RF coil with built-in vital signs detector

Abstract

An object of the present invention is to provide a radio frequency (RF) transmit / receive coil (1) for a magnetic resonance (MR) imaging system having an integrated vital sign detector (3) for detecting a patient's vital signs within the magnetic resonance (MR) imaging system. Contact sensors attached directly to the patient's body are replaced with a non-contact system for monitoring vital signs, making it much easier to measure the patient's vital signs. The object is achieved by a radio frequency (RF) transmit / receive coil (1) including a vital sign detector (3). The present invention also relates to a system for detecting a patient's vital signs within a magnetic resonance (MR) imaging system, a method for operating a system for detecting a patient's vital signs within a magnetic resonance (MR) imaging system, a software package for a magnetic resonance (MR) imaging system, and a software package for upgrading a magnetic resonance (MR) imaging system.

Description

[Technical field]

[0001] The present invention relates to the field of radio frequency (RF) transmit and receive coils for magnetic resonance (MR) imaging systems, and in particular to an RF transmit and receive coil with an integrated vital signs detector. The present invention also relates to a system for detecting a patient's vital signs in a magnetic resonance (MR) imaging system, a method for operating a system for detecting a patient's vital signs in a magnetic resonance (MR) imaging system, a software package for a magnetic resonance (MR) imaging system, and a software package for upgrading a magnetic resonance (MR) imaging system. [Background technology]

[0002] High quality triggering in medical imaging (especially MR) is crucial for many examinations, e.g. cardiac, abdominal or pelvic imaging. Only with a good quality trigger signal can the imaging sequence be performed at equal exhalation states or equal points during the cardiac cycle, resulting in excellent image quality. Typically, vital signs are recorded using dedicated sensors, which are expensive and prone to errors and misplacement. Today, electrocardiograms are used to determine the heartbeat, thereby triggering the imaging device. However, ECG requires additional efforts in preparing the patient (attaching and wiring the electrodes and activating the wireless transmitter). Capacitive electrodes for the assessment of human body biopotentials are a very attractive alternative to conventional galvanically coupled electrodes for diagnostic applications, especially when the signals have to be measured through insulating materials such as cloth, which would greatly simplify current procedures.

[0003] Capacitive electrodes can detect biopotentials with a clear gap between the sensor and the body, even through hair and clothing. Compared to standard conductive electrodes, the surface of these electrodes is electrically insulated, which makes them more stable in long-term applications. The metal electrode of the sensor and the body surface are capacitively coupled, forming a capacitive As. Thus, capacitive type electrodes detect the so-called displacement current ID, as positioned by J.C. Maxwell, which describes the magnetic field around the capacitor. This current is proportional to the rate of change of the electric field associated with the ECG signal.

[0004] From EP 2020916 A1 a wireless patient monitor for MRI is known, where the patient supported on a movable table can be positioned outside the bore of the magnet to receive a wireless patient monitor that receives signals from the patient by leads. The patient may then be moved into the bore of the magnet with the wireless patient monitor allowing continuous monitoring of the patient. The wireless patient monitor can incorporate its own power source and transmit the monitored signals from the patient, for example via a wireless transmission signal, to a base station located outside the bore near the magnet. However, the patient monitor requires additional efforts in preparing the patient, for example in attaching electrodes, wiring and connecting a wireless transmitter. Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a radio frequency (RF) transmit / receive coil for a magnetic resonance (MR) imaging system having an integrated vital sign detector for detecting a patient's vital signs in the magnetic resonance (MR) imaging system, whereby contact sensors attached directly to the patient's body are replaced with a non-contact system for monitoring the vital signs, thereby making it much easier to measure the patient's vital signs. [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, according to the present invention, a radio frequency (RF) transmit / receive coil for a magnetic resonance (MR) imaging system is provided, the RF transmit / receive coil comprising a vital sign detector for detection of a patient's vital sign in the magnetic resonance (MR) imaging system, the vital sign detector being integrated in the RF transmit / receive coil, a pair of conductive coil elements of the RF transmit / receive coil forming the vital sign detector, the vital sign detector being a capacitive vital sign detector, the capacitive vital sign detector being adapted to receive a capacitive vital sign signal. The proposed system consists of a combination of an RF transmit / receive coil with a capacitive vital sign detector for real-time vital sign monitoring and simultaneous high resolution images. The capacitive vital sign detector is formed by the conductors of the RF transmit / receive coil. The method is therefore completely passive, since it utilizes measurements of local electric fields that are corrected by body movements (in particular breathing and cardiac activity). Furthermore, the combination of RF coil and capacitive vital sign sensor technologies provides improved signal quality using cross-correlation between the systems, improved calibration schemes, or (spatial) guidance of one system using the other. In one embodiment of the present invention, the magnetic resonance (MR) imaging system may be an MR therapy system, such as an MR-LINAC.

[0008] In one embodiment of the present invention, the capacitive vital signs detector is an electrocardiogram (ECG) sensor adapted to receive an ECG signal.

[0009] According to one embodiment of the present invention, the conductive coil elements of the pair of RF transmit / receive coils forming the vital signs detector are covered with a material having a high dielectric constant. To increase the capacitance of the detector to the body, the electrodes may be covered with a material having a high dielectric constant, such as ceramic. Since the electrodes are integrated in the coil cover (close to the body surface), they have no galvanic contact and are not galvanically isolated from the body. The capacitance ECG depends on several factors, but usually corresponds to a relatively small value between 0.1 and 10 pF. For low frequency measurements such as ECG, such a weak coupling requires a high input impedance of the sensor, since the finite input resistance attenuates the input Vin. Very high impedance nodes are very susceptible to any electromagnetic interference from the environment and to motion-induced artifacts. Therefore, in an advantageous embodiment of the present invention, the electrodes can be actively shielded to suppress interference.

[0010] In another preferred embodiment of the invention, the capacitive vital signs detector and the RF transmit / receive coil are adapted to process the capacitive vital signs signal and the MRI signal acquired by the RF transmit / receive coil in different frequency spaces.

[0011] In one embodiment of the present invention, a vital signs detector is placed below the patient support of a magnetic resonance (MR) imaging system. Placing the detector below the patient support is advantageous because the ECG can be particularly well received here. This location is also particularly advantageous for measuring the patient's movements and position.

[0012] In another aspect of the present invention the object is achieved by a system for detecting a patient's vital signs in a magnetic resonance (MR) imaging system, characterised in that the system comprises a radio frequency transmit / receive coil equipped with a vital sign detector as defined in any one of claims 1 to 4, the system further comprising an output preamplifier for amplifying a capacitive vital sign signal, the pair of conductive coil elements being coupled to the output preamplifier, and the system further comprising a digital signal processor, the digital signal processor being adapted for further processing the amplified capacitive vital sign signal.

[0013] According to a preferred embodiment, the digital signal processor is a software defined radio (SDR). An SDR typically comprises analog-to-digital and digital-to-analog converters, RF components for transmitting and / or receiving signals, an FPGA for basic filtering, signal down- and up-conversion, and a two-way radio or optical output. The software resides in the computer, where it runs and sends instructions to the SDR. The received signal is amplified, for example by a preamplifier, and sent back to the radio where it is further amplified or attenuated. The ADC converts the signal to a digital signal, and the FPGA and a digital signal processor (DSP) handle the down-conversion and filtering of the digital signal. The data stream is then sent back to the computer and the real-time signal processing software.

[0014] According to another embodiment of the present invention, a system includes a relaxation oscillator and / or a microcontroller for capacitive vital signs signal detection.

[0015] In another preferred embodiment of the invention, the system includes a multiplexer for switching between different pairs of conductive coil elements of an RF transmit / receive coil forming the vital signs detector.

[0016] In a further aspect of the invention, this object is achieved by a method for operating a system for detecting a patient's vital signs in a magnetic resonance (MR) imaging system as described above, comprising the steps of: providing a radio frequency (RF) transmit / receive coil with a vital sign detector, the radio frequency (RF) transmit / receive coil and the vital sign detector forming a magnetic resonance (MR) imaging coil array, receiving at least one vital sign signal from the vital sign detector, receiving at least one MRI signal from the radio frequency (RF) transmit / receive coil, and performing correction of the MRI signal based on the vital sign signal.

[0017] According to one embodiment of the present invention, the step of performing correction of the MRI signals based on the vital signs signals includes correction based on a deep learning algorithm.

[0018] In yet another aspect of the invention, this object is achieved by a magnetic resonance (MR) imaging system comprising a system for detecting vital signs of a patient as described above.In a further aspect of the invention, this object is achieved by a software package for a magnetic resonance (MR) imaging system, which software package includes instructions for controlling a system for detecting vital signs of a patient in the magnetic resonance (MR) imaging system according to the method described above.

[0019] In another aspect of the invention the object is achieved by a software package for upgrading a magnetic resonance (MR) imaging system, whereby the software package includes instructions for controlling a radio frequency (RF) receiver system including a vital signs detector according to the method described above.

[0020] In an embodiment of the present invention, an AI-based software algorithm can be foreseen for selecting capacitive electrodes from the sensor data and for example configuring filter parameters based on training data obtained with the system. The data can be processed and filtered, for example using Kalman or SVD filtering. Data processing can be done remotely, for example in the cloud.

[0021] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter, however such embodiments do not necessarily represent the full scope of the invention, and reference is therefore made to the claims and this specification for interpreting the scope of the invention. [Brief description of the drawings]

[0022] [Figure 1] 1 illustrates a schematic diagram of a system for detection of vital signs including a radio frequency transmit / receive coil with a vital signs detector, according to an embodiment of the present invention; [Diagram 2] 1 illustrates a schematic diagram of a system for detection of vital signs including a radio frequency (RF) transmit / receive coil with a vital signs detector according to another embodiment of the present invention. [Diagram 3] 1 illustrates a schematic of a portion of a system for detecting a vital signs detector according to another embodiment of the present invention. [Figure 4] 1 illustrates a schematic flow chart of a vital signs detector and an RF transmit / receive coil signal stream, according to an embodiment of the present invention. [Diagram 5] 2 shows a flowchart of a method for operating a system for detecting vital signs according to an embodiment of the present invention. [Figure 6] 1 illustrates a vital signs detector patch with an RF transmit / receive coil and an impedance circuit, according to one embodiment of the present invention. [Figure 7] 1 shows an RF coil array with coils and vital signs detector patches and individual hybrid RF transmit and receive according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] FIG. 1 shows a schematic diagram of a system for detecting vital signs including a radio frequency transmit / receive coil 1 with a vital sign detector 3 according to an embodiment of the present invention. The conductors 4 of the radio frequency (RF) transmit / receive coil 1 form a capacitive electrode with a coupling to the body of the order of 5-20 pF. The induced ECG signal can be measured as a change in capacitance. For example, a voltage signal is measured across the capacitance and amplified via a high impedance preamplifier 5. Additionally, the capacitance can be modulated by body movement. By having an RF coil array 18, the individual measurement signals depend on the local movement and on the local ECG signal. The amplified signal is further digitally processed, for example via an FPGA unit 8. The MRI signal of the RF transmit / receive coil 1 is received in a resonant coil circuit and amplified in an RF preamplifier 2. Due to the high impedance of the ECG preamplifier 5, the RF signal is not disturbed. The RF transmit / receive coil signal is further digitized and can be used for correction and calibration of the ECG signal, for example to remove movement-induced artifacts.

[0024] The capacitive vital signs signal and the MRI signal are processed in different frequency spaces. Therefore, in one embodiment of the present invention, two separate ADC channels 6, 7 may be provided. The output of the ADC is fed to a signal processing device 8. The signal processing device 8 may be, for example, a software defined radio (SDR). The signal processing device 8 may be used, for example, for the correction of motion artifacts in the MRI signal by the vital signs signal. An interface 9, for example an optical interface, controls the communication between the signal processing device 8 and other components of the MRI system. As with other circuit schemes, only one common ADC may be realized. In another embodiment of the present invention, the capacitive sensor signal may be converted (or modulated) into a pilot tone and received at a different frequency via the MRI receiver or by a separate receiver.

[0025] For example, detecting movement due to breathing or heart rate is one application of the vital signs detector 3, and furthermore the capacitive vital signs signal can be simultaneously processed by other vital signs detectors such as a camera or RADAR sensor.

[0026] FIG. 2 shows a schematic diagram of a system for detecting vital signs including a radio frequency transmit / receive coil 1 with a vital sign detector 3 according to another embodiment of the present invention. In FIG. 2, the RF transmit / receive coil 1 is shown with four capacitive conductors 4 forming a capacitive vital sign detector 3. The conductors 4 increase the capacitance to the ECG signal, while the MRI coil resonance is determined by the loop conductors and lumped capacitors. The MRI signal is received by the conductive coil elements of the RF transmit / receive coil 1, fed to a matching and detuning circuit 11, amplified by the RF amplifier 2, and fed to an AD converter 7. The capacitive vital sign signal is received by the capacitive conductors and sent via two diodes 11 to a relaxation oscillator 12 or a microcontroller for detection of the capacitive vital sign signal.

[0027] 3 shows diagrammatically part of a system for detecting vital signs according to another embodiment of the invention. In this embodiment one can foresee several conductive coil elements 4 of an RF transmit / receive coil 1 forming a vital sign detector 3. To be able to switch between the various vital sign detectors 3, a multiplexer 14 is provided, controlled for example by means of a microcontroller 13 by means of a control signal 15. Also in this embodiment a relaxation oscillator 12 can be provided for the detection of the vital sign signals.

[0028] FIG. 4 shows a schematic flow chart of the signal stream of the vital sign detector 3 and the RF transmit / receive coil 1 according to an embodiment of the present invention. The vital sign signal from the vital sign detector 3 is analyzed in step 400. In step 410, the MRI signal from the RF transmit / receive coil 1 is analyzed. In step 420, the best signal is identified from either the vital sign detector 3 or the RF transmit / receive coil 1. Then, a signal processing device 8, e.g., a software defined radio (SDR), is used to generate a correlation of the signals in step 430. Then, in step 470, for example, the correlation of both signals can be used to generate an improved trigger signal from the vital sign signal 450 to improve the control of the MRI signal. The MRI signal 440 can also be improved using the vital sign signal. For example, the overall signal quality can be improved by setting a range of interest, which also improves the MRI reconstruction in step 460.

[0029] FIG. 5 shows a flowchart of a method for operating a system for detecting vital signs according to one embodiment of the present invention.

[0030] The method begins at step 500 where a radio frequency transmit / receive coil 1 including a vital sign detector 3 is provided, where the radio frequency transmit / receive coil 1 and the vital sign detector 3 form a magnetic resonance imaging coil array.

[0031] In step 510 , at least one vital sign signal is received from a vital sign detector 3 .

[0032] In step 520, at least one MRI signal is received from a radio frequency (RF) transmit / receive coil 1.

[0033] In step 530, correction of the MRI signal based on the vital signs signal is performed.

[0034] FIG. 6 shows a vital sign detector patch 16 with an RF transmit / receive coil 1 and an impedance circuit 17 according to an embodiment of the present invention. To increase the capacitance, additional conductive coil elements 4 forming the vital sign detector 3 can be formed as patches 16 and combined with the RF transmit / receive coil 1. The patch can be, for example, an electrocardiogram (ECG) patch with an ECG sensor, the sensor adapted to receive an ECG signal. Several patches 16 can be arranged inside the coil circumference or partially under the coil. The patches 16 are separated from each other to prevent B1 shielding effects from the excitation field of the MR body transmit coil. The individual patches 16 are connected via impedance circuits 17. The impedance circuits 17 can be RF chokes or parallel resonant circuits with high impedance at MRI frequencies and low impedance at frequencies for ECG and respiration. In FIG. 6, the signals are amplified and processed separately by different optimized amplifiers 2, 5, for example low noise amplifiers (LNAs).

[0035] 7 shows an RF coil array 18 with individual hybrid RF transmit / receive coils 1 and vital sign detector patches 16 according to one embodiment of the present invention. Each coil 1 sees an individual part of the human body. The individual signals of the vital sign detector patches 16 can be selected, for example, using a multiplexer.

[0036] 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 exemplary or illustrative 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 "comprises" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be 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]

[0037] 1 Radio Frequency (RF) Transmitting and Receiving Coil 2. RF Amplifier 3 Capacitive Vital Signs Detector 4 Conductive coil element 5 Capacitive Vital Signs Sensor Amplifier 6 ADC for vital signs signals 7 ADC for MRI signals 8 Signal Processing Circuit 9 Interface 10 Matching and detuning circuits 11 Diode 12 Relaxation Oscillator 13. Microcontrollers 14 Multiplexer 15 Control Signals 16 Vital Signs Detector Patch 17 Impedance Circuit 18 RF coil array

Claims

1. A radio frequency transmit / receive coil for a magnetic resonance imaging system, the radio frequency transmit / receive coil having a vital sign detector for detection of a vital sign of a patient in the magnetic resonance imaging system, the vital sign detector being a capacitive vital sign detector integrated within the radio frequency transmit / receive coil, a pair of conductive elements of the radio frequency transmit / receive coil forming the capacitive vital sign detector, the pair of conductive elements forming capacitive electrodes that are capacitively coupled with a patient's body, the capacitive vital sign detector configured to receive a capacitive vital sign signal through the capacitive electrodes; the capacitive vital signs detector is an electrocardiogram sensor configured to receive an electrocardiogram signal; High frequency transmit and receive coil.

2. The radio frequency transmit / receive coil of claim 1 , wherein the pairs of conductive elements of the radio frequency transmit / receive coil forming the capacitive vital signs detector are covered with a material having a high dielectric constant.

3. 3. The radio frequency transmit / receive coil of claim 1, wherein the capacitive vital sign detector and the radio frequency transmit / receive coil are configured to process the capacitive vital sign signal and the MRI signal acquired by the radio frequency transmit / receive coil in different frequency spaces.

4. 4. The radio frequency transmit / receive coil according to claim 1, wherein the capacitive vital signs detector is positioned below a patient support of a magnetic resonance imaging system.

5. A system for detection of a patient's vital signs in a magnetic resonance imaging system, comprising: A high frequency transmission / reception coil according to any one of claims 1 to 4; an output preamplifier for amplifying the capacitive vital sign signal, the pair of conductive elements being coupled to the output preamplifier; a digital signal processor configured to process the amplified capacitive vital sign signal; and The system has:

6. The system of claim 5 , wherein the digital signal processor is a software defined radio.

7. 7. The system according to claim 5 or 6, comprising a relaxation oscillator and / or a microcontroller for the capacitive vital signs signal detection.

8. 8. The system of claim 5, further comprising a multiplexer for switching between different pairs of conductive elements of the radio frequency transmit / receive coil forming the capacitive vital signs detector.

9. 5. A method of operating a system for detection of vital signs of a patient in a magnetic resonance imaging system according to claim 4, said method comprising the steps of: providing a radio frequency transmit / receive coil having a vital sign detector, the radio frequency transmit / receive coil and the vital sign detector forming a magnetic resonance imaging coil array; receiving at least one vital sign signal from the vital sign detector; receiving at least one MRI signal from the radio frequency transmit / receive coil; performing a correction of the MRI signal based on the vital sign signal; The method comprising:

10. 10. The method of claim 9, wherein performing correction of the MRI signals based on the vital signs signals comprises correction based on a deep learning algorithm.

11. A magnetic resonance imaging system comprising a system for detection of a patient's vital signs according to any one of claims 1 to 8.

12. A software package for a magnetic resonance imaging system, said software package comprising instructions for controlling a system for detection of vital signs of a patient in a magnetic resonance imaging system according to the method of claims 9-10.

13. A software package for upgrading a magnetic resonance imaging system, said software package including instructions for controlling a radio frequency receiver system having a vital signs detector according to the method of claims 8-9.

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