Detection of repetition patterns in MR sequences

Abstract

Methods for determining sequence information from an MR sequence, wherein the method comprises determining the sequence information based on at least one pattern of the MR sequence, wherein for at least one first subsection of the MR sequence, first subsection information and a first pattern of the MR sequence are determined, wherein the sequence information is determined by extrapolating the first subsection information to a section of the MR sequence, if the determined first pattern is repeated at least once in that section of the MR sequence.

Description

[0001] The invention relates to a method for determining sequence information of a magnetic resonance sequence, a computer program product and an evaluation unit for carrying out such a method, as well as a magnetic resonance device with such an evaluation unit.

[0002] Magnetic resonance imaging (MRI) is a well-known technique for generating images of a patient's internal body, based on the physical phenomenon of magnetic resonance (MR). An MR scan typically involves a temporal sequence of rapidly switched gradient pulses and radio frequency pulses (RF pulses), which can be defined by an MR sequence.

[0003] During an MRI scan, gradient pulses are typically generated by a gradient coil unit of the MRI scanner and superimposed on a static background magnetic field. These gradient pulses can induce peripheral nerve stimulation (PNS) in the patient being examined. RF pulses are typically generated by a radio frequency antenna unit of the MRI scanner and transmitted into the patient to trigger MRI signals. The energy absorbed by the RF pulses per unit of time and per kilogram of body weight is usually referred to as the specific absorption rate (SAR). The absorption of RF energy can lead to heating of the patient's body tissue.

[0004] To avoid endangering the patient, standards bodies require that MRI scans adhere to strict limits regarding their effects. To prevent scan terminations due to exceeding these limits during the MRI scan, compliance with these limits is typically estimated before the scan begins. This estimation is conventionally parameterized by a sequence developer, who, for example, defines time intervals to be checked directly in the MRI sequence code to estimate the patient's nerve stimulation and / or calculate the energy absorbed. Due to the multitude of possible input parameters that influence the MRI sequence, this parameterization is not trivial and therefore prone to errors.

[0005] In addition to the limitations described above for safely examining the patient, there are also limits imposed by the capabilities of the MRI scanner. For example, the gradient coil unit can only generate a limited gradient field, and the radio frequency antenna unit can only generate a limited B1 field.

[0006] Document DE 10 2014 219 785 A1 discloses a method for operating an imaging medical examination device, wherein functional sub-sequences of a measurement sequence are locally optimized to a corresponding effective volume.

[0007] The invention is based on the objective of quickly and reliably determining sequence information, in particular relating to one or more quantities restricted by limit values, of an MR sequence.

[0008] The problem is solved by the features of the independent claims. Advantageous embodiments are described in the dependent claims.

[0009] Accordingly, a method for determining sequence information of an MR sequence is proposed, wherein the method includes determining the sequence information based on at least one pattern of the MR sequence.

[0010] The sequence information can be determined using an evaluation unit, which in particular has a processor and / or memory. Preferably, the MR sequence is provided, for example by means of a provisioning unit, such as a database, which transfers the MR sequence to the evaluation unit.

[0011] The MR sequence can be described using sequence parameters. Preferably, the MR sequence is first simulated over its entire course; that is, the complete MR sequence can be prepared based on the sequence parameters.

[0012] In particular, a sequence diagram can be created using this method; that is, the result of such a simulation and / or processing can be a sequence diagram. A sequence diagram can have multiple sampling points, to which one or more values ​​of the MR sequence, such as the amplitude of an RF pulse and / or a gradient pulse, are assigned.

[0013] The patterns of the simulated and / or processed MR sequence and / or the resulting sequence diagram can then be used to determine the sequence information.

[0014] A pattern can be understood as a structure, particularly one that is regular and / or repetitive. At least one pattern of the MR sequence can comprise a sequence of gradient pulses and / or RF pulses, particularly one that is regular and / or repetitive. This sequence of gradient pulses and / or RF pulses can furthermore exhibit similarities and / or regularities.

[0015] The invention takes advantage of the fact that the sequence of MR measurements typically follows strong regularities, often implemented through several nested loops. The sequence can, in particular, include sub-modules that are regularly executed at certain times or during certain loops. By recognizing these patterns, a time-consuming evaluation of the complete MR sequence to determine the desired sequence information can be avoided.

[0016] Preferably, the sequence information includes at least one limiting parameter that characterizes, for example, an absorption rate, in particular a specific absorption rate, and / or nerve stimulation, in particular peripheral nerve stimulation. As already explained, these are particularly important parameters for the safe operation of an MR system.

[0017] Alternatively or additionally to these patient-related aspects, at least one limiting factor can also relate to hardware-related aspects. For example, at least one limiting factor can characterize a limit of an MR system, in particular the strength of a gradient field and / or the gradient rise rate and / or the strength of a B1 field. The strength of the gradient field and the gradient rise rate are usually limited by the gradient coil unit of the MR system, while the strength of the B1 field is limited by the radio frequency antenna unit. The sequence information can, for example, include the alternating magnetic fields generated by the radio frequency antenna unit, such as an averaged B1 field B. 1,average and / or a maximum B1 field B 1,peak.By considering these performance-relevant parameters, the MR sequence can be checked on-the-fly to ensure that the limits of the MR system are observed. This allows for more effective utilization of the MR system.

[0018] Preferably, at least one pattern is determined based on the MR sequence and / or on additional information. When determining at least one pattern based on the MR sequence, any regularities in the MR sequence are preferably analyzed and / or recognized automatically. Additional information can include prior knowledge and / or information that, in particular, contains the parameterization of repeating loops. Furthermore, the additional information can include a metric indicating in which regions of the MR sequence the patterns relevant to the determined sequence information repeat, in order to prevent changes in the sequence information over the course of the MR sequence from leading to an incorrect estimation of the sequence information.

[0019] To simplify the estimation of sequence information, the MR sequence or sequence diagram can be supplemented with information indicating that certain repetitions are fundamentally identical with respect to the evaluated parameters. For example, it can be assumed that phase coding used for spatial encoding results in a multiplication of the sampling pattern with respect to the B1 parameters, particularly assuming that techniques with variable flip angles, such as SPACE (Sampling Perfection with Application optimized Contrasts using different flip angle Evolution) or VFA-FLASH (Variable Flip Angle-Fast Low Angle Shot), are not considered.

[0020] However, a combination of additional information and automated analysis is also possible.

[0021] Preferably, the analysis of the MR sequence is stopped as soon as at least one pattern is detected. Ideally, the detected pattern can then be used to extrapolate to the entire course of the MR sequence.

[0022] Preferably, the sequence information retrieval is aborted after a defined time. For example, if no pattern is detected within a certain period, the process can be terminated. This avoids excessively long computation times and allows the desired sequence information to be determined conventionally without using a pattern.

[0023] The specified time can, for example, be entered by an operator of the MRI device and / or stored in a memory from which the specified time can be provided to the evaluation unit.

[0024] Furthermore, for at least one initial subsection of the MR sequence, initial subsection information and an initial pattern are determined. The sequence information is then extrapolated from the initial subsection information to a section of the The MR sequence is determined if the detected pattern repeats at least once in that section of the magnetic resonance sequence. Such extrapolation, which is usually based on the assumption that the patterns repeat regularly, can greatly accelerate the determination of sequence information.

[0025] Preferably, a section comprises at least one subsection; that is, a subsection is typically a subset of a section. Such a division of the MR sequence into sections and subsections advantageously reflects the structure of the MR sequence, which often has one or more loops, possibly nested within each other.

[0026] Typically, the smallest repeating structure of an MR sequence is encompassed by a repetition time (TR). A subsection can be temporally delimited by at least one, preferably fewer than ten, and in particular exactly one, repetition time. The repetition time is generally the time between two RF excitation pulses. Within the TR interval, depending on the measurement technique, MR signals are usually acquired with, for example, one or more phase encodings.

[0027] The subsection information preferably includes sequence information valid for the respective subsection. For example, if subsection information is determined for the first repetition time and a pattern is detected that is found again in a second repetition time, the first subsection information can be extrapolated to the second and also further repetition times of the section.

[0028] As previously explained, a sampling point in a sequence diagram can be understood as a time point to which one or more values ​​of the MR sequence are assigned. The first subsection can comprise several, especially consecutive, sampling points, each with one or more values ​​of the MR sequence, from which an initial pattern can be determined.

[0029] Preferably, after identifying a repetition of the first pattern in the section of the MR sequence, a further pattern from another subsection within that section is identified and compared with the first pattern. This ensures the validity of the assumption regarding the recurrence of the pattern sequence and allows the pattern to be updated if necessary.

[0030] Advantageously, the further subsection is selected randomly, i.e., the pattern of the MR sequence is evaluated by sampling and thus checked particularly reliably.

[0031] A section can contain at least one section window, which in turn contains several subsections. For each of these subsections, subsection information can be determined, particularly by extrapolating the first subsection information. The subsection information of the subsections contained within a section window can be averaged. In this case, the section windows represent averaging windows.

[0032] The section windows of a section can also include common subsections, i.e., the section windows can also overlap.

[0033] Furthermore, an evaluation unit for carrying out a procedure to determine sequence information from an MR sequence is proposed. The evaluation unit can, in particular, comprise one or more processors and / or a memory.

[0034] The advantages of the evaluation unit according to the invention essentially correspond to the advantages of the method according to the invention for determining sequence information of an MR sequence, which are described in detail below. Features, advantages, or alternative embodiments mentioned here can also be transferred to the other claimed subject matter and vice versa.

[0035] The evaluation unit can be designed to be integrated into an MRI scanner and / or include a data interface configured to transmit data to an MRI scanner. It is also conceivable that the evaluation unit operates independently of an MRI scanner.

[0036] Furthermore, an MRI device with an evaluation unit is proposed, which is configured to perform a procedure for determining sequence information from an MRI sequence. The MRI device can, for example, include a system control unit for controlling the MRI device, which in turn includes the evaluation unit.

[0037] Furthermore, a computer program product is proposed that comprises a program which can be directly loaded into the memory of a programmable processing unit (DPU) of an evaluation unit and includes program resources, e.g., libraries and auxiliary functions, for executing a method for determining sequence information of an MR sequence when the computer program product is executed in the evaluation unit. The computer program product can comprise software with source code that still needs to be compiled and bound or that only needs to be interpreted, or executable software code that only needs to be loaded into the evaluation unit for execution. The computer program product enables the method for determining sequence information of an MR sequence to be executed quickly, identically, and robustly. The computer program product is configured such that it can execute the method steps according to the invention via the evaluation unit.The evaluation unit must have the necessary prerequisites, such as adequate memory, graphics card, or logic unit, so that the respective process steps can be executed efficiently.

[0038] Further advantages, features, and details of the invention will become apparent from the exemplary embodiments described below and from the drawings. Corresponding parts are designated with the same reference numerals in all figures.

[0039] They show: Fig. 1. A schematic diagram of an MR device, Fig. 2 and Fig. 3 exemplary block diagrams of a process, Fig. 4 an exemplary sequence diagram.

[0040] In Fig. Figure 1 shows a schematic representation of an MRI scanner 10. The MRI scanner 10 comprises a magnetic unit 11, which includes a main magnet 12 for generating a strong and, in particular, time-constant main magnetic field 13. The MRI scanner 10 also includes a patient reception area 14 for receiving a patient 15. In the present embodiment, the patient reception area 14 is cylindrical and is surrounded in a cylindrical shape by the magnetic unit 11 in one circumferential direction. However, a different configuration of the patient reception area 14 is conceivable. The patient 15 can be moved into the patient reception area 14 by means of a patient positioning device 16 of the MRI scanner 10. For this purpose, the patient positioning device 16 has a patient table 17 that is movable within the patient reception area 14.

[0041] The magnet unit 11 further comprises a gradient coil unit 18 for generating gradient pulses, which are used for spatial encoding during imaging. The gradient pulses can cause nerve stimulation in the patient 15. The gradient coil unit 18 is controlled by a gradient control unit 19 of the magnetic resonance device 10. The gradient coil unit 18 is typically designed only for a limited gradient strength and / or gradient rise rate.

[0042] The magnet unit 11 further comprises a high-frequency antenna unit 20, which in the present embodiment is designed as a body coil permanently integrated into the MRI scanner 10. The high-frequency antenna unit 20 is designed to excite atomic nuclei by means of RF pulses, which are established in the main magnetic field 13 generated by the main magnet 12. The RF pulses are therefore at least partially absorbed by the patient 15, so that heating of the patient can occur. The absorption of the RF pulses by the patient 15 can be described by an absorption rate. The high-frequency antenna unit 20 is controlled by a high-frequency antenna control unit 21 of the MRI scanner 10. The high-frequency antenna unit 20 is further designed for receiving MRI signals. The performance of the high-frequency antenna unit 20 is limited, in particular with regard to the B1 field it can generate in the patient acquisition area 14.

[0043] The MRI scanner 10 includes a system control unit 22 for controlling the main magnet 12, the gradient control unit 19, and the high-frequency antenna control unit 21. The system control unit 22 centrally controls the reconstruction 10, in particular the execution of a predetermined imaging MR sequence. The system control unit 22 also includes a reconstruction unit (not shown) for reconstructing medical image data acquired during the MR examination. Furthermore, the MRI scanner 10 includes a user interface 23 connected to the system control unit 22. Control information, such as imaging parameters, as well as reconstructed MR images, can be displayed on a display unit 24, for example, on at least one monitor, via the user interface 23 for medical personnel.Furthermore, the user interface 23 has an input unit 25 by means of which information and / or parameters can be entered by the medical operating personnel during a measurement process.

[0044] Furthermore, the MR device 10 comprises an evaluation unit 26 with a processing unit, which, for example, has one or more processors and / or a memory, for carrying out a procedure to determine sequence information of an MR sequence. A program containing program means to execute a procedure for determining sequence information of an MR sequence can be loaded into the memory of the programmable processing unit when the program is executed in the processing unit.

[0045] Fig. Figure 2 shows a block diagram illustrating a possible method for determining sequence information from an MR sequence. In step 110, an MR sequence is provided to the evaluation unit 26. In step 130, sequence information is determined by the evaluation unit 26 based on a pattern of the MR sequence. Advantageously, the sequence information includes at least one limiting parameter, which, for example, characterizes an absorption rate and / or nerve stimulation and / or at least a limit of the MR device 10, in particular the gradient coil unit 18 and / or the radio frequency antenna unit 20. If the determination of the sequence information takes too long, it can be aborted after a defined time. This time can, for example, be entered using the input unit 25 and / or be permanently stored in the evaluation unit 26.

[0046] At least one pattern is identified based on the MR sequence provided in step 110. Optionally, additional information provided in step 120, such as prior knowledge about the MR sequence, can also be used to identify at least one pattern.

[0047] Step 130 can include a simulation of the, ideally entire, MR sequence. Such a simulation can result in a sequence diagram D, as shown in an example and excerpt in Fig. Figure 4 shows that the process of an MR measurement typically follows strong regularities. The MR sequence and / or the resulting sequence diagram comprises several sections U1, U2, where in this example section U1 is divided into repeating subsections S 1,1 , S 1,2 , S 1,3 , S 1,4 , S 1,5 can be divided. The subsections S 1,1 , S 1,2 , S 1,3 , S1,4 , S 1,5 Each point on the time axis t represents the length of a repetition time TR. These time points on the time axis can also be understood as sampling points of the sequence diagram D.

[0048] Furthermore, the sequence diagram D includes an amplitude axis A, on which, for example, the amplitudes of the RF pulses HF1 and / or gradient pulses G1, G2, G3 specified by the MR sequence are plotted. The sequence of the RF pulses HF1 and / or gradient pulses G1, G2, G3 forms a pattern P1, which here is identical to the pattern P1 of subsection S. 1,2 and also with those of subsections S 1,3 , S 1,4 , and S 1,5 .

[0049] Fig. 3 shows how the in Fig. The information presented in step 4 can be advantageously processed when determining the sequence information in step 130. In step 131, for at least one first subsection, here S 1,1The MR sequence identifies an initial subsection information and a first pattern, here P1. The first subsection is also the first in time. However, this is not necessarily the case; that is, the first subsection may occupy a different position in the temporal sequence of subsections within the segment. Advantageously, each of the at least one first subsection comprises fewer than ten TRs, as in this case, exactly one TR.

[0050] In step 132, it is checked whether the identified first pattern P1 is repeated at least once in section U1 of the MR sequence. Fig. In the example shown in section 4, this is the case, since the pattern P1 is located in section U1, more precisely in subsection P 1,2 , repeatedly.

[0051] If the identified first pattern is repeated at least once in the section of the MR sequence, the sequence information is determined in step 133 by extrapolating the first subsection information to section U1 of the MR sequence. Otherwise, the determination of the sequence information is aborted in step 134.

[0052] Optionally, after determining the repetition of the first pattern P1 in section U1 of the MR sequence, another pattern from a further subsection S can be determined. 1,3 , S 1,4 , S 1,5 The pattern is determined within section U1 of the MR sequence and compared with the first pattern P1. The subsequent subsection is preferably selected randomly.

[0053] Pattern recognition in a sequence simulation, particularly in the sequence diagram D, can thus be used by evaluating a subselection of sampling points in the sequence diagram D to estimate sequence information, such as B. 1,average and / or B 1,peak f to accelerate the process. Instead of determining the sequence information separately for each time point of the MR sequence, a suitable subsection U can be used. 1,1For example, a certain number of repetition times TR, which usually represent the smallest reliably repeating substructure of the MR sequence, are evaluated, and it is assumed that the pattern P1 repeats across the targeted area. The targeted areas can be, in particular, section windows M1, M2, M3, as shown in the figure. The sequence information can, for example, be averaged within a section window M1, M2, M3, so that in this case the section windows M1, M2, M3 can also be called averaging windows.

[0054] Each of the sections S 1,1 , S 1,2 , S 1,3 , S 1,4 , S 1,5 in Fig. For example, 4 could correspond to a heartbeat of patient 15. If the pattern from the first heartbeat is detected and found again in the second TR, then, for example, the sequence information B could be used. 1,averageAssuming that the pattern continues to repeat regularly, estimate the mean of B1 over any averaging window M1, M2, M3 without explicitly calculating the sequence information over the entire MR sequence.

[0055] Finally, it should be noted once again that the methods described in detail above, as well as the evaluation unit and MRI device shown, are merely exemplary embodiments which can be modified in various ways by those skilled in the art without departing from the scope of the invention. Furthermore, the use of the indefinite articles "a" or "an" does not preclude the possibility that the features in question may be present multiple times. Likewise, the term "unit" does not preclude the possibility that the components in question consist of several interacting sub-components, which may also be spatially distributed.

Claims

[1] Methods for determining sequence information of an MR sequence, wherein the method comprises determining the sequence information based on at least one pattern of the MR sequence, wherein for at least one first subsection of the MR sequence, first subsection information and a first pattern of the MR sequence are determined, wherein the sequence information is determined by extrapolating the first subsection information to a section of the MR sequence, if the determined first pattern is repeated at least once in that section of the MR sequence. [2] Method according to claim 1, wherein the sequence information includes at least one limiting factor. [3] Method according to claim 2, wherein the limiting factor is characterized by an absorption rate and / or nerve stimulation. [4] Method according to one of claims 2 or 3, wherein the limiting quantity characterizes at least one limit of an MR device. [5] Method according to any of the preceding claims, wherein the at least one pattern is determined based on the MR sequence and / or on additional information. [6] Method according to any of the preceding claims, wherein the determination of the sequence information is terminated after a specified time. [7] Method according to any of the preceding claims, wherein each of the at least one first subsection comprises fewer than ten repetition times (TR). [8] Method according to one of claims 5 or 6, wherein after identifying a repetition of the first pattern in the section of the MR sequence, a further pattern of a further subsection within the section of the MR sequence is identified and compared with the first pattern. [9] Method according to claim 8, wherein the further subsection is selected randomly. [10] Evaluation unit for carrying out a method according to any one of claims 1 to 9. [11] MR device with an evaluation unit according to claim 10. [12] Computer program product comprising a program that can be directly loaded into a memory of a programmable computing unit of an evaluation unit, comprising program means to execute a method according to any one of claims 1 to 9 when the program is executed in the computing unit of the evaluation unit.

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