Method for recording magnetic resonance data and magnetic resonance equipment

Abstract

Method for acquiring magnetic resonance data of a target area of ​​a patient moving during respiration using a magnetic resonance device (1), wherein an optical camera (5) arranged in a patient recording of the magnetic resonance device (1) and directed towards the patient is used, wherein image data of the patient acquired by the camera (5) before and / or during the acquisition of the magnetic resonance data are evaluated to obtain respiratory information describing the respiratory state, characterized in that the respiratory information is used to trigger and / or correct movement and / or assess a breath-holding process of a patient, wherein a message is issued to an operator when an interrupted breath-holding process is detected during the acquisition of magnetic resonance data.

Description

[0001] The invention relates to a method for recording magnetic resonance data of a target area of ​​a patient moved by respiration using a magnetic resonance device and a magnetic resonance device.

[0002] Magnetic resonance imaging (MRI) is particularly well-suited for imaging soft tissues, as it allows for clear differentiation between various tissue types within a patient, resulting in high soft tissue contrast. Therefore, MRI is frequently used to perform examinations of a patient's upper body, such as abdominal and / or cardiac examinations.

[0003] One challenge when performing magnetic resonance imaging (MRI) scans of the upper body is the patient's breathing. If the target area being imaged moves due to respiration, motion artifacts can occur, significantly degrading the resulting image quality. Therefore, methods have already been proposed to avoid or reduce such motion artifacts.

[0004] One known method involves acquiring magnetic resonance imaging (MRI) data during a patient's breath-hold. This involves giving breathing commands, for example via special headphones or visually, to the patient within the MRI scanner, assuming the patient will follow these commands. However, the patient's cooperation is crucial, and it is only possible to determine whether the MRI data was actually acquired during breath-holding upon viewing the reconstructed images.

[0005] It has also been proposed to use a respiratory signal, such as respiratory information, to trigger the acquisition of magnetic resonance imaging (MRI) data at specific points in the respiratory cycle. To determine the respiratory signal, one approach is to use MRI to acquire and analyze a so-called navigator, i.e., a low-dimensional image of a contrast edge moving with respiration within the patient, such as the diaphragm. Alternatively, dedicated respiratory sensors could be used, such as a breathing belt, a chest strap, a respiratory sensor integrated into the patient bed, and the like. Both navigators and the sensor data from a respiratory sensor can provide respiratory information describing the current breathing state, thus enabling the acquisition of MRI data.Each segment of the magnetic resonance data can be triggered, always when the same respiratory state is present, for example, during complete expiration. Regarding the use of navigators, extremely complex positioning of the navigator and clear contrast are required, which is not always ideal or easily achievable. Sensors represent additional objects in the imaging area, particularly in the homogeneity volume of the MRI scanner, thus further reducing the already limited space in the patient acquisition area and potentially interfering with the acquisition of the MRI data.

[0006] Methods for motion correction of magnetic resonance data have also been proposed, which can, for example, use such respiratory information; however, the application of such methods with the described respiratory information is less preferred because they cannot describe the movement in the actual target area with sufficient accuracy.

[0007] The invention is therefore based on the objective of providing a simple method for recording magnetic resonance data while taking respiration into account.

[0008] To solve this problem, a method of the type mentioned at the outset is provided according to the invention, which is characterized in that an optical camera arranged in a patient recording of the magnetic resonance device and directed towards the patient is used, wherein image data of the patient recorded by the camera before and / or during the recording of the magnetic resonance data are evaluated to provide respiratory information describing the respiratory state and the respiratory information is used to trigger and / or correct movement and / or assess a patient's breath-holding process.

[0009] The invention therefore proposes to solve the described problem of respiration-controlled or respiration-influenced magnetic resonance imaging by means of an optical camera located in the patient bore of the magnetic resonance device, which records the patient's respiratory movements as image data. Such optical imaging devices, also referred to as "in-bore cameras," have already been proposed for monitoring head movements during head scans. The cameras are designed to be magnetic resonance compatible and can, for example, be arranged on and / or in an inner casing of the patient bore, or on other devices located within the patient bore, such as on the housing of a head coil, etc.The camera is typically positioned to capture the imaging area, i.e., the homogeneous volume, thus also including the target area located within it and surrounding areas of the patient. If magnetic resonance imaging (MRI) data of a target area on the patient's upper body is to be acquired, the chest (or objects placed on it), which moves particularly during breathing, is also captured and can be detected in the image data.

[0010] Image analysis, which can be performed, for example, using an image processing unit of a control unit of the magnetic resonance imaging device, allows respiratory movements of the patient to be detected and thus inferred respiratory information that describes the current respiratory state, which is then preferably used to trigger and / or assess a patient's breath-holding process.

[0011] One of the advantages of the present invention is the ability to utilize an existing in-bore camera for monitoring respiration or controlling the sequence during the acquisition of magnetic resonance imaging (MRI) data under free breathing. The value of the camera integrated into the patient's imaging system increases with this additional application; furthermore, respiratory sensors, i.e., additional hardware components, can be avoided. The camera's functionality can be extended at the software level, particularly within the image processing capabilities, to perform or monitor respiration-controlled imaging.

[0012] In this context, it is particularly preferred if the respiratory information is obtained by locating and tracking a surface of the patient that moves during respiration and / or an object positioned on a surface of the patient that moves during respiration. It is especially advantageous if the surface under consideration is the patient's chest, which rises and falls during respiration. If an object, in particular a local coil, is positioned on the patient's chest, this movement is also transmitted to the object resting on the corresponding surface, so that its movement can also be tracked.

[0013] Locating patient surfaces, particularly those of the chest, that move during breathing can be achieved, for example, using a patient model within the framework of image processing. It is also possible to employ visually perceptible markers positioned on the patient to simplify the detection of moving surfaces. Finally, image processing also allows for the analysis of movement patterns in the image data over time. For instance, movement patterns in the image data can be evaluated for their temporal periodicity, where a specific frequency range is known for respiratory movements. For tracking purposes, a surface segment exhibiting the greatest amplitude of periodic respiratory movement, as seen in the image data, can then be selected. Naturally, combinations of these methods are also conceivable within the framework of image processing.Image processing methods that allow the tracking of points / objects in temporally successive images are already known in the prior art and can also be used within the scope of the present invention.

[0014] In this context, it is particularly advantageous if the camera is a 3D camera, especially a time-of-flight camera, and if the distance from the camera to the surface and / or object is evaluated over time to determine respiratory information. Alternatively, distance information can also be obtained by using multiple cameras positioned at different locations, as well as by optical flow methods. However, it is preferred to use the time-of-flight method to determine the distance to the moving surface / object placed on it, which is particularly suitable for describing respiratory movement. This results in a periodic change in distance that reflects the patient's corresponding respiratory movement and is particularly easy to interpret.

[0015] In a first embodiment of the present invention, the respiratory information can be used to trigger the acquisition of at least a portion of the magnetic resonance data, in particular a slice. Thus, the direct detection of respiratory movement by the camera is used to determine the presence of a specific respiratory state, for example, complete expiration, in order to initiate the acquisition of the magnetic resonance data, in particular a portion of the magnetic resonance data, which can be acquired within the expected timeframe in which the respiratory state deviates only slightly from the trigger respiratory state. Therefore, a control unit that has determined the respiratory information verifies the presence of the trigger respiratory state and generates a trigger signal that initiates the acquisition during the correct respiratory state.

[0016] Another advantageous embodiment of the invention provides that, if an interrupted breath-hold is detected during the acquisition of magnetic resonance data, a message is sent to an operator and / or the magnetic resonance data acquired during the interruption of breath-holding are marked and / or discarded. It is therefore also possible to monitor whether the patient actually holds their breath as desired for the entire measurement period during the acquisition of the magnetic resonance data, or whether the breath-hold is interrupted. If the patient breathes before the measurement is completed, for example due to disease-related limitations of the respiratory organs, corresponding information can be sent as a message to the operator.

[0017] However, a particularly preferred embodiment of the invention in this context provides that discarded or marked magnetic resonance data are automatically remeasured after breath-holding is resumed. This means that the breathing information can also be used to automatically trigger the reacquisition of entire slices or other portions of the magnetic resonance data that were acquired during an interruption of the breath-holding process.

[0018] In general, and also in this context, it is particularly advantageous if, when an interrupted breath-hold is detected during the acquisition of magnetic resonance (MRI) data, the respiratory information present during the breath-hold is stored and used as a reference to current respiratory information when restoring the same or a comparable respiratory state. This means that the respiratory state present during breath-holding, described by the corresponding respiratory information, can be stored as a reference state or reference information and used to restore the same respiratory state, i.e., the reference state, at a later time, for example, to repeat the acquisition of discarded and / or marked MRI data.For example, depending on a deviation of the current breathing information from the reference information, instructions can be issued to the patient to guide them as easily as possible to correctly restore the reference state.

[0019] In addition to the method, the invention also relates to a magnetic resonance imaging (MRI) device comprising a patient acquisition unit with an optical camera arranged therein, and a control unit comprising an image processing unit, which is configured to carry out the method according to the invention. All aspects relating to the method according to the invention can be applied analogously to the magnetic resonance imaging device according to the invention, with which the aforementioned advantages can therefore also be obtained.

[0020] It should also be noted that the procedure described here is applicable to both open and closed magnetic resonance devices, but is preferably used in so-called closed magnetic resonance devices, in which the patient intake is formed by a cylindrical bore in a main magnet unit.

[0021] Further advantages and details of the present invention will become apparent from the exemplary embodiments described below and from the drawings. These show: Fig. 1 a flowchart of a first embodiment of the method according to the invention, Fig. 2 a flowchart of a second embodiment of the method according to the invention, and Fig. 3 a magnetic resonance device according to the invention.

[0022] In the exemplary embodiments of the method according to the invention described below, magnetic resonance data of a target area of ​​the patient moving due to respiration are to be acquired with as few artifacts as possible. For this purpose, it is assumed that at the beginning of the procedure the patient is already positioned on a patient bed within the patient acquisition area in such a way that the target area, for example the heart or the abdominal region, is located within the homogeneity zone of the magnetic resonance device.

[0023] In a first embodiment, in step S1, image data is acquired with a 3D camera positioned within the magnetic resonance imaging unit and directed towards the homogeneous volume, prior to the actual acquisition of the magnetic resonance imaging data. This serves to initiate the determination of respiratory information from subsequently acquired image data by evaluating this image data. For this purpose, image processing of the image data takes place in step S1, the aim of which is to identify and subsequently track a surface of the patient that moves due to respiration, or an object located on it that is thus moved along with it. Various approaches are conceivable for this, which can also be combined within the scope of the present invention.The patient's chest is a suitable surface for this purpose, as it can be located using a patient model and appropriate object recognition algorithms, possibly also utilizing background information on the patient's positioning within the MRI scanner. The camera can also be registered with the MRI scanner's coordinate system, allowing a chest position detected by a localizer, for example, to be relocated from the MRI data to the camera's image data, or at least aiding in its relocation. If an object, particularly a local coil, is in contact with the patient, especially on the chest, it can, of course, also be located using object classification.The camera used here is a 3D camera, allowing for the determination of distances to individual features visible in the image. The Time-of-Flight (TAF) method is employed for this purpose. This also makes it possible to analyze distance profiles for various features in the image data, for example, to determine whether the frequency of the observed periodic movement lies within a reference frequency band for possible respiratory movements. The corresponding moving surfaces can then be sorted according to the amplitude of the periodic movement, whereby, for example, the surface with the highest amplitude of movement, which will usually be the chest, can be tracked to determine the respiratory state. If the moving surface to be tracked is within the specified range, the system can then analyze the data to determine the amplitude of the movement.Once the moving object to be tracked is known, the distance in the corresponding image area can be constantly monitored, thus providing breathing information that describes the current breathing state during the breathing cycle.

[0024] Step S2 indicates the now following continuous determination of breathing information from the camera's image data.

[0025] In step S3, the respiratory information is monitored to determine whether a specific, desired respiratory state, such as maximum expiration, is sufficiently accurate. If so, a trigger signal is issued, which in step S4 initiates the acquisition of magnetic resonance (MRI) data from the patient, provided the corresponding respiratory state is expected to fall within certain tolerance ranges. This can be determined, for example, from an evaluation of previously recorded respiratory information spanning several respiratory cycles, or if the respiratory information does not indicate a respiratory state outside the tolerance range. It is not necessary to acquire all required MRI data during a single acquisition session. Therefore, in step S5, it is verified whether all required MRI data have already been acquired, specifically whether all slices have been measured.If this is not the case, in step S2 the system continues to monitor whether the desired breathing state is achieved, so that further magnetic resonance data, in particular additional slices, can be acquired. Once all magnetic resonance data have been acquired, the procedure is terminated in step S6.

[0026] In the exemplary embodiment of the Fig. 2. After initialization in step S1, which corresponds to the first embodiment, at least one breath-hold command is issued to the patient in step S7. This command establishes a specific, desired breathing state for the acquisition of the magnetic resonance data, which will subsequently be referred to as the reference state. The acquisition of the magnetic resonance data begins in step S8. Parallel to the acquisition of the magnetic resonance data, breathing information is further determined in step S2. The breathing state present after the breath-hold command in step S7, described by the subsequently measured breathing information, is stored, so that the corresponding breathing information forms a reference.

[0027] In step S9, it is checked whether the current breathing information deviates from the reference information outside a tolerance range, i.e., whether the patient has interrupted breath-holding. If this is not the case, monitoring in step S2, as well as the acquisition of magnetic resonance data, continues. However, if it is determined that breath-holding has been interrupted, i.e., the reference state of breathing is no longer present, several actions are taken in step S10 of a given embodiment. First, a message about the interruption of breath-holding is issued to an operator. At the same time, the magnetic resonance data acquired during the absence of the reference state are marked and discarded. The acquisition process is interrupted.

[0028] In step S11, it is checked in every case whether all desired magnetic resonance (MRI) data have already been acquired, or, if all MRI data are available, whether MRI data have been marked. If this is the case, in step S7, renewed breathing commands are used to attempt to restore the reference state as accurately as possible. Following this, in step S8, under further monitoring in step S2, the marked or still missing MRI data can be acquired. Once all MRI data have been acquired in the reference state, the procedure is terminated in step S6.

[0029] Fig.Figure 3 shows a schematic diagram of a magnetic resonance device 1 according to the invention, which in this case comprises a main magnet unit 2 in which the magnet generating the fundamental magnetic field is arranged. A cylindrical patient receptacle 3 is provided in the main magnet unit 2, which, as is generally known, can be surrounded by a high-frequency coil arrangement and a gradient coil arrangement. A patient, not shown in detail here, can be moved into the patient receptacle 3 by means of a patient table 4.

[0030] A 3D camera 5, here a TOF camera, is arranged on a panel of the patient admission 3, the detection area 6 of which includes at least the homogeneity volume of the magnetic resonance device 1.

[0031] Image data captured by the camera 5 are transmitted to an image processing unit 7 of a control unit 8 of the magnetic resonance device 1. The control unit 8 is designed to carry out the method according to the invention, but also enables further applications of the image data from the camera 5, for example, for tracking the movement of a head.

[0032] Although the invention has been illustrated and described in detail by the preferred embodiment, the invention is not limited by the disclosed examples and other variations can be derived by the person skilled in the art without leaving the scope of protection of the invention.

Claims

[1] Method for recording magnetic resonance data of a target area of ​​a patient moving by respiration using a magnetic resonance device (1), wherein an optical camera (5) arranged in a patient recording of the magnetic resonance device (1) and directed towards the patient is used, wherein image data of the patient recorded by the camera (5) before and / or during the recording of the magnetic resonance data are evaluated to obtain respiratory information describing the respiratory state, characterized by , that the respiratory information is used to trigger and / or correct movement and / or assess a patient's breath-holding process, whereby a message is issued to an operator if an interrupted breath-hold is detected during the acquisition of magnetic resonance data. [2] Method according to claim 1, characterized bythat the respiratory information is obtained by localizing and tracking a surface of the patient that is moved by respiration and / or an object located on a surface of the patient that is moved by respiration. [3] Method according to claim 2, characterized by that the surface under consideration is the patient's chest and / or the object is a local coil. [4] Method according to claim 2 or 3, characterized by , that the camera (5) is a 3D camera (5) and that the distance from the camera (5) to the surface and / or the object is evaluated over time to determine the breathing information. [5] Method according to any of the preceding claims, characterized by that the breathing information is used to trigger the acquisition of at least part of the magnetic resonance data, in particular a slice. [6] Method according to any of the preceding claims, characterized by, that if an interrupted breath-hold is detected during the acquisition of magnetic resonance data, the magnetic resonance data acquired during the interruption of breath-holding will be marked and / or discarded. [7] Method according to claim 6, characterized by , that discarded and / or marked magnetic resonance data are automatically remeasured after breath-holding is restored. [8] Method according to any of the preceding claims, characterized by , that if an interrupted breath-hold is detected during the acquisition of magnetic resonance data, the breathing information present during the breath-hold is stored and used as a comparison to current breathing information when restoring the same or a comparable breathing state. [9] Magnetic resonance imaging device (1) comprising a patient recording device (3) with an optical camera (5) arranged therein and a control device (8) comprising an image processing unit (7) configured to carry out a method according to one of the preceding claims.

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