Radio frequency receiver coil with electronic fuse

Abstract

An independent security mechanism for a radio frequency (RF) receiver coil is provided. This is achieved by an electronic fuse (3) comprising a switching device (4) for interrupting the RF current in the RF coil loop, the switching device (4) being electrically connected to the RF coil loop (2) and being configured to interrupt the RF current in the RF coil loop (2) when a defined threshold is exceeded. The invention also relates to a method for protecting a radio frequency (RF) receiver coil (1), a magnetic resonance imaging apparatus and a computer program product.

Description

Technical Field

[0001] The present invention relates to the field of radio frequency (RF) receiver coils for magnetic resonance examination systems, and more particularly to an RF receiver coil with an electronic fuse. The present invention also relates to a method and a computer program product for protecting a radio frequency (RF) receiver coil with an electronic fuse. Background Art

[0002] MR coils are turned on and off using RF switches that are typically based on PIN diodes. For fail-safe designs (missing PIN diode drive signal), a second independent safety mechanism must be added. One final solution to this problem is to place a fuse in the coil that blows in the event of a hazardous current. Conventional fuses protect the circuit and prevent damage to the equipment by melting the built-in alloy parts by Joule heat when a current exceeding the rated value flows. However, these fuses have disadvantages such as uncertainty in disconnecting current, slow melting time, and the need for replacement work due to damage from a single overcurrent. Unfortunately, fuses cannot be used for all hazardous currents. With the advent of lightweight digital RF coils for MRI, coils can be equipped with smart features to provide a safe clinical workflow. In addition, there is a trend that components close to tissue are getting smaller and smaller, which requires more sensitive fuses than are available today.

[0003] The MR coil for signal reception needs to have two operating states:

[0004] "On" state: low noise receiving state, used to capture very weak (low to the noise floor) nuclear signals,

[0005] "Off" state: passive state, in which the coil is subjected to strong RF pulses intended to excite the nuclei.

[0006] For switching, PIN diode-based RF switches are usually used. If the coil is switched to the appropriate state, the RF current (introduced by the RF transmit pulse) is effectively blocked in the coil loop. The functionality of the detuning circuit is detected by continuously measuring the DC bias current through the diode and / or the DC bias voltage across the diode. When the expected values ​​for the "on" and "off" states (current zero and current of, for example, 80 mA) are not reached, the scan is stopped immediately. The measurement of the diode current is an indirect indicator of normal operation, but requires an additional safety measure. For fail-safe use, the individual loop elements in the coil are equipped with passive fuses. A fuse is basically a small resistor in series with the coil loop that blows once the current level is exceeded. To maintain high image quality, the resistance of the fuse must be as low as possible, otherwise the resistor will significantly increase the thermal noise received by the coil, thereby reducing the SNR.

[0007] For flexible RF coils where the coil conductor is relatively close to human skin (~5 mm), relatively low currents already constitute a dangerous situation.

[0008] Here, passive fuses do not provide a second safety measure, since fuses with low breaking current and low resistance are technically difficult / impossible to realize.

[0009] The prior art describes several alternatives to electronic fuses in RF receiver coils. For example, document US2013234715 A1 describes a magnetic resonance imaging device comprising a transmitting coil, a receiving coil, a balanced-unbalanced transformer (BALUN), an overheat protection circuit, and an imaging control unit. The transmitting coil applies a radio frequency magnetic field to a subject placed in a static magnetic field. The receiving coil receives magnetic resonance signals emitted from the subject due to the application of the radio frequency magnetic field. The BALUN is connected to the receiving coil and suppresses the unbalanced current induced in the receiving coil. When the temperature of the BALUN exceeds a temperature threshold, the overheat protection circuit indicates that the BALUN is abnormal. The imaging control unit stops imaging when the overheat protection circuit indicates that the BALUN is abnormal.

[0010] There are several problems and disadvantages with the passive fuses used in the prior art. Passive fuses are too slow for thin flexible RF coils. The measurement of the diode current is an indirect indicator for proper operation (additional safety measures are required). A failure mode where the diode is disconnected from the rest of the coil cannot be detected. A failure mode is conceivable where DC current still flows without the coil being effectively detuned, thereby creating a danger to the patient. Passive fuses as a fail-safe detection method require replacement upon disconnection. Summary of the invention

[0011] It is an object of the present invention to improve the protection of radio frequency (RF) receiver coils.

[0012] According to the invention, this object is solved by the subject matter of the independent claims. Preferred embodiments of the invention are described in the subclaims.

[0013] Therefore, according to the present invention, a radio frequency (RF) receiver coil is provided, comprising: at least one RF coil loop, at least one electronic fuse, the electronic fuse comprising a switching device for interrupting an RF current in the RF coil loop, wherein the switching device is electrically connected to the RF coil loop, the electronic fuse further comprising a switch unit for controlling the switching device, wherein the switching device is configured to interrupt the RF current in the RF coil loop through the switch unit if a defined threshold is exceeded, the RF receiver coil further comprising a local current sensor circuit for measuring the RF current, wherein the electronic fuse is configured to compare the output of the local current sensor circuit with a threshold value of the RF current in the RF coil loop for switching the switching device, and if the threshold value is exceeded, deactivate the electronic fuse to interrupt the conductive path of the RF coil loop, thereby interrupting the RF current in the RF coil loop.

[0014] An electronic fuse (also called an efuse) is a small integrated circuit (IC) used to replace a conventional fuse in a device. An electronic fuse functions like a conventional fuse. The fuse can be deactivated when an overcurrent or overvoltage is detected.

[0015] In addition, electronic fuses are not damaged by a single overcurrent and can be reused, and efuses are not constrained by physical limitations such as passive fuses, so a wider range of fusing currents and times can be selected while maintaining low resistance requirements. This achieves the advantage of reducing maintenance costs and recovery time for repairs of RF receiver coils or entire magnetic resonance imaging devices.

[0016] In an advantageous embodiment of the invention, the electronic fuse is a separate stand-alone component in addition to the RF receiver coil electronics.

[0017] In another advantageous embodiment of the invention, the switching device is a FET and / or a MEM switch and / or a bipolar junction transistor and / or a PIN diode. In an embodiment using a FET as the switching device, a charge pump and a gate driver for driving the gate contact of the FET can be foreseen. The efuse can also be a MEM switch. Here, if there is no voltage, the MEM switch is in a high impedance state. Therefore, if the coil is not connected, the coil is safe. The MEM switch can also be used as a FET switch.

[0018] In an advantageous embodiment of the invention, a radio frequency (RF) receiver coil comprises a digitizer for digitizing the output of said local current sensor circuit and comparing it to a threshold value of said RF current in the RF coil loop.

[0019] In another advantageous embodiment of the invention, the RF receiver coil comprises an additional digitizer for measuring the signal of the gate contact of the FET. The signal of the gate of the electronic fuse can be further detected by the remote digitizer. The amplitude / phase of the detected signal will follow the known envelope of the transmitted pulse. If not, there may be a problem, such as a tank circuit, a detuned circuit, a capacitor or a broken connection.

[0020] In an advantageous embodiment of the invention, the electronic fuse is arranged such that when the gate contact of the FET of the electronic fuse is not driven by the gate driver, the electronic fuse is deactivated and RF current cannot flow in the RF coil loop.

[0021] In another advantageous embodiment of the present invention, the electronic fuse is connected in series to the RF coil loop, and the FET of the electronic fuse is an enhancement MOSFET. An enhancement MOSFET (metal oxide semiconductor FET) is a common switching element in most integrated circuits. These devices are turned off at zero gate-source voltage. NMOS can be turned on by pulling the gate voltage above the source voltage, and PMOS can be turned on by pulling the gate voltage below the source voltage. In most circuits, this means pulling the gate voltage of the enhancement MOSFET towards its drain voltage to turn it on. Unlike conventional fuses, efuse ICs have a high-speed current interruption function because the built-in MOSFET is turned off when excessive current flows.

[0022] In another advantageous embodiment of the invention, the electronic fuse is arranged such that it can be reactivated after deactivation by an electronic reactivation circuit or by an external digital controller such that RF current can flow again in the RF coil loop.

[0023] In an embodiment of the invention, the switching device of the electronic fuse is connected in series with the conductor of the RF coil loop, or the electronic fuse is implemented as a parallel detuned circuit in series with the switching device. If the switching device of the electronic fuse is connected in series with the conductor of the RF coil loop, and if there is no DC voltage, meaning that the coil is not connected, the device has a high impedance. The switching device can also be implemented as a parallel detuned circuit in series with the switching device. A detuned circuit with, for example, a diode requires a low impedance device, because a resonant detuned circuit provides a high impedance, but only when the device has a low impedance. The parallel resonant circuit has a high impedance and has the same effect as a blown fuse. Here, a high impedance is achieved when the device has a low impedance when it is not supplied.

[0024] In another aspect of the invention, the object is achieved by a magnetic resonance imaging apparatus comprising a radio frequency (RF) receiver coil as described above.

[0025] The invention also relates to a method for protecting a radio frequency (RF) receiver coil, comprising the following steps:

[0026] providing a radio frequency (RF) receiver coil as described above comprising at least one electronic fuse,

[0027] The RF current in the RF coil loop is detected by a local current sensor circuit.

[0028] comparing the output of the local current sensor circuit to a defined threshold value for the RF current in the RF coil loop,

[0029] The switching device is switched by the switching unit and the electronic fuse is deactivated when the measured RF current exceeds a defined threshold value, so that the RF current in the RF coil loop is interrupted by the switching device.

[0030] In an advantageous embodiment of the invention, after deactivation of the electronic fuse by switching the switch device, the electronic fuse remains deactivated and activation is indicated by the signal. This ensures that the RF receiver coil is not accidentally switched on, which could damage the coil and endanger personnel safety.

[0031] In another advantageous embodiment, the RF current is detected by an inductive coupler and / or a capacitive voltage divider and / or by a voltage drop across a small value resistor and / or a temperature rise from a small resistor.

[0032] According to an embodiment of the invention, the radio frequency (RF) receiver coil comprises a preamplifier for amplifying the MRI signal, the method comprising the following additional steps:

[0033] The output signal of the preamplifier is measured by the sensor circuit.

[0034] The artificial intelligence learning algorithm is trained to obtain a baseline for the enablement thresholds for the sensor circuit and for the electronic fuse.

[0035] It is further envisioned that the method comprises the following additional steps:

[0036] Before an MRI scan, a preparation pulse is emitted and the operability of the electronic fuse is monitored. With the help of the preparation pulse, any damage and correct operation of the fuse can be checked. This can further increase the safety during operation of the magnetic resonance imaging device.

[0037] In an advantageous embodiment of the invention, the method comprises the following additional steps:

[0038] The RF receiver coil is re-enabled by a separate electronic re-enable circuit or by re-enabling the electronic fuse via an external digital controller. Re-enabling the fuse can also be done automatically so that the electronic fuse is not damaged by a single overcurrent and can be reused.

[0039] In another aspect of the invention, the object is achieved by a computer program product comprising instructions for causing a radio frequency (RF) receiver coil to perform the steps of the method as described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] These and other aspects of the invention will become apparent from and elucidated with reference to the embodiments described hereinafter. However, such embodiments do not necessarily represent the full scope of the invention and reference is made to the claims and this document to interpret the scope of the invention.

[0041] In the figure:

[0042] Figure 1 schematically depicts a radio frequency (RF) receiver coil with electronic fuses according to an embodiment of the present invention,

[0043] Figure 2 A flow chart of a method for protecting a radio frequency (RF) receiver coil according to an embodiment of the present invention is shown.

[0044] Reference numerals list

[0045] Radio Frequency (RE) Receiver Coil 1

[0046] RE coil circuit 2

[0047] Electronic fuse 3

[0048] Switchgear 4

[0049] Preamplifier 5

[0050] Switch unit 6

[0051] Current sensor circuit 7

[0052] Detuned circuit 8

[0053] Electronic Fuse Detector Management 9

[0054] Digital RE Coil Platform 10

[0055] Sensor circuit 11 DETAILED DESCRIPTION

[0056] Figure 1A radio frequency (RF) receiver coil 1 with an electronic fuse 3 according to an embodiment of the present invention is schematically depicted. The radio frequency (RF) receiver coil 1 comprises at least one RF coil loop 2 to receive MRI signals. Furthermore, the coil comprises at least one detuning circuit 8 connected to the RF coil loop and a preamplifier 5 for amplifying the MRI signals. Figure 1 In the embodiment, an electronic fuse 3 is integrated in the RF coil loop. The electronic fuse 3 is an active circuit protection device with an integrated switching device 4, which is used to limit the current to a safe level during a fault condition. The switching device 4 is electrically connected to the RF coil loop 2. The switching device 4 is controlled by a switching unit 6. In an embodiment, the switching device 4 is a FET and / or a MEM switch and / or a bipolar junction transistor and / or a PIN diode. For example, if a FET is used, the efuse additionally includes, for example, a charge pump and a gate driver 6 to drive the gate contact of the FET 4. In Figure 1 In one embodiment of the present invention, a FET with a charge pump and a gate driver 6 is shown. An electronic fuse 3 is configured to interrupt the RF current in the RF coil loop 2 by interrupting the conductive path of the RF coil loop in the event of exceeding a defined threshold. In one embodiment, the electronic fuse 3 is connected in series to the coil loop 2, and the FET 4 of the electronic fuse 3 is an enhancement MOSFET. An enhancement MOSFET has the following advantages: at zero gate-source voltage, the MOSFET is turned off. This can, for example, prevent damage to the (RF) receiver coil 1 or even harm to a person in the event of a malfunction of the charge pump or the gate driver 6. The RF receiver coil 1 also includes a local current sensor circuit 7 for measuring the RF current, wherein the output of the local current sensor circuit 7 is applied to a digitizer for comparing the signal with a threshold of the RF current in the RF coil loop 2 to switch the FET, and if the threshold is exceeded, deactivate the electronic fuse 3 to interrupt the RF current in the RF coil loop 2. For example, a high voltage in the RF receiver coil 1, for example caused by a transmit pulse, results in a high current in the coil loop 2. The current is measured by the local current sensor 7. The electronic fuse 3 is to be understood as a separate component in addition to the RF receiver coil 1 electronics. When the FET of the electronic fuse is enabled, the electronic fuse remains disabled and the deactivation is indicated by a signal. Due to incorrect positioning of the RF receiver coil 1 or coupling problems with other coils, sensors or cables, the threshold level may be exceeded. If this is the case, the magnetic resonance imaging device is stopped and the coil needs to be checked. In the event that there is no electrical defect in the coil, the electronic fuse will be re-enabled and the MRI scan can continue. The re-activation of the fuse can be done by a local independent circuit or by an external digital controller (e.g. by Figure 1The electronic fuse detector management 9 shown is implemented. The signal of the gate of the electronic fuse 2 can be further detected by a remote digitizer. The amplitude / phase of the detection signal will follow the known transmission pulse envelope. If this is not the case, the resonant circuit or detuned circuit, capacitor, connection may be disconnected and must be checked.

[0057] In an embodiment of the present invention, the electronic fuse 3 includes an active switching device 4 using a FET or MEM switch or a SPDT switch, which can be connected in series with the conductor of the RF coil loop 2, such as Figure 1 As shown. Therefore, if there is no DC voltage, meaning that the coil 2 is not connected, the device has a high impedance. The switching device 4 can also be implemented as a parallel detuning circuit 8 connected in series with the switching device 4. Figure 1 The detuning circuit 8 with diodes shown in FIG. 8 requires a low impedance device because the resonant detuning circuit 8 provides a high impedance, but only when the device has a low impedance. This parallel resonant circuit has a high impedance and has the same effect as a blown fuse. Here, a high impedance is achieved when the device has a low impedance when not supplied. Typically, the switching device 4 consists of a FET or MEM switch and may have additional lumped element components added, such as parallel detuning or elements for compensating for complex impedances. Figure 1 The diodes shown in the figure may also represent active switching devices, such as FETs and / or MEMs and / or SPDT switches. In embodiments of the invention, hazardous currents may be passed through the use of, for example, Figure 1 The current can also be measured by the voltage drop across a small value resistor (e.g., 0.1 ohm when the load resistance of the coil is on the order of 5 ohms). In addition, the temperature rise from a small resistor can be measured, for example, using a thermocouple or resistance temperature detector (RTD).

[0058] Figure 2A flow chart of a method for protecting a radio frequency (RF) receiver coil according to an embodiment of the present invention is shown. First, in step S1, a radio frequency (RF) receiver coil including at least one electronic fuse as described above is provided. The method comprises the following steps. In step S2, an RF current in the RF coil loop 2 is detected by a local current sensor circuit 7. As described above, the current can be detected by an inductive coupler and / or a capacitive voltage divider and / or by a voltage drop across a small value resistor and / or a temperature rise from a small resistor. In the following step S3, the signal of the local current sensor circuit 7 is fed to a digitizer, which compares the signal with a defined threshold value of the RF current in the RF coil loop 2. When the measured RF current exceeds the defined threshold value, the switch device 4 is switched by the switch unit 6 in step S3. In an embodiment, the switch unit 6 may include, for example, a charge pump and a gate driver to drive the gate contact of the FET. Thereby, the electronic fuse 3 is deactivated, so that the RF current in the RF coil loop 2 is interrupted by the switch device 4. In an embodiment of the present invention, the electronic fuse 3 remains deactivated and indicates deactivation by a signal. This then allows further safety measures to be taken. In an embodiment of the present invention, the complex (or amplitude, envelope) signal of the gate signal (preamplifier output signal) is used to train an artificial intelligence (AI) learning algorithm to obtain a baseline for the complex signal monitor and for the deactivation threshold of the electronic fuse 3. The scan will be enabled or continued only when the complex RF current is within the defined parameter window. Before the scan starts, a preparation pulse can be used to monitor the suitability of the electronic fuse 3.

[0059] Although the present invention has been illustrated and described in detail in the drawings and the foregoing description, such illustration and description are considered to be illustrative or exemplary rather than restrictive; the present invention is not limited to the disclosed embodiments. Through a study of the drawings, the disclosure and the claims, those skilled in the art can understand and implement other variations of the disclosed embodiments when practicing the claimed invention. In the claims, the word "comprising" does not exclude other elements or steps, and the attributive "one" or "an" does not exclude multiple. The fact that certain measures are recorded in mutually different dependent claims does not indicate that the combination of these measures cannot be advantageous. Any figure marks in the claims should not be interpreted as limiting the scope. In addition, for the sake of clarity, not all elements in the drawings are marked with figure marks.

Claims

1. A radio frequency (RF) receiver coil (1), comprising: at least one RF coil loop (2), at least one electronic fuse (3), the electronic fuse (3) comprising a switch device (4) for interrupting an RF current in the RF coil loop (2), wherein the switch device (4) is electrically connected to the RF coil loop (2), the electronic fuse (3) further comprising a switch unit (6) for controlling the switch device (4), wherein the switch device (4) is configured to interrupt the RF current in the RF coil loop (2) via the switch unit (6) when a defined threshold value is exceeded, The RF receiver coil (1) further comprises a local current sensor circuit (7) for measuring the RF current, wherein the electronic fuse (3) is configured to compare the output of the local current sensor circuit (7) with a threshold value of the RF current in the RF coil loop (2) for switching the switching device (4), and if the threshold value is exceeded, deactivate the electronic fuse (3) to interrupt the conductive path of the RF coil loop (2), thereby interrupting the RF current in the RF coil loop (2).

2. The radio frequency (RF) receiver coil (1) according to claim 1, wherein The electronic fuse (3) is a separate stand-alone component in addition to the RF receiver coil electronics.

3. The radio frequency (RF) receiver coil (1) according to claim 1 or 2, wherein: The switching device (4) is a FET and / or a MEM switch and / or a bipolar junction transistor and / or a PIN diode.

4. A radio frequency (RF) receiver coil (1) according to any one of the preceding claims, wherein The radio frequency (RF) receiver coil (1) comprises a digitizer for digitizing the output of the local current sensor circuit (7) and comparing it to a threshold value of the RF current in the RF coil loop (2).

5. A radio frequency (RF) receiver coil (1) according to any one of the preceding claims, wherein The electronic fuse (3) is arranged such that when the switching device (4) of the electronic fuse (3) is not driven by the switching unit (6), the electronic fuse (3) is deactivated and the RF current cannot flow in the RF coil loop (2).

6. A radio frequency (RF) receiver coil (1) according to any one of the preceding claims, the RF receiver coil (2) comprising an external digital controller (9) for controlling the electronic fuse (3).

7. A radio frequency (RF) receiver coil (1) according to any one of the preceding claims, wherein The electronic fuse (3) is arranged such that it can be reactivated by an electronic reactivation circuit or by the external digital controller (9) after deactivation, so that the RF current can flow again in the RF coil loop (2).

8. A radio frequency (RF) receiver coil (1) according to any one of the preceding claims, wherein The switching device (4) of the electronic fuse (3) is connected in series with a conductor of the RF coil loop (2), or the electronic fuse (3) is implemented as a parallel detuning circuit (8) connected in series with the switching device (4).

9. A magnetic resonance imaging apparatus comprising a radio frequency (RF) receiver coil (1) according to any one of claims 1-8.

10. A method for protecting a radio frequency (RF) receiver coil (1), wherein: The method comprises the following steps: A radio frequency (RF) receiver coil (1) comprising at least one electronic fuse (3) according to any one of claims 1 to 8 is provided, detecting the RF current in the RF coil loop (2) by means of a local current sensor circuit (7), comparing the output of the local current sensor circuit (7) with a defined threshold value for the RF current in the RF coil loop (2), The switch device (4) is switched by means of the switch unit (6), and the electronic fuse (3) is deactivated when the measured RF current exceeds a defined threshold value, so that the conductive path of the RF coil loop is interrupted, so that the RF current in the RF coil loop (2) is interrupted by the switch device (4).

11. The method according to claim 10, wherein: After the electronic fuse (3) is deactivated by switching the switching device (4), the electronic fuse (3) remains deactivated and activation is indicated by a signal.

12. The method according to any one of claims 10 or 11, wherein: The RF current is detected by an inductive coupler and / or a capacitive voltage divider and / or by a voltage drop across a small value resistor and / or a temperature rise from a small resistor.

13. The method according to any one of claims 10 to 12, wherein: The radio frequency (RF) receiver coil (1) comprises a preamplifier (5) for amplifying MRI signals, and the method comprises the following additional steps: measuring the output signal of the preamplifier (5) by means of a sensor circuit (11), An artificial intelligence learning algorithm is trained to obtain a baseline of deactivation thresholds for the sensor circuit (11) and for the electronic fuse (3).

14. The method according to any one of claims 10 to 13, comprising the following additional steps: A preparation pulse is emitted prior to an MRI scan and the operability of the electronic fuse (3) is monitored.

15. The method according to any one of claims 10 to 14, wherein: The method comprises the following additional steps: The RF receiver coil (1) is re-enabled by re-enabling the electronic fuse (3) either through a separate electronic re-enabling circuit or through an external digital controller (9).

16. A computer program product comprising instructions for causing an apparatus according to any one of claims 1 to 8 to perform the steps of a method according to any one of claims 10 to 15.

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