Radio frequency receiver arrays for magnetic resonance imaging.

Abstract

A radio frequency (RF) receiver array for magnetic resonance imaging, the RF receiver array comprising at least one receiver coil element for receiving magnetic resonance signals from at least a portion of a target region, and at least one on-board digital receiver circuit for processing the received magnetic resonance signals. For on-coil digitization of the magnetic resonance signals, the on-board digital receiver circuit comprises an application specific integrated circuit ASIC. The RF receiver array further comprises a plurality of signal lines configured and arranged to carry data between the on-board digital receiver circuit and a receiving unit. To provide capacitive communication between the on-board digital receiver circuit and the receiving unit, the ASIC comprises at least one on-chip capacitor for each signal line, the on-chip capacitor being arranged in series with the signal line.

Description

[Technical field]

[0001] The present invention relates to the field of radio frequency (RF) receiver arrays, in particular to RF receiver arrays for magnetic resonance imaging. The present invention further relates to a magnetic resonance imaging system comprising an RF receiver array for magnetic resonance imaging and a computer program product for a method for operating the RF receiver array. [Background technology]

[0002] Traditionally, coaxial cables are used to transmit the MR signals from the receiving coils to nearby analog-to-digital (ADC) converters. However, this requires bulky and heavy cable RF traps to block common-mode RF currents for safety reasons. As the number of coils in an array increases, these bulky traps are quickly becoming a bottleneck.

[0003] To overcome these problems, two attractive technologies have been proposed in many publications: optical communication over optical fibers and wireless RF communication. However, optical communication consumes significant power, on the order of 100 milliwatts, suffers from signal-to-noise ratio losses in the case of multimode transmission, and is bulky in size. On the other hand, wireless RF communication has significant challenges to recover the clock with sufficient clock quality, resulting in significant penalties in the overall noise figure and dynamic range. Furthermore, wireless communication is notoriously unreliable in normal use, and thus there are serious doubts about its ability to provide reliable communication in harsh MR environments.

[0004] Document WO2007043009A2 discloses a radio frequency antenna comprising a resonance pickup circuit configured to pick up a magnetic resonance signal, an AD converter configured to convert the magnetic resonance signal into digital data, and a frequency converter configured to convert the 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 simple high-pass filtering techniques. If the transmitted bit pattern has frequency components approaching the resonance frequency, coding techniques such as Manchester coding can be used to remove the unwanted signals. US patent application US2018 / 0348315 discloses a receiving antenna for receiving signals at MR frequencies. A signal converter is provided to digitize the received signal and upconvert it to a higher frequency band. Summary of the Invention [Problem to be solved by the invention]

[0005] It is an object of the present invention to provide a capacitive communication solution in on-coil digital radio frequency (RF) receiver arrays for magnetic resonance imaging that does not require RF traps, consumes low power, and provides high speed communication. [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] Therefore, according to the present invention, 1. A radio frequency (RF) receiver array for magnetic resonance imaging, the RF receiver array comprising: at least one receiver coil element for receiving magnetic resonance signals from at least a portion of the target region; at least one on-board digital receiver circuit for processing the received magnetic resonance signals; having the on-board digital receiver circuitry includes an application specific integrated circuit ASIC for on-coil digitization of the magnetic resonance signals; the RF receiver array having a plurality of signal lines configured to carry data between the on-board digital receiver circuitry and a receiving unit; The ASIC has at least one on-chip capacitor for each signal line for providing capacitive communication between the on-board digital receiver circuitry and the receiving unit, the on-chip capacitor being disposed in series with the signal line. A radio frequency (RF) receiver array is provided.

[0008] The main idea of ​​the present invention is to provide a capacitive communication solution for high speed and low power communication in MR receiver systems. The main advantage is that this solution eliminates the need for bulky and heavy RF cable traps, since the RF currents at MR frequencies are blocked by the capacitors while the data edges pass through. The data communication speeds (up to 1Gbps) are much faster than at MR frequencies. It is further advantageous that energy can be transferred along the data lines as a result of the galvanic connection.

[0009] The radio frequency (RF) receiver array of the present invention is configured to receive magnetic resonance signals. To that end, the receiver coil elements pick up the magnetic flux of the magnetic field of these magnetic resonance signals. The on-board RF receiver array is provided with one or more digital receiver circuits coupled by signal lines. There may be fewer digital receiver units than RF receiver coil elements, and adjacent receiver coil elements may share a single digital receiver circuit. These digital receiver circuits digitize the analog signals at the output ports of the various receiver coil elements. Furthermore, a receiver unit is provided to act as an interface between the digital receiver circuits and the output of the RF receiver array to the magnetic resonance examination system (e.g., the system host). The digitization of the magnetic resonance signals is performed by an ASIC provided in each digital receiver unit. Digital data is communicated between the various digital receiver units on signal lines (interfaces) to the receiver units and ultimately to the system host. The digital receiver units are linked to the receiver units by capacitive communication formed by on-chip capacitors in the respective ASICs in series with the respective signal lines. In fact, the capacitors in the ASIC are from a local filter that blocks the MR high frequency carrier frequency common mode, since only differential signals are transmitted and no large signal traps need to be mounted on the RF receiver array.

[0010] In one embodiment of the present invention, the receiving unit is a data interface of a magnetic resonance imaging system and / or a second on-board digital receiver circuit.

[0011] According to another embodiment of the present invention, the on-board digital receiver circuit ASIC comprises communication modules for data communication over signal lines, each communication module comprising a transmitter and / or a receiver, each communication module further comprising an on-chip capacitor arranged in series with the signal line.

[0012] In one embodiment of the present invention, the receiver of the communication module includes a common mode suppression circuit.

[0013] In another embodiment of the invention, the signal line is a wire and / or a twisted differential pair cable and / or a monolithic conductive line. The signal line can be implemented in a variety of ways.

[0014] According to one embodiment of the present invention, the on-chip capacitor is an on-chip high voltage low capacitance capacitor.

[0015] In a preferred embodiment of the present invention, the capacitance of the on-chip capacitor is approximately 50 to 100 femtofarads. Small value (50 fF-100 fF) and high voltage on-chip capacitors provide high impedance at MR frequencies. The use of small value capacitors ensures a high impedance path (>10 kOhm) at MR frequencies, blocking current flow and eliminating cable capture requirements.

[0016] The on-chip capacitor has the advantage that it is integrated into the application specific integrated circuit of the on-board digital receiver circuit.

[0017] In one embodiment of the present invention, an on-chip capacitor is formed by a bottom electrode that is part of a first metal layer of an application specific integrated circuit ASIC of an on-board digital receiver circuit, an insulating layer formed on the bottom electrode, and an upper electrode that is part of a second metal layer of the application specific integrated circuit ASIC of an on-board digital receiver circuit, providing a galvanically isolated and monolithically integrated capacitive communication solution between MR receivers of an on-coil digitizing coil array in an MR system.

[0018] In a further embodiment of the present invention, the RF receiver array comprises a plurality of on-board digital receiver circuits, which are connected in series with each other by signal lines. With the advancement of on-coil digitization of MR signals by application specific circuit (ASIC) design, the receivers in the coil array can also be connected in series similar to the conventional structure where data from each MR receiver is sent to a data interface of the magnetic resonance imaging system for further processing and image reconstruction.

[0019] In another aspect of the invention, the above object is achieved by a magnetic resonance imaging system comprising a radio frequency (RF) receiver array for magnetic resonance imaging as described above.

[0020] In a further aspect of the invention, the object is to provide a method for operating a radio frequency (RF) receiver array, comprising: providing the radio frequency (RF) receiver array; receiving magnetic resonance signals from at least a portion of a target region using at least one receiver coil element of the RF receiver array; converting the magnetic resonance signals to digital signals by an application specific integrated circuit ASIC of an on-board digital receiver circuit of the RF receiver array; transmitting said digital data to a receiving unit via at least one signal line; This is achieved by a method having the following structure:

[0021] In one embodiment of the present invention, the step of transmitting digital data to a receiving unit via at least one signal line comprises: providing a communications module in an application specific integrated circuit ASIC of the on-board digital receiver circuit, the communications module comprising a transmitter and a receiver for data communication over the signal line; transmitting said digital data by said transmitter to a receiving unit over said signal line; receiving said digital data by a receiver of a communication module in said application specific integrated circuit ASIC; has.

[0022] In a further aspect of the present invention, the object is achieved by a computer program product comprising machine executable instructions, which are executed by a processor to control the above mentioned radio frequency (RF) receiver array.

[0023] 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]

[0024] [Figure 1] 1 illustrates a schematic diagram of a radio frequency (RF) receiver array according to an embodiment of the present invention; [Diagram 2] 1 illustrates a schematic diagram of a radio frequency (RF) receiver array according to one embodiment of the present invention; [Diagram 3] FIG. 2 illustrates generally two on-board digital receiver circuits of a radio frequency (RF) receiver array connected together by a galvanic connection according to an embodiment of the present invention; FIG. 3 illustrates generally two on-board digital receiver circuits comprising an application specific integrated circuit, an ASIC according to another embodiment of the present invention. [Figure 4] 1 illustrates a schematic representation of an implementation of a capacitive communication receiver according to an embodiment of the present invention; [Diagram 5] 1 illustrates schematic diagrams of main waveforms in a high speed capacitive communication transmitter and receiver according to an embodiment of the present invention; [Figure 6] 2 shows a flowchart of a method for operating a radio frequency (RF) receiver array according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] FIG. 1 shows a schematic diagram of a radio frequency (RF) receiver array 1 according to an embodiment of the present invention. The RF receiver array 1 comprises a plurality of receiver coil elements 2 for receiving magnetic resonance signals from at least a portion of a target area. The target area may be, for example, a part of a human body. FIG. 1 further shows that the RF receiver array 1 comprises a plurality of on-board digital receiver circuits 3 for processing the received magnetic resonance signals. The on-board digital receiver circuits 3 further include an application specific integrated circuit ASIC 4 for on-coil digitization of the magnetic resonance signals. The digitization in the receive coil elements 2 allows digital data to be transmitted between the digital receiver circuits 3 or to a data interface system 7 of the magnetic resonance system, for example to allow digital communication at an upshifted frequency. The on-board digital receiver circuits 3 are connected to each other in series by signal lines 5. In an embodiment of the present invention, the signal lines 5 are wires or twisted differential pair cables or monolithic conductive lines. The signal lines 5 are configured and arranged to carry data between the on-board digital receiver circuits 3. The ASIC further comprises at least one on-chip capacitor 6 for each signal line 5. One on-chip capacitor 6 provides capacitive communication between the on-board digital receiver circuit 3 with which the on-chip capacitor 6 is placed in series with the signal line 5 .

[0026] FIG. 2 shows a schematic of two on-board digital receiver circuits 3 of a radio frequency (RF) receiver array 1 connected to each other by a galvanic connection according to an embodiment of the present invention. Each of the on-board digital receiver circuits 3 comprises an application specific integrated circuit ASIC 4, each of the ASICs 4 comprising a communication module 8. The communication modules 8 are connected by a galvanic connection via signal lines 5, which may be wires, twisted differential pair cables or monolithic conductive lines. The left receiver ASIC 4 comprises a transmitter 9 for transmitting data via the signal lines 5. The right receiver ASIC 4 comprises a receiver 10 for receiving data via the signal lines 5. For each signal line 5, an on-chip capacitor 6 is arranged in series with each signal line 5 in the communication module. The on-chip capacitor 6 may be a monolithically integrated capacitor 6, but may also be a capacitor 6 fabricated in the PCB or even a separate capacitor 6. In one embodiment of the present invention, the on-chip capacitor 6 is an on-chip high voltage and low value capacitor. In one embodiment of the present invention, the capacitor 6 has a capacitance between 50 and 100 femtofarads, for example. The use of a small value capacitor 6 reliably provides a high impedance path (>10 kΩ) at MR frequencies, blocking current flow and eliminating cable capture requirements. Additionally, it is also possible to implement an on-chip capacitor 6 capable of withstanding high voltages (>1 kV) to provide safe galvanic isolation between the communication modules 8 of the on-board digital receiver circuit 3.

[0027] FIG. 3 shows a schematic diagram of two on-board digital receiver circuits 3 with an application specific integrated circuit ASIC 4 according to another embodiment of the present invention. In particular, FIG. 3 shows the implementation of an on-chip capacitor 6 according to an embodiment of the present invention. As shown in FIG. 3, an on-substrate capacitor 6 is formed between a lower metal layer 11, e.g., a first metal layer, and an upper metal layer 12, as an example, in the ASIC. In the fabrication of the application specific integrated circuit 4, high-quality SiO2 is used as the isolation between the metal layers 11, 12, so that it can withstand high voltage (up to 1 kV / um) stress. The high impedance provided by the on-chip capacitor 6 reduces the current induced by the transmitted MR field to a level far below that which can be achieved by conventional methods using RF cable traps.

[0028] Figure 4 shows a schematic implementation of a capacitive communication receiver 10 according to an embodiment of the invention. In Figure 4, two signal lines 5 coming from the left are connected in series with two substrate capacitors 6. Between the two signal lines 5, between the positive input inp and the negative input nnp, a common mode suppression circuit 15 is provided to reject common modes and provide a DC bias point for a data reconstruction circuit 16 where the data is reconstructed. A data output 14 is located on the right side of the receiver 10.

[0029] FIG. 5 shows a schematic diagram of the main waveforms in a high-speed capacity communication transmitter 9 and receiver 10 according to an embodiment of the present invention. The above-mentioned communication method in the MR receiver system is suitable for high-speed digital communication in the range of 1 Gbps and above. The communication signal line 5 acts like a high-pass filter that blocks the MR signal and passes the high-frequency components of the data. The communication method shown in FIG. 5 is based on data edge detection according to an embodiment of the present invention. The first line of FIG. 5 shows the input data Din. The transmitter 9 transmits antiphase block wave signals to the positive output Tx_outp and the negative output Tx_outn shown in the fourth line of FIG. 5 based on the input data Din shown in the second line of FIG. 5. Due to the characteristics of the communication link, the receiver 10 receives only the high-frequency part of the transmission signal shown by Rx_inp and Rx_inn shown in the fourth and fifth lines. The data construction circuit 16 reconstructs the data and transmits it for further processing. The fifth line shows the output data Dout.

[0030] 6 shows a flow chart of a method for operating a radio frequency (RF) receiver array 1 according to an embodiment of the present invention. The method for operating an RF receiver array 1 begins in step 600 by providing an RF receiver array 1 as described above. In step 610, magnetic resonance signals are received from at least a portion of a target region using at least one receiver coil element 2 of the RF receiver array 1. In step 620, the magnetic resonance signals are converted to digital signals by an application specific integrated circuit ASIC 4 of an on-board digital receiver circuit 3 of the RF receiver array 1. In step 630, the digital data is transmitted to a receiving unit 3, 7 via at least one signal line 5.

[0031] While the present 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, and the present 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]

[0032] Radio Frequency (RF) Receiver Array 1 Receiver coil element 2 On-board digital receiving circuit 3 Application Specific Integrated Circuits 4 Signal Line 5 On-chip capacitor 6 Data Interface 7 Communication Module 8 Transmitter 9 Receiver 10 metal layer 11 metal layer 12 Data Entry 13 Data Output 14 Common mode suppression circuit 15 Data Construction Circuit 16 Positive input inp Negative input inn Data Entry Data output Dout Positive transmitter output Tx_outp Negative transmitter output Tx_outn Positive high frequency part of the transmitted signal Rx_inp Negative high frequency part of the transmitted signal Rx_inn

Claims

1. A radio frequency (RF) receiver array for magnetic resonance imaging, wherein the RF receiver array comprises: a plurality of receiver coil elements for receiving magnetic resonance signals from at least a part of a target region; several on-board digital receiver circuits for processing the received magnetic resonance signals from one or more of the receiver coil elements; and each on-board digital receiver circuit has an application-specific integrated circuit ASIC for on-coil digitization of the magnetic resonance signals; the RF receiver array has a plurality of signal lines configured to carry data between the on-board digital receiver circuits and a receiving unit; each on-board digital receiver circuit is coupled to other on-board digital receiver circuits by one of the signal lines therebetween; each on-board digital receiver circuit has an on-chip capacitor in series with the signal line coupled to the other on-board digital receiver circuits for providing capacitive communication between the on-board digital receiver circuits, and the receiving unit, and the capacitance of the on-chip capacitor is between about 50 femtofarads and 100 femtofarads; A radio frequency (RF) receiver array.

2. The receiving unit is formed by a second on-board digital receiver circuit, and the radio frequency (RF) receiver array according to claim 1.

3. Each application-specific integrated circuit ASIC of the on-board digital receiver circuits comprises a communication module for data communication via the signal lines, each communication module comprises a transmitter and / or a receiver, and each of the communication modules further comprises the on-chip capacitor arranged in series with the signal line, and the radio frequency (RF) receiver array according to any one of claims 1 to 2. **Claim 4**: The on-chip capacitor of the communication module in each on-board digital receiver circuit can withstand high voltage stress and forms a common mode rejection circuit. The radio frequency (RF) receiver array according to claim 3. **Claim 5** The signal line is a wire and / or a twisted differential pair cable and / or a monolithic conductive line. The radio frequency (RF) receiver array according to claim 1. **Claim 6** The on-chip capacitor is an on-chip high voltage, low capacitance capacitor. The radio frequency (RF) receiver array according to claim 1. **Claim 7**: In each on-board digital receiver circuit, the on-chip capacitor is monolithically integrated into an application-specific integrated circuit (ASIC) of the on-board digital receiver circuit. The radio frequency (RF) receiver array according to claim 1. **Claim 8**: In each on-board digital receiver circuit, the on-chip capacitor is formed by a lower electrode, the lower electrode is part of a first metal layer of an application-specific integrated circuit (ASIC) of the on-board digital receiver circuit, and the on-chip capacitor is formed by an insulating layer formed on the lower electrode, and formed by an upper electrode formed on the insulating layer, and the upper electrode is part of a second metal layer of an application-specific integrated circuit (ASIC) of the on-board digital receiver circuit. The radio frequency (RF) receiver array according to claim 1. **Claim 9**: A magnetic resonance imaging system having the radio frequency (RF) receiver array for magnetic resonance imaging according to claim 1. **Claim 10**: A method for operating a radio frequency (RF) receiver array, the method comprising: providing the radio frequency (RF) receiver array according to claim 1; receiving a magnetic resonance signal from at least a part of a target region using at least one receiver coil element of the RF receiver array; Converting the magnetic resonance signal into a digital signal by an application-specific integrated circuit (ASIC) of the on-board digital receiver circuit of the RF receiver array; Transmitting the digital data to a receiving unit via at least one signal line; A method comprising the steps of. **Claim 11**: The step of transmitting digital data to a receiving unit via at least one signal line comprises: In each on-board digital receiver circuit, providing a communication module in the application-specific integrated circuit (ASIC) of the on-board digital receiver circuit, the communication module comprising a transmitter and a receiver for data communication via the signal line; Transmitting the digital data to the receiving unit via the signal line by the transmitter; Receiving the digital data by a receiver of the communication module within the application-specific integrated circuit (ASIC); The method according to claim 10, comprising the steps of. **Claim 12**: A computer program product having machine-executable instructions, the machine-executable instructions being executed by a processor for controlling a radio frequency (RF) receiver array according to any one of claims 10 to 11.

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