Method for forming an image of a body using an MRI device - Patent application

Abstract

The invention relates to a method for imaging a body, the method comprising: performing a basic sequence, the basic sequence comprising: generating at least one echo signal of a sequence of RF pulses produced by an RF coil; performing an echo measurement of the at least one echo signal by the RF coil; performing a background measurement representative of a background signal by the RF coil, the method comprising the steps of: a) repeating the basic sequence as many times as necessary to form a Fourier image of the body and a Fourier image of the background from the background measurement; and b) processing the Fourier image of the body and the Fourier image of the background so as to obtain an image of the body, wherein signatures of one or more background signals are reduced or even eliminated.

Description

[Technical field]

[0001] The present invention relates to the field of magnetic resonance imaging, and in particular to a method for forming an MRI image of a body using an MRI device. [Background technology]

[0002] Magnetic resonance imaging (MRI) is now widely used to non-invasively image the interior of the body, in particular the human body. In particular, magnetic resonance imaging makes it possible to study the hydrogen nuclei of water molecules that form part of the body, in particular their nuclear spin.

[0003] In this respect, the MRI apparatus is provided with a magnet intended to impose a static magnetic field (called the "main magnetic field") on the body, under the influence of which the nuclear spins associated with the hydrogen nuclei contained in the water molecules forming part of this body become polarized.

[0004] Specifically, the magnetic moments associated with these spins are preferentially aligned along an axis called the z-axis, which is determined by the orientation of the main magnetic field to produce the magnetization of the body.

[0005] The MRI device also includes gradient coils configured to produce small amplitude, spatially varying magnetic fields when electrical current is applied to them. More specifically, the gradient coils are aligned parallel to the main magnetic field and are designed to produce magnetic field components whose amplitudes vary linearly with position along one of the axes x, y or z (each pair of axes x, y and z are perpendicular).

[0006] In this way, the combined effect of the magnetic fields imposed by the gradient coils makes it possible to spatially encode each of the body locations intended to be probed.

[0007] The MRI device also comprises at least one radiofrequency (RF) coil intended to function as a RF receiver-transmitter, specifically configured to emit RF energy pulses at a frequency equal to or close to the resonant frequency of hydrogen atomic nuclei spins, which RF energy pulses are at least partially absorbed by these atomic nuclei.

[0008] As soon as the RF emission is discontinued, the nuclear spins relax back to their initial energy state and then emit an RF signal that can be collected by at least one RF coil, which is then processed using a computer and a reconstruction algorithm to obtain an image of the body.

[0009] Generally, a main magnetic field comprised between 1.5 Tesla and 3 Tesla makes it possible to achieve a relatively reasonable signal-to-noise ratio, thus making it possible to form images of the human body of sufficient quality for durations of the order of one minute or more.

[0010] However, there are situations in which it is not possible to implement a main magnetic field of such strength, portable MRI devices being one example of this. The latter generally contain permanent magnets or electromagnets of limited capacity and are unable to impose a main magnetic field with a strength greater than 60 mT, or even greater than 200 mT, without adversely affecting the mass or volume of the MRI device considered.

[0011] This limitation on the main magnetic field strength directly affects the performance of the MRI machine and leaves noise in the obtained images, which contains two components, one correlated and the other uncorrelated.

[0012] The uncorrelated component in this respect represents noise that is essentially dependent on the environment in which the MRI device is located. The contribution of this component to the MRI image can be minimized by techniques known to those skilled in the art.

[0013] On the other hand, the correlated components have a signature that may mask certain details in the images obtained by the MRI device in question. US 9797971(B2) deals with this aspect and thus proposes an MRI device configured to remove the correlated components. In particular, the device proposed in US 9797971(B2) comprises, in addition to an RF coil dedicated to the MRI measurements, a secondary coil for evaluating the correlated noise emitted and that may be experienced by the MRI device. The secondary coil, as described in US 9797971(B2), is subject to a compromise in terms of its positioning relative to the RF coil. In particular, the secondary coil is positioned at a distance from the body to be measured, so that it remains insensitive to the signals emitted by said body, but close enough to the RF coil to detect noise of the same nature therein.

[0014] However, the MRI device proposed in US Pat. No. 9,797,971 (B2) is not satisfactory.

[0015] This is because the device does not allow for the reduction of correlated noise without taking into account the approximation, which affects the quality of the images obtained. In fact, this document proposes to ignore its uncorrelated components, even though they are detected by the secondary coil, in order to establish the transfer function between the RF coil and the secondary coil.

[0016] Furthermore, since the secondary coil is positioned to detect noise of the same nature as that experienced by the RF coil, it is necessarily also sensitive to signals emitted by the body. This last aspect, although not discussed in US 9797971(B2), may be a source of error on MRI images of the body.

[0017] It is an object of the present invention to provide a method for forming an image of a body using a magnetic resonance imaging device that reduces or even eliminates any correlated noise signatures. Summary of the Invention

[0018] The present invention relates to a method for imaging a body using an MRI device, the method comprising a basic sequence of repetition time TR, the method comprising: - generating at least one echo signal over an echo time range PE by subjecting a body positioned within an examination volume of the MRI device to a sequence of RF pulses produced by an RF coil and to magnetic field gradients produced by a gradient coil; - performing an echo measurement of at least one echo signal by an RF coil; - carrying out a basic sequence comprising: - carrying out a background measurement by the RF coil over a time range known as a background range PF, which is different from the echo range PE and represents a background signal; The method is a) repeating the base sequence as many times as necessary to form, in Fourier space, a Fourier image of the body from the echo signals and a Fourier image of the background from background measurements; b) processing either a Fourier image of the body and a Fourier image of the background, or the echo signal and the background signal, to obtain an image of the body in real space, wherein the signature of the background signal is reduced or even eliminated.

[0019] Thus, by implementing the present invention, it is possible to obtain images of the body in real space that are essentially free of background signal signatures.

[0020] In one embodiment, step b) comprises processing a Fourier image of the body and a Fourier image of the background, step b) being carried out in two sub-steps b1) and b2), step b1) comprises mathematical processing of the Fourier image of the background and the Fourier image of the body to subtract background signals from the Fourier image of the body to form a processed Fourier image in Fourier space; Step b2) involves a transformation of the processed Fourier image to obtain an image of the body in real space.

[0021] According to one embodiment, the mathematical processing step b1) comprises at least one of the following methods: spectral subtraction, anisotropic diffusion filtering, non-local means.

[0022] According to one embodiment, step b) is carried out in two sub-steps b3) and b4), Step b3) comprises transforming the Fourier image of the body and the Fourier image of the background into intermediate body images and background images in real space, respectively; Step b4) comprises processing the intermediate body image and the background image to subtract a background signal contribution in the intermediate body image to obtain an image of the body in real space.

[0023] According to one embodiment, step b4) comprises processing by principal component analysis.

[0024] According to one embodiment, generating at least one echo signal includes performing an electromagnetic pulse, known as an initial electromagnetic pulse, that is orthogonal to a permanent magnetic field B0 imposed on a body located within the examination volume of the MRI device during the repetition of the base sequence.

[0025] According to one embodiment, the initial electromagnetic pulse is preceded by at least one electromagnetic rephasing pulse and is simultaneous with the selection of a slice using one of the gradient coils, referred to as the slice plane selection coil, and the measurement of the at least one echo signal performs phase and frequency encoding by two of the gradient coils, referred to as the phase gradient coil and the frequency gradient coil, respectively.

[0026] According to one embodiment, the base sequence is a spin echo sequence comprising a single measurement of an echo signal, the background measurement being performed after said measurement of the echo signal.

[0027] According to one embodiment, the background measurement is performed with the same phase and frequency coding as that implemented during the measurement of the echo signal.

[0028] According to one embodiment, the base sequence is a fast spin echo sequence, which comprises a repeating subsequence within said sequence, the subsequence comprising an electromagnetic rephasing pulse and a measurement of the echo signal.

[0029] According to one embodiment, the basic sequence is a 3D fast spin echo sequence, which includes repeating N basic subsequences within the sequence, each basic subsequence including an electromagnetic rephasing pulse and a measurement of an echo signal.

[0030] According to one embodiment, the basic sequence comprises a single background measurement, which is advantageously performed after the basic subsequence.

[0031] According to one embodiment, the base sequence comprises N background measurements, each background measurement being performed within its own base subsequence.

[0032] A computer program comprising instructions which, when the program is executed by a computer, perform the steps of the method according to the invention.

[0033] 20. An MRI device provided with a unit configured to implement a computer program according to the invention, said MRI device comprising said computer program. [Brief description of the drawings]

[0034] Other features and advantages of the present invention will become apparent from the following detailed description of the body imaging method, which refers to the accompanying drawings. [Figure 1] 1 is a schematic exploded view of a magnetic resonance imaging device; [Diagram 2] FIG. 2 is a schematic diagram of a fast 3D spin-echo sequence that can be considered for implementing the MRI imaging process according to the invention. [Diagram 3] FIG. 3 is a first example of a fast 3D spin echo sequence from FIG. 2. [Figure 4] This is a Fourier image of the body. [Diagram 5] This is the Fourier image of the background. [Figure 6] 1 is an image of a body taken without the use of the present invention. [Figure 7] This is an image of a body in real space. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] The present invention relates to a method for forming an image of a body using a magnetic resonance imaging (hereinafter "MRI") device.

[0036] More particularly, the present invention relates to a method for forming an image of a body placed in an examination volume of an MRI device. In this regard, it is known that such devices are subject to environmental noise, hereinafter referred to as "background signals". This background signal is generally associated with ambient electromagnetic signals and can adversely affect the performance of the MRI device. More specifically, this background signal can present a signature on the image of the body that can be obtained using the MRI device, and in particular can hide details thereof.

[0037] To overcome this drawback, MRI devices are generally isolated by special shielding (e.g., Faraday cages), however this solution remains unattractive when considering portable MRI devices.

[0038] To this end, the invention relates to a method for imaging a body using an MRI device, the method comprising a basic sequence of repetition time TR, the - generating at least one echo signal over an echo time range PE by subjecting a body positioned within an examination volume of the MRI device to a sequence of RF pulses produced by an RF coil and to magnetic field gradients produced by a gradient coil; - performing an echo measurement of at least one echo signal by means of an RF coil; - carrying out a basic sequence comprising: - carrying out a background measurement by the RF coil over a time range known as a background range PF, which is different from the echo range PE and represents a background signal; The method is a) repeating the base sequence as many times as necessary to form, in Fourier space, a Fourier image of the body from the echo signals and a Fourier image of the background from background measurements; b) processing either a Fourier image of the body and a Fourier image of the background, or the echo signal and the background signal, to obtain an image of the body in real space that is essentially free of the signature of the background signal.

[0039] For example, according to a first alternative, step b) comprises processing a Fourier image of the body and a Fourier image of the background, step b) being carried out in two sub-steps b1) and b2), Step b1) comprises mathematical processing of the Fourier image of the background and the Fourier image of the body to subtract background signals from the Fourier image of the body to form a processed Fourier image in Fourier space; Step b2) comprises a transformation of the processed Fourier image to obtain an image of the body in real space.

[0040] According to a second alternative, step b) is carried out in two sub-steps b3) and b4).

[0041] Step b3) involves transforming the Fourier images of the body and the background into intermediate body and background images, respectively, in real space.

[0042] Step b4) comprises processing the intermediate body image and the background image to subtract a contribution of the background signal in the intermediate body image to obtain an image of the body in real space.

[0043] It is understood that the MRI imaging process according to the present invention is particularly suitable for use with low-field MRI devices (e.g. portable MRI devices), i.e. MRI devices operating with a main magnetic field of less than 0.5 Tesla, or even less than 0.2 Tesla. Nevertheless, the present invention does not have to be limited to this aspect. In particular, a person skilled in the art could envisage implementing the method according to the present invention to operate high-field MRI devices.

[0044] FIG. 1 is a diagram of an MRI device 1 suitable for implementing the imaging method according to the invention.

[0045] The MRI device 1 comprises a magnet 2 configured to impose a main magnetic field B0. The magnet 2 may, for example, comprise a permanent magnet. The magnet 2 may in particular extend along an axis of elongation z.

[0046] More specifically, the magnet 2 defines a bore 3 opening through a first opening 4 and a second opening 5 opposite each other along an axis of elongation z.

[0047] In this respect, the magnet 2 is positioned to allow the insertion of a body, more particularly a human body, into the bore 3 through the first opening 4 along an axis of elongation z.

[0048] The magnet 2 may be configured to impose a main magnetic field B0 oriented along an axis perpendicular to the elongation axis z, in a zone of the bore 3 referred to as the analysis zone.

[0049] In this respect, the magnet 2 may comprise an assembly of elementary magnets, in particular arranged in a series of Halbach rings. EP 3368914 B1 gives an example thereof. However, the invention is not limited solely to the configuration described in this patent.

[0050] By way of example, the magnet 2 is configured to impose a main magnetic field having an amplitude of less than 0.1 Tesla, advantageously less than 0.065 Tesla, and even more advantageously 0.05 Tesla or less.

[0051] The MRI device 1 also comprises a set of gradient coils 6. The gradient coils 6 are specifically configured to produce a small amplitude and spatially varying magnetic field when a current is applied to them.

[0052] More specifically, the gradient coils 6 are aligned parallel to the main magnetic field and are designed to produce magnetic field components whose amplitudes vary linearly with position along one of the axes x, y or z (axes x, y and z forming a Cartesian reference coordinate system).

[0053] The combined effect of the magnetic fields imposed by the gradient coils 6 thus makes it possible to spatially encode the signals present in the bore 3 and coming from the body intended to be explored. The spatial encoding is manifested in particular by a change in the resonance energy of the nuclear spin of the hydrogen nuclei contained in the body intended to be explored and present in the analysis zone. In other words, the nuclear spin of the hydrogen nuclei is subjected to a different magnetic field from one position to another.

[0054] The MRI device 1 further comprises a radio frequency coil 8 (hereinafter "RF coil"), in particular arranged within the housing 3 and defining an examination volume of the MRI device 1 in which the body is intended to be accommodated.

[0055] Finally, the MRI device 1 further comprises means for controlling said MRI device 1. In particular, these control means may include a computer 13 interfaced via interface means 11 with the various elements forming the MRI device 1.

[0056] The MRI device 1 described above can be used to implement a method for forming an MRI image of a body located within an examination volume.

[0057] Under the terms of the present invention, the body image may be two-dimensional or three-dimensional.

[0058] The method for image formation according to the invention therefore comprises implementing a basic sequence SE. In particular, the basic sequence SE may be of a duration referred to as the repetition duration TR.

[0059] Thus, Fig. 2 is a schematic diagram of a basic sequence SE that can be considered when implementing the method according to the invention. In particular, the basic sequence SE shown in Fig. 2 is a turbo spin echo 3D sequence. However, the invention is not limited to this single sequence and a person skilled in the art will be able to adapt its principles to other types of sequences. For example, a basic spin echo sequence SE that is a fast spin echo sequence may be considered for use in the invention.

[0060] Thus, a basic sequence SE according to the invention may comprise generating at least one echo signal SiE over an echo time range PE by subjecting an imaged body positioned in an examination volume of an MRI device to a sequence of RF pulses. In particular, the RF pulses are generated by an RF coil 8. Gradient coils (Gx, Gy and Gz) are used to spatially encode the body in the examination volume.

[0061] It is noted that gradient coils are also used or powered throughout the execution of a measurement sequence (specifically during execution of a basic sequence) in order to homogenize the main magnetic field B0 experienced by the body in the analysis volume. In other words, the gradient coils generate local fields which are added to the main magnetic field B0, so that the resulting fields are more homogeneous than the main magnetic field B0 in the analysis volume.

[0062] The basic sequence SE, shown in Figure 2, begins with the emission of an RF pulse known as the main electromagnetic pulse, designed to excite the entire body volume. In some circumstances, the main electromagnetic pulse is specifically referred to as a 90° pulse, when the pulse in question is in a plane orthogonal to the main magnetic field B0.

[0063] The basic sequence SE also includes N basic subsequences SSE, where N is an integer strictly greater than 1. Specifically, the N basic subsequences are executed consecutively following the emission of the main electromagnetic pulse.

[0064] Each basic subsequence SSE is (i) the emission of an RF pulse, known as a rephasing pulse, by an RF coil; (ii) Phase encoding, called CP, is performed using gradient coils Gx and Gz to select the K y line in Fourier space (also known as K-space). (iii) Simultaneous echo measurement of the SE echo signal by the RF coil and frequency coding by the Gy gradient coil are performed, which are carried out continuously.

[0065] Optionally, the basic subsequence SSE may include a step (iv) performed after step (iii) to invert the phase encoding performed by the gradient coils Gx and Gz (CPi in FIG. 2).

[0066] Step (iii) makes it possible to fill the Ky frequency lines in K-space for a given phase encoding.

[0067] It will be appreciated that echo measurements with an RF coil involve an interface means such as an analog-to-digital converter (ADC). In particular, measurements with an RF coil require activation of the analog-to-digital converter. When measurements are not required, the analog-to-digital converter is disabled.

[0068] During the elementary sequence SE, the spin echo signals SiE occur at specific times known as echo times TE. Specifically, starting from the moment of emission of the main electromagnetic pulse, the SiE spin echo signals are regularly spaced apart from one another by echo times TE. In addition, each spin echo is spread over a PE echo time range.

[0069] In addition, each base subsequence SSE has its own phase encoding. In other words, executing a base sequence SE fills as many K y lines in K space as there are base subsequences SSE in the base sequence SE. Specifically, executing a base sequence fills N different K y lines in K space.

[0070] According to the invention, the basic sequence SE comprises at least one background measurement MF representing the background signal due to the RF coil over a so-called background time range PF which is different from the echo time range PE.

[0071] By considering a background time range PF that is different from the echo time range PE (in other words, these two ranges do not overlap), it is possible for the RF coil to measure only environmental signals without including any spin echoes that are likely to originate from the body.

[0072] The background measurement may be performed at any time different from the echo time, in particular the background measurement performed by the RF coil may be performed before or after the spin echo measurement.

[0073] According to a first example shown in Fig. 3, after the SSE basic subsequence, a MF background measurement can be performed. In particular, the background measurement MF performs a frequency-frequency coding using a Gy gradient coil. This background measurement MF is used to obtain a frequency-frequency coding line. This line is therefore used to fill in the K-space as many Ky lines as there are basic subsequences SSE in the basic sequence SE.

[0074] Alternatively, according to a second example, the base sequence SE includes a number of background measurements MF. In particular, the base sequence SE includes the same number of background measurements MF as the base subsequences SSE. In particular, according to this second example, each subsequence SSE is associated with a background measurement. For example, without limiting the invention to this aspect, the background measurement can include the same Gx and Gz phase coding as that imposed when executing the associated base subsequence.

[0075] Whatever the case may be, the background measurement FM is performed over a time range different from the echo time range.

[0076] The method according to the invention therefore comprises a step a) of repeating the basic sequence as many times as necessary to form, in Fourier space, a Fourier image of the body from the echo signals and a Fourier image of the background from the background measurements.

[0077] Step a) is followed by step b) of processing either a Fourier image of the body and a Fourier image of the background, or the echo signal and the background signal, to obtain an image of the body in real space essentially free of the signature of the background signal.

[0078] For example, according to a first alternative, step b) comprises processing a Fourier image of the body and a Fourier image of the background, step b) being carried out in two sub-steps b1) and b2).

[0079] Step b1) involves mathematical processing of the Fourier image of the background and the Fourier image of the body to subtract the background signal from the Fourier image of the body to form a processed Fourier image in Fourier space.

[0080] The mathematical processing performed in step b1) may include at least one of the following methods: spectral subtraction, anisotropic diffusion filtering, non-local means.

[0081] The spectral subtraction method is described in M ​​Arcan et al.: “Denoising MRI using spectral subtraction.” IEEE transactions on bio-medical engineering vol. 60(6):1556-1562 (2013).

[0082] Those skilled in the art who wish to implement anisotropic diffusion filtering may consult the following document: Perona P, Malik J.: "Scale-space and edge-detection using anisotropic diffusion", IEEE Trans Pattern Anal Mach Intell. Jul; vol. 12(7): 629-639 (1990).

[0083] A description of non-local means can be found in Buades A et al, "Non-local algorithm for image denoising", Proc IEEE Comput Soc Conf Comput Vis Pattern Recognit, vol. 2:60-65 (2005).

[0084] In general, it may be considered to carry out step b1) according to a method belonging to at least one of the classes selected from: spectral subtraction methods, Wiener-type methods, subspace methods, statistical model-based methods.

[0085] For more information see: Shrawankar, U., Thakare, V. (2010). Noise Estimation and Noise Removal Techniques for Speech Recognition in Adverse Environment. In: Shi, Z., Vadera, S., Aamodt, A., Leake, D. (eds) Intelligent Information Processing V. IIP 2010. IFIP Advances in Information and Communication Technology, vol 340. Springer, Berlin, Heidelberg.

[0086] Step b2) comprises a transformation of the processed Fourier image to obtain an image of the body in real space.

[0087] This transformation may involve the use of a Fourier transform.

[0088] Alternatively, the present invention can perform the transformation described in Usman M, Kakkar L et al., "Joint B0 and image estimation integrated with model based reconstruction for field map update and distortion correction in prostate diffusion MRI", Magn Reson Imaging, vol. 65: 90-99 (2020).

[0089] According to a second alternative, step b) is carried out in two sub-steps b3) and b4).

[0090] Step b3) involves transforming the Fourier images of the body and the background into intermediate body and background images, respectively, in real space.

[0091] This transformation may involve the use of a Fourier transform.

[0092] Step b4) comprises processing the intermediate body image and the background image to subtract a contribution of the background signal in the intermediate body image to obtain an image of the body in real space.

[0093] Advantageously, step b4) comprises processing by principal component analysis.

[0094] This process is described in Campbell-Washburn AE et al.; "Using the robust principal component analysis algorithm to remove RF spike artifacts from MR images" Magn Reson Med.; vol. 75(6): 2517-2525 (2016).

[0095] The present invention is described using x, y, z coordinates (with respect to Gx, Gy, and Gz gradient coils), it being understood that the order of these coordinates has been arbitrarily chosen, as those skilled in the art may consider different orders.

[0096] The method according to the invention therefore makes it possible to remove the background signal of an MRI image. In particular, the method proposes to insert an additional event during the execution of the basic sequence of measurement of the background signal by means of an RF coil. Unlike the solution proposed in US 9797971 (B2), the method according to the invention does not impose any approximation when executing step b).

[0097] 4, 5, 6 and 7 are diagrams of an implementation of the invention according to a first alternative for imaging two samples E1 and E2.

[0098] Specifically, FIG. 4 is a Fourier image of the body and FIG. 5 is a Fourier image of the background.

[0099] By performing a mathematical processing step b1) on these two Fourier images of the background and the body, the background signal is subtracted from the Fourier image of the body and a processed Fourier image (not shown) is formed in Fourier space. The mathematical processing used in this example involves a spectral subtraction method.

[0100] 7 shows a Fourier image of a body (two samples E1 and E2) in real space obtained by transforming the Fourier image. The image shows the two samples E1 and E2 and a line T representing the background signal.

[0101] Figure 6 is a representation of a body image in real space without any mathematical processing to reduce or even remove the background signal signature. Comparing the images shown in Figures 6 and 7, it is clear that the background signal signature is significantly reduced compared to the signal characterizing the body.

[0102] The invention also relates to a computer program comprising instructions for carrying out the steps of the method according to the invention when the program is executed by a computer.

[0103] The invention also relates to an MRI device provided with a unit adapted to implement a computer program according to the invention, said MRI device comprising said computer program.

[0104] Naturally, the invention is not limited to the described embodiments, and variants can be added thereto without departing from the scope of the invention as defined by the claims.

Claims

1. 1. A method for imaging a body using an MRI device, the method comprising a basic sequence of repetition time TR, the method comprising: - generating at least one echo signal over an echo time range PE by subjecting the body, positioned within an examination volume of the MRI device, to a sequence of RF pulses produced by an RF coil and to magnetic field gradients produced by a gradient coil; performing an echo measurement of said at least one echo signal by means of said RF coil; - performing a basic sequence, which includes performing a background measurement by said RF coil over a time range known as a background range PF, which is different from said echo range PE and which represents a background signal, The method further comprising: a) repeating the base sequence as many times as necessary to form, in Fourier space, a Fourier image of the body from the echo signals and a Fourier image of the background from the background measurements; b) processing either the Fourier image of the body and the Fourier image of the background, or the echo signal and the background signal, to obtain an image of the body in real space, wherein a signature of the background signal is reduced or even eliminated.

2. Step b) comprises processing the Fourier image of the body and the Fourier image of the background, step b) being carried out in two sub-steps b1) and b2), step b1) comprises mathematical processing of the Fourier image of the background and the Fourier image of the body to subtract the background signal from the Fourier image of the body to form a processed Fourier image in Fourier space; The method of claim 1 , wherein step b2) comprises transforming the processed Fourier image to obtain an image of the body in real space.

3. The method of claim 2 , wherein said mathematical processing step b1) comprises at least one of the following methods: spectral subtraction, anisotropic diffusion filtering, non-local means.

4. Step b) is carried out in two sub-steps b3) and b4), step b3) comprises transforming the Fourier images of the body and the Fourier images of the background into intermediate body images and images of the background in real space, respectively; The method of claim 1 , wherein step b4) comprises processing the intermediate body image and the background image to subtract a background signal contribution in the intermediate body image to obtain an image of the body in real space.

5. The method of claim 4 , wherein step b4) comprises processing by principal component analysis.

6. The generation of the at least one echo signal is achieved by a permanent magnetic field B imposed on the body located within the examination volume of the MRI device during the repetition of the basic sequence. ０ 6. The method of claim 1, comprising carrying out an electromagnetic pulse, known as the initial electromagnetic pulse, which is orthogonal to the

7. 7. The method of claim 6, wherein the initial electromagnetic pulse is preceded by at least one electromagnetic rephasing pulse and coincides with a slice selection with one of the gradient coils referred to as a slice plane selection coil, and the measurement of the at least one echo signal performs phase and frequency encoding with two of the gradient coils referred to as a phase gradient coil and a frequency gradient coil, respectively.

8. The method of claim 7 , wherein the base sequence is a spin echo sequence comprising a single measurement of an echo signal, and the background measurement is performed after the measurement of the echo signal.

9. 9. The method of claim 8, wherein the background measurements are performed with the same phase and frequency coding as is performed during the measurements of the echo signals.

10. 8. The method of claim 7, wherein the base sequence is a fast spin echo sequence, the fast spin echo sequence including repeating subsequences within the sequence, the subsequences including the electromagnetic rephasing pulse and the measurement of an echo signal.

11. 7. The method of claim 6, wherein the basic sequence is a 3D fast spin echo sequence, the 3D fast spin echo sequence including repeating N basic subsequences within the sequence, each basic subsequence including an electromagnetic rephasing pulse and the measurement of an echo signal.

12. The method according to claim 11 , wherein the basic sequence comprises a single background measurement, which is advantageously performed after the basic subsequence.

13. The method of claim 11 , wherein the base sequence comprises N background measurements, each background measurement being performed within its own base subsequence.

14. An MRI device provided with a unit having a computer program loaded thereon, the MRI device being configured to carry out the method according to any one of claims 1 to 13.

Images