Method for forming an image of a body by means of an MRI device

Abstract

The invention relates to a method for imaging a body, the method implementing a basic sequence that comprises: - 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 by the RF coil representative of a background signal; the method comprising the following steps: a) repeating the basic sequence as many times as necessary so as to form a Fourier image of the body and a Fourier image of the background from the background measurements; b) processing the Fourier image of the body and of the background so as to obtain an image of the body in which a signature of the one or more background signals is reduced or even eliminated.

Description

METHOD FOR FORMING AN IMAGE OF A BODY USING AN MRI DEVICE FIELD OF THE INVENTION

[0001] The present invention relates to the field of magnetic resonance imaging. In particular, the present invention relates to a method for forming an MRI image of a body using an MRI device. TECHNOLOGICAL BACKGROUND OF THE INVENTION

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

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

[0004] In particular, the magnetic moments associated with these nuclear spins preferentially align along an axis, called the z axis, determined by the orientation of the main magnetic field so as to create "a magnetization of the body".

[0005] An MRI device also includes gradient coils configured to produce small-amplitude, spatially varying magnetic fields when a current is applied thereto. More specifically, the gradient coils are configured to produce a magnetic field component that is aligned parallel to the main magnetic field, and that varies linearly in magnitude with position along one of the x, y, or z axes (the x, y, and z axes being pairwise perpendicular).

[0006] Thus, the combined effects of the magnetic fields imposed by the gradient coils make it possible to spatially code each of the positions of the body to be probed.

[0007] An MRI device also comprises at least one radiofrequency (RF) coil intended to act as an RF transmitter / receiver. In particular, the at least one radiofrequency coil is configured to emit pulses of RF energy of a frequency equal to or close to the resonance frequency of the spins of the hydrogen nuclei and which is at least partly absorbed by these nuclei.

[0008] Once the RF emission is interrupted, the nuclear spins relax to return to their initial energy state and in turn emit an RF signal that can be collected by at least one RF coil. This RF signal is then processed using a computer and reconstruction algorithms to obtain an image of the body.

[0009] The main magnetic field, generally between 1.5 Tesla and 3 Tesla, makes it possible to achieve relatively reasonable signal-to-noise ratios and consequently to form images of the human body of sufficient quality and over durations of the order of a minute or more.

[0010] However, there are circumstances in which it is not possible to implement a main magnetic field of such intensity. Portable MRI devices are one example. These typically include a permanent magnet or electromagnets of limited capacity, and cannot impose a main magnetic field of an intensity greater than 60 mT, or even greater than 200 mT, without penalizing the mass or size of the MRI device in question.

[0011] This limitation in terms of main magnetic field intensity directly affects the performance of the MRI device, and the images obtained are affected by noise. This noise includes two components, respectively, the correlated component and the uncorrelated component.

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

[0013] The correlated component, for its part, has a signature that is likely to mask certain details of the images obtained using the MRI device in question. Patent US9797971B2 addresses this aspect, and thus proposes an MRI device configured to suppress the correlated component. In particular, the device proposed in patent US9797971B2 comprises, in addition to an RF coil dedicated to MRI measurement, a secondary coil intended for evaluating the correlated noise likely to be emitted and experienced by the MRI device. The secondary coil, as described in patent US9797971B2, is the subject of a compromise in terms of positioning with respect to the RF coil. More particularly, the secondary coil is arranged at a distance from the body being measured in order to remain insensitive to the signal emitted by said body, but sufficiently close to the RF coil in order to detect noise of the same nature as the latter.

[0014] However, the MRI device proposed in patent US9797971B2 is not satisfactory.

[0015] Indeed, this device does not allow a reduction of correlated noise without the consideration of approximations which affect the quality of the images obtained. Indeed, this document proposes to neglect the uncorrelated component, however detected by the secondary coil, in order to establish a transfer function between the RF coil and the secondary coil.

[0016] Furthermore, to the extent that the secondary coil is positioned to detect noise of the same nature as that to which the RF coil is subjected, said secondary coil is also, and necessarily, sensitive to the signal emitted by the body. This latter aspect, not discussed in patent US9797971B2, can be a source of error on the MRI image of the body.

[0017] An aim of the present invention is to propose a method for forming an image of a body by means of a magnetic resonance imaging device making it possible to reduce, or even eliminate, any signature of correlated noise. BRIEF DESCRIPTION OF THE INVENTION

[0018] The present invention relates to a method for imaging a body using an MRI device, the method implementing an elementary sequence of a repetition duration TR which comprises:

[0019] - generating at least one echo signal, over a PE echo time range, by subjecting the body positioned in an examination volume of the MRI device to a sequence of RF pulses produced by an RF coil, as well as to magnetic field gradients produced by gradient coils;

[0020] - an echo measurement of the at least one echo signal by the RF coil;

[0021] - a background measurement, by the RF coil, over a time range called background PF distinct from the echo range PE, and representative of a background signal;

[0022] the method comprising the following steps:

[0023] (a) repeating the elementary sequence as many times as necessary in order 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;

[0024] b) a step of processing either the Fourier image of the body and the Fourier image of the background or the echo signals and the background signals, so as to obtain an image of the body in real space and in which a signature of the background signal(s) is reduced or even eliminated.

[0025] The implementation of the present invention thus makes it possible to obtain an image of the body in real space essentially devoid of a signature of the background signal(s).

[0026] According to one embodiment, step b) comprises the processing of the Fourier image of the body and the Fourier image of the background, step b) being executed in two sub-steps b1) and b2),

[0027] step b1) comprising mathematical processing of the background Fourier images and of the body in order to subtract the background signal from the Fourier image of the body in order to form, in the Fourier space, a processed Fourier image,

[0028] and step b2) comprising a transformation of the processed Fourier image in order to obtain an image of the body in real space.

[0029] According to one embodiment, step b1) of mathematical processing comprises at least one of the methods chosen from: spectral subtraction method, anisotropic diffusion filtering, piecewise denoising.

[0030] According to one implementation method, step b) is executed in two sub-steps b3) and b4),

[0031] step b3) comprising a transformation of the Fourier image of the body and the Fourier image of the background into, respectively, an image of the intermediate body and an image of the background in real space,

[0032] step b4) comprising processing the image of the intermediate body and the background image in order to remove the contribution of the background signal in the image of the intermediate body in order to obtain an image of the body in real space.

[0033] According to one implementation mode, step b4) comprises processing by principal component analysis.

[0034] According to one embodiment, the generation of at least one echo signal comprises the implementation of an electromagnetic pulse, called the initial electromagnetic pulse, orthogonal to a permanent magnetic field B0 imposed on the body placed in the examination volume of the MRI device during the repetition of the elementary sequence.

[0035] According to one embodiment, the initial electromagnetic pulse is followed by at least one rephasing electromagnetic pulse and concomitant with the selection of a slice by means of one of the gradient coils, called the cutting plane selection coil, while the measurement of the at least one echo signal implements phase and frequency coding by two of the gradient coils called, respectively, the phase gradient coil and the frequency gradient coil.

[0036] According to one embodiment, the elementary sequence is a spin echo sequence which comprises a single measurement of an echo signal, in which the background measurement is performed after said measurement of the echo signal.

[0037] According to one implementation mode, the background measurement is performed with phase and frequency coding identical to the phase and frequency coding implemented during the measurement of the echo signal.

[0038] According to one embodiment, the elementary sequence is a fast spin echo sequence which comprises a repetition within said sequence of a sub-sequence, the sub-sequence comprising the rephasing electromagnetic pulse and the measurement of an echo signal.

[0039] According to one embodiment, the elementary sequence is a 3D fast spin echo sequence which comprises a repetition within said sequence of N elementary sub-sequences, each elementary sub-sequence comprising the rephasing electromagnetic pulse and the measurement of an echo signal.

[0040] According to one mode of implementation, the elementary sequence comprises a single background measurement, advantageously executed following the elementary sub-sequences.

[0041] According to one implementation mode, the elementary sequence comprises N background measurements, each background measurement being executed within its own elementary sub-sequence.

[0042] Computer program comprising instructions which, when the program is executed by a computer or calculator, cause the latter to implement the steps of the method according to the present invention.

[0043] MRI device provided with a unit configured to implement the computer program according to the present invention, said MRI device comprising said computer program.

[0044] Other characteristics and advantages of the invention will emerge from the detailed description of a method for imaging a body which will follow with reference to the appended figures in which:

[0045] This is a schematic representation according to an exploded view of a magnetic resonance imaging device;

[0046] This is a schematic representation of a fast 3D spin echo sequence that may be considered for implementing the method of forming an MRI image according to the present invention;

[0047] This is a representation of a first example of a fast 3D spin echo sequence of the ;

[0048] Laest is a Fourier image of a body;

[0049] This is a Fourier image of the background;

[0050] This is an image of the body obtained without implementing the present invention;

[0051] It is an image of a body in real space. DETAILED DESCRIPTION OF THE INVENTION

[0052] The present invention relates to a method for forming an image of a body using a magnetic resonance imaging (hereinafter "MRI") device.

[0053] More particularly, the present invention relates to a method for forming an image of a body arranged in an examination volume of the MRI device. In this regard, it is known that such a device is subject to surrounding noise, hereinafter referred to as a "background signal". This background signal, generally associated with surrounding electromagnetic signals, can have a negative impact on the performance of the MRI device. More particularly, this background signal can have a signature on the images of the body likely to be obtained with an MRI device, and in particular mask the details thereof.

[0054] To overcome this drawback, MRI devices are generally isolated using specific shielding (e.g. Faraday cages). However, this solution remains of little interest when considering a portable MRI device.

[0055] To this end, the present invention relates to a method for imaging a body using an MRI device, the method implementing an elementary sequence of a repetition duration TR which comprises:

[0056] - generating at least one echo signal, over a PE echo time range, by subjecting the body positioned in an examination volume of the MRI device to a sequence of RF pulses produced by an RF coil, as well as to magnetic field gradients produced by gradient coils;

[0057] - an echo measurement of the at least one echo signal by the RF coil;

[0058] - a background measurement, by the RF coil, over a time range called background PF distinct from the echo range PE, and representative of a background signal;

[0059] the method comprising the following steps:

[0060] (a) repeating the elementary sequence as many times as necessary in order 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;

[0061] (b) a step of processing either the Fourier image of the body and the Fourier image of the background or the echo signals and the background signals, so as to obtain an image of the body in real space essentially devoid of a signature of the background signal(s).

[0062] For example, and according to a first alternative, step b) comprises the processing of the Fourier image of the body and the Fourier image of the background, step b) being executed in two sub-steps b1) and b2).

[0063] Step b1) includes mathematical processing of the background and body Fourier images to subtract the background signal from the body Fourier image to form, in Fourier space, a processed Fourier image.

[0064] Step b2) includes a transformation of the processed Fourier image in order to obtain an image of the body in real space.

[0065] According to a second alternative, step b) is executed in two sub-steps b3) and b4).

[0066] Step b3) comprises a transformation of the Fourier image of the body and the Fourier image of the background into, respectively, an intermediate body image and a background image in real space.

[0067] Step b4) comprises processing the image of the intermediate body and the background image in order to remove the contribution of the background signal in the image of the intermediate body in order to obtain an image of the body in real space.

[0068] It is understood that the MRI image formation method according to the terms of the present invention is particularly suitable for the implementation of a low-field MRI device (for example of the portable MRI device type), namely an MRI device operating with a main magnetic field of less than 0.5 Tesla, or even less than 0.2 Tesla. Nevertheless, the present invention should not be limited to this aspect. In particular, those skilled in the art may consider the implementation of the method according to the present invention for operating a high-field MRI device.

[0069] This is a representation of an MRI device 1 suitable for implementing the imaging method according to the present invention.

[0070] The MRI device 1 notably 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 notably extend along an elongation axis z.

[0071] More particularly, the magnet 2 defines a housing 3 opening through a first opening 4 and a second opening 5 opposite one another along the elongation axis z.

[0072] In this regard, the magnet 2 is arranged to allow the insertion of a body, and more particularly a human body, into the housing 3 through the first opening 4 along the elongation axis z.

[0073] The magnet 2 can be configured to impose a main magnetic field B0 oriented along an axis perpendicular to the elongation axis z, in an area, called the analysis area, of the housing 3.

[0074] In this respect, the magnet 2 may comprise an assembly of elementary magnets, and in particular arranged in a series of Halbach rings. Patent EP3368914B1 gives an example of this. However, the invention is not limited to the configuration described in this patent.

[0075] For example, the magnet 2 is configured to impose a main magnetic field with an amplitude of less than 0.1 Tesla, advantageously less than 0.065 Tesla, even more advantageously less than or equal to 0.05 Tesla.

[0076] The MRI device 1 also comprises a set of gradient coils 6. The gradient coils 6 are notably configured to produce small amplitude, spatially varying magnetic fields when a current is applied to them.

[0077] More particularly, the gradient coils 6 are designed to produce a magnetic field component that is aligned parallel to the main magnetic field, and that varies linearly in magnitude with position along one of the x, y, or z axes (the x, y, and z axes forming an orthogonal coordinate system).

[0078] Thus, the combined effects of the magnetic fields imposed by the gradient coils 6 make it possible to spatially code the signals coming from a body present in the housing 3 and intended to be probed. Spatial encoding is manifested in particular by a variation in the resonance energy of the nuclear spins of the hydrogen nuclei included in the body intended to be probed and present in the analysis zone. In other words, the nuclear spins of the hydrogen nuclei are subjected to a magnetic field which differs from one position to another.

[0079] The MRI device 1 further comprises a radiofrequency coil 8 (hereinafter “RF coil”). The RF coil 8 is in particular arranged in the housing 3 and delimits an examination volume of the MRI device 1 and in which a body is intended to be housed.

[0080] Finally, the MRI device 1 also comprises means for controlling said MRI device 1. These control means may in particular comprise a computer 13 interfaced, via interfacing means 11, with the various elements forming the MRI device 1.

[0081] The MRI device 1 thus described can be implemented for carrying out the method of forming an MRI image of a body placed in the examination volume.

[0082] According to the present invention, a body image may be two-dimensional or three-dimensional.

[0083] Thus, the method for forming an image according to the present invention comprises the implementation of an elementary sequence SE. In particular, the elementary sequence SE may be of a duration called the repetition duration TR.

[0084] Thus, is a schematic representation of an elementary sequence SE that may be considered in the context of the execution of the method according to the present invention. In particular, the elementary sequence SE represented in is a so-called fast 3D spin echo sequence (“Turbo Spin Echo 3D” according to English terminology). The invention is however not limited to this sequence alone and those skilled in the art will be able to adapt the principles thereof to other types of sequences. For example, it may be considered to implement, in the context of the present invention, an elementary sequence SE of spin echo, a fast spin echo sequence.

[0085] Thus, the elementary sequence SE according to the present invention may comprise the generation of at least one echo signal SiE, over a PE echo time range, by subjecting the body to be imaged positioned in an examination volume of the MRI device to a sequence of RF pulses. The RF pulses are notably produced by the RF coil 8. The gradient coils, denoted Gx, Gy and Gz, are, for their part, implemented to spatially code the body placed in the examination volume.

[0086] Note that gradient coils are also implemented, or powered, throughout the execution of a measurement sequence (in particular during the execution of the elementary sequence(s)) in order to homogenize the main magnetic field B0 to which the body is subjected in the analysis volume. In other words, gradient coils produce local fields which are added to the main magnetic field B0 and therefore the resultant has a homogeneity greater than that of the main magnetic field B0 in the analysis volume.

[0087] The elementary sequence SE represented in the first place comprises the emission of an RF pulse, called the main electromagnetic pulse, and intended to excite the entire volume of the body. There are situations for which the said main electromagnetic pulse is called a 90° pulse, in particular when the pulse considered is in a plane orthogonal to the main magnetic field B0.

[0088] The elementary sequence SE also includes N (N integer strictly greater than 1) elementary sub-sequences SSE. In particular, the N elementary sub-sequences are executed successively and following the emission of the main electromagnetic pulse.

[0089] Each elementary SSE subsequence includes the following executed successively:

[0090] (i) the emission of an RF pulse, called rephasing, by the RF coil;

[0091] (ii) a phase coding, called CP, performed using the gradient coils Gx and Gz in order to select a line Ky in Fourier space (also known as K space).

[0092] (iii) concomitantly performing an echo measurement of an SE echo signal by the RF coil and frequency coding by the Gy gradient coil.

[0093] Optionally, the elementary subsequence SSE may include a step (iv) executed after step (iii) making it possible to invert the phase coding (denoted CPi on the) executed by the gradient coils Gx and Gz.

[0094] Step (iii) makes it possible in particular to fill, for a given phase coding, a frequency line Ky of the space K.

[0095] It is understood that echo measurement by the RF coil involves the interfacing means, for example an analog-to-digital converter (ADC). More specifically, a measurement by the RF coil involves the activation of the analog-to-digital converter. When no measurement is required, the analog-to-digital converter is deactivated.

[0096] During the course of an elementary SE sequence, the SiE spin echo signals occur at well-defined times, called TE echo times. In particular, and from the instant of emission of the main electromagnetic pulse, the SiE spin echo signals are regularly spaced from each other by a TE echo time. Furthermore, each spin echo is spread over a PE echo time range.

[0097] Furthermore, each elementary subsequence SSE is associated with its own phase coding. In other words, the execution of an elementary sequence SE makes it possible to fill as many Ky lines of the space K as there are elementary subsequences SSE in said elementary sequence SE. In particular, the execution of an elementary sequence makes it possible to fill N different Ky lines in the space K.

[0098] According to the present invention, the elementary sequence SE comprises at least one background measurement MF, by the RF coil, over a time range called background PF distinct from the echo time range PE, and representative of a background signal.

[0099] Considering a PF background time range distinct from the PE echo time range (in other words these two ranges do not have any overlap between them) allows the RF coil to measure only the environmental signal and without spin echo likely to come from the body.

[0100] A background measurement can be performed at any time distinct from the echo times. In particular, the background measurement, which is implemented by the RF coil, can occur before or after a spin echo measurement.

[0101] According to a first example illustrated in the, the MF background measurement can be performed following the SSE elementary subsequences. In particular, the MF background measurement implements frequency coding using the Gy gradient coil. This MF background measurement makes it possible to obtain a frequency coding line. This line is consequently used to fill, in the K space, as many Ky lines as there are SSE elementary subsequences in the SE elementary sequence.

[0102] Alternatively, and according to a second example, the elementary sequence SE comprises a plurality of background measurements MF. More particularly, the elementary sequence SE comprises as many background measurements MF as there are elementary sub-sequences SSE. In particular, and according to this second example, each sub-element SSE is associated with a background measurement. For example, and without however limiting the invention to this aspect, the background measurement may comprise a Gx and Gz phase coding identical to that imposed during the execution of the elementary sub-sequence with which it is associated.

[0103] Regardless of the example considered, the MF background measurement(s) is / are performed on a time range distinct from the echo time ranges.

[0104] The method according to the present invention thus comprises a step a) of repeating the elementary sequence as many times as necessary in order to form, in the Fourier space, a Fourier image of the body, from the echo signals and a Fourier image of the background from the background measurements.

[0105] Step a) is followed by a step b) of processing either the Fourier image of the body and the Fourier image of the background or the echo signals and the background signals, so as to obtain an image of the body in real space essentially devoid of a signature of the background signal(s).

[0106] For example, and according to the first alternative, step b) comprises the processing of the Fourier image of the body and the Fourier image of the background, step b) being executed in two sub-steps b1) and b2).

[0107] Step b1) includes mathematical processing of the background and body Fourier images in order to subtract the background signal from the body Fourier image and to form, in Fourier space, a processed Fourier image.

[0108] The mathematical processing carried out during step b1) may include at least one of the methods chosen from: spectral subtraction method, anisotropic diffusion filtering, piecewise denoising.

[0109] In this regard, the spectral subtraction method is described in the paper M Arcan et al.: “Denoising MRI using spectral subtraction.” IEEE transactions on bio-medical engineering vol. 60(6): 1556-1562 (2013).

[0110] Those skilled in the art wishing to implement anisotropic diffusion filtering may consult the 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).

[0111] Concerning piecewise denoising, a person skilled in the art will find a description in the document Buades A et al., “non-local algorithm for image denoising”, Proc IEEE Comput Soc Conf Comput Vis Pattern Recognit, vol. 2:60–65 (2005).

[0112] In general, it may be considered to execute step b1) according to a method belonging to at least one of the classes chosen from: spectral subtraction method, a Wiener type method, a subspace method, a method based on a statistical model.

[0113] In this regard, the skilled person may consult the document 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.

[0114] Step b2) includes a transformation of the processed Fourier image in order to obtain an image of the body in real space.

[0115] This transformation may include the implementation of a Fourier transform.

[0116] Alternatively, the invention may implement 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).

[0117] According to a second alternative, step b) is executed in two sub-steps b3) and b4).

[0118] Step b3) comprises a transformation of the Fourier image of the body and the Fourier image of the background into, respectively, an intermediate body image and a background image in real space.

[0119] This transformation may include the implementation of a Fourier transform.

[0120] Step b4) comprises processing the image of the intermediate body and the background image in order to remove the contribution of the background signal in the image of the intermediate body in order to obtain an image of the body in real space.

[0121] Advantageously, step b4) comprises processing by principal component analysis.

[0122] In this regard, this treatment is described in the document 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).

[0123] The invention has been described with coordinates x, y, z (in relation to the gradient coils Gx, Gy, and Gz). It is understood, but not necessary to specify, that the order of these coordinates has been chosen arbitrarily so that a person skilled in the art may consider a different order.

[0124] The method according to the present invention thus makes it possible to remove the background signal from an MRI image. This method proposes in particular to insert an additional event during the execution of an elementary sequence for measuring a background signal with the RF coil. Unlike the solution proposed in patent US9797971B2, the method according to the present invention does not impose any approximations during the execution of step b).

[0125] La, la, laet laare illustrations of the implementation of the present invention according to the first alternative for imaging two samples E1 and E2.

[0126] In particular, la is a Fourier image of the body while la is a Fourier image of the background.

[0127] The execution of a step b1) of mathematical processing of these two Fourier images of the background and of the body makes it possible to subtract the background signal from the Fourier image of the body and to form, in the Fourier space, a processed Fourier image (not shown). The mathematical processing implemented in the context of this example includes in particular a spectral subtraction method.

[0128] La represents the Fourier image of the body (the two samples E1 and E2), in real space, obtained by transforming the Fourier image. This image shows the two samples E1 and E2 as well as a trace T representative of the background signal.

[0129] The is a representation of the body image in real space without mathematical processing intended to reduce or even eliminate the background signal signature. Comparing the images represented at the and at the shows that the background signal signature is significantly reduced compared to the signal characterizing the body.

[0130] The invention also relates to a computer program comprising instructions which, when the program is executed by a computer or a calculator, cause the latter to implement the steps of the method according to the present invention.

[0131] The invention also relates to an MRI device provided with a unit configured to implement the computer program of the present invention, said MRI device comprising said computer program.

[0132] Of course, the invention is not limited to the embodiments described and variant embodiments can be made without departing from the scope of the invention as defined by the claims.

Claims

A method for imaging a body using an MRI device, the method employing an elementary sequence of a repetition duration TR which comprises: - the generation of at least one echo signal, over an echo time range PE, by subjecting the body positioned in an examination volume of the MRI device to a sequence of RF pulses produced by an RF coil, as well as to magnetic field gradients produced by gradient coils; - an echo measurement of at least one echo signal by the RF coil; - a background measurement, by the RF coil, over a time range called background PF distinct from the echo time range PE, and representative of a background signal; the method comprising the following steps: a) the repetition of the elementary sequence as many times as necessary in order 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) a processing step of either the Fourier image of the body and the Fourier image of the background or of the echo signals and the background signals, so as to obtain an image of the body in real space and in which a signature of the background signal(s) is reduced or even removed.; A method according to claim 1, wherein step b) comprises processing the Fourier image of the body and the Fourier image of the background, step b) being carried out in two substeps b1) and b2), step b1) comprising mathematical processing of the Fourier images of the background and the body in order to subtract the background signal from the Fourier image of the body in order to form, in Fourier space, a processed Fourier image, and step b2) comprising a transformation of the processed Fourier image in order to obtain an image of the body in real space. A method according to claim 2, wherein the mathematical processing step b1) comprises at least one of the following methods selected from: spectral subtraction method, anisotropic scattering filtering, piecewise denoising. A method according to claim 1, wherein step b) is carried out in two substeps b3) and b4), step b3) comprising a transformation of the Fourier image of the body and the Fourier image of the background into, respectively, an intermediate body image and a background image in real space, step b4) comprising a processing of the intermediate body image and the background image in order to subtract the contribution of the background signal in the intermediate body image in order to obtain a body image in real space. A method according to claim 4, wherein step b4) comprises a principal component analysis treatment. A method according to any one of claims 1 to 5, wherein the generation of at least one echo signal includes the implementation of an electromagnetic pulse, referred to as the initial electromagnetic pulse, orthogonal to a permanent magnetic field B0 imposed on the body disposed in the examination volume of the MRI device during the repetition of the elementary sequence. A method according to claim 6, wherein the initial electromagnetic pulse is followed by at least one rephasing electromagnetic pulse and concomitant with the selection of a cut by means of one of the gradient coils, referred to as the cutting plane selection coil, while the measurement of at least one echo signal implements phase and frequency coding by two of the gradient coils referred to, respectively, as the phase gradient coil and the frequency gradient coil. A method according to claim 7 wherein the elementary sequence is a spin echo sequence comprising a single measurement of an echo signal, wherein the background measurement is performed after said measurement of the echo signal. Method according to claim 8, wherein the background measurement is performed with phase and frequency coding identical to the phase and frequency coding implemented during the measurement of the echo signal. A method according to claim 7, wherein the elementary sequence is a fast spin echo sequence which includes a repetition within said sequence of a subsequence, the subsequence comprising the rephasing electromagnetic pulse and the measurement of an echo signal. A method according to claim 6, wherein the elementary sequence is a 3D fast spin echo sequence comprising a repetition within said sequence of N elementary subsequences, each elementary subsequence comprising the rephasing electromagnetic pulse and the measurement of an echo signal. A method according to claim 11, wherein the elementary sequence comprises a single background measure, advantageously executed following the elementary sub-sequences. A method according to claim 11, wherein the elementary sequence comprises N background measures, each background measure being executed within its own elementary subsequence. MRI device provided with a unit on which a computer program is loaded, said MRI device being configured to implement the method according to any one of claims 1 to 13.

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