Methods, apparatuses, and systems for correcting the effects of interference on a gradient system

Abstract

The invention relates to a method for correcting the influence of interfering effects on a gradient system of a magnetic resonance device during a magnetic resonance measurement, having the following steps: emitting a gradient pulse by means of an amplifier of the gradient system; detecting a gradient profile; detecting an output signal of the amplifier for the gradient pulse; determining a gradient system transfer function; and determining an output signal of the amplifier, which provides the desired gradient profile at the output signal. The invention also relates to a correction device, which is designed to adjust an input signal of the amplifier in accordance with the determined output signal of the amplifier and the detected output signal of the amplifier. Furthermore, the invention relates to a magnetic resonance device and a magnetic resonance system having the correction device, as well as a computer program product having a computer program and a computer-readable medium for carrying out the method according to the invention.

Description

Technical Field

[0001] This invention relates to a method for correcting the influence of interference effects on the gradient system of a magnetic resonance apparatus during magnetic resonance measurements. Furthermore, this invention relates to a magnetic resonance apparatus and a magnetic resonance system having a correction device. Background Technology

[0002] In a magnetic resonance imaging (MRI) system, the object being examined is typically subjected to a fundamental magnetic field with a strength between 0.5 and 7 Tesla by means of a fundamental field magnet system. When the fundamental magnetic field is applied, the atomic nuclei in the object being examined orient themselves along the fundamental magnetic field with non-zero nuclear magnetic dipole moments (often also called spins). This collective behavior of spins is also known as "magnetization" at the macroscopic level. Magnetization is the vector sum of all the microscopic magnetic moments at a particular location in the object.

[0003] In addition to the fundamental magnetic field, a magnetic field gradient is applied using a gradient system, through which a magnetic resonance frequency (Ramohr frequency) is determined at the corresponding location. Then, a radio frequency excitation signal or radio frequency field (HF pulse) is transmitted via a radio frequency transmitting unit using a suitable antenna device. This should cause the spins of specific atomic nuclei excited by the resonance of this radio frequency field (i.e., at the Larmor frequency at the corresponding location) to tilt relative to the magnetic field lines of the fundamental magnetic field at a defined flip angle. If this HF pulse acts on the already excited spins, the spins can tilt to different angular positions, or even flip back to their initial state parallel to the fundamental magnetic field. During the relaxation of the excited spins, the radio frequency signal, i.e., the so-called magnetic resonance signal, is resonantly emitted. The magnetic resonance signal can be received by means of a suitable receiving antenna (antenna device, also called a magnetic resonance coil or receiving coil), and is subsequently mediated, digitized, and further processed as so-called "raw data." The reception of magnetic resonance signals takes place in the spatial frequency domain, the so-called "k-space," where, during magnetic resonance measurements, slices of k-space are traversed temporally, for example, along a "gradient trajectory" (also called a k-space trajectory) defined by switching gradient pulses. Here, HF pulses are emitted in a temporally coordinated manner. Finally, image data of the examined object can be reconstructed from the acquired raw data using a two-dimensional Fourier transform. Alternatively, a three-dimensional volume can also be defined, excited, and read during this process, where the raw data is reclassified into the three-dimensional k-space after further processing steps. Accordingly, three-dimensional image data can be reconstructed using a three-dimensional Fourier transform.

[0004] Typically, to manipulate the magnetic resonance system during magnetic resonance measurements, a specific sequence of HF pulses and gradient pulses, known as a pulse sequence, is used. This pulse sequence can be emitted in different spatial directions and / or during readout time windows, during which the receiving antenna is switched to receive and acquire the magnetic resonance signal.

[0005] Gradient pulses are typically defined by the gradient amplitude, pulse duration, and the first derivative of the pulse shape, dG / dt (“Slew Rate”). Because gradient systems have a maximum load limit, the intensity and slew rate of the gradient pulse are essentially constrained.

[0006] Using a so-called measurement protocol, the pulse sequence is pre-parameterized for desired examinations, such as calculating specific contrast in the image. The measurement protocol can also incorporate other control data for magnetic resonance measurements. In principle, there are multiple possibilities for how the pulse sequence can be constructed to obtain the desired image data of the object being examined.

[0007] In the following text, "magnetic resonance recording" is understood as image data of the interior of an object being examined, generated by means of a magnetic resonance device manipulated in the course of this method, but also as a parametric map reflecting the spatial or temporal distribution of specific parameter values ​​within the object being examined and which can be generated, for example, from image data. "Recording" of magnetic resonance image data is understood here as performing magnetic resonance measurements by means of a magnetic resonance system.

[0008] As described above, in magnetic resonance measurements, the magnetic resonance signal is first measured, and its amplitude is interpreted as a Fourier transform of the image data in k-space. k-space can be understood here as the spatial frequency domain of the magnetic moment density distribution in the region to be examined, where the magnetic resonance signal is detected. If k-space is sampled accurately enough, the spatial distribution of the magnetic moment density can be obtained by means of a Fourier transform (two-dimensional in the case of slice-by-slice sampling). Typically, k-space is sampled row-by-row along a Cartesian grid. However, other sampling modes are also conceivable.

[0009] In magnetic resonance (MRI) measurements, the accuracy of the gradient pulses emitted by the gradient system significantly impacts the quality of the detected image data. Besides pulse sequences with Cartesian trajectories of gradient pulses, pulse sequences with radial or helical trajectories can also be used. Furthermore, so-called single-excitation EPI sequences are also used in MRI measurements. These later sequences place even higher demands on the temporal accuracy of the magnetic field gradient. Deviations between the emitted and desired gradient pulses can be caused by factors such as eddy currents, time tuning errors, gain errors, and field fluctuations, which arise from mechanical vibrations after switching the magnetic field gradient, but also from the thermal variations and / or nonlinear characteristics of hardware components, such as the amplifiers and / or gradient coils of the gradient system. These interference effects cause the gradient curve to deviate from the desired gradient curve. This deviation introduces errors in determining the k-space trajectory, errors in the acquired signal, and ultimately, artifacts in the image data.

[0010] If the deviation is precisely known, then the actual k-space trajectory can be determined and used to reconstruct the image data. Alternatively, the actual k-space trajectory can also be measured. Typically, gradient pulse correction is performed for a specific gradient system state at a single temperature. For example, the gradient system transfer function is determined once for room temperature and then used throughout the imaging sequence, regardless of temperature changes during imaging.

[0011] One-time, static gradient correction is based on a technique that uses a transfer function, such as the Gradient Impulse Response Function (GIRF) or the Gradient System Transfer Function (GSTF), to correct the deviation according to equation (1). Here, F is the Fourier transform, f is the frequency, and t is the time.

[0012] GSTF(f)=F{GIRF(t)} (1)

[0013] Here, the linear and time-invariant properties of the dynamic gradient system are used to correct the emitted gradient impulses during image reconstruction. One technique uses the gradient impulse response function GIRF or the gradient system transfer function GSTF of the magnetic resonance system to correct non-Cartesian trajectories. In particular, the behavior of the entire gradient system can be characterized by using the gradient system transfer function GSTF.

[0014] In so-called post-correction, the corrected gradient pulse g is used for each axis (l = x, y, z). post,l (t) by means of the nominal gradient G nom,l The Fourier transform of (f) is multiplied by the corresponding gradient system transfer function GSTF at the specific temperature state. l,l (f) and the Fourier transform to the time domain (inverse transform) yield the following results:

[0015] g post，l (t)=F -1 {F{g nom，l (t)}·GSTF l，l} (2)

[0016] The value "l" indicates that the input gradient g is emitted. nom,l (t) (also known as the nominal gradient) and used to measure the output gradient G. real,l (f) refers to the directions x, y, and z.

[0017] Alternatively, the inverse gradient impulse response function or gradient system transfer function can be used during the previous correction (so-called "pre-enhancement"). This allows for the generation of a corrected, nominal gradient impulse g. pre,l (t), which corresponds to the desired, nominal gradient impulse g. nom,l This enables the desired output gradient G to be achieved. real,l (t):

[0018]

[0019] Equations 2 and 3 show a simplified correction for the gradient pulse, where only the first-order terms of the gradient system transfer function are used. For clarity, it should be briefly mentioned here that the gradient system transfer function also includes terms describing the interaction between magnetic field components in different directions, as well as higher-order terms. To perform a full and complete correction, all terms of the gradient system transfer function from order 0 to order n must be used. However, adequate correction is achieved as follows: primarily using the 0th-order terms to correct the fundamental magnetic field (B0 field), and using the first-order terms to correct the magnetic field gradient. When determining the gradient system transfer function, the gradient system should be tested with a wide frequency spectrum. Ideally, the Dirac pulse is used as the test gradient function to achieve coverage of all frequencies.

[0020] Gradient pulses emitted by the gradient system of a magnetic resonance imaging (MRI) device are typically measured in small dynamic field samples (“fieldprobes”), which are used to determine the phase development or phase signal. The phase signal is based on the original signal, i.e., the signal measured by the receiving antenna. Only the phase of the original signal is further processed. The numerical value is not considered here. The gradient can be determined from the phase signal.

[0021] Therefore, gradient pulse correction is known. However, known techniques are limited to correcting k-space data after magnetic resonance signal acquisition or to correcting interference effects that occur continuously during the magnetic resonance recording process. To date, no compensation has been considered for the dynamic, and especially nonlinear, characteristics of the gradient system components of a magnetic resonance apparatus during magnetic resonance measurements. Summary of the Invention

[0022] The object of this invention is to provide a method for correcting the deviation between the emitted gradient pulse and the desired gradient change curve during magnetic resonance measurement.

[0023] According to the present invention, the objective is achieved through the subject matter described in the embodiments. Advantageous embodiments and improvements that meet the objectives are the subject matter of the embodiments.

[0024] The method according to the present invention for correcting the influence of interference effects on the gradient system of a magnetic resonance apparatus during magnetic resonance measurements includes the following steps:

[0025] • Emitters g are emitted by an amplifier in a gradient system. ref (t),

[0026] • Gradient change curve g is detected by measuring the magnetic field in the examination area of ​​the magnetic resonance imaging (MRI) device. real (t),

[0027] • The detection amplifier for the gradient pulse g ref The output signal i of (t) out (t),

[0028] • Based on the detected gradient change curve g real (t) and the detected amplifier output signal i out (t) Determine the gradient system transfer function (GSTF, GIRF),

[0029] • Determine the amplifier's output signal i based on the determined gradient system transfer function (GSTF, GIRF). cor (t), where the output signal provides the desired gradient change curve g. nom (t).

[0030] In one step of the method according to the invention, at least one gradient pulse g is emitted. ref (t). Gradient pulse g ref (t) can represent a portion of a pulse sequence, which can include one or more gradient pulses, but can also include one or more HF pulses. Gradient pulses can, for example, represent regular gradient pulses in the pulse sequence necessary for performing magnetic resonance measurements on the object being examined. For example, regular gradient pulses can include imaging gradients or diffusion gradients. Imaging gradients are preferably used to locate the effect of HF pulses. However, gradient pulses can also be emitted only as test gradient pulses, especially when the remaining gradient pulses in the pulse sequence are not suitable as test gradient pulses. Furthermore, gradient pulses can have a dual function: as test gradient pulses and as regular gradient pulses in a pulse sequence. Test gradient pulses can be, in particular, gradient pulses that are used directly or indirectly to correct for the effects of interference on the gradient system of the magnetic resonance apparatus during magnetic resonance measurements.

[0031] Interference effects, such as the presence of eddy currents, time tuning and gain errors, field fluctuations, variable temperature effects, and / or the nonlinear characteristics of hardware components, such as amplifiers and / or gradient coils in a gradient system, can cause deviations between the emitted gradient pulse and the desired gradient change curve.

[0032] Magnetic resonance imaging (MRI) measurements are preferably representative of the examination subject, particularly a patient. It is conceivable that two-dimensional, three-dimensional, and / or time-dependent three-dimensional image data of the examination subject are detected during MRI measurements. However, it is also conceivable that MRI measurements are performed for the purpose of calibrating and / or testing the MRI equipment, but also that MRI spectral measurements are performed. Here, the examination subject may include, for example, a reference object, a phantom, and / or a field sample, which interact in a predetermined manner with the pulse sequence emitted during the MRI measurement. In one embodiment, the purpose of performing the MRI measurement is to characterize the deviation between the emitted gradient pulses and the desired gradient change curve by means of the method according to the invention.

[0033] The emitted gradient pulse g ref (t) Preferably, it has a triangular, rectangular, or trapezoidal shape. This results in a gradient pulse that covers a wide spectrum, making it particularly suitable for correcting trajectories across the entire k-space. However, it is also conceivable that the emitted gradient pulse has a radial or helical trajectory.

[0034] Preferably, the desired or nominal gradient change curve g nom (t) and the emitted gradient pulse g ref (t) is related. If there is no interference effect in the gradient system, the expected gradient change curve can match the emitted gradient pulse. In this case, the emitted gradient pulse can be a "nominal gradient pulse," characterized by the expected nominal field strength value when the gradient pulse is emitted. However, in actual magnetic resonance measurements, the nominal field strength value deviates from the true field strength value of the gradient pulse due to dynamic interference. This deviation can be detected by correspondingly measuring the gradient change curve g. real (t) is used to determine this.

[0035] In one step, the gradient change curve g real (t) Detection is achieved by measuring the magnetic field in the examination area of ​​the magnetic resonance imaging (MRI) device. The detected gradient change curve, especially the actual field strength value, is obtained by transmitting a gradient pulse g emitted in the examination area. ref(t) Generation. For example, gradient change curves can be detected using a magnetometer or field camera. A magnetometer or field camera can be introduced into the inspection area of ​​a magnetic resonance imaging (MRI) device to detect gradient change curves. For this purpose, the field camera can have a signal connection to the input interface of the MRI device, and the detected gradient change curves can be transmitted to the input interface by means of the signal connection. Furthermore, it is conceivable that the gradient change curves are detected by the radio frequency (RF) receiving antenna of the MRI device. For this purpose, a field sample or a certain volume of reference material, such as water or oil, is introduced into the inspection area of ​​the MRI device and excited by a predetermined HF pulse. Subsequently, the MRI signal received by the RF receiving antenna of the MRI device from the field sample or reference material can be analyzed to obtain information about the characteristics of the emitted gradient pulse. The analysis of the received MRI signal can in particular include comparing the desired MRI signal of the field sample or reference material with the received MRI signal.

[0036] A gradient pulse can be understood as the magnetic field strength or a time-dependent variation curve of the magnetic field strength, provided by a gradient system. This gradient variation curve can be characterized by the field strength detected by measurement techniques or the detected time-dependent variation curve of the field strength. Therefore, the gradient variation curve should be understood in particular as the actual magnetic field gradient formed in the inspection area by emitting a gradient pulse. Due to the interference effects mentioned above, the gradient variation curve may deviate from the gradient pulse.

[0037] In another step, the detection amplifier is used for the gradient pulse g. ref The output signal i of (t) out (t). Amplifier output signal i out (t) can be the current fed into the gradient coil of the gradient system by the amplifier. Preferably, the gradient pulse g is emitted by the gradient coil of the gradient system. refDuring (t), the output signal of the amplifier is detected. The amplifier's output signal can be detected using suitable measuring devices, such as current clamps, Rogowski coils, voltage measuring devices, but also by measuring or current converters. Preferably, the detected amplifier output signal is transmitted to the input interface of the magnetic resonance device. However, it is also conceivable that the amplifier's output signal can be determined based on arbitrary measured variables and / or by means of the amplifier's known characteristic curves or operating characteristics. The term "amplifier" should be understood here particularly as a gradient amplifier, which boosts and / or transforms a signal with a low signal level (the amplifier's input signal) into a signal with a high signal level (the amplifier's output signal). The amplifier's output signal can be fed to the gradient coils of a gradient system, which accordingly generate a magnetic field gradient (the emitted gradient pulse) in the inspection region. In a preferred embodiment, the gradient system has at least three gradient coils configured to provide magnetic field gradients orthogonally oriented to each other.

[0038] In one step of the method according to the invention, based on the detected gradient change curve g real (t) and the detected amplifier output signal i out (t) Determine the gradient system transfer function (GSTF, GIRF). The gradient system transfer function can be determined here by means of the computing unit of the magnetic resonance device, which has a signal connection to the input interface. In the following text, for the sake of simplicity, the two terms "GSTF" and "GIRF" will be referred to under the term "gradient system transfer function" because the two functions can be converted to each other by means of equation (1).

[0039] The transfer function of a gradient system is typically based on the gradient G emitted by an amplifier. real (f) and the expected or nominal gradient G according to equation (4). nom The quotient of (f) is used to determine this. The transfer function of this type of gradient system represents the so-called gradient-input GSTF, where the nominal input gradient G is used. nom (f) is used to determine the transfer function of the gradient system.

[0040]

[0041] Conversely, in the method according to the invention, based on the detected gradient change curve g real (t) and the detected amplifier output signal i out (t) The transfer function of the gradient system is determined according to equation (5). This can be achieved by first converting the detected amplifier output signal i using Fourier transform. out (t) and the detected gradient change curve g real (t) transformed to the frequency domain (I)out (f), G real (f))

[0042]

[0043] Preferably, multiple different gradient pulses are used to determine the gradient system transfer function (GSTF) in order to cover a wide spectrum. The covered spectrum can, for example, include a frequency range between -20 kHz and 20 kHz, and particularly a frequency range between -10 kHz and 10 kHz.

[0044] In another step of the method according to the invention, the output signal i of the amplifier is determined based on the determined gradient system transfer function (GSTF, GIRF). cor (t), where the gradient system provides the desired gradient change curve (g) nom (t)). Determine the amplifier's output signal i cor (t) Preferably, this is performed using a computing unit of a magnetic resonance imaging (MRI) device. The computing unit preferably has a signal connection to an input interface. As described above, the input interface can be configured to receive gradient change curves and the amplifier's output signal, and transmit them to the computing unit via the signal connection. The signal connection can be configured wirelessly or wired.

[0045] The method according to the invention can advantageously compensate for interference effects, such as the nonlinear operating characteristics of the amplifier and / or the variable temperature effects on the gradient system. Furthermore, image artifacts caused by such interference effects can be reduced or avoided, and the quality of the detected image data can be advantageously improved. In particular, the amplifier can be directly adjusted via the input signal of the output amplifier. This advantageously avoids computationally intensive and / or time-intensive corrections to interference effects during image data reconstruction.

[0046] In a preferred embodiment of the method according to the invention, gradient pulses g are emitted in a repetitive manner. ref (t) and detect the gradient change curve g real (t), especially repeating at frequencies between one to five repetition intervals in the pulse sequence measured by magnetic resonance.

[0047] The transmission of gradient pulses and the detection of gradient change curves are preferably repeated at discrete time intervals. It is conceivable that the repeated transmission of gradient pulses and the detection of gradient change curves are performed at frequencies or intervals between one to five repetition intervals of the pulse sequence in the magnetic resonance measurement.

[0048] In one embodiment, the frequency of repetitive gradient pulse transmission and gradient change detection during the pulse sequence of magnetic resonance measurements is minimized. Experiments show that the relevant temperature changes during magnetic resonance measurements can be quantified by measurement after approximately five repetition intervals, or only after the duration of the five repetition intervals has ended. By reducing the frequency of repetitive gradient pulse transmission and gradient change detection, the duration of magnetic resonance measurements and / or the computational cost for correcting interference effects can be advantageously reduced.

[0049] In a preferred embodiment, the repeated transmission of gradient pulses and the detection of gradient change curves are performed at each repetition interval. This also advantageously allows for timely compensation for unexpected and rapid interference effects that affect the magnetic field gradient. Here, the repetition interval can be understood as the duration between two successive excitation pulses, especially two successive HF pulses.

[0050] In one embodiment, the method according to the invention further includes the following steps:

[0051] • Determine the temperature of the gradient coil in the gradient system.

[0052] The amplifier's output signal i is determined based on the temperature of the gradient coil. cor (t).

[0053] The temperature gradient coil is determined here according to the amplifier's output signal i. out (t) emit gradient pulse g ref The gradient coil (t) corresponds to the gradient coil. The temperature of the gradient coil can be determined, for example, by means of one or more temperature sensors positioned on the gradient system, particularly on the gradient coil. Preferably, the temperature sensor is mechanically connected to the gradient coil and has thermal coupling with the gradient coil via the mechanical connection. The temperature sensor can be configured to transmit a measured value of the gradient coil temperature, or a signal indicating the temperature of the gradient coil, to the computing unit of the magnetic resonance device via a signal connection. The computing unit can be accordingly configured to determine the amplifier's output signal based on the temperature of the gradient coil. It is also conceivable to determine the temperature of the gradient coil based on the measured value and / or the amplifier's operating characteristics, which differ from the temperature measurement.

[0054] According to another embodiment, the method according to the invention further comprises the following steps:

[0055] • Determine the resistance and / or inductance of the gradient coil.

[0056] The temperature of the gradient coil is determined based on its resistance and / or inductance.

[0057] Preferably, the temperature of the gradient coil is determined based on the resistance and / or inductance of one or more gradient coils. Alternatively, other measurements can also be used to determine the temperature of the gradient coil. Preferably, the temperature of the gradient coil is determined based on a measuring resistor (shunt resistor) connected to a voltage measuring device. However, it is also conceivable to determine the temperature of the gradient coil based on temperature-related characteristics, such as the length of a reference line, but also the inductance of the gradient coil.

[0058] In another embodiment of the method according to the invention, the temperature of the gradient coil is determined based on a model and / or a smart algorithm.

[0059] Intelligent algorithms can encompass any application of artificial intelligence. Artificial intelligence can include, for example, self-learning algorithms, neural networks, multi-layer neural networks, expert systems, etc., which determine the temperature of a gradient coil based on one or more measurements of a gradient system. It is also conceivable that intelligent algorithms can determine the temperature of a gradient coil based on known operating characteristics of the amplifier and / or the gradient coil. Furthermore, intelligent algorithms can use models of the gradient coil and / or the amplifier to determine the temperature of the gradient coil.

[0060] Furthermore, the temperature of the gradient coil can be determined based on the model. The model can be, in particular, a simulation model, an analytical model, an empirical model, and / or a model-based approach that describes or models the amplifier and / or gradient coil.

[0061] In a preferred embodiment, based on the detected amplifier output signal i out (t) Determine the temperature of the gradient coil.

[0062] Knowing the current fed into the gradient coils by the amplifier, the temperature can be determined very accurately based on the fundamental physical relationships and / or analytical models of the gradient coils. Preferably, the temperature of the gradient coils is determined by means of the computational unit of the magnetic resonance system when using models and / or intelligent algorithms. Of course, determining the temperature of the gradient coils can also include determining the temperatures of multiple gradient coils used in a pulse sequence.

[0063] By determining the temperature of the gradient coil, the amplifier's output signal can be determined advantageously with improved accuracy. Furthermore, the amplifier's output signal can be determined in a particularly robust and / or reproducible manner based on the temperature of the gradient coil, since the variable temperature effects on the gradient coil can be taken into account.

[0064] In one embodiment, the method according to the invention comprises the following steps:

[0065] • Based on the determined amplifier output signal i cor (t) and the detected amplifier output signal i out(t) is used to adjust the amplifier's input signal i in (t).

[0066] It is conceivable that the input signal of the amplifier can be adjusted using a suitable adjustment device. Such a device could, for example, be configured to adjust the amplifier's input signal based on a determined amplifier output signal and a detected amplifier output signal. More particularly, the adjustment device could be configured to adjust the amplifier's input signal based on the difference between the determined amplifier output signal and the detected amplifier output signal.

[0067] Preferably, the input signal of the amplifier is adjusted continuously or in discrete time steps. For example, the input signal of the amplifier is adjusted multiple times for each repetition interval, once for each repetition interval, every second repetition interval, every third repetition interval, or every fourth or fifth repetition interval. This is particularly effective for each transmitted gradient pulse g. ref (t) and / or detection gradient change curve g real (t) Then adjust the input signal of the amplifier.

[0068] It is also conceivable that the input signal of the amplifier is adjusted in the second repetition interval based on the amplifier's output signal determined in the first repetition interval or based on the gradient system transfer function determined in the first repetition interval. The first and second repetition intervals can also be spaced apart from each other by multiple repetition intervals. This process is also known as "pre-enhancement." In this process, correction can already be performed when gradient pulses are emitted at the second repetition interval, so that image reconstruction no longer requires correction of the gradient field.

[0069] By adjusting the input signal of the amplifier according to the present invention, interference effects in the gradient system can be corrected in a timely and / or automatic manner in an advantageous manner.

[0070] According to another embodiment of the method according to the invention, the input signal i of the amplifier is adjusted by means of an adaptive filter, especially a Volterra filter, a spline filter, and / or a kernel filter. in (t).

[0071] Preferably, the input signal of the amplifier is adaptively adjusted by using a nonlinear adaptive filter, so that interference effects in the gradient system are compensated by changing the input signal of the amplifier. Here, the input signal applied to the input terminal of the amplifier can pass through the adaptive filter and form a so-called output sequence. This output sequence can be compared with the sequence to be formed by the adaptive filter, such as the determined output signal i of the amplifier. corThe error signal is determined by comparing (t) with the output sequence. When the output sequence deviates from the desired sequence, the adaptive filter's adjustment algorithm can change the filter coefficients to minimize the error signal and adapt the adaptive filter's output sequence to the desired sequence. Here, known methods for minimizing the squared error can be used, such as the Least Mean Square (LMS) algorithm or the Recursive Least Squares (RLS) algorithm.

[0072] Preferably, the adaptive filter includes the Volterra-LMS method, in which discrete input values ​​are replaced by different nonlinear algebraic expressions, i.e., so-called Volterra series.

[0073] For example, the input signal of the amplifier can be adjusted directly or indirectly based on the output sequence of the adaptive filter. In one embodiment, the output sequence of the adaptive filter is transmitted as a control signal to the amplifier and / or the control unit of the amplifier or magnetic resonance device via a signal connection. Here, the output sequence can specifically represent the input signal of the amplifier. However, it is also conceivable that the output sequence represents a correction signal, based on which the input signal of the amplifier is adjusted.

[0074] Adaptive filters can be implemented as analog or digital filters, for example. In a preferred embodiment, the adaptive filter is implemented as part of a DSP (digital signal processor), FPGA (field-programmable gate array), and / or FPAA (field-programmable analog array).

[0075] The use of adaptive filters can also advantageously compensate for complex and / or nonlinear disturbances in gradient systems.

[0076] In another embodiment of the method according to the invention, a gradient pulse g is emitted. test (t) includes emitting multiple gradient pulses g test，i (t), where multiple gradient pulses (g) test，i (t) covers the spectrum between -20kHz and +20kHz, especially the spectrum between -10kHz and +10kHz.

[0077] Preferably, the gradient change curve g is detected. real (t) also includes detecting the gradient change curve for each of the multiple gradient pulses. Here, it is also possible to detect the amplifier's output signal i for each gradient change curve. out(t). It is conceivable that the gradient system transfer function can be determined in this way for multiple gradient pulses and multiple amplifier output currents. Here, the gradient system transfer function can be characterized by the superposition or overlap of multiple detected gradient change curves and detected amplifier output currents.

[0078] By determining the gradient system transfer function for multiple gradient pulses covering a wide spectrum, it is possible to advantageously correct or compensate for interference effects of the gradient system in any gradient pulses included by the spectrum.

[0079] The correction device according to the invention has an output interface configured to transmit at least one gradient pulse g. ref (t). The output interface can include, for example, the output channel of the amplifier of the gradient system of the magnetic resonance system.

[0080] The correction device according to the invention further includes an input interface configured to receive a gradient change curve g. real (t) and the amplifier for the gradient pulse g ref The output signal i of (t) out (t). Preferably, the input interface has a signal connection to a field camera, magnetometer, or radio frequency receiving antenna. The input interface can also be configured as part of the radio frequency receiving antenna. It is also conceivable that the input interface has a signal connection to a current sensor, voltage sensor, and / or temperature sensor. In principle, the input interface can have a signal connection to any sensor configured to detect the characteristics of the gradient system according to the above embodiments using measurement techniques. Furthermore, the correction device according to the invention has a calculation unit configured to calculate the characteristics of the gradient system based on the detected gradient change curve g. real (t) and the detected amplifier output signal i out (t) Determine the gradient system transfer function (GSTF, GIRF). The computational unit is also configured to determine the amplifier's output signal i based on the gradient system transfer function. cor (t).

[0081] The correction device according to the invention is further configured to, based on the determined amplifier output signal i cor (t) and the detected amplifier output signal i out (t) is used to adjust the amplifier's input signal i in (t). Determine the gradient system transfer function GSTF and the amplifier output signal i. cor (t), but there is still the input signal i of the amplifier to be adjusted. in (t) Here, the above-described embodiment of the method according to the invention can be carried out by means of a correction device.

[0082] The correction apparatus according to the invention shares the advantages of the method according to the invention for correcting the influence of interference effects on the gradient system of a magnetic resonance device during magnetic resonance measurements.

[0083] The magnetic resonance apparatus according to the invention includes a calibration device according to the above embodiment, wherein the magnetic resonance apparatus is configured to adjust the input signal i of the amplifier by means of the calibration device during magnetic resonance measurement of the object being examined. in (t), so as to provide the desired gradient pulse g nom (t).

[0084] In particular, the magnetic resonance apparatus according to the invention can be configured to autonomously coordinate and execute the various method steps of the method according to the invention according to the above embodiments. In this way, the input signal of the amplifier can be advantageously and reproducibly adjusted and / or automatically based on the gradient system transfer function and the determined output signal of the amplifier.

[0085] The magnetic resonance system according to the present invention includes a fundamental field magnet system, a radio frequency transmitting antenna, a gradient system, a radio frequency receiving antenna, a correction device according to the above embodiments, and a control unit for operating the fundamental field magnet system, the radio frequency transmitting antenna, the gradient system, and the radio frequency receiving antenna.

[0086] By providing a magnetic resonance system according to the invention, the components of the magnetic resonance system according to the invention, such as the basic field magnet system, radio frequency transmitting antenna, gradient system, radio frequency receiving antenna, correction device, and control unit, can be advantageously coordinated with each other, enabling time-saving and / or robust execution of the method according to the invention according to the above embodiments.

[0087] The computer program product according to the invention comprises: a computer program capable of being directly loaded into the storage unit of the control unit of the magnetic resonance system according to the invention; and a program segment that, when the computer program is executed by means of the control unit of the magnetic resonance system, performs all the steps of the method according to the invention according to the above embodiments.

[0088] The correction device according to the invention can preferably be implemented in software on a suitable programmable control unit of a magnetic resonance system having corresponding storage units. The high-frequency transmitting unit, output interface, and high-frequency receiving unit can also be implemented at least partially as software units, while other units of these components can be purely hardware units. Such hardware units can be, for example, high-frequency amplifiers, antenna devices for the high-frequency transmitting unit and / or the high-frequency receiving unit, gradient pulse generating devices for the output interface, analog-to-digital converters for the high-frequency receiving unit, etc.

[0089] In particular, the software-based implementation of the aforementioned components offers the advantage that the control unit of the magnetic resonance system currently in use can be easily retrofitted via software updates to operate according to the invention. In this regard, the objective is also achieved through a computer program product stored in a portable storage unit and / or provided via a network for transmission, thereby enabling direct loading into the memory of the programmable control unit of the magnetic resonance system. This computer program product has program segments that, when executed by means of the control unit, perform all the steps of the method according to the invention according to the above embodiments. In addition to the computer program, this computer program product may optionally include additional components, such as documentation and / or additional components, as well as hardware components for using the software, such as hardware keys (dongles, etc.).

[0090] A program segment capable of being read and executed by a computing unit is stored on a computer-readable medium according to the invention, so that when the program segment is executed by the computing unit, all steps of the method according to the invention according to the above embodiments are performed.

[0091] For transmitting a portion of the control unit and / or for storing on or within the control unit, a computer-readable medium, such as a memory stick, hard disk, or other portable or fixed-mount data medium, can be used, on which program segments of a computer program that can be read and executed by the computing unit of the control unit are stored. For this purpose, the computing unit can, for example, have one or more microprocessors working together. Attached Figure Description

[0092] Other advantages and details of the invention will become apparent from the embodiments described below and from the accompanying drawings. Hereinafter:

[0093] Figure 1 This illustrates one embodiment of the magnetic resonance system according to the present invention;

[0094] Figure 2 A schematic diagram illustrating the effect of interference during magnetic resonance measurements;

[0095] Figure 3 A graph illustrating the effect of variable temperature on the gradient system of a magnetic resonance system is shown.

[0096] Figure 4 A schematic diagram illustrating the principle of adjusting the input signal of an amplifier by means of a correction device according to the present invention;

[0097] Figure 5 The diagram illustrates a view of determining the transfer function of a gradient system based on multiple gradient impulses.

[0098] Figure 6A flowchart illustrating a possible implementation of the method according to the present invention is shown.

[0099] Specific implementation form

[0100] exist Figure 1 The magnetic resonance system 1 shown is a magnetic resonance device 2 having an examination area 3 configured as a patient channel into which the subject can be fully introduced. In this example, the subject is a patient who can be positioned relative to the magnetic resonance device 2 by means of a patient support device 8. However, in principle, the magnetic resonance system 1 according to the invention can also include another magnetic resonance device, for example, having a laterally open, C-shaped housing. Importantly, the magnetic resonance device 2 is configured to perform magnetic resonance measurements in order to detect image data of the subject.

[0101] The magnetic resonance imaging (MRI) device 2 is preferably equipped with a basic field magnet system 4, at least one gradient coil 6, and a radio frequency (RF) transmitting antenna 5 and a radio frequency (RF) receiving antenna 7. In the illustrated embodiment, the RF transmitting antenna 5 is a body coil fixedly mounted in the MRI device 2. Conversely, the RF receiving antenna 7 is one or more local coils disposed on the patient. However, in principle, the body coil can also be configured as an RF receiving antenna, and the local coils can be configured as RF transmitting antennas and / or have corresponding functions. Currently, the basic field magnet system 4 is configured to generate a basic magnetic field along the longitudinal direction of the patient, i.e., along the longitudinal axis of the MRI device 2 extending in the Z direction. Preferably, the gradient system 9 of the MRI device 2 (see...) Figure 4 It includes multiple individually operable gradient coils 6 so that gradients can be emitted independently of each other in the X, Y or Z directions.

[0102] The magnetic resonance imaging (MRI) device 1 has a central control unit 13 for controlling the MRI device 1. The central control unit 13 may also include a sequence control unit 14. With the aid of the sequence control unit 14, the order of HF pulses and gradient pulses is controlled during MRI measurements according to a selected pulse sequence PS or a series of multiple pulse sequences PS, for detecting image data of one or more slices of the relevant volume of the examined object, particularly the volume region of interest. This pulse sequence PS can, for example, be preset and parameterized within a measurement or control protocol P. Typically, different control protocols P for different MRI measurements are stored in a storage unit 19 and can be selected by the operator, changed as needed, and then used to perform MRI measurements. In the current case, the control unit 13 contains multiple pulse sequences PS for acquiring raw data.

[0103] To output the individual HF pulses of the pulse sequence PS, the central control unit 13 has a transmitting unit 15. The transmitting unit 15 generates and amplifies the HF pulses and transmits them to the radio frequency transmitting antenna 5 (not shown in detail) via a signal connection and a suitable interface. To control the gradient coil 6 of the gradient system 9, and particularly to appropriately switch or output gradient pulses according to the preset pulse sequence PS, the control unit 13 has an output interface 16. By means of the output interface 16, for example, a diffused gradient pulse or a phase-scratching gradient pulse can be applied. Currently, the output interface 16 has a connection with the gradient coil 6 of the gradient system 9 (see...). Figure 4 The gradient coil generates a corresponding magnetic field gradient in the inspection region 3 according to the applied gradient pulse. The sequence control unit 14 communicates with the transmitting unit 15 and the output interface 16 in a suitable manner to execute the pulse sequence PS, for example, by transmitting sequence control data SD.

[0104] The control unit 13 also has a radio frequency receiving unit 17 (which communicates with the sequence control unit 14 in a suitable manner) to receive magnetic resonance signals in a coordinated manner within a readout window preset by the pulse sequence PS by means of the radio frequency receiving antenna 7, thereby acquiring raw data.

[0105] The magnetic resonance system 1 may also include a reconstruction unit 120a configured to reconstruct image data of the object under examination based on the detected magnetic resonance signal. This reconstruction can be based on parameters that can be preset in a corresponding measurement or control protocol P. For example, the reconstructed image data can then be stored in a storage unit 19.

[0106] The correction device 110 has signal connections to other components, particularly the output interface 16 and / or the sequence control unit 14. Alternatively, the correction device 110 can also be configured as part of the sequence control unit 14. The correction device 110 is preferably configured to generate a suitable gradient pulse g. ref (t) and transmit it to output interface 16 or gradient coil 6. It is conceivable that the correction device 110 would include amplifier 113 of gradient system 9 for this purpose (see [link to relevant documentation]). Figure 4 And preset the input signal i of amplifier 113 in (t). Alternatively, the correction device 110 can also exist separately from the amplifier 113 and can be activated by means of a suitable signal connection to transmit the gradient pulse g. ref (t). The correction device 110 is specifically configured to, based on the determined output signal i cor (t) and the detected output signal i of amplifier 113 out (t) to adjust the input signal i of amplifier 113 in (t)(see also) Figure 4).

[0107] The central control unit 13 can be operated via a terminal 11 having an input unit 10 and a display unit 12. Preferably, the magnetic resonance system 1 can be controlled by an operator using the terminal 11. The display unit 12 can be configured to output image data of the detected magnetic resonance measurements. The input unit 10 can be configured to, if necessary, in conjunction with the display unit 12, parameterize and initiate magnetic resonance measurements using the magnetic resonance system 1. This can particularly include selecting and / or modifying the control protocol P and / or the pulse sequence PS.

[0108] Furthermore, the magnetic resonance system 1 according to the invention, and especially the control unit 13, can also have several other components, which are not shown in detail here but are generally present on this type of facility, such as a network interface to connect the entire system to a network and to exchange and / or process raw data and / or image data or parametric plots, but also other data, such as patient-related data or control protocols.

[0109] How to detect suitable magnetic resonance signals and reconstruct image data or parametric maps from them by irradiating HF pulses and emitting gradient pulses is known in principle to those skilled in the art. Similarly, various measurement sequences, such as EPI measurement sequences or other measurement sequences used to generate image data, including diffusion-weighted image data, are known in principle to those skilled in the art. Therefore, these aspects will not be discussed in detail below.

[0110] exist Figure 2 The gradient G of the emitted pulse sequence measured by magnetic resonance is shown in the figure. ref and the actual emitted gradient G real Comparison view 30. The emitted gradient G ref The field intensity value is determined by the control unit 13 of the magnetic resonance system 1. Conversely, the actual gradient G... real This corresponds to the field intensity value actually measured in the inspection area. The input gradient or emitted gradient G is shown in partial view 30a. ref The gradient is generated by the control unit 13 of the magnetic resonance device 2 and transmitted to the gradient coil 6 of the magnetic resonance device 2 in the magnetic resonance system 1. The gradient G actually emitted by the gradient coil 6 is... real Shown in partial view 30c. Figure 2 In the example shown, the emitted gradient G ref It has a triangular shape. This triangular shape covers a relatively wide frequency range, thus enabling it to map the gradient's response characteristics in the frequency domain relatively well. The actual emitted gradient G realDue to the interference effect of gradient coil 9 as described above, for example, amplifier 113 (see Figure 4 The nonlinear characteristics of the emitted gradient G, the thermal variations of the hardware components, and the eddy currents and / or time-varying tuning and gain errors all contribute to the problem. ref Different gradient forms.

[0111] Two gradients G are shown together in partial view 30d. ref and G real As can be seen in partial view 30e, the actual gradient G real Relative to the emitted gradient G ref It can also have a time offset.

[0112] A portion of partial view 30d is shown magnified in partial view 30e. In partial view 30e, the actual gradient G can be seen. real Or the actual gradient G real At t = 122 s, the amplitude A drops below the emitted gradient G. nom And at approximately t = 130 s, it is assumed that the gradient G emitted is greater than that emitted. ref A higher metric value is needed so that the emitted gradient coincides with the zero line again at the value of t = 160s.

[0113] exist Figure 3 View 30 is shown, representing the measure M of the two gradient system transfer functions GSTF at different reference temperatures. Currently, based on the actual gradient G... real With the detected output signal I of amplifier 113 out The quotient is used to determine the gradient system transfer function GSTF. Figure 3 The diagram illustrates the GSTF transfer functions for two gradient systems with two different average temperatures of 20°C and 40°C. 20 GSTF 40 GSTF 20 GSTF 40 The measure M of frequency f is plotted here in kHz. As can be seen in view 30, the measure M of the gradient system transfer function is slightly higher at 40°C than at 20°C.

[0114] Figure 4 The output signal i is shown. cor (t) and the detected output signal i of amplifier 113 out (t) to adjust the input signal i of amplifier 113 in A schematic diagram of the process (t). Preferably, the gradient system 9 of the magnetic resonance system 1 has a sensor 115 configured to detect the output signal i of the amplifier 113.out (t) Related signals. Sensor 115 can also be configured to transmit signals to computing unit 18 of magnetic resonance system 1 via signal connection.

[0115] The magnetic resonance system 1 also includes a field camera 116 configured to detect emitted gradient pulses g. ref The gradient curve g of (t) real (t) and transmits it to the computing unit 18 by means of a signal connection.

[0116] The calculation unit 18 is accordingly configured to calculate the gradient change curve g. real (t) and the detected output signal i of amplifier 113 out (t) Determine the gradient system transfer function GSTF. The computation unit 18 is also currently configured to determine the output signal i of amplifier 113 based on the gradient system transfer function GSTF. cor (t), in the case of the output signal, the gradient system 9 provides the desired gradient change curve g. ref (t). Therefore, the output signal i of amplifier 113 cor (t) specifically represents the target value of the output signal of amplifier 113, under which the interference effect of the gradient system 9 is corrected or compensated.

[0117] In this example, the computing unit 18 calculates the output signal i of the amplifier 113. cor (t) and the detected output signal i of amplifier 113 out (t) is transmitted to the correction device 110. It is also conceivable that the computing unit 18 is integrated into the correction device 110. The correction device 110 is configured to, based on the output signal i of the amplifier 113, transmit the signal to the correction device 110. cor (t) and the detected output signal i of amplifier 113 out (t) to adjust the input signal i of amplifier 113 in (t). Therefore, the correction device 110 can, for example, have an adjustment device according to the above embodiment, especially an adaptive filter.

[0118] In the example shown, the detected gradient G real (f) The variation curve and the emitted or nominal gradient G ref (f)(as in Figure 2 (as shown) is substantially consistent, because the correction device 110 uses the input signal i of amplifier 113 to... in The adjustment of (t) is used to correct the disturbance effect in gradient system 9. Therefore, the emitted gradient G ref(f) The change curve and the expected or nominal gradient G nom (f) is basically consistent.

[0119] In one embodiment, the temperature of the gradient coil 6 is detected by means of a temperature sensor 117 positioned on the gradient coil 6. It is conceivable that the temperature of the gradient coil 6 is transmitted to the input interface 112 and used to determine the output signal i of the amplifier 113. cor (t) is used by the calculation unit 18.

[0120] exist Figure 5 View 31 is shown in the figure, which illustrates the gradient pulse g constructed using twelve different triangles. ref，i The principle of determining the gradient system transfer function GSTF by combining (t) is as follows: Gradient impulse g ref,i (t) respectively have the output signal i output by amplifier 113 out,i (t), the output signal is transmitted to the gradient coil 6 via the output interface 16. The output signal i, composed of twelve triangles of the amplifier 113, is shown in partial view 31a with different line patterns (dashed lines, solid lines, dotted lines). out，i The set of (t). As the output signal passes through the gradient coil 6 of the gradient system 9 of the magnetic resonance device 2, it produces the actual gradient change curve g. real，i (t), the actual gradient change curve is shown in partial view 31b. As can be seen in partial view 31b, the actual gradient impulse g real,i (t) The gradient change curve deviates from the expected curve due to the interference effect. nom,i (t), the desired gradient change curve is substantially the same as the emitted gradient pulse g. ref,i (t)(See also: Figure 2 This is consistent with the previous view. These two partial views 31a and 31b are shown in the time domain. Conversely, partial views 31c and 31d show the output signal I of amplifier 113. out，i (f) and the true gradient G in the frequency domain real , i (f). Output signal l of amplifier 113 out,i (f) and the true gradient G real,i (f) respectively through i out,i (t) and g real,i (t) is generated from the Fourier transform (FT) in the time domain to the frequency domain. View 31 also shows the gradient system transfer function (GSTF), which is generated by passing the true gradient G. real,i (f) Divide by the input signal I of amplifier 113 out,i (f) determines this fact. Figure 5 In Chinese, the division sign “÷” is used to represent this.

[0121] Figure 6 A flowchart illustrating an embodiment of the method according to the invention for correcting the effect of interference effects on the gradient system 9 of a magnetic resonance apparatus 2 during magnetic resonance measurements is shown.

[0122] In step S1 of the method according to the invention, a gradient pulse g is emitted by means of amplifier 113. ref (t). During magnetic resonance imaging (MRI) measurements on a patient, gradient pulses are particularly representative of test gradient pulses or regular gradient pulses. Gradient pulses are provided by the output interface 16 of the amplifier 113 of the gradient system 9 and transmitted to the gradient coil 6 of the gradient system 9, which provides gradient pulses in the form of a magnetic field gradient in the examination region 3.

[0123] In one embodiment of the method according to the invention, gradient pulses g are emitted in a repetitive manner. ref (t) and detect the gradient change curve g real (t), especially the frequency of emission and detection between one to five repetition intervals measured by magnetic resonance.

[0124] In step S2, the gradient change curve g is detected in the inspection area 3 of the magnetic resonance device 2 by means of magnetic field measurement. real (t). Here, a magnetometer or field camera 116 can be used to detect the gradient change curve, which transmits information about the gradient change curve and / or the detected magnetic field data to the input interface 112 of the magnetic resonance device 2, especially the calibration device 110. For this purpose, the magnetometer or field camera 116 can be connected to the input interface 112 by means of a wired or wireless signal connection.

[0125] In another step S3, the detection amplifier 113 is used for the gradient pulse g. ref The output signal i of (t) out (t). Preferably, the output signal of amplifier 113 is detected by means of a suitable sensor 115, such as a current clamp, Rogowski coil, or voltage measuring device, but also by measuring or current converters. Sensor 115 is particularly capable of having a signal connection to input interface 112 in order to transmit information and / or measured values ​​about the output signal of amplifier 113 to control unit 13 and / or computing unit 18.

[0126] In step S4, based on the detected gradient change curve g real (t) and the measured output signal i of amplifier 113 out (t) Determine the gradient system transfer function (GSTF, GIRF). Preferably, this is done according to equation (5) and the above process (see...). Figure 4 Determine the transfer function of the gradient system.

[0127] In another step S5, the output signal i of amplifier 113 is determined. cor (t), where the gradient system provides the desired gradient change curve g according to the determined gradient system transfer function (GSTF, GIRF). nom (t). Therefore, it is preferable to determine the output signal i of amplifier 113 according to equation (6). cor (t).

[0128]

[0129] Here, the output signal i of amplifier 113 cor (t) represents the following output signal, which is required to provide the desired, nominal gradient pulse g in the examination area 3 of the magnetic resonance device 2. nom (t). Here, as long as no interference effect occurs in the gradient system 9 or by means of the correction device 110, the input signal i of the amplifier 113 is adjusted. in (t) Corrects for interference effects, nominal gradient pulse g nom (t) can be correlated with the gradient change curve g real (t) is largely consistent. Item GSTF- 1 This represents the reciprocal of GSTF, which is based on the detected gradient change curve g. real (t) and the detected output signal i of amplifier 113 out (t) is determined according to equation (5).

[0130] According to one embodiment, the output signal i of amplifier 113 is determined based on the temperature of gradient coil 6. cor (t). Therefore, the temperature of the gradient coil 6 can be integrated to the nominal output signal i for the amplifier 113. cor In equation (7) of (t), preferably, the temperature-dependent gradient system transfer function GSTF is used here. T The expression.

[0131]

[0132] For example, the temperature dependence of the gradient system transfer function GSTFT can be determined according to equation (8) using a linear model of the temperature-dependent variation of the GSTFT. Here, T meas Capable of representing different time points T t =0 to T t = N The matrix represents the measured temperature values, and m represents the model parameters. This method can include heuristic modeling, where the model parameters m are calibrated.

[0133] ΔGSTF=T meas ·m (8)

[0134] However, it is also conceivable that the gradient system transfer function GSTF can be determined based on the resistance change ΔR of gradient coil 6. T Temperature dependence. By measuring the resistance change of gradient coil 6 at different temperatures, the temperature-dependent change ΔGSTF ​​of the gradient system transfer function can be determined using the following relationship (9):

[0135] ΔGSTF=f(ΔR(T)) (9)

[0136] In optional step S5.1, the temperature of the gradient coil 6 of the gradient system 9 is determined. Preferably, here, the temperature of one or more gradient coils 6 of the gradient system 9 is detected by means of one or more temperature sensors, and transmitted to the control unit 13 and / or calculation unit 18 of the magnetic resonance system 1 by means of a signal connection. The calculation unit 18 is accordingly configured to determine the output signal i of the amplifier 113 based on the temperature of the gradient coil 6 by means of equation (7). cor (t).

[0137] In one embodiment, the temperature of the gradient coil 6 is determined based on a model and / or intelligent algorithm. It is conceivable that the temperature of the gradient coil 6 is determined based on the known operating characteristics of the amplifier 113. Furthermore, analytical models, empirical models, and / or simulation models of the amplifier 113 and the gradient coil 6 can be used to determine the temperature of the gradient coil 6. Additionally, information regarding the mechanical and / or electrical construction of the amplifier 113 and / or the gradient coil 6, the arrangement and / or electrical connections of electronic components, and / or the thermal conductivity and heat capacity of the materials used can be used when determining the temperature of the gradient coil 6.

[0138] In an alternative implementation, based on the output signal i detected by amplifier 113 out (t) Determine the temperature of gradient coil 6. Knowing the current fed into gradient coil 6 by amplifier 113, the temperature of gradient coil 6 can be determined very accurately based on a simple analytical model of gradient coil 6. Preferably, when using a model and / or intelligent algorithm, the temperature of gradient coil 6 is determined by means of computing unit 18 of magnetic resonance system 1.

[0139] In optional step S5.2, the resistance and / or inductance of the gradient coil 6 of the gradient system 9 is determined. The determination of resistance and / or inductance can be performed particularly according to the above-described embodiments of the method according to the invention. In one example, the temperature of the gradient coil 6 is determined based on the measuring resistor (shunt resistor) connected to the voltage measuring device. The resistance and / or inductance of the gradient coil 6 can then be used to determine the temperature of the gradient coil 6 in step S5.1.

[0140] In optional step S6, based on the determined output signal i of amplifier 113 cor (t) and the detected output signal i of amplifier 113 out (t) to adjust the input signal i of amplifier 113 in (t). The input signal of the amplifier can be adjusted directly or indirectly by means of a suitable adjustment device, especially by means of an adaptive filter. It is preferable to use the correction device 110 to adjust the input signal of the amplifier (see...). Figure 4 It can receive the output signal i of amplifier 113 determined according to equation (6) or equation (7) from the computing unit 18 of magnetic resonance system 1. cor (t) and in a quasi-continuous manner or with discrete time steps, the output signal i of amplifier 113 detected by means of input interface 112. cor (t) is compared. The determined output signal i cor (t) and the detected output signal i of amplifier 113 out If there is a deviation between (t), the input signal i of amplifier 113 is adjusted by means of correction device 110. in (t), thereby reducing the deviation. Therefore, when transmitting gradient pulses, the interference effect in the gradient system 6 is corrected by means of the correction device 110.

[0141] In one embodiment, the input signal i of amplifier 113 is adjusted by means of an adaptive filter, particularly a Volterra filter, spline filter, and / or kernel filter. in (t). Preferably, the adaptive filter includes the Volterra LMS method, where the least mean square algorithm (LMS) is used to minimize the squared error.

[0142] It should be noted that the methods and structures described in detail above are merely embodiments, and the basic principles can be modified by those skilled in the art in a wide range without departing from the scope of the invention, as long as they are presupposed by the claims. Furthermore, the described methods are not limited to medical applications. For the sake of completeness, it should be noted that the use of the indefinite articles “a” or “an” does not exclude the possibility that the features involved may exist multiple times. Similarly, the term “unit” does not exclude the possibility that the unit is composed of multiple components, which may also be spatially distributed if necessary.

Claims

1. A method for correcting the influence of interference effects on the gradient system (9) of a magnetic resonance apparatus (2) during magnetic resonance measurements, the method comprising the following steps: • Gradient pulses (g) are emitted (S1) by means of the amplifier (113) of the gradient system (9). ref (t)), • The gradient change curve (g) of (S2) is detected by means of magnetic field measurement in the examination area (3) of the magnetic resonance device (2). real (t)), the gradient change curve (g) real (t)) by emitting the gradient pulse (g) ref (t)) and formed in the inspection area (3), • Detect (S3) the amplifier (113) for the gradient pulse (g) ref (t)) output signal (i out (t)), • Based on the detected gradient change curve (g real (t)) and the detected output signal (i) of the amplifier (113) out (t)) Determine the gradient system transfer function (GSTF, GIRF) of (S4). Its features The following steps are required: • Determine the output signal (i) of the amplifier (113) based on the determined gradient system transfer function (GSTF, GIRF) (S5). cor (t)), where the determined output signal (i) cor In the case of (t)), the gradient system (9) provides the desired gradient change curve (g). nom (t)) • Based on the determined output signal (i) of the amplifier (113) cor (t)) and the detected output signal (i) of the amplifier (113) out (t)) to adjust (S6) the input signal (i) of the amplifier (113). in (t)).

2. The method according to claim 1, wherein the gradient pulse (g) is emitted in a repetitive manner (S1). ref (t) and detect the gradient change curve (g) described in (S2). real (t)).

3. The method according to claim 1 or 2, further comprising the following steps: • Determine (S5.1) the temperature of the gradient coil (6) of the gradient system (9), The output signal (i) of the amplifier (113) is determined (S5) based on the temperature of the gradient coil (6). cor (t)).

4. The method according to claim 3, further comprising the following steps: • Determine (S5.2) the resistance and / or inductance of the gradient coil (6) of the gradient system (9), The temperature of the gradient coil (6) is determined (S5.1) based on the resistance and / or inductance of the gradient coil (6).

5. The method according to claim 3, wherein the temperature of the gradient coil (6) is determined (S5.1) according to a model and / or intelligent algorithm.

6. The method according to claim 3, wherein the detected output signal (i) of the amplifier (113) out (t)) Determine (S5.1) the temperature of the gradient coil (6).

7. The method according to claim 1 or 2, wherein the input signal (i) of the amplifier (113) is adjusted (S6) by means of an adaptive filter. in (t)).

8. The method according to claim 1 or 2, wherein the gradient pulse (g) is emitted (S1). ref (t) includes emitting multiple gradient pulses (g) ref，i (t)), and a plurality of said gradient pulses (g) test，i (t) covers the spectrum between -20kHz and +20kHz.

9. The method of claim 1, wherein the gradient pulse (g) is emitted (S1) at a frequency between one to five repetition intervals of the pulse sequence (PS) measured by the magnetic resonance. ref (t) and detect the gradient change curve (g) described in (S2). real (t)).

10. The method according to claim 1 or 2, wherein the input signal (i) of the amplifier (113) is adjusted (S6) by means of a Volterra filter, a spline filter, and / or a kernel filter. in (t)).

11. The method according to claim 1 or 2, wherein the gradient pulse (g) is emitted (S1). ref (t) includes emitting multiple gradient pulses (g) ref，i (t)), and a plurality of said gradient pulses (g) test，i (t) covers the spectrum between -10kHz and +10kHz.

12. A calibration device (110), the calibration device (110) comprising: • Output interface (16), the output interface (16) being configured to transmit at least one gradient pulse (g ref (t)), • Input interface (112), the input interface (112) being configured to detect gradient change curve (g real (t) and amplifier (113) for gradient pulse (g) ref (t)) output signal (i out (t)), the gradient change curve (g) real (t) is detected by means of magnetic field measurement in the examination area (3) of the magnetic resonance device (2), the gradient change curve (g) real (t)) by emitting the gradient pulse (g) ref (t)) and formed in the inspection area (3), Its features are, It has • Calculation unit (18), the calculation unit (18) is configured to calculate based on the detected gradient change curve (g real (t)) and the detected output signal (i) of the amplifier (113) out (t)) Determine the gradient system transfer function (GSTF, GIRF) and the output signal (i) of the amplifier (113). out (t)), The correction device (110) is configured to, based on the determined output signal (i) of the amplifier (113), cor (t)) and the detected output signal (i) of the amplifier (113) out (t)) to adjust the input signal (i) of the amplifier (113). in (t)).

13. A magnetic resonance system (1), the magnetic resonance system (1) comprising a basic field magnet system (4), a radio frequency transmitting antenna (5), a gradient system (9), a radio frequency receiving antenna (7), and a calibration device (110) according to claim 12, and a control unit (13) for manipulating the basic field magnet system (4), the radio frequency transmitting antenna (5), the gradient system (9), and the radio frequency receiving antenna (7), wherein the magnetic resonance system (1) is configured to adjust the input signal (i) of the amplifier (113) by means of the calibration device (110) during magnetic resonance measurement of an object under examination. in (t)), in order to provide the desired gradient change curve (g) nom (t)).

14. A computer program product comprising: a computer program capable of being directly loaded into a storage unit (19) of a control unit (13) of a magnetic resonance system (1) according to claim 13; and a program segment for performing all steps of the method according to any one of claims 1 to 11 when the computer program is executed by means of the control unit (13) of the magnetic resonance system (1).

15. A computer-readable medium having stored on it a program segment that can be read and executed by a computing unit (18) so as to perform all steps of the method according to any one of claims 1 to 11 when the computing unit (18) executes the computer segment.

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