Receiving device with an intracardiac receiving antenna for magnetic resonance imaging or spectroscopy

Abstract

The invention relates to a device (DREC2) for receiving radio frequency signals for a magnetic resonance imaging / spectroscopy system comprising an intracardiac receiving resonant loop (B_REC) and a switch (INT) capable of being alternately in an open state such that the frequency of the receiving antenna (B_REC) is tuned to an operating frequency of the magnetic resonance imaging system, and in a closed state such that the frequency of the receiving resonant loop is detuned, the receiving device comprising a first transmission line (LTR) having a conductor with a distal end electrically connected to the receiving resonant loop (B_REC) and a proximal end electrically connected to the switch (INT) such that the switch is intended to be located outside the human body when the receiving resonant loop (B_REC) is located inside a patient's heart.

Description

[0001] Receiving device with intracardiac receiving antenna for magnetic resonance imaging or spectroscopy

[0002] Field of invention

[0003] The invention relates to the field of intracavitary, in particular intracardiac, magnetic resonance imaging / spectroscopy (MRI / MRS).

[0004] MRI / MRS systems typically include a main magnet to generate a uniform permanent magnetic field Bo, three gradient coils, and an external transmitting antenna to generate excitation radiofrequency (RF) signals to shift the magnetization of the patient's tissues uniformly in space.

[0005] In the context of intracavitary MR, an antenna for receiving RF signals resulting from the excitation of an organ of interest by the RF excitation signals is intended to be brought into contact with the organ of interest, the heart for intracardiac imaging, by vascular route via a natural orifice or by percutaneous route. The advantage of the intracavitary antenna is to allow obtaining optimal spatial selectivity linked to the geometry of the receiving antenna (shape, dimension) and its location as well as improved sensitivity compared to extracorporeal antennas and consequently to increase the signal-to-noise ratio. Spatial selectivity makes it possible to limit the field of view of the images to be acquired and to reduce their acquisition time.The gain in signal-to-noise ratio makes it possible to generate images of good quality and / or with better spatial resolution compared to extracorporeal antennas, which is fundamental for imaging the walls of the heart, particularly the atria whose thickness is between 2 mm and 5 mm.

[0006] The receiving antenna comprises a receiving loop, i.e. a receiving coil, and capacitors for frequency tuning and matching to the characteristic impedance of the transmission line (typically 50 Ohms). The receiving antenna is connected to a receiver of the MRI device by a transmission line integrated in a sheath and intended to carry the radiofrequency signals received by the antenna to the receiver so that the latter can record these signals.

[0007] The receiving antenna is a resonant circuit of type R, L, C whose resonant frequency fR must be equal to the Larmor frequency of the MRI system fo whose value depends on the magnetic induction Bo of the MRI (fo = yBo / 2TT). y is the gyromagnetic ratio of the nucleus of interest, which is very frequently hydrogen, 1 H. As an example, for hydrogen y= 42.57 MHz / Tesla, which gives a resonant frequency of approximately 64 MHz for a magnetic field of 1.5 Teslas.

[0008] Since the transmitting and receiving antennas operate at the same frequency fo, it is essential that the receiving antenna is tuned to the frequency fo during the reception phase of the RF signals emitted by the organ of interest and that it is detuned in frequency during the transmission phase. If this is not the case, a high intensity current can be induced in the receiving antenna during the transmission phase which leads to the following effects:

[0009] - creation of heating points which could burn the patient, or which could induce coagulation necrosis of the tissues in contact with the receiving antenna, which causes safety problems for the patient,

[0010] - creation of an inhomogeneity of the magnetic field Bi generated by the transmitting antenna near the receiving antenna modifying the characteristics of the acquisition technique (modification of contrasts) and deteriorating the quality of the MRI images,

[0011] - potential deterioration of the MRI detection device (hardware damage).

[0012] This switching system must allow rapid and dynamic switching between the two states throughout the acquisition time of the MRI sequence. For this, active decoupling equipment must be used and guarantee sufficient electrical isolation (attenuation difference between the coupled and decoupled state) at the frequency fo to avoid the problems mentioned above.

[0013] Prior art

[0014] Switching between the tuned and detuned state of the receiving antenna is performed dynamically by active decoupling equipment which is capable of temporarily modifying the frequency response of the receiving antenna.

[0015] Active decoupling devices typically include a PIN diode that is supplied with DC current during the transmit phase so that the PIN diode is on and the receiving antenna is detuned in frequency. The PIN diode is no longer supplied with DC current during the receive phase so that the receiving antenna is tuned in frequency.

[0016] The article “Intracardiac MR imaging (ICMRI) guiding-sheath with amplified expandable-tip imaging and MR tracking for navigation and arrhythmia ablation monitoring: Swine testing at 1.5 and 3T”; Schmidt et al, Magnetic Resonance in Medicine, discloses a receiving device comprising intracavitary decoupling equipment.

[0017] However, it can be dangerous for the patient to supply intracavitary equipment, particularly intracardiac equipment, with a direct current of several hundred milliamps. Indeed, such a direct current is likely to cause cardiac arrest in the event of contact between the components of the receiving antenna and the myocardium. Furthermore, this solution poses space problems.

[0018] One aim of the invention is to limit at least one of the aforementioned drawbacks.

[0019] To this end, the subject of the invention is a device for receiving radiofrequency signals for a magnetic resonance imaging system comprising an intracardiac resonant receiving antenna and a switch capable of being alternately in an open state when it is powered by a direct current having a first intensity so that the receiving antenna is tuned to an operating frequency of the magnetic resonance imaging system and in a closed state when it is powered by a direct current having a second intensity so that the receiving antenna is detuned in frequency, the receiving antenna being further intended to be connected to a receiver intended to receive the radiofrequency signals received by the resonant receiving loop, i.e. the resonant receiving antenna, when the switch is in the open state,the receiving device comprising a first transmission line having a conductor having a distal end electrically connected to the resonant receiving antenna and a proximal end electrically connected to the switch such that the switch is intended to be located outside the human body when the receiving antenna is located inside the heart of a patient. In one embodiment, the device comprises, in addition to the first transmission line, a second transmission line having a conductor comprising a distal end electrically connected to the receiving antenna and a proximal end intended to be electrically connected to the receiver and intended to be connected to the receiver to transmit thereto the radiofrequency signals received by the receiving antenna.,

[0020] Advantageously, the receiver is intended to be electrically connected to the receiving transmission line so as to receive radio frequency signals received by the receiving antenna via the receiving transmission line without passing through the decoupling transmission line.

[0021] Advantageously, the receiving antenna comprises a tuning capacitor and a matching capacitor connected in series and connected by a ground point, the tuning capacitor electrically connecting the conductor of the second transmission line to the ground point.

[0022] In another embodiment, the proximal end of the conductor of the first transmission line is intended to be connected to the receiver to transmit to it the radio frequency signals received by the receiving antenna.

[0023] Advantageously, the receiving device comprises an electrical circuit having a negative resistance mounted in series with the switch.

[0024] Advantageously, the matching capacitor electrically connects the ground point to the conductor of the first transmission line.

[0025] Advantageously, the electrical circuit having the negative resistance connects the switch to ground.

[0026] Advantageously, the electrical circuit having the negative resistance is intended to be located outside the human body when the receiving antenna is located inside the heart of a patient.

[0027] In a particular embodiment, the receiving device comprises a sheath receiving the first transmission line, the sheath comprising a proximal end mechanically connected to the switch and a distal end capable of receiving the resonant receiving antenna. Advantageously, the sheath has a diameter less than or equal to 2 mm. The invention also relates to a magnetic resonance imaging or spectroscopy system comprising a receiving device according to the invention, the system comprising a magnetic resonance imaging or spectroscopy device, the magnetic resonance imaging or spectroscopy device comprising a main magnet intended to generate a static magnetic field, a gradient generator comprising gradient coils and a transmitting antenna intended to transmit radiofrequency signals.

[0028] Advantageously, the magnetic resonance imaging or spectroscopy device comprises the receiver.

[0029] Brief description of the figures

[0030] Other characteristics and advantages of the invention will emerge on reading the detailed description which follows, with reference to the appended figures, which illustrate:

[0031] Fig. 1: a schematic representation of an MRI / SRM system having a receiving device according to a first embodiment,

[0032] Fig. 2: a representation of the electrical diagram of the receiving device according to the first embodiment,

[0033] Fig. 3: a representation of the electrical diagram of the receiving device according to a second embodiment,

[0034] Fig. 4: a representation of the electrical diagram of the receiving device according to a third embodiment,

[0035] Fig. 5: a representation of the electrical diagram of the receiving device according to a variant of the third embodiment,

[0036] Fig. 6: A schematic representation of an MRI / SRM system having a receiving device according to the third embodiment.

[0037] Description of the invention

[0038] The invention relates to a receiving device for a magnetic resonance imaging / spectroscopy or MRI / MRS system intended to operate at an operating frequency fo.

[0039] General description of the MRI / SRM system An MRI / SRM system comprising a DREC1 receiving device, a first embodiment of the invention of which is shown in Figure 1. Of course, the MRI / SRM system could alternatively comprise a receiving device according to any of the embodiments and variants described in the present patent application.

[0040] The MRI / MRS system comprises an MRI / MRS device, A, comprising a main magnet GENST for generating a static magnetic field Bo, a gradient generator GENGR comprising gradient coils, a transmitting antenna TRANS_RF for transmitting radiofrequency (RF) signals. The MRI / MRS system, A, comprises a receiving device DREC1 comprising a receiving antenna B_REC for receiving radiofrequency signals resulting from the excitation of an area of ​​interest of a patient by the transmitting antenna TRANS_RF. The MRI / MRS device, A, comprises a receiver REC for receiving the signals received by the receiving device DREC1 and processing them to generate images / spectra.

[0041] The DREC1 receiving device is electrically connected to the MRI device, A, by an INT_FC interface of the MRI / SRM device comprising COD and COT connectors.

[0042] The operating frequency or Larmor frequency fo is proportional to the static magnetic field Bo as specified previously.

[0043] The most common Bo magnetic fields in clinical MRI / MRS are 1.5 Tesla, 3.0 Tesla or 7.0 Tesla but the invention applies to other Bo magnetic fields, for example, between 0.1 Tesla and 11 Tesla.

[0044] The B_REC receiving antenna is an intracardiac resonant antenna.

[0045] By intracardiac resonant receiving antenna B_REC is meant a receiving antenna of the RLC circuit type intended to be inserted into a cavity of the heart of a patient whose body is delimited by dotted lines in figure 1 so as to image an area of ​​the heart by magnetic resonance.

[0046] The receiving device DREC1 comprises an active decoupling device ED1 electrically connected to the intracardiac receiving antenna B_REC. The decoupling device ED1 comprises a decoupling switch INT, which will be described in more detail below, capable of being alternately in an open state when it is powered by a direct current of a first intensity so that the receiving antenna resonates at the frequency fo and in a closed state when it is powered by a direct current of a second intensity so that the antenna no longer resonates at the frequency fo. For example, the decoupling switch is capable of being in the open state when it is not powered by current and in the closed state when it is powered by a second direct current.

[0047] The first current is, for example, zero and the second direct current is non-zero.

[0048] It is said that when the decoupling switch is in the open state, the receiving antenna is tuned to frequency fo and when the switch is in the closed state, the antenna is detuned in frequency and is no longer impedance matched with the transmission line at frequency fo.

[0049] The IRM / SRM device, A, comprises a control device COM capable of electrically controlling the switch by supplying it with a first intensity of direct current and a second intensity of direct current so as to make it change from the open state to the closed state and vice versa and to maintain it in the desired state for a desired duration.The control device COM advantageously comprises a current generator GENC capable of delivering the second current and electrically connected to the switch INT of the decoupling equipment ED1 via a conductor or transmission line LC connected to the interface INT_FC via the first connector COD, and a control switch INTC controlled by a control member OC of the control device COM so that alternately the current generator supplies the switch INT of the decoupling equipment ED1 by means of the second current and so that it no longer supplies the switch INT of the decoupling equipment ED1 with current.

[0050] Advantageously, the control device COM, in particular the control member OC, is capable of controlling the RF transmission antenna TRANS_RF and the switch INT of the decoupling equipment ED1 in a synchronized manner so that the reception antenna B_REC is detuned in frequency, in the transmission phase, when the transmission antenna TRANS_RF transmits RF signals and tuned to the frequency fo, in the reception phase, when the transmission antenna TRANS_RF does not transmit RF signals.

[0051] The B_REC receiving antenna is intended to be electrically connected to the REC receiver of the IRM / SRM system so that the REC receiver receives the radio frequency signals received by the B_REC receiving antenna during the reception phase.

[0052] For this purpose, the reception device DREC1 comprises a transmission line, called reception line, LTR, a first conductor of which comprises a first end connected to the reception antenna B_REC and a second end connected to a transmission connector COT of the interface INT_FC electrically connected to the receiver REC of the IRM system so that the reception transmission line LTR transmits, to the receiver REC, the RF signals received by the reception antenna B_REC when the switch INT is open, that is to say during the reception phase.

[0053] The LTR transmission line is for example a coaxial cable, a twin-wire line or a twisted pair.

[0054] In a non-limiting embodiment, the first conductor of the LTR reception transmission line is connected in series with the INT switch as we will see later.

[0055] According to the invention, the INT switch of the ED decoupling equipment is intended to be located outside the patient's body (delineated by dotted lines in Figure 1) while the receiving antenna is located inside the patient's heart.

[0056] This solution avoids the risks associated with the arrangement of the switch in the human body. In particular, it avoids having to convey a direct current in the human body to control the transition of the INT switch from the open state to the closed state, which limits the risks to the patient's health. Furthermore, this solution limits the size of the part of the DREC1 receiving device intended to be inserted into the human body, which is fundamental for intracardiac imaging requiring the passage of this part through vessels with a diameter of around 2 mm to reach the part of the heart to be imaged. Furthermore, this solution is simple to implement and is economical (it does not require the use of miniature and non-magnetic active components to produce the decoupling equipment). First embodiment

[0057] Figure 2 shows the electrical diagram of the DREC1 receiving device of Figure 1 electrically connected to the REC receiver.

[0058] The equivalent electrical diagram of the resonant receiving antenna B_REC is a loop electrical circuit comprising a receiving coil BR connected in series with a matching capacitor CM and with a tuning capacitor CT. The tuning capacitor CT and the matching capacitor CM are connected to each other by a ground point PM electrically connected to the second conductor c2 of the transmission line which is electrically connected to ground. The tuning capacitor CT electrically connects the ground point PM to the receiving coil B_REC.

[0059] The matching capacitor CM electrically connects the distal end of the first conductor c1 of the receive transmission line LTR to the ground point PM. The first conductor c1 is, for example, a core of a coaxial cable.

[0060] A second conductor c2 of the LTR receive transmission line is electrically connected to ground. The second conductor c2 is, for example, the shield or "braid" of the coaxial cable.

[0061] The proximal end of the LTR receiving transmission line is electrically connected to the REC receiver and the ED1 decoupling equipment. The LTR receiving transmission line therefore has a function of transmitting the radio frequency signals received by the B_REC receiving antenna to the REC receiver and a function of a decoupling transmission line.

[0062] The decoupling equipment ED1 comprises the switch INT which is a PIN diode in the non-limiting example of Figure 2. Alternatively, the switch is another type of controllable switch, for example a mechanical switch or a relay, for example, a reed switch.

[0063] The decoupling equipment ED1 also includes a direct current blocking capacitor CB connected in series with the switch INT and with the receive transmission line LTR, more particularly with the first conductor c1 of the receive transmission line LTR.

[0064] The blocking capacitor CB is configured to block the DC component of the current. It therefore prevents the DC control current of the INT switch from reaching the B_REC receiving antenna and thus damaging it and avoiding the harmful effects on the patient mentioned above in the document. The blocking capacitor CB must have a sufficiently high capacitance and have a sufficiently low impedance so as not to prevent the transmission of the RF signal. At 64 MHz, for example, a value greater than or equal to 1 nF.

[0065] The distal end of the first conductor c1 of the receive transmission line LTR is connected to the receive antenna B_REC at a first terminal of the matching capacitor CM, the second terminal of the matching capacitor CM being connected to the ground point PM.

[0066] The capacitance of the matching capacitor CM is defined so that the equivalent impedance of the receiving antenna B_REC is seen, by the transmission line, as an impedance equal to the characteristic impedance of the transmission line. The matching capacitor CM then has an impedance matching function between the receiving antenna B_REC and the transmission line LTR.

[0067] Advantageously, the capacitance of the CM matching capacitor is set so that the receiving antenna is seen as an impedance of 50 Ohms by the transmission line. This allows the use of a transmission line, for example, a 50 Ohm coaxial cable.

[0068] The matching capacitor CM, the receiving transmission line LTR and the decoupling equipment ED1 (blocking capacitor Cs and switch INT) form a resonant decoupling circuit surrounded by a solid line frame in Figure 2, having the function of ensuring the coupling between the receiving antenna B_REC and the MRI device A in the receiving phase and of decoupling the receiving antenna B_REC and the MRI device A in the transmitting phase.

[0069] The decoupling circuit is configured to resonate at frequency fo. The resonant frequency depends on the values ​​of the elements (capacitance, inductance depending on the length of the transmission line LTR or LTD) of the elements forming this circuit.

[0070] The LTR receive transmission line therefore has a dual function of transmitting radio frequency signals during the receive phase and as a transmission line equivalent to an inductance during the transmit phase. When the INT switch is closed (transmit phase), i.e. when it is supplied with current, the INT switch connects the blocking capacitor to ground. The equivalent diagram of the decoupling circuit is the matching capacitor CM in series with the LTR receive transmission line in series with the blocking capacitor CB and with the INT switch.

[0071] To demonstrate the decoupling function, the LTR receiving transmission line has an inductance function. The length of the LTR receiving transmission line is set so that the resonant frequency of the decoupling circuit CD1 is equal to the frequency fo. This length is calculated approximately, and the precise length is then determined experimentally to obtain the desired resonant frequency.

[0072] The length of the receive transmission line LTR is also defined so that the decoupling equipment and more particularly the switch INT is located outside the human body when the receive antenna B_REC is located in the heart.

[0073] It is typically greater than or equal to 30 cm or 40 cm when the receiving antenna is intended to be inserted into the body through jugular access and greater than or equal to 80 cm when the receiving antenna is intended to be inserted into the body through groin access.

[0074] In transmission, the decoupling circuit CD1 has a high impedance at the resonant frequency fo, which means that it behaves like an open circuit. The receiving antenna B_REC can then be compared to the receiving coil BR connected in series with the tuning capacitor CT. This latter circuit is detuned in frequency (i.e. it no longer resonates at the frequency fo). It resonates, for example, at two frequencies different from the frequency fo. The receiving antenna is well decoupled from the MRI device, A.

[0075] In reception, when the switch INT is open, i.e. when it is no longer supplied with current, the reception antenna B_REC behaves like a circuit comprising the matching capacitor CM in series with the reception coil BR connected in series with the tuning capacitor CT, i.e. like an LC circuit resonant at the frequency fo. The reception transmission line LTR behaves like an impedance-matched transmission line with the reception antenna B_REC. The reception antenna B_REC is then coupled with the MRI device, A. It receives and transmits to the receiver the RF signals resulting from the excitation of the area to be imaged.

[0076] The embodiment of Figure 2 includes a single LTR transmission line to realize the function of RF signal transmission and decoupling. It is particularly compact and has a good signal-to-noise ratio.

[0077] A disadvantage of this embodiment lies in the limited, potentially insufficient, efficiency of the decoupling, which results in artifacts on the images, and in spatial variations of the effective flip angle of the MRI sequence used and therefore in an unwanted modification of the contrasts and an associated degradation of the diagnosis. The quality factor of the decoupling circuit CD1 is inversely proportional to the resistance of the decoupling circuit CD1. The resistance of the decoupling circuit CD1 is equal to the sum of the resistance of the matching capacitor CM, the resistance of the receiving transmission line LTR, the resistance of the blocking capacitor CB, and the resistance of the switch INT.A disadvantage of limited decoupling is the possibility of inducing local hot spots around the receiving antenna B_REC due to the circulation of non-negligible electric currents in the receiving antenna during the transmission phase.

[0078] Second embodiment

[0079] Figure 3 represents an electrical diagram of a DREC2 reception device according to a second embodiment of the invention.

[0080] This second embodiment differs from the first embodiment in that the decoupling equipment ED2 of the decoupling circuit CD2 comprises an electrical circuit RN having a negative resistance connected in series with the switch INT, i.e. with the first conductor c1 of the reception transmission line LTR. By electrical circuit RN having a negative resistance, we mean an electrical circuit having a resistance, the ratio of the voltage across the circuit RN to the current flowing in the circuit RN and negative. It behaves like a component having a resistance of value less than zero Ohms. This electrical circuit RN is connected in series with the switch INT.

[0081] An advantage of this solution is that it presents a more efficient decoupling than the embodiment of Figure 2, because the decoupling circuit CD2 thus presents a quality factor of the decoupling circuit higher than that of the decoupling circuit CD1 of Figure 2. Indeed, the quality factor of the decoupling circuit CD2 is inversely proportional to the resistance of the decoupling circuit CD2. This makes it possible to limit the artifacts on the generated images. Furthermore, this solution remains compact since no additional components are added in the part inserted into the human body.

[0082] In the transmission phase, the resistance of the decoupling circuit CD2 is equal to the sum of the resistance of the matching capacitor CM, the resistance of the receiving transmission line LTR, the resistance of the blocking capacitor CB, the resistance of the switch INT and the resistance of the negative resistance circuit RN. The negative resistance circuit therefore makes it possible to increase the quality factor of the decoupling circuit by reducing the total resistance of the decoupling circuit. The quality factor of the decoupling circuit is increased in the transmission phase. This therefore makes it possible to improve the efficiency of the decoupling between the receiving antenna and the transmitting antenna in the transmission phase of the MRI / SRM device.

[0083] This solution is particularly advantageous for intracardiac applications where constraints on the maximum cable diameter are high. However, the smaller the diameter of the transmission line, the higher its resistance, which has the effect of generating losses in the LTR receive transmission line.

[0084] Advantageously, the negative resistance circuit RN is configured so that the resistance of the decoupling circuit CD2 is substantially zero.

[0085] In the non-limiting example of Figure 3, the switch INT is connected to ground by the negative resistance circuit RN connected in series with the switch INT.

[0086] Alternatively, the negative resistor RN connects the transmission line to the blocking capacitor CB OR the blocking capacitor to the switch IN. In the non-limiting example of Figure 3, the cathode of a PIN diode is connected to ground by the negative resistor circuit RN connected in series with the switch INT.

[0087] In a manner known per se, the negative resistance circuit RN can be implemented in different ways. It can comprise two metal oxide semiconductor field effect transistors also called MOSFETs cross-coupled. Alternatively, the circuit RN can be implemented based on an operational amplifier, a tunnel diode, a programmable unijunction transistor also called PUT (acronym for the English expression "Programmable unijunction transistor") or a Gunn diode.

[0088] The negative resistance electrical circuit RN requires its own power supply which is not shown in Figure 3. This power supply is advantageously connected to the negative resistance circuit by a power cable so that the power supply is located outside the human body when the receiving antenna is located in the heart.

[0089] Advantageously, as in the non-limiting example of Figure 3, the negative resistance circuit is mounted so as to be intended to be located outside the human body when the receiving antenna B_REC (or B_REC4) is located inside the patient's heart. This solution does not require the supply, inside the patient's heart, of a direct current whose leaks are likely to cause cardiac arrest.

[0090] Furthermore, this embodiment does not require the use of miniature elements for the production of the switch or the negative resistance circuit in order to be able to introduce them into the core. This allows the production of a simple and low-cost device.

[0091] Furthermore, the fact that these elements are intended to be located outside the human body makes it possible to limit the number of elements in the part of the device intended to be introduced into the heart and therefore to miniaturize this part.

[0092] The invention also relates to an MRI / SRM system comprising the MRI / SRM device A as well as the reception device DREC2 according to the variant shown in Figure 1. This amounts to replacing the decoupling equipment ED1 with the decoupling equipment ED2 in Figure 1. Third embodiment

[0093] Figure 4 represents an electrical diagram of a DREC3 reception device according to a third embodiment of the invention. The DREC3 reception device according to the third embodiment differs from that of the first embodiment in that it comprises a transmission line, called decoupling, LTD in addition to the reception transmission line LTR.

[0094] The LTR receive transmission line is intended to electrically connect the B_REC receive antenna to the REC receiver.

[0095] For this purpose, the reception transmission line LTR is advantageously intended to electrically connect (or electrically connects) the transmission connector COT to the reception antenna B_REC as shown in figure 6.

[0096] This connection is made without going through the INT switch.

[0097] The LTD decoupling transmission line, just like the LTR receiving transmission line, can be implemented as a coaxial cable, a two-wire line or a twisted pair.

[0098] The decoupling transmission line LTD comprises a first conductor c1 a comprising a proximal end intended to be electrically connected to the decoupling equipment ED1, as shown in figure 6, and a distal end electrically connected to the receiving antenna B-REC.

[0099] The LTD decoupling transmission line includes a second conductor c2a electrically connected to ground.

[0100] The decoupling efficiency of this embodiment can be higher than that of the first embodiment, which makes it possible to limit artifacts on the images. This makes it a good solution when the space constraints can accommodate the presence of two cables. This solution is simple to implement because it involves limited constraints on the geometry and configuration of the receiving transmission line LTR, only the decoupling transmission line LTD participating in the decoupling being constrained.

[0101] In the particular embodiment of Figure 4, the distal end of the first conductor c1a of the decoupling transmission line LTD is electrically connected to the receiving antenna B_REC at the first terminal of the tuning capacitor CT, the second terminal of the tuning capacitor CT being connected to the ground point PM. The receiver REC is intended to be electrically connected to the receiving transmission line LTR without being connected to the decoupling transmission line LTD so as to receive radio frequency signals received by the receiving antenna B_REC via the receiving transmission line LTR without passing through the decoupling transmission line LTD.

[0102] In other words, the receiver REC is intended to be electrically connected to the receiving transmission line LTR so as to be intended to receive radio frequency signals received by the receiving antenna B_REC via the receiving transmission line LTR without these signals passing through the decoupling transmission line LTD.

[0103] In other words, the receiver REC is intended to be electrically connected to the receiving antenna B_REC via the receiving transmission line LTR without passing through the decoupling transmission line LTD.

[0104] The conductor c1 advantageously comprises a first end electrically connected to the receiving antenna B_REC and a second end intended to be electrically connected to the receiver REC.

[0105] This connection is made, for example, via a COT transmission connector.

[0106] Furthermore, the INT switch is electrically connected to the receiving antenna via the decoupling transmission line LTD without passing through the receiving transmission line LTR.

[0107] In other words, two separate transmission lines are used to ensure:

[0108] - during the transmission phase, the decoupling between the receiving antenna and the transmitting antenna of the MRI / SRM device,

[0109] - during the reception phase, the transmission to the receiver REC of signals from the reception antenna which are intended to be received by the receiver REC.

[0110] In other words, among the functions of decoupling the receiving antenna during the transmission phase and transmitting during the reception phase, the decoupling transmission line LTD participates only in decoupling and the receiving transmission line LTR participates only in transmission. By transmission is meant the transmission from the receiving antenna to the receiver of the signals intended to be received by the receiver.

[0111] Thus, the decoupling circuit CD3, surrounded by a solid line frame in Figure 4, differs from that of the first embodiment in that it comprises the decoupling transmission line LTD, the tuning capacitor O and the decoupling equipment ED1.

[0112] To present the decoupling function, the decoupling transmission line LTD has an inductance function. The length of the decoupling transmission line LTD is set so that the resonant frequency of the decoupling circuit CD3 is equal to the frequency fo. This length is calculated approximately, and the precise length is then determined experimentally so as to obtain the desired resonant frequency. This length constraint does not apply to the receiving transmission line LTR in this embodiment.

[0113] This embodiment makes it possible, by separating the functions of the two transmission lines, to improve both the quality of the decoupling by adjusting the length of the decoupling transmission line LTD and the capacitance of the tuning capacitor CT and the quality of the reception by adapting the impedance of the reception antenna B_REC to that of the reception transmission line LTR at the working frequency fo of the IRM / SRM device.

[0114] Thus, advantageously the length of the decoupling transmission line LTD is defined so that the resonant frequency of the decoupling circuit CD3 is equal to the frequency fo and so that the impedance of the reception antenna B_REC is adapted to that of the reception transmission line B_REC at the working frequency fo of the IRM / SRM device.

[0115] In other words, the equivalent impedance of the receiving antenna B_REC is defined so as to be seen, by the receiving transmission line LTR, as an impedance equal to the characteristic impedance of the receiving transmission line LTR at the working frequency fo of the IRM / SRM device.

[0116] The characteristic impedance of the receiving transmission line LTR at frequency fo is, for example, 50 Ohms.

[0117] This technical solution jointly allows: - to optimize the quality of the remote decoupling outside the human body of the reception antenna during the transmission phase to avoid degradation of the quality of the measured signals and guarantee the safety of the patient (absence of radiofrequency currents circulating in the reception antenna during the transmission phase and absence of electrically powered components inside the human body),

[0118] - to optimize the transmission of the signal to the REC receiver during the reception phase to maximize the signal-to-noise ratio of the signals measured by the receiving antenna.

[0119] The separation of the two circuits provides additional flexibility in the choice of electronic components, allowing each function to be optimized independently (decoupling in the transmission and reception phase of the signal). This choice is advantageously made by taking into account the space constraints linked to the introduction of the reception antenna in the core, and in particular the losses generated by cables with a small diameter.

[0120] The length of the decoupling transmission line LTD is defined so that the decoupling equipment and more particularly the switch INT is located outside the human body when the receiving antenna B_REC is located in the heart.

[0121] It is typically greater than or equal to 30 cm or 40 cm when the receiving antenna is intended to be inserted into the body through jugular access and greater than or equal to 80 cm when the receiving antenna is intended to be inserted into the body through groin access.

[0122] Variant of the third embodiment

[0123] Figure 5 shows a variant of the third embodiment which differs from that of Figure 4 in that the receiving antenna B_REC4 of the receiving device DREC4 comprises an additional tuning capacitor CTA connected in series with the capacitors CM and CT. The additional tuning capacitor CTA is connected to the tuning capacitor CT at the first terminal of the tuning capacitor CT. This feature makes it possible to choose another value for the length of the decoupling transmission line LTD if necessary, or to have another value for the capacitance of the tuning capacitor CT if ever there are constraints to use certain values.

[0124] It should be noted that, in the third embodiment, as well as in its variant, the decoupling equipment of the decoupling circuit may comprise an electrical circuit RN having a negative resistance mounted in series with the switch INT, that is to say with the first conductor c1 of the decoupling transmission line LTD, as in the second embodiment. The different assemblies, arrangements and embodiments of the negative resistance described with reference to FIG. 3 are applicable to the third embodiment and to its variant.

[0125] The invention also relates to an MRI / SRM system comprising the MRI / SRM device A as well as the DREC4 reception device according to the variant shown in Figure 5. This amounts to replacing the reception antenna B_REC with the reception antenna B_REC4 in Figure 6.

[0126] Other features

[0127] To prevent heating of cables (transmission lines) inserted in the sheath, it is possible to distribute LC circuits also called traps along at least one of the transmission lines (LTR and / or LTD) to prevent the circulation of parasitic currents as described in the aforementioned article.

[0128] In the embodiments of the figures, the matching capacitor is connected in series with the tuning capacitor(s). Alternatively, the receiving antenna comprises, instead of this matching capacitor and / or in addition, a matching capacitor or a matching capacitor network connected in series with the transmission line connected in series with the decoupling equipment.

[0129] Sheath receiving device

[0130] Advantageously, the receiving device comprises a tubular sheath made of electrically insulating material.

[0131] The sheath is flexible so as to be potentially mechanically deflected. The sheath is advantageously in the form of a tube elongated along an axis of the sheath capable of having a maximum (external) diameter substantially constant over its entire length or over the entire length of its part intended to be introduced into the human body.

[0132] This external diameter is compatible with the maximum dimensions of the vessels into which it must be introduced.

[0133] Advantageously, this diameter is less than 2 mm.

[0134] The tubular sheath delimits an inner lumen elongated along the x axis and receiving the control line LC, the reception transmission line LTR and the possible decoupling transmission line LTD.

[0135] The sheath comprises a proximal end and is mechanically connected to the INT switch or, more generally, to the decoupling equipment and a distal end and capable of receiving the resonant receiving antenna B_REC or B_REC4.

[0136] The distal end of the sheath is intended to be introduced into the human body and more particularly into a vessel connected to the heart and the proximal end of the sheath is intended to remain outside the human body.

[0137] Advantageously, the receiving antenna is capable of being in a deployed state in which it has a diameter greater than that of the sheath in the axis of the sheath. The receiving antenna is then received in the sheath when it is in a folded state.

[0138] The receiving antenna may, for example, be integrated into an inflatable / deflatable balloon inside the heart cavity, or include a mechanical system allowing it to be deployed in contact with the area to be imaged and folded to maneuver it in the blood vessels connected to the heart, or any other system allowing its geometry to be modified between the phase of insertion / removal of the sheath from the human body and the imaging phase.

Claims

DEMANDS 1. Radiofrequency signal receiving device (DREC1, DREC2, DREC3, DREC4) for a magnetic resonance imaging or spectroscopy system, comprising an intracardiac resonant receiving antenna (B_REC) and a switch (INT) capable of being alternately in an open state when supplied with a direct current of a first intensity so that the receiving antenna (B_REC) is tuned to an operating frequency (fo) of the magnetic resonance imaging system, and in a closed state when supplied with a direct current of a second intensity so that the receiving antenna is frequency detuned, the receiving antenna (B_REC) further being intended to be connected to a receiver (REC) intended to receive the radiofrequency signals received by the resonant receiving antenna (B_REC) when the switch (INT) is in the open state, the receiving device comprising a first transmission line (LTR,LTD) having a conductor having a distal end electrically connected to the resonant receiving antenna (B_REC) and a proximal end electrically connected to the switch (INT) such that the switch is intended to be located outside the human body when the receiving antenna (B_REC) is located inside the heart of a patient.

2. Receiving device (DREC3, DREC4) according to claim 1, comprising, in addition to the first transmission line (LTD), a second transmission line (LTR) having a conductor comprising a distal end electrically connected to the receiving antenna (B_REC, B_REC4) and a proximal end intended to be electrically connected to the receiver (REC) to transmit to it the radio frequency signals received by the receiving antenna (B_REC, B_REC4), 3. A receiving device (DREC3, DREC4) according to claim 2, wherein the receiver (REC) is intended to be electrically connected to the receiving transmission line (LTR) so as to receive radio frequency signals received by the receiving antenna (B_REC) via the receiving transmission line (LTR) without passing through the decoupling transmission line (LTD). Receiving device (DREC3, DREC4) according to the preceding claim, wherein the receiving antenna comprises a tuning capacitor and a matching capacitor mounted in series and connected by a ground point, the matching capacitor (CM) electrically connecting the conductor of the second transmission line (LTR) to the ground point (PM). Receiving device (DREC1, DREC2) according to claim 1, wherein the proximal end of the conductor of the first transmission line (LTR) is intended to be connected to the receiver (REC) to transmit to it the radio frequency signals received by the receiving antenna (B_REC).A receiving device (DREC1, DREC2) according to claim 4, wherein the receiving antenna comprises a matching capacitor (CM) electrically connecting a ground point (PM) to the conductor of the first transmission line. A receiving device (DREC2) according to any one of the preceding claims, comprising an electrical circuit (RN) having a negative resistance connected in series with the switch (INT). A receiving device (DREC2) according to claim 7, wherein the electrical circuit having the negative resistance connects the switch to ground. A receiving device (DREC2) according to any one of claims 7 to 8, wherein the electrical circuit having the negative resistance is intended to be located outside the human body when the receiving antenna (B_REC) is located inside the heart of a patient. A receiving device (DREC1, DREC2, DREC3, DREC4) according to any one of the preceding claims, comprising a sheath receiving the first transmission line, the sheath having a proximal end mechanically connected to the switch (INT) and a distal end adapted to receive the receiving antenna (B_REC). A receiving device (DREC1, DREC2, DREC3, DREC4) according to the preceding claim, wherein the sheath has a diameter less than or equal to 2 mm.A magnetic resonance imaging or spectroscopy system comprising a receiver according to any one of the preceding claims, the system comprising a magnetic resonance imaging or spectroscopy device, the magnetic resonance imaging or spectroscopy device comprising a master magnet (GENST) for generating a static magnetic field, a gradient generator (GENGR) comprising gradient coils, and a transmitting antenna (TRANS_RF) for emitting radio frequency signals. An imaging system according to the preceding claim, wherein the magnetic resonance imaging or spectroscopy device comprises the receiver (REC).

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