RF Receiver with Detection of Malfunction of Modulation Circuit

Abstract

For RF receiver systems, a solution must be ensured for safe operation of the RF receiver system in magnetic resonance imaging. This is achieved by an RF receiver system for a magnetic resonance imaging system, the RF receiver system having at least one RF receiver coil with at least one detuning circuit 1. The detuning circuit 1 has at least a pair of cross diodes D1, D2 with an interface configured to measure current in the detuning circuit 1 to determine proper function of the PIN diodes D1, D2 by measuring a detuning DC current for a first detuning voltage polarity and a second opposite detuning voltage polarity. The present invention also provides a magnetic resonance imaging system, a method for ensuring safe RF receiver system operation in a magnetic resonance imaging system, a software package for a magnetic resonance imaging system, a software package for upgrading a magnetic resonance imaging system, and a computer program product.

Description

Technical Field

[0001] The present invention relates to the field of magnetic resonance (MR) imaging. In particular, the present invention relates to a radio frequency (RF) receiver system that provides MR information from the examination space of an MR imaging system. The present invention further relates to an MR imaging system, a method for ensuring safe radio frequency (RF) receiver system operation in magnetic resonance imaging, a software package for a magnetic resonance (MR) imaging system, a software package for upgrading a magnetic resonance (MR) imaging system, and a computer program product.

Background Art

[0002] In magnetic resonance imaging, receive coil arrays have been widely used for decades. Patient safety is a major design goal. This mainly means that the coil needs to be transparent during transmission via the surrounding body coil. However, in the receive state, the coil is switched to a resonant state to efficiently pick up the MR signal. Since transmission and reception use exactly the same frequency, it is very dangerous if the coil remains in the resonant state during transmission. In addition to safety limitations, B1 distortion during the transmission phase can cause unwanted image artifacts.

Summary of the Invention

Problems to be Solved by the Invention

[0003] The coil detuning circuit is provided by a tank circuit that uses an inductor that is switched in parallel with a resonant capacitor in almost all applications.

[0004] A particularly important, although special, fault mode is the unplugged coil, i.e., the coil that is placed on the patient but not connected to the MRI scanner. In this case, this coil is also not controlled and still has to be safe. Here, patient safety is the main design goal, but the coil should also be designed not to be damaged in such a case.

[0005] The prior art typically describes two methods used to be switched off when unplugged. The first method is to use a cross PIN diode switch. The switching element is created by the self - bias cross pair of diodes, and those diodes are supplied via the induced current from the transmit body coil. However, this method can fail if at least one of the PIN diodes breaks and then responds like an open circuit. In that case, the switch is not fully active.

[0006] The second method is to use a fuse. A simple fuse can be used in series with the coil conductor, which blows if the current is too high. This is a preferred method today to guarantee patient safety, but it comes with significant losses and thus a small SNR degradation. Furthermore, the fuse requires additional space, which is a problem in today's flexible coil arrays. Note that the current trend in RX coils aims for high channel counts and small flexible elements, and conventional fuses respond too slowly to guarantee patient safety. An additional passive detuning circuit with cross - diodes has to be used to prevent damage to the unplugged coil so that the fuse does not blow in the case of a normally operating passive detuning circuit.

[0007] U.S. Patent Application Publication No. 2002 / 080911 discloses a receiving coil arrangement for a magnetic resonance (MR) imaging system of a type having a plurality of selectively pluggable local coils, where at least some of the local coils are actively detuned and also have a passive detuning circuit for the transmission phase.

[0008] U.S. Patent Application Publication No. 2018 / 074140 discloses a magnetic resonance imaging (MRI) radio frequency (RF) coil having an LC circuit including at least one series capacitor and a decoupling circuit connected in parallel with the LC circuit. The decoupling circuit is configured to decouple the MRI RF coil from one or more other MRI RF coils using passive decoupling when generating an induced voltage in the decoupling circuit, or to actively decouple the MRI RF coil from one or more other MRI RF coils when inserting a DC bias into the decoupling circuit. The decoupling circuit has a pair of high-speed switching PIN diodes including a first PIN diode connected in anti-parallel with a second PIN diode, and the second PIN diode is connected in series with a first capacitor. The decoupling circuit further has an inductor connected in series with the pair of high-speed switching PIN diodes and the capacitor.

[0009] U.S. Patent Application Publication No. 2020 / 151890 discloses a radio frequency coil having a detuning circuit. This U.S. Patent Application Publication No. 2020 / 151890 discloses checking the proper functioning of the detuning circuit based on a comparison of the response to a test RF pulse with a threshold value.

[0010] An object of the present invention is to provide a radio frequency (RF) receiver system in magnetic resonance imaging, in which the safe operation of the radio frequency (RF) receiver system is guaranteed.

Means for Solving the Problems

[0011] According to the present invention, this object is addressed by the subject matter of the independent claims. Preferred embodiments of the invention are described in the dependent claims.

[0012] According to the present invention, there is provided a radio frequency (RF) receiver system for use in a magnetic resonance (MR) imaging system, the RF receiver system having at least one RF receiving coil, the RF receiving coil having at least one detuning circuit, the detuning circuit having at least one pair of (at least DC) cross diodes, the detuning circuit further having an interface, the interface being configured to measure the current in the detuning circuit by measuring the detuning direct current for a first detuning voltage polarity and a second opposite detuning voltage polarity to determine the proper functioning of the PIN diodes.

[0013] According to the present invention, the detuning circuit is configured to measure the detuning direct current in the detuning circuit in order to determine the proper functioning of the PIN diodes, in particular to detect whether there is a broken PIN diode. This can be done for each individual inspection or for each individual RF pulse within an inspection. Further, the cross PIN diodes detune the receiving coil when the receiving coil is not connected. The present invention safely holds the receiving coil when not connected. The detuning circuit can signal a failure of the PIN diodes, so that no additional fuses are required. Further, the detuning circuit signals a failure during operation, so that the receiver coil is prevented from being reused before it is repaired. In one embodiment of the invention, there may be an inductor in series with the diodes before connecting the diodes in reverse parallel.

[0014] In another disclosed aspect, the RF receiver system has a controller for controlling the measured value of the detuning direct current.

[0015] Furthermore, it is contemplated that the control device is configured to send a signal to the magnetic resonance (MR) imaging system when the diode is malfunctioning. The signal can be, for example, a warning signal to ensure that the coil is not used before repair. For example, a safety mechanism can be provided to prevent the RF receiving coil from being used when the signal is sent by the controller.

[0016] According to an embodiment of the present system, the detuning circuit has at least one resistor, and the resistor is connected in series to the PIN diode to ensure that a specific direct current flows.

[0017] According to an advantageous embodiment of the invention, the diode is a PIN diode.

[0018] The present invention also provides a magnetic resonance (MR) imaging system having the radio frequency (RF) receiver system described above.

[0019] The present invention is further a method for ensuring safe radio frequency (RF) receiver system operation in magnetic resonance imaging, having an RF receiver system as described above, the method comprising measuring a detuning direct current for a first detuning voltage polarity, measuring a detuning direct current for a second opposite detuning voltage polarity, and evaluating the proper functioning of the diode from the measurement of the detuning direct current.

[0020] In one embodiment of the present invention, the method further comprises defining a valid window of current levels using a lower threshold and an upper threshold to define a malfunction of the diode.

[0021] In one embodiment of the present invention, the method comprises measuring the detuning direct current by measuring the voltage across the resistor, the resistor being connected in series to the diode.

[0022] In a further embodiment of the present invention, a radio frequency (RF) receiver system has a controller that controls a measured value of a detuning direct current, and the method has a step of transmitting a signal to a magnetic resonance (MR) imaging system so as to ensure that an RF receiving coil is not used when a PIN diode malfunctions.

[0023] The present invention provides a software package for a magnetic resonance (MR) imaging system, and the software package has instructions for controlling the radio frequency (RF) receiver system described above.

[0024] The present invention further provides a software package for upgrading a magnetic resonance (MR) imaging system, and the software package has instructions for controlling the radio frequency (RF) receiver system described above.

[0025] The present invention also provides a computer program product having instructions for causing a computer to execute the steps of the method described above when the program is executed by the computer.

[0026] These and other aspects of the present invention will become apparent from the embodiments described below and will be described with reference thereto. However, such embodiments do not necessarily represent the entire scope of the present invention, and thus, reference should be made to the claims and the present specification to interpret the scope of the present invention.

Brief Description of the Drawings

[0027]

Fig. 1a

Fig. 1b

Fig. 2a

Fig. 2b

Fig. 3a

Fig. 3b

Fig. 4

Fig. 5a

Fig. 5b

Fig. 6a

Fig. 6b

Fig. 7

Fig. 8

Fig. 9

Embodiments for Carrying Out the Invention

[0028] Figure 1a shows a circuit diagram of a detuning circuit 1 having cross PIN diodes D1, D2 switches used for an active detuning receiving coil according to the prior art. Figure 1b shows the operation of the detuning circuit 1 having cross PIN diodes D1, D2 according to the prior art. In Figure 1b, it can be seen that the detuning circuit 1 reduces the induced current by more than 10 times compared with Figure 2.

[0029] Figure 2a shows a circuit that is almost the same as Figure 1a, but in the worst case, both of the PIN diodes D1, D2 are broken or simply not connected. Without a fuse, the current reaches a dangerous level of 4A as shown in Figure 2b.

[0030] Figure 3a shows a fault mode having one broken PIN diode D1 that is not detected by the current coil. In this simulation, since the remaining PIN diode D2 is powered, it detunes the coil as seen in Figure 3b.

[0031] In (a) of Figure 4, an MR sequence having a transmission pulse is shown. In (b) of Figure 4, a detuning voltage is shown. (c) of Figure 4 shows the detuning direct current of the MR sequence. The solid line shows the detuning direct current of the operating detuning circuit 1, and the dotted line shows the detuning direct current when one of the PIN diodes, specifically D1 that is not forward biased to detune the coil, is broken. Since the two lines follow the same course, it can be seen that this specific fault mode where only one PIN diode is broken cannot be detected for the non-conducting PIN diode D1, at least in the active detuning state.

[0032] FIG. 5a shows a circuit diagram of a detuning circuit 1 having a disconnected coil with one broken PIN diode D1. FIG. 5b shows a simulation of the corresponding current. FIG. 5 shows a dangerous situation where the coil is not connected, simulated by a 100 MΩ resistor R2. In such a situation, a fuse is currently implemented.

[0033] When the passive detuning circuit 1 operates as shown in FIG. 6, the current can be reduced to a safe level. The present invention proposes to use cross PIN diodes D1, D2 as the detuning circuit 1, with an improved interface and without a fuse. Such a configuration detects any broken PIN diodes D1, D2 in both directions by measuring the detuning DC current even for reverse detuning voltage polarities.

[0034] In one embodiment of the present invention, the direction of the detuning DC current alternates for each RF pulse as shown in FIG. 7. FIG. 7(a) shows an MR sequence with transmission pulses according to one embodiment of the present invention, (b) shows a detuning voltage where the detuning voltage polarity alternates for each RF pulse, and (c) shows the detuning DC current. The solid line in FIG. 7(c) shows the detuning DC current of the detuning circuit 1 in the operating state, and the dotted line shows the detuning DC current in the state where one of the PIN diodes D1, D2 is broken. Since the two lines do not follow the same course, a defective PIN diode can be detected. As shown in FIG. 7, the broken PIN diodes D1, D2 are detected before having a dangerous constellation. The operation of both PIN diodes D1, D2 is ensured each time the coil is inserted into the scanner. The probability that the broken PIN diodes D1, D2 are not detected before using the coil in a potentially unsafe situation is very low. Thereby, each single failure (disconnected coil or broken PIN diodes D1, D2) is still safe.

[0035] FIG. 8 shows another embodiment of the present invention for detecting PIN diodes D1, D2 broken in both directions, where (a) shows an MR sequence with a transmission pulse, (b) shows a detuning voltage whose detuning voltage polarity alternates for each RF pulse, and (c) shows a detuning DC current with a short prepulse detuning current. The solid line in FIG. 8(c) shows the detuning current of the operating detuning circuit 1, and the dotted line shows the detuning current in a state where one of the PIN diodes D1, D2 is broken. Already, by using a short prepulse detuning current, the two curves show different courses, and the failed PIN diodes D1, D2 can be detected. In one embodiment of the present invention, the reverse current can also be applied after the reception period.

[0036] FIG. 9 shows a flowchart of a method for ensuring safe radio frequency (RF) receiver system operation in magnetic resonance imaging according to an embodiment of the present invention. In this method, the above-described radio frequency (RF) receiver system is used. Specifically, in such a system, the interface of the RF receiver system is configured to measure the current in the detuning circuit 1 by measuring the detuning DC current for the first detuning voltage polarity and the second opposite detuning voltage polarity to determine the proper function of the PIN diodes D1, D2.

[0037] This method starts from step 900 by measuring the detuning DC current for the first detuning voltage polarity.

[0038] In step 910, the detuning DC is measured for the second opposite detuning voltage polarity. In one embodiment of the present invention, the detuning DC current is alternated by alternating the detuning voltage polarity for each RF pulse. The detuning DC current can be measured, for example, by measuring the voltage across resistor R1, where the resistor is connected in series with the PIN diode. This ensures that a constant DC current flows. In one embodiment of the present invention, the detuning DC current is alternated by alternating the detuning voltage polarity for each RF pulse.

[0039] In step 920, the proper functioning of the PIN diode from the off-tune DC measurement value is evaluated. Further, the RF receiver system can have a controller that controls the current measurement, and for example, can be set to send a signal to the magnetic resonance (MR) imaging system if the off-tune circuit malfunctions due to a faulty PIN diode. The signal can be, for example, a warning signal to ensure that the coil is not used before repair. For example, a safety mechanism can be provided to prevent the RF receiving coil from being used when the signal is sent by the controller.

[0040] In one embodiment of the present invention, a resistor is connected in series with the PIN diode so that a specific DC current reliably flows for each polarity of the off-tune voltage. The DC current can be determined by measuring the voltage across the resistor.

[0041] Although the present invention has been illustrated and described in detail in the drawings and the foregoing description, such illustration and description 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 when practicing the invention recited in the claims, 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 article "a" or "an" does not exclude a plurality. The mere fact that certain means are recited in mutually different dependent claims does not indicate that a combination of these means cannot be used advantageously. Any reference signs in the claims should not be construed as limiting the scope of that claim. Further, not all components in the drawings are labeled with reference signs for clarity.

Description of Reference Signs

[0042] Off-tune circuit 1 PIN diode D1 PIN diode D2 Resistor (for defining the off - state direct current) R1 Resistor (for simulating the unconnected coil) R2

Claims

1. An RF receiver system for a magnetic resonance imaging system, having at least one RF receiving coil, said RF receiving coil having at least one detuning circuit, said detuning circuit having at least one pair of cross diodes, said detuning circuit further having an interface, said interface being configured to measure a DC detuning current for a first detuning voltage polarity and a second opposite detuning voltage polarity that alternate for each RF pulse, to thereby measure the DC current in said detuning circuit and determine the proper functioning of said cross diodes.

2. The RF receiver system according to claim 1, wherein said RF receiver system has a controller for controlling the measurement of said DC detuning current.

3. The RF receiver system according to claim 2, wherein said controller is further configured to send a signal to said magnetic resonance imaging system if said cross diodes are malfunctioning.

4. The RF receiver system according to any one of claims 1 to 3, wherein said detuning circuit has at least one resistor, said resistor being connected in series with said cross diodes to ensure that a predetermined DC current flows.

5. The RF receiver system according to any one of claims 1 to 4, wherein said cross diodes are PIN diodes.

6. A magnetic resonance imaging system having the RF receiver system according to claim 1.

7. A method for ensuring the safe operation of an RF receiver system in a magnetic resonance imaging system, said magnetic resonance imaging system having the RF receiver system according to claim 1, said method comprising: measuring a DC detuning current for a first detuning voltage polarity; measuring a DC detuning current for a second opposite detuning voltage polarity; evaluating the proper functioning of said cross diodes from the measured values of said DC detuning current.

8. The method according to claim 7, further comprising defining a valid window of said current level having a lower threshold and an upper threshold for defining a malfunction of said cross diodes.

9. The method according to claim 8 includes the step of measuring the off-tune DC current by measuring the voltage across both ends of a resistor, wherein the resistor is connected in series with the cross diode.

10. The method according to claim 9, wherein the measurement of the off-tune DC current is alternated by alternating the off-tune voltage polarity for each RF pulse within an individual inspection.

11. The RF receiver system has a controller for controlling the measurement of the off-tune DC current, and the method further includes the step of transmitting a signal to the magnetic resonance imaging system by the controller when the cross diode malfunctions to ensure that the RF receiving coil is not used. The method according to any one of claims 8 to 10.

12. A software package for a magnetic resonance imaging system, the software package having instructions for controlling an RF receiver system according to the method of claim 7.

13. A software package for upgrading a magnetic resonance imaging system, the software package having instructions for controlling an RF receiver system according to the method of claim 7.

14. A computer program having instructions that, when executed by a computer, cause the computer to execute the steps of the method of claim 7.

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