI device exhibits erroneous behavior in its positioning, the user of the MRI device notifies after-sales service / repair technicians. These technicians perform a quality assurance diagnostic of the coil assembly and, based on the results, determine whether the coil assembly must be replaced, whether repair is feasible, etc. The problem here is that this results in a relatively large time loss and expense for the user of the MRI device. Summary of the Invention

[0012] Therefore, the purpose of this invention is to provide a feasibility for identifying changes in the measurement behavior of a magnetic field sensor, thereby enabling early maintenance.

[0013] According to the invention, the objective is achieved by a method, particularly computer-implemented, a magnetic resonance apparatus, a computer program, and an electronically readable data carrier. Advantageous improvements are described below.

[0014] According to the present invention, in order to monitor the correct operation of a magnetic field sensor, the method of the type mentioned at the beginning has the following steps:

[0015] - In the case of the first bed position of the examination bed, record the first measurement value of the magnetic field sensor at the first measurement position of the local coil device outside the patient receiving area, and obtain the first position information.

[0016] - In the case of the second bed position of the examination bed, during or after the examination bed has traveled into the patient receiving area, the second measurement value of the magnetic field sensor is recorded at the second measurement position of the local coil device, which is different from the first measurement position and is particularly located within the patient receiving area.

[0017] - Obtain at least one reference value describing the expected main magnetic field at the second measurement position, and determine the second measurement position from first position information and the movement path of the examination bed between the first bed position and the second bed position using a position determining device.

[0018] - Error messages indicating potential measurement errors are obtained by comparing a second measurement with a reference value.

[0019] This invention enables proactive error detection and triggering of corresponding measures, such as providing prompts to customers, preferably along with corresponding action recommendations, instead of reacting to errors. Here, the invention utilizes the inherent mechanism of the magnetic resonance imaging (MRI) device, for example, to implement a "button" function, and particularly leverages the feasibility of accurately determining the position of the examination bed at any time using a position-finding device. Specifically, the position of the examination bed is continuously tracked in a manner known in the prior art within the control device of the MRI device. It has now been determined that a single additional measurement using a magnetic field sensor, especially a Hall effect sensor, is sufficient to check the functionality of the magnetic field sensor.

[0020] Because it is feasible to use a magnetic field sensor to measure the main magnetic field at at least two different locations relative to the center (isocenter) of the magnet, since the local coil device moves with the examination bed. After placing the local coil device in the first measurement position, a first measurement of the main magnetic field is always performed to obtain first position information from the corresponding first measurement value of the main magnetic field, thereby also determining where the magnetic field sensor (first measurement position) and thus the local coil device are located on the examination bed, at least in the z-direction. The location of the local coil device can be determined in this manner as long as the examination bed is outside the patient receiving section (hole) (first measurement position). The local coil device can be used for corresponding functions, especially the "button" function described at the beginning, as is common practice.

[0021] It is now proposed that a second measurement of the main magnetic field be performed at the second measurement position, particularly at the position where the local coil device or magnetic field sensor is located after the examination bed has finished its journey along the z-direction into the patient receiving area. This recording of the second measurement value at the second measurement position, particularly at the end of the journey of the examination bed into the patient receiving area, can be performed quickly and without problems, even if the recording is not necessary for actual functionality, such as a "button".

[0022] There exists a large spatial distance, for example, between 0.3m and 2.2m, between the two measurements of the main magnetic field. This distance causes a significant difference between the first and second measurements. If the magnetic field sensor is functioning correctly, the expected measurement value (reference value) at the second measurement position can be predicted from the first measurement by obtaining the first position information along with the movement path of the examination bed (which can be obtained by the position-finding device through the difference between the second and first bed positions). If the expected, i.e., reference value, is now compared with the second measurement value, which is the result of the second measurement of the main magnetic field, it can be deduced whether the magnetic field sensor is functioning correctly, as described by the error message. The error message can then be evaluated by at least one mitigation condition to determine whether mitigation is necessary.

[0023] Particularly advantageously, the function check of the magnetic field sensor can be performed whenever the position recognition of the local coil device is activated and travel of the inspection bed occurs, providing a first measurement position and at least one second measurement position, thereby allowing for the retrieval of error information. Therefore, permanent checks on the functionality and quality of the magnetic field sensor and proactive action in case of errors are feasible. No dedicated quality assurance steps are required in the service software.

[0024] Therefore, it can be said that, in general, potential malfunctions of magnetic field sensors can be identified much earlier. Instructions, especially action recommendations, can be proactively provided to users very early on. Thus, users can actively participate before they inevitably become frustrated by problems.

[0025] Preferably, a three-dimensional magnetic field sensor, especially a 3D Hall sensor, is used as the magnetic field sensor (also known as a magnetic field strength sensor). Significantly better, more robust, and one-to-one position correlation is possible when measuring the main magnetic field in three dimensions. In particular, measurements taken from three orthogonal directions are used to determine the magnetic field strength (also known as the B0 value).

[0026] Here, the first measurement value is recorded while the coil device is still outside the patient receiving area, particularly at least outside the homogeneous volume. Therefore, it is feasible to determine the first measurement position from the first measurement value using the main magnetic field map. Furthermore, a difference exists between the first and second measurement values ​​during examination bed movement. The corresponding first bed position is also called "Close to Home," and can be, for example, defined as the depth to which the front end of the examination bed extends into the patient receiving area does not exceed 30 cm. Therefore, the first measurement value, first position information, and first bed position are determined at the first measurement position.

[0027] If the examination bed has been moved into the patient receiving area, specifically if the front end of the examination bed is more than 50 cm deep within the patient receiving area, a second measurement of the main magnetic field is performed, and the second measurement value is recorded using a magnetic field sensor. Therefore, the second measurement value and the second bed position are determined at the second measurement location.

[0028] Therefore, the movement segment of the inspection bed in the z direction is obtained as the difference between the second bed position and the first bed position, and the second measurement position (assuming the first position information is correct, then the second measurement position is equal to the expected position of the coil device after the inspection bed has traveled) is then obtained as the sum of the first measurement position and the movement segment based on the first position information.

[0029] To check whether the magnetic field sensor is working correctly, a reference value is now obtained for the second measurement position, and it is checked whether the deviation between the second measurement value and the reference value is small enough.

[0030] There are several possibilities for correctly obtaining reference values, including obtaining multiple reference values ​​and performing multiple comparisons to achieve the most robust basis for the measures and the most accurate logging if such logging is performed.

[0031] An improved embodiment of the invention, which achieves its objective, proposes obtaining a first reference value from at least one reference value in the main magnetic field diagram at the determined second measurement position. This means that, for this first reference value, a comparison with the calibration of the main magnetic field diagram, which is generally extremely reliable and can generally be considered error-free in principle, is necessary.

[0032] It should be noted here that changes may also occur at the main magnetic field due to various effects, such as the presence of the object being examined and / or other objects, the lifespan of the magnetic resonance apparatus, and / or changes in the environment. This change in the main magnetic field is often referred to as B0 drift. To detect these changes in the main magnetic field, it is known in the art, particularly by means of simple magnetic resonance measurements, periodically, for example, for each magnetic resonance measurement to be performed, using the current magnetic resonance frequency, i.e., the homogeneous volume... The Larmor frequency in the main magnetic field is determined as the calibration frequency, from which the strength of the main magnetic field in the homogeneous volume can be obtained by means of the gyromagnetic ratio. To account for the influence of a drifting main magnetic field on the main magnetic field diagram, and thus avoid errors in utilizing the function of the main magnetic field diagram, it is known to adjust, and thus correct, the main magnetic field diagram, for example, by shifting an absolute or relative change to a position outside the homogeneous volume. Within the scope of the invention, it is also preferred to correct the main magnetic field diagram before its use according to the current calibration frequency measured by magnetic resonance measurement, which in particular corresponds to the magnetic resonance frequency (the Larmor frequency in the homogeneous volume). As a magnetic resonance measurement, for example, an FID measurement (Free Induction Decay) can be performed, as is known in principle.

[0033] In the case of a second measurement location within a homogeneous volume, it is desirable, preferably additionally, to derive at least one second reference value from either the current calibration frequency measured by magnetic resonance measurement or the current calibration frequency, which corresponds to the magnetic resonance frequency within the homogeneous volume. If it is known that the magnetic field sensor is within the homogeneous volume during the second measurement, the second reference value can be readily derived from the current calibration frequency and the gyromagnetic ratio. Therefore, it is known very precisely within the homogeneous volume which B0 value the second measurement of the main magnetic field should provide, especially regardless of the corrections to the main magnetic field diagram discussed above due to calibration frequencies outside the homogeneous volume.

[0034] In this regard, it should also be noted that the second measurement in a homogeneous volume is particularly preferred as follows: even in the case of a small positional deviation, for example due to an erroneous measurement of the first measurement, the expected field strength of the main magnetic field remains the same, thereby allowing for particularly good evaluation of the deviation.

[0035] Particularly advantageously, at least in the case of a second measurement location within a homogeneous volume, both the first and second reference values ​​can be used for evaluation and form the basis for comparison. This results in more robust checks and additional information for evaluating potential error states and their development over time. Here, a distinction can be made, for example, that only the first reference value is used outside the homogeneous volume, while within the homogeneous volume, comparisons are made not only with the first reference value but also with the second reference value. Regarding the additional information, it has been shown, for example, that comparison with the second reference value can allow for improved evaluation as follows: the degree of calibration of the magnetic field sensor and whether the calibration has changed.

[0036] It is also conceivable to prioritize comparisons, for example, comparing a second reference value only if the comparison with a first reference value reveals an error, in order to perform a confidence check and / or obtain other information. Alternatively, it could be proposed that, when using both first and second reference values, a comparison with the second reference value is only made if the comparison with the first measurement does not reveal a measurement error. Therefore, it can be tailored to specific confidence, robustness, and information requirements.

[0037] Of course, it is also conceivable that an embodiment in which only the second reference value is used (at least in a homogeneous volume).

[0038] Generally, in a specific design of the invention, it can be proposed to determine the absolute or relative deviation between the second measured value and a reference value in a comparison, wherein a measurement error is identified when the deviation exceeds a limit value. Here, the distinction between considering absolute deviation and relative deviation can be made based on the reference value. In a specific embodiment, for example, in the case of a rated field strength of 1.5T main magnetic field, a limit value in the range of 0.08T to 0.12T, particularly 0.1T, can be used for absolute deviation, especially with respect to the first measured value. Generally, a suitable limit value can be determined experimentally at the corresponding magnetic resonance device and can vary depending on the magnetic resonance device / rated field strength.

[0039] In accordance with the objective, in the context described above, when using a second reference value, a relative deviation is calculated for the second reference value. In the specific embodiment already mentioned with a rated field strength of 1.5T main magnetic field, the limiting value for the relative deviation with respect to the second measurement value in the range of 0.05 to 0.09 (i.e., 5% to 9%) has been experimentally proven to be appropriate.

[0040] As already described, it can be particularly advantageous to propose that error messages be evaluated by at least one action condition, and that, if said action condition is met, associated actions be performed. Specifically, for example, it can be proposed that, in the case of an error message indicating a measurement error, such as exceeding at least one limit value, an optical and / or acoustic indication output for the measurement error be output, particularly in conjunction with an action recommendation. The action recommendation could, for example, involve pending repair and / or replacement of the local coil device. Other action conditions, for example, initially only induce inputs to the error memory in the case of small deviations. In this regard, for example, the presence of multiple successive inputs to the error memory can also be monitored by at least one action condition, so that subsequent indication outputs as actions are also triggered.

[0041] However, recording error information has proven particularly advantageous within the scope of this invention. This means inputting each obtained error message into a log file. This information can be used for long-term monitoring, for example, by identifying trends. In particular, the error information of this invention can be collected and evaluated together with other information recorded during field use of the magnetic resonance imaging (MRI) device to further develop the MRI device and / or facilitate new developments or determine the necessity of such developments.

[0042] As already mentioned, the first position information can be used to realize various functions in the magnetic resonance imaging device, as is known in principle. For example, the position information can be incorporated into a diagram that obtains the position of the local coil device on the examination table along with its position. Furthermore, the control device can also be configured to manipulate the examination table in relation to the first position information to move it into the patient receiving area.

[0043] Specifically and particularly preferably, it can be proposed that, after selecting one of at least one local coil device on the user side, the local coil device is positioned in the isocenter of the magnetic resonance imaging (MRI) apparatus, which is located in a homogeneous volume, by moving it onto the examination table based on the first position information of the local coil device. In this manner, the positioning of the local coil device in the isocenter of the MRI apparatus is significantly simplified, for example, as a "button" function. In particular, a diagram can be generated that schematically displays the currently used local coil device and its position based on the corresponding first position information on the examination table. This diagram can be output, for example, on a touchscreen or otherwise, allowing the user to select one of the local coil devices as the local coil device to be placed in the isocenter.

[0044] It should also be noted here that, as already mentioned, the retrieval of error information can preferably be performed for each of these positioning processes. In particular, it can be proposed that error information be retrieved for each user-side selection and positioning of the local coil device for all local coil devices. Therefore, the retrieval of error information is not limited to the selected local coil device, but can involve all local coil devices, especially when using the first reference value, and can also involve local coil devices not placed in the homogeneous volume.

[0045] In addition to the method, the present invention also relates to a magnetic resonance device having:

[0046] - A main magnet unit, the main magnet unit having a main magnet for generating a main magnetic field and, in particular, a cylindrical patient receiving portion, wherein the field lines of the main magnetic field in a homogeneous volume within the patient receiving portion extend in the field direction.

[0047] - An examination bed for moving a patient into a patient receiving area along the z-direction corresponding to the longitudinal direction of the examination bed, wherein the examination bed is associated with a position determining device for determining the bed position along the z-direction.

[0048] - At least one local coil device for placement on a patient and / or examination bed, wherein the local coil device has a magnetic field sensor, particularly a Hall sensor, for measuring the magnetic field strength of at least the main magnetic field, and

[0049] - A control device configured to obtain first position information describing a first measurement position of a local coil device by aligning a first measurement value from a magnetic field sensor with a main magnetic field map at least outside the patient receiving area.

[0050] The magnetic resonance device is characterized in that the control device is configured to perform the method according to the invention.

[0051] All embodiments of the method according to the invention can be similarly applied to the magnetic resonance apparatus according to the invention, by which the aforementioned advantages can also be obtained. In particular, the control device may have at least one storage mechanism and at least one processor. Functional units, especially functional units for performing the steps of the method according to the invention, may be formed by hardware and / or software.

[0052] Specifically, the control device may, for example, have:

[0053] - A measurement unit, which is used to record a first measurement value and a second measurement value through corresponding manipulation and reception of a magnetic field sensor.

[0054] - A first measurement position determination unit, which is used to determine first position information from a first measurement value and a main magnetic field diagram.

[0055] - A bed position determination unit, which is used to determine the bed position by means of a position determination device.

[0056] - A second measurement position determination unit, which is used to determine a second measurement position from the first position information and the bed position.

[0057] - A reference value determination unit, wherein the reference value determination unit is used to determine a reference value, and

[0058] - Comparison unit, which is used to obtain error information.

[0059] Other functional units may include, for example, a measures unit for checking measures conditions and executing corresponding measures, an output unit for outputting instructions, a user interaction unit for receiving user input / output diagrams, and a bed control unit for manipulating the examination bed (or the actuator that drives the examination bed) to move into or away from the patient accommodation. If the control device also constitutes a means of controlling other operations of the magnetic resonance imaging device, especially recording operations, it may also include a sequence unit for controlling recording operations, a reconstruction unit for obtaining magnetic resonance image datasets, etc., as is known in principle.

[0060] The computer program according to the invention can be directly loaded into the storage mechanism of the control device of the magnetic resonance apparatus and has a program mechanism that, when executed on the control device, causes the control device to perform the steps of the method according to the invention. The computer program can be stored on an electronically readable data carrier according to the invention, thus the data carrier has control information stored thereon, the control information including at least one computer program according to the invention and designed such that, when the data carrier is used in the control device of the magnetic resonance apparatus, the control device is configured to execute the method according to the invention. The data carrier can be, in particular, a non-transient data carrier, such as a CD-ROM. Attached Figure Description

[0061] Other advantages and details of the invention will become apparent from the embodiments described below and from the accompanying drawings. These are shown herein:

[0062] Figure 1 A flowchart illustrating an embodiment of the method according to the present invention is shown.

[0063] Figure 2 A diagram illustrating the method for taking measurements at the first measurement location is shown.

[0064] Figure 3A diagram illustrating the method for taking measurements at the second measurement location is provided.

[0065] Figure 4 A magnetic resonance device according to the present invention is shown, and

[0066] Figure 5 The functional structure of the control device of the magnetic resonance device is shown. Detailed Implementation

[0067] Figure 1 A flowchart illustrating an embodiment of a method for monitoring the function of a magnetic field sensor and a Hall sensor measuring in three dimensions for a local coil device according to the present invention is shown. Thus, if the local coil device is positioned on an examination bed and / or a patient placed on the examination bed, and the examination bed is positioned in a position removed from the patient receiving portion of the magnetic resonance device, the local coil device is outside the homogeneous volume of the magnetic resonance device. Here, the examination bed can move along the z-direction corresponding to its longitudinal direction, which currently also corresponds to the field direction of the main magnetic field (BO field) in the homogeneous volume. The magnetic field sensor can measure the main magnetic field (BO field) of the magnetic resonance device, and the control device can obtain position information from the corresponding measurement value by means of a main magnetic field map, the position information describing at least the current position of the local coil device with respect to the z-direction. Currently, the first position information obtained at a first measurement position of the local coil device outside the homogeneous volume can be used to achieve targeted movement of the examination bed, such that the local coil device is positioned in the isocenter of the magnetic resonance device, particularly within the range of the "button" function.

[0068] However, using measurements at the first measurement location to perform this target movement is also currently used to check the functionality of the magnetic field sensor in a simple and cost-effective manner.

[0069] Therefore, in step S1, a first measurement of the main magnetic field, which is always necessary for the function, is first performed at the first measurement position. The result is a first measurement value for the main magnetic field, and in particular, at least for the amplitude (field strength) of the main magnetic field.

[0070] In step S2, the first measurement value is aligned with the main magnetic field (corrected in terms of the calibration frequency of the current measurement) outside the patient housing to obtain the corresponding first measurement position, thereby obtaining the first position information of the local coil device.

[0071] to this end, Figure 2 The diagram schematically illustrates the situation in the first measurement position. In the removed first bed position 4, the examination bed 1 is mostly outside the patient receiving section 2 within the main magnet unit 3. Here, this refers to what is called a near-in-situ position, or the examination bed 1 extending into the patient receiving section 2 by no more than 30 cm.

[0072] Therefore, the local coil device 5 of the Hall sensor with magnetic field sensor 6, which is placed on the examination bed 1 or, if not shown, on the patient placed on the examination bed 1, is also disposed outside the homogeneous volume surrounding the isocenter 7, which is currently also defined here as the zero point of the z-direction 8b corresponding to the field direction 8a. The magnetic field sensor 6 is located at the first measurement position 9 at a distance 10 from the isocenter 7.

[0073] The variation curve 11 of the main magnetic field strength is also shown overlaid with a schematic diagram. Therefore, assuming accurate measurement, at the first measurement position 9, the magnetic field sensor 6 measures the first measurement value 12 of the main magnetic field. After knowing the variation curve 11 from the main magnetic field diagram, the first measurement position 9 can be determined from the first measurement value 12 and stored here as the first position information.

[0074] Back Figure 1 In step S3, a first bed position 4 is also determined by a position determination device associated with the examination bed 1. The accurate and robust determination of the bed position 4 can be based on corresponding feedback, control history, and / or dedicated sensors of the actuators used to move the examination bed 1 along the z-direction 8b. The corresponding detection mechanism is included by the position determination device.

[0075] In step S4, the examination bed 1 (along with the local coil devices 5 fixedly mounted thereon) is now moved into the patient receiving section 2. For example, the reason for this movement could be the use of a function to position the local coil devices 5 in the isocenter 7. Here, to achieve this function, for example as a "button" function, a diagram is generated based on first position information regarding all the local coil devices 5 mounted on the examination bed 1, for example, a schematic diagram of the local coil devices 5 on the examination bed 1. This diagram is output on a touchscreen, which may be located, for example, at the end of the examination bed 1 from which it is moved, on the cover of the main magnet unit 3. The user can select a local coil device 5 by selecting one of the local coil devices 5 or by an operating element representing the local coil device 5, and, due to the known distance 10 from the isocenter 7, the local coil device 5 is moved into the isocenter 7 by correspondingly manipulating the actuator of the examination bed 1.

[0076] The corresponding situation after the journey ends is as follows: Figure 3 The diagram is shown schematically. It can be seen that the magnetic field sensor 6 is now in the second measurement position 13, which corresponds to the isocenter 7; however, this is not necessarily mandatory. For this purpose, the examination bed 1 is in the second bed position 14, which has been moved a distance 10 relative to the first bed position 4.

[0077] Therefore, as curve 11 further indicates, the local coil device 5 and the accompanying magnetic field sensor 6 are now in a homogeneous volume with a constant magnetic field strength, such that the magnetic field strength used for the main magnetic field is determined according to... Figure 1 Determining the position one-to-one from the second measurement value 15 recorded in step S5, i.e., obtaining the second position information, is not meaningful or feasible.

[0078] However, the second measurement is still performed to check the function of the magnetic field sensor 6. For this purpose, the position 14 of the second bed is determined in step S6 by means of a position acquisition device.

[0079] In step S7, as preparation for obtaining the reference value, the second measurement position 13 is determined by moving the first measurement position 9 according to the first position information to check the movement segment of the bed 1 (the movement segment is directly derived from the difference between the first bed position and the second bed positions 4 and 14). Currently, the second measurement position 13 is within a homogeneous volume.

[0080] Subsequently, in step S8, at least one reference value can be determined, and the second measured value 15 is compared with the at least one reference value to check whether the magnetic field sensor 6 is functioning correctly. Therefore, the reference value here corresponds to the expectation based on the second measured position 13, as obtained in step S7.

[0081] In this embodiment, the first reference value is obtained in all cases by retrieving the expected main magnetic field from the main magnetic field diagram at the second measurement position 13 (based on calibration frequency correction as described above). Therefore, for the first reference value, a comparison is made with the expected value based on the main magnetic field diagram. However, a case distinction is also made in step S8. Only when the second measurement position 13 is within a homogeneous volume, the second reference value is also obtained by simply dividing the calibration frequency derived from the current measurement and corresponding to the magnetic resonance frequency within the homogeneous volume by the gyromagnetic ratio.

[0082] Subsequently, in step S9, error information is obtained by comparing with an available reference value. For this purpose, a first deviation, in this case, an absolute deviation, is determined for the first reference value, and the magnitude of the difference between the first reference value and the second measured value 15 is calculated. If the first deviation is greater than a first limit value, which is exemplarily a first limit value of 0.1T for a main magnetic field with a rated field strength of 1.5T, an error condition can be identified, thus determining an erroneous measurement. Not only the first deviation, but also the result of the comparison with the limit value is stored in the error information.

[0083] If the second measurement position 13 is within a homogeneous volume, a second reference value also exists, and a second deviation, in this case, a relative deviation, is calculated for this second reference value. This means that the second deviation is calculated by dividing the difference between the second reference value and the second measurement value 15 by the second reference value. If the second relative deviation is greater than a second limit value, which is 0.07 (i.e., 7%) in the case mentioned above, an error can be identified again. Not only the second deviation, but also the comparison result is stored again in the error message.

[0084] It should be noted that an embodiment is also conceivable in which the second reference value is used alone only at the second measurement position 13 in the homogeneous volume. Furthermore, cross-comparisons are also conceivable, particularly cross-comparisons with multiple first and / or second limit values.

[0085] In step S10, the obtained error information is stored in a log file in the storage mechanism of the magnetic resonance device's control unit or in an external storage mechanism, particularly along with other operating data of the magnetic resonance device. The error information can then be provided there for subsequent evaluation.

[0086] Then, in step S11, it is checked whether at least one action condition is met. Each action condition is associated with an action. For example, an action condition may check whether one or both comparisons show that a first limit value or a second limit value has been exceeded. Subsequently, as an action to be performed in step S12, an optical and / or acoustic indication output may be associated, and among the indication outputs is an action recommendation, in this case, the replacement of the local coil device 5. Other action conditions may check, for example, whether an input to the error memory should be made.

[0087] If the conditions for the measures are not met or all related measures have been implemented, then for the next target movement, that is, the next use of the positioning function when using the magnetic field sensor 6, the process returns to step S1 again. In other words, for each retrieval of the first positioning information, the function of the magnetic field sensor 6 is checked, and then the examination bed 1 is moved into the patient receiving section 2.

[0088] It should be pointed out again at this point that the second measurement position 13 does not necessarily have to be in a homogeneous volume, because after the expectation for the second measurement value 15 is also derived from the main magnetic field diagram, the functional check of the magnetic field sensor 6 is still feasible.

[0089] Figure 4 A schematic diagram of the magnetic resonance device 16 according to the present invention is shown. (As already shown...) Figure 2 and Figure 3As illustrated in the schematic diagram, the magnetic resonance imaging device 16 includes a main magnet unit 3 with a cylindrical patient reception section 2 into which the examination bed 1 can be moved. The main magnet unit 2 also includes a superconducting or permanent magnet main magnet 17, shown only herein.

[0090] Furthermore, a position determination device 18 for determining the bed position of the examination bed 1 is also shown. For example, a diagram of the examination bed 1 together with the local coil device 5 disposed on the examination bed can be output on the touch screen 20 located at the end side 19 of the cover of the main magnet unit 3, so that the local coil device 5 can be selected for positioning in the isocenter 7 through interaction with the diagram and / or operating elements.

[0091] The operation of the magnetic resonance device 16 is controlled by the control device 21. Figure 5 Reference Figure 1 The method more precisely illustrates the functional construction of the control device 21 for performing the method.

[0092] Accordingly, the control device 21 first includes a storage mechanism 22, in which different information, or different information of the method, can be stored. Furthermore, the control device 21 includes: a measurement unit 23 for recording the first and second measurement values ​​12 and 15 according to steps S1 and S5; a first measurement position determination unit 24 for determining the first position information from the first measurement value 12 and the main magnetic field diagram according to step S2; a bed position determination unit 25 for determining the first bed position and the second bed positions 4 and 14 according to steps S3 and S6; a second measurement position determination unit 26 for determining the second measurement position 13 from the first position information and the bed positions 4 and 14 according to step S7; a reference value determination unit 27 for determining at least one reference value according to step S8; and a comparison unit 28 for determining error information according to step S9. The control device 21 is also configured to store error information in a log file according to step S10; alternatively, a logging unit may also be provided.

[0093] In addition, as part of the control device 21, there is a measure unit 29 for checking the measure conditions according to steps S11 and S12 and executing the corresponding measures; and a user interaction unit 30 for receiving user input and outputting diagrams and / or instructions. Finally, a bed control unit 31 is also provided, which is used to operate the examination bed 1 (or drive the actuator of the examination bed 1) to move into and out of the patient receiving section 2, especially according to step S4.

[0094] After the control device 21 is configured to control other operations of the magnetic resonance device 16, it is also provided with other corresponding functional units not shown here.

[0095] Although the details of the invention have been described and illustrated with reference to preferred embodiments, the invention is not limited to the disclosed examples and other variations can be derived by those skilled in the art without departing from the scope of protection of the invention.

[0096] Regardless of the grammatical gender of a particular term, people with male or female gender identities are included.

Claims

1. A method for operating a magnetic resonance apparatus (16), the magnetic resonance apparatus (16) having - a main magnet unit (3) with a main magnet (17) for generating a main magnetic field and a patient receiving portion (2), wherein field lines of the main magnetic field in a homogeneous volume in the patient receiving portion (2) stretch in a field direction (8a), - an examination bed (1) for moving a patient into the patient receiving portion (2) along a z-direction (8b) corresponding to a longitudinal direction of the examination bed (1), wherein the examination bed (1) is associated with a position determination device (18) for determining a bed position along the z-direction (8b), - at least one local coil device (5) for placing on the patient and / or the examination bed (1), wherein the local coil device (5) has a magnetic field sensor (6) for measuring a measurement value of a magnetic field strength of at least the main magnetic field, and - a control device (21) which is configured for determining first position information of the local coil device (5) describing a first measurement position (9) by aligning a first measurement value (12) of the magnetic field sensor (6) with a main magnetic field map at least outside the patient receiving portion (2), the method comprising - recording a first measurement value (12) of the magnetic field sensor (6) at a first measurement position of the local coil device (5) outside the patient receiving portion (2) at a first bed position (4) of the examination bed (1) and determining the first position information, - recording a second measurement value (15) of the magnetic field sensor (6) at a second measurement position (13) of the local coil device (5) different from the first measurement position (9) during or after the end of a travel of the examination bed (1) into the patient receiving portion (2) at a second bed position (14) of the examination bed (1), - determining at least one reference value describing an expected main magnetic field at the second measurement position (13), the second measurement position (13) being determined from the first position information and a movement section of the examination bed (1) between the first bed position and the second bed position (4, 14) by the position determination device (18), and - determining an error information showing a potential measurement error by comparing the second measurement value (15) with the reference value, wherein an absolute or relative deviation of the second measurement value (15) from the reference value is determined in the comparison, wherein a measurement error is identified when the deviation exceeds a limit value.

2. The method as claimed in claim 1, characterized in that the patient receiving portion is configured to be cylindrical.

3. The method as claimed in claim 1, characterized in that characterized in that the second measurement position (13) is within the patient receiving portion.

4. The method as claimed in any of claims 1 to 3, characterized in that ​ ​ ​ ​ ​ ​ ​ ​ ​ - a first reference value of the at least one reference value is determined from the main magnetic field map at the second measurement position (13) sought.

5. The method according to any one of claims 1 to 3, characterized in that the main magnetic field map is corrected in terms of a current calibration frequency measured by means of a magnetic resonance measurement before the main magnetic field map is used.

6. The method according to any one of claims 1 to 3, characterized in that at least one second reference value of the at least one reference value is determined from a current calibration frequency measured by means of a magnetic resonance measurement in the case of a second measurement position (13) within the homogenous volume, the calibration frequency corresponding to the magnetic resonance frequency in the homogenous volume.

7. The method according to claim 6, characterized in that a relative deviation is determined for the second reference value when the second reference value is used.

8. The method according to any one of claims 1 to 3, characterized in that in the case of displaying an error message for a measurement error, an optical and / or acoustic indication output is output for the measurement error and / or the error message is logged.

9. The method according to claim 8, characterized in that the optical and / or acoustic indication output is output together with an action recommendation.

10. The method according to any one of claims 1 to 3, characterized in that after a selection of one of the at least one local coil device (5) on the user side, the local coil device (5) is positioned in an isocenter (7) of the magnetic resonance device (16) by moving into the examination bed (1) on the basis of first position information of the local coil device (5), the isocenter (7) being in the homogenous volume.

11. The method according to claim 10, characterized in that the error message is determined for each user-side selection and positioning of a local coil device (5) for all local coil devices (5).

12. A magnetic resonance device (16), having - a main magnet unit (3) having a main magnet (17) for generating a main magnetic field and a patient accommodation (2), wherein field lines of the main magnetic field in a homogenous volume in the patient accommodation (2) stretch in a field direction (8a), - an examination bed (1) for moving a patient into the patient accommodation (2) along a z direction (8b) corresponding to a longitudinal direction of the examination bed (1), wherein the examination bed (1) is associated with a position determination device (18) for determining a bed position along the z direction (8b), - at least one local coil device (5) for placing on the patient and / or the examination bed (1), wherein the local coil device (5) has a magnetic field sensor (6) for measuring a measurement value of a magnetic field strength of at least the main magnetic field, and - a control device (4) for determining a homogenous volume in the patient accommodation (2) in which a magnetic resonance frequency is constant, and for determining at least one reference value of the magnetic resonance frequency in the homogenous volume from a main magnetic field map of the main magnetic field in the patient accommodation (2), and for determining a measurement position (13) in the homogenous volume in which the magnetic resonance frequency corresponds to the magnetic resonance frequency in the homogenous volume, and for positioning the local coil device (5) in the measurement position (13) by moving into the examination bed (1) on the basis of first position information of the local coil device (5). - a control device (21), which is designed to determine first position information describing a first measurement position (9) of the local coil arrangement (5) by aligning a first measurement value (12) of the magnetic field sensor (6) with a main magnetic field map at least outside the patient accommodation (2), characterized in that the control device (21) is designed to carry out the method according to any one of claims 1 to 11.

13. The magnetic resonance apparatus (16) as claimed in claim 12, characterized in that the patient accommodation is designed to be cylindrical.

14. A computer program product having a computer program which, when executed on a control device (21) of a magnetic resonance apparatus (16), causes the control device to carry out the steps of the method according to any one of claims 1 to 11.

15. An electronically readable data carrier on which a computer program of the computer program product according to claim 14 is stored.

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