CN217244417U

CN217244417U - Signal measurement circuit and differential voltage measurement system

Info

Publication number: CN217244417U
Application number: CN202122015412.0U
Authority: CN
Inventors: 乌尔里克·巴策尔; 马蒂亚斯·布鲁姆哈德
Original assignee: Siemens Healthineers AG
Current assignee: Siemens Healthineers AG
Priority date: 2020-08-26
Filing date: 2021-08-25
Publication date: 2022-08-23
Anticipated expiration: 2031-08-25
Also published as: DE202020104940U1

Abstract

The utility model relates to a signal measurement circuit (30) for differential voltage measurement system (1), differential voltage measurement system is used for measuring patient's (P) biological electricity signal (S (k)), signal measurement circuit has: a sensor electrode (3); a measurement amplifier circuit (27); a sensor line (6a) between the measurement amplifier circuit and the sensor electrode; and a first fluid protective layer (41), the first fluid protective layer (41) being disposed between the sensor electrode and the patient.

Description

Signal measurement circuit and differential voltage measurement system

Technical Field

The utility model relates to a signal measurement circuit for difference voltage measurement system, difference voltage measurement system is used for measuring patient's biological electricity signal with the help of the fluid protective layer. Furthermore, the utility model discloses still relate to a differential voltage measurement system.

Background

Voltage measurement systems, in particular differential voltage measurement systems, are used for measuring bioelectric signals, for example in medicine for measuring an Electrocardiogram (EKG), an electroencephalogram (EEG) or an Electromyogram (EMG).

Measuring the heart activity by means of the mentioned voltage measuring system is necessary in particular for cardiac imaging in order to be able to adapt the imaging process to the significant movement of the heart during the heartbeat. For this purpose, sensors are usually used, which must be fastened to the body of the patient. One possibility for heartbeat measurement is a capacitive EKG, in which the EKG signal is intercepted purely capacitively, without direct contact of the patient with the sensor, in particular through the patient's clothing. In order to achieve a good signal quality of the heartbeat signal, the signal amplitude preferably has to be large. This can be achieved by a large volume between the patient and the sensor. The volume can be influenced via the size of the coupling surface between the sensor and the patient. The larger the coupling surface, the larger the capacity achieved. The maximum coupling surface is predetermined by the size or base surface of the sensor. For example, a signal amplitude that is more than three times larger than that which can be achieved with a sensor base surface of 9x9cm than with a sensor base surface of 5x5cm, and thus a significantly higher signal quality, can be achieved.

However, if the sensor is so large that it cannot be completely covered by the patient's body, i.e. one (small edge) area of the sensor is exposed, the electric field disturbing the heartbeat signal acts directly on this area as a differential disturbance, which may be many times stronger than the common mode effect, in addition to its common mode effect with respect to the patient. Thus, the capacitive sensors known to date are constructed with a base surface of at most about 5 × 5 cm. This is an acceptable compromise between sufficient signal amplitude and the time taken to position the patient accurately at, on or above the sensor, the larger the base area the sensor has, the larger the compromise is to achieve complete coverage of the sensor before measurement.

Even in the case of capacitive sensors with a base surface of 5x5cm, careful positioning of the patient is required, since only those sensors that are completely covered can be used to measure the cardiac signal.

SUMMERY OF THE UTILITY MODEL

In contrast, it is an object of the present invention to provide a mechanism which allows the detection of heartbeat signals with a high signal quality without a large expenditure on positioning. Furthermore, the object of the invention is also to minimize the interference effects during signal detection.

This purpose is through according to the utility model discloses a signal measurement circuit with according to the utility model discloses a differential voltage measurement system realizes. In addition, particularly advantageous embodiments and refinements of the invention are found in the description, wherein the individual features of the different embodiments or variants can also be combined to form new embodiments or variants.

In a first aspect, the present invention relates to a signal measurement circuit of a differential voltage measurement system for measuring a bioelectric signal of a patient.

According to the utility model discloses, signal measurement circuit has sensor electrode, measurement amplifier circuit and is located the sensor circuit between measurement amplifier circuit and the sensor electrode. The signal measurement circuit also has a first fluid protective layer disposed between the sensor electrode and the patient.

The sensor electrode is configured as a planar electrode. The sensor lines serve to transmit measurement signals detected by means of the sensor electrodes to the measurement amplifier circuit.

The measuring amplifier circuit preferably comprises an operational amplifier, which can be designed as a so-called follower. That is, the negative input, also referred to as the inverting input, of the operational amplifier is coupled to the output of the operational amplifier, thereby creating a high virtual input impedance at the positive input.

The fluid protective layer is provided as a component of a signal measurement circuit between the sensor electrode and the patient. The fluid protection layer can be arranged in particular between the patient-facing outer side of the signal measurement circuit and the sensor electrode. The fluid protection layer is designed such that it exposes the sensor electrode in a partial region of the base surface of the sensor electrode that is covered or covered by the patient and shields the electrical interference field in a partial region that is not covered by the patient. This advantageously makes it possible to achieve a particularly large base surface of the sensor electrode in the sense of a large capacitance between the patient and the sensor electrode, without increasing the positioning effort.

In a second aspect, the present invention relates to a differential voltage measurement system for measuring a bioelectrical measurement signal of a patient. The voltage measuring system has at least two signal measuring circuits, which each correspond to a useful signal path and each comprise a sensor electrode. At least one of the signal measuring circuits, preferably all of the signal measuring circuits comprised, is constructed as described above and below.

As already mentioned at the outset, the differential voltage measurement system according to the invention detects bioelectric signals, for example from human or animal patients. For this purpose, the differential voltage measuring system has a plurality of measuring lines or useful signal paths. They connect, for example as a single cable, the electrodes, which are arranged at the patient for detecting signals, with other components of the voltage measurement system, in particular an electronic device for evaluating or displaying the detected bioelectric signals, in particular heartbeat signals.

The basic mode of operation of the differential voltage measuring system is known to the person skilled in the art, so that a more detailed explanation is omitted here. The differential voltage measurement system can be designed in particular as an Electrocardiogram (EKG), electroencephalogram (EEG) or Electromyogram (EMG).

According to the utility model discloses a differential voltage measurement system has at least one and according to the utility model discloses a signal measurement circuit. Therefore, according to the utility model discloses a differential voltage measurement system shares according to the utility model discloses a signal measurement circuit's advantage.

In an embodiment of the signal measurement circuit according to the invention, the first fluid protection layer comprises a pad filled with a liquid, the pad being arranged parallel to the sensor electrode plane. The mat is preferably designed in a planar manner, i.e., it has a significantly smaller extension in one spatial direction than in the other two spatial directions. The height can be configured in the range of 1mm to 20 mm. The height can be, for example, 5 mm. In some embodiments, the height of the mat can be related to the size of the base surface of the mat. The larger the mat, the higher the base size. In a preferred embodiment, the mat has a base shape adapted to the base shape of the sensor electrodes. In embodiments, the mat can have a circular, rectangular or square basic shape. The corners can be rounded here. The liquid in the pad is configured such that when a patient is positioned at, on or above the sensor electrodes, the liquid can be expelled from the partial region with strong mechanical load into the sub-volume with little or no mechanical load. In other words, the liquid in the mat is configured such that it can move in the mat.

The mat can be completely or only partially filled with liquid. The material of the mat can be designed to be movable and in particular elastic in order to be able to yield at least partially to particularly strong mechanical loads. The mat can be formed of plastic, for example. The mat can be formed, for example, of PVC (polyvinyl chloride), PE (polyethylene) or PU (polyurethane). However, all liquid-impermeable, electrically non-conductive materials are conceivable, for example films made of cellophane or the like.

The fluid protective layer advantageously results in that partial regions of the sensor electrode which are not covered or covered by the patient himself after the patient has been positioned are covered with liquid and the coupling-in of the surrounding electrical interference fields is significantly reduced.

In an embodiment of the signal measurement circuit according to the invention, the base surface of the mat corresponds at least to the base surface of the sensor electrode. Thus, the fluid protection layer ensures: after the patient is positioned, the sensor electrodes are covered by the patient or by the liquid that the patient displaces. In a particularly preferred embodiment, the fluid protection layer has a base surface which is larger than the base surface of the sensor electrode. In other words, the fluid protection layer extends beyond the edges of the sensor electrodes. For example, the base surface of the fluid protection layer can protrude by 1cm or 2cm above the base surface. In this way, the fluid protection layer provides a bypass volume for the liquid for the case where the patient covers the entire base surface of the sensor electrode after positioning and does not need to be shielded by the fluid protection layer. This is of particular interest in the case of sensor electrodes having a small base surface, since complete coverage by the patient is relatively easy to achieve here.

In an embodiment of the invention, the base surface of the sensor electrode, e.g. in the shape of a square, can have a size in the range of 5x5cm to 12x12 cm. A larger base surface may impair the spatial resolution of the sensor electrodes. For example, a size of 6x6cm or 10x10cm can be set particularly preferably. For example, in the case of a circular design of the sensor electrodes, a corresponding radius can be provided.

In a further embodiment of the signal measuring circuit according to the invention, the liquid has a surface tension higher than 60 mN/m. This advantageously causes a complete displacement of liquid from the partial region of the mat which is subjected to mechanical stress during positioning. The liquid is preferably a salt solution or water. Glycerol admixed with additives is also contemplated herein.

In a further embodiment of the signal measuring circuit according to the invention, the mat has hydrophobic surface properties at least on its inner face. This prevents liquid from adhering to the inner face of the mat and also supports complete displacement of liquid from the partial region of the mat that is mechanically loaded at the time of positioning. In embodiments, the mat can have a hydrophobic coating on its inner face. In other embodiments, the pad can be formed from a material that is hydrophobic in nature. For example, the mat can preferably have a polytetrafluoroethylene layer on its inner face. Alternatively, the coating can comprise a fluoropolymer or a nanostructure with water-repellent properties.

In a further embodiment of the signal measuring circuit according to the invention, the liquid is configured to be electrically conductive, so that in a further embodiment the fluid protection layer can be electrically connected with an active protective cover which is likewise comprised by the signal measuring circuit and surrounds the sensor line and the measuring amplifier circuit. The active protective cover also only partially surrounds the sensor electrodes. The active guard is preferably connected to the output of the operational amplifier. The potential of which is controlled or adjustable. The potential of the active shield is maintained close to the potential of the sensor electrode so that current is prevented from flowing from the sensor electrode onto the active shield. The active shield dissipates interference applied thereto so that the interference does not reach the sensor electrodes. The active shield is characterized by a high virtual input impedance.

In a further embodiment of the signal measuring circuit according to the invention, a shielding surrounding the active protective cover and a second fluid protection layer are further provided, wherein the second fluid protection layer is arranged between the first fluid protection layer and the patient and is electrically connected with the shielding.

Such a passive shield can be formed in particular by the housing or the metal foil of the signal measuring circuit. It serves to intercept particularly strong electric fields which can overload the operational amplifier which controls the active protection shield. In such an embodiment, even very strong electric interference fields can be effectively shielded.

Drawings

The invention is explained in detail below with the aid of embodiments with reference to the drawings. In the different figures, identical components are provided with the same reference symbols.

The drawings are generally not to scale. The figures show:

FIG. 1 shows a view of a differential voltage measurement system disposed on a patient in an embodiment;

FIG. 2 shows a view of a signal measurement circuit for a differential voltage measurement system in an embodiment;

FIG. 3 shows a detailed view of the signal measurement circuit according to FIG. 2;

FIG. 4 shows another detailed view of the signal measurement circuit according to FIG. 2; and

FIG. 5 shows a view of a signal measurement circuit for a differential voltage measurement system in another embodiment.

Detailed Description

In the figure, the EKG measurement system 1 is exemplarily assumed to be a differential voltage measurement system 1, respectively, in order to be able to measure the bioelectric signal s (k), here the EKG signal s (k). However, the present invention is not limited thereto.

Fig. 1 therefore shows a view of a differential voltage measurement system 1 in the form of an EKG measurement system 1 arranged on a patient P. The voltage measurement system 1 comprises an EKG device 17 with its electrical terminals and electrodes 3, 4, 5 connected thereto via a cable K in order to measure an EKG signal s (K) at the patient P.

For measuring the EKG signal s (k), at least one first electrode 3 and one second electrode 4, which are arranged at, above or below the patient P, are required. The electrodes 3, 4 are connected to the EKG device 17 via terminals 25a, 25b, usually plug connections, by means of a signal measurement cable K. The first electrode 3 and the second electrode 4 comprise a signal measurement cable K, which here forms part of a signal detection unit, by means of which an EKG signal s (K) can be detected.

The third electrode 5 serves as a reference electrode in order to be able to provide a potential balance between the patient P and the EKG device 17. Classically, the third electrode 5 is arranged on the Right Leg of the patient ("Right-Leg-Drive" or "RLD"). However, as here, the third electrode 5 can also be positioned at a different location. Furthermore, a large number of further contacts for further output lines (potential measurement) can be attached to the patient P via further terminals, not shown, on the EKG device 17 and used to form suitable signals.

A voltage potential UEKG is formed between the respective electrodes 3, 4, 5 ₃₄ 、UEKG ₄₅ And UEKG ₃₅ The voltage potential is used to measure the EKG signal s (k).

The directly measured EKG signals s (k) are displayed on the user interface 14 of the EKG device 27.

During the EKG measurement, the patient P is capacitively coupled at least to the ground potential E (indicated by the coupling on the right leg).

The signal measurement cable K leading from the first electrode 3 and the second electrode 4 to the EKG device 17 is part of the useful signal path 6a, 6 b. The signal measurement cable K leading from the electrode 5 to the EKG device 17 corresponds here to a part of the third useful signal path 7N. The third useful signal path 7N transmits an interference signal, which is coupled in via the patient P and the electrodes.

The cable K has a shielding S, which is here schematically illustrated as a cylinder enclosing a dashed line of all useful signal paths 6a, 6b, 7N. However, the shield does not necessarily surround all the cables K together, but the cables K can also be shielded individually. However, the terminals 25a, 25b, 25c preferably have poles for the shield S in an integrated manner. The poles are then brought together on a common shield terminal 25 d. The shield S is, for example, a metal foil which is formed to surround the conductor of the corresponding cable K, but is instead isolated from the conductor.

Furthermore, as shown in fig. 1, the EKG device 17 can have an external interface 15 in order to provide terminals, for example for a printer, a storage device and/or even a network. According to an embodiment of the invention, the EKG device 17 also has a signal measurement circuit 30 (see below) associated with the respective terminal 25a, 25 b. The signal measurement circuits 30 are connected to the ground E via ground switches 31, respectively.

FIG. 2 shows a view of a signal measurement circuit 30 for the differential voltage measurement system 1 in one embodiment. The individual sensors 3 or the arrangement of the individual sensor electrodes 3 of the signal measuring circuit 30 in the form of an EKG measuring circuit is illustrated here. The patient P and the sensor electrodes 3 are spatially close to each other. The patient P can be provided with a fabric garment 21, for example. A cover 22 transparent to the X-ray beam can also be located over the patient. Alternatively, the sensor electrodes 3 can be arranged in a mat-like support 22 for an examination bed or electrode mat 22. The sensor 3 is not in direct electrical contact with the patient P, but rather the sensor is electrically isolated from the patient P by at least the sensor cover 3 a. However, capacitive coupling-in of EKG signals is not hindered by the sensor cover 3 a. The sensor electrode 3, the sensor line 6a extending from the sensor electrode 3 to the operational amplifier 27, and the measurement circuit including the operational amplifier 27 are surrounded by a so-called active shield 25 and a shield S. The operational amplifier 27 is configured as a so-called follower. That is, negative input 27a of operational amplifier 27 is coupled to output 28 of operational amplifier 27. In this way, a high virtual input impedance is achieved for the operational amplifier 27 at the positive input 27 b. This means that almost no current flows between the sensor 3 and the active protective cover 25 due to the voltage adaptation between the output 28 and the positive input 27 b. Furthermore, the positive input 27b of the operational amplifier 27 is held at a bias voltage by means of a resistor 26 connected with respect to the measuring device ground (also referred to as "measuring ground"). The positive input can therefore be set to the desired measuring potential. In this way, the dc component is suppressed. This is desirable, since the sensor electrodes 3 should be capacitively coupled in particular and varying potentials should be avoided.

The signal measuring circuit 30 shown here further comprises a first fluid protection layer 41, said first fluid protection layer 41 being arranged between the sensor electrode 3 and the sensor cover 3 a. The first fluid protection layer is arranged in plane parallel to the sensor electrode 3. The fluid protection layer is designed as a flat pad filled with liquid, which covers the entire, here square, base surface of the sensor electrode 3. More precisely, the fluid protection layer 41 in this embodiment protrudes even minimally above the sensor electrode base surface.

As long as no mechanical load is applied to the fluid protection layer 41 by the respective patient positioning, the liquid in the interior of the pad is distributed substantially uniformly (as shown here), and thus capacitive coupling-in of external interference signals is prevented over the entire base surface of the sensor electrode 3.

As soon as the patient P is positioned on, above or at the sensor electrode and the arrangement is mechanically loaded, liquid is displaced from the region of force action and a capacitive coupling between the patient P and the sensor electrode 3 can be achieved in this region.

Fig. 3 shows a corresponding detailed view of the signal measuring circuit according to fig. 2. In this case, the patient P covers the base surface of the sensor electrode as far as possible. The liquid of the fluid protection layer escapes into the small edge regions of the cushion of the fluid protection layer 41, so that a large coupling surface is formed between the patient P and the sensor electrode 3. This corresponds to a large capacity and advantageously promotes a high signal quality.

Fig. 4 shows another detailed view of the signal measuring circuit according to fig. 2. In this case, the patient P covers only approximately half of the base surface of the sensor electrode 3. The coupling surface formed here is correspondingly smaller, so that the capacitance between the patient P and the sensor electrode 3 is also smaller. This is similar to sensor electrodes having a smaller base surface. However, in the partial region not covered by the patient P, the fluid protection layer 41 effectively ensures shielding against external electrical interference fields. In contrast to sensors with a smaller base surface, a possibly complex, precise positioning of the patient P can be dispensed with, it being sufficient for the patient P to be positioned completely in the region of the sensor electrode 3, in particular lying therein.

In order to promote a uniform distribution of the liquid in the mat of the fluid protection layer 41 or a complete displacement thereof from the mechanically loaded partial region, the liquid is designed here as a salt solution with a high surface stress in the range of up to 60 mN/m. The mat is formed from a thin plastic layer which additionally has a teflon coating on its inner face.

As shown in fig. 3 and 4, the fluid protection layer 41 is electrically connected to the active protection cover 25 of the signal measurement circuit. Accordingly, the liquid of the fluid protection layer 41 can be formed electrically conductive.

Fig. 5 shows a view of a signal measurement circuit 40 for the differential voltage measurement system 1 in another embodiment. In addition to the first fluid protection layer 41, the arrangement shown here also comprises a second fluid protection layer 42, which is arranged between the first fluid protection layer 41 and the sensor cover 3 a. The structure and size of the second fluid protection layer 42 corresponds to the structure and size of the first fluid protection layer 41, wherein minor deviations are possible. By providing a further fluid protective layer 42, shielding is improved, so that particularly strong electrical interference fields can also be shielded.

The signal measuring circuit 40 also has an electrical connection between the shield S surrounding the active protective cover 25 and the second fluid protective layer 42. This electrical connection advantageously achieves a potential equalization between the sensor electrode 3 and the active guard 25.

The advantages of the utility model are summarized again below:

compared to known circuit arrangements, the base surface of the sensor electrode of the signal measuring circuit according to the invention is increased. For example in the range between 5x5cm and 12x12 cm. A better signal quality results when the patient is positioned well on the sensor electrode, because the (EKG) signal amplitude increases and at the same time the noise is less, due to the best possible coverage of the entire base surface of the sensor electrode.

In the case of an optimal patient positioning as described above which is too costly or not feasible due to the individual size of the patient, a high tolerance with respect to unfavorable patient positions results by providing at least one fluid protection layer. The coupling surface between the patient and the sensor electrode that is nevertheless realized corresponds to the coupling surface of the smaller sensor electrode, wherein external disturbances can be effectively shielded.

The utility model discloses can realize: by means of the capacitive signal measuring circuit, a particularly high signal quality is achieved, and at the same time a wide use of the capacitive signal measuring circuit is made possible with an acceptable signal quality, irrespective of anatomical or disease-related preconditions, even for inexperienced users or for each patient.

Finally, it is pointed out once more that the device described in detail above is merely an example, which can be modified in various ways by a person skilled in the art without departing from the scope of the invention. Thus, the differential voltage measurement system can be not only an EKG device, but also a medical device, by means of which bioelectric signals, such as EEG, EMG, etc., are detected. Furthermore, the use of the indefinite article "a" or "an" does not exclude: the associated feature can also exist multiple times.

The various embodiments, various sub-aspects or features thereof can be combined with or exchanged with each other without departing from the scope of the invention, which is not yet clear but reasonable and within the meaning of the invention. The advantages of the invention described with reference to the embodiments apply also to other embodiments, without explicit mention of the possibility of switching.

Claims

1. A signal measurement circuit for a differential voltage measurement system (1) for measuring a bioelectric signal (s (k)) of a patient (P), the signal measurement circuit having:

-a sensor electrode (3);

-a measurement amplifier circuit (27);

-a sensor line (6a) between the measurement amplifier circuit and the sensor electrode; and

-a first fluid protection layer (41), the first fluid protection layer (41) being arranged between the sensor electrode and the patient.

2. The signal measurement circuit of claim 1, wherein the first fluid protective layer comprises a liquid-filled pad disposed parallel to the sensor electrode plane.

3. The signal measurement circuit of claim 2, wherein a base surface of the pad corresponds to at least a base surface of the sensor electrode.

4. A signal measuring circuit according to claim 2 or 3, wherein the liquid has a surface stress higher than 60 mN/m.

5. A signal measurement circuit according to claim 2, 3 or 4 in which the mat has hydrophobic surface properties on at least its inner face.

6. A signal measurement circuit according to any of claims 2 to 5, wherein the liquid is configured to be electrically conductive.

7. The signal measurement circuit of claim 6, comprising an active protective shield surrounding sensor lines and measurement amplifier circuitry, wherein the fluid protective layer is electrically connected to the active protective shield.

8. The signal measurement circuit of claim 7, comprising a shield surrounding the active protective cover and a second fluid protective layer disposed between the first fluid protective layer and the patient, wherein the second fluid protective layer is electrically connected to the shield.

9. Differential voltage measurement system for measuring bioelectrical signals (s (k)) of a patient (P), having at least two signal measurement circuits which respectively correspond to useful signal paths and respectively comprise sensor electrodes (3, 4), wherein at least one of the signal measurement circuits is constructed according to any one of claims 1 to 8.