Stranded coaxial cable transmission line

Abstract

According to the present invention, there is provided a data and power transmission line 10, comprising a first coaxial cable 20 having a first inner conductor 21 and a first outer conductor 22, and a second coaxial cable 30 having a second inner conductor 31 and a second outer conductor 32, the first coaxial cable 20 and the second coaxial cable 30 having an additional shield surrounding the first coaxial cable 20 and the second coaxial cable 30, and / or the first coaxial cable 20 and the second coaxial cable 30 are twisted together to form a twisted transmission line 10, and the first outer conductor 22 and the second outer conductor 32 are galvanically isolated from each other. In this way, there is provided a data and power transmission line 10 that is suitable for use in an MRI device and can be manufactured at low cost.

Description

[Technical field]

[0001] The present invention relates to the field of transmission lines for transmitting data and power, and in particular to transmission lines for transmitting data and power in MRI devices. [Background technology]

[0002] Almost all electronic applications tend to digitize the signal as early as possible in the receive chain. The main reason for this is reduced sensitivity to disturbances (electromagnetic compatibility, EMC). The amount of data received by a single MRI coil element can be estimated as follows: a resolution of 24 bits results in a dynamic range of 144 dB, which is sufficient for MRI. For a 500 kHz bandwidth, a sample rate of 1 MHz is required, which defines a data rate of about 25 Mbit / s. Summary of the Invention [Problem to be solved by the invention]

[0003] Conventional cabling of the receive coil requires a cable from each preamplifier to the distribution unit. By using one or more digital inputs as well as digital outputs, data from several channels can be combined and transmitted over a single physical channel, thereby reducing the number of cables in the receive coil. A short standard digital link using a single twisted pair such as USB 3.0 can reach data rates of about 5 Gbit / s, which is enough to transfer the data of about 200 coil elements without compression.

[0004] However, the cable for transmitting this data within the MRI machine must be compatible with high magnetic field transmission, as is usual in the field of MRI, i.e., the cable must be protected from acting as a receiving antenna for the B1 field of the transmitting body coil when transmitting the excitation pulse. Furthermore, the data must be sufficiently shielded so as not to couple back into the very sensitive receiving array antenna during acquisition. In addition to the data transmission, power must also be provided to the receiving elements to drive the receiver and control electronics.

[0005] It is an object of the present invention to provide a transmission line that meets the above requirements, in particular a lightweight and flexible transmission line for simultaneous data and power transmission that is suitable for use in MRI machines and can be manufactured at low cost. [Means for solving the problem]

[0006] According to the invention, this object is addressed by the subject matter of the independent claims. Preferred embodiments of the invention are set forth in the dependent claims.

[0007] Thus, in accordance with the present invention, there is provided a transmission line for transmitting data and power, comprising a first coaxial cable having a first inner conductor and a first outer conductor, and a second coaxial cable having a second inner conductor and a second outer conductor, the first coaxial cable and the second coaxial cable having an additional shield surrounding the first coaxial cable and the second coaxial cable, and / or the first coaxial cable and the second coaxial cable are twisted together to form a twisted transmission line, and the first outer conductor and the second outer conductor are galvanically isolated from each other.

[0008] The object of the present invention is to provide a transmission line suitable for high magnetic fields for MRI devices. According to the present invention, a transmission line can be provided having a first coaxial cable and a second coaxial cable that are twisted together. The twisted coaxial cables can serve as data and power connections in the MRI coil. A capacitor can be provided between the outer conductors, which acts like a short circuit at the signal frequency and can minimize the effect of the outer conductor, especially the reduction of common mode noise injection. By twisting the cable, the coupling from B1 and gradient magnetic fields to the power line formed by the outer conductor can be reduced.

[0009] In this way, an inexpensive digital transmission line can be achieved that transmits data in a manner similar to conventional shielded twisted pair wires such as those used in USB, Ethernet, or Low Voltage Differential Signaling (LVDS), but is compatible with magnetic resonance.

[0010] Preferably, at both ends, both outer conductors are connected to a common AC ground. The outer conductors are preferably connected to each other via a capacitor. Such a capacitor avoids a galvanic connection so as to ground the cable for data but still allow power to be transmitted. Thus, one outer conductor may be connected directly to ground and the other via a capacitor.

[0011] In general, different impedances can be used for the coaxial cables. According to a preferred embodiment of the invention, the first coaxial cable and the second coaxial cable each have an impedance of 50 Ω. By using twice the standard 50 Ω cable, the impedance obtained for the signal between the inner conductors is given by 100 Ω, thus conforming well to the standards defined for most serial digital data transmission lines.

[0012] According to a preferred embodiment of the invention, the first coaxial cable and / or the second coaxial cable are micro-coaxial cables, in particular having an outer diameter of 0.2-1.0 mm. Such coaxial lines should preferably be selected by a very thin type in order to obtain a flexible cable. The two cables may be of the same type, but also of different types.

[0013] According to a preferred embodiment of the present invention, there is provided a capacitor connecting the first outer conductor and the second outer conductor, and preferably such a capacitor is disposed on each end of the transmission line.

[0014] According to a preferred embodiment of the invention, the transmission line has at least one additional capacitor connected between the first outer conductor of the first coaxial cable and the second outer conductor of the second coaxial cable, so that a capacitor can be used to connect at least two outer shields at the ends of the transmission line, but also in the middle.

[0015] According to a preferred embodiment of the present invention, the transmission line further comprises a third coaxial cable having a third inner conductor and a third outer conductor, and a fourth coaxial cable having a fourth inner conductor and a fourth outer conductor, the third outer conductor and the fourth outer conductor being galvanically isolated from each other and from the first outer conductor and the second outer conductor. Preferably, all four outer conductors are connected via a set of capacitors such that the impedance seen between the corresponding outer conductors of each transmission line is connected at a low impedance that is significantly lower than the characteristic impedance at all relevant signal frequencies. Preferably, the third outer conductor is connected to the first outer conductor via a capacitor and to the fourth outer conductor via a capacitor, and the fourth outer conductor is connected to the second outer conductor via a capacitor. Thus, the transmission line may also be made of four twisted coaxial cables forming two shielded digital transmission lines. At very low frequencies, the shielding of the coaxial cables is not very efficient. To prevent coupling, it is preferable to use diagonal neighbors to build a channel. In this way, electrical and magnetic coupling is reduced since the resulting fields are orthogonal. Thus, the transmission line can be used for bidirectional transmission with physically separated lines. For this design, the preferred embodiment of the invention is to have a capacitor between the outer conductors of the corresponding diagonal transmission lines, or between each outer conductor and a shared ground plane at both ends.

[0016] Further, according to the present invention, there is provided an MRI radio frequency coil having a transmission line as described above. In particular, the transmission line is used to transmit data in a radio frequency receiving coil for a radio frequency receiver system for an MRI device. The transmission line is used in a digital MRI coil, which is used in very EMC challenging environments, such as an MRI transmitting body coil. Other examples of applications may be other mixed analog and digital applications with particularly challenging EMC requirements.

[0017] Further, according to the present invention, there is provided a method of operating a transmission line, the transmission line comprising a first coaxial cable having a first inner conductor and a first outer conductor, and a second coaxial cable having a second inner conductor and a second outer conductor, the first coaxial cable and the second coaxial cable being twisted together to form a twisted transmission line, the first outer conductor and the second outer conductor being galvanically isolated from each other and connected to each other via one or more capacitors, the method comprising the steps of conducting power through the first outer conductor of the first coaxial cable and the second outer conductor of the second coaxial cable, and transmitting data through the first inner conductor of the first coaxial cable and the second inner conductor of the second coaxial cable. Power is transferred, for example by DC current, through the outer conductor of the coaxial cable. For signals, the two inner conductors are used as a conventional twisted pair cable or a twinax cable. Further according to the present invention, there is provided a method of operating a transmission line, the transmission line comprising a first coaxial cable having a first inner conductor and a first outer conductor, a second coaxial cable having a second inner conductor and a second outer conductor, a third coaxial cable having a third inner conductor and a third outer conductor, and a fourth coaxial cable having a fourth inner conductor and a fourth outer conductor, the first coaxial cable, the second coaxial cable, the third coaxial cable and the fourth coaxial cable being twisted together to form a twisted transmission line, with all outer conductors being galvanically isolated from all other outer conductors. Preferably, the outer conductors are connected in an AC direction to share the same ground potential. Further according to a preferred embodiment of the present invention, a DC power supply for this four-cable solution is provided between each of the two cables corresponding to one direction. This reduces coupling from non-stationary DC currents into the transmission line, further reducing potential EMC issues.Preferably, the first outer conductor and the second outer conductor are connected to each other via a capacitor, the third outer conductor is connected to the first outer conductor via a capacitor and to the fourth outer conductor via a capacitor, and the fourth outer conductor is connected to the second outer conductor via a capacitor, and the method includes conducting power via the first outer conductor of the first coaxial cable, the second outer conductor of the second coaxial cable, the third outer conductor of the third coaxial cable, and the fourth outer conductor of the fourth coaxial cable, transmitting data in a first data transmission direction via the first coaxial cable and the fourth coaxial cable, and transmitting data in a second data transmission direction via the second coaxial cable and the third coaxial cable, the first data transmission direction and the second data transmission direction being at least temporarily opposite to each other. Thus, the transmission line can be used for bidirectional transmission with physically separated lines. Power is transmitted via the outer conductor of the coaxial cable. Signals are transmitted in two different bidirectional transmission directions via the inner conductor of the coaxial cable.

[0018] Alternatively, the four outer conductors can be used to carry three different supply or control signals. Preferably, the control signals are safety related signals that can add redundancy to further improve patient safety, for example to ensure that the coil elements are sufficiently detuned during the transmit pulse.

[0019] In a configuration with only two coaxial cables, the transmission direction of the first coaxial cable is the same as that of the second coaxial cable, whereas in a configuration with four coaxial cables, the signal transmission direction is bidirectional, the transmission direction of the first coaxial cable is the same as that of the fourth coaxial cable, and the transmission direction of the second coaxial cable is the same as that of the third coaxial cable.

[0020] According to a preferred embodiment of the invention, an implementation with only two cables can be used as a bidirectional line. In case of good ends, in principle both signals can be separated at both ends. Alternatively, each single cable can transmit a signal in one direction.

[0021] According to a preferred embodiment of the present invention, in a cross section of the transmission line along most of its length, the central axis of each coaxial cable is aligned with one of the corners of a rectangle, the central axes of the first and fourth coaxial cables are aligned with opposite corners of the rectangle, and the central axes of the second and third coaxial cables are aligned with the other opposite corners of the rectangle. Here, "along most of its length" means more than 50% of its length. Furthermore, "opposite corners of a rectangle" means diagonally opposite corners or corners. Thus, in this way, two highly shielded digital transmission lines are formed. To reduce coupling at low frequencies, the diagonally opposite coaxial cables form a digital channel.

[0022] According to a preferred embodiment of the present invention, the rectangle is a diamond, in that respect if all the coaxial cables have the same diameter and are arranged as described above, the diamond becomes a square.

[0023] According to a preferred embodiment of the invention, the data transmitted is digital data and / or the power is a DC current. Although digital transmission is described above, technically the invention also works well in the analog domain. Power is transferred through the outer conductor of the coaxial cable by a DC current.

[0024] According to a preferred embodiment of the present invention, the transmission line is preferably combined and preferably wrapped with a flexible, preferably elastic thread to make the cable bundle more robust against twisting, bending and mechanical pulling forces. According to a preferred embodiment of the present invention, the transmission line can also be combined with a further cable, such as a separate single wire or an optical fiber. According to a preferred embodiment of the present invention, the transmission line can be integrated into a flexible RF MRI coil to provide an analog or digital connection between an RF preamplifier or a sensor to a processing unit. According to a preferred embodiment of the present invention, the transmission line can be integrated into a catheter for cardiac ablation or other diagnostic purposes. According to a preferred embodiment of the present invention, the transmission line can be applied to a sensor (camera, LIDAR, RADAR) providing a digital output data stream to bypass the distance to a processing unit. According to a preferred embodiment of the present invention, the sensor can be an ultrasound, temperature, pressure and / or acceleration sensing element.

[0025] According to a preferred embodiment of the invention, the method is used in a radio frequency receiving coil of an MRI apparatus.

[0026] Further in accordance with the present invention there is provided a non-transitory computer readable medium storing instructions which, when executed on a processor, cause a radio frequency receiver system for an MRI device to perform the above-described method.

[0027] BRIEF DESCRIPTION OF THE DRAWINGS

[0028] 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]

[0029] [Figure 1] 1 is a schematic cross-sectional view of a transmission line according to a preferred embodiment of the present invention; [Diagram 2] 1 is a schematic diagram of a transmission line according to a preferred embodiment of the present invention in a perspective view; [Diagram 3] FIG. 2 is a schematic cross-sectional view of a transmission line according to a further preferred embodiment of the present invention; [Figure 4] FIG. 1 is a schematic diagram of a transmission line according to a preferred embodiment of the present invention; [Diagram 5] FIG. 1 is a perspective view illustrating a transmission line according to a further preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] FIG. 1 shows a schematic cross-sectional view of a transmission line 10 according to a preferred embodiment of the present invention. The transmission line 10 comprises a first coaxial cable 20 and a second coaxial cable 30. The first coaxial cable 20 comprises a first inner conductor 21 and a first outer conductor 22. The second coaxial cable 30 comprises a second inner conductor 31 and a second outer conductor 32. Both coaxial cables 20, 30 are electrically insulated from the outside by an outer insulation 60. The first outer conductor 22 and the second outer conductor 32 are connected via a capacitor C1.

[0031] Fig. 2 is a schematic perspective view of a transmission line similar to that of Fig. 1. A first coaxial cable 20 and a second coaxial cable 30 are twisted together. Here, both ends of the transmission line 10 are connected to each other via capacitors C1a and C1b.

[0032] FIG. 3 shows a schematic cross-sectional view of a transmission line 10 having four coaxial cables 20, 30, 40, 50. The first coaxial cable 20 has a first inner conductor 21 and a first outer conductor 22. The second coaxial cable 30 has a second inner conductor 31 and a second outer conductor 32. The third coaxial cable 40 has a third inner conductor 41 and a third outer conductor 42. The fourth coaxial cable 50 has a fourth inner conductor 51 and a fourth outer conductor 52. The first outer conductor 22 and the second outer conductor 32 are connected via a first capacitor C1. The second outer conductor 32 and the fourth outer conductor 52 are connected via a second capacitor C2. The fourth outer conductor 52 and the third outer conductor 42 are connected via a third capacitor C3. The third outer conductor 42 and the first outer conductor 22 are connected via a fourth capacitor C4. The coaxial cables 20, 30, 40, 50 are arranged in a square, with the first coaxial cable 20 and the fourth coaxial cable 50 arranged in diagonally opposite corners of the square, and the second coaxial cable 30 and the third coaxial cable 40 arranged in the other diagonally opposite corners of the square.

[0033] Fig. 4 shows a schematic diagram of a method according to a preferred embodiment of the present invention. As shown in Fig. 1, in a configuration using only two coaxial cables 20, 30, in a first step S1, power is conducted through the first outer conductor 22 of the first coaxial cable 20 and the second outer conductor 32 of the second coaxial cable 30, and in a second step S2, data is transmitted through the first inner conductor 21 of the first coaxial cable 20 and the second inner conductor 31 of the second coaxial cable 30. In a configuration using four coaxial cables 20, 30, 40, 50 as shown in Fig. 3, power is conducted through the first outer conductor 22 of the first coaxial cable 20, the second outer conductor 32 of the second coaxial cable 30, the third outer conductor 42 of the third coaxial cable 40, and the fourth outer conductor 52 of the fourth coaxial cable 50. In a second step S2, data is transmitted via the first inner conductor 21 of the first coaxial cable 20, the second inner conductor 31 of the second coaxial cable 30, the third inner conductor 41 of the third coaxial cable 40 and the fourth inner conductor 51 of the fourth coaxial cable 50. For both described configurations, the first step S1 and the second step S2 are performed in parallel.

[0034] FIG. 5 shows the four coaxial cables 20, 30, 40, 50 shown in FIG. 3 in a perspective view. The first coaxial cable 20 and the fourth coaxial cable 50 are arranged at diagonally opposite corners, and the second coaxial cable 30 and the third coaxial cable 40 are arranged at the other diagonally opposite corners. The first inner conductor 21 of the first coaxial cable 20 and the fourth inner conductor 51 of the fourth coaxial cable 50 transmit data in a first transmission direction T1. The second inner conductor 31 of the second coaxial cable 30 and the third inner conductor 41 of the third coaxial cable 40 transmit data in a second transmission direction T2. ​​The first transmission direction T1 and the second transmission direction T2 are anti-parallel.

[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 "comprises" 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 of the claims. Moreover, for the sake of clarity, not all elements in the drawings have been labeled with reference signs. [Explanation of symbols]

[0036] Transmission Line 10 First coaxial cable 20 First inner conductor 21 First outer conductor 22 Second coaxial cable 30 Second inner conductor 31 Second outer conductor 32 Third coaxial cable 40 Third inner conductor 41 Third outer conductor 42 4th Coaxial Cable 50 4th inner conductor 51 Fourth outer conductor 52 Insulation 60 Capacitor C1 Capacitor C1a Capacitor C1b Capacitor C2 Capacitor C3 Capacitor C4 First data transmission direction T1 Second data transmission direction T2 S1, which conducts power S2 transmits data

Claims

1. A transmission line for transmitting data and power, a first coaxial cable having a first inner conductor and a first outer conductor; a second coaxial cable having a second inner conductor and a second outer conductor; the first coaxial cable and the second coaxial cable have an additional shield surrounding the first coaxial cable and the second coaxial cable, the first coaxial cable and the second coaxial cable being twisted together to form a twisted transmission line; the first outer conductor and the second outer conductor are galvanically isolated from each other; the transmission line having at least one additional capacitor connected between the first outer conductor of the first coaxial cable and the second outer conductor of the second coaxial cable; Transmission line.

2. 2. The transmission line of claim 1, wherein the first coaxial cable and the second coaxial cable each have an impedance of 50 ohms.

3. 3. The transmission line according to claim 1, wherein the first coaxial cable and / or the second coaxial cable is a micro-coaxial cable having an outer diameter of 0.2 to 1.0 mm.

4. The transmission line according to claim 1 , further comprising a capacitor disposed on each end of the transmission line.

5. the transmission line includes a third coaxial cable having a third inner conductor and a third outer conductor; a fourth coaxial cable having a fourth inner conductor and a fourth outer conductor; the third outer conductor and the fourth outer conductor are galvanically isolated from each other and from the first outer conductor and the second outer conductor; the third outer conductor is connected to the first outer conductor via a capacitor and to the fourth outer conductor via a capacitor; the fourth outer conductor is connected to the second outer conductor via a capacitor; The transmission line according to claim 1 .

6. 6. An MRI radio frequency coil comprising a transmission line according to any one of claims 1 to 5.

7. 1. A method of operating a transmission line, the transmission line comprising: a first coaxial cable having a first inner conductor and a first outer conductor; and a second coaxial cable having a second inner conductor and a second outer conductor, the first coaxial cable and the second coaxial cable being twisted together to form a twisted transmission line, the first outer conductor and the second outer conductor being galvanically isolated from each other, the transmission line having at least one additional capacitor connected between the first outer conductor of the first coaxial cable and the second outer conductor of the second coaxial cable, the method comprising: conducting power through the first outer conductor of the first coaxial cable and the second outer conductor of the second coaxial cable; transmitting data via a first inner conductor of the first coaxial cable and the second inner conductor of the second coaxial cable; The method according to claim 1,

8. 1. A method of operating a transmission line having a first coaxial cable having a first inner conductor and a first outer conductor, a second coaxial cable having a second inner conductor and a second outer conductor, a third coaxial cable having a third inner conductor and a third outer conductor, and a fourth coaxial cable having a fourth inner conductor and a fourth outer conductor, wherein the first coaxial cable, the second coaxial cable, the third coaxial cable, and the fourth coaxial cable are twisted together to form a twisted transmission line, with all outer conductors being galvanically isolated from all other outer conductors, the transmission line having at least one additional capacitor connected between the first outer conductor of the first coaxial cable and the second outer conductor of the second coaxial cable, the method comprising: conducting power through the first outer conductor of the first coaxial cable, the second outer conductor of the second coaxial cable, the third outer conductor of the third coaxial cable, and the fourth outer conductor of the fourth coaxial cable; transmitting data in a first data transmission direction via the first coaxial cable and the fourth coaxial cable; and transmitting data in a second data transmission direction via the second coaxial cable and the third coaxial cable. wherein the first data transmission direction and the second data transmission direction are at least temporarily opposite to each other.

9. 9. The method of claim 8, wherein in a cross-section of the transmission line along the majority of its length, each central axis of each coaxial cable is aligned with one corner of a diamond, the central axes of the first coaxial cable and the fourth coaxial cable are each aligned with diagonally opposite corners of the diamond, and the central axes of the second coaxial cable and the third coaxial cable are each aligned with the other diagonally opposite corners of the diamond.

10. The method of claim 9 , wherein the diamond is a square.

11. 11. The method according to any one of claims 7 to 10, wherein the transmitted data is digital data and / or the power is a DC current.

12. 12. The method according to any one of claims 7 to 11, wherein the method is used for a radio frequency receiving coil of an MRI device.

13. 13. The method of claim 7, wherein the outer conductors are connected to each other via one or more capacitors.

14. A computer-readable medium storing instructions for causing a processor to execute a method according to any one of claims 7 to 13.

15. A computer program for causing a processor to execute a method according to any one of claims 7 to 13.

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