Radio frequency antenna system

Abstract

According to the present invention, a radio frequency antenna system (1) for a magnetic resonance imaging apparatus comprises: a radio frequency coil (2) having a total coil impedance including a coil impedance and a patient-specific impedance of a patient when installed in a bore of the magnetic resonance imaging apparatus; a preamplifier (3) connected to the radio frequency coil (2), by means of which a signal received by the radio frequency coil (2) can be amplified and an amplified output signal can be output; a matching network (4) interconnected between the radio frequency coil (2) and the preamplifier (3), with which the total coil impedance of the radio frequency coil (2) can be adjusted; the radio frequency coil (2) comprises a first coil loop (6) and at least one further coil loop (7), and a controller (5) connected to the radio frequency coil (2), the matching network (4) and the preamplifier (3), and the controller (5) is adapted for noise impedance matching between the radio frequency coil (2) and the preamplifier (3) as a function of patient-specific parameters by controlling the adoption of the first coil loop (6) and the at least one further coil loop (7) and by controlling the matching network (4). In this manner, a radio frequency antenna system with improved impedance matching is provided.

Description

Technical Field

[0001] The present invention relates to the field of magnetic resonance imaging. In particular, the present invention relates to the field of radio frequency antenna systems for magnetic resonance imaging devices. Background Art

[0002] Every magnetic resonance imaging device has a radio frequency antenna system for receiving and converting magnetic resonance signals. The radio frequency antenna system includes a radio frequency coil, a matching network, a preamplifier, and an analog-to-digital converter. In magnetic resonance imaging, the body coil integrated in the system generates an excitation magnetic field for the spin system, thereby causing the foregoing relaxation. The precession of the net magnetization induces a current in the radio frequency coil via electromagnetic induction. The radio frequency coil generally includes a wire having inductance and coil resistance. Like any radio frequency operating system, the radio frequency antenna system is vulnerable to noise. Therefore, the most important requirement is to achieve the lowest noise figure. If the source impedance matches the noise impedance of the preamplifier, the noise figure can be minimized. In particular, for magnetic resonance imaging in the low field range (<1T), the signal-to-noise ratio depends on the geometry of the patient, the size of the bore, and the relative position of the radio frequency coil within the bore. This means that the signal-to-noise ratio cannot be maintained at a constant level because it depends on the patient, the coil to be used, and the position of the coil on the patient.

[0003] The article “An adjustable RF coil loading device” by C.E. Hayes (Journal of Magnetic Resonance Imaging, Vol. 99, 1993, pp. 81-86) describes an adjustable loading device having two conductive end rings connected by an adjustable even number of uniformly spaced resistive straight segments or straight strips. This adjustable loading device can replace the tissue loss of patients of various body sizes in a whole body magnetic resonance imaging device. The conductor structure does not change due to the load. The birdcage structure includes fixed resistors. The entire setup simulates a liquid load phantom within the transmit / receive coil.

[0004] Accurate and effective impedance matching is crucial for achieving the lowest noise figure in magnetic resonance imaging. However, most existing methods recommend using radio frequency coils for imaging entities where patient- and device-related matching cannot be immediately seen.

[0005] The article "MEMS switch integrated radio frequency coils and arrays for magnetic resonance imaging" by S.B. Bulumulla et al. (Review of scientific instruments, Vol. 88, 2017, 025003) discloses a configurable coil that can be switched into a small configuration and a large configuration. Summary of the Invention

[0006] An object of the present invention is to provide a radio frequency antenna system with improved impedance matching.

[0007] According to the present invention, this object is solved by the subject matter of the independent claims. Preferred embodiments of the present invention are described in the dependent claims.

[0008] Thus, according to the present invention, there is provided a radio frequency antenna system for a magnetic resonance imaging device, the radio frequency antenna system comprising: a radio frequency coil having a total coil impedance including a coil impedance and a patient-specific impedance when attached to a patient; a preamplifier connected to the radio frequency coil, by means of which the preamplifier can amplify a signal generated due to the reception of a magnetic resonance signal by the radio frequency coil and can output an amplified output signal; a matching network interconnected between the radio frequency coil and the preamplifier, by means of which the matching network can adjust the total coil impedance of the radio frequency coil; and a controller, wherein the radio frequency coil includes a first coil loop and at least one additional coil loop, the controller is connected to the radio frequency coil, the matching network and the preamplifier, and the controller is adapted to perform noise impedance matching between the radio frequency coil and the preamplifier according to patient-specific parameters by controlling the adoption of the first coil loop and the at least one additional coil loop and by controlling the matching network. The first coil loop and / or the additional coil loop captures a signal representing the magnetic flux generated due to the magnetic resonance signal received by the radio frequency coil. The first coil loop and the additional coil loop are configured to cover substantially equal regions, and substantially equal magnetic flux passes through these substantially equal regions. Thus, regardless of whether the first coil loop or the additional coil loop is adopted, the radio frequency coil collects substantially equal magnetic flux from substantially equal fields of view. When both the first coil loop and the additional coil loop are used to pick up magnetic flux from substantially the same field of view.

[0009] Here, the term "attached to the patient" means that the radiofrequency coil is positioned in the bore of the magnetic resonance imaging device relative to the patient. Advantageously, the radiofrequency coil can be placed on the surface of the patient's body to reduce signal transmission through air. However, as is well known to those skilled in the art, this is not always the case. In the case of a birdcage coil, for example, it is not possible to arrange the radiofrequency coil on the surface of the patient's body. In fact, in such cases, the radiofrequency coil is near the patient but still close to the patient in the bore of the magnetic resonance imaging device. The bore is an opening in the magnetic resonance imaging device that is designed to accommodate a treatment table with the patient and the radiofrequency coil.

[0010] As previously mentioned, a radiofrequency coil typically includes a section of wire having inductance and coil resistance. If the radiofrequency coil is loaded with a patient, the coil resistance changes to a total coil impedance, which is a combination of the radiofrequency coil impedance and the patient impedance.

[0011] It must be taken into account that when the received radio signal is transferred to the preamplifier, the impedance of the preamplifier is different from the total coil impedance. Therefore, for low-noise signal transmission, patient-specific impedance matching is recommended in order to adapt the total coil impedance to the impedance of the preamplifier. The goal is to achieve a minimum noise figure, which is defined as the ratio of the input signal-to-noise ratio to the output signal-to-noise ratio. The output signal-to-noise ratio corresponds to the output signal-to-noise ratio of the preamplifier.

[0012] In particular, magnetic resonance imaging low-field systems below 1T require a rethinking of the radiofrequency coil topology. Although the radiofrequency coil is mainly loaded with the patient at higher field strengths, if the coil design is not good, the radiofrequency coil at lower field strengths is prone to exhibit additional electronic noise contributions. In addition, in clinical applications, the radiofrequency coil is placed directly on the patient's body or a dedicated coil suitable for the patient's body shape is applied. However, there are clinical situations where the optimal coil-to-tissue distance cannot be applied, for example, pediatric imaging, magnetic resonance used in linear accelerators, and interventional applications.

[0013] Therefore, in the case of low-field magnetic resonance imaging, the total coil impedance and the resulting noise behavior may not be dominated by the inductive load of the patient's body but by the radiofrequency coil design itself. At the same time, due to changes in the radiofrequency coil shape, for stretchable or flexible radiofrequency coils, additional total coil impedance adjustment must be considered.

[0014] This problem is solved by connecting a controller to a radio frequency coil and a matching network. Based on patient-specific parameters, the controller is configured to run one or more rules to create a state of the matching network and the number of switched loops by turning individual coil loops on or off and / or by using the matching network for additional impedance adjustment, such that the total coil impedance can match the impedance of the preamplifier and the signal can be amplified by the preamplifier.

[0015] Generally, a radio frequency antenna can be operated by a controller in different ways. However, according to a preferred embodiment of the present invention, the radio frequency coil is provided with switches and additional switches, the switches being controllable by the controller and enabling individual coil loops to be switched on and off separately, and the additional switches being controllable by the controller and arranged between the matching network and the preamplifier. This allows for establishing switching options with low insertion losses.

[0016] Different coil loop configurations are possible. However, according to a preferred embodiment of the present invention, the at least one additional coil loop is formed as an additional series or parallel winding in the first coil loop. By increasing the number of windings, the impedance of the input part of the loop is higher, thus reducing the losses in the matching network. By switching the number of loops and / or the series, parallel winding mode, a matching transformation ratio to the matching network can be achieved, and thus a matching transformation ratio to the preamplifier can also be achieved.

[0017] In principle, different algorithms can be implemented in the controller. However, according to a preferred embodiment of the present invention, a trained artificial neural network is implemented in the controller. Employing an artificial intelligence system such as an artificial neural network enables dynamic matching with respect to the k-space magnitude. Decision-making for even complex tasks (where thresholds and manually determined logic or rules may be inappropriate for k-space applications) can be achieved. In addition, due to the output of the artificial neural network, a pre-scan can be omitted. The k-space is defined as a digital array representing the spatial frequencies in a magnetic resonance image. The setup of the artificial neural network can depend on many parameters, such as the position and shape of the coil, the distance to the tissue and the bore wall, the region of interest, the field strength, and the type of coil typically employed.

[0018] Data for training the artificial neural network can be acquired by using a prototype coil and scanning several phantom anatomies with different matching network settings. The raw data should be the resulting images for each coil and artificial neural network setup. Additionally, data from an RF calibration process from typical applications, such as noise correlation matrix measurements and frequency response curves, are used. Furthermore, electromagnetic simulation techniques can be used to calculate the sensitivity distribution, which can be modified to resemble the imaging data, which will eliminate the need for experimental trials.

[0019] These elements are input data, which can be used in combination with output data generated by offline reconstruction to train an artificial neural network. In the case of offline reconstruction, the output data is obtained by combining images of the coils of the array (including calculating the optimal fitting network settings). Then, the trained artificial neural network can generate output data based on a complete or incomplete input data set.

[0020] The controller can be a field programmable gate array or some other processor, where, due to bandwidth limitations, the rule-based machine of the field programmable gate array communicates directly with the magnetic resonance imaging sequencer. In the case of patient table movement, start and stop aborts can be activated so that the dynamic matching process does not generate image artifacts.

[0021] Generally, various patient-specific parameters can be used. However, according to a preferred embodiment of the present invention, the patient-specific parameters include the distance and position of the radio frequency coil relative to the patient and the total coil impedance. These patient-specific parameters are determined before image acquisition when the patient is lying on the patient table in the bore.

[0022] It is possible to determine the total coil impedance in different ways. However, according to a preferred embodiment of the present invention, the radio frequency coil has an impedance sensor, and with the impedance sensor, the total coil impedance can be measured. Thus, the possibility of measuring the individual total coil impedance is given.

[0023] In principle, various methods can be selected to determine the noise of the received signal. However, according to a preferred embodiment of the present invention, the controller is adapted to determine the coil circuit to be employed and is adapted to control the matching network by means of noise measurement. This noise measurement is carried out in the form of a pre-scan before image acquisition.

[0024] Generally, an internal signal source can be used for noise measurement. However, according to a preferred embodiment of the present invention, an external signal source is provided to support the noise measurement. The external signal source is part of the system and is galvanically isolated from the controller. In addition, the external signal source is known and is remotely controllable, so that the measurement system can be tuned over the entire frequency range of interest. Since the signal source is separate from the radio frequency coil, the signal source can be placed directly next to the radio frequency coil. This reduces cable attenuation and improves the signal-to-noise ratio of the measurement results.

[0025] The preamplifier can be placed outside the radio frequency coil. However, according to a preferred embodiment of the present invention, the preamplifier is integrated in the radio frequency coil housing. This means that each radio frequency coil has a dedicated preamplifier.

[0026] In principle, the RF coil can be analog. However, according to a preferred embodiment of the present invention, the RF coil is a digital coil, and the controller is positioned within the RF coil housing, and a digital preamplifier is used for signal amplification. The use of a digital coil enables the direct acquisition and processing of digital signals on the patient. The signals are digitized directly in the RF coil closest to the patient and then transmitted and processed throughout the imaging chain, which generally provides a better signal-to-noise ratio.

[0027] Furthermore, according to the present invention, a method for operating an RF antenna system for a magnetic resonance imaging device is provided. The method comprises the following method steps: attaching an RF coil to a patient to be examined by the magnetic resonance imaging device, wherein the RF coil has a total coil impedance comprising a coil impedance and a patient-specific impedance, and the RF coil comprises a first switchable coil loop and at least one additional switchable coil loop; analyzing patient-specific parameters; determining the coil loops to be switched on and off respectively and controlling a matching network based on the analyzed patient-specific parameters; receiving signals via the switched coil loops of the RF coil; impedance-matching the received signals to the impedance of a preamplifier via the matching network; and amplifying the received signals by the preamplifier. In this context, impedance-matching to the impedance of the preamplifier means "approximate", i.e., it is intended that the difference between the impedances is small, preferably less than a predefined threshold. Preferably, the RF coil comprises a plurality of receive channels each having its own amplifier and matching network, and the method is performed for all of these receive channels.

[0028] According to a preferred embodiment of the present invention, the method further comprises a trained artificial neural network mounted on a controller, the trained artificial neural network determining the coil loops to be switched on and off respectively and controlling the matching network. This is performed digitally such that the user does not need to have any specific knowledge about the implementation.

[0029] According to a preferred embodiment of the present invention, noise measurements are employed to determine the coil loops to be switched on and off respectively and to control the matching network.

[0030] Furthermore, according to the present invention, a computer program for noise impedance matching for a magnetic resonance imaging device, the computer program comprising instructions which, when the program is run by a computer, cause the computer to perform the method according to any one of the claims (from the first method claim to the last method claim).

[0031] Generally, a radio frequency coil can be dedicated to signal reception. However, according to a preferred embodiment of the present invention, the switch of the radio frequency coil is used as a detuning circuit. Depending on the configuration, the coil elements may be located away from the examination area and contribute little to the image. However, the preamplifier still generates noise. In this case, it is desirable to mismatch the radio frequency coil with the preamplifier to create a noise trap.

[0032] Different types of switches can be used. However, according to a preferred embodiment of the present invention, the switch is a gallium nitride field effect transistor (GaN-FET) or a single-pole double-throw (SPDT) switch with low insertion loss. Compared with silicon field effect transistor switches, GaN-FET or SPDT switches have very low switching losses due to their fast switching ability.

[0033] There are several ways to detect the position of the radio frequency coil on the surface of a patient in the bore. However, according to a preferred embodiment of the present invention, the radio frequency coil is provided with a marker that can be detected by a camera. For this purpose, special infrared markers can be provided on the coil, which can be detected by an infrared-sensitive camera and do not distort the magnetic field.

[0034] In principle, a rigid radio frequency coil can also be provided. However, according to a preferred embodiment of the present invention, the radio frequency coil is designed to be flexible and stretchable. This allows the radio frequency coil to be positioned as conformally as possible on the patient's surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] These and other aspects of the present invention will become apparent and be elucidated with reference to the embodiments described below. However, such embodiments do not necessarily represent the full scope of the present invention, and thus the scope of the present invention is to be construed with reference to the claims and the present text.

[0036] In the drawings:

[0037] Figure 1 A radio frequency antenna system according to a preferred embodiment of the present invention is schematically depicted;

[0038] Figure 2 A second radio frequency antenna system according to a preferred embodiment of the present invention is schematically depicted;

[0039] Figure 3 A third radio frequency antenna system according to a preferred embodiment of the present invention is schematically depicted;

[0040] Figure 4 A fourth radio frequency antenna system according to a preferred embodiment of the present invention is schematically depicted; and

[0041] Figure 5Schematically depicts the scheme of a method according to a preferred embodiment of the present invention.

[0042] List of reference numerals

[0043] 1 Radio frequency antenna system

[0044] 2 Radio frequency coil

[0045] 3 Preamplifier

[0046] 4 Matching network

[0047] 5 Controller

[0048] 6 First coil loop

[0049] 7 Additional coil loop

[0050] 8 Switch

[0051] 9 Additional switch

[0052] 10 Artificial neural network

[0053] 11 Impedance sensor

[0054] 12 External signal source

[0055] 13 Digital preamplifier

[0056] 14 Radio frequency coil housing Detailed implementation

[0057] Figure 1Schematically depicts a radio frequency antenna system 1 according to a preferred embodiment of the present invention. The radio frequency antenna system 1 includes a radio frequency coil 2, wherein the radio frequency coil 2 includes a coil impedance and a patient-specific impedance when adjacent to a patient in the bore of a magnetic resonance imaging device. The total coil impedance includes the coil impedance and the patient-specific impedance. A second part of the radio frequency antenna system 1 is a matching network 4. The matching network 4 is interconnected with the radio frequency coil 2 via a switch 8 and with a preamplifier 3 via a further switch 9. The switches 8, 9 are gallium nitride field effect transistor (GaN-FET) switches with low insertion loss. The radio frequency coil 2 includes a first coil loop 6 and a further coil loop 7. The first coil loop 6 and the further coil loop 7 are arranged parallel to each other and connected to the switch 8. The switch 8, which can be controlled by a controller 5, enables the individual coil loops 6, 7 to be switched on or off. The first coil loop and the further coil loop are geometrically configured to be closely adjacent to each other. The first coil loop and the further coil loop can be positioned adjacent to each other radially, or one can be positioned on top of the other, orthogonal to the regions of the first coil loop and the further coil loop. Thus, the geometric dimensions and shapes of the first coil loop and the further coil loop are substantially equal and can differ by a margin of at most 2% to 5% of their linear dimensions. The controller 5 is a rule-based unit of a field programmable gate array that includes a trained artificial neural network 10, and in addition to the switch 8, the unit is also connected to the matching network 4, the further switch 9, the preamplifier 3, and an impedance sensor 11. The impedance sensor 11 is also installed in the bore of the magnetic resonance imaging device such that the measured impedance corresponds to the total coil impedance. This measured impedance is transmitted as an input parameter to the trained artificial neural network 10, and then the trained neural network 10 determines the number of coil loops 6, 7 switched to the on state and the matching impedance adjustment to be made in the matching network 4, thereby ensuring a noise impedance adjustment of the impedance of the preamplifier 3, which in turn enables a more favorable signal transmission.

[0058] Figure 2 Schematically depicts a second radio frequency antenna system 1 according to a preferred embodiment of the present invention. The further coil loop 7 is provided as a further winding arranged in series with the first coil loop 6, and the controller 5 is adapted to determine the first coil loop 6 and the second coil loop 7 of the radio frequency coil 2 to be employed and is adapted to control the matching network 4 by means of a noise measurement. Such a noise measurement can be performed in a patient-specific manner before a diagnostic imaging sequence or, alternatively, using a phantom as part of a quality assurance process, wherein the phantom is used to simulate a patient. For this purpose, an external signal source 12 is provided, and the external signal source 12 is part of the radio frequency antenna system 1 but is galvanically isolated from the system.

[0059] Figure 3Schematically depicts a third radio frequency antenna system 1 according to a preferred embodiment of the present invention, wherein a preamplifier 3 is integrated in a radio frequency coil housing 14 such that each radio frequency coil 2 has a dedicated preamplifier 3.

[0060] Figure 4 Schematically depicts a fourth radio frequency antenna system 1 according to a preferred embodiment of the present invention, wherein the radio frequency coil 2 is a digital coil, and a controller 5 is located in the radio frequency coil housing 14, and a digital preamplifier 13 is used for signal amplification.

[0061] Figure 5 Schematically depicts a scheme of a method according to a preferred embodiment of the present invention, wherein, in a first step, the radio frequency coil 2 is attached to a patient. The patient will be examined by a magnetic resonance imaging device. The radio frequency coil 2 has a total coil impedance including a coil impedance and a patient-specific impedance, and the radio frequency coil 2 includes a first switchable coil loop 6 and at least one additional switchable coil loop 7.

[0062] Secondly, analyze the patient-specific parameters.

[0063] Thirdly, determine the coil loops 6, 7 to be switched on or off, and additionally, control the matching network 4 based on the analyzed patient-specific parameters to achieve noise impedance matching with the preamplifier.

[0064] Fourthly, receive the signals generated by the switched coil loops 6, 7 of the radio frequency coil 2,

[0065] Fifthly, perform impedance matching between the signals received by the matching network 4 and the impedance of the preamplifier 6.

[0066] Sixthly, amplify the received signals by the preamplifier 3.

[0067] Although the present invention has been described in detail in the drawings and the foregoing description, such description and illustration are to be considered illustrative or exemplary and not restrictive; the present invention is not limited to the disclosed embodiments. By studying the drawings, the disclosure, and the appended claims, those skilled in the art can understand and implement other variations of the disclosed embodiments when practicing the claimed invention. In the claims, the word "comprising" does not exclude other elements or steps, and the words "a" or "an" do not exclude a plurality. The fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used advantageously. Any reference signs in the claims should not be construed as limiting the scope. Additionally, for clarity, not all elements in the drawings are provided with reference signs.

Claims

1. A radio frequency antenna system (1) for a magnetic resonance imaging device, comprising: a radio frequency coil (2) which, when attached to a patient, has a total coil impedance including a coil impedance and a patient-specific impedance, a preamplifier (3) connected to the radio frequency coil (2), by means of which a signal representing the magnetic flux captured by the radio frequency coil (2) can be amplified and an amplified output signal can be output, a matching network (4) interconnected between the radio frequency coil (2) and the preamplifier (3), by means of which the total coil impedance of the radio frequency coil (2) can be adjusted, and a controller (5), wherein the radio frequency coil (2) includes a first coil loop (6) and at least one additional coil loop (7), and the first coil loop and the second coil loop cover substantially equal fields of view, the controller (5) is connected to the radio frequency coil (2), the matching network (4) and the preamplifier (3), and the controller (5) is adapted to perform noise impedance matching between the radio frequency coil (2) and the preamplifier (3) according to patient-specific parameters by controlling the use of the first coil loop (6) and the at least one additional coil loop (7) and by controlling the matching network (4).

2. The radio frequency antenna system (1) according to claim 1, wherein the radio frequency coil (2) is provided with a switch (8) and an additional switch (9), the switch can be controlled by the controller and enables individual coil loops (6, 7) to be switched on and off respectively, and the additional switch can be controlled by the controller (5) and is arranged between the matching network (4) and the preamplifier (3).

3. The radio frequency antenna system according to any one of the preceding claims, wherein the at least one additional coil loop (7) is formed as an additional series or parallel winding in the first coil loop (6).

4. The radio frequency antenna system (1) according to any one of the preceding claims, wherein a trained artificial neural network (10) is implemented in the controller (5).

5. The radio frequency antenna system (1) according to any one of the preceding claims, wherein the patient-specific parameters include the distance and position of the radio frequency coil (2) relative to the patient and the total coil impedance.

6. The radio frequency antenna system (1) according to any one of the preceding claims, wherein the radio frequency coil (2) has an impedance sensor (11), by means of which the total coil impedance can be measured.

7. The radio frequency antenna system (1) according to any one of claims 1 to 3 and 6, wherein the controller (5) is adapted to determine the coil loops (6, 7) to be used and is adapted to control the matching network (4) by means of noise measurement.

8. The radio frequency antenna system (1) according to claim 7, wherein an external signal source (12) is provided to support the noise measurement.

9. The radio frequency antenna system (1) according to any one of the preceding claims, wherein, the preamplifier (3) is integrated in the radio frequency coil housing (14).

10. The radio frequency antenna system (1) according to any one of the preceding claims, wherein, the radio frequency coil (2) is a digital coil, and the controller (5) is positioned in the radio frequency coil housing (14), and a digital preamplifier (13) is used for signal amplification.

11. A method of operating a radio frequency antenna system (1) for a magnetic resonance imaging device according to claim 1, comprising the following method steps: attaching the radio frequency coil (2) to a patient to be examined by the magnetic resonance imaging device, wherein, the radio frequency coil (2) has a total coil impedance including a coil impedance and a patient-specific impedance, and the radio frequency coil (2) includes a first switchable coil loop (6) and at least one additional switchable coil loop (7), analyzing patient-specific parameters, determining the coil loops (6, 7) to be switched on and off respectively based on the analyzed patient-specific parameters and controlling the matching network (4), receiving signals through the switched coil loops (6, 7) of the radio frequency coil (2), impedance-matching the received signals to the impedance of the preamplifier (3) through the matching network (4), and amplifying the received signals by the preamplifier (3).

12. The method of operating a radio frequency antenna system (1) according to claim 11, wherein, a trained artificial neural network (10) is installed on the controller (5), and the trained artificial neural network determines the coil loops (6, 7) to be switched on and off respectively and controls the matching network (4).

13. The method of operating a radio frequency antenna system (1) according to claim 11, wherein, noise measurement is employed to determine the coil loops (6, 7) to be switched on and off respectively and control the matching network (4).

14. A computer program for noise impedance matching for a magnetic resonance imaging device, comprising instructions which, when the program is run by a computer, cause the computer to perform the method according to any one of claims 11 to 13.

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