MAGNETIC RESONANCE FINGERPRINTING PROCEDURE FOR IMAGES WITH CONTRAST AGENT

Description

[0001] The present invention relates to the technical field of magnetic resonance imaging. The present invention relates to a method, a system, and a computer program product for determining different states of a contrast agent in different tissue types in a magnetic resonance fingerprinting method.

[0002] Magnetic resonance imaging, abbreviated MRI or MR (English: Magnetic Resonance Imaging ) is an imaging technique that is used primarily in medical diagnostics to depict the structure and function of tissues and organs in the human or animal body.

[0003] In MR imaging, the magnetic moments of protons in a subject are aligned in a basic magnetic field, resulting in a macroscopic magnetization along a longitudinal direction. This magnetization is then deflected from its resting position by applying radiofrequency (RF) pulses (excitation). The return of the excited states to their resting position (relaxation), or the magnetization dynamics, is subsequently detected as relaxation signals using one or more RF receiver coils.

[0004] For spatial encoding, rapidly switched magnetic gradient fields are superimposed on the basic magnetic field. The acquired relaxation signals, or the detected and spatially resolved MR data, are initially available as raw data in spatial frequency domain and can be transformed into spatial domain (image space) by subsequent Fourier transformation.

[0005] In native MRI, the tissue contrasts are generated by the different relaxation times (T1 and T2) and the proton density.

[0006] T1 relaxation describes the transition of the longitudinal magnetization to its equilibrium state, where T1 is the time required to reach 63.21% of the equilibrium magnetization before resonance excitation. It is also called the longitudinal relaxation time or spin-lattice relaxation time.

[0007] The T2 relaxation describes in an analogous way the transition of the transverse magnetization to its equilibrium state.

[0008] MRI contrast agents exert their effect by altering the relaxation times of the structures that absorb the contrast agent. Two groups of substances can be distinguished: paramagnetic and superparamagnetic. Both groups of substances contain unpaired electrons that induce a magnetic field around the individual atoms or molecules.

[0009] Superparamagnetic contrast agents lead to predominantly T2 shortening, while paramagnetic contrast agents essentially lead to T1 shortening.

[0010] The effect of these contrast agents is indirect, since the contrast agent itself does not emit a signal, but only influences the signal intensity in its surroundings.

[0011] An example of a superparamagnetic contrast agent is iron oxide nanoparticles (SPIO, superparamagnetic iron oxide ).

[0012] Examples of paramagnetic contrast agents are gadolinium chelates such as gadopentetate dimeglumine (trade name: Magnevist ®< among others), gadoteric acid (Dotarem ®< , Dotagita ®< , Cyclolux ®< ), gadodiamide (Omniscan ®< ), gadoteridol (ProHance ®< ) and gadobutrol (Gadovist ®< ).

[0013] Contrast agents based on gadoxetic acid are characterized by their specific absorption by liver cells, the hepatocytes, their accumulation in the functional tissue (parenchyma), and their contrast enhancement in healthy liver tissue. The cells of cysts, metastases, and most hepatocellular carcinomas no longer function like normal liver cells, do not absorb the contrast agent or absorb it only minimally, are not enhanced, and are therefore recognizable and localizable. Examples of contrast agents based on gadoxetic acid are described in US Pat. No. 6,039,931A; they are commercially available, for example, under the brand names Primovist® or Eovist®.

[0014] The contrast-enhancing effect of Primovist ® / Eovist ® is mediated by the stable gadolinium complex Gd-EOB-DTPA (gadolinium-ethoxybenzyl-diethylenetriamine-pentaacetic acid). DTPA forms a complex with the paramagnetic gadolinium ion that exhibits extremely high thermodynamic stability. The ethoxybenzyl moiety (EOB) mediates hepatobiliary uptake of the contrast agent. Hepatocellular uptake is mediated by an organic anion transport system, which is also involved in the uptake of bilirubin into the liver cell (O. Clément et al., Gadolinium-ethoxybenzyl-DTPA, a new liver-specific magnetic resonance contrast agent. Kinetic and enhancement patterns in normal and cholestatic rats; Invest Radiol (1992); 27: 612-619).

[0015] AD Karaosmanoglu et al. disclose an MRI method for the detection of liver metastases using Gd-EOB-DTPA as a contrast agent (Magnetic Resonance Imaging of Liver Metastasis, Semin Ultrasound CT MR, 2016, 37(6): 533-548).

[0016] E. Unal et al. disclose an MRI procedure for assessing liver function using Gd-EOB-DTPA as a contrast agent (Multiparametry or practical quantitative liver MRI: towards millisecond, fat fraction, kilopascal and function era, Expert Review of Gastroenterology & Hepatology, 2017, 11(2), 167-182).

[0017] Magnetic resonance fingerprinting techniques allow for more detailed images of a subject to be acquired in a shorter time. Magnetic resonance fingerprinting techniques are described, for example, in Ma et al., "Magnetic Resonance Fingerprinting," Nature, 495: 187-192 (2013); Jiang et al., "MR Fingerprinting Using Fast Imaging with Steady State Precession (FISP) with Spiral Readout," Magnetic Resonance in Medicine 74: 1621-1631 (2015); and Cloos et al., "Online Radial Multiband Magnetic Resonance Fingerprinting," ISMRM 2016: 608.

[0018] BB Mehta et al.: provide a technical insight into magnetic resonance fingerprinting in a review article (Magnetic resonance fingerprinting: a technical review, Magnetic Resonance in Medicine, 2019, 81(1): 25-46).

[0019] Magnetic resonance fingerprinting is a quantitative measurement technique in which several magnetic resonance images of an examination subject are initially generated using varying acquisition parameters. The acquisition parameters are typically varied in a pseudorandomized manner. A location-dependent magnetic resonance signal waveform is then generated for the individual pixels (voxels) of the magnetic resonance images. The determined signal waveform is then compared for each voxel with several signal waveforms stored in a database, with each signal waveform in the database being assigned a specific value for at least one tissue parameter. The database signal waveforms represent expected signal waveforms and are determined and / or calculated in advance.A volume element of a sample in which the value of at least one tissue parameter corresponds to the specific database value should display the signal curve stored in the database in a magnetic resonance measurement. Thus, if a matching signal curve is identified, the corresponding value of at least one tissue parameter can be read from the database.

[0020] In this way, the spatial distribution of tissue-specific parameters (such as transverse relaxation T2 or longitudinal relaxation T1; so-called T1 and T2 maps) in the imaged object can be quantitatively determined from MR measurement data. One advantage of the magnetic resonance fingerprinting method is that several tissue parameters can be acquired simultaneously in a single measurement.

[0021] JD Kaggie et al. disclose a magnetic resonance fingerprinting procedure in patients suffering from knee osteoarthritis (T1 and T2 Mapping of Delayed Gadolinium Enhancement in Osteoarthritis with MR Fingerprinting, Proceedings of the International Society for Magnetic Resonance Medicine, 20th Annual Meeting and Exhibition, Melbourne, Australia, 5-11, No. 1435, June 1, 2018).

[0022] WO2018 / 187760A1 discloses a dynamic multi-contrast magnetic resonance fingerprinting method. The method comprises: a) introducing two or more contrast agents into an examination region of a subject, wherein the two or more contrast agents have different relaxivities; b) measuring a T1 relaxation time and a T2 relaxation time for locations within the examination region using magnetic resonance fingerprinting; c) determining, using equations relating the different relaxivities, the T1 relaxation time, the T2 relaxation time, and the concentrations of the two or more contrast agents, the concentrations of the two or more contrast agents for each of the locations within the examination region; and d) generating an image representing the examination region based at least in part on the concentrations of the two or more contrast agents.

[0023] CE Anderson et al. report on the simultaneous measurement of tissue parameters from two simultaneously administered contrast agents (Dual Contrast - Magnetic Resonance Fingerprinting (DCMRF): A Platform for Simultaneous Quantification of Multiple MRI Contrast Agents; Scientific Reports 7; 8431: 1-10; DOI: 10.1038 / s41598-017-08762-9). This method takes advantage of the fact that the contrast agents used differ in their relaxivities and can therefore be differentiated.

[0024] When a contrast agent is administered, it is distributed throughout the body. A measured relaxation change is caused by the contrast agent, which can be present in various tissue areas. The signals can originate from different tissue types (e.g., functional tissue (parenchyma), interstitial tissue (interstitium), and / or tissue fluid (e.g., blood, lymph, bile).

[0025] We are looking for a solution that allows different tissue types present in a volume element to be differentiated in a single measurement using only one contrast agent.

[0026] This object is achieved by the subject matter of the independent patent claims. Preferred embodiments can be found in the dependent patent claims as well as in the present description and the figures.

[0027] A first object of the present invention is a method comprising the following steps: Providing a magnetic resonance fingerprint database, wherein the magnetic resonance fingerprint database comprises database signal curves for a specific contrast agent in at least two different tissue types, a first tissue type and a second tissue type, wherein the contrast agent comprises gadoxetic acid or a salt of gadoxetic acid as a contrast-enhancing agent, wherein the first tissue type is hepatocytes, wherein the contrast agent has a different state in the first tissue type than in the second tissue type, wherein the state is the molar T1 relaxivity and / or T2 relaxivity, Acquiring a magnetic resonance signal curve for a volume element of an examination region by means of a magnetic resonance fingerprinting method using the contrast agent, wherein the volume element comprises the first tissue type and the second tissue type,wherein the examination region is the liver or a part of the liver of an examination subject, receiving database signal waveforms from the magnetic resonance fingerprint database, each database signal waveform being assigned a T1 relaxation time and a T2 relaxation time in both tissue types as database values, comparing the magnetic resonance signal waveform with database signal waveforms, identifying a database signal waveform with a defined match to the magnetic resonance signal waveform, determining corresponding database values ​​of the T1 and T2 relaxation times in both tissue types in the volume element based on the identified database signal waveform. Calculating the concentration of the contrast agent in the first tissue type and the concentration of the contrast agent in the second tissue type for the volume element from the determined T1 and T2 relaxation times,Output of the determined T1 and T2 relaxation times and / or the calculated concentrations of the contrast agent in the first tissue type and in the second tissue type for the volume element.

[0028] A further object of the present invention is a corresponding system according to claim 7.

[0029] A further subject of the present invention is a corresponding computer program product according to claim 8.

[0030] The invention is explained in more detail below, without distinguishing between the subject matter of the invention (method, system, computer program product). Rather, the following explanations are intended to apply analogously to all subject matter of the invention, regardless of the context (method, system, computer program product) in which they occur.

[0031] If steps are mentioned in a particular order in this description, this does not necessarily mean that the invention is limited to that order. Rather, it is conceivable that the steps may be performed in a different order or even in parallel; unless a step builds on another step, which absolutely requires that the subsequent step be performed (which will become clear in individual cases). The specified sequences thus represent preferred embodiments of the invention, and the scope of the invention is defined by the claims.

[0032] The present invention uses a magnetic resonance fingerprinting method to simultaneously detect different states of a contrast agent in different tissue types in one measurement.

[0033] A tissue type is defined as a collection of differentiated cells, including their extracellular matrix. Examples of tissue types include epithelial tissue, connective and supporting tissue (bone tissue, cartilage tissue, fatty tissue), muscle tissue, nerve tissue, and liver tissue. Tissue fluids or liquid tissues (e.g., blood, lymph, bile) are also considered tissue types. Furthermore, diseased and healthy tissue can represent two distinct tissue types.

[0034] A contrast agent is a substance or mixture of substances whose presence leads to a modified signal in a magnetic resonance imaging scan. The contrast agent preferably leads to a shortening of the T1 and / or T2 interval.

[0035] The contrast agent is present in at least two tissue types in different states. This means that there is a first tissue type and a second tissue type. Contrast agent administered to an examination subject is distributed among the tissue types; administered contrast agent is therefore present in both the first and second tissue types. How the contrast agent is distributed among the tissue types can, in principle, be determined experimentally and specified, for example, by a distribution coefficient. Such a distribution coefficient can, for example, be the quotient of the concentration of the contrast agent in the first tissue type and the concentration of the contrast agent in the second tissue type. It is conceivable that the distribution coefficient itself is concentration-dependent, meaning that it can change with the concentration of the contrast agent in a tissue type.

[0036] The contrast agent has a different state in the first tissue type than in the second tissue type. A different state leads to an altered relaxation. A state can be characterized by at least one value of a tissue parameter. In one embodiment, the terms "different state" or "different (various) states" mean that the contrast agent has a different molar T1 relaxivity in the first tissue type than in the second tissue type. In another embodiment, the terms "different state" or "different (various) states" mean that the contrast agent has a different molar T2 relaxivity in the first tissue type than in the second tissue type.In a further embodiment, the terms "different state" or "different (various) states" mean that the contrast agent has both a different molar T1 relaxivity and a different molar T2 relaxivity in the first tissue type than in the second tissue type.

[0037] Molar relaxivity is a common measure of the efficacy, i.e., the relaxation-shortening effect, of a contrast agent. Its unit can be expressed as (s·mol / L) -1< (second x mol / liter) -1< .

[0038] Preferably, a molar relaxivity in the first tissue type is at least 1.5 times greater than in the second tissue type, particularly preferably it is at least 2 times greater, even more preferably it is at least 2.5 times greater. In a particularly preferred embodiment, the molar relaxivities in the two different tissue types differ by a factor of at least 1.5 (preferably at least 2, even more preferably at least 2.5) at a magnetic field strength of the basic magnetic field of at least 1.5 Tesla, preferably at least 2 Tesla, even more preferably at least 2.5 Tesla, even more preferably at least 3 Tesla, most preferably at a magnetic field strength of 0.4 Tesla to at least 3 Tesla.

[0039] The contrast agent is a substance or mixture of substances containing gadoxetic acid or a salt of gadoxetic acid as the contrast-enhancing agent. The disodium salt of gadoxetic acid (Gd-EOB-DTPA disodium) is particularly preferred. Gd-EOB-DTPA exhibits a significantly higher molar relaxivity in liver cells (hepatocytes) than, for example, in plasma, and a significantly higher molar relaxivity in plasma than in bile.

[0040] Table 1 shows molar relaxivities (in (s·mMol / L) -1< ) ​​of Gd-EOB-DTPA in different tissue types at different magnetic field strengths of the basic magnetic field. Table 1 0,47 T 1,41 T 1,5 T 3 T Water 5,3 (1)< 4,7 (1)< 4,3 (1)< bile 5,6 ± 0,3 5,6 ± 0,4 5,6 ± 0,3 urine 5,5 ± 0,1 5,5 ± 0,2 5,6 ± 0,1 plasma 8,7 (1)< 6,9 (1)< 6,2 (1)< blood 11,0 (2)< 8,1 ± 0,2 7,3 (1)< / 8,3 ± 0,3 7,2 ± 0,1 Liver tissue 16,6 (2)< 14,0 ± 2,8 16,4 ± 3,1 13,4 ± 4,0 (1): Rohrer et al. Radiol 2005; 40(11): 715-724 (2): Schuhmann-Giampieri et al. Radiol. 1992; 183:59-64

[0041] Surprisingly, the high molar relaxivity in liver tissue is maintained even at high (clinically relevant) magnetic field strengths.

[0042] The invention makes it possible to distinguish contrast agent located in the first tissue type from contrast agent located in the second tissue type, even if both tissue types are located in the same volume element, which is imaged as a voxel in magnetic resonance image data.

[0043] The object under examination is usually a living being, preferably a mammal, and most preferably a human. The examination area is a part of the object under examination, for example, an organ such as the liver or a part of an organ.

[0044] The examination area, also known as the recording volume (English: field of view, A field of view (FOV) represents a volume that is depicted in the acquired magnetic resonance image data. The examination area is typically defined by a user, for example, on an overview image (English: localizer). Of course, the examination area can alternatively or additionally be determined automatically, for example based on a selected protocol.

[0045] A contrast agent is administered to the subject, which is distributed throughout the examination area. The examination area is placed in a basic magnetic field. The examination area is subjected to a magnetic resonance fingerprinting procedure, and a magnetic resonance signal curve is determined for at least one volume element of the examination area (for details, see Fig. 2 and the corresponding description).

[0046] The magnetic resonance fingerprinting method typically involves acquiring a magnetic resonance signal waveform for a large number of voxels using a pseudorandomized or incoherent acquisition scheme. It is also conceivable for the magnetic resonance signal waveform to be acquired from a region with a coarser resolution than a single voxel. In this case, the magnetic resonance signal waveform can be acquired, for example, averaged over several voxels.

[0047] The magnetic resonance fingerprinting method specifically involves setting different acquisition parameters for the acquisition of the various magnetic resonance signals. These acquisition parameters can be varied in a pseudorandomized or incoherent manner. Possible acquisition parameters that can be changed during the acquisition of the magnetic resonance signal include, for example, an echo time, the pattern and / or number of radiofrequency pulses, the pattern and / or number of gradient pulses, diffusion coding, etc. In this way, the magnetic resonance fingerprinting method can be used to capture a magnetic resonance signal characteristic of the voxel, a so-called fingerprint of the voxel.

[0048] In a further step of the method according to the invention, the magnetic resonance signal waveforms are compared with signal waveforms stored in a magnetic resonance fingerprint database (database signal waveforms).

[0049] The database signal waveforms can, for example, be determined in a calibration measurement and / or simulated. Methods for generating database signal waveforms are described in the prior art (see, for example, J. Xie et al.: Fast dictionary generation and searching for magnetic resonance fingerprinting, Conf Proc IEEE Eng Med Biol Soc. 2017 Jul;2017:3256-3259. doi: 10.1109 / EMBC.2017.8037551).

[0050] The magnetic resonance fingerprinting method typically involves assigning a database signal waveform to the acquired magnetic resonance signal waveform based on the result of the signal comparison. The signal comparison may include determining the similarity of the acquired magnetic resonance signal waveform to the multiple database signal waveforms, with the database signal waveform that exhibits the greatest similarity to the magnetic resonance signal waveform being assigned to the magnetic resonance signal waveform.

[0051] It is also conceivable that a similarity threshold is set that must be reached in order to make an assignment.

[0052] Methods for comparison and identification of similarities are described in the state of the art (see, for example, SF Cauley et al., Fast group matching, for MR, fingerprinting reconstruction, Magnetic Resonance in Medicine 74:523-528 (2015)).

[0053] The different database signal curves are each assigned specific database values ​​of tissue parameters.

[0054] The database values ​​associated with the assigned database signal curve can then be set, for example, as measured values ​​of tissue parameters for the volume element under consideration. As a result of the signal comparison, the measured values ​​of the tissue parameters obtained using the magnetic resonance fingerprinting method can be output or saved for the corresponding voxel.

[0055] A selection of possible tissue parameters that can be quantified using the magnetic resonance fingerprinting method is: a T1 relaxation time, a T2 relaxation time, a diffusion value (e.g. an apparent diffusion coefficient, apparent diffusion coefficient,ADC), a magnetization moment, a proton density, a resonance frequency, a concentration of a substance, etc. Of course, other tissue parameters that appear useful to the expert are also conceivable.

[0056] According to the invention, the database values ​​or measured values ​​of the tissue parameters are related to the different states of the contrast agent used in the at least two different tissue types

[0057] According to the invention, the database values ​​include T1 and T2 relaxation times of both tissue types in the volume element.

[0058] If, according to the invention, two different tissue types are present in a volume element under consideration and a magnetic resonance signal curve is acquired for the volume element after administration of a contrast agent, the T1 relaxation time and the T2 relaxation time are determined simultaneously for both tissue types as associated database values ​​by identifying the associated database signal curve and the concentration of the contrast agent in the first tissue type and the concentration of the contrast agent in the second tissue type are calculated therefrom for the corresponding volume element.

[0059] The determined database values ​​and / or values ​​derived from the database values ​​can be saved and / or output. A derived value is typically a value resulting from a calculation of the database value. An example of a derived value is the concentration of the contrast agent in a tissue type.

[0060] An object of the present invention is a system with which the method according to the invention can be carried out.

[0061] The system comprises a receiving unit, a control unit, a signal comparison unit, and an output unit. It is conceivable that these units are components of a single computer system; however, it is also conceivable that these units are components of several separate computer systems that are interconnected via a network to transmit data and / or control signals from one unit to another.

[0062] A "computer system" is an electronic data processing system that processes data using programmable computing instructions. Such a system typically includes a "computer," the unit that includes a processor for performing logical operations, and peripherals.

[0063] In computer technology, "peripherals" refers to all devices that are connected to the computer and serve to control the computer and / or as input and output devices.

[0064] Examples include monitor (screen), printer, scanner, mouse, keyboard, drives, camera,

[0065] Microphone, speakers, etc. Internal connectors and expansion cards are also considered peripherals in computer technology.

[0066] Today's computer systems are often divided into desktop PCs, portable PCs, laptops, notebooks, netbooks and tablet PCs and so-called handhelds (e.g., smartphones); all of these systems can be used to implement the invention.

[0067] Inputs into the computer system are made via input devices such as a keyboard, mouse, microphone, and / or the like. Input also includes selecting an item from a virtual menu or list, clicking a checkbox, and the like.

[0068] The system according to the invention is configured to receive at least one magnetic resonance signal waveform and a plurality of database signal waveforms, to compare the at least one magnetic resonance signal waveform with the database signal waveforms, to identify, as a result of the comparison, a database signal waveform with a defined correspondence with the magnetic resonance signal waveform, to determine database values ​​in the form of the T1 and T2 relaxation times of both tissue types that are assigned to the identified database signal waveform, to calculate the concentration of the contrast agent in the first tissue type and the concentration of the contrast agent in the second tissue type for the volume element from the determined T1 and T2 relaxation times, and to store and / or output the determined database values ​​and / or the calculated concentrations.

[0069] The control unit serves to control the receiving unit, the signal comparison unit, and the output unit, as well as to coordinate the data and signal flows between different units. It is conceivable that multiple control units may be present.

[0070] The receiving unit serves to receive the at least one magnetic resonance signal waveform. The at least one magnetic resonance signal waveform can, for example, be transmitted from a magnetic resonance system or read from a data storage device. The magnetic resonance system can be a component of the system according to the invention. However, it is also conceivable that the system according to the invention is a component of a magnetic resonance system.

[0071] The receiving unit also serves to receive multiple database signal waveforms from a magnetic resonance fingerprinting database. The magnetic resonance fingerprinting database can be a component of the system according to the invention. A plurality of database signal waveforms are stored in the magnetic resonance fingerprinting database. Specific values ​​(database values) of tissue parameters are assigned to each database signal waveform, which, according to the invention, are T1 and T2 relaxation times of the two tissue types in the volume element. The database signal waveforms indicate the expected signal waveform of a sample that has corresponding values ​​of the tissue parameters. Some of the database signal waveforms indicate the expected signal waveforms of a sample in which at least two different tissue types are present in a volume element and an administered contrast agent has different states in the at least two tissue types.One state is characterized by a specific value (database value) of a first tissue parameter, the other state by a specific value (database value) of a second tissue parameter.

[0072] The receiving unit transmits at least one magnetic resonance signal waveform and the plurality of database signal waveforms to the signal comparison unit.

[0073] The signal comparison unit is configured to compare the at least one magnetic resonance signal waveform with various database signal waveforms in order to identify a database signal waveform that has a defined match with the magnetic resonance signal waveform.

[0074] Once the database signal curve has been identified, the database values ​​associated with the database signal curve are determined, which according to the invention are the corresponding T1 and T2 relaxation times of the two tissue types in the volume element.

[0075] The output unit is configured to store and / or output the determined database values. Storage typically occurs in a data storage device that is part of the system according to the invention or is connected to it via a network. Output typically occurs on a screen. It is conceivable that the output is in the form of a two- or three-dimensional image. It is conceivable that the image represents the examined region and that a color and / or a shade of gray is selected for individual volume elements based on one or more database values ​​determined for the volume element.

[0076] It is conceivable that derived values ​​could be calculated based on the determined database values. According to the invention, the control unit calculates the contrast agent concentrations in both tissue types in the volume element from the determined T1 and T2 relaxation times.

[0077] The invention is explained in more detail below with reference to figures, without wishing to limit the invention to the features or combinations of features shown in the figures.

[0078] They show: Figure 1 shows schematically a sequence of the method according to the invention in the form of a sequence of consecutive steps. The sequence comprises the steps Providing a magnetic resonance fingerprint database (10) Acquiring a magnetic resonance signal curve for a volume element of an examination region by means of a magnetic resonance fingerprinting method using a contrast agent (20) Comparing the magnetic resonance signal curve with database signal curves (30) Identifying a database signal curve with a defined match to the magnetic resonance signal curve (40) Determining the states of the contrast agent in the volume element (50) Outputting information on the states of the contrast agent in the volume element (60).

[0079] Figure 2 shows schematically a preferred embodiment for the acquisition of a magnetic resonance signal waveform by means of a magnetic resonance fingerprinting method (step 20 in Figure 1 ).

[0080] A pulse sequence is selected in the usual way, e.g. according to a desired contrast or other desired properties of the measurement data readable with the pulse sequence (21).

[0081] The pulse sequence is performed with a first set (i=1) of acquisition parameters P i , whereby measurement data are to be sampled along a first k-space trajectory T i (P, T) i . A k-space trajectory along which measurement data are measured in a repetition can sample k-space Cartesian, spiral, radial, or in a combination of the aforementioned sampling types, or along a freely conceived trajectory.

[0082] According to the pulse sequence, RF pulses are radiated into the examination area, gradients are switched, and the echo signals generated by the radiated RF pulses and the switched gradients are read out (22). After excitation with an RF excitation pulse, measurement data are acquired along the k-space trajectory T i and stored in a measurement data set MDS i.

[0083] An image data set BDS i is reconstructed from each measurement data set MDS i (25), whereby only a portion of the measurement data contained in the measurement data set MDS i can be used for the reconstruction. This results in one image data set BDS i per repetition i, i.e., a total of N image data sets BDS i . A query (23) queries whether all N desired repetitions have already been performed and the corresponding N measurement data sets MSD i have been saved. If this is not the case ("n"), a k-space trajectory is selected for the next repetition, and the parameters of the pulse sequence are adjusted accordingly and, if necessary, further varied (24). As a rule, a selected further k-space trajectory T i+1 will differ from a previous k-space trajectory T i.

[0084] Using the next parameter P i+1 thus obtained and the selected further k-space trajectory T i+1 ((P, T) i+1 ), the pulse sequence is repeated, and a new measurement (22) is thus performed, such that, in successive repetitions, measurement data are measured along the selected k-space trajectories T i , T i+1 . For the selection of trajectories, reference is made to the extensive literature on magnetic resonance fingerprinting methods; as an example, the published patent application DE102016217675A1 is mentioned, the content of which is incorporated in this description by reference.

[0085] If all N desired repetitions have already been performed and the corresponding N measurement data sets MSD i have been saved ("y"), no further measurement is performed ("stop"), and a voxel time series (x,y,z)(i) is created for at least one voxel (x,y,z) in the reconstructed image data sets BDS i , which represents a signal intensity of the voxel (x,y,z) over the course of the acquisition times (and thus over the course of the successively performed repetitions (i) of the measurement data sets MDS i ). Typically, such a voxel time series (x,y,z)(i) is performed for all voxels (x,y,z) that lie in the examination region of interest. The created voxel time series (x,y,z)(i) are saved.

[0086] Figure 3 shows schematically the relationship between measurement data sets MDS i and image data sets BDS i over time, ie over the course of i.

[0087] The top row shows the measurement data sets MDSi as they were acquired consecutively in the repetitions TRi, with the repetitions i = 1, i = 2, i = 3, i = 4 and i = N being explicitly shown as examples. The second row shows the image data sets BDSi reconstructed from the measurement data sets MDSi in the same way, with a voxel (x,y,z) marked in the image data sets BDSi as an example. For example, for this voxel (x,y,z), the respective intensity of the voxel (x,y,z) at the times Ti corresponding to the repetitions Ti can be plotted against time as a voxel time series. A voxel time series (x,y,z)(i) is a magnetic resonance signal curve for a volume element of the examination region.

[0088] Figure 4 shows schematically the comparison of magnetic resonance signal curves with database signal curves (step 30 in Figure 1 ).

[0089] Each stored voxel time series (x,y,z)(i) from Figure 2 is compared with several of the database waveforms VDS 1 to VDS j stored in a magnetic resonance fingerprinting database (DB) (30). The result of each comparison can be a similarity value R, which indicates how similar a voxel time series (x,y,z)(i) is to a database waveform.

[0090] Figure 5 shows schematically the identification of a database signal waveform with a defined match to the magnetic resonance signal waveform (step 40 in Figure 1 ).

[0091] Typically, each voxel time series (x,y,z)(i) is assigned a database signal curve VDS k , usually the database signal curve that has the greatest match with the voxel time series (x,y,z)(i) (maximum R value).

[0092] Figure 6shows schematically the determination of the states of the contrast agent for the volume element depicted in the respective voxel-time series (x,y,z)(i) (step 50 in Figure 1 ). The states of the contrast agent are characterized by specific values ​​of two tissue parameters GP1 and GP2. These values ​​(database values) result from the database signal curve VDS k identified in step 50. They are typically stored in the magnetic resonance fingerprinting database for the database signal curve VDS k and can be read out after VDS k has been identified.

[0093] Figure 7schematically shows an embodiment of the system according to the invention. The system comprises a receiving unit (1), a control unit (2), a signal comparison unit (3), and an output unit (4). These units are components of a computer system (CS). The receiving unit (1) is configured to receive magnetic resonance signal waveforms from a magnetic resonance system (MA) and database signal waveforms from a magnetic resonance fingerprinting database (DB). Reception can take place via a network (represented by dashed lines).

Claims

1. Method comprising the following steps: • providing a magnetic resonance fingerprint database (DB), - wherein the magnetic resonance fingerprint database (DB) comprises database waveforms (CDS1, ..., CDSj) for a specific contrast agent in at least two different tissue types, a first tissue type and a second tissue type, wherein the contrast agent comprises gadoxetic acid or a salt of gadoxetic acid as contrast-enhancing active substance, the first tissue type being hepatocytes, - wherein the contrast agent has a different state in the first tissue type than in the second tissue type, the state being the molar T1 relaxivity and / or T2 relaxivity, • acquiring a magnetic resonance waveform ((x,y,z)(i)) for a volume element of an examination region by means of a magnetic resonance fingerprinting method using the contrast agent, wherein the volume element includes the first tissue type and the second tissue type, wherein the examination region is the liver or part of the liver of an examination object, • receiving database waveforms (CDS1, ..., CDSj) from the magnetic resonance fingerprint database (DB), wherein each database waveform (CDS1, ..., CDSj) is matched to a T1 relaxation time and a T2 relaxation time in both tissue types as database values, • comparing the magnetic resonance waveform ((x,y,z)(i)) with database waveforms (CDS1, ..., CDSj), • identifying a database waveform (CDSk) having a defined correspondence with the magnetic resonance waveform ((x,y,z)(i)), • determining the associated database values for the T1 and T2 relaxation times in both tissue types in the volume element, based on the identified database waveform (CDSk), • calculating the concentration of the contrast agent in the first tissue type and the concentration of the contrast agent in the second tissue type for the volume element from the determined T1 and T2 relaxation times, • outputting the determined T1 and T2 relaxation times and / or the calculated concentrations of the contrast agent in the first tissue type and in the second tissue type for the volume element.

2. Method according to Claim 1, wherein a molar relaxivity in the first tissue type is at least 1.5 times greater, preferably at least 2 times greater, even more preferably at least 2.5 times greater, than in the second tissue type.

3. Method according to Claim 2, wherein a molar relaxivity at a magnetic field strength of the basic magnetic field of at least 1.5 tesla, preferably at least 2 tesla, even more preferably at least 2.5 tesla, even more preferably at least 3 tesla, most preferably at a magnetic field strength of 0.4 tesla to at least 3 tesla, is in the first tissue type at least 1.5 times greater, preferably at least 2 times greater, even more preferably at least 2.5 times greater, than in the second tissue type.

4. Method according to any of Claims 1 to 3, wherein the contrast agent has a higher molar T1 relaxivity in the first tissue type than in the second tissue type.

5. Method according to any of Claims 1 to 4, wherein the contrast agent comprises Gd-EOB-DTP disodium.

6. Method according to any of Claims 1 to 5, wherein the first tissue type is healthy liver tissue and the second tissue type is diseased liver tissue.

7. System comprising • a receiving unit (1), • a control unit (2), • a signal comparison unit (3) and • an output unit (4), - wherein the control unit (2) is configured to cause the receiving unit (1) to receive a magnetic resonance waveform ((x,y,z) (i)) for at least one volume element of an examination region, the magnetic resonance waveform ((x,y,z)(i)) having been generated in a magnetic resonance fingerprinting method using a contrast agent, wherein the contrast agent comprises gadoxetic acid or a salt of gadoxetic acid as contrast-enhancing active substance, wherein the examination region is the liver or part of the liver of an examination object, wherein the volume element comprises a first tissue type and a second tissue type, the first tissue type being hepatocytes, - wherein the control unit (2) is configured to cause the receiving unit (1) to receive a plurality of database waveforms (CDS1, ..., CDSj) from a magnetic resonance fingerprint database (DB), wherein each database waveform (CDS1, ..., CDSj) is matched to a T1 relaxation time and a T2 relaxation time in both tissue types as database values, - wherein the control unit (2) is configured to cause the signal comparison unit (3) to compare the magnetic resonance waveform ((x,y,z) (i)) with the database waveforms (CDS1, ..., CDSj), to identify a database waveform (CDSk) having a defined correspondence, and to determine for both tissue types the database values for the T1 and T2 relaxation times matched to the identified database waveform (CDSk); - wherein the control unit (2) is configured to calculate from the determined T1 and T2 relaxation times a concentration of the contrast agent in the first tissue type and a concentration of the contrast agent in the second tissue type for the volume element, - wherein the control unit (2) is configured to cause the output unit (4) to store and / or output the determined T1 and T2 relaxation times and / or the calculated concentrations of the contrast agent in the first tissue type and in the second tissue type for the volume element.

8. Computer program product comprising a computer program that can be loaded into a memory of a computer, where it causes the computer to execute the following steps: • receiving a magnetic resonance waveform ((x,y,z)(i)) for a volume element of an examination region from a magnetic resonance fingerprinting method using a contrast agent, wherein the contrast agent comprises gadoxetic acid or a salt of gadoxetic acid as contrast-enhancing active substance, wherein the examination region is the liver or part of the liver of an examination object, wherein the volume element comprises a first tissue type and a second tissue type, the first tissue type being hepatocytes, wherein the contrast agent has a different state in the first tissue type than in the second tissue type, the state being the molar T1 relaxivity and / or T2 relaxivity, • receiving database waveforms (CDS1, ..., CDSj) from a magnetic resonance fingerprint database (DB), wherein each database waveform (CDS1, ..., CDSj) is matched to a T1 relaxation time and a T2 relaxation time in both tissue types as database values, • comparing the magnetic resonance waveform ((x,y,z)(i)) with the database waveforms (CDS1, ..., CDSj), • identifying a database waveform (CDSk) having a defined correspondence with the magnetic resonance waveform ((x,y,z)(i)), • determining the associated database values for the T1 and T2 relaxation times in both tissue types in the volume element, based on the identified database waveform (CDSk), • calculating the concentration of the contrast agent in the first tissue type and the concentration of the contrast agent in the second tissue type for the volume element from the determined T1 and T2 relaxation times, • outputting the determined T1 and T2 relaxation times and / or the calculated concentrations of the contrast agent in the first tissue type and in the second tissue type for the volume element.