CIRCUIT ASSEMBLY FOR CORRECTION OF AN INPUT SIGNAL, USE OF THE CIRCUIT ASSEMBLY FOR DETECTION OF A PHYSIOLOGICAL SIGNAL IN A MAGNETIC RESONANCE (MR) SYSTEM

Abstract

A circuit assembly for correction of an input signal including a useful signal and a disturbance signal comprises: a voltage-controlled circuit having at least one voltage-controlled circuit element, an input interface and an output interface, a resistor connected upstream of the voltage-controlled circuit in series with the voltage-controlled circuit, an operational amplifier having a first amplifier input, a second amplifier input and an amplifier output, and a low-pass filter connected between the input interface of the at least one voltage-controlled circuit element and the first amplifier input of the operational amplifier, wherein the output voltage from the operational amplifier is fed back to the low-resistance terminal of the circuit element in that the low-resistance terminal of the at least one voltage-controlled circuit element is electrically connected to the amplifier output of the operational amplifier and to the second amplifier input of the operational amplifier.

Claims

1. A circuit assembly for correction of an input signal, wherein the input signal at an input interface (Li_in) of the circuit assembly comprises a useful signal and a disturbance signal, wherein the circuit assembly comprises: a voltage-controlled circuit (S) having at least one voltage-controlled circuit element (T1, T2), having a first terminal (K) and a low-resistance second terminal (E), a resistor (R2) connected upstream of the voltage-controlled circuit (S) in series with the voltage-controlled circuit (S), an operational amplifier (U1) having a first amplifier input (VE+), a second amplifier input (VE?) and an amplifier output (VA), and a low-pass filter (R3-C1) connected between the first terminal (K) of the at least one voltage-controlled circuit element (T1, T2) and the first amplifier input (VE+) of the operational amplifier (U1), wherein the output voltage from the operational amplifier (U1) is fed back to the low-resistance terminal (E) of the circuit element (T1, T2) in that the low-resistance terminal (E) of the at least one voltage-controlled circuit element (T1, T2) is electrically connected to the amplifier output (VA) of the operational amplifier (U1) and to the second amplifier input (VE?) of the operational amplifier (U1).

2. The circuit assembly according to claim 1, further comprising a further electrical resistor (R4) that is connected between the low-resistance terminal (E) of the voltage-controlled circuit (S) and the second amplifier input (VE?).

3. The circuit assembly according to claim 1, wherein the operational amplifier (U1) has an amplification factor V with 0.9<V<1.

4. The circuit assembly according to claim 1, wherein the at least one voltage-controlled circuit element (T1, T2) has a control input (B) electrically connected to the input interface (Li_in) via a control resistor (R1).

5. The circuit assembly according to claim 4, wherein the voltage-controlled circuit (S) comprises at least one transistor as circuit element (T1, T2).

6. The circuit assembly according to claim 5, wherein the voltage-controlled circuit (S) comprises two voltage-controlled circuit elements (T1, T2) of opposite polarity.

7. The circuit assembly according to claim 1, wherein the useful signal is a physiological signal.

8. The circuit assembly according to claim 7, wherein the physiological signal is an ECG signal.

9. The circuit assembly according to claim 1, wherein the disturbance signal is a signal generated by an MR imaging scanner.

10. The circuit assembly according to claim 9, wherein the disturbance signal is a signal generated by a gradient coil assembly of the MR imaging scanner.

11. The circuit assembly according to claim 1, wherein the low-pass filter (R3-C1) is an RC circuit, the capacitor of which (C1) is at a reference potential.

12. Use of the circuit assembly according to claim 1 for correcting an input signal, wherein the input signal at the input interface (Li_in) comprises a useful signal and a disturbance signal.

13. Use of the circuit assembly according to claim 1 in a magnetic resonance (MR) system having an MR apparatus in order to reduce disturbance signals caused by the MR apparatus.

14. Use of the circuit assembly according to claim 13, wherein the MR apparatus comprises an MR imaging scanner and an assembly for detection of a physiological signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 shows a circuit assembly according to the invention.

[0031] FIG. 2 shows:

[0032] the expected signal progression of a disturbance that has been caused by gradient coils of an MR apparatus,

[0033] the expected signal progression of respiration monitoring,

[0034] the expected signal progression of an ECG, and

[0035] the expected signal progression of the superimposition of ECG and respiration monitoring.

[0036] FIG. 3 shows:

[0037] the signal progression of a useful signal with a low-frequency and a high-frequency disturbance signal superimposed thereon,

[0038] the signal progression of an input signal applied to the input interface,

[0039] the signal progression of a signal applied to the interface to the first terminal of the voltage-controlled circuit and

[0040] the signal progression of the signal applied to the interface to the operational amplifier.

[0041] FIG. 4 shows the components of a signal processing device comprising a circuit assembly according to the invention.

[0042] FIG. 5 shows a schematic of a measurement assembly comprising an MR imaging scanner, an assembly for detection of a physiological signal and the signal processing device from FIG. 4.

DETAILED DESCRIPTION

[0043] FIG. 1 shows a preferred embodiment of the circuit assembly according to the invention. The circuit assembly according to the invention comprises an input interface Li_in to which an input signal V(li_in) is applied, a voltage-controlled circuit S, an operational amplifier U1 and an output interface out. The operational amplifier U1 routes the output signal V(li_c) to the output interface out. The voltage-controlled circuit S controls the forwarding of the input signal V(li_in) to the operational amplifier U1. The output interface out outputs an output signal V(li_C).

[0044] The voltage-controlled circuit S in the present case comprises two voltage-controlled circuit elements T1, T2 each comprising a first terminal K (in the case of a transistor as circuit element: collector), a low-resistance terminal E (in the case of a transistor as circuit element: emitter) and a control input B (in the case of a transistor as circuit element: base). The voltage-controlled circuit S is disposed between the input interface Li_in and the operational amplifier U1. The voltage V(li_in) is applied to the first terminal K of the voltage-controlled circuit elements T1, T2 via the control resistor R1 with the control inputs B of the voltage-controlled circuit elements T1, T2 and via a resistor R2.

[0045] Connected between the interface Li_S at the first terminal K of the voltage-controlled circuit elements T1, T2 and an interface Li_C to the operational amplifier U1 is an RC low-pass filter with a capacitor C1 and a resistor R3.

[0046] The operational amplifier U1 comprises a first amplifier input VE+, a second amplifier input VE? and an amplifier output VA.

[0047] The low-resistance terminals E of the voltage-controlled circuit elements T1, T2 are electrically connected to the amplifier output VA of the operational amplifier U1. In this way, the output voltage from the operational amplifier U1 is fed back to the low-resistance terminals E of the circuit elements T1, T2. In order to avoid oscillations here, a low-resistance resistor R4 is connected between the low-resistance terminals E of the voltage-controlled circuit elements T1, T2 and the amplifier output VA, and this ensures that the amplification factor of the operational amplifier U1 is always less than the value of 1.

[0048] FIG. 2 shows, with the upper curve, a progression of a disturbance signal V(udist) of a gradient coil assembly of an MR apparatus. Below that are shown the signal progressions of two physiological signals V(uresp), V(uecg) (here: respiration and ECG) and the superimposition V(out1) of the two physiological signals V(uresp), V(uecg); the superimposition V(out1) of the two physiological signals V(uresp), V(uecg) should be measured as useful signal during NMR measurement. It is clearly apparent that the disturbance signal V(udist) is a whole order of magnitude greater than the highest amplitude of the useful signal V(out1).

[0049] FIG. 3 shows, with the upper curve, the superimposition V(filter) of a useful signal with a disturbance signal. The superimposition V(filter) is to be processed by means of the circuit assembly 1 according to the invention. For this purpose, the signal V(filter) to be processed can be amplified in multiple stages, such that the useful signal component has a usable intensity (especially about 0.5 V). In order to keep the overloading of the amplifier stages owing to the high amplitude of the disturbance signal within limits here, each amplifier stage is preferably followed by limitation of the amplitude (small signal amplification). This then results in the input signal V(li_in) (second signal progression from the top in FIG. 3) for the circuit assembly according to the invention.

[0050] In FIG. 1, the circuit elements T1, T2 are configured as transistors. For the on state, generally about 0.7 V is needed between base and emitter of the transistors. In the following, the mode of function of the circuit according to the invention using the example of a circuit having two transistors T1, T2 is described. The use of two transistors enables the processing both of positive and negative useful signals and disturbance signals. For this purpose, the circuit S of the circuit assembly shown in FIG. 1 comprises an NPN transistor T1 and a PNP transistor T2. The two transistors T1, T2 are connected to one another such that the bases, the emitters and the collectors are each electrically connected to one another. The mode of function is applicable analogously to other voltage-controlled circuit elements or to circuits having just one or more than two circuit elements.

[0051] By the circuit according to the invention, the input signal V(li_in) to be processed is routed via a resistor R1, R2 in each case at the base B and collector K of the transistors T1, T2. At the interface Li_S to the collector K, a processing signal V(li_S) is tapped and forwarded with amplification of <1 via the low-pass R3-C1 to the operational amplifier U1 which functions as impedance converter. The limiting frequency of the low-pass R3-C1 will preferably be chosen here such that the highest frequency of the useful signal is attenuated only insignificantly. The output signal from the operational amplifier U1 is sent to the emitter E of the transistors.

[0052] Provided that the input signal does not exceed the base-emitter voltage (threshold about 0.6 V), the transistor remains nonconductive and the output signal V(li_C) of the impedance converter virtually follows the input voltage of the circuit. For this purpose, the small signal amplification and the voltage at which the circuit S switches to the on state are matched to one another such that the useful signal just fails to switch the circuit S to the on state. If there is no disturbance (i.e. the input signal reflects the useful signal), the input signal V(li_in) is then applied to the capacitor C1 of the low-pass filter R3-C1 via the resistors R2 and R3 and to the amplifier output VA of the operational amplifier U1 and is output as output signal V(li_C)=V(li_in).

[0053] If the threshold voltage of the transistors T1, T2 is exceeded (when, for example, the input signal, as well as the useful signal, also includes a disturbance signal greater than the useful signalV(li_in) from FIG. 3), one of the transistors T1, T2 switches to a conductive state and hence brings about, via the resistor R4, a low-resistance connection between the amplifier output VA of the operational amplifier U1 and the low-resistance terminal E of the corresponding transistor T1, T2. The voltage of the input signal V(li_in) then drops at the resistor R2 connected in series to the voltage-controlled circuit S. This means that the voltage at the collector K corresponds virtually to the voltage at the emitter E. For the period within which the transistor T1, T2 is conductive, there is no change in the output voltage V(li_c) of the impedance converter U1 and the disturbance does not appear in the output VA of the impedance converter U1. The low-pass filter R3-C1 downstream of the circuit S, with the operational amplifier (impedance transducer) U1 downstream in turn, thus ensures intermediate storage of the voltage value of the input signal V(li_in) before the occurrence of the disturbance. Thus, in the event of a disturbance, the value stored before the occurrence of the disturbance is output to the operational amplifier U1. This means that the output voltage of the impedance converter U1 does not change during the period in which the circuit element T1, T2 is conductive, and the error does not appear at the output interface out.

[0054] The low-pass filter R3-C1 in the present invention does not serve to eliminate the disturbance signal. Instead, the disturbance has already been very substantially suppressed at the interface Li_S to the collector K, since the elimination of the disturbance signal is already brought about by the voltage-controlled circuit. The low-pass filter R3-C1 therefore serves merely to filter the high-frequency components of the useful signal and to store the voltage applied without disturbance. The signal at the interface Li_C is ultimately a useful signal that has been very substantially freed of the disturbances.

[0055] FIG. 4 shows the components of a signal processing device 6 that are traversed by a signal detected by electrodes a1, a2, a3 attached on a living measurement object (see FIG. 5) as they are converted to a utilizable useful signal. The signals detected by the electrodes a1, a2, a2 are routed via an interface 4 for detection of physiological signals to a limiter L, an amplifier F and a further limiter L. These serve to achieve the above-described small signal amplification, with limitation of the amplitude before the signal is sent as input signal V(li_in) to the circuit assembly 1 according to the invention. The output signal V(li_C), after leaving the circuit assembly 1 according to the invention, can be processed further, for example, by means of a further amplifier H.

[0056] FIG. 5 shows a measurement system comprising an MR apparatus 2 with gradient coil assembly 3, an interface 4 for detection of physiological signals from a living measurement object 5 and a circuit assembly 1 according to the invention for elimination of disturbance signals caused by the gradient coil assembly 3.

LIST OF REFERENCE NUMERALS

[0057] 1 circuit assembly [0058] 2 MR apparatus [0059] 3 gradient coil assembly [0060] 4 interface for detection of physiological signals [0061] 5 measurement object [0062] 6 signal processing device [0063] a1, a2, a3 electrodes [0064] B control input of the circuit element [0065] C1 capacitor of the low-pass filter [0066] E low-resistance second terminal of the circuit element [0067] F, H operational amplifier [0068] K first terminal of the circuit element [0069] L limiter [0070] Li_C interface to the operational amplifier [0071] Li_in input interface [0072] Li_S interface to the first terminal of the voltage-controlled circuit (or of the first terminals of the circuit elements) [0073] out output interface [0074] R1 control resistor (resistor upstream of voltage-controlled circuit) [0075] R2 resistor upstream of low-pass filter [0076] R3 resistor of the low-pass filter [0077] R3-C1 low-pass filter [0078] R4 resistor between low-resistance terminal of the voltage-controlled circuit and second amplifier input of the operational amplifier [0079] S voltage-controlled circuit [0080] T1, T2 voltage-controlled circuit elements [0081] U1 operational amplifier [0082] VA amplifier output [0083] VE+ first amplifier input (noninverting) [0084] VE? second amplifier input (inverting) [0085] V(filter) signal progression of a second physiological signal (ECG) [0086] V(li_in) input signal (input voltage) [0087] V(li_C) output signal (output voltage) [0088] V(li_S) processing signal [0089] V(uresp) signal progression of a first physiological signal (respiration) [0090] V(uecg) signal progression of a second physiological signal (ECG) [0091] V(out1) superimposition of respiration signal and ECG signal [0092] V(udist) disturbance signal from a gradient coil assembly of an MR apparatus

LIST OF LITERATURE

[0093] [1] EP 2 854 630 B1 [0094] [2] WO 2012/145285 A1