Abstract:
A device ( 10 ) for processing data ( 3 ), which were obtained from a medical device suitable for imaging the lungs or the thorax, particularly an electrical impedance tomography device ( 30 ), provides improved visualization of a three-dimensional thoracic dimension ( 350 ) of the lungs. A characteristic contour ( 34, 350 ) is determined continuously by continuous reference to a previously determined outer contour ( 905 ) of the lungs as a comparison variable and is outputted, provided and visualized as an output signal ( 35 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority under 35 U.S.C. §119 of German Patent Application 10 2014 018107.3 filed Dec. 9, 2014, the entire contents of which are incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention pertains to a device for processing and visualizing data relating to a three-dimensional thoracic dimension of the lungs, wherein the data were obtained from a medical device suitable for generating data for imaging, especially from an electrical impedance tomography device. The three-dimensional thoracic dimension of the lungs corresponds to a position and extension of the lungs of a patient within the patient&#39;s thorax. 
       BACKGROUND OF THE INVENTION 
       [0003]    Devices for electrical impedance tomography (EIT) are known from the state of the art. These devices are designed and intended for generating an image, a plurality of images or a continuous sequence of images from signals obtained by means of electrical impedance measurements and data and data streams obtained therefrom. These images or sequences of images show differences in the conductivity of different tissues of the body, bones, skin, body fluids and organs, especially the lungs, which are useful for observing the situation of a patient. 
         [0004]    U.S. Pat. No. 6,236,886 describes an electrical impedance tomograph with an array of a plurality of electrodes, power input at at least two electrodes and a method with an algorithm for image reconstruction for determining the distribution of conductivities of a body, such as bone, skin and blood vessels in a general embodiment with components for signal detection (electrodes), signal processing (amplifier, A/D converter), power input (generator, voltage/current converter, current limitation) and with components for controlling (C). 
         [0005]    It is stated in U.S. Pat. No. 5,807,251 that it is known in the clinical application of EIT that a set of electrodes is provided, which are arranged at a defined distance from one another, for example, around the chest of a patient in electrical contact with the skin. An electric current or voltage input signal is to be applied alternatingly between different pairs of electrodes or between all the possible pairs of electrodes among electrodes arranged mutually adjacent to one another. While the input signal is applied to one of the pairs of electrodes arranged mutually adjacent to one another, the currents or voltages are measured between each pair of the other electrodes, which pairs are located adjacent to one another, and the measured data obtained are processed in the known manner in order to obtain a visualization of the distribution of the specific electric resistance over a cross section of the patient, around which the electrode ring is arranged, and to display it on a display screen. 
         [0006]    In addition to devices for electrical impedance tomography (EIT), further medical devices suitable for imaging, for example, a great variety of radiological devices, such as X-ray apparatuses (X-ray), computed tomographs (CTs), nuclear magnetic resonance (NMR) devices, nuclear spin or magnetic resonance tomographs (MRI), as well as also sonographic devices for imaging, which make possible imaging and the providing of signals or data, as well as devices for so-called bioimpedance measurement or impedance plethysmography, are used in the area of health care. Thus, an X-ray tomography system based on gamma radiation is known from U.S. Pat. No. 4,075,482 A. U.S. Pat. No. 4,806,867 A shows a magnetic resonance imaging system. A device for improved image reconstruction of computed tomograms is described in U.S. Pat. No. 4,149,081 A. A computer-assisted system for pulmonary diagnostics, which makes it possible to identity anatomic structures of volumetric medical images, is known from U.S. Pat. No. 6,944,330 B2. A sonography device, which is suitable for an examination of the lungs and for the diagnosis especially of pulmonary diseases, especially pulmonary embolism, is known from U.S. Pat. No. 8,170,640 BB. U.S. Pat. No. 7,717,849 B2 describes a method and a device for controlling a display device in an ultrasound device, wherein selected elements of a dimensional visualization are transformed into another dimensional visualization. 
         [0007]    Unlike imaging methods using X-ray or gamma radiation, electrical impedance tomography (EIT) has the advantage that no radiation burden that is disadvantageous for the patient occurs. Unlike sonographic methods, EIT makes possible image acquisition over a representative cross section of the entire thorax and the lungs of the patient by means of the electrode belt. In addition, the need for using a contact gel, which must be applied before each examination and thus makes a continuous sonographic examination over a longer period of time difficult, is eliminated. Thus, electrical impedance tomography (EIT) offers the advantage of making a continuous monitoring of the lungs possible in order to observe and document the course of a therapy of an artificially ventilated or spontaneously breathing patient. 
         [0008]    It is possible by means of electrical impedance tomography (EIT) to generate so-called EIT image data for a two-dimensional image of the lungs in the plane in which the EIT electrodes are placed horizontally through the thorax of a patient. Due to the position of the EIT electrodes around the thorax, it is not possible therefore to generate frontal views or lateral views, but images are generated in the horizontal plane, the so-called transverse plane, in the EIT electrodes placed around the thorax. Additional image data can be generated for a nearly three-dimensional image of the lungs and additional views can be subsequently generated by computing in the plane of the body, such as a frontal view or sagittal view, by placing additional EIT electrodes around the thorax in different horizontal positions. 
         [0009]    The regional distribution of the breathing air in the lungs of a patient can be considered by means of the EIT image data of electrical impedance tomography (EIT). The availability of an individually available thoracic dimension of the lungs within the individual thorax of the patient in question is of great advantage for the assessment of the current status of an artificially ventilated or spontaneously breathing patient. 
       SUMMARY OF THE INVENTION 
       [0010]    An object of the present invention is to provide a device for processing tomographic data in order to visualize the course of a therapy. 
         [0011]    Another object of the present invention is to provide a device that makes it possible to continuously determine and provide a current thoracic dimension of the lungs of a patient. 
         [0012]    According to the invention a device is provided for processing and visualizing data of at least one area of the lungs and of the thorax for determining and visualizing a three-dimensional thoracic dimension of the lungs over an observation period. The device comprises a data input unit for receiving data obtained from a medical device, suitable for imaging the lungs or the thorax, the data input unit being configured to receive and provide the data of at least one area of the lungs or of the thorax a computing and control unit and a data output unit. The computing and control unit is configured to determine a first image data set which represents a first characteristic outer contour of the lungs, from data for a first ventilation situation and to generate and provide an output signal which represents the first characteristic outer contour of the lungs and to determine at least one additional image data set, which additional image data set represents an additional characteristic outer contour of the lungs, from data for at least one additional ventilation situation. The computing and control unit compares the first image data set with the at least one additional image data set on the basis of a comparison criterion and generates and provides the output signal, as a function of the comparison, on the basis of the first image data set or on the basis of the second image data set. The data output unit is configured to output, provide or represent the characteristic outer contour of the lungs corresponding to the output signal. 
         [0013]    Some of the terms used within the framework of this patent application will be explained in more detail as follows. 
         [0014]    A time segment in a time course is defined as the observation period in the sense of the present invention. The beginning and the end of such an observation period are defined either by fixed or adaptable times or by events, which are determined by breathing or ventilation. Examples of observation periods, which are based on breathing or ventilation, are a breathing cycle, a plurality of breathing cycles, parts of breathing cycles, such as breathing in (inspiration), inspiratory pause, breathing out (expiration), expiratory pause, as well as also parts of one or more breathing cycles, e.g., a plurality of inspirations, a plurality of expirations. Further observation periods, especially in case of artificial ventilation, may be time periods with defined pressure levels, such as plateau pressure PIP, PIP pressure (Positive Inspiratory Pressure, PIP), or PEEP pressure (Positive End Expiratory Pressure, PEEP), PIP or PEEP pressure stages, rising or declining PIP pressure ramps or PEEP pressure ramp as part of a special ventilation maneuver or time segments, which correspond to defined properties of ventilation modes (e.g., Bi-Level Positive Airway Pressure, BiPAP). 
         [0015]    Tomographic data are defined in the sense of the present invention as the following signals or data:
       raw EIT data, i.e., measured signals detected with an EIT device by means of a group of electrodes or by means of an electrode belt, such as voltages or currents, associated with electrodes or groups of electrodes or with positions of electrodes or of groups of electrodes on the electrode belt;   EIT image data, i.e., data or signals that are determined from the raw EIT data and represent local impedances, impedance differences or impedance changes of areas of the lungs of a patient;   data of a medical device, which provides an imaging based on computed tomography (CT) or X-ray radiation (X-ray);   data of a medical device, which provides imaging based on magnetic resonance imaging (MRI) or on nuclear spin tomography, data of a medical device that provides imaging based on sonography (ultrasound), or data of a medical device that provides imaging based on bioimpedance measurement or plethysmography.       
 
         [0020]    For processing and visualizing data for at least one area of the lungs or thorax, which data were obtained by means of a medical device suitable for generating data for imaging, especially of an electrical impedance tomography device, the device according to the present invention comprises:
       a data input unit,   a computing and control unit; and   a data output unit.       
 
         [0024]    The data input unit is configured to receive and provide data of at least one area of the lungs or of the thorax. The data represent, for a plurality of lung areas, regional ventilation situations of the lungs for at least one location of the lungs over an observation period. The data input unit preferably has interface elements for this, for example, level converters, amplifiers, A/D converters, components for overvoltage protection, logic elements and additional electronic components for the wired or wireless reception of the data and signals, as well as adaptation elements such as code or protocol conversion elements for adapting the signals and data for the further processing in the computing and control unit. 
         [0025]    The computing and control unit is configured to determine a first image data set, which represents a first characteristic outer contour of the lungs, from the data for a first ventilation situation, and to generate and provide an output signal, which represents the first characteristic outer contour of the lungs. 
         [0026]    The computing and control unit is configured, furthermore, to determine at least one additional image data set, which represents an additional characteristic outer contour of the lungs, from the data for at least one additional ventilation situation. 
         [0027]    The computing and control unit is configured, furthermore, to compare the first image data set with the at least one additional image data set on the basis of a comparison criterion and to generate and provide the output signal as a function of the comparison on the basis of the first image data set or on the basis of the second image data set. The computing and control unit has elements for data processing, computing and process control, such as microcontrollers (μC), microprocessors (μP), digital signal processors (DSP), logical units—Field-Programmable Gate Array (FPGA), Programmable Logic Device (PLD), memory components—Read-Only Memory (ROM), Random Access Memory (RAM), Synchronous Dynamic Random Access Memory (SD-RAM) and combination variants thereof, for example, in the form of an “embedded system,” which are designed together with one another and are adapted to one another and are configured by programming to carry out the necessary steps for processing and visualizing data obtained by means of a medical device suitable for degenerating data for imaging for a three-dimensional thoracic dimension of the lungs within the thorax of a patient during the observation period. The image data sets contain contour information on the three-dimensional thoracic dimension of the lungs in the thorax. The three-dimensional thoracic dimension of the lungs in the thorax is determined, on the one hand, by the position of the lungs in relation to the vertical body axes (sagittal body plane and frontal body plane) and the horizontal body axis (transverse body plane) and, on the other hand, by the distance of the lungs from ribs, sternum (retrosternally) and spine (prevertebrally). The circumference of the thorax thus determines essentially the maximum thoracic dimension, which the lungs can assume in the thorax. The thoracic dimension of the lungs comprises, in this case, the shape, form, extension, circumference or even areas projected to the body axes, as they are usual for visualization in medical imaging. In principle, especially the transverse view is employed for electrical impedance tomography (EIT). Especially the outer contour of the lungs of the patient is obtained as a three-dimensional thoracic dimension in this transverse view of the electrical impedance tomography (EIT) as a projection in the horizontal plane in the horizontal position of the EIT electrodes placed around the patient&#39;s thorax. 
         [0028]    It is therefore essential for the present invention that contour information is obtained from the tomographic data provided as image data sets for output and display of the three-dimensional thoracic dimension of the lungs, especially of the characteristic outer contour. The image data sets are determined continuously at different times from the tomographic data in order to determine and provide a particular current outer contour. The particular current outer contour is compared to the characteristic outer contour being displayed on the basis of a specific comparison criterion, which can preferably be selected or set by the user. Finally, the previous outer contour continues to be outputted as a characteristic outer contour depending on the result of the comparison and/or the display is left unchanged or replaced with the output and/or visualization of the outer contour last detected. The particular outer contour of the lungs, which was outputted and/or displayed last, will hereinafter be used as and called a characteristic outer contour of the lungs. The size of the circumference of the lungs and/or the size of the lung area projected in the body plane and/or special shapes of outer contours of the lungs will preferably be used as a specific comparison criterion. 
         [0029]    Examples and samples of special shapes of outer contours of the lungs can be derived, for example, on the basis of typical circumferential shapes or typical area shapes of lung images from the tomographic imaging of the lungs. 
         [0030]    It is decisive for the continuous determination and provision of a current three-dimensional thoracic dimension of the lungs of a patient as well as for visualizing same and for making it possible to use and analyze same for the therapeutic result that the visualized three-dimensional thoracic dimension of the lungs of the patient be in relation to the current health status of the patient. The device according to the present invention offers the user the possibility of placing the current tomographic data in a context to the characteristic outer contour of the lungs of the patient. If, for example, the computing and control unit preferably uses a maximum outer contour as a characteristic outer contour of the lungs of the patient by means of a comparison of the circumference or area of the lungs, the user is thus enabled to put the current tomographic data or image data in relation to a situation of the lungs with maximum ventilation. This makes it possible for the user, for example, if the current ventilated contour of the lungs is small compared to the previously determined maximum outer contour, to take this as an indicator that the ventilation can still be optimized for this patient. Such an optimization can then be carried out without undue delay by changing or adapting ventilation parameters, for example, the respiration rate, the inspiration-to-expiration ratio (I:E ratio), inspiratory and expiratory pause times, ventilation pressures (PEEP pressure, PIP pressure) or even by changing the dosage of certain drugs. In addition, the continuous determination and provision of the current three-dimensional thoracic dimension (maximum outer contour) of the lungs of the patient also offers the possibility of selecting a further and, for example, larger and hence improved new maximum outer contour as a new valid characteristic outer contour due to the recovery or due to the change in ventilation parameters and of continuously and automatically resetting, as it were, the reference point, to which the user can then adapt the subsequent further tomographic data and image data. 
         [0031]    For processing the tomographic data and for performing the comparison of the outer contours therefor, the computing and control unit is configured to suitably select and apply a method from a group of mathematical methods for signal and data analysis, such as 
         [0032]    mathematical model functions for data separation, such as Principal Component Analysis; PCA), Independent Component Analysis; ICA), 
         [0033]    mathematical methods for image processing, such as pixel mapping, 
         [0034]    mathematical methods for data comparison, such as correlation functions, 
         [0035]    statistical methods for data comparison, such as computations, analyses and sorting of data sets based on distribution functions, frequency distributions, standard deviation, scattering, mean value or median, 
         [0036]    transformations, such as Discrete Fourier Transform (DFT), Fast Fourier Transform (FFT), Z Transform, LaPlace Transform, wavelet transform, in order to determine the characteristic outer contour as a three-dimensional thoracic dimension of the lungs from the tomographic data. 
         [0037]    The data output unit is configured to output, provide or visualize the characteristic outer contour of the lungs with the use of the output signal. 
         [0038]    The data output unit is configured to generate, provide or visualize the output signal. The output signal is preferably configured as a video signal (e.g., Video Out, Component Video, S-Video, HDMI, VGA, DVI, RGB) to make possible a graphic, numeric or pictorial visualization of a three-dimensional thoracic dimension of the lungs within the thorax of a patient during the observation period on a display unit connected to the output unit in a wireless or wired manner (WLAN, Bluetooth, WiFi) or on the data output unit itself. 
         [0039]    In a preferred embodiment, the comparison criterion is based on a difference in the size, in the circumference or in the size in the area of the first characteristic outer contour of the lungs and the additional characteristic outer contour of the lungs. 
         [0040]    In another preferred embodiment, a maximum outer contour of the lungs within the thorax is determined as the characteristic outer contour of the lungs based on the circumference and/or on the area of the characteristic outer contour of the lungs. 
         [0041]    In another preferred embodiment, the characteristic outer contour of the lungs is determined relative to a predefined time interval or an observation period. 
         [0042]    In a special embodiment variant, boundary conditions of the EIT acquisition are also included in the determination of the characteristic outer contour. 
         [0043]    Information on the diameter of an electrode belt, which was used to obtain EIT data, may be included as a boundary condition of the EIT acquisition in order to ensure the plausibility of the characteristic outer contour in respect to the circumference of the patient&#39;s thorax. 
         [0044]    Anatomic boundary conditions are also included in the determination of the characteristic outer contour in a special embodiment variant in order to check the plausibility of the characteristic outer contour determined. Anatomic boundary conditions may be derived, for example, from information on age, height, body weight and gender of the patient. For example, the circumference of the patient&#39;s thorax can be approximately estimated in many cases from gender, height and body weight. 
         [0045]    A number of previous maximum outer contours of the lungs within a predetermined time interval or an observation period is also included in the determination of the characteristic outer contour in another embodiment. 
         [0046]    In another embodiment, the determination of the characteristic outer contour is performed by means of filtering the data or image data sets over a predetermined time interval or an observation period in order to achieve an improvement of the characteristic outer contour. Many different types of signal smoothing, such as frequency filtering, averaging or median filtering may be preferably used. 
         [0047]    A comparison with a predetermined, anatomically typical, stored comparison shape is performed for determining the characteristic contour in a special embodiment variant. The anatomically typical comparison shape is preferably stored in the form of a transverse visualization of the lungs and may have preferably been obtained by means of an electrical impedance tomography device, but also by means of other devices suitable for medical imaging (CT, MRI, sonography, X-ray, plethysmography). This makes it possible to compensate possible defects in the contour or in the course of the contour and thus to obtain a closed characteristic outer contour and to improve the shape of the contour. 
         [0048]    In a preferred embodiment, the data of the medical device suitable for imaging are provided as data of an electrical impedance tomography device. The data represent local impedance values of the lungs or of the thorax in different ventilation situations of the lungs. 
         [0049]    In a preferred embodiment, the data input unit, the computing and control unit or the data output unit are configured as components of the electrical impedance tomography device, or the data input unit, the computing and control unit or the data output unit are combined with the electrical impedance tomography device into a medical system. 
         [0050]    In another preferred embodiment, the data of the medical device suitable for imaging are provided as data of an electrical impedance tomography measuring unit, of a computed tomography device (CT), of a nuclear spin tomography or magnetic resonance imaging (MRI) device, of a bioimpedance measuring device, of an impedance plethysmography device or of a sonographic medical device. 
         [0051]    The embodiments described represent, in themselves as well as combined with one another, special embodiments of the device according to the present invention for processing and visualizing data obtained by means of a medical device suitable for generating data for imaging in respect to a three-dimensional thoracic dimension of the lungs within the thorax of a patient. Advantages arising from a combination or combinations of a plurality of embodiments and further embodiments are equally covered by the idea of the invention, even though not all possibilities of combination of embodiments are described in detail for this. 
         [0052]    The present invention will be explained now in more detail by means of the following figures and the corresponding description of the figures without limitations of the general idea of the invention. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0053]    In the drawings: 
           [0054]      FIG. 1  is a schematic view of functional elements for processing EIT data. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0055]    Referring to the drawings,  FIG. 1  shows a device  10  composed of functional elements for processing EIT data  3  in a schematic form. 
         [0056]    This device  10  comprises as the basic components a data input unit  50 , a computing and control unit  70  and a data output unit  90 . The connections between the elements and units of the device  10  are shown only schematically in this embodiment according to this  FIG. 1 ; for example, the essential data connections and data inputs and data outputs are shown, but no supply lines are shown, and not all connection lines between the elements and units with one another are shown. Furthermore, a display unit  99  connected to the data output unit  90  is shown in this  FIG. 1 . The display unit  99  comprises visualization means  901 , such as display elements, display screens, displays for visualizing graphics, curves, diagrams or images or even numerical value displays for reproducing numerical values. Furthermore, the display unit  99  comprises input elements and operating elements  902 , such as switches, buttons, knobs, and rotary knobs. 
         [0057]    A special embodiment variant is a touch-sensitive display (touch screen) with combination of input and visualization functionalities. 
         [0058]    The data input unit  50  inputs EIT data  3  from an EIT device  30 . In this embodiment shown in  FIG. 1 , the EIT device  30  is connected as an external measuring unit to the device  10  with an electrode array, not shown in this  FIG. 1 . However, optional technical variants of the embodiment according to this  FIG. 1  are may be provided according to the invention, wherein the EIT device  30  may be configured as a component of the device  10 , and the device  10  may also be configured as a part of the EIT device  30 . The display unit  99  is configured in this embodiment shown in  FIG. 1  as an external device connected to the device  10  composed of elements, but the device  10  may also be made together with the display unit  99  to form a global EIT system in an optional technical variant in the sense of the present invention. A detailed representation of these optional technical embodiment variants is not shown in  FIG. 1  for reasons of clarity, and the integration of the device  10  composed of functional elements with the EIT device  30  and/or with the display unit  99  is indicated only by dots, dashes and lines in the view shown in  FIG. 1 . The data input unit  50  stores the data after inputting for further processing either in an unchanged format as EIT data  3  or in a form adapted for a further processing as preprocessed EIT image date 3′. The data output unit  90  is configured to provide data or signals, for example, an output signal  35  from the computing and control unit  70  at an interface  91  for a visualization as numbers  92 , images  93 , diagrams  94 , signal curves or curves over time  95  or compilations  96  of data on a display unit  99  (display screen, monitor, data display unit). Provision is defined in the sense of the present invention as any form of providing a signal or data for transmission, outputting, visualization, display, printing, sending, further processing to additional devices or to parts of devices. The display unit  99  is configured in this  FIG. 1  as an external device connected to the data output unit  90  via the interface  91 . However, the scope of the present invention also covers the possibility of designing the display unit  99  as an external unit of the data output unit  90  or also of the device  10 . For example, wireless or wired provision of data for a data network  300  (LAN, WLAN, Ethernet), wireless or wired provision of data for mutual transmission of measured values and control data (e.g., USB, RS232, RS485, FireWire, NMEA 0183, IrDA, Bluetooth, CAN, UMTS [SMS, MMS]) in data exchange with different other external devices  200  (anesthesia devices or ventilators, physiological monitors, monitors suitable for monitoring the cardiac minute volume, personal computers, hospital management systems), as well as the provision of audio/video data (e.g., Video Out, Component Video, S-Video, HDMI, VGA, DVI, RGB) in different data formats (e.g., MPEG, JPEG, etc.) for connection to the display unit  99  or to other display devices (display screens, monitors, tablet PCs) are possible by means of the interface  91 . The computing and control unit  70  performs a plurality of tasks within the device  10 , such as the coordination with the data input unit  50  and with the data output unit  90 . The computing and control unit  70  is preferably configured, for example, as a central computing unit (CPU), a microprocessor (μP) or as an array of individual microcontrollers (μC). 
         [0059]    The computing and control unit  70  comprises, furthermore, an internal memory unit  71  or is connected to an external memory unit  71 ′. The memory units  71 ,  71 ′ are configured for storing and providing the EIT data  3 ,  3  as a set of data sets in the form of EIT image data sets { 33 }, { 34 }. The EIT data  3  or EIT image data  3 ′ being stored by the data input unit  50  are stored and provided as image data sets  33 ,  33 ′,  33 ″,  33 ′″, . . .  33   n  in the memory units  71 ,  71 ′. The computing and control unit  70  comprises a contour determination unit  72 , which is configured to determine a set of contour data sets { 34 ,  34 ′,  34 ″,  34 ′″, . . .  34   n }ε{ 34 } from each of the image data sets from the set of image data sets { 33 ,  33 ′,  33 ″,  33 ′″, . . .  33   n }ε{33} and to make it available to the memory units  71 ,  71 ′ for storage. The contour data sets  34  contain information on the contour of the circumference and/or the area shape of the lungs within the thorax of a patient, not shown in this  FIG. 1 , especially relative to the transverse axis of the lungs. It is advantageous in this connection to perform a reduction of the image data sets during the generation of the contour data sets  34 . For example, image data, which represent information on the center of the left or right lobe of the lung, may be stored in the contour data sets at the time of such a reduction with a lower information density than image data that contain information in the transition area of the lungs to surrounding body areas (ribs, diaphragm, myocardium, aorta, intercostal muscles). This leads, on the one hand, to a reduction in the amount of storage space needed in the memory unit  71 ,  71 ′, and it becomes, in addition, possible to increase the speed at which the contour data sets  34  are processed due to the reduction, while a high acquisition rate is maintained. This is the prerequisite for the output, provision or visualization of the contour data sets in real time, i.e., with only a time delay between data generation and visualization in further steps of the data processing. Furthermore, a comparison unit  73 , which is configured to perform a comparison of at least two contour data sets from the set of contour data sets  34 ′,  34 ″,  34 ′″, . . .  34   n  and to determine therefrom the output signal  35 , which reflects a characteristic contour  350  of the lungs within the thorax as a three-dimensional thoracic dimension of the lungs over an observation period, is provided in the computing and control unit  70 . The comparison unit  73  preferably uses a size comparison of the contours of the circumference and/or area shapes of the lungs, which are contained in the contour data sets  34 , as a criterion. The comparison of at least two contour data sets  34 ,  34 ′ by the comparison unit  73  takes place as follows: 
         [0060]    If the currently determined contour in the circumference or area with the use of the criterion is larger than the characteristic contour  350  determined previously, the current contour is selected as the current characteristic contour  350 , and the output signal  35  is determined on the basis of this newly selected characteristic contour  350 . A variant of a characteristic contour  350  is, for example, a lung outer contour  350 ′, which represents the maximum extension of the lungs in the thorax over a preceding predetermined time interval or observation period. In a special embodiment variant, boundary conditions or preset values are also included in the determination of the characteristic contour  350  in order to ensure the plausibility of the characteristic contour  350 . For example, information on the diameter of the electrode belt, not shown in this  FIG. 1 , which diameter was used to obtain EIT data  3 , EIT image data  3 ′ or the image data sets  33 ,  33 ′,  33 ″,  33 ′″, . . .  33   n , or a comparison with an anatomically typical comparison shape can be taken into account when determining the characteristic contour  350  or the outer contour  350 ′ of the lungs. The output signal  35  is made available by the comparison unit  73  to the data output unit  90  as a characteristic contour  350  or the outer contour  350 ′ of the lungs. 
         [0061]    The characteristic contour  350  or the outer contour  350 ′ of the lungs is displayed on the visualization means  901  of the display unit  99 . 
         [0062]    A current ventilation situation of the lungs is schematically shown in this  FIG. 1 , based on the set of image data sets { 33 ,  33 ′,  33 ″,  33 ′″, . . .  33   n }, as a graphic element in a transverse view of the lungs on the display unit  99  as an area contour  909 . The characteristic contour  350  of the lungs, based on the set of contour data sets { 34 ,  34 ′,  34 ″,  34 ′″, . . .  34   n }, is schematically shown in this  FIG. 1  as another, graphically visualized element in a transverse view of the lungs as an outer contour  905  of the lungs on the display unit  99 . It is seen on the display unit  99  in this way in what relation the current ventilation situation  909  of the lungs is to the outer contour  905  of the lungs. It can be derived from this to what extent the possibilities of lung ventilation individually given for this patient or these lungs are exhausted by the current ventilation situation  909 . 
         [0063]    The described functional units of the computing and control unit  70  may be designed as individual components of the computing and control unit  70 , but the present invention also covers the case in which the computing and control unit  70  may be integrated in other partial modules and may be configured by programming to provide the functions of the memory units  71 , contour determination unit  72  and comparison unit  73 , with the same effect as described in connection with  FIG. 1  in the same form or in a modified form of processing. 
         [0064]    While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles. 
         [0000]    
       
         
               
               
             
           
               
                   
               
             
             
               
                 3, 3′ 
                 EIT data 
               
               
                 10 
                 Device composed of functional elements 
               
               
                 30 
                 EIT device 
               
               
                 33 
                 Image data sets 
               
               
                 34 
                 Contour data sets 
               
               
                 35 
                 Output signal 
               
               
                 50 
                 Data input unit 
               
               
                 70 
                 Computing and control unit 
               
               
                 71, 71′ 
                 Memory unit 
               
               
                 72 
                 Contour determination unit 
               
               
                 73 
                 Comparison unit 
               
               
                 90 
                 Data output unit 
               
               
                 91 
                 Interface 
               
               
                 92 
                 Numerical values 
               
               
                 93 
                 Images 
               
               
                 94 
                 Diagrams 
               
               
                 95 
                 Curves, courses of curves, signal 
               
               
                   
                 curves over time 
               
               
                 96 
                 Data sets, data compilations 
               
               
                 99 
                 Display unit 
               
               
                 200  
                 External devices 
               
               
                 300  
                 Data network 
               
               
                 350, 350′ 
                 Three-dimensional thoracic dimension, 
               
               
                   
                 characteristic contour, outer contour 
               
               
                 901, 902     
                 Visualization means, input means 
               
               
                 905  
                 Outer contour 
               
               
                 909  
                 Area contour