DE102014018490A1 - Apparatus and method for removing pulse-like noise signals from mis-signals of an electro-impedance tomography apparatus suitable for lung imaging - Google Patents

Abstract

The invention relates to a method for processing EIT signal waveforms (5, 6), which were obtained from a suitable for imaging of lung electro-impedance tomography device (EIT). The method enables a removal of pulse-like interference signals (7, 9) from the EIT signal waveforms (5, 6) and thus an improvement in the quality for visualization of the EIT waveforms (5, 6) to an image (10) of a ventilation situation of the lung , The method is suitable and advantageous, without a significant time delay after provision or detection of the EIT signal waveforms (5, 6) of pulse-like interference signals (7, 9) to provide cleaned signals for generating the mapping (10). Furthermore, a device is provided with which a removal of pulse-like interference signals (7, 9) from the EIT signal waveforms (5, 6) is made possible.

Description

The present invention relates to an apparatus and a method for removing pulse-like interference signals from measurement signals of an electro-impedance tomography device suitable for imaging the lungs of a patient. The device and the method enable a removal of pulse-like interference signals, in particular pulses of a pacemaker, so-called pacemaker pulses, which are superimposed during operation of the electro-impedance tomography device the measurement signals with simultaneous use of the pacemaker to the patient, from the measurement signals of the electro-impedance tomography device. Devices for electro-impedance tomography (EIT) are known from the prior art. These devices are designed and intended to generate an image, a plurality of images or a continuous image sequence from signals obtained by means of electro-impedance measurements and from data and data streams obtained therefrom. These images or sequences of images show differences in the conductivity of various body tissues, bones, skin, body fluids and organs, especially the lungs, which are useful for observing the patient's situation.

That's how it describes US 6,236,886 an electrical impedance tomograph with an array of multiple electrodes, current feed to at least two electrodes, signal detection at the other electrodes and a method with an algorithm for image reconstruction to determine the distribution of conductivities of a body, such as bone, skin and blood vessels in a basic embodiment with Components for signal acquisition (electrodes), signal processing (amplifier, A / D converter), power supply (generator, voltage-to-current converter, current limiting) and components for control.

In the US 5,807,251 It is stated that in the clinical application of EIT it is known to provide a set of electrodes which are placed at a certain distance from one another, for example around the chest of a patient in electrical contact with the skin. For an electrical current or voltage input signal, alternating between different or all of the possible pairs of electrodes adjacent to each other is alternately applied. While the input signal is applied to one of the pairs of electrodes disposed adjacent to each other, the currents or voltages between each adjacent pair of the remaining electrodes are measured and the obtained measurement data is processed in a known manner to provide a representation of the resistivity distribution over a cross section of the Patient to whom the electrode ring is arranged to receive and display on a screen.

Electro-impedance tomography (EIT), unlike other imaging radiological procedures (X-ray machines, radiological computer tomographs), has the advantage that no negative radiation exposure to the patient occurs. In contrast to sonographic procedures, the EIT can be used for continuous image acquisition over a representative cross-section of the entire thorax and the patient's lungs with the help of the electrode belt. In addition, there is no need to use a contact gel, which must be applied before each examination. Electro-impedance tomography (EIT) thus offers the advantage of enabling continuous monitoring of the lungs in order to observe and document a course of therapy of a mechanically-ventilated or spontaneously-breathing patient.

The measurements of the voltages and currents by means of an electrode arrangement around the chest of a patient with an EIT device, such as those from the US 5,807,251 is known, are interfering signals in the signal detection, exposed in the voltage or current measurement. Interference signals thereby couple both into the electrodes attached to the patient's body itself, as well as in line connections from the electrodes to the EIT device. In addition to disturbances due to noise, short-term or discrete accidental sources of interference, in particular when they occur in pulses of high power density, influence the EIT image reconstruction. In particular, such sources of interference have a great influence on the detected voltages or currents, which are very close to the Act, couple or radiate electrode assembly. These include, in particular, interference signals from the direct environment. Almost directly at the site of the EIT measurement, a pacemaker in the region of the thorax is used in some patients, for example in patients with cardiac problems. Such a pacemaker is, for example, implanted below the skin on the breast muscle. The pacemaker stimulates the heart muscle with electrical stimuli. Usually, these electrical stimuli are designed as electrical impulses. Such electrical impulses have a high edge steepness in the temporal signal curve, so that the frequency spectrum of these pulses is very broadband and thus results in a broadband coupling into the electrode arrangement of the EIT device.

In principle, a filtering by means of a low-pass arrangement can be carried out to remove or damp the high-frequency components However, disadvantageous to such a low-pass filtering are the significant signal delays, which result especially in a low-pass filtering, the more effective, for example, with low-pass filter arrangements of higher order, such as a configuration of a Butterworth or Chebyshev low-pass 2 -th order, 3rd order, the low-pass filtering is designed. For example, when filtering and / or amplifying low-pass filtering with or without signal amplification with a system of low-pass filters representing a linear time-invariant (LTI) system, the group delay may be considered to be a suitable measure of the signal transit time of the system the transfer function of the system or from the 3 dB cutoff frequency can be estimated. From the signal transit time results in the amount of signal delay, which is due to the low-pass filtering.

Another way to remove unwanted superimposed interference is the so-called median filtering. In this case, using a detection time window, that value is selected for further processing, which in the time window is the mean value of the group of several values. Simple examples of median filtering are so-called "1 out of 3", "1 out of 5" filters or "1 out of n" filters. In contrast to low-pass filtering, this type of filtering has a non-linear behavior, but there is also a delay in the signals, at least in the order of magnitude of the duration of the selected time window, predetermined in duration and conditioned by the number "n" of the values in the selected one acquisition time window.

Another way to remove unwanted spurs is by assuming that there is a normal distribution of readings, on the basis of a standard deviation and arithmetic mean of a recorded series of measurements, to subsequently remove those values that are outside a certain statistical range Confidence range lie. As a result, a new series of measurements is generated offline, from which unwanted interference has been removed. In this way, in measurement series with an almost constant signal level, such as DC voltage levels of sensors in the millivolt range, so-called "outliers" as extreme disturbances very well remove, such as disturbances that couple into the power supply or the signal amplifier of the sensors and to lead a measured value in the amount of power supply, very effective subsequently remove. Such disturbances are, for example, switching pulses of fluorescent tubes or valves. In most cases, this further possibility is used if subsequent post-processing of the recorded measurement series is carried out anyway, because, for example, an averaging of the signal is used as a subsequent measure for smoothing or for reducing superimposed noise. Since a recorded series of measurements is also subsequently processed in this further possibility, a delay of the signals in the order of magnitude of the duration of the signal recording and the time required for the Signalbereinigungsmaßnahem also results here.

The low-pass filtering, median filtering and outlier removal methods described previously have in common that they require a delay of the signals.

For an application for the removal of pulse-like interference signals, in particular pacemaker pulses, from EIT measurement signals acquired by means of electro-impedance tomography (EIT), such delays are unacceptable, since the impedance values, impedance distribution and impedance differences in the lungs of a living being determined from the EIT measurement signals or a patient, as far as possible, to be outputted or displayed as values or images without any time delay in order to have an immediate temporal reference of the output value or image to the current situation of respiration or ventilation of the animal. Near-instantaneous simultaneity and synchronicity of the illustrated impedance distribution in the lungs with the current respiratory phase, such as inhalation and exhalation or time periods of the respiratory phases, such as inhalation triggers, inspiratory or expiratory pauses, is therefore a meaningful application of electroimpedance tomography (EIT) an appraisal of a course of therapy advantageous and desirable.

Therefore, an application of the methods mentioned with methodically induced signal delays (low-pass filtering, median filtering and "outlier" removal) in the form described above is not immediately feasible.

Another common method for removing pulse-like noise is a kind of "lock-in" to a periodically occurring noise signal. In this case, a signal is first analyzed over a period of time with respect to a periodic disturbance, then this determined periodicity of the interfering signal is used for subsequent measurements either to invalidate the signal at predictable times, or the signal sample is adjusted or delayed so that the predictable times no signal detection for the signal of interest occurs and thus the predictable interference signals are not detected. Removal of pacemaker pulses with such a predictive method is not possible in principle, since the Heart beat in the heart rate (pulse) has a high variability, for example, from 55 pulse beats per minute to 150 pulse beats per minute and therefore the pulses generated by the pacemaker are not generated in a rigidly synchronized periodic sequence and are passed to the heart muscle. Rather, the pulses generated by the pacemaker are sometimes generated as required with different time intervals between the individual pulses, so that no predictable periodicity and thus no heartbeat-correlated pre-information is available, which to a targeted suppression, for example, with a kind of "gating" as it also used to blank out R-waves of an ECG signal overlay on an EMG signal can be used.

In addition, boundary conditions also arise from the measuring principle of electro-impedance tomography itself, which for example significantly complicates the previously described type of "outlier" removal. Due to the EIT measurement principle results in such a large amount of measured signals to be processed that methods based on a subsequent analysis of the amount of measurement signals over a recorded period of time, in practical application does not make sense, d. H. can only be used under the condition of very high computing power of the data processing unit and high speed in transfers and storage of the data streams. However, such a high computational power reduces the problem of delays only symptomatically, but not fully compensated, but with increased costs due to the above conditions.

Here is an example to clarify the situation described above:
With a comparatively small number of altogether 16 electrodes attached to the thorax of a patient, an EIT system can image the lungs in one cycle of current feeds to two electrodes each and record voltage readings (EIT measurement signals) on each of the 13 remaining electrodes generated by 32 × 32 pixels. In this case, a number of 208 measured values are recorded at the electrodes at the electrodes. From the 208 measured values, 1024 impedance values then result with the EIT image reconstruction.

If an "outlier" removal is to take place as described above, for example with an analysis of a number of, for example, 200 measured values over time for each of the 208 measured values, then more than 40,000 measured values would have to be used in the analysis in order to calculate the "outliers". To perform removal in this way.

A comparable approach based on the 1024 impedance values would result in an analysis of more than 200,000 impedance values. Increasing the desired resolution by increasing the number of electrodes to 32 or even to 64 electrodes again increases the amount of processed values by a multiple.

The object of the present invention, having regard to the above-described drawbacks of the known prior art, is to specify a method for removing pulse-like interference signals from tomographic measuring signals. The object of the present invention is in particular to specify a method for removing pacemaker pulses from tomographic measuring signals.

A further object of the present invention is to provide a device which allows removal of pulse-like interference signals from tomographic measurement signals. The object of the present invention is, in particular, to provide a device which makes it possible to remove pacemaker pulses from tomographic measuring signals.

These and other objects are achieved by the appended independent claims.

According to a first aspect of the invention, the object is achieved by a method having the features of patent claim 1.

According to a further aspect of the invention, the object is achieved by a device having the features of patent claim 14.

Advantageous embodiments of the invention will become apparent from the subclaims and are explained in more detail in the following description with partial reference to the figures.

At the beginning some of the terminology used in this patent application will be explained in more detail.

For the purposes of the present invention, the observation period is a time segment in a time course. The beginning and end of such a period of observation are given either by fixed or adjustable times or by events given by the characteristics of respiration or respiration. Examples of observation periods which are based on respiration or respiration are a respiratory cycle, several respiratory cycles, parts of respiratory cycles such as inhalation (inspiration), inspiratory pause, exhalation, expiratory pause.

For the purposes of the present invention, EIT measurement signals are to be understood as the following signals or data which can be detected with an EIT device by means of a group of electrodes or by means of an electrode belt. These include EIT measurement signals in different signal characteristics, such as electrical voltages or voltage measurement signals, electrical currents or current measurement signals associated with electrodes or groups of electrodes or positions of electrodes or groups of electrodes on the electrode belt, as well as voltages and currents derived electrical resistance or impedance values.

For the purposes of the present invention, a measuring circulation means a signal feed to two feeding electrodes, a so-called feed electrode pair, in which EIT measuring signals are recorded at other electrodes, which are different from these two feeding electrodes.

For the purposes of the present invention, a measuring cycle is understood to mean a sequence of feeds at a plurality of feed-electrode pairs, each with an associated measuring cycle at remaining electrodes.

Such a measurement cycle is typically referred to as a so-called "frame" or "time frame" when processing EIT data. Accordingly, a measurement cycle as part of the measurement cycle is typically referred to as a "partial frame" in the processing of EIT data.

For the purposes of the present invention, an identical measurement situation means an unambiguous assignment or constellation of two signal-feeding electrodes and other two signal-detecting electrodes from a multiplicity of electrodes. The plurality of electrodes are embodied, for example, by an electrode arrangement, for example embodied as an electrode belt attached to the thorax of a patient of a certain number of electrodes. Exemplary numbers of electrodes in the electrode belt are 16, 32 or 64 electrodes. Each of such an identical measurement situation in each case forms a specific so-called EIT measurement channel. This results in a plurality of EIT measurement channels or identical measurement situations, which include different assignments or constellations of on the one hand feeding and on the other hand different measuring electrodes. The EIT measurement channels or identical measurement situations are preferably addressed in the form of an index-based manner, and the data acquired on the EIT measurement channels are preferably addressed in the form of indexed vectors, indexed data fields or indexed matrices, stored for further processing (vector analysis). Operations, matrix operations).

• – einlesen und sortieren der EIT-Messsignale eines EIT-Messkanals in eine Zeitreihe mit EIT-Messsignalen,
• – ermitteln einer messkanalspezifischen Vergleichsgröße auf Basis einer statistischen Kennzahl in der Zeitreihe mit EIT-Messsignalen
• – identifizieren eines aktuellen EIT Messsignals als ein gestörtes Messsignal durch Vergleich des aktuellen EIT-Messsignale des EIT-Messkanals mit der Messkanalspezifischen Vergleichsgröße,
• – ersetzen des als gestörtes Messsignal identifizierten EIT-Messsignals durch einen Ersatzwert,
• – überprüfen der Zeitreihe des EIT-Messkanals, ob ein Kriterium hinsichtlich einer Störungssituation überschritten wurde,
• – einbeziehen des aktuellen EIT-Messsignale EIT-Messsignals in das Ermitteln der statistischen Kennzahl aus den EIT-Messsignalen der Zeitreihe des EIT-Messkanals, falls in dem EIT-Messkanal das Kriterium hinsichtlich der Störungssituation nicht überschritten wurde,
• – bereitstellen bereinigter EIT-Messsignale, welche von impulsartigen Störsignalen insbesondere Herzschrittmacherimpulsen, bereinigt sind.

A solution according to the invention results from a method for processing EIT measurement signals, wherein the EIT measurement signals are from an electromagnetic impedance tomography device (EIT device) or an electro-impedance tomography suitable for imaging the lungs and the thorax Measuring device over a period of observation. With the aid of the method according to the invention, pulse-like interference signals, in particular pacemaker pulses, can be removed from the EIT measurement signals. The method according to the invention for removing pulse-like interference signals, in particular pacemaker pulses, processes EIT measurement signals of an electro-impedance tomography device suitable for imaging the lung in a step sequence with the following steps:

• Reading in and sorting the EIT measuring signals of an EIT measuring channel into a time series with EIT measuring signals,
• Determine a measurement channel-specific comparison variable based on a statistical key figure in the time series with EIT measurement signals
• Identifying a current EIT measurement signal as a disturbed measurement signal by comparing the current EIT measurement signals of the EIT measurement channel with the measurement channel-specific comparison variable,
• Replacing the EIT measuring signal identified as a faulty measuring signal with a substitute value,
• - checking the time series of the EIT measuring channel, whether a criterion with regard to a fault situation has been exceeded,
• - Include the current EIT measurement signal EIT measurement signal in the determination of the statistical characteristic number from the EIT measurement signals of the time series of the EIT measurement channel, if in the EIT measurement channel the criterion regarding the disturbance situation was not exceeded,
• - Provide adjusted EIT measurement signals, which are cleaned up by pulse-like interference signals, in particular pacemaker pulses.

This sequence of steps ensures and ensures that a replacement value in the case of an identified disturbance variable replaces the original EIT measurement signal of the respectively disturbed EIT measurement channel and is also used in the further evaluation and data processing for imaging the lung, preferably and for example with a reconstruction algorithm , This frees the imaging of the lungs from artifacts, which could become noticeable over the observation period in the course of ventilation of the lungs, for example as a brief flickering of individual areas of the lungs when viewing the ventilation.

The identification of disturbances is preferably carried out specifically in each of the EIT measurement channels, wherein in each case the measurement channel-specific comparison variable itself is determined from EIT measurement signals within the time series on the basis of the statistical characteristic number. The statistical measure contains a statement or information about how a signal situation in one or more of the EIT measurement channels has been over a past period of time.

In the context of the present invention, the term "signal situation" encompasses temporal signal curves of the EIT measurement signals and their properties without and under the influence of interference. Examples of interference are superpositions of 50 Hz or 60 Hz power hums, superpositions of various types of noise (resistance noise, thermal noise, white noise, shot noise, flicker noise, 1 / f noise, cosmic noise), superimpositions by radio frequency signals ( Mobile radio [GSM, UTMS], LW, MW and FM radio stations, 2.4 GHz Bluetooth, 2.4 GHz WLAN, 5 GHz WLAN), crosstalk or signal coupling of data lines or power supply lines to individual EIT electrodes, Electrode cables, EIT measurement channels, crosstalk from other EIT measurement channels and signal couplings, as well as pulse-like overlays or pulse-like interference, which are generated by a pacemaker time-limited or discrete and interfere with one or more of the EIT measurement channels.

In the context of the present invention, the term disturbance situation encompasses situations on one or more EIT measurement channels in which EIT measurement signals are not present in undisturbed form. The aforementioned disturbances represent a multiplicity of different disturbance situations, wherein the disturbances individually or with one another at the same time or in chronological succession may occur statistically coincidentally and in a manifold manner and form further disturbance situations and act on the signal situations. In the signal situations, the respective EIT measuring arrangement with the type of electrode arrangement on the patient's thorax and the EIT electrode / cable arrangement are thus reflected directly and indirectly in the statistical key figures. In addition, both the measurement environment in general and the closer measurement environment with or without the presence of a cardiac pacemaker are in particular in the signal situation and thus also in the statistical index.

The measurement channel-specific comparison variable is compared with a current EIT measurement signal to determine whether the current EIT measurement signal is disturbed or not. If the current EIT measurement signal is identified as a fault, the current EIT measurement signal is replaced by a substitute value. The use of the substitute value reduces the influence on the subsequent data processing by the identified EIT measurement signal and thus also artifacts in the imaging, such as the short-term image flicker. It is thus essential to the invention that to remove pulse-type interference from the EIT measurement signals, those EIT measurement signals are removed and replaced which are atypical for EIT measurement signals (electrical gap measurement signals, electrical current measurement signals, electrical resistance or impedance values) of an electric current. Impedance tomography measurement are. As substitute values, different variants of substitute values can be used, preferred embodiments are possible in which the substitute value is generated on the basis of other EIT measuring signals, it is also possible to use preferred embodiments which use fixed or predetermined values as substitute values.

When determining the statistical key figure, it is essential to the invention that in the determination of the statistical key figure essentially only those EIT measuring signals are received which have not themselves been changed, alienated or disturbed by a pulse-like disturbance.

The criterion regarding the disturbance situation includes statements as to whether or in what way within the previous EIT measuring signals of an EIT measuring channel the EIT measuring signals were frequently or clearly disturbed. On the one hand, the criterion with regard to the disturbance situation means that the current EIT measurement signal is included in the determination of the statistical characteristic number whenever the current EIT measurement signal itself was not identified as a disturbance. On the other hand, the criterion with regard to the disturbance situation causes, depending on the situation, whether and / or how often previously an EIT measuring signal was identified as a disturbed EIT measuring signal in the same or another EIT measuring channel, in which case the current disturbed EIT Measurement signal is not used to determine the statistical index - and thus not to determine the comparison size.

For a refinement of the criterion with respect to the disturbance situation, different configurations are possible, so preferred embodiments are possible in which the temporally previous EIT measuring signals of the same EIT measuring channel are included in the criterion. Further preferred embodiments are possible in which the interference situations of other EIT measurement channels are included in the criterion.

The application of the criterion with regard to the disturbance situation has the consequence that the influencing of the statistical index and the Influencing the measuring channel-specific reference variable is kept low by interference. If, in another embodiment and method different from the method according to the invention, no criterion with respect to the disturbance situation is applied, the statistic index may no longer be representative of the signal situation of the EIT measuring signals in the EIT measuring channels in the event of a longer lasting disturbance can become increasingly representative of the disturbance situation itself. This would have the distinct disadvantage that in such cases on the basis of the statistical index no more comparative variables could be determined which can be used to identify impulse-like interference signals, in particular cardiac pacemaker pulses.

The special feature of the method according to the invention is that immediately after the continuous EIT measurement operation, each individual current EIT measurement signal immediately after it is available as an input to the method according to the invention, ie, for example, directly after the signal acquisition and analog-to-digital conversion, based on the measurement channel specific Comparable size can be analyzed and can be determined whether this current measurement signal is to be used for further processing or replaced by the substitute value instead. A particular advantage of the method according to the invention is that with the derivation of the comparison variable from the statistical characteristic number, the respective typical statistical distribution of the EIT measurement signals of the respective EIT measurement channel has an effect on the identification of disturbed EIT measurement signals and the identification of the disturbed EIT measurement signals. Measuring signals are thus adapted to the typical statistical distribution of previously recorded EIT measurement signals. In addition, it is particularly advantageous that with the criterion concerning the disturbance situation, which is directly included in the dataset from which the statistical index is determined, a mechanism inherent in the method that the disturbance situation only in so far included in the comparison size, as long as the statistical index representative for the signal situation of the EIT measuring signals in the respective EIT measuring channel and the method according to the invention, however, is ensured that the statistical index can be representative of disturbances instead of the EIT measuring signals.

Although the method according to the invention can not distinguish whether a pulse-type disturbance has a pacemaker pulse as the cause or another source of interference is the cause, the determination of the comparison variable on the basis of the statistical index implicitly includes the properties of the measurement environment in a statistical manner and the comparison quantity is adapted in this way adaptively and continuously to the current measurement situation. This ensures by the inventive method that even with changes in the measurement environment or measurement situation, a removal of pulse-like interference signals, in particular pacemaker pulses, is possible.

In a preferred embodiment of the method, in a further step, control signals for a visualization with regard to a ventilation situation of the lung are generated and provided from the provided adjusted measurement signals.

In a further preferred embodiment of the method, the EIT measurement channels result as identical situations of the measurement signal acquisition during the acquisition of the EIT measurement signals by the electro-impedance tomography device as assignments of EIT measurement signals in that each measurement channel has a specific one Detection configuration of each two measuring electrodes of a plurality of electrodes in combination with a particular feed configuration of two feeding electrodes of the plurality of electrodes is based. The respective measuring electrodes of the respective EIT measuring channel are different from the feeding electrodes.

• • welche Typen von Ersatzwerten verwendet werden können,
• • auf welche Weise Ersatzwerte gewonnen werden können,
• • wie die statistische Kennzahl ermittelbar ist,
• • wie die Vergleichsgröße auf Basis der statistischen Kennzahl ermittelbar ist,
• • wie das Kriterium hinsichtlich der Störungssituation ermittelbar ist,

sowie weitere Ausgestaltungen des Verfahrens zur Entfernung impulsartiger Störsignale, insbesondere Herzschrittmacherimpulse.The further preferred embodiments of the method described below for removing pulse-like interference signals, in particular pacemaker pulses, describe embodiments and variants with regard to:

• • which types of substitute values can be used,
• • how substitute values can be obtained,
• • how the statistical key figure can be determined
• • how the comparison variable can be determined on the basis of the statistical key figure,
• • how the criterion with regard to the disturbance situation can be determined,

and further embodiments of the method for removing pulse-like interference signals, in particular pacemaker pulses.

In a further preferred embodiment of the method, the statistical characteristic number is in each case indicative of a statistical distribution or scattering of the measurement signals within the time series of the respective measurement channels in the measurement cycle or in the measurement cycle. Characteristic of a statistical distribution or scattering of the measurement signals are, for example, a sliding standard deviation, a sliding variance or dispersion, a moving average or a median value. For example, the mathematical-statistical relationships between the standard deviation and the mean value are implicitly included in the statistical key figure. The statistical index is determined in this further preferred embodiment from the time series with temporally previous EIT measurement signals and a current EIT measurement signal, preferably based on a sliding standard deviation from the time series with temporally previous EIT measurement signals and a current EIT measurement signal. The current EIT measurement signal is always included in the calculation of the statistical key figure if the criterion regarding a fault situation has not been exceeded.

In a further preferred embodiment of the method, the criterion with regard to the disturbance situation is based on a frequency of disturbances of chronologically previous EIT measuring signals in a predetermined temporally preceding time interval. The criterion relating to the disturbance situation is thereby formed and generated by how frequently a disturbance situation was identified in the predetermined time interval. The frequency of disturbances can preferably be determined individually in each of the EIT measurement channels. As an example for the determination of the criterion with regard to the disturbance situation, it should be mentioned that the criterion is then effective for the determination of the statistical index as soon as more than 10 EIT measuring signals are identified as disturbances in an EIT measuring channel within a temporally previous time interval of 60 seconds have been. In a particular variant of this further embodiment, frequencies of disturbances of other measuring channels in the measuring cycle or in the measuring cycle, for example measuring channels, in which the feeding or detecting electrodes are arranged adjacent to the electrodes of the EIT measuring channel can also be included. As an example for the determination of the criterion with regard to the disturbance situation involving adjacent measuring channels, it should be mentioned that the criterion is then effective for the determination of the statistical index as soon as more than 3 EIT in the EIT measuring channel within the chronologically preceding time interval of 60 seconds Measurement signals have been identified as interference and have been identified in other, for example, adjacent EIT measurement channels within a temporally previous time interval of 60 seconds more than 4 disturbances.

In a further preferred embodiment of the method, the criterion relating to the interference situation is based on a frequency of disturbances within a predetermined number of EIT measurement signals. In this further embodiment of the method, the frequency of disturbances is not related to a temporally preceding time interval, but related to a predetermined number of previously recorded EIT measurement signals. In this case, the predetermined number may preferably be related to a time series of a single measurement channel. The frequency of disturbances in each of the EIT measurement channels is determined on its own. As an example for the determination of the criterion with regard to the disturbance situation, it should be mentioned that the criterion is then effective for the determination of the statistical characteristic number as soon as more than 10 EIT measurement signals as disturbances in an EIT measuring channel within the last previously recorded 20 EIT measuring signals have been identified. In a particular variant of this further embodiment, frequencies of disturbances of other measuring channels in the measuring cycle or in the measuring cycle, for example measuring channels, in which the feeding or detecting electrodes are arranged adjacent to the electrodes of the EIT measuring channel can also be included. As an example for the determination of the criterion with regard to the disturbance situation involving adjacent measuring channels, it should be mentioned that the criterion is then effective for the determination of the statistical index as soon as more than 5 in the EIT measuring channel within the last previously recorded 20 EIT measuring signals EIT measurement signals have been identified as disturbances and in total more than 3 disturbances have been identified in other, for example, adjacent EIT measurement channels within the last 10 EIT measurement signals recorded previously.

In a further preferred embodiment of the method, the criterion with respect to the disturbance situation is based on a periodicity of identified disturbed EIT measurement signals. A periodicity is given, for example, when, in a time interval, a number of EIT measurement signals in the signal amplitude fluctuate periodically between two limit values over a specific period of time, which are superimposed on the actual signal amplitude of the EIT measurement signals. An example of such a situation is an amplitude modulation of EIT measurement signals by an external source of interference where the frequency of the sample in the EIT system coincidentally approximates to the disturbance. Such changes in the EIT measurement signals do not represent pulse-like disturbances and enter into the criterion with respect to the disturbance situation in such a way that, although a large number of such disturbances occurs, the criterion with respect to the disturbance situation does not become effective for the determination of the statistical characteristic number.

In a further preferred embodiment of the method, the determination of the measurement channel-specific comparison variable is based on a predetermined maximum or a predetermined minimum threshold value. In this further preferred embodiment of the method, EIT measurement signals having signal amplitudes which are above a predetermined maximum threshold or below a predetermined minimum threshold value are identified as interference. That's the way it is Advantageously and with little effort possible to immediately identify drastic disturbances. For example, in this way it is possible to identify measuring signals which occur in the order of magnitude of a voltage supply of an EIT measuring system with the aid of a predetermined maximum or predetermined minimum threshold value derived from the magnitude of the voltage supply.

In a further embodiment of the method, the comparison variable is determined from the statistical characteristic number. In a preferred variant of this further embodiment of the method, the comparison variable is determined from the statistical code, preferably with calculation of the statistical code in the form of a moving average or a sliding standard deviation of the time series of the EIT measurement signals. The determination of the statistical index involves time-previous EIT measurement signals of the time series and, if the criterion with respect to a fault situation is not exceeded, a current EIT measurement signal. The measurement channel-specific comparison variable is described, for example, as a multiple, typically as an integer multiple (1, 2, 3... 50) of the determined sliding standard deviation or as a multiple, typically as an integer multiple (1, 2, 3. ..10) of the determined moving average.

In a further embodiment of the method, the substitute value is derived from an EIT measurement signal or a plurality of EIT measurement signals from the time series with temporally preceding EIT measurement signals of an EIT measurement channel, preferably the current EIT measurement channel. The derivation of the substitute value can advantageously take place with the aid of conventional interpolation, regression or estimation methods, for example by means of linear regression or by spline approximation on the basis of the previous EIT measurement signals of the current EIT measurement channel. This ensures a specific formation of substitute values from signals of the same EIT measuring channel, which in the substitute value then sets the measuring situation of the specific EIT measuring signal to a trend in the previous signal curve of the EIT measuring signal of the specific EIT measuring channel in the measuring cycle.

In a further embodiment of the method, the substitute value of EIT measurement signals is derived from the time series with temporally preceding EIT measurement signals of a plurality of EIT measurement channels. The derivation of the substitute value also relates to temporally previous EIT measurement signals of other measurement channels and / or current EIT measurement signals of other measurement channels, for example of EIT measurement channels, in which the feeding or detecting electrodes are arranged adjacent to the electrodes of the EIT measurement channel, as well as preferably also EIT measuring signals of the current EIT measuring channel with a. This ensures inclusion of signals of other EIT measurement channels in the measurement cycle or in the measurement cycle into the substitute value, which can be helpful in particular in measurement situations when only the EIT measurement signal of the current EIT measurement signal is disturbed. For this purpose, for example, the EIT measurement signals of a plurality of adjacent EIT measurement channels, preferably using a median determination, averaging or use of other suitable methods for compensation calculation (interpolation, regression) or estimation methods for forming the substitute value can be used.

In a further embodiment of the method, a value with a predetermined value is used as substitute value. Such a predetermined value is preferably a value corresponding to a time-prior EIT measurement signal of the current EIT measurement signal of the same EIT measurement channel or a value having a fixed predetermined numerical value. An example of a fixed numeric value is a numeric value of zero.

In a further preferred embodiment of the method, a number of the identified disturbed measuring signals is detected in one or more of the EIT measuring channels and an identifier is determined from the number of disturbed measuring signals, which represents a degree of disturbance influencing. With this identifier, it is advantageously possible to provide information to the user as to whether and to what extent one or more EIT measurement channels, single or multiple measurement cycles or measurement cycles are influenced by disturbances. In addition, information can be given to the user as to whether the method for removing pulse-like interference signals, in particular pacemaker pulses, from measurement signals of an electromagnetic impedance tomography device suitable for imaging of the lung is active in the current measurement mode and a replacement of identified disturbed measurement signals takes place or whether the degree of interference is such that the method in the current signal situation and disturbance situation is no longer able to remove disturbed measurement signals.

The described embodiments constitute in each case, as well as in combination with each other, special embodiments of the method according to the invention for removing pulse-like interference signals, in particular pacemaker pulses, from EIT measurement signals of an electro-impedance tomography device suitable for imaging the lung and possible resulting from combination or combinations of several embodiments Nevertheless, further embodiments and their advantages are included in the concept of the invention, although not all possible combinations of embodiments of this are detailed in each case. The above-described embodiments of the method according to the invention can also be embodied in the form of a computer-implemented method as a computer program product with a computer, wherein the computer is made to carry out the method according to the invention described above when the computer program is stored on the computer or on a processor of the computer or a so-called embedded system as part of a medical device. In this case, the computer program can also be stored on a machine-readable storage medium. In an alternative embodiment, a storage medium may be provided, which is intended for storing the above-described computer-implemented method and is readable by a computer. It is within the scope of the present invention that not all steps of the method necessarily have to be performed on one and the same computer instance, but they can also be executed on different computer instances. The sequence of the method steps can also be varied if necessary. Furthermore, it is possible that individual sections of the method described above in a separate, for example, self-sellable unit such. On a preferably in the vicinity of the patient arranged EIT measuring system, other parts on another salable unit, such. B. on a data evaluation system or on a display and visualization unit, so to speak, as a distributed system, can be executed. In the foregoing, the solution of the problem has been described in relation to the method claimed as the first aspect of the invention. In addition, a device according to the invention which is designed to carry out the method according to the invention in the sense of at least one of the described embodiments results as a further aspect.

Features, advantages, or alternative embodiments mentioned for the method are also to be applied to the other claimed subject matter, and vice versa. The corresponding functional features of the method are formed by corresponding physical modules of a device, in particular by hardware components (.mu.C, .mu.P, DSP, FPGA, ASIC, GAL, logic components), which are for example in the form of a processor (.mu.P), multiple processors or in the form of instructions in a memory area that are processed by the processor.

The advantages described for the method according to the invention can be achieved in the same or similar manner with the device according to the invention. Furthermore, the described embodiments and their features and advantages of the method are transferable to the device, as well as the described embodiments of the device are transferable to the method.

• – Sortierung der EIT-Messsignale eines EIT-Messkanals in eine Zeitreihe mit EIT-Messsignalen,
• – Ermittlung einer messkanalspezifischen Vergleichsgröße auf Basis einer statistischen Kennzahl in der Zeitreihe mit EIT-Messsignalen,
• – Identifikation eines aktuellen EIT Messsignals als ein gestörtes Messsignal durch Vergleich des EIT-Messsignals des EIT-Messkanals mit der Messkanalspezifischen Vergleichsgröße,
• – Ersetzung des als gestörtes Messsignal identifizierten EIT-Messsignals durch einen Ersatzwert,
• – Überprüfung der Zeitreihe des EIT-Messkanals, ob ein Kriterium hinsichtlich einer Störungssituation überschritten wurde,
• – Einbeziehung des aktuellen EIT-Messsignals in die Ermittlung der statistischen Kennzahl aus den EIT-Messsignalen der Zeitreihe des
• EIT-Messkanals, falls in dem EIT-Messkanal das Kriterium hinsichtlich der Störungssituation nicht überschritten wurde,
• – Bereitstellung von bereinigten EIT-Messignalen, welche von impulsartigen Störsignalen, insbesondere Herzschrittmacherimpulsen, bereinigt sind,

According to the invention, the object is achieved according to the further aspect of the invention by an electro-impedance tomography device (EIT device), which is designed to remove pulse-like interference signals. Such an electro-impedance tomography device, which is suitable for the removal of pulse-like interference signals, in particular pacemaker pulses, has, in addition to an electrode arrangement, a signal detection unit, a signal processing unit and an image reconstruction unit. The signal detection unit is designed and provided for detecting EIT measurement signals of the electrode arrangement and has, for example, signal amplification circuits (OP amps), signal filter circuits, for example in the form of 50 Hz filters or ripple filters, analog to digital converter (A / D converter). , as well as other switching elements, such as matching circuits, for example, to an impedance matching of measurement leads on. The signal processing unit is designed and provided for carrying out a processing of the EIT measurement signals and is, for example, in the form of a processor unit (μC, μP, DSP) with associated memory elements (RAM, ROM, EEPROM), data inputs (input), address bus, data bus, output module. Interface (output) designed. In addition, a typical electro-impedance tomography device preferably has an output unit. The output unit is used for displaying, outputting and / or displaying measured values, numerical values, calculated results or curves, images or other graphical representations of the impedance values, impedance distribution and impedance differences in the lungs of a living being or patient and the information determined therefrom a ventilation situation of the lungs, as well as the local and temporal ventilation of the lungs. In addition, an input unit may preferably be arranged and provided in the electro-impedance tomography device. Such an input unit typically serves as an input means for a user, for example in the form of touch elements, buttons, switching elements, rotary knobs to make adjustments or parameterizations for the operation of the electro-impedance tomography device. The input unit and the output unit can also be designed jointly as an input and output unit, for example in the form of a touch-sensitive display (touch screen). By doing Electro-impedance tomography device, the signal detection unit is configured to detect EIT measurement signals of the electrode assembly. The electrode assembly has a plurality of electrodes attachable to a thorax of a living being. The output unit is configured to represent impedance values or display values or graphs derived from the impedance values. The impedance values represent the ventilation situation and the course of the ventilation of the lungs of the living being. The signal processing unit is configured to control a following sequence for signal processing:

• Sorting the EIT measurement signals of an EIT measurement channel into a time series with EIT measurement signals,
• Determination of a measurement channel-specific comparison variable on the basis of a statistical key figure in the time series with EIT measurement signals,
• Identification of a current EIT measurement signal as a disturbed measurement signal by comparison of the EIT measurement signal of the EIT measurement channel with the measurement channel-specific comparison variable,
• Replacement of the EIT measuring signal identified as a disturbed measuring signal by a substitute value,
• - Checking the time series of the EIT measuring channel as to whether a criterion with regard to a fault situation has been exceeded,
• - Inclusion of the current EIT measurement signal in the determination of the statistical key figure from the EIT measurement signals of the time series of the
• EIT measuring channel, if the criterion concerning the disturbance situation was not exceeded in the EIT measuring channel,
• Provision of adjusted EIT measurement signals which are adjusted for pulse-like interference signals, in particular pacemaker pulses,

The image reconstruction unit is configured to convert the set of adjusted EIT measurement signals into impedance values by means of a reconstruction algorithm. The unit for image reconstruction is typically designed as a unit for performing mathematical operations, logic operations and Boolean algebra and time step sequences, for example in the form of one or more processors (μC, μP, DSP). Preferably, the image reconstruction unit is implemented in common with the signal processing unit as a central control and calculation unit. The output unit provides appropriate control signals based on the impedance values for output with respect to ventilation of the lung. The provided output is, or the control signals provided are thereby adjusted by pulse-like interference signals, in particular pacemaker pulses. The output of the control signals can be effected, for example, at a data interface, for example as a video interface (RGB, HDMI) for a connection of an internal data display device arranged in the electro-impedance tomography device or an external device suitable for display. The output is preferably in the form of a graphic visualization in a transverse view of the lung. Different degrees of ventilation of the lungs correspond to differences in impedance of different areas of the lung as determined by image reconstruction and are graphically represented by different gray levels, different colors, color saturation levels, brightness levels or transparency levels to visually distinguish different degrees of ventilation.

In a preferred embodiment of the electro-impedance tomography device, the signal processing unit is configured from the time-previous EIT measurement signals of the time series of the EIT measurement channel and the current EIT measurement signal, the statistical index preferably based on a sliding standard deviation or a moving average or to determine a median value.

• – eine Häufigkeit von Störungen von zeitlich vorherigen EIT-Messsignalen in einem vorbestimmten Zeitintervall und/oder
• – eine Häufigkeit von Störungen innerhalb einer vorbestimmten Anzahl von zeitlich vorherigen EIT-Messsignalen und/oder
• – eine Periodizität von identifizierten gestörten EIT-Messsignalen

mit einzubeziehen.In a preferred embodiment of the device for removing pulse-like interference signals, the signal processing unit is configured in the criterion with regard to the interference situation

• A frequency of disturbances of temporally previous EIT measurement signals in a predetermined time interval and / or
• A frequency of disturbances within a predetermined number of previous EIT measurement signals and / or
• A periodicity of identified disturbed EIT measurement signals

to involve.

In a preferred embodiment of the electro-impedance tomography apparatus, the signal processing unit is configured to include in the determination of the measurement channel-specific comparison variable a predetermined maximum or a predetermined minimum threshold value.

In a preferred embodiment of the electro-impedance tomography device, the signal processing unit is designed to determine the measurement channel-specific comparison variable as a multiple of the statistical characteristic. The measuring channel-specific comparison variable is preferably determined by the signal processing unit as a multiple or an integer multiple (1, 2, 3... 50) of the determined sliding standard deviation, the moving average or the median value.

In a preferred embodiment of the electro-impedance tomography device, the signal processing unit is configured, the substitute value of one EIT measurement signal or multiple EIT measurement signals from the time series with EIT measurement signals of the EIT measurement channel, preferably the current EIT measurement channel and EIT measurement channel or derive previous EIT measurement signals from several EIT measurement channels.

In a preferred embodiment of the electro-impedance tomography device, the signal processing unit is designed as a substitute value a predetermined value, preferably a value corresponding to a time previous value of the current EIT measurement signal of the same EIT measurement channel or a value with a fixed predetermined numerical value to be used instead of the identified disturbed EIT measurement signal. These substitute values are then used in the course of further signal processing together with the undisturbed EIT measurement signals from the image reconstruction unit for determining the impedance values and then from the output unit for generating the control signals for providing and / or output, for example in the form of a graphical representation or visualization used.

The present invention will now be explained in more detail with the aid of the following figures and the associated description of the figures without any limitations on the general concept of the invention.

Show it:

1 a schematic representation of a temporal waveform of a pulse-perturbed EIT measurement signal,

2 a schematic representation of functional elements for signal processing with removal of pulse-like noise in an electro-impedance tomography device.

In the 1 is a schematic diagram of a diagram 2 with EIT waveforms 5 . 6 two randomly selected measurement channels 5 . 6 , In the EIT waveforms 5 . 6 are acting impulsive disturbances 7 . 9 shown. The measuring channels 5 . 6 in each case unambiguous assignments of each two signal-feeding electrodes and other two signal-detecting electrodes from EIT electrode arrangement 13 ( 2 ). The diagram 2 is by an abscissa 3 as time axis (t) and with an ordinate 4 shown scaled as signal axis S (t) and shows a time course of the two randomly selected waveforms 5 . 6 , The EIT waveform 6 exemplifies any measurement channel as a function of time (t).

The EIT waveform 5 puts in this 1 by way of example a further measuring channel as a function of time (t), which in a further signal processing as a reference variable or a reference channel for further, in this 1 not with pictured EIT measurement channels. Below the diagram 2 is schematically an EIT image series 10 shown as a sequence of five pictures 101 . 102 . 103 . 104 . 105 with the signal curves 5 . 6 correlated in time, so that the disturbing effect of the impulses acting 7 . 9 in the five pictures 101 . 102 . 103 . 104 . 105 each becomes visible. The five pictures 101 . 102 . 103 . 104 . 105 each show an image of a lung of a living being in a transverse representation. The pictures of the lungs are in the five pictures 101 . 102 . 103 . 104 . 105 shown in different hatching. These hatches are intended to approximate that over time (t) 3 - due to the breathing of the animal - the ventilation of the lungs is different. An assignment to respiratory phases, such as inhalation or exhalation is intended in this 1 neither by the signal curves 5 . 6 , nor through the EIT series of pictures 10 being represented.

In the pictures 101 . 102 . 103 . 104 . 105 is an artifact 11 shown, as it were permanently the representation of the lung, in the EIT series of pictures 10 adversely affected. The cause of this is that this artifact 11 in this 1 to show an effect, as a pulse-like disorder 7 in the signal course 5 of a measurement channel used as a reference / reference channel for other measurement channels in an EIT image reconstruction application. This makes it clear that pulse-like disturbances can not only adversely affect individual images of an EIT image series, but in certain constellations also multiple images 101 . 102 . 103 . 104 . 105 in the sequence 10 can affect the image representation sustainably negatively. The impulsive disorder 9 in the signal course 6 however, this affects itself in this 1 For example, very clearly, but only for a limited time as an artifact 12 in the picture 104 out. Such a temporally limited effect, for example, in the form of image flicker in the image representation of the EIT image series 10 visible and perceptible to the user.

In the 2 is a schematic arrangement of functional elements 1 shown in an EIT system. By means of an EIT electrode arrangement 13 become signals of a signal detection unit 14 supplied, which signals, which are usually in the form of electrical voltage signals at the electrodes 13 present, converts to digital data and over a data connection 17 in a storage unit 16 as voltages of a voltage series [U ₁ , U ₂ , U ₃ ... U _n ] as EIT measurement signals 161 stores. This series of tension 161 for example, an associated EIT signal profile is assigned for illustration purposes 56 any EIT measurement channel 5 . 6 ( 1 ) from the voltage series [U ₁ , U ₂ , U ₃ ... U _n ] 161 with one in, one time interval 57 existing fault 561 shown. In this case, a measuring channel provides an unambiguous assignment of two signal-feeding electrodes and other two signal-detecting electrodes from the EIT electrode arrangement 13 in the course of time continuously from the signal acquisition unit 14 detected signals of a measuring channel form a time series [ 161 _t1 , 161 _t2 , 161 _t3 ... 161 _tx ] with EIT measuring signals 161 out. From the signal acquisition unit 14 be the tensions 161 via a data connection 17 a signal processing unit 15 fed. In the signal processing unit 15 becomes the disorder 561 in the time series [ 161 _t1 , 161 _t2 , 161 _t3 ... 161 _tx ] of the EIT measurement signals 161 in the respective measuring channel by means of a comparison with a measuring channel-specific comparison variable, which is based on a statistical index, identified and by a substitute value or several substitute values 581 replaced and thus removed from the time series [ 161 _t1 , 161 _t2 , 161 _t3 ... 161 _tx ] and then over a data line 17 as a series of disturbances adjusted by disturbances [U ' ₁ , U' ₂ , U ' ₃ ... U' _n ] 181 to a storage unit 18 pass and in the storage unit 18 stores. Also this voltage series 181 for example, an associated EIT waveform is shown to illustrate the effect of removing impulsive noise 58 with one in a time interval 57 ' by means of a substitute value 581 or more substitute values 581 distant impulsive disorder 561 shown. As substitute values 581 were in this 2 By way of example, interpolated values are used on the basis of previous values and / or a previous measuring cycle. The measuring channel-specific comparison variable is in the signal processing unit 15 determined on the basis of the statistical key figure. The statistical key figure itself is calculated by calculating a moving standard deviation, possibly with an additional auxiliary calculation of an arithmetic mean, from time-previous EIT measurement signals of the time series [ 161 _t1 , 161 _t2 , 161 _t3 ... 161 _tx ] of the EIT measuring channel 5 . 6 , or a previous predetermined value of the moving standard deviation, and a current EIT measurement signal 161 _x0 determined. The measurement channel-specific comparison variable is, for example, as a multiple, typically as an integer multiple (1, 2, 3 ... 50) of the determined moving standard deviation in the signal processing unit 15 certainly. From the storage unit 18 be the tensions 181 via a data line 17 to a unit for image reconstruction 19 to hand over. In this image reconstruction unit 19 is calculated from the voltages [U ' ₁ , U' ₂ , U ' ₃ ... U' _n ] 181 first a series of impedance values [Z ₁ , Z ₂ , Z ₃ ... Z _m ] 191 reconstructed, converted this into image data (pixels) and then using a data connection 17 to an output unit for EIT image display 20 passed to an imaging of the lungs. The imaging of the lung shows in this 2 a simplified typical image of the lung in a transverse view, as can typically be obtained with an electro-impedance tomography system. In the illustrated simplified typical image on the output unit for EIT imaging 20 is a partial area in dashed lines 21 shown as an example, in which the disorder 561 would be effective if this in the time interval 57 not identified and in the time interval 57 ' not by substitute values 581 would have been replaced. The storage units 16 . 18 are preferably designed as a ring memory (FILO: First In - Last Out), so that values of a previous measurement cycle are still in memory 16 . 18 and can serve as the basis for the formation of the substitute values, whether as an unchanged measure in the form of a direct substitute value or as a substitute value based on multiple values derived by means of interpolation, regression or estimation methods. The storage units 16 . 18 may be implemented as separate memory units, a configuration as a shared memory unit, as well as a combination of memory units 16 . 18 with the signal processing unit 15 and / or the signal acquisition unit 14 and / or the image reconstruction unit 19 in a common arithmetic unit is in technical embodiments of functional elements 1 of EIT systems typical and common.

The data connections 17 are preferably designed as an EIT bus system to which the signal processing unit 15 , the storage units 16 . 18 , Signal acquisition unit 14 as well as the image reconstruction unit 19 and the output unit for EIT imaging 20 are preferably connected. The concrete design is thereby by this 1 not specified or restricted, but rather depends on the specific application and location of the EIT system and the development and design constraints, such as size, measurement performance, material costs, interfaces or requirements from a composite device to a medical workstation.

To illustrate the constant number of voltage value comparisons needed to identify disturbances 161 Comparative quantities here are exemplary details for an arrangement of a total of sixteen electrodes as an EIT electrode arrangement 13 called. With a number of 16 electrodes, a number of 208 voltage values [U ₁ , U ₂ , U ₃ ... U ₂₀₈ ] are obtained for one measuring cycle. 161 and thus also a number of 208 corrected voltage values [U ' ₁ , U' ₂ , U ' ₃ ... U' ₂₀₈ ] 181 , In an exemplary mapping to 32 × 32 pixels for an EIT representation, the reconstruction of the 208 voltage values yields 1024 impedance values [Z ₁ , Z ₂ , Z ₃ ... Z ₁₀₂₄ ]. 191 , Even this example, with a low image resolution of 32x32 pixels, highlights the importance of having a method that requires the least amount of computational effort to continually identify the perturbations in each measurement channel. An embodiment of an EIT measuring system with 32 or even 64 electrodes increases the voltage values and / or impedance values to be processed by a multiple. On the one hand, a method with as little computation as possible leads to the fact that the components (μP) used for calculation and comparison do not have to be designed to be very powerful and thus do not cost too much; on the other hand, the delay caused by the method may be due to the measurement of the voltages at the EIT-electrode assembly 13 until displayed on the output unit for EIT image display 20 be kept low. Keeping these delays low is particularly important for evaluability, since, if the ventilation situation is too long, the lung is displayed on the output unit for EIT imaging 20 the ventilation state of the lungs of a living being then shown is no longer in accordance with the then current physical state of the lungs in the course of the respiration of inhalation and exhalation.

LIST OF REFERENCE NUMBERS

1

Arrangement of functional elements

2

diagram

3

Abscissa, time axis (t)

4

Ordinate, signal axis S (t)

5, 6

EIT signal waveforms, measuring channels

7, 9

Coupled Pulse-like Interference

10

EIT Series

11, 12

Artifacts in the EIT series 10

13

EIT-electrode assembly

14

Signal acquisition unit [DAQ]

15

Signal processing unit [μP]

16, 18

Memory unit with EIT measuring signals / voltage measured values

 17

data connections

19

Unit for image reconstruction

20

Output unit for EIT image display

21

Part of the EIT image / removed artifact

56

EIT measurement signal with fault

58

EIT measurement waveform with remote fault

57, 57 '

Time interval with fault or substitute value

561

disorder

581

substitute values

101-105

Pictures of the EIT picture series 10

161

Voltage series EIT Measurement signals in the memory unit 16

161 _tx ... 161 _tx

Time series with EIT measurement signals

161 _x0

Current EIT measurement signal

181

Voltage series of adjusted EIT measurement signals in the memory unit 18

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 6236886 [0002]
• US 5807251 [0003, 0005]

Claims (20)

Method for processing EIT measurement signals ( 161 ), whereby the EIT measurement signals ( 161 ) were obtained by an electromagnetic impedance tomography measuring device suitable for imaging the lung and the thorax over a period of observation, pulse-like interference signals ( 7 . 9 ), in particular pacemaker pulses, from the EIT measurement signals ( 161 ) are removable, whereby a step sequence ( 1 ) is repeated with the steps: - read in and sort the EIT measurement signals ( 161 ) of an EIT measuring channel ( 5 . 6 ) into a time series [ 161 _t1 , 161 _t2 , 161 _t3 ... 161 _tx ] with EIT measuring signals ( 161 ) 161 _x0 ), - determining a measurement channel-specific comparison variable based on a statistical key figure in the time series [ 161 _t1 , 161 _t2 , 161 _t3 ... 161 _tx ] with EIT measuring signals ( 161 ), - identify a current EIT measurement signal ( 161 _x0 ) as a disturbed measurement signal ( 7 . 9 ) by comparing the EIT measuring signals ( 161 ) of the EIT measuring channel ( 5 . 6 ) with the measuring channel-specific comparison variable, - replace the disturbed measuring signal ( 7 . 9 ) identified EIT measurement signal ( 161 ) by a substitute value ( 581 ), - check the time series [ 161 _t1 , 161 _t2 , 161 _t3 ... 161 _tx ] of the EIT measuring channel ( 5 . 6 ), whether a criterion with regard to a fault situation has been exceeded, - include the current EIT measuring signal ( 161 _x0 ) in the determination of the statistical index from the EIT measurement signals ( 161 ) of the time series [ 161 _t1 , 161 _t2 , 161 _t3 ... 161 _tx ] of the EIT measuring channel ( 5 . 6 ), if in the EIT measuring channel ( 5 . 6 ) the criterion regarding the disturbance situation has not been exceeded, - provide adjusted EIT measurement signals ( 18 ), which of impulsive interference signals ( 7 . 9 ), in particular pacemaker pulses, are adjusted. Method according to claim 1, wherein in a further step control signals ( 17 ) to a visualization from the provided adjusted EIT measurement signals ( 18 ) are provided. Method according to claim 1, wherein the EIT measuring channels ( 5 . 6 ) as identical situations of the measurement signal acquisition in the acquisition of the EIT measurement signals ( 161 ) as assignments of EIT measurement signals ( 161 ) indicate that each measuring channel ( 5 . 6 ) each have a particular detection configuration of each two measuring electrodes of a plurality of electrodes ( 13 ) in combination with a particular feed configuration of two each of the plurality of electrodes ( 13 ), wherein the respective measuring electrodes of the respective EIT measuring channel ( 5 . 6 ) are different from the feeding electrodes. The method of claim 1, wherein the statistical index is indicative of a statistical distribution or dispersion of the EIT measurement signals within the time series [ 161 _t1 , 161 _t2 , 161 _t3 ... 161 _tx ] of the respective EIT measurement channels ( 5 . 6 ) and the statistical key figure from the time series [ 161 _t1 , 161 _t2 , 161 _t3 ... 161 _tx ] with temporally previous EIT measurement signals ( 161 ) and a current EIT measurement signal ( 161 _x0 ), preferably determined by calculating a sliding standard deviation. Method according to claim 1, wherein the criterion with respect to the disturbance situation is based on a frequency of disturbances of chronologically previous EIT measuring signals ( 161 ) based on a predetermined time interval. The method of claim 1, wherein the disturbance situation criterion is based on a frequency of disturbances within a predetermined number of prior time EIT measurement signals. 161 ). The method of claim 1, wherein the criterion of the disturbance situation is based on a periodicity of identified disturbed EIT measurement signals ( 161 ). The method of claim 1, wherein the determination of the measurement channel-specific comparison quantity is based on a predetermined maximum or a predetermined minimum threshold value. Method according to claim 1, wherein the measurement channel-specific comparison variable is a multiple of the statistical characteristic, preferably calculating the statistical index as a moving average or a sliding standard deviation of the time series [ 161 _t1 , 161 _t2 , 161 _t3 ... 161 _tx ] of the EIT measurement signals ( 161 ). Method according to claim 1, wherein the substitute value ( 581 ) from an EIT measurement signal ( 161 ) or several EIT measuring signals ( 161 ) from the time series [ 161 _t1 , 161 _t2 , 161 _t3 ... 161 _tx ] with time-prior EIT measurement signals ( 161 ) of the EIT measuring channel ( 5 . 6 ), preferably the current EIT measuring channel ( 5 . 6 ) is derived. Method according to claim 1, wherein the substitute value ( 581 ) of EIT measurement signals ( 161 ) from the time series [ 161 _t1 , 161 _t2 , 161 _t3 ... 161 _tx ] with time-prior EIT measurement signals ( 161 ) of several EIT measuring channels ( 5 . 6 ), preferably including the current EIT measurement channel ( 5 . 6 ) is derived. Method according to claim 1, wherein as substitute value ( 581 ) is a predetermined value, preferably a value that corresponds to a time-previous value of current EIT measurement signal from the same EIT measurement channel ( 5 . 6 ) or a value with a fixed numeric value. Method according to one of the preceding claims, wherein in one or more of the EIT measuring channels ( 5 . 6 ) a number of the identified disturbed measurement signals is detected and from the number of disturbed measurement signals, an identifier is determined, which represents a degree of disturbance interference. Electro-impedance tomography device for processing EIT measuring signals ( 161 ) to a removal of pulse-like interference signals, in particular pacemaker pulses, with a signal detection unit ( 14 ), with a signal processing unit ( 15 ), with an image reconstruction unit ( 19 ) and with an output unit ( 20 ) wherein the signal acquisition unit ( 14 ) to acquire EIT measurement signals ( 161 ) of an electrode arrangement ( 13 ), wherein the electrode arrangement ( 13 ) has a plurality of electrodes attachable to a thorax of a living being, the dispensing unit ( 20 ) to a representation ( 10 ) of impedance values ( 19 ) with regard to a ventilation situation of a lung of the living being, wherein the signal processing unit ( 15 ) is configured to control a following sequence for signal processing: - sorting of the EIT measurement signals ( 161 ) 161 _x0 ), an EIT measurement channel ( 5 . 6 ) into a time series [ 161 _t1 , 161 _t2 , 161 _t3 ... 161 _tx ] with EIT measuring signals ( 161 ), - determination of a measurement channel-specific comparison variable on the basis of a statistical key figure in the time series [ 161 _t1 , 161 _t2 , 161 _t3 ... 161 _tx ] with EIT measuring signals ( 161 ), - identification of a current EIT measuring signal ( 161 _x0 ) as a disturbed measurement signal ( 7 . 9 ) by comparing the current EIT measurement signal ( 161 _x0 ) of the EIT measuring channel ( 5 . 6 ) with the measuring channel-specific comparative variable, - replacement of the as disturbed measuring signal ( 7 . 9 ) identified EIT measurement signal ( 161 ) by a substitute value ( 581 ), - Review of the time series [ 161 _t1 , 161 _t2 , 161 _t3 ... 161 _tx ] of the EIT measuring channel ( 5 . 6 ), whether a criterion with regard to a fault situation has been exceeded, - inclusion of the current EIT measuring signal ( 161 _x0 ) in the determination of the statistical key figure from the EIT measurement signals ( 161 ) of the time series [ 161 _t1 , 161 _t2 , 161 _t3 ... 161 _tx ] of the EIT measuring channel ( 5 . 6 ), if in the EIT measuring channel ( 5 . 6 ) the criterion regarding the disturbance situation was not exceeded, - provision of adjusted EIT measuring signals ( 18 ), which of impulsive interference signals ( 7 . 9 ), in particular pacemaker pulses, are cleaned up, the image reconstruction unit ( 19 ), the set of adjusted EIT measurement signals ( 18 ) by means of a reconstruction algorithm into impedance values ( 191 ), the output unit ( 20 ) based on the impedance values ( 191 ) Control signals ( 17 ) to an issue ( 10 ) with respect to ventilation of the lung, the output ( 10 ) of pulse-like interference signals ( 7 . 9 ), especially pacemaker pulses, is adjusted. An electro-impedance tomography apparatus according to claim 14, wherein the signal processing unit ( 15 ) is configured from the previous EIT measurement signals ( 161 ) of the time series [ 161 _t1 , 161 _t2 , 161 _t3 ... 161 _tx ] of the EIT measuring channel ( 5 . 6 ) and the current EIT measurement signal ( 161 _x0 ) to determine the statistical measure preferably based on a moving standard deviation or a moving average or median value. An electro-impedance tomography apparatus according to claim 14, wherein the signal processing unit ( 15 ) in the criterion regarding the disturbance situation - a frequency of disturbances of chronologically previous EIT measuring signals ( 161 ) in a predetermined time interval and / or - a frequency of disturbances within a predetermined number of temporally previous EIT measurement signals ( 161 ) and / or a periodicity of identified disturbed EIT measurement signals ( 161 ). An electro-impedance tomography apparatus according to claim 14, wherein the signal processing unit ( 15 ) is configured to include in the determination of the measuring channel-specific comparison variable a predetermined maximum or a predetermined minimum threshold value. An electro-impedance tomography apparatus according to any of claims 14 to 15, wherein the signal processing unit ( 15 ) is configured to determine the measurement channel-specific comparison variable as a multiple, the statistical characteristic, preferably as a multiple of the determined moving standard deviation, the moving average or the median value. An electro-impedance tomography apparatus according to claim 14, wherein the signal processing unit ( 15 ), the substitute value ( 581 ) from an EIT measurement signal ( 161 ) or several EIT measuring signals ( 161 ) from the time series [ 161 _t1 , 161 _t2 , 161 _t3 ... 161 _tx ] with temporal previous EIT measurement signals ( 161 ) of the EIT measuring channel ( 5 . 6 ), preferably the current EIT measuring channel ( 5 . 6 ) and / or temporally previous EIT measurement signals ( 161 ) of several EIT measuring channels ( 5 . 6 ). An electro-impedance tomography apparatus according to claim 14, wherein the signal processing unit ( 15 ) is designed as a substitute value ( 581 ) has a predetermined value, preferably a value, which corresponds to a previous value in time of the current EIT measurement signal of the same EIT measurement channel ( 5 . 6 ) or to use a value with a fixed numerical value instead of the identified disturbed EIT measurement signal.

Images