Tunable radio frequency receiving coil

Abstract

To detect errors in a magnetic resonance inspection system, a tunable RF receiver coil assembly is provided, the RF receiver coil assembly comprising at least one RF receiver coil, an electronic detuning circuit for switching between a low noise receiving state of the tunable RF receiver coil and a passive state of the tunable RF receiver coil, and a monitor circuit, the monitor circuit being electrically isolated from and reactively coupled to the electronic detuning circuit and adapted to inductively measure an AC current or an AC voltage in the electronic detuning circuit induced by an RF transmit signal generated by the magnetic resonance inspection system, or the monitor circuit being adapted to couple to a RE signal tunable RF receiver coil, where the tunable RF receiver coil is configured to receive an RE signal coupled by a magnetic resonance preamplifier.

Description

[Technical field]

[0001] The present invention relates to the field of tunable radio frequency (RF) receiver coil assemblies, and more particularly to a system and method for detecting errors in a magnetic resonance inspection system using a tunable radio frequency (RF) receiver coil. [Background technology]

[0002] MR devices apply a main magnetic field through an examination region during examination and / or treatment of a patient. This strong field, typically designated B0, acts to align the nuclear spins of body tissue within the patient being examined. In some MR devices, the B0 field is oriented horizontally, while in other MR devices, the B0 field is oriented vertically.

[0003] In both horizontal and vertical systems, magnetic resonance occurs when a relatively strong orthogonal radio frequency (RF) field (typically B i ) is excited by B i The magnetic field throws the aligned nuclear spins into a plane perpendicular to the static magnetic field B0. As the nuclear spins relax, they return to alignment with the B0 field, which emits a relatively weak radio frequency magnetic resonance signal. This resonance is detected by an RF coil tuned to a particular resonance frequency. These resonance signals are sent to a processing device to reconstruct the signal into an image representation or to derive spectroscopic information. Typically, the transmitted RF magnetic excitation signal is orders of magnitude larger than the received magnetic resonance signal produced by the relaxed nuclear spins that is detected by the RF receiving coil.

[0004] MR coils for signal reception need to have two operating states: an "on" state, or more precisely a low-noise receiving state for capturing very weak (down to the noise floor) nuclear signals, and an "off" state, or more precisely a passive state of a tunable RF receiver coil, the coil needs to withstand the strong RF pulses intended to excite the nuclei. In addition to other means, the two states are achieved by placing one or more detuning switches along the coil conductor. Impedance transformation and transmission lines can be used so that a real switch can be placed in the same spot, while the real switch is effective at a remote location. Currently, the switches consist of diodes that are biased accordingly. Available diodes are far from being ideal switches that exhibit a non-zero forward bias impedance and infinite impedance when reverse biased. In the case of MR, this problem is typically solved by adding a parallel resonant circuit as a switch in series with the coil.

[0005] To maintain patient safety and protect sensitive receiver equipment, the receive coils are typically decoupled or detuned during the transmit phase of the MR procedure. To minimize the above-mentioned problems, the coils include specific detuning circuits whose function is to prevent the receiver equipment from receiving the transmitted RF excitation signal. It is therefore known to decouple MRI coils using PIN diodes in the detuning circuits.

[0006] Current detuning circuits for MR receive coils use PIN diodes to switch the receive coil between tuned and detuned states. PIN diodes are semiconductor devices that can operate as DC current / voltage controlled RF switches. When forward biased with DC current, a PIN diode acts like a closed switch with low on-resistance. When reverse biased with a DC voltage, a PIN diode acts like an open switch with high off-resistance and low parasitic capacitance. Because forward biasing uses DC current, forward biasing requires a non-negligible amount of power.

[0007] In MRI receive coils, PIN diodes are used in a resonant tank circuit configuration so that whenever the PIN diode is forward biased, i.e., the RF switch is "on", the MRI receive coil is detuned. This configuration is preferred for MRI receive coils because it allows the DC drive signal to be kept low. In addition, the tank circuit configuration also allows partial generation of a DC bias current that transfers from the RF excitation current through the diode. On the other hand, if the PIN diode is placed directly in the antenna structure, the diode is reverse biased during transmission. The reverse bias DC voltage must exceed the RF voltage, which can be on the order of several hundred volts. Such a setup also requires a relatively high forward DC current (up to 100 mA) during reception to keep losses low.

[0008] FIG. 1 shows a schematic diagram of a tunable radio frequency (RF) receiver coil assembly according to the prior art. The RF receiver coil assembly comprises an RF receiver coil 1 and an electronic detuning circuit 2 for switching between "on" and "off" states. The tank circuit 3 consists of a capacitor 4 and an inductance 5. As switch 6, a PIN diode is used. In the "on" state, the diode 6 is reverse biased and disables the inductance 5 in a parallel resonant circuit. The RF current (induced from the nuclear signal) can circulate freely in the coil loop. One of the capacitors forming the resonant circuit of the MR coil is almost doubled for the detuning circuit. The diode 6 is forward biased, so that the inductance 5 can form a parallel resonant circuit with its resonant capacitor 4. This provides a high blocking impedance, much higher than the impedance of the reverse biased diode itself. The functioning of the circuit is detected by continuously measuring the bias current through the diode 6. When two expected values ​​are not reached: a low noise reception state and a passive state (zero and e.g. 80 mA), a stop of the scan is triggered. The RF current (induced by the RF transmit pulse) is effectively blocked within the coil loop.

[0009] Measuring the diode 6 current is an indirect indicator of proper functioning, but requires additional measures for safety. The reason is that in a failure mode the diode 6 is disconnected from the rest of the coil 1, which cannot be detected. The situation does not change if the inductance 5 is included in the bias loop 9. Due to this uncertainty, a fuse can be added along the MR coil 1. The fuse will blow when the current reaches a certain threshold that is considered dangerous to the patient. However, this method also has drawbacks. A fuse is basically a resistor that is heated (and destroyed) by the surging current. The resistor adds to the thermal noise received by the preamplifier, thus worsening the signal-to-noise ratio (SNR). For small coils placed close to the patient, the current threshold is large enough that a fuse is not available and it will blow fast enough and still be acceptable in terms of their effect on the SNR. Monitoring the functioning of the entire tank circuit 3 is the only fail-safe detection method, and if the tank circuit 3 is disconnected, the coil 1 will be damaged but is essentially safe. A damaged MR coil 1 will be detected, since it will no longer provide an MRI received signal.

[0010] US Patent Application US2021 / 0190890 discloses a local coil with active and passive detuning facilities. Local coil monitoring is provided for the detuning facilities. A current sensor is looped into the signal line of the local coil activation. Summary of the Invention [Problem to be solved by the invention]

[0011] It is an object of the present invention to improve the safety of RF transmissions into the examination zone of a magnetic resonance examination system. [Means for solving the problem]

[0012] According to the invention, this object is addressed by the subject matter of the independent claims. Preferred embodiments of the invention are set forth in the dependent claims.

[0013] Therefore, according to the present invention there is provided a tunable RF receiver coil assembly for use in a magnetic resonance examination system, the tunable RF receiver coil assembly comprising at least one RF receiver coil, an electronic detuning circuit for switching between a low noise reception state of the tunable RF receiver coil and a passive state of the tunable RF receiver coil, and a monitor circuit, the monitor circuit being electrically isolated from the electronic detuning circuit and reactively coupled to the electronic detuning circuit, the monitor circuit being adapted to inductively measure an AC current or an AC voltage in the electronic detuning circuit induced by an RF transmit signal generated by the magnetic resonance examination system, or the monitor circuit being adapted to couple an RF signal into a tunable RF receiver coil, the tunable RF receiver coil magnetically coherently receiving the coupled RF signal. a tunable RF receiver coil assembly configured to receive an RF signal received by a magnetic resonance preamplifier, or the monitor circuit is configured as a transceiver and adapted to couple an RF signal to the tunable RF receiver coil and measure a reflection coefficient of the RF signal coupled into the tunable RF receiver coil, the RF receiver coil assembly further comprising a correlator device connected to the monitor circuit and configured to correlate the inductively measured current in the electronic detuning circuit to an RF transmit operating condition of an RF transmit pulse envelope for an RF transmit signal generated by the magnetic resonance inspection system, or the correlator device is configured to correlate the coupled RF signal received by a magnetic resonance preamplifier to an RF transmit operating condition of an RF transmit pulse envelope for an RF transmit signal generated by the magnetic resonance inspection system.

[0014] In one embodiment, a correlator device is configured to correlate the coupled RE signal received by the magnetic resonance preamplifier, the inductively measured current in the electronic detuning circuit, to an RF transmit operating condition of an RF transmit pulse envelope for an RF transmit signal generated by the magnetic resonance inspection system.

[0015] For example, if the operating conditions are correlated with the inductively measured AC current or AC voltage in the electronic detuning circuit, a certain level of incoming signal is predicted. If the operating conditions are correlated with the coupled RE signal received by the magnetic resonance preamplifier, another signal level is predicted. Only if both signals are within the expected values, the coil is normal, otherwise the deviation pattern helps to track down faults in the magnetic resonance inspection system. In an advantageous embodiment of the invention, the electronic detuning circuit comprises a tank circuit having at least one first inductance, and the monitor circuit comprises at least one second inductance, the monitor circuit being configured to weakly couple the second inductance to the first inductance to pick up a portion of the current induced by the RF transmit signal, the monitor circuit being further configured to generate a signal in response to the RF transmit signal, or the monitor circuit being configured to weakly couple the second inductance to the tunable RF receiver coil to couple the RF signal to the tunable RF receiver coil.

[0016] In an advantageous embodiment of the invention, the monitor circuit further comprises a detector device, which is configured to rectify or directly sample a signal dependent on the RF transmission signal.

[0017] In an advantageous embodiment of the invention, the detector device is part of the control logic of a tunable RF receiver coil.

[0018] In an advantageous embodiment of the invention, the detector arrangement is integrated into a magnetic resonance preamplifier of a tunable high frequency RF receiving coil.

[0019] In an advantageous embodiment of the invention, the electronic detuning circuit comprises at least one switch for switching between a low-noise reception state of the tunable RF receiver coil and a passive state of the tunable RF receiver coil, the switch being a field-effect transistor and / or a MEMS switch. Conventional detuning circuits use PIN diode switches, but PIN diodes require a continuous control signal that can cause electric field distortion along the control signal transmission line unless properly shielded. Thus, with higher power transmit RF excitation pulses, increasingly higher control signals for biasing the PIN diodes are required to ensure that the coil segments remain decoupled. Therefore, the use of FET and / or MEMS switches is particularly advantageous.

[0020] In an advantageous embodiment of the invention the correlator device is further adapted to distinguish between different signal levels, the different signal levels describing a respective functional state of at least one of the electronic detuning circuits.

[0021] According to one aspect, there is provided a magnetic resonance imaging system comprising a tunable high frequency RF receiver coil assembly as described above.

[0022] According to another aspect, a method for detecting errors in a magnetic resonance inspection system, the magnetic resonance inspection system having a tunable RF receiver coil assembly, the tunable RF receiver coil assembly including at least one RF receiver coil, an electronic detuning circuit for switching between a low noise reception state of the tunable RF receiver coil and a passive state of the tunable RF receiver coil, a monitor circuit, the monitor circuit being electrically isolated from and reactively coupled to the electronic detuning circuit, the monitor circuit being adapted to inductively measure an AC current or an AC voltage in the electronic detuning circuit induced by an RF transmit signal generated by the magnetic resonance inspection system, and a correlator device, the correlator device being adapted to magnetically detune the electronic detuning circuit. and a correlator device configured to correlate an inductively measured current in the electronic detuning circuit with an RF transmit operating state of an RF transmit pulse envelope for an RF transmit signal generated by the magnetic resonance inspection system, the method comprising the steps of: monitoring a current in the electronic detuning circuit induced by the RF transmit signal generated by the magnetic resonance inspection system with a monitor circuit; correlating the inductively measured current in the electronic detuning circuit with an RF transmit operating state of the RF transmit pulse envelope for the RF transmit signal generated by the magnetic resonance inspection system; and determining, using the correlator device, whether the electronic detuning circuit is in an abnormal state based on the RF transmit operating state of the RF transmit pulse envelope for the RF transmit signal.

[0023] In an advantageous embodiment of the invention, the method includes mapping the position of the tunable RF receiver coil based on the monitored current in the electronic detuning circuit.

[0024] In an advantageous embodiment of the present invention, the step of mapping the location of the tunable RF receiver coil comprises using deterministic matrix operations or AI techniques.

[0025] According to another aspect, a method for detecting an error in a magnetic resonance examination system, the magnetic resonance examination system having a tunable RF receiver coil assembly, the tunable RF receiver coil assembly having at least one RF receiver coil, an electronic detuning circuit for switching between a low noise reception state of the tunable RF receiver coil and a passive state of the tunable RF receiver coil, and a monitor circuit, the monitor circuit being electrically isolated from the electronic detuning circuit and reactively coupled to the electronic detuning circuit, the monitor circuit being adapted to couple an RF signal to the tunable RF receiver coil, the tunable RF receiver coil being configured to receive the coupled RF signal by a magnetic resonance MR preamplifier, the tunable RF receiver coil being configured to receive the coupled RF signal by a magnetic resonance MR preamplifier, the monitor circuit being electrically isolated from the electronic detuning circuit and reactively coupled to the electronic detuning circuit, the monitor circuit being adapted to couple an RF signal to the tunable RF receiver coil, the tunable RF receiver coil being configured to receive the coupled RF signal by a magnetic resonance MR preamplifier, the monitor circuit being electrically isolated from the electronic detuning circuit and reactively coupled to the electronic detuning circuit, the monitor circuit being adapted to couple an RF signal to the tunable RF receiver coil, the tunable RF receiver coil being configured to receive the coupled RF signal by a magnetic resonance MR preamplifier, the monitor circuit being configured to couple the RF signal to the tunable RF receiver coil ... The tunable RF receiver coil assembly further comprises a correlator device configured to correlate an RF signal received by the magnetic resonance preamplifier with an RF transmit operating state of an RF transmit pulse envelope for an RF transmit signal generated by the magnetic resonance inspection system, the method comprising the steps of coupling an RF signal to the tunable RF receiver coil by the monitor circuit, receiving the RF signal by the MR preamplifier, correlating the received RE signal in the MR preamplifier with an RF transmit operating state of an RF transmit pulse envelope for an RF transmit signal generated by the magnetic resonance inspection system using the correlator device, and determining whether the electronic detuning circuit is in an abnormal state.

[0026] In an advantageous embodiment of the invention, the step of coupling the RF signal by the monitor circuitry to the tunable RF receiver coil is interleaved with the magnetic resonance sequence.

[0027] In an advantageous embodiment of the invention, the step of coupling the RE signal into a tunable RF receiver coil by a monitor circuit uses an RE signal close to the Larmor frequency, and the magnetic resonance sequence is interleaved by combining it with a pilot tone technique.

[0028] According to one aspect, a computer program product is provided that includes instructions for detecting errors in a magnetic resonance examination system by controlling a tunable high frequency RF receiver coil assembly according to the above-described method.

[0029] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter, but such embodiments do not necessarily represent the full scope of the invention, and therefore reference should be made to the claims and this specification for interpreting the scope of the invention. [Brief description of the drawings]

[0030] [Figure 1] 1 illustrates a schematic diagram of a tunable radio frequency receiver coil assembly according to the prior art; [Diagram 2] 1 illustrates a schematic diagram of a tunable radio frequency receiver coil assembly according to one embodiment of the present invention; [Diagram 3] 2 shows a flowchart of a method for detecting errors in a magnetic resonance examination system according to an embodiment of the present invention. [Figure 4] 4 shows a flowchart of a method for detecting errors in a magnetic resonance examination system according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] FIG. 1 has already been described as prior art in the general part of the specification.

[0032] Fig. 2 shows a schematic diagram of a tunable radio frequency receiver coil assembly according to an embodiment of the present invention. The RF receiver coil assembly comprises an RF receiver coil 1 and an electronic detuning circuit 2 for switching between a low-noise receiving state of the tunable radio frequency receiver coil 1 and a passive state of the tunable radio frequency receiver coil 1. The RF receiver coil assembly further comprises a monitor circuit 7, which is electrically isolated from and reactively coupled to the electronic detuning circuit 2. On the one hand, the monitor circuit 7 is adapted to inductively measure an AC current or an AC voltage in the electronic detuning circuit 2 induced by an RF transmission signal generated by a magnetic resonance examination system, or on the other hand, to couple an RE signal to the tunable RF receiver coil 1, which is configured to receive the RE signal coupled by a magnetic resonance preamplifier 12. In practice, the monitor circuit 7 inductively measures an AC current or a voltage in the electronic detuning circuit in a high-frequency Larmor frequency band related to a spin resonance frequency for a type of atomic nucleus and a main magnetic field strength. In another embodiment, the monitor circuit 7 is configured as a transceiver and is adapted to couple the RE signal to the tunable RF receiver coil 1 and measure the reflection coefficient of the RF signal coupled to the tunable RF receiver coil 1. Based on the measurement of the reflection coefficient, a simple binary decision can be made whether the RF receiver coil 1 is still operational. In one embodiment of the present invention, the electronic detuning circuit 2 comprises a tank circuit 3 having at least one first inductance 5, the monitor circuit 7 comprises at least one second inductance 8, the monitor circuit 7 is configured to weakly couple the second inductance 8 to the first inductance 5 to pick up a portion of the current induced by the RF transmit signal, and the monitor circuit 7 is further configured to generate a signal in response to the RF transmit signal. In one embodiment, the monitor circuit 7 comprises a detector device. The detector device is configured to rectify or directly sample the RF transmit signal dependent signal. The detector device can be, for example, part of the control logic of the tunable RF receiver coil. A PIN diode is used in the electronic detuning circuit 2 as a switch 6 for switching between a low noise reception state of the tunable RF receiver coil 1 and a passive state of the tunable RF receiver coil 1.In the "on" state, the diode 6 is reverse biased, nullifying the inductance 5 of the parallel resonant circuit. RF current (induced from the nuclear signal) can circulate freely in the coil loop. In most cases, one of the capacitors 4 that form the resonant circuit of the MR coil 1 is used double for its detuning circuit. The diode 6 is forward biased, allowing the inductor to form a parallel resonant circuit 3 with the resonant capacitor 4. This provides a high blocking impedance, much higher than the impedance of the reverse biased diode 6 itself. However, PIN diodes require a continuous control signal that can cause field distortion along the control signal transmission line unless properly shielded. Thus, with higher power transmit RF excitation pulses, increasingly higher control signals to bias the PIN diode 6 are required to ensure that the coil segments remain decoupled. It is therefore particularly advantageous to use a FET as the switch 6. The diode may in the near future be replaced by a FET, which would remove the option for current source-based switching. This would also remove the option for current-based malfunction testing. It would require an additional DC connection to monitor the integrity of the drain-source (DS) trace of the FET, still presenting the same problems as diode monitoring. Therefore, the present invention is particularly advantageous when using a FET as switch 6. In one embodiment of the present invention, the RF current is measured in tank circuit 3. A high voltage induced in the RF receiver coil 1 (by the transmit pulse) results in a large current in inductance 5, I. L1 =I MRcoil where Q in ×Q is the Q factor of the tank circuit 3, and I MRcoilindicates a small residual current in the detuned receive loop. The measurement is made by using an inductance 8 which weakly couples to the inductance 5, thus picking up a proportion of the current induced by the transmit field. The signal picked up by the inductor 8 is then rectified or directly sampled using a detector device which is part of the control logic of the coil 1. The data is transmitted to the logic via data lines 11, 13. The requirements in terms of dynamic range and bandwidth are lower for this detector than for the receiver used to detect the spin signal. In one embodiment, this function is part of the magnetic resonance preamplifier 12 of the RF receiver coil 1. The signal magnitude should reach a certain threshold and follow the transmit pulse envelope. Instead of coupling directly to the RF receiver coil, which would otherwise destroy the tank circuit (or in any case be a safe situation, e.g. oriented so as to hardly capture any flux of the transmit magnetic field), the indirect detection method via the tank circuit 3 prevents noise or other adverse effects from the inductor 8 and the connected electronics from coupling to the magnetic resonance preamplifier 12.

[0033] Typically, an RF receiver coil assembly has several tank circuits 3, each with a detuning circuit 2. A simple approach would be to monitor each and every circuit, but that may result in other problems, e.g. more wires, component elements, etc. In addition to monitoring several coils of the array in one embodiment of the present invention, it is proposed to make it more complex to monitor a single tank circuit. This can be, for example, the tank circuit 3 closest to the preamplifier 12. If one detuning circuit 2 fails, it will result in a higher voltage drop than the other circuits. Therefore, in one embodiment of the present invention, the correlator device 10 is configured to distinguish between different signal levels. For example, different levels may indicate that during the transmission phase, very little signal is coupled out of the tank circuit 3. This means that the directly connected tank circuits 3 will break, resulting in a malfunction or interlock. When a certain demand signal level is reached, it means that all tank circuits 3 are in sequence, and there is no malfunction. If the signal level is higher than the demand signal level, it means that the remote tank circuit 3 of the coil 1 will break, leading to a malfunction or interlock. In one embodiment of the present invention, the magnitude, phase and coil position of the transmit signal can serve as inputs for decision making by the tank circuit 3. Thus, the RF receiver coil 1 is configured such that information regarding faults is provided to the front end, and in particular to the receiver coil 1.

[0034] Typically, the inductance 5 is aligned to generate a magnetic field perpendicular to that of the RF receiver coil 1 so that it does not couple to the MR TX and RX fields under normal circumstances. As a result, if the RF receiver coil 1 is misaligned, the inductance 8 effectively couples to the TX field leading to a detectable signal (indicative of the functioning of the tank circuit). For certain coils, such as flexible surface arrays, this can still result in false malfunction detections. In one embodiment of the present invention, the method is changed. Instead of picking up the signal via the inductance 8, the RE signal is coupled to the coil via the inductance 8 and received by the MR preamplifier 12. Also, now a typical magnitude or signal envelope should be detected, otherwise the coil 1 is malfunctioning. In this scenario, a coil integrity test is interleaved with the MR sequence. This can be combined with a pilot tone technique that uses the RE signal rather than the Larmor frequency. Typically, an array of many coils 1 must be monitored. By considering the measurement results of all coil elements, the position of the coil 1 in the scanner can be estimated, thus preventing false positive results. This can include a calibration measurement of the coil 1 (or at least the coil type in the factory). Mapping techniques that estimate the current position based on actual measurements (signals at the inductance 8) and calibration results can be implemented using deterministic matrix operations or AI techniques. The magnitude, envelope, complex signals (magnitude and phase) of the detection methods, sensing or transmission through the inductance 8, and consideration of the coil vicinity vary in the complexity and outcome of the MR sequence, and the choice of the appropriate technique depends on the coil. The position of the coil 1 can be monitored during the imaging sequence. In case of misalignment the coil 1 can be repositioned or measures can be taken to correct the calibration scan for the sensed images. The complex signal is used to train an AI learning algorithm to obtain a baseline for the complex signal monitor. The scan is activated or continued only if the complex RF current is within a defined parameter window.Before starting the scan, a preparation pulse can be used to monitor the fitness of the detuning state. The RF current in coil 1 depends on the coil's Q value and is an indicator of the coil-patient fitting. In addition, the temperature of the detuning circuit can be calculated as T(coil i) = f(Q, duty cycle, amplitude, phase, fitting parameters). In one embodiment, a software monitor on the operator console can show the status of the detuning circuit including reports, data mining history, and diagnostic service tools. In addition, the complex magnitude of the RF current in the coil is a measure of the local B1 field inhomogeneity, thus allowing correction of the total B1 field in the image reconstruction.

[0035] 3 shows a flow chart of a method for detecting an error in a magnetic resonance examination system according to an embodiment of the present invention. In step 300, an MRI system is provided. The MRI system comprises a tunable radio frequency receiver coil 1 including a tunable radio frequency receiver coil assembly, an electronic detuning circuit 2 for switching between a low noise reception state of the tunable radio frequency receiver coil 1 and a passive state of the tunable radio frequency receiver coil 1, and a monitor circuit 7, the monitor circuit 7 being electrically isolated from and reactively coupled to the electronic detuning circuit 2, the monitor circuit 7 being configured to inductively measure an AC current or an AC voltage in the electronic detuning circuit 2 induced by an RF transmit signal generated by the magnetic resonance examination system, and the correlator device 10 being configured to correlate the inductively measured current in the electronic detuning circuit 2 to an RF transmit operating state of an RF transmit pulse envelope for the RF transmit signal generated by the magnetic resonance examination system.

[0036] In step 310, the current in the electronic detuning circuit 2 induced by the RF transmit signal generated by the magnetic resonance examination system is monitored by the monitor circuit 7.

[0037] In step 320 , the induced measured current in the electronic detuning circuit 2 is correlated to the RF transmit operating conditions of the RF transmit pulse envelope of the RF transmit signal generated by the magnetic resonance examination system with the correlator device 10 .

[0038] In step 330, it is determined whether the electronic detuning circuit 2 is in an abnormal state based on the RF transmit operating condition of the RF transmit pulse envelope of the RF transmit signal.

[0039] FIG. 4 shows a flow chart of a method for detecting errors in a magnetic resonance examination system according to another embodiment of the invention.

[0040] In step 400, an MRI system is provided, the MRI system comprising a tunable RF receiver coil assembly comprising at least one RF receiver coil 1, an electronic detuning circuit 2 for switching between a low noise reception state of the tunable RF receiver coil 1 and a passive state of the tunable RF receiver coil 1, and a monitor circuit 7 adapted to couple an RF signal to the tunable RF receiver coil 1, the tunable RF receiver coil 1 being configured to receive the coupled RF signal by a magnetic resonance MR preamplifier 12, and a correlator device 10 configured to correlate the coupled RF signal received by the magnetic resonance preamplifier 12 to an RF transmit operating state of an RF transmit pulse envelope of an RF transmit signal generated by the magnetic resonance examination system.

[0041] In step 410 , the RF signal is coupled to the tunable RF receiver coil 1 by the monitor circuit 7 .

[0042] In step 420 , the RF signal is received by the MR preamplifier 12 .

[0043] In step 430 , the received RE signal in the MR preamplifier 12 is correlated to the RF transmit operating state of the RF transmit pulse envelope for the RF transmit signal generated by the magnetic resonance examination system having the correlator device 10 .

[0044] In step 440 it is determined whether the electronic detuning circuit 2 is in an abnormal state.

[0045] In one embodiment, the monitor circuit 7 is configured as a transceiver and is adapted to couple the RE signal to the tunable RF receiver coil 1 and measure the reflection coefficient of the RF signal coupled to the tunable RF receiver coil 1. This effectively represents a third possibility, i.e. a mixture of the method described in Figure 3 and the method described in Figure 4. Based on the measurement of the reflection coefficient, a simple binary decision can be made whether the RF receiver coil 1 is still operational.

[0046] While the present invention has been illustrated and described in detail in the drawings and the foregoing description, such illustration and description are to be considered as exemplary or illustrative and not restrictive, and the present invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be interpreted as limiting the scope. Moreover, for the sake of clarity, not all elements in the drawings have been labeled with reference signs. [Explanation of symbols]

[0047] Tunable Radio Frequency (RF) Receiver Coil 1 Electronic detuning circuit 2 Tank Circuit 3 Capacitor 4 Inductance 5 Switch 6 Monitor circuit 7 Inductance 8 Bias 9 Correlator device 10 Data Line 11 Magnetic Resonance Preamplifier 12 Data Line 13

Claims

1. 1. A tunable RF receiver coil assembly for use in a magnetic resonance examination system, the tunable RF receiver coil assembly comprising: at least one RF receiver coil; an electronic detuning circuit for switching between a low noise receive state of the tunable RF receiver coil and a passive state of the tunable RF receiver coil; a monitor circuit, the monitor circuit being electrically isolated from and reactively coupled to the electronic detuning circuit, the monitor circuit being adapted to inductively measure an AC current or an AC voltage in the electronic detuning circuit induced by an RF transmit signal generated by the magnetic resonance examination system; or the monitor circuit is configured as a transceiver and adapted to couple an RF signal into the tunable RF receiver coil and measure a reflection coefficient of the RF signal coupled into the tunable RF receiver coil. Monitor circuit and having the RF receiver coil assembly further comprising a correlator device connected to the monitor circuit and configured to correlate the inductively measured current in the electronic detuning circuit to an RF transmit operating condition of an RF transmit pulse envelope for an RF transmit signal generated by the magnetic resonance examination system. A tunable RF receiver coil assembly.

2. the electronic detuning circuit comprises a tank circuit having at least one first inductance, and the monitor circuit comprises at least one second inductance; the monitor circuit is configured to weakly couple the second inductance to the first inductance to pick up a proportion of a current induced by the RF transmit signal, the monitor circuit being further configured to generate a signal dependent on the RF transmit signal; or the monitor circuit is configured to weakly couple the second inductance to the tunable RF receiver coil to couple the RE signal to the tunable RF receiver coil.

2. A tunable RF receiver coil assembly as defined in claim 1.

3. 3. A tunable RF receiver coil assembly as claimed in claim 1, wherein the monitor circuit further comprises a detector arrangement configured to rectify or directly sample the signal dependent on the RF transmit signal.

4. 4. The tunable RF receiver coil assembly of claim 3, wherein the detector arrangement is part of a control logic of the tunable RF receiver coil.

5. 5. A tunable RF receiver coil assembly according to claim 3 or 4, wherein the detector arrangement is integrated into a magnetic resonance preamplifier of the tunable RF receiver coil.

6. 6. A tunable RF receiver coil assembly as claimed in any one of claims 1 to 5, wherein the electronic detuning circuit comprises at least one switch for switching between a low noise reception state of the tunable RF receiver coil and a passive state of the tunable RF receiver coil, the switch being a field effect transistor and / or a MEMS switch.

7. 7. A tunable RF receiver coil assembly as claimed in any one of claims 1 to 6, wherein the correlator device is further configured to distinguish between different signal levels, the different signal levels describing respective functional states of at least one of the electronic detuning circuits.

8. A magnetic resonance examination system comprising a tunable RF receiver coil assembly according to any one of claims 1 to 7.

9. 1. A method for detecting an error in a magnetic resonance examination system, the magnetic resonance examination system comprising:

1. A tunable RF receiver coil assembly, comprising: at least one RF receiver coil; an electronic detuning circuit for switching between a low noise receive state of the tunable RF receiver coil and a passive state of the tunable RF receiver coil; a monitor circuit, the monitor circuit being electrically isolated from the electronic detuning circuit and reactively coupled to the electronic detuning circuit, the monitor circuit being adapted to inductively measure an AC current or an AC voltage in the electronic detuning circuit induced by an RF transmit signal generated by the magnetic resonance examination system; a correlator device configured to correlate the inductively measured current in the electronic detuning circuit to an RF transmit operating condition of an RF transmit pulse envelope for an RF transmit signal generated by the magnetic resonance examination system; said method comprising: monitoring, with the monitor circuitry, a current in the electronic detuning circuit induced by an RF transmit signal generated by the magnetic resonance examination system; correlating the inductively measured current in the electronic detuning circuit with the correlator device to an RF transmit pulse envelope RF transmit operating condition for an RF transmit signal generated by the magnetic resonance examination system; determining whether the electronic detuning circuit is in an abnormal state based on an RF transmit operating condition of an RF transmit pulse envelope for the RF transmit signal; The method comprising:

10. The method comprises: mapping a position of the tunable RF receiver coil based on the monitored current in the electronic detuning circuit. The method of claim 8, further comprising:

11. 10. The method of claim 9, wherein mapping the position of the tunable RF receiver coil comprises using deterministic matrix operations or AI techniques.

12. 1. A method for detecting errors in a magnetic resonance inspection system, the magnetic resonance inspection system having a tunable RF receiver coil assembly, the tunable RF receiver coil assembly comprising: at least one RF receiver coil; an electronic detuning circuit for switching between a low noise receive state of the tunable RF receiver coil and a passive state of the tunable RF receiver coil; a monitor circuit, the monitor circuit being electrically isolated from the electronic detuning circuit and reactively coupled to the electronic detuning circuit, the monitor circuit being adapted to couple an RF signal to the tunable RF receiver coil, the tunable RF receiver coil being configured to receive the coupled RF signal by a magnetic resonance MR preamplifier; having The tunable RF receiver coil assembly further comprises a correlator device configured to correlate an RF signal received by the magnetic resonance preamplifier with an RF transmit operating state of an RF transmit pulse envelope for an RF transmit signal generated by the magnetic resonance examination system, the method comprising: coupling an RF signal to the tunable RF receiver coil by the monitor circuit; receiving the RF signal by the MR preamplifier; correlating the received RE signal in the MR preamplifier with an RF transmit operating condition of an RF transmit pulse envelope for an RF transmit signal generated by the magnetic resonance examination system using the correlator device; determining whether the electronic detuning circuit is in an abnormal state; The method comprising:

13. The method of claim 12 , wherein the step of coupling an RF signal by the monitor circuitry to the tunable RF receiver coil is interleaved with a magnetic resonance sequence.

14. 14. The method of claim 13, wherein the step of coupling an RE signal to the tunable RF receiver coil by the monitor circuit is interleaved with a magnetic resonance sequence combined with a pilot tone technique using an RE signal close to the Larmor frequency.

15. A computer program product having instructions for detecting errors in a magnetic resonance examination system by controlling a tunable RF receiver coil assembly according to the method of any one of claims 9 to 11 or 12 to 14.

Images