High-Frequency (RF) Receiver Coil with Electronic Fuse

Abstract

An independent safety mechanism for a radio frequency (RF) receiving coil should be provided. This is achieved by an electronic fuse 3, which is a switching device 4 galvanically connected to the RF coil loop 2 and has a switching device 4 for interrupting the RF current in the RF coil loop 2 in order to interrupt the RF current in the RF coil loop 2 when the RF current in the RF coil loop 2 exceeds a predetermined threshold. The present invention further relates to a method for protecting a radio frequency (RF) receiving 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) receive coils for magnetic resonance examination systems, and more particularly to RF receive coils having electronic fuses. The present invention further relates to a method and a computer program product for protecting a radio frequency (RF) receive coil using an electronic fuse.

Background Art

[0002] MR coils are typically turned on and off using RF switches based on PIN diodes. For fail-safe design (absence of the PIN diode drive signal), an independent second safety mechanism needs to be added. One ultimate solution to this problem is to place a fuse in the coil that blows when a dangerous current flows. Conventional fuses protect the circuit and prevent damage to the device by melting the built-in alloy parts with Joule heat when a current exceeding the rating flows.

Summary of the Invention

Problems to be Solved by the Invention

[0003] However, these fuses have drawbacks such as an uncertain interrupting current, a slow fusing time, and the need for replacement work due to destruction by a single overcurrent. Unfortunately, fuses cannot handle the entire range of dangerous currents. With the advent of lightweight digital RF coils for MRI, the coils can be equipped with smart functions to achieve a safe clinical workflow. Furthermore, elements close to the tissue tend to be smaller, and fuses with higher sensitivity than those currently available are required.

[0004] The MR coil for signal reception needs to have two operating states:

[0005] “On” state: A low-noise reception state for capturing very weak (up to the noise floor) nuclear signals.

[0006] "Off" state: A passive state where the coil needs to withstand strong RF pulses for exciting the nucleus.

[0007] For switching, an RF switch based on PIN diodes is typically used. When the coil is switched to the appropriate state, the RF current (induced by the RF transmission pulse) is effectively blocked within the coil loop. The function of the detuning circuit is detected by continuously measuring the DC bias current flowing through the diode and / or the voltage across the diodes. If the expected values (zero current, e.g., 80 mA) for the "on" and "off" states are not reached, the scan is immediately stopped. Measuring the diode current is an indirect indicator of proper functioning but requires additional means for safety. In fail-safe use, individual loop elements within the coil are equipped with passive fuses. The fuse is basically a small resistor in series with the coil loop and blows when the current level is exceeded. To maintain high image quality, the resistance of the fuse needs to be as low as possible. Otherwise, the resistor significantly affects the thermal noise received by the coil and reduces the SNR.

[0008] In the case of a flexible RF coil where the coil conductor is relatively close (about 5 mm) to human skin, even relatively low currents can lead to dangerous situations.

[0009] Here, the passive fuse does not provide a safe second means because it is technically difficult / impossible to realize a fuse with such a low blow current and low resistance.

[0010] The prior art shows some alternatives to electrical fuses in RF receiving coils. For example, U.S. Patent Application Publication No. 2013234715A1 describes a magnetic resonance imaging apparatus having a transmitting coil, a receiving coil, a balun, an overheat protection circuit, and an imaging control unit. The transmitting coil applies a high-frequency magnetic field to a subject placed in a static magnetic field. The receiving coil receives a magnetic resonance signal radiated from the subject by the application of the high-frequency magnetic field. The balun is connected to the receiving coil and suppresses the unbalanced current induced in the receiving coil. The overheat protection circuit indicates that the balun is abnormal when the temperature of the balun exceeds a temperature threshold. The imaging control unit stops imaging when the overheat protection circuit indicates an abnormality of the balun.

[0011] There are several problems and drawbacks with passive fuses used in the prior art. Passive fuses are too slow for thin flexible RF coils. Measuring the diode current is an indirect indicator of whether it is functioning properly (requiring additional means for safety), and the failure mode where the diode is disconnected from the rest of the coil cannot be detected. A failure mode is conceivable where DC current is still flowing while the coil is not effectively detuned, which poses a danger to the patient in this case. Passive fuses with fail-safe detection methods need to be replaced when damaged.

[0012] An object of the present invention is to improve the protection of a high-frequency (RF) receiving coil.

Means for Solving the Problem

[0013] According to the present invention, this object is addressed by the subject matter of the independent claims. Preferred embodiments of the present invention are described in the dependent claims.

[0014] Accordingly, according to the present invention, a radio frequency (RF) receiving coil has at least one RF coil loop and at least one electronic fuse, the electronic fuse having a switching device for interrupting an RF current in the RF coil loop, the switching device being galvanically connected to the RF coil loop, the electronic fuse further having a switching unit for controlling the switching device, the switching device being configured to interrupt the RF current in the RF coil loop by the switching unit when a predetermined threshold value is exceeded, the RF receiving coil further having a local current sensor circuit for measuring the RF current, the electronic fuse comparing the output of the local current sensor circuit with a threshold value of the RF current in the RF coil loop and, when the measured RF current exceeds the threshold value, switching the switching device to deactivate the electronic fuse and interrupting the conductive path of the RF coil loop to interrupt the RF current in the RF coil loop.

[0015] An electronic fuse, also known as an e-fuse, is a small integrated circuit (IC) used to replace a conventional fuse within a device. The electronic fuse functions in a similar manner to a conventional fuse. When an overcurrent or overvoltage is detected, the fuse can be deactivated.

[0016] Also, the electronic fuse is not destroyed by a single overcurrent and can be used repeatedly, not being restricted by physical limitations such as passive fuses, so that a wider range of fusing currents and times can be selected while maintaining the low resistance requirement. This achieves the advantage of reducing the maintenance cost and recovery time for the repair of the RF receiving coil or the complete magnetic resonance imaging device.

[0017] In an advantageous embodiment of the present invention, the electronic fuse is an independent stand-alone component in addition to the RF receiving coil electronics.

[0018] In another advantageous embodiment of the present 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 where a FET is used as the switching device, a charge pump and a gate driver for driving the gate contact of the FET may be envisaged. The electronic fuse may be a MEM switch. Here, when there is no voltage, the MEM switch has a high impedance. Thus, when the coil is not connected, the coil is safe. The MEM switch can also be used as a FET switch.

[0019] In an advantageous embodiment of the present invention, the high-frequency (RF) receiving coil has a digitizer for digitizing the output of the local current sensor circuit and comparing it with a threshold value of the RF current in the RF coil loop.

[0020] In another advantageous embodiment of the present invention, the RF receiving coil has 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 a remote digitizer. The magnitude / phase of the detected signal follows a known transmission pulse and envelope. Otherwise, there may be problems such as a tank circuit, a detuning circuit, a capacitor, or a broken connection.

[0021] In an advantageous embodiment of the present invention, the electronic fuse is set 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 the RF current cannot flow through the RF coil loop.

[0022] In another advantageous embodiment of the present invention, the electronic fuse is connected in series with the RF coil loop, and the FET of the electronic fuse is an enhancement-mode MOSFET. The enhancement-mode MOSFET (metal-oxide-semiconductor FET) is a common switching element in most integrated circuits. These devices are off at zero gate-source voltage. An NMOS can be turned on by pulling the gate voltage higher than the source voltage, and a PMOS can be turned on by pulling the gate voltage lower than the source voltage. In most circuits, this means that pulling the gate voltage of an enhancement-mode MOSFET to its drain voltage turns it on. Unlike conventional fuses, it has a fast current interruption function because the built-in MOSFET turns off when an excessive current flows.

[0023] In another advantageous embodiment of the present invention, the electronic fuse is configured to be reactived after deactivation by an electronic reactivation circuit or by an external digital controller so that RF current can flow again within the RF coil loop.

[0024] In one embodiment of the present invention, the switching device of the electronic fuse is in series with the conductor of the RF coil loop, or the electronic fuse is realized as a parallel detuning circuit together with a series switching device. The switching device of the electronic fuse is connected in series with the conductor of the RF coil loop. When no DC voltage is present, this means that the coil is not connected, and in this case, the switching device has a high impedance. The switching device can also be realized as a parallel detuning circuit together with a series switching device. For example, a detuning circuit having a diode requires a low-impedance device because the resonant detuning circuit provides a high impedance only when the device has a low impedance. This parallel resonant circuit has a high impedance and has the same effect as a fuse. Here, the high impedance is realized when the switching device has a low impedance without being voltage-supplied.

[0025] In a further aspect of the present invention, the above object is achieved by a magnetic resonance imaging apparatus having the above-described radio frequency (RF) receiving coil.

[0026] The present invention further relates to a method for protecting a radio frequency (RF) receiving coil, the method comprising providing an RF receiving coil having at least one electronic fuse as described above; detecting an RF current in the RF coil loop by a local current sensor circuit; comparing an output of the local current sensor circuit with a threshold defined for the RF current in the RF coil loop; and switching a switching device by a switching unit to deactivate the electronic fuse such that the RF current in the RF coil loop is interrupted by the switching device when the measured RF current exceeds the defined threshold.

[0027] In an advantageous embodiment of the present invention, after the electronic fuse is deactivated by switching the switching device, the electronic fuse remains deactivated and indicates deactivation by a signal. This prevents the RF receiving coil from being accidentally turned on and the coil from being damaged or a person from being put at risk.

[0028] 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.

[0029] According to an embodiment of the present invention, the radio frequency (RF) receiving coil has a preamplifier for amplifying an MRI signal, and the method further comprises measuring an output signal of the preamplifier by a sensor circuit and training an artificial intelligence learning algorithm to obtain a baseline of the sensor circuit and a threshold for activation of the electronic fuse.

[0030] It is further contemplated that the above method further comprises the step of emitting a preparation pulse prior to the MRI scan to monitor the operability of the electronic fuse. The preparation pulse can check for fuse damage and normal operation. Thereby, the safety during the operation of the magnetic resonance imaging apparatus can be further enhanced.

[0031] In an advantageous embodiment of the invention, the method further comprises the step of reactivating the RF receive coil by reactivating the electronic fuse by means of an independent electronic reactivation circuit or an external digital controller. The reactivation of the fuse can also be automatically performed so that the electronic fuse is not destroyed by a single overcurrent and can be reused.

[0032] In another aspect of the invention, the above object is achieved by a computer program product having instructions for causing the steps of the above method to be performed on a radio frequency (RF) receive coil.

[0033] Brief Description of the Drawings

[0034] These and other aspects of the invention will become apparent from the embodiments described hereinafter and will be described with reference to them. However, 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 the purpose of interpreting the scope of the invention.

Brief Description of the Drawings

[0035]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0036] Figure 1 schematically shows a radio frequency (RF) receiving coil 1 having an electronic fuse 3 according to an embodiment of the present invention. The radio frequency (RF) receiving coil 1 has at least one RF coil loop 2 for receiving an MRI signal. Further, the coil has at least one detuning circuit 8 connected to the RF coil loop and a preamplifier 5 for amplifying the MRI signal. In Figure 1, the electronic fuse 3 is incorporated into the RF coil loop. The electronic fuse 3 is an active circuit protection device having an embedded switching device 4 used to limit the current to a safe level during a fault condition. The switching device 4 is galvanically connected to the RF coil loop 2. The switching device 4 is controlled by a switching unit 6. In one 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, when a FET is used, the use further has, for example, a charge pump and a gate driver 6 to drive the gate contact of the FET4. In Figure 1, in one embodiment of the present invention, a FET having a charge pump and a gate driver 6 is shown. The electronic fuse 3 is configured to cut off the RF current in the RF coil loop 2 exceeding a predetermined threshold by cutting off the conductive path of the RF coil loop. In one embodiment, the electronic fuse 3 is connected in series with the coil loop 2, and the FET4 of the electronic fuse 3 is an enhancement mode MOSFET. The enhancement mode MOSFET has the advantage that the MOSFET is switched off at a zero gate-source voltage. Thereby, for example, damage to the (RF) receiving coil 1 or damage to a person can be prevented in the event of a failure of the charge pump or the gate driver 6. The RF receiving coil 1 further has a local current sensor circuit 7 for measuring the RF current, and the output of the local current sensor circuit 7 is applied to a digitizer that compares the signal with a threshold value of the RF current in the RF coil loop 2 and switches the FET to deactivate the electronic fuse 3 when the threshold value is exceeded, thereby cutting off the RF current in the RF coil loop 2. For example, a high voltage induced in the RF receiving coil 1 by a transmission pulse results in a large current in the coil loop 2.The current is measured by the local current sensor 7. The electronic fuse 3 should be understood as an independent component added to the electronics of the RF reception coil 1. When the FET of the electronic fuse is deactivated, the electronic fuse remains deactivated and indicates deactivation by a signal. Causes for exceeding the threshold level may include incorrect positioning of the RF reception coil 1 or problems with coupling to other coils, sensors, or cables. In this case, it is necessary to stop the magnetic resonance imaging apparatus and check the coil. If there is no electrical defect in the coil, the electronic fuse can be reactivated and the MRI scan can be continued. The reactivation of the fuse can be achieved by a local independent circuit or by an external digital controller, for example, by the electronic fuse detector management unit 9 shown in FIG. 1. The signal of the gate of the electronic fuse 2 can be further detected by a remote digitizer. The magnitude / phase of the detected signal follows a known transmission pulse envelope. Otherwise, there may be a break in the tank circuit or detuning circuit, capacitor, or connection, and it is necessary to check them.

[0037] In one embodiment of the present invention, the electronic fuse 3 has an active switching device 4 that uses a FET or MEM switch or SPDT switch that can be in series with the conductor of the RF coil loop 2 as shown in FIG. 1. Thus, when there is no DC voltage, it means that the coil 2 is not connected and the device has a high impedance. The switching device 4 can also be realized as a parallel detuning circuit 8 in series with the switching device 4. The detuning circuit 8 having the diode shown in FIG. 1 requires a low-impedance device, and the resonant detuning circuit 8 provides a high impedance only when the device has a low impedance. This parallel resonance circuit has a high impedance and has the same effect as a fuse. Here, the high impedance is realized when the device has a low impedance when not powered. Generally, the switching device 4 has a FET or MEM switch and can add additional lumped element components such as elements for parallel detuning or complex impedance compensation. The diode shown in FIG. 1 can represent a FET and / or MEM and / or SPDT switch.

[0038] In an embodiment of the present invention, a dangerous current can be detected using an inductive coupler or a capacitive voltage divider as shown in FIG. 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). Further, the temperature rise from the small resistor can be measured using, for example, a thermocouple or a resistance temperature detector (RTD).

[0039] FIG. 2 shows a flowchart of a method for protecting a radio frequency (RF) receiving coil according to an embodiment of the present invention. First, in step S1, the aforementioned high frequency (RF) receiving coil having at least one electronic fuse is provided. This method has the following steps. In step S2, the RF current in the RF coil loop 2 is detected by the local current sensor circuit 7. As described above, the current can be detected by an inductive coupler and / or capacitive voltage divider, and / or by a voltage drop across a resistor with a small resistance value and / or a temperature rise of a resistor with a small resistance value. In the next step S3, the signal of the local current sensor circuit 7 is supplied to a digitizer, and the digitizer compares the signal with a defined threshold value of the RF current in the RF coil loop 2. When the measured RF current exceeds a predetermined threshold value, in step S3, the switching device 4 is switched by the switching unit 6. In one embodiment, the switching unit 6 can have, for example, a charge pump and a gate driver for driving 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 blocked by the switching device 4. In one embodiment, in the present invention, the electronic fuse 3 remains deactivated and indicates deactivation by a signal. Thereby, further safety measures can be taken. In one embodiment of the present invention, an artificial intelligence (AI) learning algorithm is trained to obtain the baseline of the complex signal monitor and the threshold value of the deactivation of the electronic fuse 3 using the complex (or magnitude, envelope) signal of the gate signal (preamplifier output signal). The scan is activated or continued only when the complex RF current is within a defined parameter window. Before starting the scan, the suitability of the electronic fuse 3 can be monitored using a preparation pulse.

[0040] Although the present invention has been illustrated and described in detail in the drawings and the foregoing description, such illustrations and descriptions should be considered illustrative or exemplary and not restrictive. The present invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments will be understood and can be implemented by those skilled in the art in practicing the claimed invention, from a review 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 articles "a" or "an" do 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 advantageously used. Any reference signs in the claims should not be construed as limiting the scope. Further, for clarity, not all elements in the drawings are provided with reference signs.

Explanation of Reference Signs

[0041] High-frequency (RF) receiving coil 1 RF coil loop 2 Electronic fuse 3 Switching device 4 Preamplifier 5 Switching unit 6 Current sensor circuit 7 Detuning circuit 8 Electronic fuse detector management 9 Digital RF coil platform 10 Sensor circuit 11

Claims

1. A radio frequency (RF) receiving coil, The electronic fuse comprises at least one RF coil loop and at least one electronic fuse having a switching device for interrupting the RF current in the RF coil loop, wherein the switching device is galvanically connected to the RF coil loop, and the electronic fuse further comprises a switching unit for controlling the switching device, wherein the switching device is configured by the switching unit to interrupt the RF current in the RF coil loop when it exceeds a predetermined threshold. An RF receiving coil having, the RF receiving coil further having a local current sensor circuit for measuring RF current, the electronic fuse being configured to interrupt the conductive path of the RF coil loop and interrupt the RF current in the RF coil loop by switching the switching device to deactivate the electronic fuse when the measured RF current exceeds the threshold, and the RF receiving coil having a digitizer that digitizes the output of the local current sensor circuit and compares the output to a threshold of RF current in the RF coil loop in order to switch the switching device.

2. The RF receiving coil according to claim 1, wherein the electronic fuse is an independent, standalone component added to the RF receiving coil equipment.

3. The RF receiving coil according to claim 1 or 2, wherein the switching device is an FET and / or a MEM switch and / or a bipolar junction transistor and / or a PIN diode.

4. The RF receiving coil according to claim 1 or 2, wherein the electronic fuse is deactivated so that the RF current cannot flow into the RF coil loop when the switching device of the electronic fuse is not driven by the switching unit.

5. The RF receiving coil according to claim 1 or 2, wherein the RF receiving coil has an external digital controller that controls the electronic fuse.

6. The RF receiving coil according to claim 1 or 2, wherein the electronic fuse is reactivated by an electronic reactivating circuit or an external digital controller so that the RF current can flow again into the RF coil loop after the deactivation.

7. The RF receiving coil according to claim 1 or 2, wherein the switching device of the electronic fuse is in series with the conductor of the RF coil loop, or the electronic fuse is implemented as a parallel detuning circuit together with the series switching device.

8. A magnetic resonance imaging apparatus having an RF receiving coil as described in claim 1 or 2.

9. A method for protecting an RF receiving coil, The steps of preparing the RF receiving coil according to claim 1 or 2, The local current sensor circuit detects the RF current in the RF coil loop. The steps include comparing the output of the local current sensor circuit with a predetermined threshold value of the RF current in the RF coil loop, If the measured RF current exceeds the threshold, the switching unit switches the switching device to deactivate the electronic fuse, thereby interrupting the conductive path of the RF coil loop and causing the RF current in the RF coil loop to be interrupted by the switching device. A method of having.

10. The method according to claim 9, wherein the electronic fuse remains deactivated after being deactivated by switching the switching device, and the deactivation is indicated by a signal.

11. The method according to claim 9, wherein the RF current is detected by an inductive coupler and / or a capacitive voltage divider, and / or by a voltage drop across a resistor with low resistance and / or a temperature rise across a resistor with low resistance.

12. The RF receiving coil has a preamplifier that amplifies the MRI signal, and the method further The steps include measuring the output signal of the preamplifier using a sensor circuit, The steps include training an artificial intelligence learning algorithm to obtain the baseline of the sensor circuit and the deactivation threshold of the electronic fuse, The method according to claim 9, having the following characteristics.

13. The method according to claim 9, further comprising the step of emitting a preparation pulse before an MRI scan to monitor the operability of the electronic fuse.

14. The method according to claim 9, further comprising the step of reactivating the RF receiving coil by reactivating the electronic fuse using an independent electronic reactivation circuit or an external digital controller.

15. A computer program having an instruction to cause the apparatus according to claim 1 or 2 to perform the steps of the method according to claim 9.

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