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

Abstract

The invention relates to a device (DREC 2) for receiving a radio frequency signal of a magnetic resonance imaging / spectroscopy system, the device (DREC 2) comprising an intracardiac receive resonant tank (BREC) and a switch (INT) which can be alternately in an open state such that the frequency of the receive antenna (BREC) is tuned to an operating frequency of the magnetic resonance imaging system, the receiving device includes a first transmission line (LTR) having a conductor, the distal end of which is electrically connected to the receiving resonant tank (BREC) and the proximal end of which is electrically connected to a switch (INT) such that the switch is located outside the human body when the receiving resonant tank (BREC) is located inside the patient's heart.

Description

Technical Field

[0001] The present invention relates to the field of intracavitary, in particular intracardiac magnetic resonance imaging / spectroscopy (MRI / MRS).

[0002] An MRI / MRS system generally includes a main magnet for generating a uniform permanent magnetic field B0, three gradient coils, and an external transmitting antenna for generating a radio frequency (RF) excitation signal to uniformly magnetize the patient's tissue in space.

[0003] In the case of intracavitary MRI, the antenna used to receive the RF signal generated by the excitation of the organ of interest by the RF excitation signal is intended to be in contact with the organ of interest (the heart for intracardiac imaging) through a natural orifice or percutaneously. The purpose of the intracavitary antenna is to make it possible to obtain an optimal spatial selectivity related to the geometry (shape, size) of the receiving antenna and its position and an improved sensitivity relative to an external antenna, and thus to increase the signal-to-noise ratio. The spatial selectivity makes it possible to limit the field of view of the images to be acquired and to reduce their acquisition time. The signal-to-noise ratio gain makes it possible to generate images of high quality and / or with better spatial resolution compared to an external antenna, which is crucial for the imaging of the heart wall (especially the atria), as the thickness of the atria is between 2 mm and 5 mm.

[0004] The receiving antenna includes a receiving loop (i.e., a receiving coil) and a capacitor for frequency tuning and matching the characteristic impedance of the transmission line (usually 50 ohms). The receiving antenna is connected to the receiver of the MRI device through a transmission line integrated in the sheath and is used to transmit the radio frequency signals received by the antenna to the receiver so that the receiver records these signals.

[0005] The receiving antenna is an RLC type resonant circuit, whose resonant frequency fR must be equal to the Larmor frequency f0 of the MRI system. The value of fR depends on the magnetic flux density B0 of the MRI (F0 = γB0 / 2π). γ is the gyromagnetic ratio of the nucleus of interest (usually hydrogen, 1H). For example, for hydrogen, γ = 42.57 MHz / Tesla, which gives a resonant frequency of about 64 MHz for a magnetic field of 1.5 Tesla.

[0006] Since the transmitting antenna and the receiving antenna operate at the same frequency f0, it is necessary that the receiving antenna is tuned to the frequency f0 during the reception phase of the RF signal emitted by the organ of interest and that the receiving antenna is frequency detuned during the transmission phase. If this is not the case, high currents may be induced in the receiving antenna during the transmission phase, which can lead to the following effects:

[0007] - Producing hot spots that can burn the patient or can cause coagulation and necrosis of tissue in contact with the receiving antenna, which leads to unsafe conditions for the patient,

[0008] - the inhomogeneity of the magnetic field B1 generated by the transmitting antenna in the vicinity of the receiving antenna changes the characteristics of the acquisition technique (change in contrast) and deteriorates the quality of the MRI image,

[0009] - Potential degradation of MRI detection equipment (hardware damage).

[0010] This switching system must be able to switch between the two states quickly and dynamically throughout the acquisition time of the MRI sequence. To this end, it is necessary to use active decoupling devices and ensure sufficient electrical isolation (attenuation difference between coupled and decoupled states) at frequency f0 to avoid the above problems. Background Art

[0011] Switching between tuned and detuned states of the receiving antenna is performed dynamically by an active decoupling device that is able to temporarily modify the frequency response of the receiving antenna.

[0012] Active decoupling devices usually include PIN diodes, to which DC current is supplied during the transmission phase, so that the PIN diode is turned on and the frequency of the receiving antenna is detuned. During the reception phase, DC current is no longer supplied to the PIN diode, thereby tuning the frequency of the receiving antenna.

[0013] The article "Intracardiac Magnetic Resonance Imaging (ICMRI) Guide Sheath with Amplified Expandable Tip Imaging and Magnetic Resonance Tracking for Navigation and Arrhythmia Ablation Monitoring: Testing in Pigs at 1.5 and 3T"; Schmidt et al., "Magnetic Resonance in Medicine" discloses a receiving device including an intracavitary decoupling device.

[0014] However, powering intracavitary devices (especially intracardiac devices) with direct currents of several hundred milliamperes can be dangerous for the patient. In fact, such direct currents can cause cardiac arrest if the components of the receiving antenna come into contact with the myocardium. In addition, this solution brings with it the problem of bulkiness. Summary of the invention

[0015] It is an object of the present invention to limit at least one of the above-mentioned disadvantages.

[0016] To this end, the present invention relates to a device for receiving radio frequency signals for magnetic resonance imaging, the device comprising: an intracardiac receiving resonant antenna and a switch, the switch being capable of being alternately in an open state when powered by a direct current having a first strength, so that the receiving antenna is tuned to the operating frequency of the magnetic resonance imaging system, and the switch being capable of being alternately in a closed state when powered by a direct current having a second strength, so that the frequency of the receiving antenna is detuned, the receiving antenna being also used to be connected to a receiver, the receiver being used to receive the radio frequency signal received by a receiving resonant circuit (i.e., a receiving resonant antenna) when the switch is in the open state, the receiving device comprising a first transmission line having a conductor, the conductor having a distal end electrically connected to the receiving resonant antenna and a proximal end electrically connected to the switch, so that when the receiving antenna is located inside the patient's heart, the switch is intended to be located outside the human body.

[0017] In one embodiment, in addition to the first transmission line, the receiving device also includes a second transmission line having a conductor, the conductor including 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 the radio frequency signal received by the receiving antenna to the receiver.

[0018] Advantageously, the receiver is intended to be electrically connected to the receiving transmission line in order to receive radio frequency signals received by the receiving antenna via the receiving transmission line without passing through the decoupling transmission line.

[0019] Advantageously, the receiving antenna comprises a tuning capacitor and a matching capacitor mounted in series and connected via a ground point, the tuning capacitor electrically connecting the conductor of the second transmission line to the ground point.

[0020] In another embodiment, the proximal end of the conductor of the first transmission line is intended to be connected to the receiver in order to transmit to the receiver the radio frequency signal received by the receiving antenna.

[0021] Advantageously, the receiving device comprises a circuit having a negative resistance mounted in series with the switch.

[0022] Advantageously, a matching capacitor electrically connects the ground point to the conductor of the first transmission line.

[0023] Advantageously, the circuit having the negative resistance connects the switch to ground.

[0024] Advantageously, the circuit with the negative resistance is intended to be located outside the human body when the receiving antenna is located inside the patient's heart.

[0025] In a particular embodiment, the receiving device includes a sheath receiving the first transmission line, the sheath including a proximal end mechanically connected to the switch and a distal end capable of receiving the receiving resonant antenna.

[0026] 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 comprising a main magnet for generating a static magnetic field, a gradient generator with gradient coils and a transmitting antenna for transmitting radio frequency signals.

[0027] Advantageously, the magnetic resonance imaging or spectroscopy device comprises a receiver. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Other features and advantages of the present invention will become more apparent by reading the following detailed description with reference to the accompanying drawings, in which:

[0029] Figure 1 shows a schematic diagram of an MRI / MRS system having a receiving device according to a first embodiment;

[0030] Figure 2 A circuit diagram of a receiving device according to a first embodiment is shown;

[0031] Figure 3 shows a circuit diagram of a receiving device according to a second embodiment;

[0032] Figure 4 A circuit diagram of a receiving device according to a third embodiment is shown;

[0033] Figure 5 shows a circuit diagram of a receiving device according to an alternative to the third embodiment;

[0034] Figure 6 is a schematic diagram of an MRI / MRS system having a receiving apparatus according to a third embodiment. DETAILED DESCRIPTION

[0035] Description of the invention

[0036] The invention relates to a receiving device of a magnetic resonance imaging / spectroscopy system or MRI / MRS, intended to operate at an operating frequency f0.

[0037] MRI / MRS System Overview

[0038] The MRI / MRS system includes a receiving device DREC1. The receiving device DREC1 of the first embodiment of the present invention is Figure 1 Of course, in an alternative solution, the MRI / MRS system may include a receiving device according to any one of the embodiments and alternative solutions described in this patent application.

[0039] The MRI / MRS system comprises an MRI / MRS device A, which comprises a main magnet GENST for generating a static magnetic field B0, a gradient generator GENGR comprising gradient coils, and a transmitting antenna TRANS_RF for transmitting radio frequency (RF) signals. The MRI / MRS system A comprises a receiving device DREC1, which comprises a receiving antenna B_REC, which is used to receive the radio frequency signal generated by the transmitting antenna TRANS_RF to excite the patient's region of interest. The MRI / MRS device A comprises a receiver REC, which is intended to receive the signals received by the receiving device DREC1 and process them to generate an image / spectrum.

[0040] The receiving device DREC1 is electrically connected to the MRI device A through an interface INT_FC of the MRI / MRS device including connectors COD and COT.

[0041] As mentioned above, the operating frequency or Larmor frequency f0 is proportional to the static magnetic field B0.

[0042] The most common magnetic fields B0 in clinical MRI / MRS are 1.5 Tesla, 3.0 Tesla or 7.0 Tesla, but the present invention is applicable to other magnetic fields B0, for example between 0.1 Tesla and 11 Tesla.

[0043] The receiving antenna B_REC is an intracardiac resonant antenna.

[0044] The intracardiac receiving resonant antenna B_REC is a receiving antenna of the RLC circuit type, which is inserted into the heart cavity of the patient. Figure 1 The heart region is delimited by a dotted line to facilitate imaging of the heart region by magnetic resonance.

[0045] 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 more precisely below) which can alternately be in an open state when powered by a direct current of a first strength, so that the receiving antenna resonates at a frequency f0, and can alternately be in a closed state when powered by a direct current of a second strength, so that the antenna no longer resonates at the frequency f0. For example, the decoupling switch can be in an open state when no current is supplied, and in a closed state when the second direct current is supplied.

[0046] For example, the first current is zero and the second DC current is non-zero.

[0047] It can be understood that when the decoupling switch is in the open state, the receiving antenna is tuned to the frequency f0, and when the switch is in the closed state, the antenna is frequency detuned and no longer matches the transmission line impedance at the frequency f0.

[0048] The MRI / MRS device A comprises a control device COM capable of electrically controlling a switch by supplying it with a direct current of a first intensity and a direct current of a second intensity, so as to change the switch from an open state to a closed state and vice versa and to keep it in the desired state for a desired duration. The control device COM advantageously comprises a current generator GENC capable of conveying a second current and electrically connected to the switch INT of the decoupling device ED1 through a conductor or transmission line LC connected to the interface INT_FC via a first connector COD, and a control switch INTC controlled by a control member OC of the control device COM so that the current generator alternately supplies the switch INT of the decoupling device ED1 with the second current and it no longer supplies the switch INT of the decoupling device ED1.

[0049] Advantageously, the control device COM (in particular the control member OC) is capable of controlling the RF transmitting antenna TRANS_RF and the switch INT of the decoupling device ED1 in a synchronized manner, so that when the transmitting antenna TRANS_RF transmits an RF signal, the frequency of the receiving antenna B_REC is detuned in the transmitting phase, while when the transmitting antenna TRANS_RF does not transmit an RF signal, the frequency of the receiving antenna B_REC is tuned to the frequency f0 in the receiving phase.

[0050] The receiving antenna B_REC is intended to be electrically connected to a receiver REC of the MRI / MRS system, such that the receiver REC receives radio frequency signals received by the receiving antenna B_REC during a reception phase.

[0051] To this end, the receiving device DREC1 comprises a transmission line (i.e. a so-called receiving LTR), a first conductor of which comprises a first end connected to a receiving antenna B_REC and a second end connected to a transmission connector COT connected to an interface INT_FC, which is electrically connected to a receiver REC of the MRI system, so that the receiving transmission line LTR transmits the RF signal received by the receiving antenna B_REC to the receiver REC when the switch INT is disconnected (i.e. during the receiving phase).

[0052] The transmission line LTR is, for example, a coaxial cable, a two-wire line or a twisted pair.

[0053] In a non-limiting embodiment, the first conductor of the reception transmission line LTR is mounted in series with a switch INT, as will be seen later.

[0054] According to the invention, the switch INT of the decoupling device ED is located outside the patient's body (by Figure 1 ), and the receiving antenna is located inside the patient's heart.

[0055] This solution makes it possible to avoid the risks of placing the switch inside the human body. In particular, it makes it possible to avoid having to transmit a direct current in the human body to control the passage of the switch INT from the open state to the closed state, which limits the risks to the patient's health. Moreover, this solution makes it possible to limit the volume of the portion of the receiving device DREC1 intended to be inserted into the human body, which is essential for intracardiac imaging that requires this portion to enter a blood vessel of the order of 2 mm in diameter in order to reach the portion of the heart to be imaged. Moreover, this solution is simple and economical to implement (no need to use miniature and non-magnetic active elements to produce the decoupling device).

[0056] First embodiment

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

[0058] The equivalent circuit diagram of the receiving resonant antenna B_REC is a ring circuit, including a matching capacitor C M and tuning capacitor C T Series receiving coil B R . Tuning capacitor C T and matching capacitor C M Through the ground point P M Connect to each other, ground point P M A second conductor c2 electrically connected to the transmission line, the second conductor c2 being electrically connected to ground. Tuning capacitor C T The ground point P M Electrically connected to the receiving coil B_REC.

[0059] Matching capacitor C M The far end of the first conductor c1 of the receiving transmission line LTR is electrically connected to the ground point P M The first conductor c1 is, for example, a core wire of a coaxial cable.

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

[0061] The near end of the reception transmission line LTR is electrically connected to the receiver REC and the decoupling device ED1. The reception transmission line LTR thus has the function of transmitting the radio frequency signal received by the reception antenna B_REC to the receiver REC and the decoupling transmission line function.

[0062] The decoupling device ED1 comprises a switch INT. Figure 2 In a non-limiting example, the switch INT is a PIN diode. Alternatively, the switch is another type of controllable switch, such as a mechanical switch or a relay, such as a reed switch.

[0063] The decoupling device ED1 also includes a DC blocking capacitor C installed in series with the switch INT and the receiving transmission line LTR. B , more specifically, the DC blocking capacitor C B Installed in series with the first conductor c1 of the receiving transmission line LTR.

[0064] Blocking capacitor C B is configured to block the DC component of the current. It thus prevents the control direct current of the switch INT from reaching the receiving antenna B_REC and thus damaging it, as well as avoiding the harmful effects on the patient described above in this document. The blocking capacitor C B It must have a high enough capacitance and low enough impedance so as not to hinder the transmission of the RF signal. For example, at 64MHz, this value is greater than or equal to 1nF.

[0065] The far end of the first conductor c1 of the receiving transmission line LTR is connected to a matching capacitor C M The first terminal of the receiving antenna B_REC, the matching capacitor C M The second terminal is connected to the ground point P M .

[0066] Matching capacitor C M The capacitance of is defined as the impedance that makes the equivalent impedance of the receiving antenna B_REC regarded by the transmission line as equal to the characteristic impedance of the transmission line. Therefore, the matching capacitor C M There is an impedance matching function between the receiving antenna B_REC and the transmission line LTR.

[0067] Advantageously, the matching capacitor C M The capacitance is defined so that the receiving antenna is seen by the transmission line as an impedance of 50 ohms. This allows the use of a transmission line (e.g., a 50 ohm coaxial cable).

[0068] Matching capacitor C M , receiving transmission line LTR and decoupling device ED1 (blocking capacitor C B and switch INT) form a Figure 2 The resonant decoupling circuit is surrounded by a solid line frame in , and the function of the resonant decoupling circuit is to ensure the coupling between the receiving antenna B_REC and the MRI device A in the receiving stage, and to decouple the receiving antenna B_REC and the MRI device A in the transmitting stage.

[0069] The decoupling circuit is configured to resonate at a frequency f0. The resonant frequency depends on the values ​​of the components forming the circuit (capacitors, inductors, depending on the length of the transmission line LTR or LTD).

[0070] Therefore, the receiving transmission line LTR has a dual function: transmitting the RF signal during the receiving phase; and acting as an inductor during the transmitting phase.

[0071] When the switch INT is closed (transmission phase), that is, when it is supplied with current, the switch INT connects the blocking capacitor to ground. The equivalent diagram of the decoupling circuit is a matching capacitor C in series with the receiving transmission line LTR. M , the matching capacitor C M With blocking capacitor C B Connect in series with switch INT.

[0072] In order to have a decoupling function, the receiving transmission line LTR has an inductance function. The length of the receiving transmission line LTR is defined so that the resonant frequency of the decoupling circuit CD1 is equal to the frequency f0. The length is approximately calculated, and then the exact length is determined by experiment in order to obtain the desired resonant frequency.

[0073] The length of the receiving transmission line LTR is also defined such that when the receiving antenna B_REC is located in the heart, the decoupling devices (especially the switch INT) are located outside the human body.

[0074] When the receiving antenna is intended to be inserted into the body through the jugular vein access, 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 the inguinal access, it is typically greater than or equal to 80 cm.

[0075] In transmission, the decoupling circuit CD1 has a high impedance at the resonant frequency f0, which means that it behaves as an open circuit. Therefore, the receiving antenna B_REC can be connected to the tuning capacitor C T Receiving coil B installed in series R Similarly, the latter circuit is frequency detuned (ie, it no longer resonates at frequency f0). For example, it resonates at two frequencies different from frequency f0. The receiving antenna is properly decoupled from the MRI device A.

[0076] When receiving, when the switch INT is open (ie, when it is no longer supplied with current), the receiving antenna B_REC behaves as if it includes a tuning capacitor C T Receiving coil B installed in series R The matching capacitor C in series MThe circuit is a circuit LC that behaves as a resonance at frequency f0. The receiving transmission line LTR is similar to a transmission line impedance-matched to the receiving antenna B_REC. The receiving antenna B_REC is then coupled to the MRI device A. It receives and transmits to the receiver the RF signal generated by the excitation of the area to be imaged.

[0077] Figure 2 The embodiment comprises a single transmission line LTR for performing the functions of transmitting the RF signal and decoupling. The single transmission line LTR is particularly compact and has a good signal-to-noise ratio.

[0078] A disadvantage of this embodiment is the limited, possibly insufficient, decoupling efficiency, which leads to artifacts on the image and to spatial variations of the effective tilt angle of the MRI sequence used and thus to undesired variations of the contrast and associated diagnostic degradation. 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 matching capacitor C M The sum of the resistance of the receive transmission line LTR, the resistance of the blocking capacitor CB, and the resistance of the switch INT. A disadvantage of limited decoupling is that local hot spots may be caused around the receive antenna B_REC due to non-negligible current circulation in the receive antenna during the transmit phase.

[0079] Second embodiment

[0080] Figure 3 A circuit diagram of a receiving device DREC2 according to a second embodiment of the present invention is shown.

[0081] The second embodiment differs from the first embodiment in that the decoupling device ED2 of the decoupling circuit CD2 comprises a circuit R having a negative resistance. N , the circuit R N Installed in series with the switch INT, ie in series with the first conductor c1 of the receiving transmission line LTR. Circuit R with negative resistance N Refers to a circuit with resistance, whose circuit R N The voltage at the terminals of the circuit R N The ratio between the currents flowing in is negative. It is similar to a component with a resistance value less than zero ohms. N Install in series with switch INT.

[0082] The advantage of this solution is that it has Figure 2 The embodiment is more effective in decoupling because the decoupling circuit CD2 has a Figure 2The decoupling circuit CD1 has a higher decoupling circuit quality factor. In fact, 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 artifacts on the generated image. In addition, this solution remains compact because no additional components are added to the part inserted into the human body.

[0083] In the transmission phase, the resistance of the decoupling circuit CD2 is equal to the matching capacitor C M The resistance of the receiving transmission line LTR, the blocking capacitor C B The resistance of the switch INT and the negative resistance R N The negative resistance circuit can therefore improve the quality factor of the decoupling circuit by reducing the total resistance of the decoupling circuit. The quality factor of the decoupling circuit increases during the transmission phase. Therefore, this makes it possible to improve the decoupling efficiency between the receiving antenna and the transmitting antenna during the transmission phase of the MRI / MRS device.

[0084] This solution is particularly advantageous for intracardiac applications where the maximum cable diameter restrictions are high. However, the smaller the diameter of the transmission line, the higher its resistance, which has the effect of generating losses in the receiving transmission line LTR.

[0085] Advantageously, the negative resistance circuit R N The configuration is such that the resistance of the decoupling circuit CD2 is substantially zero.

[0086] exist Figure 3 In a non-limiting example, the switch INT is connected to the switch INT by a negative resistance circuit R connected in series with the switch INT. N Ground.

[0087] Alternatively, the negative resistance R N Connect the transmission line to the blocking capacitor C B , or connect a blocking capacitor to switch IN.

[0088] exist Figure 3 In a non-limiting example, the cathode of the PIN diode is connected to the negative resistance circuit R in series with the switch INT. N Ground.

[0089] In a manner known per se, the negative resistance circuit R N can be made in different ways. It can include two cross-coupled metal oxide semiconductor field effect transistors (also called MOSFETs). Alternatively, the circuit R N It can be based on an operational amplifier, a tunneling diode, a programmable unijunction transistor (also called a PUT (an acronym for “Programmable unijunction transistor”) or a Gunn diode.

[0090] Negative resistance circuit R N Requires its own power supply, which Figure 3 The power source is advantageously connected to the negative resistance circuit via a power supply cable so that when the receiving antenna is located in the heart, the power source is located outside the human body.

[0091] Advantageously, as in Figure 3 In a non-limiting example, the negative resistance circuit is installed so that when the receiving antenna B_REC (or B_REC4) is inside the patient's heart, the negative resistance circuit is located outside the human body. This solution does not require providing direct current in the patient's heart, the leakage of which may cause cardiac arrest.

[0092] Furthermore, this embodiment does not require the use of micro-components to create switches or negative resistance circuits that can introduce them into the heart. This makes it possible to produce a simple and low-cost device.

[0093] Furthermore, the fact that these elements are intended to be located outside the human body makes it possible to limit the number of elements of the part of the device intended to be introduced into the heart, and therefore to miniaturize this part.

[0094] The present invention also relates to an MRI / MRS system, which comprises an MRI / MRS device A and a Figure 1 The alternative receiving device DREC2 shown is equivalent to using Figure 1 The decoupling device ED2 replaces the decoupling device ED1.

[0095] Third embodiment

[0096] Figure 4 A circuit diagram of a receiving device DREC3 according to a third embodiment of the invention is shown. The receiving device DREC3 according to the third embodiment differs from the first embodiment in that, in addition to the reception transmission line LTR, it also comprises a transmission line, a so-called decoupling LTD.

[0097] The reception transmission line LTR is intended to electrically connect the reception antenna B_REC to the receiver REC.

[0098] To this end, the reception transmission line LTR is advantageously intended to electrically connect the transmission connector COT to the reception antenna B_REC, such as Figure 6 shown.

[0099] This connection does not go through switch INT.

[0100] Just like the receiving transmission line LTR, the decoupling transmission line LTD can be made in the form of a coaxial cable, a two-wire line or a twisted pair.

[0101] The decoupling transmission line LTD comprises a first conductor c1a, the first conductor c1a comprising a proximal end (eg, Figure 6 as shown) and electrically connected to the far end of the receiving antenna B_REC.

[0102] The decoupling transmission line LTD includes a second conductor c2a electrically connected to the ground.

[0103] The decoupling efficiency of this embodiment can be higher than that of the first embodiment, which makes it possible to limit artifacts on the image. This is a good solution when space restrictions can accommodate two cables. This solution is easy to implement because it means limited constraints on the geometry and configuration of the receiving transmission line LTR, only the decoupling transmission line LTD participating in the decoupling is constrained.

[0104] exist Figure 4 In a specific embodiment of the present invention, the first conductor c1a of the decoupling transmission line LTD is connected to the tuning capacitor C at the far end thereof. T The first terminal is electrically connected to the receiving antenna B_REC, the tuning capacitor C T The second terminal is connected to the ground point P M The receiver REC is intended to be electrically connected to the reception transmission line LTR and not to the decoupling transmission line LTD, so as to receive a radio frequency signal received by the reception antenna B_REC via the reception transmission line LTR and not through the decoupling transmission line LTD.

[0105] In other words, the receiver REC is intended to be electrically connected to the reception transmission line LTR and is thus intended to receive radio frequency signals received by the reception antenna B_REC via the reception transmission line LTR, without these signals passing through the decoupling transmission line LTD.

[0106] 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.

[0107] 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.

[0108] This connection is realized, for example, via a transmission connector COT.

[0109] Furthermore, the switch INT is electrically connected to the receiving antenna via the decoupling transmission line LTD without passing through the receiving transmission line LTR.

[0110] In other words, two independent transmission lines are used to ensure:

[0111] - decoupling between the receiving and transmitting antennas of MRI / MRS devices during the transmission phase,

[0112] - In the reception phase, a signal from a reception antenna is transmitted to a receiver REC, the signal being intended to be received by the receiver REC.

[0113] In other words, in the decoupling function of the receiving antenna during transmission in the transmitting phase and the receiving phase, the decoupling transmission line LTD only participates in decoupling, while the receiving transmission line LTR only participates in transmission. Transmission refers to the transmission of a signal from the receiving antenna to the receiver for reception by the receiver.

[0114] Therefore, in Figure 4 The decoupling circuit CD3 surrounded by a solid line frame in the figure is different from the first embodiment in that it includes a decoupling transmission line LTD, a tuning capacitor C T and decoupling device ED1.

[0115] In order to have a decoupling function, the decoupling transmission line LTD has an inductance function. 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 f0. The length is approximately calculated and then the exact length is determined by experiment in order to obtain the desired resonant frequency. In this embodiment, this length restriction does not apply to the receiving transmission line LTR.

[0116] By separating the functions of the two transmission lines, this embodiment makes it possible to adjust the length of the decoupling transmission line LTD and the tuning capacitor C T The decoupling quality is improved by using a capacitor, and the reception quality is improved by matching the impedance of the receiving antenna B_REC with the impedance of the receiving transmission line LTR at the operating frequency f0 of the MRI / MRS device.

[0117] Therefore, advantageously, the length of the decoupling transmission line LTD is defined such that the resonant frequency of the decoupling circuit CD3 is equal to the frequency f0 and such that the impedance of the receiving antenna B_REC matches the impedance of the receiving transmission line B_REC at the operating frequency f0 of the MRI / MRS device.

[0118] In other words, the equivalent impedance of the receiving antenna B_REC is defined as an impedance regarded by the receiving transmission line LTR as being equal to the characteristic impedance of the receiving transmission line LTR at the operating frequency f0 of the MRI / MRS apparatus.

[0119] The characteristic impedance of the receiving transmission line LTR at the frequency f0 is, for example, 50 ohms.

[0120] In summary, this technical solution makes it possible to:

[0121] - optimize the decoupling quality of the receiving antenna located far outside the human body during the transmit phase to avoid degradation of the measured signal quality and ensure the safety of the patient (no RF current circulates in the receiving antenna during the transmit phase and there are no powered parts inside the body),

[0122] - Optimizing the process of transmitting the signal to the receiver REC during the reception phase, thereby maximizing the signal-to-noise ratio of the signal measured by the receiving antenna.

[0123] The separation of the two circuits provides additional flexibility in the choice of electronic components, allowing each function to be optimized independently (decoupling at the transmission and reception phases of the signal). This choice can be advantageously made by taking into account the space constraints associated with introducing the receiving antenna into the heart and, in particular, the losses generated by the small diameter cables.

[0124] The length of the decoupling transmission line LTD is defined such that when the receiving antenna B_REC is located in the heart, the decoupling device (especially the switch INT) is located outside the human body.

[0125] When the receiving antenna is intended to be inserted into the body through the jugular vein access, it is usually greater than or equal to 30 cm or 40 cm. When the receiving antenna is intended to be inserted into the body through the inguinal access, it is usually greater than or equal to 80 cm.

[0126] Alternative to the Third Embodiment

[0127] Figure 5 An alternative to the third embodiment is shown, which is Figure 4 The difference is that the receiving antenna B_REC4 of the receiving device DREC4 includes a capacitor C M and C T Additional tuning capacitor C in series TA . Additional tuning capacitor C TA The tuning capacitor C T The first terminal is connected to the tuning capacitor C T This feature makes it possible to choose another value for the length of the decoupling transmission line LTD if necessary, or for the tuning capacitor C if there is a constraint to use certain values. T Choose another value for the capacitor.

[0128] It should be noted that in the third embodiment, and in its alternatives, the decoupling device of the decoupling circuit may include a circuit R having a negative resistance installed in series with the switch INT (ie, installed in series with the first conductor c1 of the decoupling transmission line LTD). N (As in the second embodiment). Figure 3 The different components, configurations and embodiments of the negative resistor described are applicable to the third embodiment and its alternatives.

[0129] The present invention also relates to an MRI / MRS system, which comprises an MRI / MRS device A and a Figure 5 The alternative receiving device DREC4 shown is equivalent to using Figure 6 The receiving antenna B_REC4 in replaces the receiving antenna B_REC.

[0130] Other Features

[0131] To prevent heating of the cables (transmission lines) inserted into the sheath, a circuit LC (also called a trap) may be distributed along at least one transmission line (LTR and / or LTD) to prevent circulation of parasitic currents, as described earlier in this document.

[0132] In the embodiment shown in the figures, the matching capacitor is installed in series with the tuning capacitor. Alternatively, the receiving antenna comprises a matching capacitor or a matching capacitor network instead of and / or in addition to the matching capacitor, which is installed in series with the transmission line installed in series with the decoupling device.

[0133] Sheath receiving device

[0134] Advantageously, the receiving device comprises a tubular sheath made of an electrically insulating material.

[0135] The sheath is flexible so that it can be mechanically deflected.

[0136] The sheath is advantageously in the form of an elongated tube along the sheath axis and can have a substantially constant maximum diameter (outer diameter) over its entire length or over the entire length of its portion intended to be introduced into the human body.

[0137] The outer diameter is adapted to the largest size of the blood vessel to be inserted.

[0138] Advantageously, this diameter is less than 2 mm.

[0139] The tubular sheath defines an elongated inner cavity along the x-axis and defines a receive control line LC, a receive transmission line LTR and possibly a decoupling transmission line LTD.

[0140] The sheath comprises a proximal end, which is mechanically connected to the switch INT or, more generally, to the decoupling device, and a distal end, which is able to receive the receiving resonant antenna B_REC or B_REC4.

[0141] The distal end of the sheath is used to be introduced into the human body, more specifically, into a blood vessel connected to the heart, and the proximal end of the sheath is used to remain outside the human body.

[0142] Advantageously, the receiving antenna can be in an unfolded state, in which the diameter of the receiving antenna in the axis of the sheath is greater than the diameter of the sheath.Then, when the receiving antenna is in a folded state, the receiving antenna is housed in the sheath.

[0143] For example, the receiving antenna can be integrated with an inflatable / deflatable balloon within the heart cavity, or include a mechanical system that allows the receiving antenna to be deployed in contact with the area to be imaged and allows the receiving antenna to be folded to maneuver it into a blood vessel connected to the heart, or the receiving antenna includes any other system that allows its geometry to be modified between the insertion / removal phase of the sheath into the human body and the imaging phase.

Claims

1. A device (DREC1, DREC2, DREC3, DREC4) for receiving radio frequency signals of a magnetic resonance imaging or spectroscopy system, the device (DREC1, DREC2, DREC3, DREC4) comprising: An intracardiac receiving resonant antenna (B_REC) and a switch (INT), when the switch is powered by a direct current with a first strength, the switch can be alternately in an open state so that the receiving antenna (B_REC) is tuned to the operating frequency (f0) of the magnetic resonance imaging system, and when the switch is powered by a direct current with a second strength, the switch can be alternately in a closed state so that the frequency of the receiving antenna is detuned, the receiving antenna (B_REC) is also used to connect to a receiver (REC), when the switch (INT) is in the open state, the receiver (REC) is used to receive the radio frequency signal received by the receiving resonant antenna (B_REC), the receiving device includes a first transmission line (LTR, LTD) having a conductor, the conductor has a distal end electrically connected to the receiving resonant antenna (B_REC) and a proximal end electrically connected to the switch (INT), so that when the receiving antenna (B_REC) is located inside the patient's heart, the switch is intended to be located outside the human body.

2. The receiving device (DREC3, DREC4) according to claim 1, in addition to including the first transmission line (LTD), also includes a second transmission line (LTR) having a conductor, the conductor including a far end electrically connected to the receiving antenna (B_REC, B_REC4) and a near end for electrically connecting to the receiver (REC) to transmit the radio frequency signal received by the receiving antenna (B_REC, B_REC4) to the receiver (REC).

3. The receiving device (DREC3, DREC4) according to claim 2, wherein: The receiver (REC) is used to be electrically connected to the receiving transmission line (LTR) so as to receive the radio frequency signal received by the receiving antenna (B_REC) via the receiving transmission line (LTR) without passing through the decoupling transmission line (LTD).

4. Receiving device (DREC3, DREC4) according to the preceding claim, wherein The receiving antenna comprises a tuning capacitor and a matching capacitor which are installed in series and connected through a ground point. M ) electrically connects the conductor of the second transmission line (LTR) to the ground point (P M ).

5. The receiving device (DREC1, DREC2) according to claim 1, wherein The proximal end of the conductor of the first transmission line (LTR) is used to be connected to the receiver (REC) to transmit the radio frequency signal received by the receiving antenna (B_REC) to the receiver (REC).

6. The receiving device (DREC1, DREC2) according to claim 4, wherein: The receiving antenna includes the ground point (P M ) is electrically connected to a matching capacitor (C M ).

7. A receiving device (DREC2) according to any one of the preceding claims, comprising a circuit (R N ).

8. The receiving device (DREC2) according to claim 7, wherein: The circuit having the negative resistance connects the switch to ground.

9. A receiving device (DREC2) according to any one of claims 7 to 8, wherein: The circuit with the negative resistance is intended to be located outside the human body when the receiving antenna (B_REC) is located inside the patient's heart.

10. A receiving device (DREC1, DREC2, DREC3, DREC4) according to any of the preceding claims, comprising a sheath for receiving the first transmission line, the sheath comprising a proximal end mechanically connected to the switch (INT) and a distal end capable of receiving the receiving antenna (B_REC).

11. Receiving device (DREC1, DREC2, DREC3, DREC4) according to the preceding claim, wherein The sheath has a diameter less than or equal to 2 mm.

12. A magnetic resonance imaging or spectroscopy system comprising a receiving device according to any of the preceding claims, the system comprising a magnetic resonance imaging or spectroscopy device, the magnetic resonance imaging or spectroscopy device comprising a main magnet (GENST) for generating a static magnetic field, a gradient generator (GENGR) with gradient coils and a transmitting antenna (TRANS_RF) for transmitting radio frequency signals.

13. An imaging system according to the preceding claim, wherein: The magnetic resonance imaging or spectroscopy device comprises a receiver (REC).

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