Radio Frequency Coil Assembly with Signal Conditioning Circuit - Patent application

Abstract

In the case of a radio frequency (RF) coil assembly for a magnetic resonance (MR) imaging system, interference in a galvanic transmission line 1 configured to transmit a digital signal should be avoided. This is achieved in that a signal circuit Pr2 is provided that is configured to monitor a non-differential asymmetry around the Larmor frequency in a signal passing through the galvanic transmission line 1, the signal circuit Pr2 is configured to provide feedback to a digital adjustment circuit 4, the digital adjustment circuit 4 is configured to compensate for the non-differential asymmetry around the Larmor frequency in the digital signal by adjusting the phase and / or amplitude of the digital signal based on the monitored measurements of the signal circuit Pr2. Furthermore, the present invention relates to a method for compensating for a non-differential asymmetry around the Larmor frequency in a digital signal in a galvanic transmission line 1 of a radio frequency (RF) coil assembly.

Description

[Technical field]

[0001] The present invention relates to the field of radio frequency (RF) coil assemblies for magnetic resonance (MR) imaging systems, and in particular to conditioning circuits for digital signals (eg, digitized MR signals). [Background technology]

[0002] The galvanic transmission of digital signals in the vicinity of sensitive analog electromagnetic receivers, for example in connection with magnetic resonance imaging (MRI), poses great challenges because digital data usually uses a wide spectrum and always radiates to some extent through the shielding of the transmission line. This leakage increases significantly in the case of imperfect transmission lines or terminations of the data signal. Shaping the signal to reduce its spectral content entails additional costs. Summary of the Invention [Problem to be solved by the invention]

[0003] Typically, galvanic transmission lines 1 for digital signals use differential signals. The simplest transmission line for such signals is a twisted pair cable. However, such unshielded cables cannot be used in MRI receivers with high sensitivity (constant thermal noise level) because they radiate too much energy. The shielded cable 1 has one more galvanic conductor 3, so the shield 2 is threefold overall, as shown in Figure 1. It forms a so-called coupled transmission line, which obtains additional modes for signal propagation. The first two modes are the so-called TEM modes (Transverse Electromagnetic Modes). The differential mode is the most desirable mode to carry the transmitted signal, as shown in Figure 1(a). In case of asymmetry in the excitation, a second mode is also excited. This mode, shown in Figure 1(b), is here called the coaxial mode, since the current distribution looks like a coaxial cable. In a low-voltage differential signaling (LVDS) cable, the two inner conductors 3 just share the same potential in this mode, so they act together like the inner conductors of a coaxial cable. The third mode, shown in Figure 1(c), is called here the "common" mode, and is the only mode that has a net current (the sum of all currents is not equal to zero). It couples strongly to the receiving element and must be avoided. However, the coaxial mode typically transfers some of its energy to the coaxial mode only due to imperfections in the cable and connectors. Therefore, excitation of the coaxial mode should be avoided at the transmitter side.

[0004] Fiber optics can also be an option to reduce crosstalk. However, they can have several drawbacks. The required fiber optic transceivers (FOTs) are bulky and require a lot of power. They have temperature dependent delays that make it difficult to recover the clock signal. Furthermore, they are expensive.

[0005] As with radio frequency (RF) coil assemblies for MRI, there is a need to reduce spurious noise to digital data transmissions.

[0006] U.S. Patent No. 9,407,268 B1 discloses a low voltage differential signaling (LVDS) driver having an output voltage swing regulator that regulates the output voltage swing of the LVDS driver by receiving a differential output signal from a switch polarity current generator of the LVDS driver at the LVDS driver output voltage swing regulator, detecting an output voltage amplitude of the differential output signal, comparing the output voltage amplitude to a reference voltage at the output voltage swing regulator, and adjusting a steering current of the LVDS driver based on the comparison of the output voltage amplitude to the reference voltage to regulate the amplitude of the differential output signal at one or more loads of the LVDS driver.

[0007] US Patent No. 1,112,470 B1 discloses a magnetic resonance imaging apparatus having a data acquisition circuit configured to generate magnetic resonance data, the apparatus having a digital encoder connected to receive the magnetic resonance data and configured to digitally encode the magnetic resonance data using an encoding scheme having a spectral null at approximately the Larmor frequency, and an electrical data transmission line connected to transmit the digitally encoded magnetic resonance data.

[0008] US Patent Application Publication No. 2009 / 121717 discloses a radio frequency antenna having a resonance pickup circuit configured to pick up a magnetic resonance signal, an analog-to-digital converter configured to convert the magnetic resonance signal into digital data, and a frequency converter configured to convert a primary band of frequencies of the digital data. By upshifting the frequency of the transmitted bit stream, it is possible to RF trap the transmission channel by a simple high-pass filtering technique.

[0009] The present invention aims to avoid or reduce spurious noise in radio frequency coil assembly digital signal paths. [Means for solving the problem]

[0010] According to the invention, this object is addressed by the subject matter of the independent claims. Preferred embodiments of the invention are described in the dependent claims. Thus, according to the invention, a radio frequency (RF) coil assembly for a magnetic resonance (MR) imaging system is foreseen, said assembly comprising a galvanic transmission line configured to transmit a digital signal via low voltage differential signaling, and a signaling circuit configured to monitor a non-differential asymmetry about a Larmor frequency in the digital signal via the galvanic transmission line, the signaling circuit configured to provide feedback to a digital adjustment circuit, the digital adjustment circuit configured to compensate for the non-differential asymmetry about the Larmor frequency in the digital signal by adjusting the phase and / or amplitude of the digital signal based on the monitored measurements of the signaling circuit.

[0011] The basic idea of ​​the present invention is to provide a signal delay adjustment circuit, or an amplitude adjustment circuit, or a signal delay and amplitude adjustment circuit, that adjusts the symmetry around the Larmor frequency in the galvanic transmission line. Very small asymmetries in the digital signal around the MR frequency can cause large coupling artifacts. To compensate for such non-differential asymmetries along the signal path, a highly symmetrical signal around the Larmor frequency can be generated by monitoring and correcting the phase difference, or the amplitude difference, or the phase and amplitude difference between the channels of the digital signal in a feedback loop. The feedback can include a complex number that takes into account the phase and / or amplitude asymmetry at a selected frequency around the Larmor frequency. Compensating for the asymmetry around the Larmor frequency means that the coupling of the digital signal path to the elements of the RF coil, and the noise introduced thereby, can be significantly reduced. This can also allow for thin flexible digital cables on the coil assembly, since thicker shielding would otherwise be required.

[0012] In an advantageous embodiment of the invention, the digital adjustment circuit comprises at least one amplifier, the digital adjustment circuit being configured to adjust the amplitude by changing the bias point of the amplifier.

[0013] In another advantageous embodiment of the present invention, the digital adjustment circuit comprises a programmable delay line for adjusting the phase of the digital signal. By means of the programmable delay line, the phase of the digital signal can be easily delayed according to requirements.

[0014] In an advantageous embodiment of the invention, the digital adjustment circuit comprises at least one single pole double throw (SPDT) switch for adjusting the phase of the digital signal, by means of which the phase of the digital signal can be changed in a simple manner.

[0015] In another advantageous embodiment of the invention, the digital adjustment circuit has two tunable ports for jointly adjusting the amplitude and phase of the digital signal.

[0016] In an advantageous embodiment of the invention, the tunable two-port is a lumped element transmission line. Particularly advantageously, the capacitors of the lumped element transmission line can be realized as digital capacitors, such as switchable capacitors in a binary array, to adjust a wide range of values. These two degrees of freedom are sufficient to adjust the amplitude and phase at the output.

[0017] In another advantageous embodiment of the invention, the digital signal is a digital magnetic resonance (MR) signal. The invention can be used for any digital data stream transmitted in a (narrowband) sensitive environment. In a radio frequency (RF) coil assembly for a magnetic resonance (MR) imaging system, a digital data link is placed near the MRI receiver. Thus, in one embodiment of the invention, MR received signal data is provided to be transmitted via a transmission line, and interference is compensated for by the invention.

[0018] The present invention further relates to a magnetic resonance (MR) imaging system comprising the radio frequency (RF) coil assembly described above.

[0019] The present invention also provides a method for compensating for a non-differential asymmetry about the Larmor frequency in a digital signal in a galvanic transmission line of a radio frequency (RF) coil assembly for a magnetic resonance (MR) imaging system, comprising the steps of providing the radio frequency (RF) coil assembly as described above; measuring the non-differential asymmetry about the Larmor frequency of a signal passing through the galvanic transmission line by a signal circuit; and compensating for the non-differential asymmetry about the Larmor frequency in the digital signal by adjusting the phase and / or amplitude of the digital signal by a digital adjustment circuit based on the monitored measurement value of the signal circuit.

[0020] In an advantageous embodiment of the invention, the step of compensating for a non-differential asymmetry about the Larmor frequency of the digital signal by adjusting the phase and / or amplitude of the digital signal by a digital adjustment circuit comprises a step of adjusting the amplitude and phase together by tuning two ports.

[0021] In another advantageous embodiment of the invention, parameters for the step of compensating for non-differential asymmetry about the Larmor frequency in the digital signal by adjusting the phase and amplitude of the digital signal by a digital adjustment circuit are loaded into the adjustment circuit by a remote operator or by control service software.

[0022] The invention also relates to a computer program product having instructions for causing the above-mentioned radio frequency (RF) coil assembly to carry out the steps of the above-mentioned method.

[0023] In an advantageous embodiment of the invention, the computer program product is executed on a neural network.

[0024] The present invention also relates to the use of the radio frequency (RF) coil assembly described above in a flexible magnetic resonance CT receive array.

[0025] 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]

[0026] [Figure 1] Schematic diagram of the three different modes within a state-of-the-art shielded LVDS cable. [Diagram 2] a) shows a simulated circuit and corresponding signal of an imperfect LVDS transmitter; b) shows the received signal at the LVDS receiver; c) shows the coupled signal to the MRI receiving element; and d) shows an eye diagram showing the quality of the digital transmission. [Diagram 3] a) A simulated circuit of an imperfect LVDS transmitter with the proposed conditioning circuit and corresponding signals; b) A received signal at an LVDS receiver; c) A coupled signal to an MRI receiving element; and d) An eye diagram of the quality of digital transmission according to an embodiment of the present invention. [Figure 4] FIG. 1 illustrates a circuit of a lumped element transmission line acting as a digital conditioning circuit in accordance with an embodiment of the present invention. [Diagram 5] FIG. 2 illustrates a flowchart of a method for compensating for non-actuation asymmetry about the Larmor frequency in a digital signal in a radio frequency (RF) coil assembly, in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] FIG. 1 shows three different modes inside a shielded LVDS cable 1 according to the state of the art, already explained in the introductory part of the description.

[0028] The simulations presented below represent only embodiments of the present invention. In particular, the galvanic transmission line 1 may be a shielded LVDS cable. The drawings described below, as well as the components and component sizes shown in the drawings, represent only embodiments of the present invention and are not limiting.

[0029] In Fig. 2(a) a simulated circuit and corresponding signals of an imperfect LVDS transmitter, for example a voltage-dependent voltage source SRC1, are shown. Fig. 2(b) shows the received signal at the LVDS receiver and Fig. 2(c) shows the coupled signal to the MRI receiving element. Fig. 2(d) shows an eye diagram showing the quality of the digital transmission. Fig. 2(a) shows a realistic imperfect LVDS transmitter SRC1. The signal generator is simulated with a delay of 50 ps for the negative channel and an increased amplitude of 1%. The received (differential) signal is shown in Fig. 2(b). On the right Fig. 2(d) shows the corresponding eye diagram, which is very open and therefore sufficient for the detector. The small coupling to the MRI receiver coil is modeled using a symmetric inductive coupling. As can be seen in Fig. 2C) the induced signal reaches a level of around a few hundred mV and is therefore significantly above the thermal noise level that defines the sensitivity of the MR receiving element. This makes MRI imaging almost impossible due to the extra spurious noise. Furthermore, in Fig. 2a) the principle of the LVDS generator SRC1 is shown with a (ideal) 100 ohm transmission line 1 and a signal circuit Pr2. This signal circuit Pr2, for example an asymmetry-sensing detector, can be integrated on both sides of the transmission line. It is potentially more sensitive at the receiving end resistors R3 and R4. On the left side, the voltage source V1 contains a digital time-dependent signal. The following voltage-dependent voltage source SRC1 is dimensioned such that the time-dependent part always forms an opposite signal (to form a differential signal). The differential signal is received at the right side probe Pr1. Instead of terminating the differential signal directly by a resistor corresponding to the differential mode impedance (here 100 ohms), it is proposed to use half of its impedance (here 50 ohms) R3, R4 in series and measure the potential of its connection to ground (or the shield of the cable). The simulations already assumed an imperfect signal with a 1% larger amplitude (G=1.01) in the lower connection and a relatively small delay of T=50 ps (compared to period duration MRI 127.7 MHz: 8 ns; signal baseband: 1 GHz: 1 ns). This does not change the signal received by the probe Pr1 very much, as shown in Figure 2b).Pr2 is a common mode detector because it is mostly sensitive to differential modes and therefore can be easily tolerated for digital signal transmission. However, this small imperfection causes significant coupling to the receiving elements of the MRI coil. The detector depicted by the signal circuit Pr2 is very sensitive to common modes and therefore can detect these defects well, as shown in Figure 2c).

[0030] FIG. 3(a) shows a proposed mitigation of an imperfect transmitter. By compensating for the amplitude difference and delay of the two channels, the signal becomes highly symmetrical, significantly reducing the coupling to the receiving coil elements, as shown, for example, in FIG. 3C). A standard LVDS receiver simply senses the differential signal containing the data. Small imperfections in the symmetry are not critical for data transmission, but significantly increase the noise emitted by the imperfectly shielded transmission line 1. To reduce interference, a signal circuit Pr2 and an adjustment circuit 4 configured to monitor the non-differential asymmetry around the Larmor frequency in the digital signal passing through the galvanic transmission line 1 are provided to precisely adjust that symmetry, which significantly reduces the noise coupling. The detector represented by the voltage probe Pr2 is the signal circuit for monitoring the non-differential asymmetry. In one embodiment, the digital adjustment circuit shown in FIG. 3(a) can have a phase adjustment circuit 5 and / or an amplitude adjustment circuit 6. The phase adjustment circuit 5 can be a signal delay circuit. By combining the signal delay and amplitude adjustment circuit 6, the symmetry in the LVDS transmission line 1 can be adjusted completely or almost completely. In one embodiment, the digital adjustment circuit 4 has at least one amplifier 10, and the digital adjustment circuit 4 is configured to adjust the amplitude by changing the bias point of the amplifier 10. In another embodiment, the digital adjustment circuit 4 can have a programmable delay line for adjusting the phase of the digital signal. A single-pole double-throw (SPDT) switch can also be provided to adjust the phase. To adjust the phase and amplitude together, in one embodiment, a tunable two-port can be provided. For example, this tunable two-port can be a lumped element transmission line 7. Such a lumped element transmission line 7 is described in more detail in FIG. 4. In this example, thanks to the adjustment of the phase and amplitude by the digital adjustment circuit 4 shown in FIG. 3(a), the coupling to the adjacent MR receiving element is significantly reduced as shown in FIG. 3(c).

[0031] FIG. 4 shows a circuit of a lumped element transmission line 7 functioning as a digital adjustment circuit 4 according to an embodiment of the present invention. In an embodiment of the present invention, it is possible that the amplitude and phase are not adjusted separately from each other. For example, a tunable two-port can be provided for this purpose. FIG. 4 shows a lumped element transmission line 7 as an example of a tunable two-port consisting of a coil and a capacitor. In the circuit shown in FIG. 4, the capacitor 8 can be realized as a digital capacitor, such as a switchable capacitor in a binary array, to tune a wide range of values. These two degrees of freedom are sufficient to adjust the amplitude and phase at the output. Also, losses are acceptable since a sufficient signal is available.

[0032] In a coil array with LVDS cables, twinax wires can be coupled to nearby individual coils. The tuning process can also be specified in the form of a method and in particular controlled by a computer program product. The method and in particular the computer program product can be based on a neuron network to reduce noise coupling in one embodiment of the present invention.

[0033] 5 shows a flow chart of a method for compensating for non-differential asymmetry around the Larmor frequency in a digital signal in a radio frequency (RF) coil assembly according to an embodiment of the present invention. The method starts at step S1 by providing a radio frequency (RF) coil assembly, the RF coil assembly having at least one galvanic transmission line 1 configured to transmit a digital signal, and a signal circuit Pr2 configured to monitor the non-differential asymmetry around the Larmor frequency in the digital signal through the galvanic transmission line 1, the signal circuit Pr2 configured to provide feedback to a digital adjustment circuit 4, the digital adjustment circuit 4 configured to compensate for the non-differential asymmetry around the Larmor frequency in the digital signal by adjusting the phase and / or amplitude of the digital signal. In step S2, the non-differential asymmetry around the Larmor frequency in the signal through the galvanic transmission line 1 is measured by the signal circuit Pr2. In step S3, the non-differential asymmetry around the Larmor frequency in the digital signal is compensated by adjusting the phase and / or amplitude of the digital signal by the adjustment circuit 4. In one embodiment, parameters for the step of compensating for non-differential asymmetry around the Larmor frequency of the digital signal by adjusting the phase and / or amplitude of the digital signal by the digital adjustment circuit 4 are loaded into the adjustment circuit by a remote operator or by a control service software. Furthermore, the parameters also depend on the position, shape or combination of the coil with other coils. A computer program product is provided for the execution of instructions of the method. The parameters are also included in the computer program product. In an advantageous embodiment of the invention, the computer program product is executed on a neural network.

[0034] Thus, in one embodiment, a method is disclosed to avoid any common / coaxial mode excitation from the signal generation circuitry by monitoring the asymmetry at the same selected frequency, in this case the frequency and very precise adjustment of the amplitude and / or phase of both channels around the Larmor frequency, thus ensuring very high symmetry.

[0035] While the invention has been illustrated and described in detail in the drawings and the foregoing description, such illustration and description are to be considered as illustrative or exemplary and not restrictive. The 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]

[0036] Galvanic Transmission Line 1 Shield 2 Conductor 3 Digital Adjustment Circuit 4 Phase Adjustment Circuit 5 Amplitude adjustment circuit 6 Lumped Element Transmission Line 7 Capacitor 8 Coil 9 Amplifier 10 Probe Pr1 Signal circuit Pr2 Resistor R1 Resistance R2 Resistance R3 Resistance R4 Voltage source V1 Voltage dependent voltage source SRC1

Claims

1. A high-frequency coil assembly for a magnetic resonance imaging system, A galvanic transmission line that transmits digital signals via low-voltage differential signaling, A signal circuit that monitors non-differential asymmetry about Larmor frequency in a digital signal via a galvanic transmission line, wherein the signal circuit is configured to provide feedback to a digital adjustment circuit, and the digital adjustment circuit is configured to compensate for the non-differential asymmetry about Larmor frequency in the digital signal by adjusting the phase and / or amplitude of the digital signal based on the monitored measurement of the signal circuit, A high-frequency coil assembly having [a specific feature / feature].

2. The high-frequency coil assembly according to claim 1, wherein the digital adjustment circuit has at least one amplifier, and the digital adjustment circuit is configured to adjust the amplitude by changing the bias point of the amplifier.

3. The high-frequency coil assembly according to claim 1 or 2, wherein the digital adjustment circuit has a programmable delay line for adjusting the phase of the digital signal.

4. The high-frequency coil assembly according to claim 1 or 2, wherein the digital adjustment circuit has at least one single-pole double-throw (SPDT) switch for adjusting the phase of the digital signal.

5. The high-frequency coil assembly according to claim 1 or 2, wherein the digital adjustment circuit has two tunable ports for adjusting the amplitude and phase of the digital signal together.

6. The high-frequency coil assembly according to claim 5, wherein the two tunable ports are centrifugal element transmission lines.

7. The high-frequency coil assembly according to claim 1 or 2, wherein the digital signal is a digital magnetic resonance signal.

8. A magnetic resonance imaging system having the high-frequency coil assembly described in claim 1 or 2.

9. A method for compensating for non-differential asymmetry of digital signals centered on the Larmor frequency in a galvanic transmission line of a high-frequency coil assembly for a magnetic resonance imaging system, The steps of providing a high-frequency coil assembly according to claim 1 or 2, The steps include: measuring the non-differential asymmetry around the Larmor frequency in the signal passing through the galvanic transmission line using the signal circuit; The steps include: compensating for non-differential asymmetry in the digital signal centered on the Larmor frequency by adjusting the phase and / or amplitude of the digital signal using the digital adjustment circuit based on monitored measurements of the signal circuit; A method of having.

10. The method according to claim 9, wherein the step of compensating for non-differential asymmetry in the digital signal with respect to the Larmor frequency by adjusting the phase and / or amplitude of the digital signal with the digital adjustment circuit comprises the step of adjusting the amplitude and the phase together with two tunable ports.

11. The method according to claim 10, wherein parameters for the step of compensating for non-differential asymmetry in the digital signal about the Larmor frequency are loaded into the adjustment circuit by a remote operator or control service software, by adjusting the phase and amplitude of the digital signal using the digital adjustment circuit.

12. A computer program having instructions to cause the high-frequency coil assembly described in claim 1 or 2 to perform the steps of the method described in claim 9.

13. The computer program described in claim 12 is executed on a neural network.

14. Use of the high-frequency coil assembly according to claim 1 or 2 within a flexible magnetic resonance imaging receiving array.

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