Circuit assembly for correcting an input signal and use of a circuit assembly for detecting a physiological signal in a magnetic resonance system

Abstract

The invention relates to a circuit assembly for correcting an input signal and to the use of a circuit assembly for detecting a physiological signal in a magnetic resonance system. The circuit assembly comprises a voltage control circuit having at least one voltage control switching element, a resistor connected in series with the voltage control circuit upstream of the voltage control circuit, an operational amplifier having a first amplifier input, a second amplifier input and an amplifier output, and a low-pass filter connected between a first terminal of the at least one voltage control switching element and the first amplifier input of the operational amplifier, and the low-ohmic terminal of the at least one voltage control switching element is electrically connected to the amplifier output of the operational amplifier and to the second amplifier input of the operational amplifier in order to feed back the output voltage of the operational amplifier to the low-ohmic terminal of the switching element.

Description

Technical Field

[0001] The present invention relates to a circuit assembly for correcting an input signal, wherein the input signal at the input interface of the circuit assembly includes a useful signal and an interference signal. Background Technology

[0002] A circuit assembly for correcting input signals is known from EP 2 854 630 B1[1].

[0003] Especially during magnetic resonance imaging (MRI) measurements, vital parameters of living organisms, such as electrocardiogram (EKG) and respiration, are monitored. However, interference signals caused by gradient switching on the MRI equipment can be many times larger than the physiological signals being monitored, making it difficult to assess the vital parameter data.

[0004] To suppress interference, a sample-and-hold circuit [2] can be used, in which interference is identified by a detector circuit in one circuit section, while the signal processing chain in another circuit section is interrupted during the time of interference. However, this method cannot eliminate interference immediately, so there are still interference peaks that distort the signal during the time before the interference is eliminated.

[0005] DE 699 27 328 T2 discloses a method and apparatus for limiting the peak value of an input signal. The apparatus and method isolate the peak value of the input signal based on a limiting threshold voltage, generate an extremum signal representing a local extremum of the signal isolated from the peak value, filter the extremum signal based on a suitable pulse filter response to generate a filter signal, and combine the filter signal with an input signal delayed by a predetermined time period to generate a pulse limiting signal.

[0006] DE 60 2004 012 671 T2 discloses an amplification system and method that reduces the peak value associated with an input signal and provides correction for signal distortion and out-of-band emissions caused by peak reduction in one or more spectral bands. The correction signal for eliminating signal distortion and out-of-band emissions associated with peak reduction is calculated or electronically derived. The correction signal is combined with the peak-reduced signal before or after amplification of the peak-reduced input signal.

[0007] US 2003 / 0086507 A1 discloses a method for limiting a signal. Here, the highest peak value above a threshold is searched within a first window generated by a set of sampled values ​​of the signal. A threshold correction signal is then appended to the found highest peak value.

[0008] US 2019 / 0159733 A1 discloses a method that allows for the identification and labeling of electromagnetic interference in multiple signals. The system uses an adaptable, versatile, modular architecture with a series of modules for various filtering, conditioning, processing, and wireless transmission functions, which can be assembled in different configurations for different settings.

[0009] EP 2 854 630 B1[1] discloses a circuit for using a filter in a magnetic resonance (MR) system to reduce MR interference of a physiological signal S(f), such as an ECG signal. The circuit in EP 2 854 630 B1 includes a first summation / subtraction node, a high-pass filter, and a second summation / subtraction node. The first summation / subtraction node takes a first signal and a second signal as inputs, wherein the first signal contains all interference components N(f) generated by the MRT scanner and the physiological signal S(f), the second signal contains the physiological signal S(f) and an error signal E(f), and the first summation / subtraction node combines the second signal by subtracting the first signal to produce a difference signal N(f)-E(f). The high-pass filter filters the difference signal N(f)-E(f) from the first summation / subtraction node. The second summation / subtraction node subtractively combines the first signal S(f)+N(f) and the filtered signal H(f)*[N(f)-E(f)] from the high-pass filter to generate the second signal S(f)+E(f). However, the use of such a filter is only effective for small interference amplitudes. However, since interference occurs especially in MR measurements, where the amplitude difference between the useful signal and the interference can be as high as 1000 times, the method known in [1] is not suitable for such measurements. Summary of the Invention

[0010] The object of this invention is to provide a circuit assembly that can quickly and effectively suppress interference with large amplitude. In particular, the circuit assembly should be suitable for suppressing interference signals that may be generated, for example, by gradient pulses in MR equipment, thereby enabling better further processing of useful signals.

[0011] According to the present invention, this objective is achieved by a circuit assembly.

[0012] The circuit components according to the present invention include:

[0013] • A voltage control circuit having at least one voltage-controlled switching element, said voltage-controlled switching element having a first terminal and a low-ohm second terminal.

[0014] • A resistor connected in series with the voltage control circuit upstream of the voltage control circuit.

[0015] • An operational amplifier having a first amplifier input terminal, a second amplifier input terminal, and an amplifier output terminal; and

[0016] • A low-pass filter connected between the first terminal of the at least one voltage-controlled switching element and the first amplifier input of the operational amplifier.

[0017] In the circuit assembly according to the invention, the output voltage of the operational amplifier is fed back to the low-ohmic terminal of the switching element of the voltage-controlled switching element. For this purpose, the low-ohmic terminal of the at least one voltage-controlled switching element is electrically connected to both the amplifier output and the second amplifier input (inverting amplifier input) of the operational amplifier. In this way, interference signals are detected and suppressed via this same at least one voltage-controlled switching element. It is not necessary to filter out interference signals from the signals directed to the operational amplifier. Instead, once interference is detected, signal transmission to the operational amplifier is stopped, and the signal applied to the operational amplifier before the interference is detected is output as a clearing signal until the interference is no longer present.

[0018] Preferably, another resistor is connected between the low-ohm terminal of the voltage control circuit and the input terminal of the inverting amplifier. This other resistor allows the amplification factor to be set. This additional resistor ensures better stability of the circuit components.

[0019] To avoid oscillations, the operational amplifier's amplification factor V is set to approximately 1, but less than 1, specifically 0.9 < V < 1. For this reason, the other resistor (the resistor between the switching element and the amplifier output) is chosen to be low ohms. The closer the amplification of the operational amplifier's interaction with the rest of the circuitry (especially with the resistor between the switching element and the operational amplifier, as well as the voltage-controlled switching element) is to a value of 1, the better the suppression of interference pulses.

[0020] Preferably, the at least one voltage-controlled switching element has a control input terminal electrically connected to the input interface via a control resistor. If the voltage at the control input terminal of the voltage-controlled switching element exceeds a threshold (e.g., due to interference), the switching element becomes conductive, preventing the signal at the first terminal of the switching element from being transmitted to the operational amplifier. The voltage at the first terminal of the switching element is then almost identical to the voltage at the low-ohm second terminal of the switching element. This, in turn, approximates the voltage applied there before the interference occurred.

[0021] The voltage control circuit preferably includes at least one transistor as a switching element. Alternatively, a relay, field-effect transistor (FET), tube, or analog switch can also be used as the voltage control switching element.

[0022] In one particular implementation, the voltage control circuit includes two voltage-controlled switching elements with opposite polarization. This allows for the suppression of both positive and negative interference signals. This specifically relates to circuit assemblies in which transistors or FETs are used as voltage-controlled switching elements. The semiconductors of these switching elements are then also doped differently (NPN+PNP transistors). Thus, PNP and NPN transistors are used, with their bases electrically connected to each other, their emitters electrically connected to each other, and their collectors electrically connected to each other.

[0023] If it is ensured that the switching process is triggered in each polarity of the disturbance, for example if an analog switch is used as the switching element, the second switching element can be omitted.

[0024] Useful signals can be physiological signals, especially EKG signals.

[0025] Interference signals can be generated by MR imaging scanners, especially gradient coils.

[0026] In a particularly preferred embodiment of the circuit assembly according to the invention, the low-pass filter is an RC component whose capacitor is located at a reference potential. The voltage applied when there is no interference is stored through the capacitor of the low-pass filter. The cutoff frequency of the RC component is here determined to be greater than the frequency of the useful signal in order to minimize distortion.

[0027] The circuit assembly according to the invention is used to correct an input signal, wherein the input signal at the input interface includes a useful signal and a interference signal.

[0028] The circuitry according to the invention is particularly preferred in magnetic resonance (MR) systems having an MR imaging scanner and components for detecting physiological signals to reduce interference signals caused by the MR imaging scanner.

[0029] The core of the circuit assembly according to the invention is a circuit having at least one switching element (preferably two switching elements), wherein the at least one switching element has a resistor connected before and after the first terminal of the voltage-controlled switching element. This simple circuit assembly forms an interference detector and simultaneously results in interference cancellation. Due to the small number of components and the short signal path, only a minimal operating time difference is generated between interference detection and the signal path. Thus, interference can be almost perfectly eliminated.

[0030] Further advantages of the invention become apparent from the specification and drawings. Similarly, the features described above and further to be described according to the invention can be used individually or in combination in any way. The embodiments shown and described should not be construed as an exclusive enumeration, but rather as exemplary features used to describe the invention. Attached Figure Description

[0031] Figure 1 A circuit assembly according to the present invention is shown.

[0032] Figure 2 It is shown that:

[0033] - The expected signal variation curve of interference caused by the gradient coil of the MR device.

[0034] - Expected signal change curve for respiratory monitoring;

[0035] -Expected signal change curve of EKG; and

[0036] -Expected signal change curve superimposed from EKG and respiratory monitoring.

[0037] Figure 3 It is shown that:

[0038] -Signal variation curves of the useful signal superimposed with low-frequency and high-frequency interference signals;

[0039] - The signal variation curve of the input signal applied at the input interface.

[0040] - The signal variation curve of the signal applied at the interface of the first terminal of the voltage control circuit; and

[0041] - The signal variation curve of the signal applied at the interface of the operational amplifier.

[0042] Figure 4 A component of a signal processing apparatus having a circuit assembly according to the present invention is shown.

[0043] Figure 5 The illustration schematically shows an MR imaging scanner, components for detecting physiological signals, and... Figure 4 The measurement component of the signal processing device in the system. Detailed Implementation

[0044] Figure 1 A preferred embodiment of the circuit assembly according to the invention is shown. The switching assembly according to the invention includes an input interface Li_in, a voltage control circuit S, an operational amplifier U1, and an output interface out, at which an input signal V(Li_in) is applied. The operational amplifier U1 transmits an output signal V(Li_C) to the output interface out. The voltage control circuit S regulates the transmission of the input signal V(Li_in) to the operational amplifier U1. The output interface out outputs the output signal V(Li_C).

[0045] The voltage control circuit S, in its current form, includes two voltage-controlled switching elements T1 and T2, each having a first terminal K (collector when the transistor is used as a switching element), a low-ohm terminal E (emitter when the transistor is used as a switching element), and a control input terminal B (base when the transistor is used as a switching element). The voltage control circuit S is positioned between the input interface Li_in and the operational amplifier U1. A voltage V (Li_in) is applied via a control resistor R1 through the control input terminal B of the voltage-controlled switching elements T1 and T2, and via a resistor R2 at the first terminal K of the voltage-controlled switching elements T1 and T2.

[0046] An RC low-pass filter with capacitor C1 and resistor R3 is connected between the interface Li_S at the first terminal K of the voltage-controlled switching elements T1 and T2 and the interface Li_C to the operational amplifier U1.

[0047] Operational amplifier U1 includes a first amplifier output terminal VE+, a second amplifier input terminal VE-, and an amplifier output terminal VA.

[0048] The low-ohm terminal E of the voltage-controlled switching elements T1 and T2 is electrically connected to the amplifier output terminal VA of operational amplifier U1. Therefore, the output voltage of operational amplifier U1 is fed back to the low-ohm terminal E of the switching elements T1 and T2. To prevent oscillation, a low-ohm resistor R4 is connected between the low-ohm terminal E of the voltage-controlled switching elements T1 and T2 and the amplifier output terminal VA, ensuring that the amplification factor of operational amplifier U1 is always less than 1.

[0049] Figure 2 The curve above shows the variation of the interference signal V(ustör) of the gradient coil assembly of the MR device. Below it are the signal variation curves of two physiological signals V(uatmung) and V(uekg) (here: respiration and ECG), as well as the superposition V(out1) of the two physiological signals V(uatmung) and V(uekg), where the superposition V(out1) of the two physiological signals V(uatmung) and V(uekg) should be measured as the useful signal during MR measurement. It can be clearly seen that the maximum amplitude of the interference signal V(ustör) is a whole order of magnitude larger than that of the useful signal V(out1).

[0050] Figure 3The curve above illustrates the superposition of the useful signal and the interference signal, V(filter). This superposition V(filter) should be processed using the circuit assembly 1 according to the invention. For this purpose, the signal V(filter) to be processed can be amplified in multiple stages so that the useful signal component has a usable strength (particularly approximately 0.5V). Here, in order to keep the over-control of the amplifier stages due to the high amplitude of the interference signal within limits, amplitude limiting (small-signal amplification) is preferably applied after each amplifier stage. The input signal V(li_in) for use with the circuit assembly according to the invention is then obtained. Figure 3 (The second signal change curve from the top).

[0051] exist Figure 1 In this circuit, switching elements T1 and T2 are constructed as transistors. To switch between the base and emitter of the transistors, approximately 0.7V is typically required. The function of the circuit according to the invention is described below using an example of a circuit with two transistors T1 and T2. Using two transistors allows for the processing of both positive and negative useful signals and interference signals. For this purpose, Figure 1 The circuit S shown includes an NPN transistor T1 and a PNP transistor T2. The two transistors T1 and T2 are connected to each other such that their bases, emitters, and collectors are electrically connected to each other. This function is similar to other voltage-controlled switching elements or can be adapted to circuits with only one or more switching elements.

[0052] Using the circuit according to the invention, the input signal V(li_in) to be processed is conducted via resistors R1 and R2 at the base B and collector K of transistors T1 and T2, respectively. At the interface Li_S to the collector K, the processed signal V(Li_S) is acquired and transmitted to operational amplifier U1 via low-pass resistor R3-C1, which acts as an impedance converter with an amplification factor < 1. Here, the cutoff frequency of low-pass resistor R3-C1 is preferably selected such that the highest frequency of the useful signal is only attenuated in a non-significant manner. The output signal of operational amplifier U1 is fed to the emitter E of the transistor.

[0053] As long as the input signal does not exceed the base-emitter voltage (a threshold of approximately 0.6V), the transistor remains non-conducting, and the output signal V(Li_C) of the impedance converter almost follows the input voltage of the circuit. Small-signal amplification and the voltage during circuit S switching are thus matched so that the useful signal just before switching circuit S. In the absence of interference (where the input signal thus reflects the useful signal), the input signal V(Li_in) is then applied via resistors R2 and R3 at capacitor C1 of the low-pass filter R3-C1 and at the amplifier output VA of operational amplifier U1, and output as the output signal V(Li_C) = V(li_in).

[0054] If the threshold voltages of transistors T1 and T2 are exceeded (for example, if the input signal contains components greater than the useful signal in addition to the useful signal— Figure 3 If the interference signal V(li_in) is detected, one of transistors T1 and T2 switches to the on state, thus creating a low-ohm connection between the amplifier output VA of operational amplifier U1 and the corresponding low-ohm terminal E of transistor T1 or T2 via resistor R4. The voltage of the input signal V(li_in) then drops at resistor R2, which is connected in series with the voltage control circuit S. This means that the voltage at collector K almost corresponds to the voltage at emitter E. During the on-time of transistors T1 and T2, the output voltage V(Li_C) of impedance converter U1 does not change, and no interference occurs at the output VA of impedance converter U1. The low-pass filter R3-C1 downstream of circuit S and the operational amplifier (impedance converter) U1 downstream thereafter ensure that the voltage value of the input signal V(li_in) is stored in the middle before the interference occurs. Therefore, in the case of interference, the value stored before the interference occurs is output to operational amplifier U1. This means that the output voltage of impedance converter U1 does not change during the on-time of switching elements T1 and T2, and the error does not appear at the output interface out.

[0055] In this invention, the low-pass filter R3-C1 is not used to eliminate interference signals. Instead, the interference has already been largely suppressed at the interface Li_S to the collector K because interference signal elimination has been achieved by the voltage control circuit. Therefore, the low-pass filter R3-C1 is only used to filter the high-frequency components of the useful signal and store the applied voltage without interference. Ultimately, a useful signal with as much interference as possible is present at the interface Li_C.

[0056] Figure 4 The components of the signal processing device 6 are shown, which are mounted on the live measurement object (see...). Figure 5 The signals detected by electrodes a1, a2, and a3 on the circuit assembly according to the invention are processed until a useful signal is available. The signals detected by electrodes a1, a2, and a2 are transmitted via interface 4 for detecting physiological signals to limiter L, amplifier F, and another limiter L. These are used for the aforementioned small signal amplification, wherein the amplitude is limited before the signal is provided as the input signal V (li_in) of the circuit assembly 1 according to the invention. The output signal V (li_c) can be further processed, for example, by another amplifier H after leaving the circuit assembly 1 according to the invention.

[0057] Figure 5The measurement system is shown, which includes an MR device 2 with a gradient coil assembly 3, an interface 4 for detecting physiological signals of a live measurement subject 5, and a circuit assembly 1 according to the invention for eliminating interference signals caused by the gradient coil assembly 3.

[0058] List of reference numerals

[0059] 1 Circuit Component

[0060] 2 MR equipment

[0061] 3-gradient coil assembly

[0062] 4. Interface for detecting physiological signals

[0063] 5. Measurement Objects

[0064] 6. Signal processing device

[0065] Electrodes a1, a2, a3

[0066] B control input terminal of the switching element

[0067] C1 low-pass filter capacitor

[0068] The low-ohm second terminal of the E-switch element

[0069] F and H operational amplifiers

[0070] The first terminal of the K switching element

[0071] L limiter

[0072] Li-C to operational amplifier interface

[0073] Li_in input interface

[0074] The interface between Li_S and the first terminal of the voltage control circuit (or the first terminal of the switching element).

[0075] out output interface

[0076] R1 is the control resistor (the resistor upstream of the voltage control circuit).

[0077] The resistor upstream of the R2 low-pass filter

[0078] The resistor of the R3 low-pass filter

[0079] R3-C1 low-pass filter

[0080] The resistor between the low-ohm terminal of the R4 voltage control circuit and the second amplifier input terminal of the operational amplifier.

[0081] S voltage control circuit

[0082] T1, T2 voltage control switching elements

[0083] U1 operational amplifier

[0084] VA amplifier output terminal

[0085] VE+ First amplifier input (non-inverting)

[0086] VE - Input terminal of the second amplifier (inverting)

[0087] Signal change curve of V(filter) second physiological signal (EKG)

[0088] V(li_in) Input signal (input voltage)

[0089] V(Li_C) Output signal (output voltage)

[0090] V(Li_S) processes the signal

[0091] Signal change curve of V(uatmung) first physiological signal (respiration)

[0092] Signal change curve of V(uekg) second physiological signal (EKG)

[0093] Superposition of V(out1) respiratory signal and EKG signal

[0094] Interference signals from the gradient coil assembly of the V(ustör)MR device

[0095] List of Literature

[0096] [1] EP 2 854 630 B1

[0097] [2] WO 2012 / 145285 A1

Claims

1. A circuit assembly (1) for correcting an input signal, wherein, The input signal at the input interface (Li_in) of the circuit component (1) includes a useful signal and a interference signal, wherein the circuit component (1) includes: • A voltage control circuit (S) having at least one voltage-controlled switching element (T1, T2) having a first terminal (K) and a low-ohm second terminal (E). • The control resistor R1 is used to electrically connect the input interface (Li_in) to the control input terminal (B) of the voltage-controlled switching elements (T1, T2). • Resistor R2, which is connected in series with the voltage control circuit (S) upstream of the voltage control circuit (S), and the input interface (Li_in) is electrically connected to the first terminal (K) of the voltage-controlled switching elements (T1, T2) via resistor R2. • Operational amplifier (U1), the operational amplifier having a first amplifier input terminal (VE+), a second amplifier input terminal (VE-), and an amplifier output terminal (VA), and • Low-pass filter (R3-C1), the low-pass filter being connected between the first terminal (K) of the at least one voltage-controlled switching element (T1, T2) and the first amplifier input terminal (VE+) of the operational amplifier (U1). In order to feed back the output voltage of the operational amplifier (U1) to the low-ohm second terminal (E) of the switching elements (T1, T2), the low-ohm second terminal (E) of the at least one voltage-controlled switching element (T1, T2) is electrically connected to the amplifier output terminal (VA) of the operational amplifier (U1) and the second amplifier input terminal (VE-) of the operational amplifier (U1).

2. The circuit assembly (1) according to claim 1, characterized in that, Another resistor R4 is connected between the low-ohm second terminal (E) of the voltage control circuit (S) and the second amplifier input terminal (VE-).

3. The circuit assembly (1) according to claim 1, characterized in that, The operational amplifier (U1) has an amplification factor V of 0.9 < V < 1.

4. The circuit assembly (1) according to claim 1, characterized in that, The voltage control circuit (S) includes at least one transistor as a switching element (T1, T2).

5. The circuit assembly (1) according to claim 4, characterized in that, The voltage control circuit (S) includes two voltage-controlled switching elements (T1, T2) with opposite polarities.

6. The circuit assembly (1) according to any one of claims 1 to 3, characterized in that, The useful signals are physiological signals.

7. The circuit assembly (1) according to any one of claims 1 to 3, characterized in that, The interference signal is generated by an MR imaging scanner.

8. The circuit assembly (1) according to any one of claims 1 to 3, characterized in that, The low-pass filter (R3-C1) is an RC component, and the capacitor (C1) of the RC component is at a reference potential.

9. The circuit assembly (1) according to claim 6, characterized in that, The useful signal is the EKG signal.

10. The circuit assembly (1) according to claim 7, characterized in that, The interference signal is generated by the gradient coil assembly (3).

11. A method for correcting an input signal using a circuit assembly (1) according to any one of claims 1 to 10, wherein, The input signal at the input interface (Li_in) includes useful signals and interference signals.

12. A method for reducing interference signals caused by an MR device when using a circuit assembly (1) according to any one of claims 1 to 10 in a magnetic resonance (MR) system, the magnetic resonance system having the MR device (2) and a component for detecting physiological signals.

13. The method according to claim 12, characterized in that, The MR device (2) is an MR imaging scanner.

Images