Optimized acquisition of measurement data using magnetic resonance technology

Abstract

In a method for improved acquisition of measurement data of an object under investigation, desired imaging parameters for acquiring measurement data using an acquisition method in which gradients to be switched for spatial encoding of the measurement data have their full strength during an irradiation of the RF excitation pulses, and a desired flip angle are loaded. A quantification value of an expected disturbance for the imaging procedure is determined based on the desired imaging parameters, and a feasibility study of a correction of the disturbance is performed based on the quantification value and on the basis of the desired flip angle. If the test confirms the feasibility of the correction, the acquisition procedure is performed with the loaded imaging parameters and the loaded flip angle. If the test denies feasibility, based on the quantification value, the pulse duration of the RF excitation pulses to be applied during the acquisition procedure and / or the desired flip angle are adjusted to a modified flip angle and / or at least one of the desired imaging parameters are adjusted to a modified imaging parameter, and the acquisition procedure is performed with the modified pulse duration and / or flip angle and / or imaging parameter. The measurement data acquired with the performed acquisition procedure are stored and / or further processed.

Description

[0001] The invention relates to an improved recording of measurement data using magnetic resonance technology, in particular with a radial recording method with a recording gap.

[0002] Magnetic resonance imaging (MRI) is a well-known technique used to generate images of the interior of an object. In simplified terms, the object is positioned in a magnetic resonance imaging (MRI) scanner within a relatively strong, static, homogeneous background magnetic field, also known as the B0 field, with field strengths ranging from 0.2 Tesla to 7 Tesla and higher. This causes the object's nuclear spins to align with the background magnetic field. To trigger measurable nuclear spin resonances, high-frequency excitation pulses (RF pulses) are applied to the object. The resulting nuclear spin resonances are measured as so-called k-space data using specially designed coils, and MR images or spectroscopic data are then derived from these measurements. The alternating magnetic field generated by the excitation pulses applied via at least one transmitting coil is also referred to as the B1 field.To spatially encode the measurement data, rapidly switched magnetic gradient fields, or gradients for short, are superimposed on the underlying magnetic field. A scheme used that describes a temporal sequence of RF pulses to be applied and gradients to be switched is called a pulse sequence (or simply sequence). The recorded measurement data are digitized and stored as complex numerical values ​​in a k-space matrix. From this k-space matrix containing values, a corresponding MR image can be reconstructed, for example, using a multidimensional Fourier transform.

[0003] Using conventional sequences, such as a (T)SE sequence (“(Turbo) Spin Echo”) or a GRE sequence (“Gradient Echo”), it is therefore not possible to record substances or tissues, such as bones, tendons, ligaments, teeth or even ice, which have T2* times of significantly less than 500 microseconds (µs), because a corresponding signal from these substances or tissues has already decayed at the time of recording in (T)SE or GRE sequences.

[0004] However, MRI techniques are already known that allow very short echo times (e.g., TE < 500 µs), which are in the range of the corresponding decay time. With these techniques, it is possible, for example, to visualize bones, teeth, or ice in an MRI image, even though the T2* time of these objects is in the range of 30–80 µs.

[0005] These MRI techniques include, for example, the UTE sequence (“Ultrashort Echo Time”), as described, among other places, in the article by Sonia Nielles-Vallespin, “3D radial projection technique with ultrashort echo times for sodium MRI: Clinical applications in human brain and skeletal muscle,” Magn. Res. Med. 2007; 57; pp. 74–81. In this sequence type, after a waiting period following non-selective or slice-selective excitation, the gradients are ramped up and data acquisition begins simultaneously. The k-space trajectory sampled in this way runs radially outward from the k-space center. Therefore, before reconstructing the image data from the raw k-space data using Fourier transformation, this raw data must first be converted to a Cartesian k-space grid, for example, by a process called regridding.

[0006] Other MRI techniques that allow for particularly short echo times include zTE (zero echo time), PETRA (pointwise encoding time reduction with radial acquisition), and WASPI (water- and fat-suppressed proton projection MRI) sequences. These are described, for example, in the article by Weiger et al., "MRI with Zero Echo Time: Hard versus Sweep Pulse Excitation," Magnetic Resonance in Medicine 66: pp. 379-389, 2011, in US8878533B2 (PETRA), and in the article by Wu et al., "Density of Organic Matrix of Native Mineralized Bone Measured by Water- and Fat-Suppressed Proton Projection MRI," Magn. Reson. Med. 50: pp. 59-68, 2003. In both methods, measurement data are recorded in k-space along radial spokes, whose gradients, switched for spatial coding, are already fully ramped up at the time of excitation of the spins in a test object, thus saving valuable coding time.However, this also creates a region in the k-space center that cannot be scanned by these radial spokes. Compared to UTE methods, zTE and PETRA methods are more robust because eddy currents or unintentional, small time shifts of switched gradients or irradiated RF pulses have no or at most a negligible influence on the measurements.

[0007] An example of part of a pulse sequence for such acquisition of measurement data along radial spokes, as used in zTE, WASPI and PETRA methods, is shown in Fig. Figure 1 shows the diagram. The top row, "Tx / Rx," displays the applied RF excitation pulses RF and the readout time windows ADC, during which the measurement data is acquired. The middle row, "G," shows the gradients switched in one coding direction, each of which has reached its desired strength for subsequent data acquisition at the moment an RF excitation pulse RF1 is applied. The bottom row, "k-sp," shows the corresponding k-space points sampled along the k-space trajectory defined by the applied gradient field for data acquisition. Measured k-space points are shown as black dots, while k-space points that lie before the start of the readout time window ADC, and are therefore not read out, are shown as "empty" dots. The fact that k-space points are not read out is due to the constant gradient field being applied before the RF excitation pulse RF is applied, as described above.This would mean that the central k-space point (k=0) would be measured simultaneously with the arrival of the RF excitation pulse RF1, which is technically impossible. Only after a minimum switching time Ts, dependent on the hardware of the magnetic resonance system used, following the end of an RF excitation pulse RF1, can the acquisition of measurement data begin within the ADC readout window, resulting in a (shortest) echo time TE. The first k-space point k* readout within the ADC readout window has the minimum distance from the k-space center k0 among all readout k-space points. The last k-space point readout within the ADC readout window is k. maxThe maximum distance between the k-space points read out is k0, and the maximum distance is between the k-space center. The duration of the ADC readout window (acquisition time) is determined by the strength of the applied gradient field G and the required resolution or the desired field of view (FOV), or the matrix of the image to be created from the measurement data.

[0008] A corresponding sampling scheme of k-space is given in Fig. Figure 2 shows a radial k-space spoke corresponding to a k-space trajectory along which ADC measurement data is acquired within a readout time window. Measurement data is acquired along radial spokes in various encoding directions until, for example, a desired k-space sampling density is achieved. The radius of the central region B, in which no measurement data is acquired along the described radial spokes, depends on the k-space moment accumulated after excitation until the acquisition of the measurement data, and thus on the echo time TE, during which the gradient is switched with constant strength, and the strength of the switched gradient field G. The longer this echo time TE and the stronger the gradient strength, and thus the higher the readout bandwidth, the more k-space points are not measured on the radial k-space trajectories.zTE, WASPI, and PETRA methods are characterized by the fact that they acquire echo signals and record them as measurement data along radial k-spatial trajectories. However, these measurements exhibit a recording gap that depends on the smallest echo time used. This gap can correspond to the described non-radially sampled region B, since no measurement data is acquired for k-spatial points k < k*. Therefore, when radial acquisition methods with a recording gap are generally referred to below, this refers to methods such as zTE, WASPI, or PETRA, in which the gradients for encoding measurement data reach their desired strength at the beginning of an excitation by an RF excitation pulse and are kept constant during a subsequent ADC readout window.

[0009] MR data from this non-radially scanned region B can be algebraically reconstructed from the measurement data of the radial spokes using zTE methods. In WASPI methods, a small number of additional measurements are performed along second radial k-space trajectories, with reduced gradient strengths to acquire measurement data closer to the k-space center.

[0010] In PETRA procedures, measurement data from the non-radially scanned area B can be acquired using a single-point MR imaging technique, e.g., RASP (“rapid single point”) as described in the article by Heid et al., “Rapid Single Point (RASP) imaging”, Proc. Intl. Soc. Mag. Reson. Med., p. 684, 1995, or a “single point SPRITE” technique as described in the article by Balcom et al., “Single-Point Ramped Imaging with T1 Enhancement (SPRITE)”, J. Magn. Reson. A 123(1): pp. 131-134, 1996, particularly on a Cartesian grid.

[0011] The fact that the gradients are already switched on during excitation also presents certain disadvantages for zTE, WASPI, and PETRA sequences compared to, for example, UTE sequences, as this limits the possible types of excitation. While spatially restricted RF excitation pulses can be used in UTE sequences, e.g., for two-dimensional (2D) or three-dimensional (3D) spatially selective excitation, the respective excitation in zTE, PETRA, or WASPI sequences must be performed with a spatially non-selective rectangular pulse, also called a "hard pulse." As described in the article by Grodzki et al., "Correcting slice selectivity in hard pulse sequences," Proc. Intl. Soc. Mag. Reson. Med. 20, p.As described in 2479, 2012, despite the use of such spatially non-selective hard pulses as RF excitation pulses, unwanted layer selectivity can occur precisely because of the gradients already switched during the application of the RF excitation pulses. This selectivity can only be corrected within certain limits. Correction is possible if at least one zero point of a spectral pulse profile of a used RF excitation pulse, which corresponds to a sinc in the case of a rectangular RF excitation pulse, lies outside the field of view (FOV). Considering that the excitation bandwidth of an RF pulse, which indicates the spectral width of the possible excitation, is given by the inverse of the duration of the RF pulse, it is advantageous to use the shortest possible RF excitation pulse.A high excitation bandwidth, and thus a high half-width of a pulse profile of a used RF excitation pulse, facilitates the correction based on matrix inversion described in the aforementioned article by Grodzki et al. However, the achievable flip angle decreases as the RF excitation pulse becomes shorter.

[0012] Other correlations between common imaging parameters and the RF excitation pulses used include, for example: i) The strength of the gradient switched during the application of the RF excitation pulses is proportional to the selected readout bandwidth and the selected resolution, which in turn is the quotient of the desired field of view with the desired matrix size of the k-space matrix to be filled with measurement data. [FOV / matrix size=resolution]. ii) The selected flip angle of the RF excitation pulses used is (with the same B1 amplitude) proportional to the pulse duration of the RF excitation pulses.

[0013] In previously known radial imaging techniques with a gap in the image acquisition, particularly for zTE, WASPI, and PETRA methods, the same hard-coded hard pulse is generally always used as the RF excitation pulse with fixed pulse parameters, especially a fixed pulse duration, which, together with a maximum pulse amplitude, also defines a maximum flip angle. For most users of such radial imaging techniques with a gap in the image acquisition, the relationships described above are too complex to independently optimize the imaging parameters and pulse parameters, especially if correction of disturbances caused by unwanted slice selectivity is also desired. Currently, it is still the user's responsibility to determine the readout bandwidth or pulse parameters for their chosen field of view.The resolution (and thus the strength of the gradient switched during the application of the RF excitation pulses) should not be chosen too high to prevent artifacts. This is often not successful. Furthermore, due to the fixed pulse duration of the RF excitation pulses used so far, the achievable flip angle is always the same, even though larger or significantly smaller flip angles than the maximum possible flip angle might be desirable depending on the application.

[0014] The invention is based on the objective of enabling the determination of optimized parameters, in particular optimized pulse parameters, such as pulse durations, for RF excitation pulses and / or imaging parameters for radial imaging methods with an imaging gap, in such a way that a possible correction of disturbances caused by unwanted layer selectivity is also facilitated or enabled, whereby imaging parameters tailored to desired imaging protocols and applications can be taken into account in particular.

[0015] The problem is solved by a method for improved acquisition of measurement data from a test object located in a measurement volume of a magnetic resonance system according to claim 1, a magnetic resonance system according to claim 10, a computer program according to claim 11, and an electronically readable data carrier according to claim 12.

[0016] An inventive method for improved acquisition of measurement data from a test object located in a measurement volume of a magnetic resonance system comprises the following steps: - Loading desired imaging parameters for recording echo signals generated after RF excitation pulses as measurement data using a recording method in which gradients to be switched for spatial encoding of the measurement data along radial spokes in k-space have their full strength during an irradiation of the RF excitation pulses, wherein the desired imaging parameters include a desired field of view and at least one imaging parameter from the group consisting of a desired readout bandwidth, a desired resolution, and a desired matrix size of the matrix in which the measurement data are to be stored. - Loading a desired flip angle for radiated RF excitation pulses, - Determining a quantification value of an expected disturbance for the acquisition procedure based on the desired imaging parameters, - Conducting a feasibility study of correcting the disturbance based on the quantification value, - Performing the acquisition procedure with the loaded imaging parameters and the loaded flip angle, if the test confirms the feasibility of the correction, and, if the test denies feasibility, adjusting the pulse duration of the RF excitation pulses to be applied during the acquisition procedure based on the quantification value and / or adjusting the desired flip angle to an adapted flip angle and / or adjusting at least one of the desired imaging parameters to an adapted imaging parameter, and performing the acquisition procedure with the adapted pulse duration and / or with the adapted flip angle and / or with the adapted imaging parameter. - Storing and / or further processing the measurement data recorded using the implemented recording method.

[0017] An invention provides for testing the feasibility of correcting a disturbance expected in the acquisition process and, if necessary, for automatically adjusting parameters relevant to the acquisition process such that the feasibility of the correction is achieved. This enables optimized acquisition of measurement data, taking into account imaging parameters desired by the user (e.g., for specific imaging protocols or applications), the results of which are free from artifacts that would arise from the aforementioned disturbance without correction.

[0018] Especially when using radial imaging techniques with a gap, particularly zTE, WASPI, and PETRA methods, to acquire measurement data, unwanted layer selectivity can occur, as described above. The present method ensures that boundary conditions arising from the complex relationships between the RF excitation pulses used and other imaging parameters, and facilitating (or even enabling) the correction of this interference, are automatically met without requiring the user to understand these relationships.Rather, the method can automatically define pulse parameters of RF excitation pulses to be used from user-adjustable desired parameters such as a readout bandwidth, a field of view (FOV) and a matrix size (which together determine the strength of the gradient switched during excitation), or a flip angle, whereby limitations in hardware-related achievable amplitude of the RF excitation pulse (B1m) can be taken into account and limit a parameter space selectable by a user, in particular the imaging parameters such as the readout bandwidth, the resolution or possible flip angles.

[0019] A magnetic resonance system according to the invention comprises a magnet unit, a gradient unit, a radio frequency unit and a control device designed for carrying out a method according to the invention with an optimization unit.

[0020] A computer program according to the invention implements a method according to the invention on a control device when it is executed on the control device. For example, the computer program includes instructions that, when the program is executed by a control device, e.g., a control device of a magnetic resonance system, cause this control device to execute a method according to the invention. The control device can be in the form of a computer.

[0021] The computer program can also be in the form of a computer program product that can be directly loaded into a memory of a control device, with program code means to execute a method according to the invention when the computer program product is executed in a computing unit of the computing system.

[0022] A computer-readable storage medium according to the invention comprises instructions which, when executed by a control device, e.g. a control device of a magnetic resonance system, cause it to execute a method according to the invention.

[0023] The computer-readable storage medium can be designed as an electronically readable data carrier which includes electronically readable control information stored on it, which includes at least one computer program according to the invention and is designed in such a way that, when the data carrier is used in a control unit of a magnetic resonance system, it carries out a method according to the invention.

[0024] The advantages and explanations given regarding the procedure also apply analogously to the magnetic resonance system, the computer program product and the electronically readable data carrier.

[0025] Further advantages and details of the present invention will become apparent from the exemplary embodiments described below and from the drawings. The examples shown do not constitute a limitation of the invention. They show: Fig. 1 a schematically represented part of a pulse sequence scheme for recording measurement data, Fig. 2 a schematically represented exemplary k-space scanning scheme, Fig. 3 a schematic flowchart of a method according to the invention, Fig. 4 a schematically illustrated magnetic resonance system according to the invention.

[0026] Fig. Figure 3 is a schematic flowchart of a method according to the invention for improved acquisition of measurement data MDS from a test object located in a measurement volume of a magnetic resonance system.

[0027] For the acquisition of echo signals generated by RF excitation pulses as measurement data using an acquisition method in which gradients G, used for spatial encoding of the measurement data, are switched at their full strength during the application of the RF excitation pulses, desired imaging parameters BP and a desired flip angle FA are loaded (Block 101). The desired imaging parameters include a desired field of view and at least one imaging parameter from the group consisting of a desired readout bandwidth, a desired resolution, and a desired matrix size for storing the measurement data. Such an acquisition can be performed, for example, using a radial acquisition method with a recording gap, in particular a zTE, a WASPI, or a PETRA method.

[0028] Based on the desired imaging parameters BP, a quantification value SG of an expected disturbance is determined for the acquisition procedure (Block 103). The quantification value SG is chosen to be characteristic of the expected disturbance.

[0029] For radial imaging techniques with a gap in the acquisition, suitable quantification values ​​SG include those that characterize the shape of a pulse profile of the RF excitation pulses used, since the expected disturbance can be described as an inversion of a pulse profile into the magnetization distribution recorded as echo signals. In particular, a value correlating with an excitation bandwidth and / or half-width of an RF excitation pulse profile can be used as the quantification value SG, since – as described above with reference to the article by Grodzki et al. – the feasibility of correcting disturbances by the proposed matrix inversion depends on the pulse profile, especially on the first zero points of the pulse profiles.

[0030] The quantification value SG can, in particular, correspond to the strength of the gradients G switched during the irradiation of RF excitation pulses, which are proportional to the imaging parameters readout bandwidth and field of view (and thus also proportional to the imaging parameter resolution and inversely proportional to the imaging parameter matrix size).

[0031] Based on the determined quantification value SG, a feasibility test of a disturbance correction is performed. For example, the feasibility test of a disturbance correction can include a comparison of the position of a first zero point of a pulse profile of irradiated RF excitation pulses, determined based on the quantification value SG, with a desired field of view, whereby feasibility is confirmed, for example, if the first zero point lies outside the field of view.

[0032] If check 100 confirms the feasibility of the correction (100, “y”), the acquisition procedure is carried out with the loaded imaging parameters BP and the loaded flip angle FA, so that measurement data MD is acquired (block 109) which can be stored and / or further processed.

[0033] If test 100 denies feasibility (100, "n"), an optimization is performed which, based on the quantification value SG, a) adjusts the pulse duration of the RF excitation pulses to be applied during the acquisition procedure to an adapted pulse duration PD' and / or b) adjusts the desired flip angle to an adapted flip angle FA' and / or c) adjusts at least one of the desired imaging parameters to an adapted imaging parameter BP' (Block 107). The acquisition procedure is then performed with at least one adapted parameter from the group consisting of an adapted pulse duration PD', an adapted flip angle FA', and / or at least one adapted imaging parameter BP', so that measurement data MD are acquired (Block 109).

[0034] Adjusting the pulse duration of the RF excitation pulses used in the imaging procedure to a modified pulse duration PD' (Block 107.2) can be achieved such that the modified pulse duration PD' places the first zero point of the pulse profile of the injected RF excitation pulses outside a desired field of view. In particular, the modified pulse duration PD' can be shorter than a previously given, unmodified pulse duration. As mentioned above, modifying a pulse duration by reducing its length shifts the position of the first zero point outwards.

[0035] Adjusting the pulse duration of the RF excitation pulses used in the acquisition process to a customized pulse duration PD' can be achieved by considering the maximum amplitude B1m of the RF excitation pulses inherent in the magnetic resonance imaging (MRI) system being used. Particularly for smaller desired flip angles, which do not fully utilize the maximum amplitude B1m of the RF excitation pulses at a preset pulse duration, the customized pulse duration can be reduced compared to the preset pulse duration, while simultaneously increasing the amplitude of the RF excitation pulses to achieve the desired flip angle. For example, the amplitude can be increased to the maximum amplitude B1m of the RF excitation pulses to determine a minimum customized pulse duration PD'.

[0036] Based on the determined quantification value SG and the adjusted pulse duration PD', a further feasibility check (100') can be performed to assess the viability of correcting the disturbance. For example, this further feasibility check (100') can include comparing the position of a first zero point of an RF excitation pulse (determined based on the quantification value SG) with a desired field of view. The feasibility is confirmed, for example, if the first zero point lies outside the field of view.

[0037] If the further check 100' confirms the feasibility of the correction (100', "y"), a suitable adjusted pulse duration could be determined and the acquisition procedure can be carried out with the loaded imaging parameters BP and the loaded flip angle FA and with the adjusted pulse duration PD', so that measurement data MD are acquired (Block 109) which can be stored and / or further processed.

[0038] When adjusting the desired flip angle FA to a modified flip angle FA', the modified flip angle FA' may be smaller than the (originally) desired flip angle FA. Smaller flip angles FA' offer greater flexibility for adjusting the pulse duration and make it more likely that error correction will be feasible.

[0039] Adjusting the desired flip angle FA to a modified flip angle FA' is particularly useful when adjusting the pulse duration of the RF excitation pulses used in the recording process is not possible for the loaded, desired flip angle FA. This adjustment would result in a first zero point of the pulse profile of the RF excitation pulses lying outside a desired field of view. The flip angle FA (and additionally the pulse duration) can be adjusted so that the first zero point of the pulse profile of the RF excitation pulses lies outside a desired field of view. For this purpose, a maximum modified flip angle FA' can be determined, e.g.,based on the maximum amplitude B1m, and by determining a longest possible changed pulse duration with which a position of first zero points of a pulse profile of irradiated RF excitation pulses lies just outside a desired field of view, based on this longest possible changed pulse duration, wherein the largest possible flip angle can be determined as proportional to a product of the maximum amplitude B1m with the longest possible pulse duration.

[0040] In addition to or as an alternative to adjusting the flip angle FA to a modified flip angle FA', at least one of the desired imaging parameters BP can be adjusted to a modified imaging parameter BP' if adjusting the pulse duration of the RF excitation pulses to be applied during the acquisition procedure is not possible, even with a modified flip angle FA'. This adjustment would result in the first zero point of a pulse profile of applied RF excitation pulses lying outside a desired field of view. Since the loaded desired imaging parameters BP are specified by the user, they should only be adjusted if, otherwise—i.e., despite an already modified flip angle FA' and a modified pulse duration PD'—the feasibility of correcting the interference cannot be confirmed.

[0041] Such an adjustment of at least one imaging parameter BP can be carried out in such a way that a feasibility check of the correction, performed on the basis of an adjusted quantification value SG determined on the basis of adjusted imaging parameter BP', confirms its feasibility. In other words, those imaging parameters on the basis of which the quantification value SG is determined are adjusted in such a way that an adjusted quantification value results which enables the correction of the disturbance to be feasible. Using the example of the strength of a gradient G switched during excitation by irradiation with RF excitation pulses as the quantification value SG, a reduction in the strength of the gradient G leads to a broadening of the pulse profile of the RF excitation pulse and thus to a shift of the position of the first zero point of the pulse profile outwards.In this way, a maximum reduced gradient G strength can be determined. To achieve such a maximum reduced gradient G strength, for example, a desired resolution (as the desired imaging parameter BP) can be reduced to a suitable resolution, and / or a desired readout bandwidth (as the desired imaging parameter BP) can be lowered to a suitable readout bandwidth to reduce the gradient G strength.

[0042] In this process, a user may be offered either a reduction of a desired resolution to an adapted resolution and / or a reduction of a desired readout bandwidth to an adapted readout bandwidth, or a combination of both measures, so that the user can choose the adjustment of imaging parameters that is best suited to the desired imaging protocol or application, e.g., for a specific imaging area, and is thus perceived as the smallest limitation.

[0043] Thus, adjusting at least one of the desired imaging parameters BP to an adjusted imaging parameter BP' can include reducing a desired resolution to an adjusted resolution and / or lowering a desired readout bandwidth to an adjusted readout bandwidth.

[0044] Since the adjusted imaging parameters BP' are determined just so that they allow for the feasibility of correcting the disturbance, the acquisition procedure can be carried out with the adjusted imaging parameters BP' so that measurement data MD are acquired (Block 109).

[0045] Measurement data MD acquired using the recording method can be stored or further processed, for example reconstructed into image data BD (Block 111).

[0046] Fig. Figure 4 schematically represents a magnetic resonance system 1 according to the invention. This comprises a magnet unit 3 for generating the basic magnetic field, a gradient unit 5 for generating the gradient fields, a radio frequency unit 7 for irradiating and receiving radio frequency signals, and a control device 9 designed for carrying out a method according to the invention.

[0047] In the Fig.Figure 4 shows these subunits of the magnetic resonance system 1 only in a rough schematic representation. The high-frequency unit 7 can consist of several subunits and, for example, comprise several coils. In particular, the high-frequency unit 7 can comprise a body coil that is permanently integrated into the magnetic resonance system 1 and, in turn, can comprise, for example, two antenna elements 7.1 and 7.2. Furthermore, the high-frequency unit 7 can comprise one or more different local coils 7*, which can be designed either only for transmitting high-frequency signals or only for receiving the triggered high-frequency signals, or for both, and which themselves can comprise several antenna elements and associated coil channels.

[0048] To examine a test object U, for example a patient or a phantom, it can be placed on a table L in the magnetic resonance imaging (MRI) system 1 within its measurement volume. Layers S1 or S2 represent exemplary target volumes of the test object, from which echo signals can be recorded and acquired as measurement data.

[0049] The control unit 9 serves to control the magnetic resonance system 1 and can, in particular, control the gradient unit 5 by means of a gradient controller 5' and the radio frequency unit 7 by means of a radio frequency transmit / receive controller 7'. The radio frequency unit 7 can comprise several channels on which signals can be transmitted or received.

[0050] The high-frequency unit 7, together with its high-frequency transmit / receive control 7', is responsible for generating and transmitting a high-frequency alternating field to manipulate the spins in a region to be manipulated (for example, in layers S to be measured) of the object under investigation U. The center frequency of the high-frequency alternating field, also referred to as the B1 field, is generally set as close as possible to the resonance frequency of the spins to be manipulated. Deviations from the center frequency to the resonance frequency are referred to as off-resonance. To generate the B1 field, controlled currents are applied to the RF coils in the high-frequency unit 7 by means of the high-frequency transmit / receive control 7'.

[0051] Furthermore, the control unit 9 comprises an optimization unit 15 for adjusting the pulse duration of the RF excitation pulses to be applied during the imaging procedure and / or for adjusting a desired flip angle to a specific flip angle and / or for adjusting at least one desired imaging parameter to a specific imaging parameter. The control unit 9 is configured overall to carry out a method according to the invention.

[0052] A computing unit 13, encompassed by the control unit 9, is designed to perform all the necessary calculations for the required measurements and determinations. Intermediate results and final results required for this purpose, or determined in the process, can be stored in a storage unit S of the control unit 9. The units shown here are not necessarily to be understood as physically separate units, but merely represent a subdivision into conceptual units, which can also be realized, for example, in fewer or even just a single physical unit.

[0053] Via an input / output device (I / O) of the magnetic resonance system 1, control commands can be sent to the magnetic resonance system by a user, for example, and / or results from the control device 9, such as image data, can be displayed.

[0054] The method described herein may also be in the form of a computer program comprising instructions that execute the described method on a control unit 9. Likewise, a computer-readable storage medium may be present, comprising instructions that, when executed by a control unit 9 of a magnetic resonance system 1, cause it to execute the described method.

[0055] Regardless of the grammatical gender of a particular term, persons with male, female or other gender identities are included.

Claims

[1] Method for improved acquisition of measurement data (MD) from a test object (U) located in a measurement volume of a magnetic resonance system (1) comprising the steps: - Loading desired imaging parameters (BP) for recording echo signals generated after RF excitation pulses as measurement data (MD) using a recording method in which gradients (G) to be switched for spatial encoding of the measurement data (MD) along radial spokes in k-space have their full strength during an irradiation of the RF excitation pulses, wherein the desired imaging parameters (BP) comprise a desired field of view and at least one imaging parameter from the group consisting of a desired readout bandwidth, a desired resolution, and a desired matrix size of the matrix in which the measurement data are to be stored, - Loading a desired flip angle (FA) for radiated RF excitation pulses, - Determining a quantification value (SG) of an expected disturbance for the imaging procedure based on the desired imaging parameters, - Conducting a feasibility study (100) of correcting the disturbance based on the quantification value (SG), - Perform the acquisition procedure with the loaded imaging parameters (BP) and the loaded flip angle (FA), if the test (100) confirms the feasibility of the correction, and, if the test denies feasibility, based on the quantification value (SG), adjust a pulse duration of the RF excitation pulses to be irradiated during the acquisition procedure to an adjusted pulse duration (PD') and / or adjust the desired flip angle (FA) to an adjusted flip angle (FA') and / or adjust at least one of the desired imaging parameters (BP) to an adjusted imaging parameter (BP'), and perform the acquisition procedure with adjusted pulse duration (PD') and / or with adjusted flip angle (FA') and / or with adjusted imaging parameter (BP'), - Storing and / or further processing the measurement data (MD) recorded using the implemented recording method. [2] Method according to claim 1, wherein the quantification value (SG) correlates with a half-width of a pulse profile of irradiated RF excitation pulses, in particular wherein the quantification value (SG) corresponds to the strength of the gradients (G) switched during the irradiation of RF excitation pulses. [3] Method according to one of the preceding claims, wherein the feasibility test of a correction of the disturbance comprises a comparison of the position of a first zero point of a pulse profile of irradiated RF excitation pulses with a desired field of view, and the feasibility is confirmed if the first zero point is outside the field of view. [4] Method according to one of the preceding claims, wherein an adjustment of the pulse duration of the RF excitation pulses to be irradiated in the context of the recording method to an adapted pulse duration (PD') is carried out such that, by the adapted pulse duration (PD'), a first zero point of a pulse profile of irradiated RF excitation pulses lies outside a desired field of view. [5] Method according to one of the preceding claims, wherein an adjustment of the pulse duration of the RF excitation pulses to be irradiated in the context of the recording method to an adapted pulse duration (PD') is carried out taking into account a maximum amplitude (B1m) of RF excitation pulses to be irradiated. [6] Method according to any of the preceding claims, wherein an adapted flip angle (FA') is smaller than a desired flip angle (FA). [7] Method according to one of the preceding claims, wherein an adjustment of the desired flip angle (FA) to an adapted flip angle (FA') is carried out when an adjustment of a pulse duration of the RF excitation pulses to be irradiated within the framework of the recording method to an adapted pulse duration (PD') such that a first zero point of a pulse profile of irradiated RF excitation pulses lies outside a desired field of view is not possible for the loaded desired flip angle (FA), and the desired flip angle (FA) and the pulse duration are adjusted such that a first zero point of a pulse profile of irradiated RF excitation pulses lies outside a desired field of view. [8] A method according to any of the preceding claims, wherein at least one of the desired imaging parameters (BP) is adapted to an adapted imaging parameter (BP') when it is not possible to adapt a pulse duration of the RF excitation pulses to be irradiated in the context of the imaging procedure to an adapted pulse duration (PD') such that the adapted pulse duration (PD') results in a first zero point of a pulse profile of irradiated RF excitation pulses lying outside a desired field of view, and the adaptation of the at least one imaging parameter (BP) is carried out such that a feasibility check of the correction, based on a quantification value (SG) determined on the basis of adapted imaging parameters (BP'), confirms the feasibility. [9] Method according to any of the preceding claims, wherein adapting at least one of the desired imaging parameters (BP) to an adapted imaging parameter (BP') comprises reducing a desired resolution to an adapted resolution and / or reducing a desired readout bandwidth to an adapted readout bandwidth. [10] Magnetic resonance system (1) comprising a magnet unit (3), a gradient unit (5), a radio frequency unit (7) and a control unit (9) with a radio frequency transmit / receive control (7') and with an optimization unit (15), wherein the control unit (9) is configured to perform a method according to any one of claims 1 to 9 on the magnetic resonance system (1). [11] Computer program comprising commands which, when the program is executed by a control device (9) of a magnetic resonance system (1), cause it to execute the method according to any one of claims 1 to 9. [12] Computer-readable storage medium comprising instructions which, when executed by a control device (9) of a magnetic resonance system (1), cause it to execute the method according to any one of claims 1 to 9.

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