Method for checking a magnetic resonance threshold based on the patient's head position

Abstract

The invention relates to a method for determining the position of a specific body part of a patient on a patient table and for checking a medical threshold value during a magnetic resonance examination. The method comprises determining position information of a specific body part of a patient on a patient table and checking a magnetic resonance sequence for compliance with at least one threshold value based on the position information of the specific body part. The invention enables a specific determination of the absorption rate of specific body parts and increases the performance of a magnetic resonance device.

Description

[0001] The invention relates to a method for determining position during a magnetic resonance examination and a test of a medical limit value.

[0002] During a magnetic resonance examination of a patient, i.e., during magnetic resonance imaging (MRI), magnetic fields, particularly gradient fields, and radio-frequency signals or radio-frequency fields are typically used to acquire magnetic resonance signals using a magnetic resonance device according to a measurement protocol. To generate the gradient fields, a magnetic resonance device typically has a gradient coil unit. Furthermore, the magnetic resonance device typically includes a radio-frequency antenna unit, with which the radio-frequency signals can be generated to excite atomic nuclei.

[0003] During an MR scan, it is of key importance to ensure patient safety throughout the entire examination. Safety measures are typically based on standards such as IEC 60601-1 and IEC 60601-2-33. These standards, among others, specify physical parameters that must be adhered to to ensure patient safety. In particular, the specific absorption rate (SAR) is often a crucially important parameter. The SAR value or parameter typically indicates the amount of energy absorbed by an object during a magnetic resonance examination. A high SAR value leads to significant heating of the tissue. It is therefore important which part of the body is located at the isocenter, the point of most concentrated radiation, during the examination period. Different limit values ​​apply to different patient body regions.Maximum values ​​have been determined empirically. Typically, the patient's head is the body part with the highest absorption rate, at 3.2 watts per kilogram. The positioning of a patient's head is therefore a crucial factor during an MRI scan and must be determined as accurately as possible.

[0004] Typically, magnetic resonance imaging (MRI) examinations distinguish between two patient positioning options: head-first or feet-first. When the patient is positioned head-first, the position of the head is clearly defined, primarily through the use of a head coil. The head coil is mechanically connected to the patient bed and is always in a defined position. This is not the case when the patient is positioned feet-first, as a head coil is not usually used in this positioning option. This means that there are no mechanical constraints for clearly positioning the head. To ensure compliance with the SAR values, particularly for the head area, the position of the head is estimated during the examination.To avoid exceeding absorption values, it is assumed that the patient's head is positioned at the isocenter of the magnetic resonance scanner in every patient position. This approach only represents a rough estimate of the position and therefore leads to performance degradation during the examination.

[0005] Methods and devices for detecting the position of a patient in a magnetic resonance imaging device are described, for example, in DE 102007011695 A1. Methods for performing a magnetic resonance examination are known, for example, from DE 102005019859 A1. DE 102018212091 A1 describes a method for determining a load-optimized MR sequence. A method for operating a cleaning system of a medical imaging device is known from DE 102020214808 A1.

[0006] The object of the present invention can be considered to be to increase the performance of the magnetic resonance apparatus during the examination of a patient while simultaneously adhering to defined safety measures for the patient. This object is achieved by the features of the independent claims. Advantageous embodiments are described in the dependent claims.

[0007] The proposed solution to the problem is described below with respect to both the claimed devices and the claimed method. Features, advantages, or alternative embodiments mentioned here are also applicable to the other claimed subject matter, and vice versa. In other words, the subject claims (which, for example, are directed to a device) can also be developed with the features described or claimed in connection with a method. The corresponding functional features of the method are implemented by corresponding subject modules.

[0008] A method for checking a magnetic resonance sequence for compliance with at least one limit value is proposed. The method comprises determining position information of a specific body part of a patient on a patient table. Furthermore, the method comprises checking the magnetic resonance sequence for compliance with at least one limit value based on the position information of the specific body part.

[0009] The specific body part of the patient can, in particular, be the patient's head. However, the specific body part can also include other body parts of the patient, for example, the patient's feet, the chest area, the torso, and / or the heart (the area surrounding the heart). Embodiments of the invention are described below, particularly with reference to the patient's head as a specific body part. Likewise, the claimed aspects are transferable and / or applicable to other specific body parts of a patient.

[0010] A magnetic resonance sequence typically refers to a pulse sequence, i.e., a chronological sequence of radiofrequency pulses and / or gradient pulses used to excite an image volume to be measured, for signal generation, and for spatial encoding. Typical pulse sequences can include spin echoes, particularly turbo spin echoes (TSE), and / or gradient echoes.

[0011] The (tested) limit value preferably comprises a SAR value (“specific absorption rate”), in particular a partial-body SAR value, and / or an SED value (specific energy dose). The limit value can also comprise other medical values. The SAR value typically represents a safety value or parameter during a magnetic resonance examination. The specific absorption rate is usually the value of absorbed radiofrequency energy per unit of time and per kilogram of body weight. The absorption of radiofrequency energy can lead to heating of body tissue. Energy absorption is preferably an important parameter for setting safety limits. Inadmissibly high local concentrations of radiofrequency energy can result in radiofrequency burns, which is why local SAR values, such as those on a patient's head, are preferably determined.When the radiofrequency energy is evenly distributed across the entire body, the strain on the patient's thermoregulation or cardiovascular system is crucial. Therefore, the whole-body SAR is preferably determined. Possible remedial measures for excessively high SAR values ​​can include: using radiofrequency pulses that result in a low SAR value, smaller flip angles, longer repetition times (TR), and / or fewer acquisition slices. The specific energy dose (SED) represents another possible safety value or parameter during a magnetic resonance examination. The specific energy dose is typically the value of the accumulated whole-body SAR during the entire examination, often given in J / kg (= Ws / kg). The partial-body SAR value is another possible safety value or parameter during a magnetic resonance examination.Partial body SAR values ​​typically refer to the SAR that is averaged per unit of time over the body mass of a patient exposed to a volume coil (radio frequency transmit coil).

[0012] The position information can preferably describe the (ideally actual) spatial position of the patient's head on the patient table. The position information can preferably comprise a three-dimensional and / or two-dimensional description (in x and y) of a point, in particular a center point, of the head starting from a reference object, in particular a reference point, by means of a coordinate system. The reference point (e.g. zero point of the coordinate system) is preferably arranged on or at the patient table. The position of the head can preferably be determined by means of the center point of the head, but also by means of another point on / at the patient's head, for example the vertex (in particular the point at which the local maximum of the function is located that describes the upper half of the patient's skull when viewed from the front when standing).

[0013] Magnetic resonance apparatuses preferably have a patient receiving area. During the examination of the patient, the patient is typically located entirely or partially in the patient receiving area. The patient receiving area is preferably cylindrical and / or tubular in shape. The patient receiving area is preferably also surrounded by a gradient coil unit and a main magnet. A patient support device, in particular a patient table, can preferably be moved into the patient receiving area. The patient table can preferably accommodate a horizontally lying patient. The patient table can comprise electronic components and connections that can, for example, enable a change in position (or movement) of the patient table. The patient receiving area can also be referred to as the examination area and / or comprise the examination area.The examination area is in particular the area in which an imaging examination of the patient is carried out.

[0014] Determining the position information of the patient's head on the patient table can comprise measuring, capturing, and / or determining the position of the patient's head. The position information can preferably be measured, captured, and / or determined using a sensor designed for this purpose. In particular, the position can be determined based on measurement data that can be captured using the sensor designed for this purpose.

[0015] The magnetic resonance sequence is checked for compliance with at least one limit value based on the determined position information, in particular position data, of the patient's head. The check preferably comprises determining and / or calculating an absorption value, in particular an SAR value, based on the position information. For example, a lookup table (LUT or conversion table) can be used here, which assigns one or more absorption values ​​to the position information, in particular the position data, of the head, in particular taking process parameters into account. The check preferably also comprises comparing a limit value, in particular an SAR limit value, with a determined absorption value.

[0016] By determining the position information of the patient's head, the corresponding local load and / or strain on that body region can be advantageously determined and ensured that this does not exceed a specified limit. This can replace an estimation of the head position, thus increasing the system's performance, as potentially higher loads or strain on body regions remote from the head become possible.

[0017] The method further comprises acquiring distance measurement data for measuring a distance between a target object and a reference object, in particular a reference point, of the patient table. The target object is in particular the patient's head. According to this aspect, the position information of the target object, in particular the head, is advantageously determined based on the distance measurement data.

[0018] The distance measurement data comprises at least data from a measurement of a distance between the target object (measurement object) and a reference point. The data from several measurements can preferably also be included. The target object can in particular be the patient's head. Due to the presence of other objects on the patient table, such as blankets, pillows, paper towels or hearing protectors (headphones), the distance to other objects can be the measurement result instead of the distance to the patient's head starting from the reference point. This is particularly the case if another object, which is required or used during the examination, for example, is placed between the patient's head and the reference point on the patient table. For example, the patient or medical staff can place an object on the patient table during the examination.

[0019] The reference object, in particular the reference point, is preferably the starting point for the distance measurement, i.e. for the acquisition of the distance measurement data. The reference object, in particular the reference point, can preferably be stationary or fixed on the patient table. Alternatively, the reference object, in particular the reference point, can also be movable or displaceable (in a defined relationship) with the patient table. The reference object is in particular a point arranged on the patient table. Alternatively, the reference object can also comprise a line arranged on the patient table or a region of the patient table. In particular, the spatial position of the reference object can be known, for example in a (global) coordinate system of the magnetic resonance device, or can be determined.The determination of the position information can preferably comprise a combination, in particular an addition, of the position information of the reference point and the distance measurement data. In particular, the reference object can be the origin of a patient coordinate system or be arranged at a point in the patient coordinate system. A patient coordinate system is preferably a patient-related coordinate system designed to display the position of a patient (or a slice in MR images) in the viewing direction of a viewer. The axes of the patient coordinate system preferably run sagittally from right to left, transversely from head to toe, and coronally from anterior (bottom) to posterior (top).

[0020] Distance measurements typically represent a robust, accurate and reliable measurement method, so that the position of the head can advantageously be determined with sufficient accuracy and certainty.

[0021] According to one possible aspect of the invention, the distance measurement data is acquired by means of a distance sensor.

[0022] In other words, the distance data is preferably measured using at least one distance sensor. Alternatively, multiple and / or different distance sensors can be used. Distance sensors can also be referred to, among other things, as displacement measuring sensors, path sensors, position sensors, displacement transducers, and / or distance sensors. The distance sensor is preferably designed to determine a distance to a measurement object starting from a reference object, in particular a reference point (measurement starting point), or between two points (or objects). The reference object or reference point preferably corresponds to the position of the sensor. The distance sensor can preferably measure and / or determine the spatial position of a measurement object. The distance sensor can have a defined measuring range and / or a specific measuring accuracy.The distance sensor can preferably be designed to detect the position change of a (target) object and / or to acquire distance measurement data over time. The distance sensor can, in particular, be a non-contact distance sensor. The distance sensor can preferably be an optical distance sensor. The distance sensor can, for example, be a laser distance sensor, a laser time-of-flight sensor, a confocal chromatic sensor, an interferometer, a capacitive distance sensor, or an eddy current sensor. Tactile or contact sensors, such as buttons, can represent an alternative, but can lead to patient discomfort due to the contact measurement and are therefore less preferred.

[0023] Non-contact distance sensors are particularly well-suited for distance measurement in medical applications. The acquisition of distance measurement data using a distance sensor is advantageously cost-effective and robust.

[0024] According to one possible aspect of the invention, the distance sensor comprises an ultrasonic sensor.

[0025] In particular, the distance sensor can be an ultrasonic sensor. The ultrasonic sensor preferably comprises a transmitter designed to generate a sound wave and a receiver designed to receive a sound wave. The distance to an object is preferably calculated based on the time in which the sound wave emitted by the transmitter and reflected by the measurement object is received by the receiver. The ultrasonic sensor can in particular have an operating range of between 20 centimeters and 5 meters. Since the attenuation of the sound can depend on environmental parameters such as air temperature, humidity, and air pressure, these parameters can be determined and taken into account during the distance measurement. In particular, the ultrasonic sensor can be designed to capture spatially resolved information.

[0026] Advantageously, ultrasonic sensors enable surface-independent, contactless distance measurements of various objects, especially the target object. Dust or other possible light contamination advantageously does not affect the measurement. Furthermore, ultrasonic sensors can also be advantageous in confined or cramped installation conditions.

[0027] According to one possible aspect of the invention, the distance measurement data comprises two- and / or three-dimensional distance measurement data.

[0028] The two- and / or three-dimensional distance measurement data can, in particular, represent an arrangement of measurement points within a measurement area and / or a measurement space. Two-dimensional distance measurement data preferably comprise mutually associated data pairs consisting of an X and a Y value. Three-dimensional distance measurement data preferably also comprise a height value Z associated with the XY data pair. In particular, the distance measurement data can contain the results of multiple distance measurements starting from a reference object, in particular a reference point. In other words, distance measurement data can be a list (sequence) of distances or distance vectors starting from (linked to) a reference point. The list of distance measurement data can preferably be stored in a document. The two- and / or three-dimensional distance measurement data can preferably be graphically displayed to an operator by means of a display unit.The two- and / or three-dimensional distance measurement data can spatially resolve a shape property of an object, in particular a head.

[0029] By acquiring spatially resolved distance measurement data, a more accurate determination of the position of the head (as a target object) and / or the detection / differentiation (classification) of the head and other objects can be improved.

[0030] The procedure also includes the acquisition of object measurement data. Based on this data, the target object is verified as the patient's head.

[0031] The object measurement data particularly comprise the data of a measurement of a physical property of an object, particularly of the target object. In other words, the object measurement data can particularly be the measured physical properties of an object, particularly of the target object. The object measurement data can preferably comprise the temperature of an object, particularly of the target object. In particular, the object measurement data can comprise the surface temperature of an object, particularly of the target object. Alternatively / additionally, object measurement data can comprise the shape of an object, particularly of the target object, particularly the arrangement and shape of surfaces of an object, particularly of the target object. Alternatively / additionally, object measurement data can comprise the surface quality, particularly an absorption coefficient and / or reflection coefficient, and / or the surface roughness of an object, particularly of the target object.Alternatively / additionally, object measurement data can include the density properties of an object, in particular the target object. Alternatively / additionally, object measurement data, in particular the target object, can include: temperature properties of the object, for example, a temperature profile; color properties of the object, in particular a color of a / the surface of the object.

[0032] Based on the object measurement data, an object, in particular the target object, can be identified or verified. In this case, verification is in particular a check using objective means to determine whether specific object properties are met. In this case, identification or verification can preferably comprise a comparison of expected values ​​and the object measurement data. The expected values ​​can be the physical properties of an object, in particular the target object, that are typically present (under room conditions). For example, the expected body temperature of a (healthy) person is typically between 36.5 and 37.5 degrees Celsius (°C) (under normal measurement conditions). The head of a patient can thus preferably be distinguished from another object (located on the patient table), which, for example, has a room temperature of 23°C, by determining a temperature difference.The measurement conditions (ambient temperature, ambient pressure, humidity) can be preferentially taken into account when measuring the object measurement data. In particular, the measurement conditions can be linked to the object measurement data or stored in a processing unit. In particular, a verification step can be provided that checks the automatic detection or verification of an object, especially the target object, in the event of significantly deviating measurement conditions.

[0033] If an image sensor is used as a verification sensor to generate image data of the object, in particular the target object, the verification of the object, in particular the target object, can preferably be carried out by analyzing the image using transformation steps, for example Fournier or Hough transformations. The object, in particular the target object, can be identified using the transformed image data. In particular, physical properties of the object, in particular the target object, can only be recognizable and / or verified using transformed image data. For example, the patient's hair can be identified using transformed image data of an image of a patient's head, thereby enabling the object to be verified as the patient's head. The object measurement data can enable unambiguous identification and / or verification of an object, in particular as the patient's head (as the target object).Physical properties of an object, especially the target object, can typically be determined reliably and cost-effectively using established measurement methods. This can advantageously enable reliable testing or determination of the energy radiated into a patient's head area. This can increase examination safety for the patient.

[0034] According to one possible aspect of the invention, the object measurement data is acquired by means of a verification sensor.

[0035] In other words, the object data is preferably measured using at least one verification sensor. Alternatively, multiple and / or different verification sensors can be used. Verification sensors within the meaning of the invention can also be referred to, among other things, as identification sensors, object sensors, or temperature sensors. The verification sensor can have a defined measuring range and / or a specific measuring accuracy. The verification sensor can be designed to detect a change in a property, for example a temperature change of an object, in particular the target object, or to detect object measurement data over time. The verification sensor can preferably be a contactless sensor. The verification sensor can preferably be an optical sensor. The verification sensor can preferably be a laser- or light-based sensor.The verification sensor can be, for example, a camera, a temperature sensor, or an ultrasonic sensor. For example, the verification sensor can be a depth imaging camera that records one-dimensional, two-dimensional, and / or three-dimensional image data.

[0036] Verification sensors can advantageously enable (automatic) detection and / or verification of an object, in particular the target object, without the involvement of a human operator. Contactless verification sensors, in particular, are advantageously suited for verifying or identifying an object, in particular the target object, in a medical examination context. The acquisition of object measurement data using a verification sensor is advantageously cost-effective, fast, and reliable.

[0037] According to one possible aspect of the invention, the verification sensor comprises a temperature sensor.

[0038] In particular, the verification sensor can be a temperature sensor. The temperature sensor can also be referred to as a heat sensor, temperature probe, or heat sensor. In particular, the temperature sensor can determine the temperature of an object, in particular the target object, without contact. The temperature sensor can be designed, in particular, to measure thermal radiation. For example, the temperature sensor can be a radiation thermometer, a pyrometer, an infrared sensor, or a thermal imaging camera. Since the temperature measurements can depend on environmental parameters such as air temperature, humidity, and air pressure, these parameters can be determined and / or taken into account during the temperature measurement. In particular, the temperature sensor can be designed to capture spatially resolved information.

[0039] Temperature sensors advantageously enable shape-independent, fast (ms-scale), and simple determination of an object's temperature. Contactless temperature sensors are particularly suitable in medical contexts due to their non-interference (no (mechanical) impact on the object / patient) and hygiene requirements (no contact with the patient).

[0040] According to a possible aspect of the invention, the object measurement data comprises two- and / or three-dimensional object measurement data.

[0041] The two- and / or three-dimensional object measurement data can, in particular, represent an arrangement of measurement points linked to physical properties within a measurement surface and / or a measurement space. Two-dimensional object measurement data preferably comprise data from a localization value (X / Y value) and a measured value, for example, a temperature value. Three-dimensional object measurement data preferably also comprise a height value Z associated with the localization value. In particular, the localization values ​​can be determined based on a reference value. In particular, the localization values ​​can comprise distance measurement data based on a reference object, in particular a reference point. The two- and / or three-dimensional object measurement data can preferably be graphically displayed to an operator by means of a display unit.The two- and / or three-dimensional object measurement data can spatially resolve a shape property of an object, in particular a head (as target object).

[0042] By capturing spatially resolved object measurement data, more precise object verification and / or the detection / differentiation (classification) of objects, particularly the target object, can advantageously be enabled. Furthermore, spatially resolved object measurement data can advantageously include additional distance information or distance measurement data.

[0043] According to a possible aspect of the invention, the position information of the head (target object) is further determined based on the object measurement data.

[0044] Preferably, the object measurement data can be used not only for identifying and / or verifying the object, but also for determining the position of the head. This can be done particularly when using spatially resolved verification sensors. Distance information can preferably be determined from the object measurement data and compared and / or combined with the distance measurement data determined by a distance sensor. Analogously, the distance measurement data can also preferably be used for detecting and / or verifying an object.

[0045] Advantageously, by using the position information from the object measurement data, the initial data set for position determination can be expanded or improved. Advantageously, the position of the patient's head can be determined with improved reliability and / or accuracy.

[0046] According to one possible aspect of the invention, the method comprises providing patient data. According to this aspect, the position information of the patient's head is preferably determined based on the patient data.

[0047] For example, the patient data can be available in the form of an electronic (patient) file. Patient data can include anatomical information and / or measurements, but also previous findings or image data. For example, the patient data can include height, head circumference, body weight, or body temperature. Based on the patient's height, for example, the specific head position on the patient table can be checked. Based on the head circumference, for example, the head recognition can be simplified and / or verified. Preferably, the electronic patient data can be recorded by a computing unit, and the data relevant for position determination can be provided.

[0048] Advantageously, the available patient information is taken into account and used during position determination. Patient information can simplify both position measurement and / or position determination, as well as object measurement and / or object determination.

[0049] According to one possible aspect of the invention, a defined estimated value can be determined as position information. According to this aspect, this can preferably be done when the position information of the head cannot be determined with sufficient certainty and / or accuracy based on measurement data.

[0050] Due to circumstances during the examination, for example the positioning of an (unrecognizable) object on the patient table, an incorrect determination of the head position may result, or a position determination may (generally) be impossible. In order to be able to perform an examination despite an undetermined error, an estimated value can be used as position information. The estimated value is preferably determined in such a way that the patient's safety is guaranteed during the examination. This means that a "worst-case" case (worst-case scenario) with regard to the head position is used. The arrangement of the head is assumed to be in the isocenter of the magnetic resonance scanner, the location with the greatest local energy density acting on the patient.

[0051] Sufficient security and / or accuracy with regard to the determination of the head position information based on the measurement data refers in particular to the achievement of a specified security value. The method can in particular comprise a check of the (determined) head position information. The check of the position information can in particular result in a security value that can preferably be compared with the specified threshold value. The check of the head position information can in particular be carried out by a trained function. The input data of the trained function can in particular comprise the measurement data and the determined head position information. The trained function can preferably output a classification of the head position information as "secure" or "unsecure". Alternatively, a check of the determined head position value can also be carried out by a user.

[0052] Preferably, estimating position information is only an option that advantageously allows for at least an (inefficient) examination in the event of a malfunction. Especially in situations where a rapid or timely examination of a patient is necessary, estimation can provide significant time savings.

[0053] According to one possible aspect of the invention, determining the position information of the patient's head can preferably comprise a computer-implemented object classification method. The object classification method can comprise a trained function. The trained function can be designed to classify the objects that could be detected, determined, and / or identified using the object measurement data. The objects can be classified, in particular, into the following categories: patient's head, other object. Furthermore, according to this aspect, input of object measurement data into the trained function can be included. Furthermore, according to this aspect, a classification of an object detected by the trained function can be returned.

[0054] The input data of the trained function can thus comprise two- and / or three-dimensional object measurement data and / or distance data. In particular, the input data can be in the form of a file containing a point cloud. The input of the object measurement data can comprise manual input into a user interface or, preferably, automatic input or transfer of the object measurement data via a first (input) interface. A sensor that acquires object measurement data, in particular a verification sensor, can preferably transmit object measurement data directly to the interface or be linked to it. The classification information can be output, in particular, via a second user interface or, preferably, via an (output) interface. The output interface can preferably be linked and / or connected to the user interface of the magnetic resonance device designed to carry out the examination.The classification of objects can preferably include additional categories. In particular, the classification of objects that cannot be assigned to the "patient's head" classification can be more detailed. For example, the additional categories can include pillows, headrests, other examination items, and other body parts (arms, for example).

[0055] In other words, the method for testing a magnetic resonance sequence for compliance with at least one limit value can comprise a machine learning model. Machine learning models can also be referred to as a trained function, trained machine learning model, function with trained parameters, artificial intelligence-based algorithm, or machine learning algorithm. In general, trained functions are designed to generate defined output data by processing input data. Machine learning models represent the cognitive learning processes typically associated with humans or the human brain. In particular, functions trained with training data can be used in pattern recognition. The parameters of a trained function can be updated, in particular, at regular intervals and / or iteratively through training.Commonly used training methods include supervised training, semi-supervised training, unsupervised training, or reinforcement training. In particular, the trained function can be trained using supervised and / or semi-supervised training. In particular, the trained function can comprise a neural network, a support vector machine, or a decision tree. In particular, the neural network can be a deep neural network, a convolutional neural network, or a convolutional deep neural network.

[0056] Advantageously, the check as to whether the recorded sensor data information depicts a patient's head, especially when spatially and / or temporally resolved temperature and distance information is available, can be significantly improved by machine learning methods such as neural networks.

[0057] According to one possible aspect of the invention, determining the head position information may comprise providing a trained function. Providing a trained function may comprise training a function, for example, a neural network. Training a function may in particular comprise: inputting training input data, preferably by means of a (first) training user interface; inputting (expected) training result data associated with the training input data, preferably by means of a (second) training user interface; training the function using the training input data and training result data, preferably by means of a training calculation unit; providing the trained function, preferably by means of a (third) training user interface. Object identification and / or object verification can advantageously be improved by training the function.

[0058] According to one aspect of the invention, a magnetic resonance apparatus comprising a magnet unit, a patient table, and a position-determining device is also proposed. According to this aspect, the magnet unit surrounds a patient receiving area. According to this aspect, the patient table can be moved into the patient receiving area. According to this aspect, the position-determining device can be configured to perform all steps or aspects of the described method for determining the head position.

[0059] The position-determining device can, in particular, comprise a distance sensor and / or a verification sensor. However, the position-determining device can, for example, also comprise only one verification sensor or more than two sensors. The position-determining device can preferably be a component or assembly consisting of the distance sensor, verification sensor, and a computing unit. Furthermore, the position-determining device can preferably comprise a housing. In particular, the position-determining device can be connected to the system control unit and / or the user interface of the magnetic resonance device.

[0060] A (conventional) magnetic resonance imaging system can advantageously be supplemented with a position-determining device. Retrofitting an existing magnetic resonance imaging system is also preferably possible. For example, the patient support device can be replaced with a patient support device including a position-determining device. Consequently, extensive structural modifications to the magnetic resonance imaging system and / or the patient support device are preferably not necessary.

[0061] According to one possible embodiment of the magnetic resonance apparatus, the position-determining device can be arranged on the patient table at one end of the patient table. In particular, the position-determining device can be arranged at a foot end of the patient table.

[0062] The patient table end can in particular be the head end or foot end of the patient table. The head end can in particular be the end of the patient table which, in the initial position of the patient table, has a shorter distance to the magnet unit of the magnetic resonance device. The foot end can therefore in particular be the end of the patient table which, in the initial position of the patient table, has a greater distance to the magnet unit. Since the typically more frequently used, preferred patient positioning is the head-first position, the sensors are preferably positioned at the foot end of the patient table. For a feet-first examination, the patient is positioned inverted on the patient table, i.e. with the head at the foot end of the patient table.

[0063] Advantageously, the sensor is located at a position (at the end of the patient table) that does not move into the patient admission area (examination area). Positioning the sensors at a large distance from the magnetic resonance system at the foot of the patient table enables cost-effective implementation and simplified sensor selection.

[0064] 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. A repeated description of corresponding parts in the respective exemplary embodiments is omitted. Exemplary embodiments may differ essentially in the arrangement of the units.

[0065] They show: Fig. 1 a head-first positioning of a patient in a magnetic resonance device with position determination device in a schematic representation, Fig. 2 a procedure for testing a magnetic resonance sequence for compliance with at least one limit value, Fig. 3 shows a schematic representation of a foot-first positioning of a patient in a magnetic resonance device with a position determination device and a disturbing object, Fig. 4 shows a schematic representation of a foot-first positioning of a patient in a magnetic resonance device with a position determination device, Fig. 5 a process flow of testing a magnetic resonance sequence for compliance with at least one limit value with further process steps, Fig. 6 a process flow of testing a magnetic resonance sequence for compliance with at least one limit value with intermediate steps.

[0066] In Fig. 1 schematically illustrates a magnetic resonance apparatus 10. 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. Furthermore, the magnetic resonance apparatus 10 comprises a patient receiving area 14 for receiving a patient 15. The patient receiving area 14 in the present exemplary embodiment is cylindrical and is surrounded in a circumferential direction by the magnet unit 11. In principle, however, a different design of the patient receiving area 14 is conceivable at any time. The patient 15 can be pushed into the patient receiving area 14 by means of a patient support device 16 of the magnetic resonance apparatus 10. For this purpose, the patient support device 16 comprises a patient table 17 designed to be movable within the patient receiving area 14.

[0067] The magnet unit 11 further comprises a gradient coil unit 18 for generating gradient fields 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 further 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 radio-frequency magnetic resonance sequences into an examination space, which is essentially formed by a patient receiving area 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.

[0068] 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 controls the magnetic resonance apparatus 10, for example, performing a predetermined imaging gradient echo sequence. The system control unit 22 can also connect the radio-frequency antenna control unit 21 and the gradient control unit 19 and forward control commands to the corresponding control unit. Furthermore, the system control unit 22 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 and reconstructed magnetic resonance images can be displayed on a display unit 24, for example, on at least one monitor, of the user interface 23 for medical personnel. Furthermore, the user interface 23 has an input unit 25, by means of which information and / or parameters can be entered by the medical personnel during a measurement process.

[0069] Patient 15 is in Fig. 1 in a position referred to as head-first position on the patient table 17. The patient's head 29 is supported by a head coil 26. The head coil 26 is mechanically fastened, for example screwed, clamped, or clamped, in a (spatially) defined position. The position of the patient's head 29 is thus always defined or known by the head coil 26, even when the patient table 17 is moved by the patient support device 16. The patient table 17 of the magnetic resonance device 10 also has a position determination device 33 consisting of a distance sensor 30, a verification sensor 31, and a computing unit 32. The two sensors 30, 31 are connected to the computing unit 32. Measured data from the sensors 30, 31 can be forwarded to the computing unit 32, where they can be stored and processed.At the same time, the computing unit can define measurement tasks, in particular commands, and send them to the sensors 30, 31.

[0070] Due to the head-first positioning of patient 15, Fig. 1, the head position is not measured by the sensors 30, 31; instead, the patient's head position is determined by the computing unit 32 based on the position of the head coil 26, for example, via contact detection. However, the position-determining device 33 can also comprise a sensor and / or tracker, unlike the one shown, that can detect or determine the position of the head coil. Alternatively, the position of the head coil or the patient's head can also be entered by a user via the user interface 23. From the entered head position, the system control unit 22 or the computing unit 32 can calculate compliance with the limit values ​​with regard to the local energy input for or into the patient 15 based on the main magnetic field 14 generated by the main magnet 12, the gradient fields generated by the gradient coils 18, or the radio-frequency pulses generated by the radio-frequency antenna unit 20.In this exemplary embodiment, the head position of the patient 15 is preferably not determined by the distance sensor 30 or verification sensor 31.

[0071] The type of positioning of the patient 15, or the determination of whether it is a head-first positioning (shown) or a foot-first positioning (not shown), can be performed by the computing unit 33 or the system control unit 22. Alternatively, the type of positioning of the patient 15 can also be entered via the user interface 23. Alternatively, the type of positioning of the patient 15 can be determined by the verification sensor. For example, the verification sensor 31 can be configured to detect whether a nearest object is the feet or the head of a patient 29.

[0072] In Fig. 2 shows the method flow for checking a magnetic resonance sequence for compliance with at least one limit value. After determining the position information of a specific body part of a patient, in particular the head, in 45, the magnetic resonance sequence is checked for compliance with at least one limit value based on the position information of the specific body part, in particular the head, in 50. Further features of the method or method steps, in particular the determination of the position information of the specific body part, are described in the Fig. 5 and Fig. 6. The acquisition of distance measurement data and object measurement data using respective sensors is described in the Fig. 3 and Fig. 4 executed.

[0073] Patient 15 is in Fig. 3 in a position referred to as feet-first positioning on the patient table 17. With this type of positioning, no head coil is usually used, but the patient 15 is positioned on the patient table without any mechanical constraints. For example, in the illustration of the Fig. 3 positioned closer to the head end of the patient table, or at a greater distance A from the reference point 28 (foot end of the patient table 17). The type of positioning of the patient 15 can be entered by an operator via a user interface 23 or can be (automatically) detected from a scan protocol or examination instruction by the magnetic resonance device 10 or the system control unit 22. Alternatively, the type of positioning can be checked or detected by the verification sensor 31.

[0074] The distance sensor 30 and the verification sensor 31 are attached to one end of the patient table 17 of the patient support device 16. The sensors 30 and 31 are attached to the front side of the patient table 17, referred to as the foot end. When the patient table 17 is moved into the patient receiving area 14 of the magnetic resonance device 10 during an examination (image acquisition), the sensors 30, 31 are thus always arranged at a distance from the main magnet 12, the gradient coils 18, or the radio-frequency antenna unit 20. The sensors 30, 31 are therefore not moved into the patient receiving area 14 (also referred to as the examination area and / or magnetic field area). In particular, the sensors 30, 31 are spaced from the isocenter 27 of the magnetic field area. The isocenter 27 designates the area located in the center of the examination area (patient receiving area).Typically, the magnetic field is strongest at isocenter 27. This means that the energy acting on the patient during an examination is typically greatest at isocenter 27.

[0075] This embodiment of the magnetic resonance device does not have a computing unit 32. The processing of the sensor signals, or distance data and object data, is performed by the system control unit 22, to which the sensors 30 and 31 are connected. The system control unit 22 can include a computing unit (designed for this purpose).

[0076] The position of the patient's head 29 can be determined by the vertex. The vertex here is the point on the patient's head 29 that is closest to the sensor arrangement 30, 31. Between the sensors 30, 31 and the patient's head 29, objects can (unintentionally) lie / store on the patient table 17, as shown by way of example in Fig. 3 the (obstacle) object 27. The objects can have different sizes. Larger objects, in particular, can impair and / or prevent the distance and / or verification measurement. Due to its nature, particularly its geometry, the object 27 shields the head of the patient 29, causing the verification sensor 31 to detect the object 27 rather than the patient's head. The distance measurement by the sensor 30 therefore does not determine the head position of the patient 15, but rather that of the object 27. An (error) message is output, and an estimated value or safety value is used for the examination.

[0077] Also in Fig. 4, the patient 15 is in a foot-first position on the patient table 17. The comparison of the Fig. 2 and Fig. 3 particularly illustrates the possible different positions of the patient 15 on the patient table 17. While in Fig. 2 a larger distance A between patient 15 and reference point 28 is shown, in Fig. 3 a smaller distance B is shown. In Fig. 4 there is also no obstacle between the patient 15 and the positioning device 33.

[0078] The sensors, distance sensor 30 and verification sensor 31, and the computing unit 32 form a common assembly and / or component, the position-determining device 33. The position-determining device 33 is integrated into the patient support device 16 or into the patient table 17. For example, the position-determining device 33 is built into a housing of the patient table 17. The reference point can therefore be defined as a point at the end of the patient table 17 at which the sensor device or position-determining device 33 is arranged. Preferably, the center of the component or assembly can be selected as the reference point 28. The position of the patient's head 29 can also be described by the center of the head.

[0079] In Fig. Figure 5 shows a possible, detailed sequence of the method steps for testing a magnetic resonance sequence for compliance with at least one limit value. Based on the object measurement data determined by a verification measurement 41, an object recognition (verification of the head) 44 is performed. The verification measurement can preferably be carried out as shown in Fig. 3 and Fig. 4, by a verification sensor. Classification and / or object recognition can preferably be carried out by a trained function. For example, a neural network can be trained in advance using object data marked accordingly by a medical professional. Training of the neural network can continue during the examinations. For this purpose, object measurement data without further patient information is preferably used. The training and / or the results of object recognition can be checked at regular intervals, for example by sampling. Preferably, the object is classified as a patient's head or another object. Alternatively, further classifications can be made, for example, according to the type of object.

[0080] The distance 45 of the target object is determined after the object 44 has been identified. A distance sensor is used to measure the distance 42, preferably as shown in Fig. 3 and Fig. 4, the determination of distance measurement data. Preferably, the distance measurement is performed in parallel with the object detection 44 or the verification measurement 41. However, the distance measurement can also be performed after the object detection 44. The distance determination 45 is performed in particular on the basis of the distance measurement data, but can also be performed on the basis of the object measurement data or a combination of both data sets.

[0081] Finally, in a method step 50, compliance with a limit value is checked. For example, a maximum energy input is calculated based on the determined head position. This value is preferably compared with a threshold value, and a warning is issued if the threshold value is exceeded. However, a positive result, i.e., the limit value is exceeded, can also be returned.

[0082] In Fig.Figure 6 shows the method flow for testing a magnetic resonance sequence for compliance with at least one limit value, with additional intermediate and / or partial steps. In a first step, patient position detection 40 occurs. This can be performed by a user / operator of the magnetic resonance device. Alternatively, detection can be performed by sensors, in particular distance sensors and / or verification sensors. This is followed in parallel by a verification measurement 41 and a distance measurement 42 using respective sensors. After the measurement data 43, consisting of object measurement data and distance measurement data, have been combined, object detection 44 and position determination 45 occur. The combination of the measurement data can take place in a computing unit, in particular the computing unit of the position determination unit. For example, the object data can be compared with the distance measurement data, and deviations can be saved.All information can be listed in a document, for example, a text document, using a defined list (separated by spaces). The document containing the combined information from the distance measurement and object measurement (verification measurement) can form the information basis for object recognition 44 and distance calculation (position determination) 55. If a patient's head is recognized or verified with sufficient certainty in the object recognition 44, the position calculation 45 of the patient's head is carried out consecutively. In a verification step 46, the checking 46 of the position information can take place. This can be done manually by a user / operator or automatically by, for example, a neural network. The checking 46 can be based on provided patient information 49.However, previous examinations, the type of examination, the user, or other environmental conditions can also be taken into account. If the head cannot be verified, or if an object other than the head of the patient 15 is detected, an estimated value 48 is returned from the verification step 44. If irregularities, errors, or uncertainties are detected during the check of the position information 46, an estimated value 48 is also returned. If the verification 44 and check 46 are positive, the position value of the patient's head is output. Finally, a check is performed to determine whether a limit value for the energy absorption rate for the head of the patient 15 would be exceeded.

[0083] 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 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] Method for testing a magnetic resonance sequence for compliance with at least one limit value, the method comprising: Determination of position information of a patient’s head on a patient table, Acquisition of distance measurement data for measuring a distance between a target object and a reference object, in particular a reference point, of the patient table, where the target object is the patient’s head, whereby the position information of the head is determined based on the distance measurement data, Recording of object measurement data, whereby the target object is verified as the patient’s head based on the object measurement data, Checking the magnetic resonance sequence for compliance with at least one limit value based on the head position information. [2] Method according to claim 1, wherein the distance measurement data is acquired by means of a distance sensor. [3] The method of claim 2, wherein the distance sensor comprises an ultrasonic sensor. [4] Method according to claim 2 or 3, wherein the distance measurement data comprises two- and / or three-dimensional distance measurement data. [5] Method according to one of the preceding claims, wherein the acquisition of the object measurement data is carried out by means of a verification sensor. [6] The method of claim 5, wherein the verification sensor comprises a temperature sensor. [7] Method according to claim 5 or 6, wherein object measurement data comprises two- and / or three-dimensional object measurement data. [8] Method according to one of claims 5 to 7, wherein the determination of the position information of the head is further carried out on the basis of the object measurement data. [9] Method according to one of the preceding claims, wherein the method comprises providing patient data, wherein the determination of the position information of the patient's head is further carried out on the basis of the patient data. [10] Method according to one of the preceding claims, wherein a fixed estimated value is defined as position information if the position information of the head cannot be determined with sufficient certainty and / or accuracy from measurement data. [11] Method according to one of the preceding claims, wherein the determination of the position information of the head comprises a computer-implemented, trained function-comprising object classification method, comprising the following steps: Input of object measurement data into the trained function, Applying a trained function that is designed to detect and classify objects using the object measurement data, Return a classification of an object detected using the trained feature. [12] Magnetic resonance apparatus comprising a magnet unit surrounding a patient receiving area, a patient table that can be moved into a patient receiving area, and a position determining device that is designed to carry out all steps of the method for head position determination according to one of claims 1 to 11. [13] Magnetic resonance apparatus according to claim 12, wherein the position determining device is arranged on the patient table at a foot end of the patient table.

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