DESCRIPTION

FIELD OF APPLICATION

[0001] The present invention relates to an apparatus for data acquisition and the creation of magnetic resonance images, and to a method for data acquisition and creation of magnetic resonance images.

PRIOR ART

[0002] As is known, the creation of magnetic resonance images (magnetic resonance imaging) is based on the use of a static magnetic field (indicated as Bo) and radiofrequency electromagnetic fields.

[0003] The object under examination, usually a patient, is immersed in the main static magnetic field and uniform Bo so that the magnetization vectors of the protons of the atoms begin a precession motion about an axis that has the same direction as the field Bo.

[0004] The precession frequency is said the Larmor frequency and is dependent on the physical properties of the nuclei under examination, and in particular on the gyromagnetic ratio y and on the intensity of the field Bo according to the relation:

fL= yBo .

[0005] By exciting the nuclei with RF (radiofrequency) pulses to the Larmor frequency, the various magnetization vectors are rephased and their direction is changed so as to make a magnetization component appear in the plane that is orthogonal to the direction of Bo.

[0006] After having excited the system to a sufficient degree, the radiofrequency pulse is interrupted. Under the action of Bo, the system will tend to return to a state of equilibrium, thereby transferring the accumulated energy to the external environment in the form of an electromagnetic wave.

[0007] The relaxation signal is collected by RF antenna elements called RF coils (MRI - Magnetic Resonance Imaging - coils ) .

[0008] The signal detected during the relaxation process is processed and, on account of this, it is possible to obtain data and to create the images by means of the principle of physics of nuclear magnetic resonance.

[0009] In order to award the various signals received a spatial position and therefore to reconstruct the images, the main magnetic field Bo needs to be changed in the three directions by means of three field gradients: Gx, Gy and Gz .

[0010] An apparatus as per the prior art for creating magnetic resonance images, which is used in medical diagnostic, will now be briefly described. [0011] The apparatus comprises a main magnet that generates the static magnetic field Bo, which, in clinical applications, assumes values that are generally between 0.2 T and 4 T.

[0012] There are essentially three types of magnets used in magnetic resonance tomographs: permanent magnets, resistive magnets and superconductor magnets. As described previously, in order to have an origin and a spatial orientation of the data obtained and therefore to correctly reconstruct the image, three magnetic field gradients have to be available in the three spatial directions. This task is fulfilled by gradient coils.

[0013] A shield is generally positioned between the field coils and the gradient coils.

[0014] The radiofrequency coils with which a magnetic resonance system is provided can essentially be categorized into two categories: body coil and other RF coils intended for specific anatomical districts.

[0015] The body coil is generally housed inside the space that also contains the magnet and the gradient coils.

[0016] This type of coil is generally both a transmitting and a receiving (T/R) coil and can solely be used to transmit the radiofrequency impulse or to transmit the impulse and then to receive the return signal that originates from the anatomical district under examination. [0017] In particular, it is used exclusively as a transmitter (T) when used in combination with a coil that is exclusively assigned with collecting the magnetic resonance signal.

[0018] Instead, said coil can be used as a T/R coil, for example, when examining particularly voluminous districts, such as the chest or abdomen.

[0019] As already mentioned, the dedicated RF coils are the specific types of antenna that are directly applied to the patient and are conceived and designed for optimizing the transfer and collection of the signal from the particular anatomical district, these can be exclusively receiving (R) or both transmitting and receiving (T/R) .

[0020] The patient is typically laid down on a bed that, by means of an electromechanical movement system, allows to correctly position the anatomical district to be examined inside the magnet.

[0021] Lastly, it is provided the electronic unit necessary for managing the different peripheral devices that the system consists of. The electronic part may be of different types and it may comprise different components; in any event, the electronics can be summarized, purely by way of example, as indicated in the following.

[0022] The electromagnetic fields of the RF coils are managed by means of an RF amplifier that can generate radiofrequency signals in a frequency band that is dependent on the static field Bo of the system. The three gradients are typically managed individually by devices called gradient amplifiers that, in turn, are generally supplied with power by one or more dedicated power supplies .

[0023] Instead, the signals collected in order to form the image are sent to a reconstructor that reconstructs the images. The reconstructor is a computer provided with dedicated software and algorithms.

[0024] Although the prior art is widely appreciated and used, it is not devoid of disadvantages.

[0025] In clinical environments, the magnetic resonance images are currently generally processed by the signals from the hydrogen nuclei ¹ H, even if it is known that the physical phenomenon of the nuclear magnetic resonance would also make it possible to receive information from other species, such as ² H, ¹⁵ N, ¹⁷ 0, ³ He, ¹³ C, ¹⁹ F, ²³ Na, ³¹ P and ¹²⁹ Xe .

[0026] As mentioned previously, different atoms have different gyromagnetic ratios y and therefore, when the magnetic field Bo is the same, they resonate at different frequencies .

[0027] Once they resonate at different frequencies, specific RF coils are necessary for the transmission and receipt of the signal for these frequencies, and an electronic unit that can manage all of these frequencies.

[0028] Alternatively, broadband coils may be provided, adapted to receive different frequencies but this would worsen the performances of the entire system in terms of the quality of the images. Furthermore, the costs associated with the apparatus would be considerably greater and the system would also be more complex than the current systems.

The present invention intends to overcome the limitations of the current nuclear magnetic resonance systems, making the collection of information from not only the hydrogen atoms ¹ H, but also from other nuclei, for example ² H, ¹⁵ N, ¹⁷ 0, ³ He, ¹³ C, ¹⁹ F, ²³ Na, ³¹ P and ¹²⁹ Xe, in order to be able to obtain images, and therefore magnetic resonance examinations possible, which are able to provide more information than the systems of the prior art.

PRESENTATION OF THE INVENTION

[0029] There is therefore the need to overcome the drawbacks and limitations cited with reference to the prior art .

[0030] Therefore, there is the need to provide an apparatus and a method that make it possible to carry out examinations that are able to provide more information than that obtainable by means of the systems of the prior art, in particular by proceeding to use additional atom nuclei .

[0031] This object is achieved by an apparatus for data acquisition and the creation of magnetic resonance images as per claim 1, and by a method for data acquisition and the creation of magnetic resonance images as per claim 10. DESCRIPTION OF THE DRAWINGS

[0032] Additional features and the advantages of the present invention will become clearer from the description given in the following of preferred and non-limiting examples thereof, in which:

Fig. 1 is a schematic view of a possible embodiment of an apparatus according to the present invention; and

Fig. 2 is a schematic view of an alternative embodiment of an apparatus as per the present invention.

[0033] The elements or parts of elements that the embodiments described in the following have in common will be indicated by the same reference numerals.

DETAILED DESCRIPTION

[0034] In fig. 1 it is shown a schematic view of an apparatus for data acquisition and the creation of magnetic resonance images, which is indicated by general reference numeral 12.

[0035] In its essential form, the apparatus 12 comprises : - a first unit 14 adapted to generate a static magnetic field Bo, comprising a main magnet 140;

- a second unit 16 adapted to generate three magnetic field gradients in three directions (x, y, z) that are perpendicular to one another, comprising gradient coils 160;

- a third unit 18 adapted to generate and receive an electromagnetic field having a frequency that is equal to the Larmor frequency, comprising at least one radiofrequency coil 180; and

- a control unit 20 that is connected to the second unit 16 and to the third unit 18.

[0036] The apparatus is characterized in that it comprises an auxiliary unit 22 comprising at least one auxiliary magnet 220, which is adapted to selectively generate a second static magnetic field Boi so as to change the value of the magnetic field Bo generated by the first unit 14 to a value Bo' .

[0037] The second unit 16 adapted to generate the magnetic field gradients may comprise a unit for managing the gradients 50, comprising gradient amplifiers for each gradient coil, which are supplied with power by at least one power supply.

[0038] The auxiliary unit 22, which is adapted to selectively generate a second static magnetic field Boi, may comprise an auxiliary power supply unit 40.

[0039] In accordance with one embodiment, the main magnet 140 can be an electromagnet, a permanent magnet or a superconductor magnet. The main magnet can be adapted to generate a static magnetic field Bo that, for clinical applications, is generally between 0.2 T and 4 T. However, larger ranges, for example up to 8 T or even higher, are possible .

[0040] In accordance with a possible embodiment of the present invention, the first unit 14 can be connected to the control unit 20, for example when the main magnet is an electromagnet or superconductor magnet. In alternative embodiments, the first unit can be provided with an independent control unit (not shown in the attached figures) .

[0041] As mentioned above, for a correct reconstruction of the image, three magnetic field gradients need to be available in the three spatial directions. This task is fulfilled by the second unit 16, and in particular by the gradient coils 160.

[0042] A shield 24 can be positioned between the main magnet 140 and the gradient coils. As shown schematically in Fig. 1, the shield can be grounded.

[0043] The radiofrequency coils 180 with which a magnetic resonance system is provided can be of two types: a body coil 182 and RF coils 184 intended for specific anatomical districts.

[0044] In this regard, the third unit 18 can be provided with at least one power supply unit 60 for the radiofrequency coils 180, which is adapted to send signals to the body coil 182 and to the dedicated RF coils 184.

[0045] In accordance with a possible embodiment of the present invention, the apparatus 12 can comprise an electronic unit 70 that is adapted to receive the signals from the at least one radiofrequency coil 180, and may be suitable for pre-processing the signals.

[0046] The apparatus may also comprise a reconstructor 80, which is connected to the electronic unit 70 that receives the signals processed by the electronic unit 70 in order to present the data received, and to possibly reconstruct the magnetic resonance image.

[0047] The electronic unit 70 and the reconstructor 80 will not be further analyzed because they are elements known per se to an expert in the field.

[0048] In accordance with a possible embodiment, the apparatus 12 can comprise a bed on which the subject to be subjected to resonance is positioned and a bed-controlling unit 30. In accordance with a possible embodiment, shown in the example in Fig. 2, the bed-controlling unit 30 can be connected to the control unit 20. [0049] The control unit 20 is adapted to generate the system signals directed at the radiofrequency amplifiers, to the gradients and to the signal receivers. In addition to this, it is adapted to generate a reference signal that is sent to each peripheral device in order to synchronize the different activities. Therefore, with the type of scanning and the time base specified, the control unit 20 is adapted to manage the signals sent by coordinating the times at which the signal is received by the receiving coils. These signals, entering the receivers, are therefore synchronized by the control unit 20 and converted into images and/or graphs that shall therefore be sent directly to and displayed directly on the operating station 26 of the operator.

[0050] The body coil 182 can be housed inside the space that also contains the main magnet 140 and the gradient coils 160.

[0051] In accordance with a possible embodiment, the body coil 182 can be both a transmitter and a receiver (T/R) . Therefore, the body coil 182 can be exclusively used for transmitting the radiofrequency pulse or for transmitting the pulse and then receiving the return signal from the anatomical district under examination.

[0052] When the body coil 182 is only a transmitter or is only used for transmission, it can be used in combination with a dedicated RF coil 184 exclusively assigned with collecting the magnetic resonance signal.

[0053] In contrast, said coil can also be used as a T/R coil, typically when examining particularly voluminous districts, such as the chest or abdomen.

[0054] As already mentioned, the dedicated RF coils 184 are particular probe types that are directly applied to the patient and are conceived and designed to optimize the transfer and collection of the signal from the particular anatomical district.

[0055] In accordance with a possible embodiment, the dedicated RF coils 184 can be exclusively receiving coils (R) or both transmitting and receiving coils (T/R) .

[0056] The radiofrequency coils 180 can comprise a transmission band and a receiving band of a few MHz (the band is less selective and the coil is more selective) and centered at the Larmor frequency, which is dependent on the static magnetic field of the system. For example, for systems from 1.5 T, for hydrogen ¹ H this is equal to approximately 63.87 MHz.

[0057] In accordance with a possible embodiment of the present invention, a shield 24 can be provided between the gradient coils 160 and the body coil 182.

[0058] In accordance with a possible embodiment, the at least one auxiliary magnet 220 is provided between the main magnet 140 and the gradient coils 160.

[0059] In accordance with alternative embodiments, the at least one auxiliary magnet 220 can be positioned on the outside of the body coil.

[0060] The at least one auxiliary magnet 220 can be an electromagnet or a superconductor magnet.

[0061] When the at least one auxiliary magnet 220 is supplied with power, it will generate a magnetic field Boi that will be added to or subtracted from the main magnetic field Bo generated by the main magnet 140. When the winding of the auxiliary magnet 220 is not supplied with power, the static magnetic field will be equal to that generated by the main magnet 140.

[0062] In accordance with a possible embodiment, the power supply of the auxiliary magnet may be adapted to be adjusted such that, with regards to the field Bo and on the basis of the atom intended to be examined and on the scanning type that has been selected by the operator, the power supply is adapted to generate a predetermined electric current value having a specific direction, for a certain time interval.

[0063] In the description above, it is assumed that just one auxiliary winding is inserted into a superconductor system and is positioned between the main magnet 140 and the gradient coils 160. However, the invention is also applicable to systems comprising different types of magnets and different configurations. Furthermore, several auxiliary magnets 220 might be required, for example two.

[0064] In accordance with a possible embodiment of the present invention, additional shielding, a system for compensating for induced currents, etc. can be provided according to specific requirements, for example in order to prevent spurious currents being created in the various windings, which are able to deform the various fields and change the values for the various physical quantities that are outside the range of optimum values.

[0065] In accordance with a possible embodiment, the apparatus may comprise a magnetic field measurer (not shown) for measuring and verifying the effective attainment of the desired magnetic field.

[0066] The at least one auxiliary magnet 220 adapted to selectively generate a second static magnetic field Boi can be connected to power supply means that can be selectively activated.

[0067] The apparatus 12 is therefore adapted to acquire data and generating magnetic resonance images - nuclear magnetic resonance imaging (MRI) - by using the signal coming from a plurality of atomic species, varying the static magnetic field and always using the same radiofrequency coils 180 used for the transmission and receipt of the RF signals.

[0068] The static magnetic field can be changed using the at least one auxiliary magnet 220, which can generate at least one magnetic field Boi that can be concordant or discordant with respect to the magnetic field Bo generated by the main magnet 140.

[0069] The intensity of the magnetic field Boi is dependent on the current intensity that is passed through said windings, while the direction is dependent on the direction of the currents that are passed through the auxiliary windings.

[0070] In this way, it is possible to establish the intensity and preset directions for the currents that have to circulate in the windings of the auxiliary magnets 220 in order to generate, at the same time as the main static magnetic field Bo, resultant static magnetic fields Bo' , which make it possible to receive information from a group of atoms of interest.

[0071] The resultant static magnetic fields Bo' can also be preset in terms of the type of nucleus from which information is intended to be obtained and can be selectable by the operator by means of an operating station

26.

[0072] The following table shows, purely by example, a few of the most interesting nuclei in nuclear magnetic resonance imaging that is applied to the diagnostics for images and the respective gyromagnetic module ratios. Assuming a static magnetic field Bo that is equal to 1.5 tesla for these immersed atoms, the relative Larmor frequencies are calculated according to the relationship fL= gB ₀ .

[0073] Assuming the transmission and receiving bands of the various RF coils are equal to 1 MHz, it can easily be noted how a set composed of an extremely high number of RF coils would be necessary in order to be able to analyze the different anatomical districts, in addition an electronic unit that is able to manage frequencies that differ from one another to such an extent would be necessary. This results in extremely high acquisition and managing costs and renders the entire system extremely complex and extremely large.

[0074] In accordance with the present invention, a similar table can be created by keeping the resonance frequencies of the various nuclei almost constant, for example around 63,87 MHz (with a deviation of ± 0,5 MHz assuming a transmission band and a receiving band for the various RF coils that is equal to 1 MHz and centered at 63.87 MHz), and by changing the static magnetic field in which the various nuclei are immersed.

[0075] By means of this system, it is therefore possible to carry out the entire examination, thereby analyzing different nuclei, without the need to have to move the patient, who will therefore not be subjected to further stress. As a result, the duration of the examination will be significantly shorter and it is possible to obtain superimposable images that significantly simplify the processing thereof.

[0076] The method for data acquisition and the creation of magnetic resonance images according to the present invention comprises the steps of:

(a) providing an apparatus (12) comprising:

- a first unit 14 adapted to generate a static magnetic field Bo, comprising a main magnet 140;

- a second unit 16 adapted to generate three magnetic field gradients in three directions (x, y, z) that are perpendicular to one another, comprising gradient coils 160;

- a third unit 18 adapted to generate and receive an electromagnetic field having a frequency that is equal to the Larmor frequency, comprising at least one radiofrequency coil 180; and

- a control unit 20 connected to the second unit 16 and to the third unit 18;

(b) applying a first static magnetic field Bo;

(c) acquiring data from a first atomic species and storing such data;

(d) applying a second static magnetic field that is different from said first static magnetic field by means of an auxiliary unit 22 comprising at least one auxiliary magnet 220;

(e) acquiring data from a second atomic species and storing such data;

(f) processing said acquisitions in order to obtain images and/or information by means of magnetic resonance.

[0077] In accordance with a possible embodiment, step

(d) of applying a second static magnetic field that is different from said first static magnetic field is carried out by switching the power supply to the at least one auxiliary magnet 220 on or off.

[0078] According to the present invention, the method provides a first step in which the data coming from a first atomic species that is intended to be analyzed is acquired. This step can be carried out in the presence of the sole static magnetic field Bo generated by the main magnet 140, or with a magnetic field obtained as the sum of the magnetic field Bo and the magnetic field Boi generated by the at least one auxiliary magnet 220.

[0079] Under these conditions, the protons precede at the first Larmor frequency.

[0080] Once this data has been acquired, a second step takes place in which the data of a second atomic species is acquired. This step obviously depends on the preceding step in regards to the definition of the magnetic field, and can be carried out in particular with a magnetic field that is obtained as the sum of the magnetic field Bo and the magnetic field Boi generated by the at least one auxiliary magnet 220 or in the presence of the sole static magnetic field Bo generated by the main magnet 140.

[0081] In any event, the second value of the magnetic field can be predetermined so as to make the nuclei of the second atomic species to be examined resonate at the same Larmor frequency as the first species.

[0082] The data coming from the second atomic species are then acquired.

[0083] The data of the first species and that of the second species can therefore advantageously be acquired by using the same radiofrequency coils for both transmission and receipt.

[0084] In accordance with a possible embodiment, the data from the first atomic species and from the second atomic species are therefore processed and the relative images or graphs are created.

[0085] The above is merely an example of how an examination could be carried out, and therefore does not exhaust all the application possibilities of the invention .

[0086] For example, the method according to the present invention could comprise a second change to the resultant static magnetic field in order to enable a third acquisition and to collect the data relating to a third atomic species. The method could therefore be repeated in order to also acquire data from other atomic species of interest .

[0087] Furthermore, it is possible to carry out a first acquisition using all the active magnets (main magnet 140 and auxiliary magnets 220) and to then subsequently continue to not supply the auxiliary magnets 220 with power and to then lastly acquire data using the sole active field Bo .

[0088] The data can also be processed and images or graphs generated at different times to those mentioned above .

[0089] In particular, in accordance with a possible embodiment of the present invention, the apparatus of the present invention can be used to stabilize the presence and/or the concentration of one or more atomic species of interest .

[0090] In this regard, the apparatus remains substantially the same with respect to that described above, but the information that is received by the control unit is not converted into an image, but is made available in terms of data relating to the presence and/or to the concentration .

[0091] Therefore, the apparatus can also be used in a diagnostic scanning method for detecting the presence and/or the concentration of specific atomic species of interest .

[0092] Furthermore, by supplying appropriate quantities of energy to the various nuclei, it would also be possible to use the apparatus of the present invention in therapy.

[0093] By managing to make only specific atomic species resonate, it is possible to only supply energy thereto in a selective manner. If the quantity of energy supplied is enough to cause a localized and consistent temperature increase, it is possible to carry the cells that find themselves bonded to the resonant atoms to the necrosis.

[0094] In accordance with a possible embodiment of the present invention, the step of processing and displaying the images could follow each acquisition step.

[0095] This second way of carrying out the examination may be preferable when wanting to obtain as soon as possible information regarding the first atomic species analyzed. For example, it would already be possible to immediately start examining the information from the first acquisition while the examination is still taking place. [0096] The examples given are not intended to be restrictive in any way with regard to the mode of acquiring, processing and presenting the data.

[0097] A practical example of applying the principles of the present invention will now be described.

[0098] A system having a static magnetic field Bo from 1.5 T that is generated by the main superconductor magnet 140 is assumed.

[0099] In this case, the resonance frequency of hydrogen ¾ is 63.87 MHz.

[00100] Now suppose that fluorine ¹⁹ F is intended to be examined, which has a gyromagnetic ratio g equal to 40.06 MHz/T. This means that, in order to make fluorine resonate at a frequency of 63.87 MHz, the field will have to increase up to approximately 1.596 T and therefore the at least one auxiliary magnet 220 will have to generate a magnetic field of approximately 0.096 T that is concordant with the static magnetic field generated by the main magnet 140.

[00101] However, in this way, all the rest of the apparatus 12 will continue to work as if it were examining the hydrogen atom, therefore additional modifications are not required.

[00102] Another application relates to the fluorine atom that could be used as a contrast liquid for identification, localization and treatment of tumors, similarly to what is already the case with PET (Positron Emission Tomography) , but with a contrast liquid that does not have to be made radioactive. In fact, during the PET examination, a contrast liquid is generally used, in which the fluorine atoms are radioactive ( ¹⁸ F) and bonded to a transporter molecule that allows them to accumulate at the points of interest (generally cancerous cells) . The fluorine atoms, which are radioactive during the decay, emit positrons and, on account of suitable systems, it is possible to localize the position of the tumors and to study the activity thereof. However, the localization is very rough in PET and this type of examination is therefore often associated with a TAC examination or magnetic resonance examination that gives more information regarding the anatomy. In fact, these days TAC-PET and PET-RM exist, which make it possible to carry out the two types of examinations on the same diagnostic equipment. The implementation of the present invention on magnetic resonance would render this type of examination just as effective as that of PET-RM, but using a non-radioactive contrast liquid.

[00103] It would also be possible to excite the molecules bonded to the tumor cells using electromagnetic fields having suitable frequencies and energies, in order to go straight to therapeutic treatment. For example, it is possible to inject a contrast liquid containing transporter molecules, to which atoms are bonded that, on account of the change in the static magnetic field provided by the apparatus of the present invention, can resonate at a certain known frequency and can be managed by the system. These transporter molecules are the type that only anchor themselves to certain types of cells, for example tumor cells. In this way, the atoms of interest can also be found bonded to the cells to be treated. At this point, it is possible to stimulate the atoms by means of signals having a suitable frequency and energy so as to only heat up the zones in which said atoms are to be deposited in significant amounts. The pulses are provided up until there is enough localized heat to take the cells to which the atoms are bonded to the necrosis.

[00104] The advantages that can be obtained by the apparatus and the method of the present invention are therefore now evident.

[00105] In particular, images are not formed by a fixed static magnetic field and by using different RF coils for the different resonance frequencies or broadband frequencies, together with all the problems that ensue, but by varying the static magnetic field with the aid of one or more additional auxiliary windings. [00106] Furthermore, it is possible to create multinuclear magnetic resonance images on account of the change in the magnetic field that is obtained by supplying or not supplying one or more auxiliary windings with power in combination with that generating the main static magnetic field Bo. In this way, reference is made to just one resonance frequency that makes it possible to use calibrated coils at just one resonance frequency.

[00107] With this application, it is possible to avoid the use of radioactive substances that are very common in nuclear medicine and to therefore render certain examinations harmless for patients, operators and for the community .

[00108] On account of this invention, multinuclear magnetic resonance equipment is therefore provided.

[00109] The principles of the present invention could also be applied to pre-existing equipment.

[00110] In order to meet specific needs, a person skilled in the art will be able to make modifications to the embodiments described above and/or to substitute elements described with equivalent elements, without thereby departing from the scope of the attached claims.