Reconstruction of image data from measurement data of an object under investigation acquired using a magnetic resonance system.

Abstract

An inventive method for reconstructing image data from measurement data of an object under investigation acquired using a magnetic resonance system comprises the following steps: - Selecting a desired image area in which measurement data of the object under investigation are to be measured, - Loading a measurement protocol to be used for acquiring the measurement data, which includes gradients to be switched and RF pulses to be irradiated as well as a desired resolution, which trigger echo signals that are received for acquiring the measurement data, - Acquiring a set of measurement data oversampled in at least one direction according to an oversampling factor, which comprises measurement data to be acquired for the desired image area according to Nyquist and additional measurement data resulting from the oversampling, - Determining a portion of the additional measurement data, - Forming a reduced set of oversampled measurement data.which includes the measurement data to be acquired according to Nyquist for the desired image area and the portion of the additional measurement data; - providing a processing matrix whose matrix size is designed for the reduced set of oversampled measurement data; - reconstructing result image data based on acquired measurement data using the processing matrix. By using a processing matrix according to the invention for processing acquired measurement data, artifacts in the reconstructed image data can be avoided. Image data with increased image quality is thus obtained, while keeping computational effort low.

Description

[0001] The invention relates to a reconstruction of image data from measurement data of an object under investigation recorded by means of a magnetic resonance system, in which so-called ringing artifacts are avoided in particular.

[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] Often, k-space is scanned line by line along k-space rows running in the readout direction on a Cartesian grid, thus filling a corresponding k-space matrix line by line with values, whereby, for example, a k-space row is scanned after an excitation. If the captured field of view (FOV), which can be selected as a desired image area, has insufficient coverage, various artifacts, such as inversion artifacts, can occur.

[0004] In position encoding using gradient fields, the gradient fields used are ideally linear, so that when a gradient is applied in a specific spatial direction, a linear relationship is generated between the position in that direction and the local resonance frequency of the spins under investigation. In practice, however, the gradient field generated by a gradient coil is not perfect. The main magnetic field B0, which is superimposed on the gradient fields, can also exhibit non-linearities. These imperfections can lead to so-called image distortions, meaning that the imaged object appears compressed, stretched, and "bent" in the directly reconstructed image.

[0005] Since the imperfections of the gradient coils and the main magnetic field are known or can be measured, the distortions in the images can be corrected. Algorithms can be used for this purpose, either operating within a two-dimensional image or in three spatial directions. After such distortion correction, the object's representation is largely accurate again. An example of such a method is described in the article by Doran et al., "A complete distortion correction for MR images: I. Gradient warp correction.", Phys Med Biol 2005; 50: pp. 1343-1361.

[0006] However, a side effect of such methods is that, due to the "re-bending" of the image, no measurement data is available for the peripheral areas in the corrected image. This is because, due to imperfections in the gradient coils and possibly the main magnetic field B0, these areas should have been measured outside the original, uncorrected image area (field of view; FOV). These areas are typically displayed as black, meaning they provide no information. Since the originally planned image area was not fully captured due to the aforementioned imperfections, important information may be missing in the peripheral regions. Furthermore, such black areas at the edges of reconstructed images, also known as cropping artifacts, are visually unappealing.

[0007] Besides directory correction algorithms that can generate cropping artifacts, other algorithms used to reconstruct image data from magnetic resonance imaging (MRI) measurements are also susceptible to high image intensities or strong contrast changes in a specific image area (FOV), particularly at the edge of the field of view (FOV), from which the measurement data is acquired and from which the image data is generated. For example, algorithms that rely on a Fourier transform can produce ringing artifacts due to a sharp transition from high intensity to zero (no intensity).

[0008] To counteract cropping and / or infolding artifacts, k-space can be oversampled, meaning that measurement data is acquired at more k-space positions than would be required for imaging according to Nyquist's theorem. This approach is also known as oversampling. Here, the sampled field of view in the image space, in the direction where oversampling is applied, is increased by the oversampling factor, which also indicates the increase in the number of acquired measurement data points, compared to a field of view without oversampling (which a user has specified as the desired image area). Thus, more k-space positions are sampled in the encoding direction affected by oversampling.

[0009] In the phase encoding direction, more k-space lines have to be sampled when scanning the k-space line by line, which significantly increases the overall required measurement time, as it increases by a repetition time TR for each additional phase encoding to be sampled.

[0010] Later, the resulting image is cropped to the desired image area containing the object under investigation. After this cropping, the oversampled measurement data is no longer available, for example, for further reconstruction steps.

[0011] In the readout direction, oversampling, also called readout oversampling, often occurs automatically by a sampling factor of 2. Unlike oversampling in a phase-encoding direction, readout oversampling does not double the total measurement time required, as only the readout process—the period in which measurement data is acquired after excitation—needs to be extended. This extension of the readout process accounts for only a small fraction of the time in most sequences compared to the additional TR periods required for oversampling in the phase-encoding direction. However, the number of measured data points increases by the selected sampling factor, which also increases the size of any matrix used in processing the measurement data by the same sampling factor in the direction in which the oversampling is performed.

[0012] Increasing the matrix size by an oversampling factor generally also increases the computation time required for processing the measurement data by the same factor. Since, for example, doubling the matrix size also doubles the reconstruction time, the additional measurement data acquired through oversampling is discarded as soon as possible to avoid excessively increasing the computation time. The removal of measurement data acquired through readout oversampling typically occurs after the first Fourier transform in the readout direction, and thus very early in the reconstruction chain. This prevents subsequent reconstruction steps from using information outside the desired image area.

[0013] The invention is based on the objective of enabling improved reconstruction of image data from measurement data of an object of investigation acquired by means of a magnetic resonance system with increased image quality, in which artifacts, in particular so-called ringing artifacts, are avoided, and the computing time required for the reconstruction is kept as low as possible.

[0014] The problem is solved by a method for reconstructing image data from measurement data of an object of investigation recorded by means of a magnetic resonance system according to claim 1, a magnetic resonance system according to claim 11, a computer program according to claim 12, and an electronically readable data carrier according to claim 13.

[0015] An inventive method for reconstructing image data from measurement data of an object under investigation recorded by means of a magnetic resonance system comprises the following steps: - Selecting a desired image area in which measurement data of the object under investigation should be measured, - Loading a measurement protocol to be used for recording the measurement data, which includes gradients to be switched and RF pulses to be irradiated as well as a desired resolution, which trigger echo signals that are received to record the measurement data, - Acquiring a set of measurement data oversampled in at least one direction according to an oversampling factor, which according to Nyquist includes measurement data to be acquired for the desired image area and additional measurement data due to the oversampling, - Determining some of the additional measurement data, - Forming a reduced set of oversampled measurement data, which includes the measurement data to be acquired according to Nyquist for the desired image area and the portion of the additional measurement data, - Providing a processing matrix whose matrix size is designed for the reduced set of oversampled measurement data, - Reconstructing result image data based on recorded measurement data using the processing matrix.

[0016] By using a processing matrix according to the invention for processing recorded measurement data, the matrix size of which is larger than that of a matrix for measurement data recorded according to Nyquist, artifacts, in particular ringing artifacts, in the reconstructed image data can be avoided or at least reduced. This results in image data with improved image quality, while the increased effort, particularly in terms of time, due to the larger matrix size of the processing matrix used is kept low compared to processing all oversampled measurement data.

[0017] 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 a proportion determination unit.

[0018] 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.

[0019] 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 a computing system of the control device.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] Further advantages and details of the present invention will become apparent from the exemplary embodiments described below and from the drawings. The examples listed do not constitute a limitation of the invention. They show: Fig. 1 a schematic flowchart of a method according to the invention for reconstructing image data from measurement data of an object under investigation recorded by means of a magnetic resonance system, Fig. 2 a schematic representation of possible image areas for a method according to the invention, Fig. 3 a schematically illustrated magnetic resonance system according to the invention.

[0024] Fig. Figure 1 is a schematic flowchart of a method according to the invention for reconstructing image data from measurement data of an object under investigation recorded by means of a magnetic resonance system.

[0025] A desired field of view (FOV) is selected within which measurement data (MD) of the object under investigation (U) are to be recorded (Block 101). This can be done in a familiar way, e.g., by displaying a planning image in which a user can select the desired field of view.

[0026] A measurement protocol MP to be used for recording the measurement data MD is loaded, which includes gradients to be switched and RF pulses to be irradiated as well as a desired resolution, which trigger echo signals that are received to record the measurement data MD, (Block 103).

[0027] A set of oMDS of measurement data oversampled in at least one direction according to an oversampling factor OS is recorded, which includes measurement data MD to be recorded according to Nyquist for the desired image area and additional measurement data oMD due to the oversampling (Block 105).

[0028] Oversampling can be performed in the readout direction and / or in the phase-encoding direction in a known manner. The oversampling factor (OS) can be automatically preset, e.g., depending on the loaded measurement protocol (MP), or selected by a user.

[0029] Fig. Figure 2 schematically shows possible image areas for a method according to the invention. A desired image area FOV has been selected. In the example shown, the desired image area FOV does not completely cover the object U under investigation in the direction R. Due to oversampling in at least one direction R, an image area gFOV, larger than the desired image area FOV, is scanned in at least one direction R. The image area gFOV shown, enlarged by oversampling in direction R, has a greater extent in direction R compared to the desired image area FOV, according to the oversampling factor used. The enlarged image area gFOV, scanned when acquiring the set oMDS of oversampled measurement data MD, oMD, is extended symmetrically by the desired image area FOV in the direction R.

[0030] Part A of the additional measurement data oMD is determined and a reduced set MDS of oversampled measurement data is formed, comprising the measurement data MD to be acquired according to Nyquist for the desired image area and Part A of the additional measurement data oMD, in particular consisting of the measurement data MD to be acquired according to Nyquist for the desired image area FOV and Part A of the additional measurement data oMD, (Block 107).

[0031] Part A of the additional measurement data oMD, which is only recorded because of the oversampling performed during the recording of the set oMDS of measurement data, is larger than an empty set and smaller than a complete set of all additional measurement data oMD recorded only because of the oversampling performed during the recording of the set oMDS of measurement data.

[0032] Part A of the additional measurement data oMD should be taken into account when further processing recorded measurement data into result image data BD.

[0033] Determining the proportion A of the additional measurement data oMD can involve reducing the enlarged image area gFOV to a reduced image area vFOV, where the reduced image area vFOV remains larger than the desired image area FOV, and the proportion A correlates with the reduction of the enlarged image area gFOV achieved by this reduction. In particular, the reduction can correspond to the value obtained by dividing the difference between the number of additional measurement data points oMD and the number of additional measurement data points oMD reduced according to the proportion A (dividend), with the number of additional measurement data points oMD (divisor). A reduction factor can thus be calculated, for example, as the difference between one and the proportion factor, where the proportion factor is the factor obtained by dividing the proportion A of the additional measurement data oMD by the total number of additional measurement data points oMD.

[0034] The reduction of the enlarged image area gFOV to the reduced image area vFOV can be performed by a predetermined number of pixels in at least one direction or by a predetermined percentage of pixels in at least one direction. The predetermined number of pixels or the predetermined percentage can be specified based on empirical values ​​and / or taking into account a maximum permissible or desired computation time for the reconstruction and the available computing power.

[0035] The reduction of the enlarged image area gFOV to the reduced image area vFOV can also be performed depending on a spatial extent D of the object under investigation U in at least one direction and the desired image area FOV. For example, the reduction of the enlarged image area gFOV to the reduced image area vFOV can be achieved such that the reduced image area vFOV covers the specific spatial extent D of the object under investigation U in the direction R, particularly more than completely. This reduction of the enlarged image area gFOV to the reduced image area vFOV can involve comparing the extent of the desired image area FOV in at least one direction R with the spatial extent D of the object under investigation U in at least one direction R.

[0036] In particular, ringing artifacts can be effectively reduced, because abrupt fluctuations in signal intensity in the edge area of ​​the reduced image area vFOV, which is sampled by the measurement data MD included in the processing matrix M and the component A of the additional measurement data oMD, are reduced or even eliminated in at least one direction R by the greater extent of the reduced image area vFOV compared to the desired image area FOV in at least one direction R.

[0037] The spatial extent D of the object under investigation U can be determined based on a preliminary measurement (also called "prescan") which is carried out in advance in a large number of MR measurements anyway, from which image data, for example a planning image, of the object under investigation were or can be generated.

[0038] The spatial extent D of the object under investigation U can also be determined from the recorded measurement data MD, oMD of the set of recorded measurement data. For this purpose, a Fourier transform can be performed, for example, in at least one direction R, to convert the recorded measurement data MD, oMD in this direction into the image space.

[0039] In image data generated from a preliminary measurement or also in image data generated from the recorded measurement data MD, oMD at least in one direction, the extent D can be determined, for example, using a segmentation method such as a region-growing method.

[0040] The subject of investigation U can be a patient. In this case, reducing the enlarged image area gFOV to the reduced image area vFOV can involve comparing known information about the patient's size and weight with a standard size and weight of the subject. The reduction can then be performed, for example, such that the extent of the reduced image area vFOV in at least one direction R has a ratio as similar as possible to the extent of the desired image area FOV in at least one direction R, just as the known information about the patient's size and weight relates to the standard values ​​of size and weight of a subject. This ensures that even without image information, the reduced image area vFOV covers an extent D of the subject U in the direction R, estimated from the information about size and weight.

[0041] To employ a known distortion correction method, non-linearity data V describing the non-linearity of a gradient unit 5 of the magnetic resonance system 1 can be loaded, and distortion information KD in at least one direction R can be determined (Block 113). This represents the distortion by which an image reconstructed from Nyquist-acquired measurement data MD and, if applicable, from additional measurement data oMD would be distorted without correction due to the non-linearity. If such a distortion correction method is employed, the determination of part A of the additional measurement data oMD can be carried out taking into account the determined distortion information KD. For example,It must be ensured that the reduced image area vFOV covered by the recorded measurement data MD and the component A of the additional measurement data oMD, even after distortion correction using the distortion correction method, covers an extent D of the object under investigation in at least one direction R. Thus, the reduction of the enlarged image area gFOV to the reduced image area vFOV can be performed taking into account the specific distortion information KD.

[0042] A processing matrix M is provided, the matrix size of which is designed for the reduced set MDS of oversampled measurement data (Block 109).

[0043] Result image data BD are reconstructed based on acquired measurement data, at least the measurement data MD acquired according to Nyquist, or also the proportion of additional measurement data oMD, using the processing matrix M (Block 111). The reconstruction of the result image data BD can include various known correction methods, e.g., for distortion correction and / or for the reduction of other artifacts, and / or, if the measurement protocol MP used includes slice multiplexing (SMS, short for "simultaneous multi-slice"), so that measurement data MD and additional measurement data oMD are acquired simultaneously from at least two slices, a slice separation method, such as sliceGRAPPA as described in the article by Setsompop et al. "Blipped-controlled aliasing in parallel imaging for simultaneous multislice echo planar imaging with reduced g-factor penalty", MAgn. Reson. Med., 67, pp. 1210-1224, 2012, which already include image data and / or hybrid spatial data, e.g.are determined only in one direction into the local space and are present in at least one other direction in the k-space, before finally the result image data BD are calculated using the processing matrix M, which are stored as a result of the carried out recording of measurement data MD and additional measurement data oMD and may be displayed to a user.

[0044] By using a processing matrix M to process recorded measurement data MD, oMD, with a larger matrix size compared to a matrix for measurement data recorded according to Nyquist, artifacts in the reconstructed image data can be avoided or at least reduced. In particular, ringing artifacts can be effectively reduced because abrupt fluctuations in signal intensity at the edge of the reduced image area vFOV, which is sampled by the measurement data MD contained in the processing matrix M and the portion A of the additional measurement data oMD, are reduced or even eliminated in at least one direction R by the larger extent of the reduced image area vFOV compared to the desired image area FOV in at least one direction R.

[0045] The processing matrix M can be filled with the acquired measurement data MD and the component A of the additional measurement data oMD when reconstructing the resulting image data BD. In this way, more than just the measurement data MD required according to Nyquist are used for the reconstruction. The resulting larger data set allows for improved image quality, in particular a better signal-to-noise ratio (SNR), and reduces artifacts such as ringing artifacts. The resulting increase in computational effort remains within acceptable limits (corresponding to the specific component A).

[0046] It is also conceivable to fill the processing matrix M with zeros during reconstruction using the acquired measurement data MD and, instead of the additional measurement data, with the component A of the additional measurement data oMD. Such a procedure, also called "zero-filling," does not, as with the known discarding of all acquired additional measurement data oMD, access the measurement data oMD acquired through oversampling; nevertheless, ringing artifacts are reduced in this case as well, because the processing matrix M used is further enlarged by the component A of the additional measurement data oMD compared to a conventional matrix that only includes the measurement data MD acquired according to Nyquist.

[0047] Fig. Figure 3 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.

[0048] In the Fig.Figure 3 shows only a rough schematic representation of these subunits of the magnetic resonance system 1. 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 two or more antenna elements. Furthermore, the high-frequency unit 7 can comprise one or more different local coils 7.1 and 7.2, 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.

[0049] 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 system 1 within its measuring volume. The layer S irepresents an exemplary target volume of the object under investigation, in which a desired image area can be selected, and from which echo signals can be recorded and captured as measurement data.

[0050] 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.

[0051] 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'.

[0052] Furthermore, the control unit 9 comprises a proportion determination unit 15 for determining a proportion according to the invention of measurement data additionally acquired by oversampling for the reconstruction of image data. The control unit 9 is configured overall to carry out a method according to the invention.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] Regardless of the grammatical gender of a particular term, persons with male, female or other gender identities are included. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited non-patent literature

[0000] Doran et al., “A complete distortion correction for MR images: I. Gradient warp correction.”, Phys Med Biol 2005; 50: pp. 1343-1361

[0005] Setsompop et al. “Blipped-controlled aliasing in parallel imaging for simultaneous multislice echo planar imaging with reduced g-factor penalty,” MAgn. resonance. Med., 67, pp. 1210-1224, 2012

[0043]

Claims

[1] Method for reconstructing image data from measurement data of an object of investigation acquired using a magnetic resonance system, comprising the steps: - Selecting a desired field of view (FOV) in which measurement data of the object under investigation (U) are to be measured, - Loading a measurement protocol (MP) to be used for recording the measurement data (MD), which includes gradients to be switched and RF pulses to be irradiated as well as a desired resolution, which trigger echo signals that are received for recording the measurement data (MD), - Acquiring a set (oMDS) of measurement data oversampled in at least one direction according to an oversampling factor (OS), which according to Nyquist includes measurement data (MD) to be acquired for the desired image area and additional measurement data (oMD) through oversampling, - Determining a part (A) of the additional measurement data (oMD), - Forming a reduced set of oversampled measurement data (MDS) comprising the measurement data (MD) to be acquired according to Nyquist for the desired image area and the part (A) of the additional measurement data (oMD), - Providing a processing matrix (M) whose matrix size is designed for the reduced set of oversampled measurement data, - Reconstructing result image data (BD) based on recorded measurement data (MD, oMD) using the processing matrix. [2] Method according to claim 1, wherein the processing matrix (M) is filled with the recorded measurement data (MD) and the proportion (A) of the additional measurement data (oMD) during the reconstruction. [3] Method according to claim 1, wherein the processing matrix (M) is filled with zeros when reconstructing with the recorded measurement data (MD) and instead of the additional measurement data of the proportion (A) of the additional measurement data (oMD). [4] Method according to one of the preceding claims, wherein oversampling involves sampling an image area (gFOV) that is enlarged compared to the desired image area (FOV), and determining the proportion (A) of the additional measurement data (oMD) comprises reducing the enlarged image area (gFOV) to a reduced image area (vFOV), wherein the reduced image area (vFOV) is still larger than the desired image area (FOV), and the proportion (A) correlates with a reduction of the enlarged image area (gFOV) achieved by reducing. [5] Method according to claim 4, wherein the reduction of the enlarged image area (gFOV) is carried out by a predetermined number of pixels in the at least one direction (R) or by a predetermined percentage of pixels in the at least one direction (R). [6] Method according to claim 4, wherein the reduction of the enlarged image area (gFOV) is carried out depending on a spatial extent (D) of the object under investigation (U) in at least one direction (R) and the desired image area (FOV). [7] Method according to claim 6, wherein the spatial extent (D) of the object under investigation (U) is determined by means of a preliminary measurement. [8] Method according to claim 6, wherein the spatial extent (D) of the object under investigation (U) is determined on the basis of measurement data recorded from the set of measurement data (oMDS). [9] Method according to claim 4, wherein the subject of investigation (U) is a patient and reducing the magnified field of view (gFOV) comprises comparing known information about the size and weight of the patient with a standard size and weight of a subject of investigation. [10] Method according to one of the preceding claims, wherein non-linearity data (V) describing a non-linearity of a gradient unit (5) of the magnetic resonance system (1) are loaded, and distortion information (KD) is determined in the at least one direction (R) in which an image reconstructed from recorded measurement data (MD, oMD) is distorted without correction due to the non-linearity, and wherein the determination of the part (A) of the additional measurement data (oMD) is carried out taking into account the determined distortion information (KD). [11] 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 a proportion determination unit (15), wherein the control unit (9) is configured to perform a method according to any one of claims 1 to 10 on the magnetic resonance system (1). [12] 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 10. [13] 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 10.

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